Method and apparatus for cooperative wireless communications

METHOD AND APPARATUS FOR COOPERATIVE WIRELESS COMMUNICATIONS

The present invention relates to wireless communication.

Cooperative communication enables wireless transmit/receive units (WTRUs) to assist each other in transmitting information to their desired destination. This approach enables alleviation of some of the problems facing modern wireless communication systems without the costs associated with extensive wired infrastructure. Using collaboration, it is also possible to exploit the spatial diversity associated with conventional multiple-input multiple-output (MIMO) techniques without each node having to have multiple antennas. Finally, regenerative relay, basic collaboration techniques can reduce the effects of path loss and shadowing on coverage and throughput.

<p>A challenge in incorporating collaboration into modern wireless systems is the need to advance system architectures to enable collaboration. Particularly in wireless systems, effective collaboration techniques are usually lower layers of the communication stack, e.g., Layer 1 (Physical Layer, PHY) and Layer 2/3 (Medium Access Control (MAC), Radio Link Control (RLC), or depending on the system). In Logical Link Control (LLC), it includes advanced algorithms, however, such algorithms are in receiver design, error correction code design, automatic repeat request (ARQ) and hybrid automatic repeat request (HARQ) processes and multi-user systems. It requires advanced skills such as scheduling in</p><p>Accordingly, there is a need to consider the impact of cooperation on cellular systems, including system-architectural aspects. The downlink and uplink, separately and in each case, consider several cooperative schemes leading to different architectures. In each case, the impact on the system operation along with the emphasis of scheduling and ARQ/HARQ is considered and a solution is proposed.</p><p>As user demand for various quality and data rate services and applications advances, the capacity of wireless communication links is being depleted. Single-antenna systems do not appear to be able to address these needs, and operators are now moving to multi-antenna systems. Despite unprecedented achievable data rates, multi-antenna systems do not provide significant gain for long range or low signal-to-noise ratio (SNR) applications.</p><p>Relay communications appear to be solving these problems and are now central to many research activities. Unlike conventional point-to-point communication techniques, relay introduces a third entity called a "relay" that assists in communication between a source and a destination.</p><p>When assisting the source, the relay and the source negotiate various protocols for delivery of the intended message to the destination, for example, hopping and diversity protocols. In the case of hopping, the message is sent by the source, received by the repeater, and then retransmitted to the destination. In the case of the diversity protocol, the repeater and the source transmit simultaneously to the destination using some diversity scheme.</p><p>The flexibility introduced by the repeater in terms of placement and provision of additional virtual antennas is a key advantage of the repeater system. For example, since multiple antennas are limited in size and cost, it is difficult to implement with more than four antennas. However, with repeaters, the number of antennas in the link can be increased in a distributed manner, thus introducing a higher gain in the data rate. Also, by adjusting the repeater position or selecting a repeater with appropriate channel conditions, low SNR and far range links receive a significant boost. Furthermore, cell edge users generally do not benefit fully because of the high interference they experience. Relaying in this case can be used to increase throughput and redistribute across the cell and to enhance non-benefit links.</p><p>Despite extensive theoretical developments in cooperative communication and the significant advantages of such relays, little work has been done on introducing the benefits of cooperative communication into practical cellular systems. Part of the reason is the lack of efficient collaboration protocols and broad implementations with demonstrated benefits in real-world scenarios. Consequently, there is a need for a cooperative communication protocol suitable for cellular communication systems.</p><p>Repeater communication has recently shown much hope in improving communication over weak communication links. By allowing repeaters to send the entire message to the destination in a multi-hop manner, extremely remote communication ends were connected. However, multi-hop introduces unacceptable communication delays in some real-time applications.</p><p>A more advanced architecture for relayed communication is cooperative communication. Unlike multi-hopping, the source and repeater or multiple repeaters cooperate to provide diversity or multiplexing gain. For example, the source and repeater may transmit in the Alamouti scheme. Repeaters are provided with the option to decode the message after it has adapted its power to the channel, either before forwarding the message or assisting in such forwarding. These techniques are called Decode and Forward (DF) and Amplify and Forward (AF), respectively.</p><p>The main disadvantage of these techniques is that delay is introduced by the repeaters in the DF. One way to avoid this is to use a form of coding that allows the destination to gather data from the communication initiation while the repeaters are receiving. By doing so, the delay due to the DF protocol is reduced. Thus, the destination sees a continuous transmission all the way.</p><p>In another scheme, a fountain code, a special case of an optimally configured rateless code for an erasure channel, has been used for broadcast applications. However, there is a need to efficiently use rateless coding for an actual repeater system.</p><p>Due to propagation delay between RS and BS, the frequency offset between the BS and RS local oscillator, as well as the processing delay at the RS, the timing of RS transmission to the WTRU may be different from the timing of the BS transmission to the WTRU. During the cooperation phase, misalignment of streams received by the WTRU from BS and RS, respectively, may cause interference with each other. Inter-stream interference may reduce the data rate that may be achieved by the WTRU, thereby reducing potential benefits from cooperation.</p><p>Therefore, it would be desirable to alleviate this problem by synchronizing the BS and RS DL transmissions. The use of synchronized BS and RD DL transmission helps to reduce interference between RS and BS transmissions to the WTRU and to allow the use of various diversity schemes (eg, Alamouti or MIMO schemes) while avoiding complex WTRU receiver designs. becomes this</p>

<p>Conventional solutions show that transmission timing adjustment of an uplink (UL) WTRU can be achieved through a timing adjustment (TA) mechanism. While the TA concept is commonly used for UL, it has not been used for DL, which is required in the context of cooperative networks.</p><p>It would be desirable to improve link performance through intelligent use of repeaters. However, a simple multi-hop relay (relay in which a repeater forwards the very data it receives) will seldom lead to significant gains. Instead, more sophisticated cooperative coding schemes may be employed. Among these are cooperative coding schemes such as distributed beam-forming and distributed spatial multiplexing techniques. Accordingly, it would be desirable to use a multi-user detector, or more precisely, a continuous interference canceller (SIC), to optimize the performance of the joint reception of transmissions from the source and repeater. The least squares mean error successive interference canceller (MMSE-SIC) receiver is an official candidate receiver for use in the Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) technology to separate spatial streams flowing from the same transmitter. . Therefore, it would be desirable to place the source and repeater transmissions in separate transport streams and use SIC to receive these transmissions. In fact, it would not even require an additional receiver structure, at least for OFDM MIMO techniques.</p><p>Specifically, SIC receivers will have obvious practicality, and once such a receiver is introduced into a communication system, many of the benefits of cooperative diversity can be transferred to the MAC layer. Instead of cooperative transmission and coding, a well-scheduled combination of direct transmission and simple multi-hop would be desirable to achieve the benefits of cooperative repeaters, which in some cases could be achieved by well-designed PHY-layer schemes. will be superior to</p>

<p>A method and apparatus are provided for collaboration in wireless communication. Cooperation between multiple network elements including at least one radio transmit/receive unit, at least one relay station, and at least one base station is contemplated.</p>

A more detailed understanding of the present invention may be obtained from the following detailed description of embodiments given by way of example in connection with the accompanying drawings. 1 is a four repeater architecture diagram for use in a cellular system. 2 is an exemplary cooperative repeater architecture diagram. 3 is an exemplary multi-WTRU-serving relay architecture diagram. 4 is a diagram of a modification of the forwarding repeater architecture when a plurality of repeaters are wirelessly connected in series. 5 is a diagram of multiple cells in a system where the association between RS and BS is static or dynamic. 6 is an exemplary architecture diagram in which an RS may be associated with more than one BS. 7 is a diagram illustrating an exemplary TDM repeater that transmits and receives signals in different time intervals. 8 is a flow diagram illustrating the sequence of operations involved in the decode-and-forward scheme. 9 is a flowchart of protocol 1 (P1) defined for downlink (DL). 10 is a flow diagram illustrating an exemplary multicast-split RTS defined for the DL case, referred to as protocol 2 (P2). 11 is an exemplary overall information relay diagram. 12 is an exemplary forwarding relay diagram. 13 is an exemplary cooperative relay diagram. 14 is an exemplary forwarding relay diagram in FDM MIMO. 15 is an exemplary TDDR solution diagram. 16 is another exemplary embodiment using a Fountain Extended Time Division Duplex Relaying (FDDR) scheme. 17 is a PTDR (Parallel Transmission Duplex Relaying) protocol diagram. 18 is an exemplary STDDR diagram. 19 is an exemplary protocol stack diagram. 20 is a second alternative diagram for implementing a WTRU protocol stack. 21 is a third alternative diagram for implementing a WTRU protocol stack. 22 is a flow diagram of an event sequence involved in sending an IP packet from a BS to a WTRU via an RS. 23 is a flowchart of an event sequence involved for a MAC-level RS. 24A and 24B are alternative embodiments for data transmission using RLC-level RS. 25 is an operation diagram in a user plane in a two-hop mode. 26 is an exemplary diagram of the MAC-relay sublayer of the MAC located between the RS and the BS. 27 is an exemplary protocol architecture diagram for a PHY-level RS. 28 is an exemplary protocol architecture diagram for a MAC-level RS. 29 is a protocol architecture diagram for an RLC-level RS. 30 is an event sequence diagram involved in sending an IP packet from a BS to a WTRU via an RS. 31 is a flowchart of a data transmission operation when the BS does not know the detailed relay operation. 32 is an exemplary signal flow diagram for smart relay and slave relay. 33A and 33B are exemplary protocol architecture diagrams in which the BS and the relay station include a layer 2 contour plane entity. 34 is an exemplary cooperative header diagram. 35 is an example technique that can separate channel coding for header and payload. 36 is a flow diagram of an example technique used to separate channel coding for header and payload. 37 is a diagram of a downlink data packet with header and payload; 38 is a diagram of a relay system using five channel states. Figure 39 is a transport header diagram including a "legacy" header appended with one bit called "Cooperation.Header Indicator Bit". 40 is an exemplary downlink scheme. 41 is an exemplary downlink scheme. 42 is an exemplary downlink scheme. 43 is an exemplary downlink scheme. 44 is an exemplary downlink scheme. 45 is an exemplary downlink scheme. 46 is an exemplary downlink scheme. 47 is an exemplary downlink scheme. 48 is an exemplary downlink scheme. 49 is an exemplary diagram of control channels for UL. 50 is an exemplary diagram of control channels for UL. 51 is an exemplary frame structure diagram for SI. 52 is an exemplary synchronization diagram of BS and RS DL transmissions for a WTRU using a timing adjustment procedure.

As used hereinafter, the term "wireless transmit/receive unit (WTRU)" refers to a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a PDA, a computer, or any other type capable of operating in a wireless environment. of user devices, but are not limited thereto. As used herein, the term "base station" includes, but is not limited to, a Node B, site controller, access point (AP), or any other type of interfacing device capable of operating in a wireless environment. When referred to below, the term "relay station" refers to a repeater or RS.

Although the present invention is described in terms of a third generation (3G) cellular radio system, it should not be construed as limiting to this system alone, the 3G system serving merely as an example.

<b>relay physical architecture</b>

Relay can be used in a number of ways in a cellular system. In this section, four main architectures are described and illustrated in FIG. 1 . These four exemplary architectures may be used alone or in any combination. These exemplary architectures include: Architecture-1: forwarding relay architecture 110; Architecture-2: multiple WTRU-serving-relay architecture 120 (shown in more detail in FIG. 3 ); Architecture-3: cooperative relay architecture 130 (shown in more detail in FIG. 2 ); and Architecture-4: Multi-BS-Shared-Relay Architecture 140 . Each example architecture includes at least one WTRU 150 , at least one relay station (RS) 160 , and a base station (BS) 195 .

Each WTRU 150 may include a transmitter 165 , a receiver 170 , and a processor 175 . Each RS 160 may include a transmitter 180 , a receiver 185 , and a processor 190 .

Various signals may be transmitted and received by various nodes in each of these architectures and will be described in detail below. In fact, there may be several signaling implementations for each architecture. We will call these embodiments collectively "relay transmission scheme" or simply "transmission scheme". The advantages and applications of this architecture are discussed below.

In Architecture-1 110 , the WTRU receives signals only from RS 160 , not directly from BS 195 . That is, the WTRU 110 is in a deeply shadowed region of BS coverage or simply in a hall of BS coverage. This is an architecture useful for serving WTRUs at the edge of cells with high inter-cell interference from neighboring cells. In this case, the forwarding repeater 160 receives the DL data from the BS 195 and forwards it to the WTRU 150, and vice versa for the UL data. One variation on the forwarding relay architecture is where there are multiple repeaters (wireless) connected in series. This is shown in FIG. 4 .

In Architecture-2, RS 160 serves a plurality of WTRUs 150 located in the coverage area of RS 160 . An advantage of this architecture is that BS-RS data communications can be pooled together to reduce overhead. For example, the overhead associated with various packet headers can be reduced by defining a combined header for aggregated packets.

In Architecture-3, the WTRU 150 may receive and process a signal directly from the BS 195, although typically weaker than the signal received from the RS 160. This configuration has two important effects. First, when the BS 195 is sending DL data to the RS 160 , the WTRU 150 may monitor and receive some or all of that data with a certain probability of error. This type of data is often referred to as 'soft' data. This reduces the amount of data forwarded by RS 160 , or increases the probability of successful reception of data 'forwarded' by RS 160 . Second, the BS 195 and RS 160 can transmit two 'cooperative' signals to the WTRU 150 simultaneously, emulating a multi-antenna scenario, in which case the 'multi-antenna' is not co-located. For this reason, we call this a "distributed MIMO configuration". The benefits of this architecture are similar to those of using MIMO.

Architecture-4 (140) allows multiple RSs (160) to assist WTRUs (150). This example may be viewed as a distributed MIMO configuration, the result of which improves performance.

Combining two or more of the four basic architectures in a technically direct manner yields a practical configuration that overcomes the aforementioned problems.

In each of the architectures of FIG. 1 , RS 160 is shown associated with a given cell. When there are multiple cells in the system, this association between RS 160 and BS 195 may be static or dynamic, as shown in FIG. 5 . In other embodiments, RS 160 , as shown in FIG. 6 , allows for coordination between multiple cells and the ability to effectively serve a group of WTRUs via a set of shared RSs.

Referring to FIG. 1 , when a single BS-RS channel 155 is serving a single WTRU 150 , a technical problem that needs to be addressed is how the WTRU 150 is notified about the RS 160 . whether to receive For example, this can be done by BS 195 broadcasting information about RS 160 . Alternatively, RS 160 may broadcast their presence. Another technical problem is how the WTRU 150 selects the RS 160 and how it associates itself with the selected RS 160 . This adds complexity that the associated information must also be transmitted to the BS 195 .

With respect to synchronization, the delay induced in the relay adds bulk transmission delay between the BS 915 and the WTRU 150 . In turn, round trip time (RTT), which can affect the performance of certain protocols such as TCP and ARQ, is also affected. As a result, buffer requirements at BS 195 and WTRU 150 may also increase.

Between the WTRU-relay, BS-relay, and WTRU-relay-BS, a minimal amount of signaling information must be exchanged. Therefore, it is necessary to determine what these signaling require, and how they will be conveyed. For example, the power control message and the timing advance message need to go between the WTRU 150 and the RS 160 and do not need to be sent to the BS 195 .

Relay Transmission Scheme (RTS)

In the previous section, various physical architectures for using RSs in cellular networks were introduced, keeping in mind that each architecture may support different signal selection for transmission and reception by different nodes. This section describes a number of such 'transmission schemes' and analyzes their performance. 7 is an exemplary TDM repeater for transmitting and receiving signals in different time intervals. For example, in the DL, the TDM-repeaters 705a...705j will receive a signal from the BS 710 in one time period and transmit it to the WTRU in a subsequent time period. These time intervals are called steps or transmission time intervals (TTUs), T1 720 and T2 730 . Although T1 720 and T2 730 are shown contiguous in FIG. 7 , T2 need not be contiguous to T1 . Indeed, in some embodiments, T2 730 will not be contiguous with T1 720 , perhaps due to scheduling constraints. Also, the duration of T1 720 and T2 730 is flexible and depends on channel conditions. This in turn determines the time it takes for successful reception of a given block of data. In one example, the transmission medium is slotted into fixed sized TTIs, such that T1 720 and T2 730 may be integer multiples of the fixed TTI. However, the TTI size may be variable or may vary dynamically. T1 720 and T2 730 may have different sizes.

It is also possible to design other types of repeaters, such as, for example, FDM repeaters that transmit and receive in different frequency bands. These designs are generic and apply to other types of repeaters other than TDM repeaters. For simplicity, the details of various designs within the context of a TDM repeater will be discussed. Although the design is discussed in the context of DL data transmission, this design also applies to UL data transmission.

Referring back to FIG. 7 , the basic principle of the TDM-repeater 705 is to receive the DL data transmitted from the BS 710 during step 1, denoted T1 720 , and this during phase 2, denoted T2 730 . is to transmit These transmissions are referred to as "simple" phase 1 transmissions and "forwarding" phase 2 transmissions. During phase 1, the WTRU 740 also receives and attempts to decode the DL data sent from the BS 710. This is referred to as a "multicast" phase 1 transmission. Likewise, during phase 2, the BS 710 is also capable of sending DL data to the WTRU 740 . This is called "cooperative" phase 2 transmission. These variants to step 1 and step 2 are now called four basic TDM-relays, called simple-forwarding relay transmission scheme, multicast-forwarding relay transmission scheme, simple-cooperative relay transmission scheme, and multicast-cooperative relay transmission scheme. Create a transmission scheme.

In the simple-forwarding relay transmission scheme, the BS includes channel codes, including forward-error correction codes such as convolutional codes turbo codes or LDPC codes, and error detection codes such as CRC-block codes, M-ary QAM, etc. DL data may be transmitted using the same modulation scheme and multi-antenna (MIMO) mapping scheme. The signal forwarded in step 2 may be based on a received baseband signal, a received demodulated signal, or received decoded data. The resulting scheme is referred to as "amplification-and-forward", "demodulation-and-forward", "decode-and-forward", respectively. In the last two cases, the new modulation and/or new channel code used for forwarding may be different from the modulation and/or channel code used in step 1, which means that the quality of the RS-WTRU link depends on the quality of the BS-RS link. because it is different from

8 is a flow diagram of a sequence of operations involved in decode-and-forward scheme 800 . Here, the BS selects an RS (810) and transmits a message for the WTRU to the selected RS (820). The RS decodes the message and re-encodes the message according to the channel quality metric (830). If necessary, the BS retransmits the DL data to the RS until the RS receives it without errors (not shown). ARQ and/or HARQ protocols may be used to achieve error-free transmission. In this case, step 1 is essentially defined by the time it took for the RS to receive the data transmitted by the BS without error. Likewise, during step 2, the RS transmits and possibly retransmits the DL data until the WTRU decodes the DL data correctly.

In the multicast-forwarding relay transmission scheme, the signal transmitted by the BS is received not only by the RS but also by the WTRU in step 1 . In step 2, the RS will forward the received signal to the WTRU, and the WTRU will 'combine' it with the BS signal received during step 1 to correctly receive the BS data. This 'join' process enables this relay transmission scheme to outperform the simple-forwarding scheme. Decode-and-forward for simplicity while RS forwards the received BS data using one of three possible forwarding schemes (i.e., amplification-and-forward or demodulation-and-forward or decode-and-forward) Only schemes will be discussed. In this case, once again, the BS transmits and possibly retransmits the DL data until the RS decodes it correctly. Correct decoding by RS marks the end of step 1.

The transmitted signal of step 1 is forward error correction &amp; It may be channel coded using a detection code. In this case, the WTRU will have, at the end of step 1, a soft-coded version of the DL data sent by the BS. In fact, the WTRU will typically not decode the DL data correctly during phase 1 (because the worse the BS-WTRU channel the worse the BS signal is than the BS-RS channel), and the associated reliability metric (i.e. soft data) You need to decode the data. During phase 2, the WTRU soft-combines the phase 1 soft data with the data forwarded by the RS, and possibly after some retransmissions, correctly decodes the RS transmitted data.

Alternatively, the retransmitted signal of step 1 may be coded using rateless codes. These codes are channel codes suitable for use in single transmitter and multiple receiver communication scenarios. One advantage of these codes is that at the end of step 1, while the RS has decoded all the DL data correctly, the WTRU will only decode a subset of the total DL data (due to poor channel conditions). Since this is 'hard' data (i.e. corrected with probability 1), phase 2 data transmission by the RS may be limited to transmitting only residual DL data (not decoded correctly by the WTRU), and the WTRU By simply combining correctly decoded DL data in steps 1 and 2, the need for 'soft-combining' will be avoided. Finally, the transmitted signal may be channel coded using any of the existing point-to-multipoint optimal channel codes.

In the simple-cooperative relay transmission scheme, the phase 1 transmission details are the same as in the case of the simple-forwarding relay transmission scheme. At the end of step 1, the relay successfully decoded the DL data transmitted by the BS. In step 2, the BS and RS may transmit signals in a 'cooperative' manner and improve the efficiency of data transmission to the WTRU. There are several ways in which the BS and RS can cooperate, including diversity transmission of the same signal (which may be used for multipath diversity reception), coordinated transmission of signals for beamforming at the WTRU (transmitter). require channel state information), diversity transmission of distributed space-time coded signals (eg, Alamouti coding), and higher rate transmission using distributed spatial multiplexing schemes.

Effective data rates that can be achieved using these various transmission schemes are discussed below. To calculate the effective data rate, the rates achievable on each link (BS-RS, RS-WTRU, and BS-WTRU) during each of the two steps are combined to obtain the effective achievable rate for each relay transmission scheme. get This combined rate is the "effective throughput TP_effIt can be understood that the achievable rate for each link is either a theoretical information capacity rate or a rate curve calculated from SINR vs. link level simulations.

TPeff for simple-forwarding RTS

This RTS is also referred to as a 'two-hop' scheme for simplicity. In this example, the BS sends b information bits to the selected RS until the selected RS decodes all of the information bits. The RS may then send the decoded bits. Only then does the WTRU initiate the decoding process. The effective throughput in this case is expressed by the following equation.

<img file="KR20100109984A_D0001.tif" />

Equation (1)

here,<img file="KR20100109984A_D0002.tif" />ego, <img file="KR20100109984A_D0003.tif" />

<b>TP for multicast-forwarding RTS</b><b>_eff</b>

As mentioned above, channel codes and rateless codes can be used for multicast-phase 1. In this example, rateless codes are used. In a theoretical sense, rateless codes are an infinite length stream of encoded bits that make the decoding process independent of channel conditions. The WTRU may start decoding DL data sent from the BS to the RS upon initiation of communication by the BS. Thus, the WTRU rates some of the bits being transmitted from the BS in step 1<img file="KR20100109984A_D0004.tif" />decode it with In step 2, the RS rates only the remaining bits that the WTRU has not yet decoded.<img file="KR20100109984A_D0005.tif" />Resumes transmission from the BS by transmitting to . This is as follows:

<img file="KR20100109984A_D0006.tif" /> Equation (2) is

<img file="KR20100109984A_D0007.tif" /> Equation (3)

In this example, the effective throughput satisfies the following equation.

<img file="KR20100109984A_D0008.tif" /> Equation (4)

<b>TP for simple-cooperative RTS</b><b>_eff</b>

As described above, the DL cooperative transmission from the BS and RS in step 2 may be viewed as a distributed antenna array transmission. Therefore, this scheme is also called simple-DAA (DAA scheme). The DAA scheme enables the BS and RS to simultaneously transmit different bits of information to the WTRU. Therefore, those signals inevitably interfere with each other. The WTRU uses Successive Interference Cancellation (SIC) to distinguish between interfering signals. Assuming perfect interference cancellation at the WTRU, the rate achieved at the WTRU in step 2 satisfies the following equation.

<img file="KR20100109984A_D0009.tif" /> Equation (5)

where R_BS-U(2) is the transmission rate of the BS in step 2, R_BS-U(1) is the BS rate in step 1.

Now the effective throughput is given by equations (1) and (5) as:

<img file="KR20100109984A_D0010.tif" /> Equation (6)

<b>TP for Multicast-Cooperative RTS</b><b>_eff</b>

As mentioned above, channel codes and rateless codes can be used for multicast-phase 1. In this example, rateless codes are used. The BS and RS will split only the bits that the WTRU did not recover during phase 1. Effective Throughput TP_eff(Rateless-DAA) is derived from the following equation.

TP_eff(lateless) = <img file="KR20100109984A_D0011.tif" /> Equation (7)

As an alternative, but in more detail, an example of this RTS called Protocol 1 (P1) will now be described.

9 is a flowchart of Protocol 1 (P1) 900 defined for downlink (DL) as follows. Assuming a message of m bits, BS 910 can perform rate R1; BS; Encode the m bits with RS and transmit them in step 1. RS9920) must decode all data successfully, so m is<img file="KR20100109984A_D0012.tif" />should follow During T1, the WTRU 930 also receives a signal and attempts to decode it.

In step 2, BS 910 and RS 920 use layered distributed space-time codes with incrementally redundant encoding of the data to transmit data to WTRU 920 . The WTRU 930 uses its best space-time decoder and then combines the two incrementally redundant transmissions to fully decode the data at the end of step 2. The WTRU 930 combines the data from the two transmissions to successfully decode the data. In this example, R_1,BS,USis the maximum rate at which reliable transmission from the BS 910 to the WTRU is possible in step 1. R_{2, COOP}Let be the maximum rate at which reliable transmission to the WTRU 930 is possible by the cooperation of the RS 920 and the BS 910 in step 2 . Assuming an ideal incremental redundancy combining, the WTRU 930 can store the R of information for the message from the first transmission._1,BS,UEThe T1 bit and the R of the information for the message from the second transmission_{2, COOP}owns the T2 bit. To successfully decode the data, m is<img file="KR20100109984A_D0013.tif" />should have The maximum amount of data that can be transmitted during TTI (time T) is given by

<img file="KR20100109984A_D0014.tif" /> Equation (8)

To maximize equation (8),

<img file="KR20100109984A_D0015.tif" /> Equation (9)

This rate-balancing equation allows for both splitting the TTI into Phase 1 and Phase 2 and the maximum achievable transmission rate. The maximum achievable rate is:

<img file="KR20100109984A_D0016.tif" /> Equation (10)

<img file="KR20100109984A_D0017.tif" /> Equation (11)

Protocol 1 (P1) is also applicable for the uplink (UL). The UL example is similar to that shown in FIG. 8 , but the BS 910 and WTRU 930 roles are reversed (not shown). Protocol 1 (P1) is described below for the UL case. The WTRU 930 generates message/packet m. Such a message/packet may be in the form of a MAC protocol data unit (PDU) or any other form. In step 1, for example, in the first TTI, the WTRU sends m to RS 920 and BS 910 using a modulation and coding scheme (MCS) appropriate for the WTRU-RS link. The BS also monitors this transmission in step 1. In step 2, e.g., at a later TTI, WTRU 930 and RS 920 send m to BS 910 using a distributed space-time code, in a different increment than that sent in step 1 Transmits an Incremental Redundancy (IR) version.

BS 910 uses an appropriate receiver, e.g., an optimal space-time decoder in step 2. Since m may have received multiple IR versions in steps 1 and 2, BS 910 combines the received versions to improve decoding of m (e.g., hybrid automatic repeat request (HARQ) combine) do.

<b>Split RTS or MAC-level cooperative RTS</b>

Split RTS uses multicast-forwarding RTS in conjunction with direct transmission to improve performance. In any of the four RTSs introduced above, the key factor determining the effective throughput is the duration (T1) of phase 1, the period during which DL data is moved from the BS to the RS. In these examples, the effective throughput increases if the time taken to do so is reduced. In one example of split RTS, BS converts DL data b bits into two data streams b_RS and b_BSStep 1 can be shortened to divide by . BS to RS in the first step b_RSwill forward only b to the WTRU in step 2_BSwill send where b = b_BS + b_RSis assumed to be In this embodiment, the BS, prior to the start of step 1, contains the original b bits in two parts, b_RS and b_BSIt will ask you to know if it will be split into . Splitting the b bits can be performed at the MAC level or the PHY level. The original data dedicated to the WTRU from the start may be partitioned according to channel conditions and to accommodate simultaneous transmission. Another embodiment combines two different messages intended for the WTRU and b for each according to the channel constraint._RS and b_BSsend using These constraints are b_RS teen b_BS ratio or T₁ vs T₂ converted with respect to the ratio.

Two variants of split RTS are possible, depending on whether the phase 1 data transmission is 'simple' (eg using channel coding) or 'multicast' (eg using rateless coding).

In the simple-split RTS embodiment, assuming that the phase 1 transmission is 'simple' as described above, the BS uses a coding technique that allows the RS to decode only the transmitted codewords, b_RS Bits will be sent to RS in step 1. The supported rate on the BS-RS link is R<i>_BS-RS</i>is marked with here,

<img file="KR20100109984A_D0018.tif" /> or <img file="KR20100109984A_D0019.tif" /> Equation (12)

In step 2, RS is successfully decoded b_RS bit rate R_RS-Uwill be forwarded to the WTRU. BS is b_BS bit rate R_BS-U(2) will transmit at the same time. this is,

<img file="KR20100109984A_D0020.tif" /> Equation (13)

thus, <img file="KR20100109984A_D0021.tif" /> Equation (14)

The split in the data is <img file="KR20100109984A_D0022.tif" />is satisfied with Equation (15)

soon, <img file="KR20100109984A_D0023.tif" /> Equation (16)

In the multiplexed mode transmission in phase 2 where there is perfect successive interference cancellation at the WTRU side, the overall rate achieved at the WTRU is

<img file="KR20100109984A_D0024.tif" /> Equation (17)

achieve

The effective throughput achieved in the WTRU is

<img file="KR20100109984A_D0025.tif" /> Equation (18)

can be expressed as

In the multicast-split RTS embodiment, assuming that the step 1 transmission is 'multicast', the BS sends b to the RS in step 1 using the rateless coding technique._RS bits can be transmitted. In this example, the RS can fully decode the transmitted message, but will enable other receivers to decode parts of it. b₁, indicates bits that the WTRU can intercept and extract from the BS-RS transmission in step 1. b₂indicates the bits the WTRU receives in step 2. where b = b₁ + b₂am.

The supported rate on the BS-RS link is R<i>_BS-RS</i>w, BS-WTRU link rate R<i>_BS-U</i>is marked with here,

<img file="KR20100109984A_D0026.tif" /> Equation (19)

or <img file="KR20100109984A_D0027.tif" /> Equation (20)

In step 2, BS b_BS bit rate R_BS-U(2) can be transmitted, and RS is b_BS - b₁ Bits to WTRU rate R_RS-Uwill be forwarded at the same time.

<img file="KR20100109984A_D0028.tif" /> Equation (21)

thus, <img file="KR20100109984A_D0029.tif" />

The split in the data is <img file="KR20100109984A_D0030.tif" /> Equation (22)

is satisfied with

This equation can be temporally transformed as follows.

<img file="KR20100109984A_D0031.tif" /> Equation (23)

Assuming multiplexed mode transmission in step 2 and perfect successive interference cancellation to the receiver, the overall rate achieved at the WTRU is

<img file="KR20100109984A_D0032.tif" /> Equation (24)

is satisfied with

And, the effective throughput achieved at the WTRU may be expressed as:

<img file="KR20100109984A_D0033.tif" /> Equation (25)

<b><u>Data Flow Analysis of Multicast-Split RTS</u></b>

10 is a flow diagram illustrating a multicast-split RTS embodiment referred to as protocol 2 (P2) 1000 and defined as follows for the DL case. BS 1010 generates two messages of m1 and m2 bits. In step 1, BS 1010 sends a first message (m1 bits) to RS 1020 at a rate R_1,BS,RS, In other words, <img file="KR20100109984A_D0034.tif" />send to As in P1, the WTRU 103 monitors for this transmission. In step 2, the RS 1020 forwards the information it received in step 1 to the WTRU 1030. This is rate R_2,RS,UEis performed with BS 1010 at the same time the second message (m₂ bit) to the WTRU 1030 . This is rate R_2,BS,UEis performed with The WTRU 1030 uses a multi-user detector (not shown), eg, SIC, in step 2 and in conjunction with incremental redundancy for the first message to receive data. To analyze the performance of this protocol, various limitations exist. First, as for P1, efficient transmission of the first message may occur according to the rate-balancing equation as follows.

<img file="KR20100109984A_D0035.tif" /> Equation (26)

However, rate R<i>_2,RS,UE</i> and R<i>_2,BS,UE</i>are also dependent on each other. In addition to satisfying the per-link capacity constraint, the rate must also satisfy the MAC capacity constraint.

<img file="KR20100109984A_D0036.tif" /> Equation (27)

Hypothesized rate R as defined for P1_2;COOPis the optimal transmitter cooperation rate. Although cooperation at the PHY layer is not part of P2 (see above), a close relationship between the achievable throughput for P1 and P2 is shown here. Obviously, maximizing throughput requires that equation (27) satisfy the equation. Therefore, Equation (26) and the constraint<img file="KR20100109984A_D0037.tif" />with:

<img file="KR20100109984A_D0038.tif" /> Equation (28)

In interference limited cellular deployments, P2 provides slightly better performance than P1. Either both provide a significant improvement over the relay-free case, or simple two-hop relay and P2 outperform P1. The key difference lies in the management of cooperation. In P1, a single flow is sent by the MAC during (T1+T2), while creating and sending two MAC flows.

To schedule the data, the MAC knows that the quality of the composite link includes three component PHY links (BS-to-RS, RS-to-WTRU, BS-to-WTRU). In addition, to ensure cooperation between BS 1010 and RS 1020 in step 2, RS 1020 must be centrally scheduled by BS 1010, and PHY and RS 1020 of BS 1010 are It must be strictly synchronized to the channel symbol level.

P2 manages the transmission of the two flows almost independently and without strict PHY layer synchronization. A constraint on the two flows is that the sum rate at the WTRU 1030 does not exceed its sum rate constraint. Assuming that this constraint is satisfied, the BS MAC 1040 manages RS transmission only in a limited manner. BS MAC 104 schedules data to RS 1020 (based solely on BS-to-RS link quality) to ensure that the RS buffer (not shown) is not empty. The BS and RS MAC 1040 (RS MAC not shown) must negotiate how the rates will be repartitioned in step 2 so that the combined rate for the WTRU 1030 does not violate the sum rate constraint. However, the BS MAC 1040 need not specify to the RS MAC (not shown) which particular packets are scheduled for transmission. Once RS 1020 indicates receipt of a packet, HARQ management for that packet may be surrendered to the RS.

The RS MAC scheduler (not shown) may operate independently of the BS MAC scheduler (not shown) so that the BS 1010 control of the RS 1020 occurs at a slower rate. PHY layer operation of P2 does not require coordination, since BS 1010 and RS 1020 simply transmit different flows in step 2 in a non-cooperative manner.

P2 is also applicable to UL. The UL scenario is similar to that shown in FIG. 10 , but the BS 1010 and the WTRU 1030 serve interchangeably (not shown). P2 is described herein for the UL case.

In this embodiment, the WTRU 1030 generates any two messages/packets m1 and m2. m1 and m2 may be created at different times. These two messages may be in the form of two MAC PDUs, or any other form. In step 1, for example, in the first TTI, the WTRU 1030 sends m1 to the RS 1020 and the BS 1010 using a MAC suitable for the WTRU-RS link. BS 1010 also monitors this transmission in step 1. In step 2, e.g., at a later TTI, RS 1020 forwards the information received in step 1 to BS 1010 using an MCS suitable for the RS-BS link, and receives from WTRU 1030 It transmits a different IR version than In step 2, eg, at a later TTI, the WTRU 1030 also sends a second message m2 to BS91010 using an MCS suitable for the WTRU-BS link.

BS 1010 may use, in step 2, an appropriate receiver, eg, a multi-user detector or SIC (not shown) to receive m1 and m2. Since some messages, such as m1, may receive multiple IR versions (eg, in steps 1 and 2), BS91010 combines the received version (eg, HARQ) to improve decoding of the message. combine).

<b><u>Relay transmission scheme for OFDM type system</u></b>

The frequency dimension may be used in the cooperative relay scheme. The following embodiments apply to DL, but UL is discussed for simplicity.

The frequency band allocated for transmission between the WTRU and the BS is divided into two frequency bands, W11 and W12. W11 is used for transmission from WTRU to BS, and W12 is used for transmission from WTRU to RS. In general, a WTRU may use different subcarriers to transmit data to different receivers, RS and BSs. This embodiment assumes that the channel between the WTRU and the relay station is better than the channel between the WTRU and the BS. For the full and partial information relay examples below, it is assumed that the relay operates in TDM mode, which means that the relay cannot receive and transmit signals at the same time. For the continuous transmission example, it is assumed that the relay operates in FDM mode, which means that the relay cannot receive and transmit signals in the same frequency band.

<b><u>Full information relay</u></b>

11 is an exemplary diagram of an embodiment of the entire information relay 1100. In this embodiment, RS 1110 has full information during the uplink call, and below, the signaling sequence between WTRU 1120 , RS 1110 and BS 1130 is described.

The WTRU 1120 sends packets 1121 and 1122 to RS 1110 and BS 1130 at the same time but at different frequencies (at f1 and f2), and RS 1110 sends the packet before BS 1130 does. You will get that packet exactly. After the RS 1110 successfully receives the signal from the WTRU 1120 , the RS 1110 sends an ACK 1125 to the WTRU 1120 . The BS 1130 now correctly gets the b1 bits from the direct transmission 1135 of the WTRU 1120 . There are three options for sending the remaining b2 bits.

The first option is a forwarding relay 1140 . In this option, the WTRU 120 stops transmitting at W11, and the RS 1110 sends the b2 bits using W11 and W12 to the BS 1130 until it receives an ACK 1145 from the BS 1130. Forward (1142). Benefits under this option include power savings at the WTRU 1120, which results in signaling at the WTRU 1120 as the WTRU 1120 transmits its packets only after the RS 1110 successfully receives the transmission. Because it is less demanding. The required signaling includes an ACK 1125 from the RS 1110 to the WTRU 1120 and an ACK 1145 from the BS 1130 to the RS 1110 . However, the BS 1130 needs to be notified that a transmission is coming from the RS 1110 after the RS 1110 sends back the ACK 1125 to the WTRU 1120 . The effective rates are:

<img file="KR20100109984A_D0039.tif" /> Equation (29)

here,

<img file="KR20100109984A_D0040.tif" />

The second option is cooperative relay 1150 . In this option, the WTRU 1120 does not stop transmitting at W12. The WTRU 1120 and the RS 1110 cooperatively transmit b2 bits at W11 ( 1152 ) and at W12 ( 1155 ) to the BS using a predetermined distributed MIMO mode or predetermined cooperative diversity, respectively. It should be noted that "predetermined" in this example means that no signaling is required between the RS and the WTRU as to the distribution and how cooperative diversity is performed.

The advantage of this option is that a shorter time is required for a successful transmission, and thus a possibly higher effective rate is possible compared to the first option. However, to achieve this higher effective rate, more power consumption at the WTRU 1120 is required compared to the first option, and the ACK 1125 from RS 1110 to WTRU 1120, RS 1110 and More signaling is required for synchronization between WTRUs 1120 , ACK 1145 from BS 1130 to RS 1110 and WTRU 1120 , and BS 1130 indicates that a transmission is coming from WTRU 1120 . needs to be notified, and the BS 1130 also needs to be informed of the transmission mode.

The effective rate is: For cooperative diversity in phase 2, RS 1110 and WTRU 1120 cooperatively transmit the same bits (b2 bits) to BS, but increased frequency diversity enhances communication reliability of b2 bits different frequency bands are used. For distributed MIMO in step 2, RS 1110 and WTRU 1120 transmit different bits to the BS independently, and the total number of bits transmitted by RS 1110 and WTRU 1120 is b2.

<img file="KR20100109984A_D0041.tif" /> Equation (30)

A third option is FDM MIMO 1160 . In the third option, RS 1110 forwards all remaining bits (b2 bits) to BS 1130 at W12 until receiving ACK 1165 from BS 1130, and WTRU 1120 Initiate a new transmission at W11 ( 1167 ). During this period, there are b bits successfully transmitted from the WTRU 1120 and the BS 1130 .

The advantage of this option is that the overall throughput is probably higher compared to the first and second options described above due to the efficient transmission. However, more signaling is required for ACK from RS to WTRU and ACK from BS to RS, BS tells RS that RS forwards the remaining bits and that WTRU initiates a new transmission after RS sends back ACK to WTRU. need to be informed. In order to maximize throughput, the bandwidth allocation in step 1 and step 2 may be different.

<b><u>partial information in relay</u></b>

For the embodiment described above with respect to relaying of full information, several schemes may be used to describe how relaying is used in FDM mode to help the WTRU send information to the BS. In these schemes, before the RS initiates relaying information to the BS (this duration is defined as step 1), only an ACK will be sent from the RS to the WTRU after the RS has succeeded in receiving all bits from the WTRU. required, which reduces signaling overhead. However, in this embodiment, the WTRU sends all bits to the RS, some of which are redundant because the WTRU sent some bits to the BS in step 1. In order to save power at the WTRU, it would be more efficient to avoid sending to the RS these bits sent by the WTRU to the BS in step 1 .

Thus, in this embodiment, an example is described in which the RS receives some bits from the WTRU before forwarding them to the BS. 12-14, the WTRU sends b1 bits (1210) and sends b2 bits (1220) to BS and RS, respectively, at different frequencies (f11 and f12). A proper design of bit allocation/bandwidth allocation between the transmitting WTRU-RS and the WTRU-BS is such that the BS and RS detect those bits successfully simultaneously. After RS successfully receives the b2 bits, there are three options for sending the b2 bits from RS to BS, similar to the full information relay embodiment.

12 is a diagram of an exemplary forwarding relay 1200 . After the WTRU sends b1 bits to BS and RS respectively ( 1210 ) and sends b2 bits ( 1220 ), the RS forwards the b2 bits to BS 1230 in step 2 .

13 is a diagram of an exemplary cooperative relay 1300 . Using cooperative diversity in step 2, the RS and WTRU cooperatively transmit the same bits (b2 bits) to the BS, but use different frequency bands to increase frequency diversity. Using cooperative MIMO in step 2, RS and WTRU transmit different bits to BS independently and the total number of bits transmitted by RS and WTRU is b2. The effective bit rate for cooperative MIMO is:

<img file="KR20100109984A_D0042.tif" />

thus,

<img file="KR20100109984A_D0043.tif" /> Equation (31)

14 is a diagram of an exemplary forwarding relay using FDM MIMO. The WTRU sends b1 bits ( 1210 ) and b2 bits ( 1220 ) to the BS and RS, respectively. The WTRU sends b' bits to the BS (1410) and the RS sends b2 bits to the BS (1420).

To maximize throughput, bandwidth allocation in steps 1 and 2 may be different.

<b><u>continuous transmission</u></b>

In this clause, it is assumed that RS is a forwarding repeater operating in FDM mode. The RS and WTRU keep sending packets to the BS, making full use of radio resources. All nodes always transmit. That is, it is not TDM. However, step 1 and step 2 are separated to distinguish between BS transmission and RS auxiliary steps. Table 1 shows the WTRU and RS operations during continuous transmission.

<tables num="1"><table><tgroup cols="3"><colspec colnum="1" align="justify" colname="col1" colwidth="4127" /><colspec colnum="2" align="justify" colname="col2" colwidth="3065" /><colspec colnum="3" align="justify" colname="col3" colwidth="3597" /><tbody><row><entry align="justify" colname="col1">hour</entry><entry align="justify" colname="col2">RS action</entry><entry align="justify" colname="col3">WTRU behavior</entry></row><row><entry align="justify" colname="col1">T11 (i.e. phase 1 of timeslot 1)</entry><entry align="justify" colname="col2">N/A</entry><entry align="justify" colname="col3">WTRU sends B1 (ie data block 1) on f11</entry></row><row><entry align="justify" colname="col1">T12 (i.e. phase 2 of timeslot 1)</entry><entry align="justify" colname="col2">RS forwards B1 on f12 </entry><entry align="justify" colname="col3">The WTRU sends a new data block B2 on f11.</entry></row><row><entry align="justify" colname="col1">T21 (phase 1 of timeslot 2)</entry><entry align="justify" colname="col2">RS forwards B2 on f12. </entry><entry align="justify" colname="col3">The WTRU sends a new data block B3 on f11.</entry></row><row><entry align="justify" colname="col1">T22 (phase 2 of timeslot 2)</entry><entry align="justify" colname="col2">RS forwards B3 on f12.</entry><entry align="justify" colname="col3">The WTRU sends a new data block B4 on f11.</entry></row><row><entry align="justify" colname="col1">TN1 (phase 1 of timeslot N)</entry><entry align="justify" colname="col2">RS forwards B2 on f12.</entry><entry align="justify" colname="col3">The WTRU sends a new data block B(N+1) on f11. </entry></row><row><entry align="justify" colname="col1">TN2 (phase 2 of timeslot N)</entry><entry align="justify" colname="col2">RS forwards B(N+1) on f12.</entry><entry align="justify" colname="col3">The WTRU sends a new data block B(N+2) on f11.</entry></row></tbody></tgroup></table></tables>

As a result, the WTRU continuously transmits data on f11 and the RS always forwards data on f12. Just as time is divided into two steps for WTRU and RS transmission, frequencies are also divided into two segments for WTRU and RS transmission.

<b><u>Relay Transmission Scheme for Multiple WTRUs</u></b>

In the following example RTS, a cell may include one or more WTRUs and one or more RSs. Depending on the channel conditions between the WTRU and the BS and RS, a direct transmission scheme between the BS and RS or a specific RTS comprising one or more RSs may be optimal. In this section, multiple protocols are discussed for serving multiple WTRUs in a cell with multiple RSs using one of the RTSs described above. Three fundamentally different methods are discussed below.

The first method (Method 1) is TDDR &amp; It is referred to as FTDDR. In this example, the BS serves different WTRUs in different time 'slots'. In TDDR, phase 1 DL transmissions are received only by RS. In FTDDR, phase 1 DL transmissions are received by the RS as well as the WTRU. See Figures 15 and 16.

The second method (Method 2) is referred to as PTDDR. In this example, the BS may serve multiple WTRUs in step 2 of the TDM-relay operation scheme. See FIG. 18 .

The third method (Method 3) is referred to as STDDR and FSTDDR. In this example, the BS serves multiple WTRUs in both phase 1 and phase 2 of the TDM relay scheme. 19 is an exemplary diagram for STDDR 1900 . FSTDDR is described later.

<b><u>TDDR solution</u></b>

15 is a diagram of an example TDDR solution 1500 . Assuming there are L repeaters in a cell, there are a number of available options for directing data to the WTRU. The BS may communicate directly with the WTRU ( 1510 ). Alternatively, the BS selects a particular repeater, sends data to this repeater, and allows the repeater to forward the data (1520). Finally, this method may involve several repeaters simultaneously. Here, they all operate identically as distributed multiple-input multiple-output (MIMO) antennas in the relay stage. Whether transmitting directly to a particular WTRU, through a single repeater, or through a set of repeaters depends, for example, on the availability of repeaters, the location of the WTRU, and the relative channel quality between the WTRU and relative transmitters.

The protocol for determining how to transmit to a particular WTRU may be based on maximizing the resulting throughput to the WTRU as follows. For example, R_BRdenotes the achievable data rate between BS and RS, and R_RUdenotes the achievable data rate between the RS and the WTRU, R_BULet n denote the data rate achievable between the BS and the WTRU.

If the WTRU is sent directly by the BS, its throughput is calculated directly:

<img file="KR20100109984A_D0044.tif" /> formula (32)

If a single repeater is used, the throughput is calculated as follows:

<img file="KR20100109984A_D0045.tif" /> Equation (33)

Equation (22) is determined by discounting the relay-to-WTRU throughput by taking into account the time required to send data to the relay and balancing the two parts. Values T1 and T2 are each R_RU and R_BRindicates the duration corresponding to .

For multiple repeaters, there are several options. In one option, the plurality of repeaters are treated as a single multi-antenna repeater, and thus the rate R_BR and R_RUis calculated In another option, throughput can be calculated as in equation (33) for each repeater and then added for the group. Equation (33) is determined by discounting the repeater-to-WTRU throughput by taking into account the time required to send data to the repeater and balancing the two parts.

The transmission direction determination is then made as follows (ignore the case of "grouped delay" for simplicity, but scalability is obvious). Whether the WTRU is served directly by the BS or served by the BS via RS is the discounted throughput<img file="KR20100109984A_D0046.tif" />(L is the number of RSs) and the direct link throughput <img file="KR20100109984A_D0047.tif" />depend on Among these throughputs, the maximum throughput is<img file="KR20100109984A_D0048.tif" />, which is the end-to-end throughput that can be achieved. That is, the station that can achieve the highest throughput will serve the WTRU directly. For multiple WTRU scenarios,<img file="KR20100109984A_D0049.tif" />is taken as input of the scheduler.

<b><u>scheduler</u></b>

Whether or not a WTRU will receive transmission in a particular TTI depends on the scheduling function (eg, HSDPA scheduler at the BS). The scheduling function can input decision variables (e.g.,<img file="KR20100109984A_D0050.tif" />) can be used as

According to the prescribed protocol, the decision variable is the channel quality condition (i.e. R_RU, R_BR, R_BRis calculated according to the channel condition). A typical HARQ scheduler is used to determine the scheduling.

<b><u>feedback</u></b>

The channel condition may be reported to the BSs using feedback (eg, CQI using HSDPA). Note that the quality of the repeater-to-WTRU channel may be reported to the BS either directly from the WTRU or by the repeater. When reported by repeaters, feedback from multiple WTRUs may be summed into one transmission.

The ACK/NACK may be transmitted directly or forwarded through the repeater by the uplink. In this case, different ACK/NACK may or may not be summed across WTRUs and TTIs.

<b><u>FTDDR solution</u></b>

16 is a diagram of another embodiment using a Fountain Extended Time Division Duplexed Relaying (FTDDR) scheme 1600 . In all of the preceding schemes, WTRUs to be delivered via a repeater must wait for the repeater to transmit in order to initiate collection of useful data. Thus, a delay is introduced and the throughput gain is reduced. One way to overcome this problem is to use fountain encoding at each transmitter.

The fountain code refers to a type of code capable of driving an outage probability to 0 without channel state information from a source. The transmitter encodes the data and streams it into an infinite length code (in packets), like a fountain generating an endless water drop. The receiver collects information until it completely recovers the data, much like holding a bucket under a spring and collecting drops until the bucket is full. One of the points regarding Fountain Code is that the source data can be recovered from any set of sufficiently encoded packets.

A relay protocol based on the fountain code and TDD is shown in FIG. 16 . Data is transmitted directly from the BS to the WTRU (1610)<img file="KR20100109984A_D0051.tif" />is transmitted with the help of RS (1620). here,<img file="KR20100109984A_D0052.tif" />indicates the achievable data rate between the BS and the RS, <img file="KR20100109984A_D0053.tif" />denotes the data rate directly achievable between the BS and the WTRU. mark of the right ear<img file="KR20100109984A_D0054.tif" />indicates that this is for a system with FTDDR. if,<img file="KR20100109984A_D0055.tif" />back side, <img file="KR20100109984A_D0056.tif" />and where, <img file="KR20100109984A_D0057.tif" />denotes the achievable throughput between the BS and the WTRU. In this case, all data is sent directly to the WTRU without the help of RS. if<img file="KR20100109984A_D0058.tif" />If,

<img file="KR20100109984A_D0059.tif" /> Equation (34).

in this case, <img file="KR20100109984A_D0060.tif" />In , the BS broadcasts information to both the RS and the WTRU, and the RS sends some "new" information. <img file="KR20100109984A_D0061.tif" />receive as <img file="KR20100109984A_D0062.tif" />, the RS relays "new" information to the WTRU. Here, the term "new" means that the information broadcast from the BS is received by the RS,<img file="KR20100109984A_D0063.tif" /> It means that it is not received by the WTRU. Maximization of the selection of all L RSs,<img file="KR20100109984A_D0064.tif" />this is obtained here,<img file="KR20100109984A_D0065.tif" />is the throughput achievable with the FTDDR scheme.

According to the HARQ scheduling protocol, unlike the previous schemes, the BS does not pre-dedicate the repeater. In this method, the repeater transmits only ACK to the BS. Once received, either the first relay ACKing is selected for scheduling, or the BS will allow a time observation frame to collect sufficient relay ACKs and select among them according to a selected criterion.

If more than one repeater is selected, the repeaters may be scheduled using the cellular scheduler. If more than one WTRU is served by one repeater, the data to these WTRUs may be pooled in one transmission or scheduled separately. Scheduling between WTRUs may be accomplished using, for example, a scheduler of a type similar to a conventional cellular system, such as HSDPA. According to this method, channel state feedback is not required in FTDDR because the codes are rateless.

The repeater only needs to send an ACK to the BS to allow for further scheduling. WTRU ACK/NACK needs to be available only in BS. It may be transmitted directly or forwarded through the repeater by the uplink. In this case, different ACK/NACK may or may not be aggregated across WTRUs and TTIs.

<b><u>PDTR solution</u></b>

17 is an exemplary diagram illustrating parallel transmission 1700 (Parallel Transmission Duplexed Relaying). According to this protocol, a cell has L repeaters. For each WTRU, one of the following L+1 transmission options is selected: transmission via relay L or direct transmission from the BS. In this example, the scheduling is based on channel conditions. Explicitly stated, it may change periodically and at a rate achievable for the WTRU.

At each TTI, the transmission is also split into two sub-TTIs (steps). During step 1 ( 1710 ), the BS transmits to the repeater. These transmissions contain information that the relay must send to the WTRUs. During phase 2 ( 1720 ), the repeater and the BS transmit (simultaneously) to the WTRUs. It should be noted that not all WTRUs (or repeaters) are scheduled at each stage. Scheduling within each stage and at each transmitter (BS/ready for stage 2) is performed according to a scheduling process, as in current HSDPA, downlink LTE, etc. The decision as to how to transmit to a particular WTRU can be calculated as described above, i.e., via Equation (33) or (34), or a discounting formula customized for this particular protocol. may be based on maximizing the resulting throughput for the WTRU.

Unlike TDDR, HARQ scheduling can be performed independently by the base station and by each repeater. In step 1 (1710), the base station schedules transmission to the repeater as follows. WTRU data for WTRUs associated with the same repeater is either "pooled" into a single transmission, or scheduled separately. Scheduling is performed using the same type of scheduler as for a conventional cellular system, such as, for example, HSDPA. At step 2 1720, each relay and BS independently schedule the transmission of data to the WTRU as in a conventional protocol such as, for example, HSDPA.

Channel state information is reported back to the base station using feedback, as in current systems (eg, CQI using HSDPA). However, the repeater must be aware of the quality of the repeater-to-WTRU channel in order to perform its own independent scheduling. Thus, while the quality of the repeater-to-WTRU channel is reported by the WTRU directly to the BS, reporting through the repeater is preferred. When reported by repeaters, feedback from multiple WTRUs may be aggregated into a single transmission.

Step 1 and Step 2 require separate ACK/NACK processes ((Repeater-to-BS in Step 1) and (WTRU-to-Smitter (Relay or BS in Step 2)). Thus, each Each operation in an HARQ system without HARQ operates independently, depending on the structure of the control and signaling protocol, the repeater may or may not need to forward its WTRU's ACK/NACK to the BS.

<b><u>STDDR solution</u></b>

18 is an exemplary timing diagram 1800 of a Superposition Time Division Duplexed Relaying (STDD) relay scheme. This method is an extension of the PTDDR protocol described above. According to this STDDR protocol, the BS 1810 schedules the different WTRUs 1820 based on their needs and channel conditions. In this example, these schedules are communicated to the WTRU 1820 either directly or via a repeater 1830 . As described above, TTIs are divided into two steps. At step 1 1840 , the BS 1810 transmits directly to the repeater and the WTRU 1820 simultaneously using superposition coding. Resources such as power may be shared equally or according to known power allocation algorithms. Following a second step 1850 , the repeater 1830 may take over part of the communication to forward the data they have received to their intended WTRUs 1820 . On the other hand, BS 1810 continues to serve these WTRUs 1820 scheduled on the direct link at full power.

According to this method, <img file="KR20100109984A_D0066.tif" />denotes the achievable data rate between BS and RS, <img file="KR20100109984A_D0067.tif" />Let n denote the achievable data rate between BS and WTRU1 in step 1. In step 2,<img file="KR20100109984A_D0068.tif" />denotes the achievable data rate between BS and WTRU1, <img file="KR20100109984A_D0069.tif" />Let be denote the achievable data rate between RS and WTRU2. Therefore, for WTRU1,

<img file="KR20100109984A_D0070.tif" /> Equation (35)

And, for WTRU2,

<img file="KR20100109984A_D0071.tif" /> Equation (36)

<b><u>FSTDDR solution</u></b>

In another embodiment, Fountain &amp; A superposition coding time division duplex relay (FSTDDR) protocol may be used. According to this method, FTDDR and STDDR are combined. By doing this, WTRUs that do not need to be delivered via the relay are scheduled to transmit at the start of the communication, and thus do not wait for the relay to complete its service. Also, all data streams are fountain-type encoded, thus avoiding feedback.

Thus, assuming L relays, M WTRUs may be delivered via these relays, and N other WTRUs may be delivered directly. Communication in each TTI is performed in two steps as in STDDR. Transmission through each repeater is performed as in FTDDR. Thus, assuming a power saving scenario, in step 1, the repeater and N WTRUs are scheduled simultaneously. In step 2, the repeaters schedule and serve the M WTRUs, while the other N WTRUs continue to be served by the BS at a higher power level.

In the case of HARQ scheduling, communication through the repeater is scheduled as in the above-described FTDDR example. Direct communication is scheduled as in a typical cellular system, for example HSDPA. The repeater and WTRUs are served on the direct link and are scheduled as in STDDR. Because the codes used are rateless, channel state feedback is not required in FTDDR. In case of ACK/NACK delivery, the relay sends only ACK to the BS to allow further scheduling. ACK/NACK is available only in BS. It may be transmitted directly or forwarded through the repeater by the uplink. In this case, different ACK/NACK may or may not be aggregated across WTRUs and TTIs.

<b><u>relay protocol architecture</u></b>

The following example operations in the user plane may be used for single cell-single relay cooperation in both the two-hop mode and the diversity mode. A dedicated BS-RS channel may be used in the two-hop mode. Assume a single cell (ie, a single BS), M repeaters, and multiple WTRUs. Repeaters are designed to improve the link quality between a base station (BS) and users (WTRUs). Each WTRU is served by a single repeater.

The BS treats the repeater as a WTRU and communicates with it. On the other hand, the repeater operates as a BS towards the WTRU and performs communication. To describe the next level of communication operation, it is necessary to assume the protocol layers supported by the repeater.

Consider the BS side of RS. Since this aspect simulates a WTRU, there is a choice as to how many WTRU protocol stacks are implemented. There are various alternatives, such as:

19 shows a first alternative 1900 . The BS side of the repeater 1910 implements the WTRU protocol stack down to the PHY level. PHY processing in RS may be performed in alternative methods. A first alternative, labeled amplification and forward (AF) relaying, involves simple amplification and forwarding at the RF level. A second alternative is demodulation-remodulation-forwarding. In this alternative, noise can be removed or suppressed only if the link to the repeater has a very high fidelity (ie no channel code is actually needed). Here, the signal is further processed so that errors are corrected in the RS.

During the relay process, the radio signal characteristics on the BS-RS link and the RS-WTRU link need not be identical. In a first option, the RS-WTRU link may use a different frequency or code compared to the BS-RS link. In a second option, the modulation on the RS-WTRU link may be different from the modulation on the BS-RS link. In a third option, the error protection (ie, detection and/or correction) codes may be different on the BS-RS and RS-WTRU links.

Another type of relay technique is called compression and forward (CF) relaying. This technique requires that an alternative signal path exist between the BS and the WTRU so that, for example, a compressed signal transmitted from a repeater in the downlink can supplement the direct signal from the BS. This configuration is dealt with below in conjunction with the diversity mode.

20 illustrates a second alternative for implementing the WTRU protocol stack 2000 . In this alternative, the BS side of the repeater 2010 implements the WTRU protocol stack down to the MAC level. This scheme provides flexibility in resource allocation on the BS-RS and RS-WTRU links due to the incorporation of the MAC protocol into the RS. This also allows for a separate HARQ scheme for retransmission of erroneously received radio blocks between the BS-RS and RS-WTRU.

This exemplary approach is fairly transparent from the network/BS point of view as well as the WTRU's point of view. The impact includes modifications in the RLC protocol and knowledge of the part of the repeater's DRX interval in the BS scheduler.

The user-plane protocol stack within the repeater (and hence the complexity of the repeater) is minimized. Beyond the required PHY-layer functions, the repeater is a "mirror" of the MAC to the WTRU (to emulate the WTRU communicating with the BS) and the "mirror" of the MAC to the BS (to emulate the BS communicating with the WTRU). " is required to be maintained.

21 shows a third alternative for implementing the WTRU protocol stack 2100 . In this alternative, the BS side of repeater 2110 implements the WTRU protocol stack down to the RLC level. This example allows for various radio link control (RLC) functions such as link adaptation and retransmission between the RS and the BS/WTRU.

The RLC protocol can operate in any of ACK mode, no ACK mode, transparent mode, and persistent mode. Furthermore, the modes of the RLC protocol between BS and RS, and between RS and WTRU may be different.

By considering the transport of a single IP block, the data transfer between the BS and the WTRU via RS(s) will now be described. 21-23 are sequence diagrams illustrating various alternatives.

A first alternative is a PHY-level station. 22 shows an event sequence 2200 involved in the delivery of IP packets from BS 2210 to WTRU 2220 via RS 2230 . RS 2220 is assumed to be a simple PHY-level variant of the amplify-and-forward or decode-and-forward type.

PHY processing at RS 2220 may be performed in alternative manners. The first scheme, denoted amplification-and-forward (AF) relaying, involves simple amplification and forwarding at the RF level. The second method is demodulation-remodulation-forwarding. In this way, it can be eliminated or suppressed only if the link to the repeater has very high fidelity (ie, the channel code is not actually needed). The third method is decode-re-encode-forward (DF) relay. In this example, the signal is further processed to correct errors at RS 2230 . The fourth method is denoted as an adaptation scheme. In this scheme, the repeater can be adaptively switched to any of the above three schemes. For example, if the relay successfully decodes the message, it applies the decode-and-forward scheme. Otherwise, any of the remaining schemes may be applied, for example the AF scheme. As another example, if the repeater is heavily loaded, an AF scheme that consumes less resources may be applied. Otherwise, any of the other schemes, such as the DF scheme, can be applied.

During the relay process, the radio signal characteristics on the BS-RS link and the RS-WTRU link need not be identical. In a first option, the RS-WTRU link may use a different frequency or code compared to the BS-RS link. In a second option, the modulation on the RS-WTRU link may be different from the modulation on the BS-RS link. In a third option, the error protection (ie, detection and/or correction) codes may be different on the BS-RS and RS-WTRU links.

A second alternative to data transmission involves a MAC-level relay station. In this example, the BS treats the repeater like a WTRU and schedules it accordingly. However, this "repeater-WTRU" has a DRX cycle known to the BS.

The ACK from the repeater-WTRU is treated as a MAC-level (HARQ) ACK by the BS. The repeater-WTRU then acts as a BS for the WTRUs it communicates with. One particular problem is what to do if the repeater has an ACKed packet to the BS but fails to deliver it to the WTRU.

An example of a common strategy for solving this problem is: The repeater (acting as the BS) tries to forward the packet several more times according to the MAC (HARQ) protocol. However, at some point, the repeater must give up. The repeater can no longer perform HARQ-NACK because the repeater has already received an ACK (as if it were a WTRU). Thus, the NACK should occur at the RLC level, if necessary. Assuming that the RLC is operating in an acknowledged mode, the WTRU's RLC is likely already doing this. Solving the problem of impossible MAC NACK cannot be effectively solved by delaying MAC-level ACK. If such a delay occurs, in principle, the repeater may request the BS to retransmit. However, such retransmission only includes data already owned by the repeater. Therefore, there is no reason to request retransmission. In this example, the repeater can only delay the HARQ time-out.

If the RLC is in non-ACK mode, the packet is considered lost, which is acceptable (by the definition of non-ACK mode). However, the RLC of the network needs to be modified to see that the MAC-layer ACK is no longer an indication that the packet has actually been delivered.

23 is an exemplary diagram illustrating an event sequence 2300 involved for a MAC-level RS. The illustrated FIG. 23 does not solve the potential buffer overflow problem in the repeater's MAC. Specifically, since the BS 2310 does not know when the relay successfully (or unsuccessfully) forwarded data to the WTRU 2320, it attempts to push more data than the RS buffer can handle. . To prevent this, one or more of the following options may be used. These options are not exclusive and may be combined.

In a first embodiment, BS 2310 autonomously maintains an estimate of the state of the repeater buffer by knowing the maximum number of attempts RS 2330 makes to transmit data and how long it will take. In addition, the average time to forward a packet from the RS 2330 to the WTRU 2320 may be taken into account. This average time may be updated periodically by the repeater.

In the second embodiment, the RS 2330 may periodically communicate the buffer occupancy status to the BS 2310 . This can be done by introducing new MAC-level feedback signaling. This feedback signaling may be combined in a Relay Feedback CHannel (RFCH) along with other RS MAC-level feedback.

In a third embodiment, RS 2330 incorporates the buffer occupancy state (eg, along with channel state information) into the feedback that BS 2310 uses to schedule its transmission. There are a number of options for doing this. Often, standards provide a method for the WTRU 2320 to report its ability to receive data via a channel quality indicator (CQI). Such information may be provided to BS 2310 by RS 2330 . By artificially reducing the CQI, the RS 2330 may reduce the amount of data it receives. In this case, however, BS 2320 never really knows whether the reduction is due to buffer occupancy problems or channel conditions.

In a fourth embodiment, if the buffer is full, RS 2330 responds with a special "buffer full" NACK whenever BS 2310 pushes data. This is done when the first BS-to-relay is attempted, until the specified back-off period has elapsed, the repeater sends a special data request communication signal to the BS 2310, or the buffer is reported to be empty. (2310) prevents retransmission.

Similar to the fourth embodiment, the fifth embodiment is to have a special ACK indicating that the buffer is almost full. In this example, RS 2330 will accept this packet, but not the next packet. BS 2310 behavior is similar to before. - that is, back-off and/or wait until RS 2330 reports that the buffer is OK.

A sixth embodiment introduces a delayed auxiliary ACK/NACK from RS 2330 to BS 2310 that may be reported to BS 2310 when delivery of a particular packet to WTRU 2320 is successful or abandoned. This allows the BS 2310 to maintain the state of the repeater buffer and schedule accordingly.

A third alternative to data transmission involves RLC-level RS. 24A and 24B illustrate an event sequence 2400 involved in this alternative. 24A and 24B, the RS receives (and, if necessary, acknowledges) the data packet before forwarding it to the WTRU. If the BS considers the packet to be delivered, the RS is responsible for delivery to the WTRU. No fallback mechanism is provided and is not required. However, because of RLC-level operation, the delay associated with this process can be significantly greater than the delay associated with MAC-level relaying.

<b><u>RS-WTRU channel</u></b>

To understand how WTRU assignment to a repeater is performed in two-hop mode, the use of a dedicated RS-WTRU channel will now be considered. Once again, consider a single cell (ie, a single BS 2410 ), M RSs 2420 , and multiple WTRUs 2430 . The RS 2420 is designed to improve the link quality between the BS 2410 and the user (WTRU 2430 ). The WTRU 2430 is divided into two categories. One category includes WTRUs 2430 connected to BS 2410 and capable of communicating with BS 2410 without any assistance from RS 2420 . Another category includes WTRUs 2430 that are disadvantaged in connectivity to BS 2410 and require assistance from RS 2420 . It is also assumed that each WTRU 2430 is associated with only one RS 2420 at a given time. Since there are M RSs 2420, as shown in FIG. 25, (M+1) WTRU groups {Gm, m=0, 1..M} can be defined.

group G₀The WTRU 2510 belonging to the BS 2520 communicates directly. On the other hand, WTRUs 2530 , 2535 belonging to group Gm communicate with BS 2520 via RS m 2540 , 2550 . For example, in the downlink, packets sent to the WTRUs 2560 in group 0 follow the normal direct transmission from the BS 2520 to the WTRU 2510 . Similarly, packets sent to the WTRUs 2530, 2535 in groups 1,..., M are transmitted via a two-hop route, i.e. BS92520 to RS 2540, 2550 and RS 2540, 2550 to WTRU 2530. , 2535).

Which group each WTRU is in may be determined by different alternative criteria. According to the first criterion, WTRUs at the cell edge belong to group 0 (2560), while WTRUs at the cell edge belong to group 1,..., M (2570, 2580). Cell center/edge separation may be accomplished using one (or other method) of the following techniques: at the base station, round trips from/to/to the evaluated WTRU while the connection is being established or while the connection is being maintained. using time delay. This delay can be estimated, since WTRUs in any system are required to synchronize their transmissions to predefined BS signals in a predefined manner. The BS may then measure how out of sync the signal received from the WTRU is, for example, that the delay must have been due to a round trip delay. If the BS has issued a timing adjustment command to the WTRU, these are also considered. At the WTRU, using the estimated pathloss, which can be calculated by considering the difference between the received BS power on a given reference channel on which the transmitted power is signaled (most systems include at least one such channel), The cell edge/cell center distinction may be made using an auxiliary location estimation device such as GPS.

According to a second criterion, the RS 2540 , 2550 may monitor communication between the WTRUs 2530 , 2535 and the RS 2520 as well as the channel metrics they report to each other. The RS 2540, 2550 compares these metrics with its own observations of relative channels and determines which WTRUs 2530, 3535 will benefit from indirect communication with it. RS 2540, 2550 then manages the indirect connection setup.

According to a third criterion, the RS 2540, 2550 periodically emits a beacon signal that allows the WTRUs 2530, 2535 to decide whether to benefit from the relay, and sends this information to the BS 2520. forward to The WTRUs may transmit a response to the beacon signal.

According to a fourth criterion, the WTRUs 2530, 2535 periodically update their location (or CELL_DCH and CELL_FACH signaling are used). The RS 2540, 2550 and BS 2520 may determine which group the WTRU 2530, 2535 belongs to after exchanging their respective information regarding the WTRU's location or signaling.

Another technical problem relates to how handover will be performed when a WTRU enters the coverage area of an RS, when it leaves the RS coverage area and moves to the coverage area of another RS, or when it enters the coverage area of a BS. Due to the mobility of WTRUs, there is a need to dynamically change WTRU groups (a kind of intra-cell inter-relay handover). A possible signaling strategy to enable this is described in the examples below.

<b><u>Aggregated relay transmission</u></b>

In some examples it may be beneficial for the BS to treat the RS 2540 , 2550 as a super-WTRU by aggregating transmissions for all WTRUs associated with the RS. In this case, the network and the WTRUs have an RS (and therefore not transparent), and the repeater may have any WTRUs (more specifically any RNTI - how many RNTIs per WTRU there can be and also have some common/shared ones). possible) should be known. By aggregating them into a single transmission, the network/BS makes better use of the air interface and allows repeaters to break-up them.

In order to enable aggregated-repeater transmission, additional and/or modified functions are required compared to the standard BS MAC. These include the RNTI Pool Manager, MAC Buffer Manager, and Modified Scheduler. The RNTI pool manager entity maintains the association between the actual RNTI and the group RNTI assigned for communication purposes with the repeater, and the RNTI group. A MAC SDU arrives at the MAC associated with each individual data stream (each RNTI). However, they need to be multiplexed into a common stream by the MAC buffer manager.

To assume the best possible behavior, it may be necessary to provide scheduling preferences for grouped transmissions to repeaters. The amount of preference depends on how many individual streams are grouped into a repeater. The modified scheduler needs to be able to take all of this information into account. Since there is no 1-1 correspondence between BS-RS physical resources (shared) and RS-WTRU physical resources (dedicated), PHY-level cooperation is unlikely in this case.

On the other hand, RLC-level resources, even if mapped to a shared physical resource (eg, HSPA in WCDMA), are likely to remain dedicated. Therefore, assuming that MAC cooperation is well defined, RLC-level cooperation is less likely to change from the previous case.

26 is an exemplary diagram of the MAC-repeater sublayer of MAC 2600 located between RS 2610 and BS 2620 . This layer handles the transmission of data over grouped RNTIs. The HARQ response may be handled in an alternative manner. In a first alternative, a single ACK/NACK is generated by the MAC-repeater 2630 at RS 2610 . This is interpreted as an ACK/NACK for all data contained within the HARQ TTI and passed by the MAC repeater 2640 to the MAC-WTRU 2650 in the BS/network 2620 . In a second alternative, a separate ACK/NACK is generated for each data packet. It is also forwarded by the MAC-repeater 2640 to the MAC-WTRU 2650 in the BS/network 2620 . In both cases, the MAC-WTRU-mirror 2660 in the repeater is transparent in nature and does virtually no work.

On the transmitting side, RS 2610 includes a more complex MAC entity 2670 that can perform multiple tasks. This can schedule transmissions for RSs in the group. As before, transmission may be continuously scheduled for relaying between groups. It may maintain HARQ (ie, ACK/NACK exchange) with the WTRU 2680 . The protocol stack architecture described above can be extended to the case of multi-hop relay. The data transmission operation in this example is the same as in the case of matched BS-RS and RS-WTRU resources. This was previously considered.

The use of a shared RS-WTRU channel is now described. If the RS-WTRU channel is shared, the situation is similar to the case of dedicated BS-RS or dedicated RS-WTRU resources (if sharing is the same across both hops). Alternatively, a scenario where the sharing strategy is not the same leads to an operation similar to the example in which the BS-RS link is shared and the RS-WTRU link is dedicated.

The user plane system operation in diversity mode is disclosed as follows. First, a dedicated BS-RS channel is considered. In this mode, all WTRUs can dynamically switch their connections between repeaters or BSs. The WTRUs may be simultaneously linked to the BS and RS so that cooperative transmitter operation is achieved. WTRUs in this mode have more flexibility, and since the connection between the BS and the WTRU and the connection between the BS and the RS are more dynamic, the scheduling algorithm and system setup become more complex. In particular, it is no longer possible for RS to mirror BS to WTRU and WTRU to BS. The WTRU and the BS must know each other directly as well as the RS.

As with two-hop operation, the RS protocol stack must be considered. The system operation will be defined based on the RS protocol stack which should be terminated at the PHY, MAC, or RLC layer.

27 is a diagram of an exemplary protocol architecture for a PHY-level RS 2700 . The dotted line indicates a direct connection between the BS 2710 and the WTRU 2720 . PHY-relay operation depends only on the transport format of PHY messages and L1 control (eg, TPC). Protocol layers at MAC and higher levels are unchanged at BS and WTRU.

This example shows RS 2730 . This RS assists in data transmission, but cannot make any decisions on its own. PHY processing at RS 2370 may be performed in an alternative manner.

amplification &amp; A first alternative, labeled forward (AF) relaying, involves simple amplification and forwarding at the RF level. A second alternative is demodulation-remodulation and forward. In this alternative, it can be eliminated or suppressed only if the link to the repeater has very high fidelity (ie no channel code is actually needed). Here, the signal is further processed so that errors are corrected in the RS. A third alternative is decode-re-encode-and forward (DF) relay. Here, the signal is further processed so that errors are corrected in the RS. A fourth alternative is compression-and-forward. This method is used when the link to the repeater is poor and data cannot be demodulated even using the channel code. However, partial information about the data can still be obtained through proper code design. This partial (ie, "compressed") information is forwarded to the destination by the repeater.

A fifth alternative is an adaptive scheme. In this scheme, the repeater can adaptively switch to any of the four schemes described above. For example, if the relay successfully decodes the message, it applies the decode-and-forward scheme. Otherwise, apply any of the remaining schemes, eg the amplification-and-forward scheme. In another example, if the repeater is heavily loaded, an amplification-and-forward scheme that consumes less resources can be applied. Otherwise, any of the other schemes, such as a decode-and-forward scheme, may be applied.

During the relay process, the radio signal characteristics on the BS-RS link and the RS-WTRU link need not be identical. In a first option, the RS-WTRU link may use a different frequency or code compared to the BS-RS link. In a second option, the modulation on the RS_WTRU link may be different from the modulation on the BS-RS link. Finally, in a third option, the error protection (ie, detection and/or correction) codes may be different on the BS-RS and RS-WTRU links.

28 is a diagram of an exemplary protocol architecture for a MAC-level RS 2800 . The dotted line represents a direct connection between the BS 2810 and the WTRU 2820 . As in the two-hop case, the introduction of MAC 2830 in RS 2840 allows RS 2840 to participate in the HARQ operation of the system, potentially handling retransmissions, and the like. While this flexibility will be described when system operation is discussed, it allows for tremendous potential in improving overall system operation. For the time being, it should be noted that the use of RS MAC 2830 as a mirror is no longer possible.

29 is an exemplary protocol architecture diagram for an RLC-level RS 2900. The dotted line represents a direct connection between the BS 2910 and the WTRU 2920 .

Since various physical architectures, protocol architectures as well as radio channels have been described so far, data transmission between the BS and the WTRU via RS(s) will be described. As before, the transport of a single IP block will be considered.

30 is a diagram of an event sequence 3000 involved in the transmission of an IP packet from a BS via an RS to a WTRU. RS 3010 is assumed to be simple PHY-level using any of the techniques described above. The illustrated approach applies to decode-and-forward and demodulate-and-forward approaches. In the case of compression-and-forward and amplification-and-forward, RS 3010 continues to receive successive enhancements of packets and transmit them until transmission is complete (ie, until the BS stops transmitting data). can (alternate receiver and transmitter operation).

Scheduling options may include the following. In an example where RS 3010 must decode or demodulate a signal prior to any transmission, it may be scheduled by BS 3120 to transmit at the same TTI as BS 3020 or at a different TTI. In either case, since the WTRU 3030 has stopped receiving this particular packet, it needs to know when to stop transmitting. This can be done in one of the following alternative ways.

In a first alternative, the actual transmission is scheduled directly by BS 3020 using a side control channel (which RS 3010 should receive). In a second alternative, RS 3010 continues to monitor for retransmissions, even if no longer needed. This carries minimal control overhead, but since RS 3010 is assumed to be half-duplex, BS 3020 and RS 3010 are prevented from transmitting in the same TTI using the same RRU. In a third alternative, a PHY-layer control signal is used, and BS93020 notifies RS 3010 which packets it is still actively transmitting or when to stop transmitting packets. This alternative carries some signaling load, but maintains sufficient flexibility in scheduling the RRU of RS 3010 (eg, overlapping with BS 3020).

If RS 3010 is capable of dynamically switching transmit and receive operations, the above options are still viable. The difference is that RS 3010 now has several options as to when to initiate transmission.

As a first option, if we wait until we successfully decode the information, the situation is the same as described for the two-hop operation. Therefore, we will only consider the case where the repeater initiates transmission before the entire information becomes available. As a second option, after each BS transmission, it may transmit something (depending on the protocol) until it successfully decodes the data. At the time of successfully decoding the data, as in the decode-and-forward case described above, transmission only (no reception) continues until interruption. As a third option, alternatively, the repeater waits until its accumulated information is above a predetermined quality threshold or receives a predetermined minimum number of transmissions from the BS.

MAC level cooperation will now be considered. Assume a repeater with a PHY+MAC layer. Two fundamentally different approaches to cooperative technology can be considered, which must deal with how the repeater is controlled by the BS. In one case, the BS does not know the detailed repeater operation and cannot apply sophisticated control. In other cases, the opposite is true. Because the BS transmission is always available, the repeater protocol may be based on a decode-and-forward (DF) or compression-and-forward (CF) approach.

If the BS does not know the detailed repeater operation, data transmission operates as shown in FIG. The BS 3110 continues to transmit packets to the WTRU 3120 until an ACK is received from the WTRU 3120 or the maximum number of transmissions is exceeded. RS 3130 may participate in the transmission if it is ready (depending on whether it is doing CF or DF) and the WTRU 3120 sends a NACK to BS 3110 . Thus, in this mode, cooperative transmitter diversity is activated no faster than the first retransmission only if the channel to RS 3130 is really better than the channel to WTRU 3120 (WTRU 3120 sends data first). allowed to receive).

A key factor in this case is RS 3130's definition "ready to transmit. If DF is used, this means that the repeater has successfully decoded the BS transmission. If CF is used, this means that the repeater has It means that we have accumulated a sufficient amount of information about the BS transmission to pass the defined threshold.

Two approaches can be defined for using repeaters without detailed BS control. In the first approach, called a smart repeater, every frame contains some distributed RRU reserved for RS 3130 . After this pre-allocation, BS 3110 does not know what RS93130 will do with them. The RS 3130 determines which WTRUs are its "supplemental set". That is, the BS 3110 determines which WTRUs 3120 are the auxiliary set and whether it can process the CQI information to transmit this information to the RS 3130 .

32 is a diagram illustrating an example signal flow diagram 3200 for a smart repeater and a slave repeater. Referring to FIG. 32 , a smart RS 3210 monitors BS transmissions to these WTRUs 3220 . It also monitors the WTRU feedback 3220 (ACK/NACK). Once the RS 3210 is READY 3215 and the WTRU 32320 sends a NACK 3235 (this goes to the BS 3240, but the RS 3210 can see it), the will schedule retransmission 3250 . A retransmission is either a) scheduled slots allocated in advance of the RS by the BS for transmission to the WTRU, or b) a scheduled slot selected from the set of slots allowed to use for scheduling to any of the associated WTRUs. (including other physical resources such as channelization codes and/or subcarriers). The BS 3240 will generally be aware of the rules used by the RS 3210 - thus, it can infer which WTRU 3230 is the "auxiliary set" of the RS 3230 and make retransmission decisions accordingly. (i.e., schedule retransmissions less frequently in the hope that the repeater will pick up the load. Alternatively, the RS 3210 may explicitly inform the BS 3240 of the WTRU 3230 it is currently assisting or planning to assist in the future. can be signaled). The WTRU 3230 being assisted is signaled with its index by the RS 3210 . In this way, the WTRU 3230 may switch its receiver operation to support cooperative transmission from this WTRU 3230 .

In a second approach, called the slave repeater 3260, only after the BS 3240 gets a NACK 3270 from the WTRUs 3230 in its auxiliary set (similar to approach 1, the BS knows which WTRUs are in the auxiliary set). may be based on CQI information to determine), BS 3240 signals RS 3210 ( 3245 ). When ready 3280 , RS 3210 initiates transmission 3290 to WTRU 3230 . Continue until signaled to stop. In this approach, the RS 3210 does not need to detect/share the ACK/NACK information sent from the WTRU 3230 to the BS 3240 .

Consider now an example MAC-level collaboration with fine-grained control from the BS. In this mode of operation, two-level HARQ is required (between WTRU and BS, and between repeater and BS). Using the DF or CF communication scheme, the repeater informs the BS when it is ready using a special repeater ACK (RAC) associated with a particular HARQ process. At this point, the BS uses direct signaling to tell the relay which packet should be transmitted in which RRU. Scheduling may be performed for each transmission or in bulk (ie, until "success or timeout). If done in bulk, the repeater may be ordered to abort by the BS. Or ACK/NACK from the WTRU may be ordered to monitor and stop when an ACK is detected The BS may use any of the following methods to schedule repeater transmissions. The first method maximizes the MIMO effect by scheduling transmissions in the same RRUs. The second method maximizes time diversity/minimizes interference by scheduling transmissions in different RRUs.

Consider WTRU-controlled adaptive NACK transmission. In this scheme, the WTRU tracks the quality of the WTRU-BS and WTRU-RS channels and optionally sends a NACK to the RS or the BE or both.

The selection criterion may be based, for example, on the channel quality of the respective channels. That is, the WTRU may elect to send a NACK to a network node that is presumed to have a higher probability of successful retransmission.

Selective transmission may be performed at the PHY level or higher. At the PHY level, a directional antenna at the WTRU may be used to selectively transmit a NACK transmission to the RS or BS. At a higher level, the NACK message may include an identifier, which identifies the message meant for RS or BS. Non-selective transmission is accomplished with an omni-directional antenna (or broad-beam antenna) at the PHY level, or as a broadcast message at a higher level.

Consider the control plane system operation. A key control-plane operation that must be addressed in the context of a mode A relay configuration is mobility management, ie, management of the mobility of the WTRU between different groups of relays, including group 0 (no relays are used).

As described above, measurements associated with assigning a WTRU to a particular group of repeaters may be performed at different locations within the cell, such as at the WTRU or at the repeater or at the BS. Combinations of these may also be used.

These measurements are provided to the BS/network regardless of where the measurements are performed. Based on these measurements, the BS (and perhaps the BS, not the network) assigns the WTRU to a specific group of repeaters and forwards the appropriate command to the involved repeaters (originating and receiving repeaters) and the WTRU. In fact, from a control point of view, the BS acts as the RNC in modern WCDMA systems, while the repeater acts as the BS. This operation requires the following changes to the control-plane access stratum protocol stack.

33A is a diagram of an exemplary protocol architecture 3300 in which the BS and repeater include a layer 2 contour plane entity (which does not currently exist in many systems) (we refer to herein as repeater-RRC 3310 ). This entity manages the mobility of WTRUs between repeater groups. 33B is a diagram of an alternative exemplary protocol architecture 3300 in which the BS and repeater include a repeater-RRC 3310 .

Since the WTRU does not generally know which group it belongs to, such an entity may not be needed in the WTRU. When the WTRU performs measurements to support inter-relay mobility, the existing RRC operation needs to be modified to provide them to the network. Alternatively, layer 2 RRC entities may be defined to report them to the BS.

Turning our attention to the specific coding process in the presence of a repeater, consider a diagram of an exemplary collaboration header 3400 . Referring to FIG. 34 , the cooperative header 3410 includes 2 bits 3420 indicating M0 or M1 or M2 (each indicating a different relay method), k bits indicating a specific implementation in M1 or M2 or other cooperative Includes, but is not limited to, the ~k bit indicating specific details of the enemy scheme. These "information bits" can be compactly coded to generate a cooperative header. For example, 2 bits pointing to M0/M1/M2 and K bits are coded together to remove unused code points from the 2-bit field (2 bits = 4 code points, if there are only 3 modes to be coded), and possibly ( Reduce the header size by 1 or more bits (instead of 2 + k + ~k bits).

The data packet is further processed for over-the-air transmission (eg, error correction/detection codes are applied and modulated). The transmitted signal s(t) is carried on a "common" radio channel that can be heard by the WTRU, RS1 and RS2. Here, RS1 and RS2 are associated with the WTRU, and "common" refers to the WTRU, RS1, RS2, which is not necessarily common to other WTRUs or RSs in the system.

Because the channel quality is different on BS-&gt;RS1, BS-&gt;RS2 and BS-&gt;WTRU, so that three entities, WTRU, RS1 and RS2 can decode the header correctly, channel coding, modulation similar "transmission related parameters" ' should be selected. This can be done using several techniques, some of which are discussed below.

35 is a diagram of an example technique 3500 that may be separate channel coding for the header and payload, eg, FEC1 3510 for the header and FEC2 3520 for the payload. Here, FEC1 (3510) is stronger than FEC2 (3520). An exemplary overall flow diagram (shown for DL similar to that applied for UL) is shown in FIG. 36 . This technique may use channel coding FEC1 3510 for both header and payload. For example, FEC1 3510 is chosen such that the header is strong enough to be reliably received by the WTRU, RS1, RS2. The robust coding of mode bits, e.g., two mode bits, is coded and modulated separately, and the symbols are placed in a fixed position 3610 (known as WTRU, RS1, RS2), so that WTRU, RS1, RS2 are in the full header and /or demodulate and decode mode-symbols without having to decode the payload. Other similar techniques may be used based on variations of these examples.

The data packet is received 3620 by the WTRU, RS1 and RS2. Each of these detects, demodulates, and decodes the mode bits (3630). Depending on the value of the mode bits, the nodes WTRU, RS1, RS2 will act accordingly. That is, if mode 0 is indicated (3635), RS1 and RS2 stop further processing of the data block, while the WTRU decodes the data packet (3640). The WTRU will continue processing if mode 1 is indicated (3645), RS2 and WTRU will stop further processing, while RS1 will continue (3650). If M1 or M2 is selected, step 2 will be initiated 3655 after the data packet has been correctly received by RS1 or RS2. Upon receipt of the decoded data packet, the WTRU sends an ACK/NACK to the BS or RS (3670).

The structure of the data packet transmitted in step 2 of M1 or M2 need not include a cooperation header. This prevents some bits from being transmitted unnecessarily, reducing interference and increasing throughput.

<b><u>DL &amp; UL Tuning</u></b>

So far, DL &amp; A solution for UL has been described separately. Next, a method for efficiently tuning them is described.

The basic concept is that the DL data or control packet contains information about the cooperative scheme to be used for UL transmission. Examples of "piggy-back" are described below. 37 shows a downlink data packet 3700 with a header and payload. The header 3710 includes a DL-cooperation header 3720 , and a UL-cooperation header 3730 that contains details of the collaboration scheme to be used in the "next" UL cooperative transmission. As a variant, the period for which the UL-cooperation scheme should be used is specified. The specification of "period" may be in terms of "absolute" time (eg, time slot number) or "logical time" (eg, temporary block flow identity, etc.). The UL-cooperation header 3730 may also include the address of the WTRU if multiple WTRUs are served.

Regarding the availability of channel state information, it should be noted that, in the above description , it is assumed that the BS has information on the five channel states 1-5 shown in FIG. 38, or a subset thereof. This information can be obtained in a variety of ways. For example, it may be periodically fed back from the WTRU 3810 , RS1 3820 , or RS2 3830 , or fed back upon polling by the BS 3840 , RS1 3820 or RS2 3830 . The period of feedback reporting may be dynamically adjusted or fixed at the start of the communication such that the resulting overhead and latency are acceptable. BS 3840 or RS 3820, 3830 may use an interpolation or prediction method to estimate a channel state value between feedback reports. In a TDD system, the channel state may be estimated by the BS 3840 under the assumption of the reciprocity of the DL and UL channels.

FIG. 39 shows a transport header 3900 that includes a "legacy" header 3910 appended with one bit called "cooperation header indicator bit" 3920 . A value of this bit indicates the presence of the collaboration header 3930 . Another (binary) value of this bit indicates the absence of the collaboration header 3930.

In this example, cooperative header 3930 indicates only M1 or M2 mode (ie, all modes including repeaters), except for mode M0. The absence of cooperative header 3930 indicates mode M0. This will reduce the average header size when observed over many transmissions.

As a variation on using "bits" to indicate the presence or absence of collaboration header 3930 , any unused "code point" from legacy header 3910 can be used. That is, the unused bit pattern of the legacy header is used. One variation is to use Rate Compatible Punctured Convolution (RCPC) codes. This code has the ability to protect different parts of a data packet to different levels.

In one example, the BS and RS transmit the same channel coded data with distributed beamforming (BF) so that the WTRU receives the coherent combined signal with improved SINR. This method requires some information (eg, channel state information or beamforming weights) feedback from the WTRU to the BS and RS, and may be viewed as a variant of the 'closed loop transmit diversity' scheme. In another example, the BS and RS transmit different portions of the coded bit stream, which portions are received by the WTRU and separated by successive interference cancellation techniques. Subsequently, the two demodulated bit streams are combined at the channel decoding level. Combining this with the partial data received in step 1, the WTRU completes the recovery of the original data sent by the BS. These examples are called distributed-BF and distributed-MIMO joint schemes.

<b><u>Protocol 1 Behavior</u></b>

Protocol 1 - Scheme 1 Downlink is shown in FIG. 40 . Referring to FIG. 40 , the BS sends data 4010 to the RS in the first TTI, using the appropriate MCS for the BS-RS link, or by considering the entire BS-RS, BS-WTRU, RS-WTRU link. ) can be transmitted. The WTRU is transmitted (e.g., using a distributed space-time code) by the BS alone 4030 or by both the BS and the RS 4040 (or by the RS alone as a third probability ( not shown)) a single codeword (eg, HARQ PDU) is received in the TTI.

This may be extended/generalized to multiple codewords, for example, if MIMO transmission from BS and/or RS to WTRU is used. The codeword transmission is described/indicated to the WTRU via the control channel(s) (ie, TCC). The WTRU may send HARQ feedback (eg, ACK/4040/NACK 4050) to indicate whether the codeword was successfully received. Such feedback may be transmitted using HCC channel(s). The RS may send HARQ feedback (eg, ACK/NACK) to the BS (not shown) to indicate whether the codeword sent by the BS was successfully received by the RS. Such feedback may be transmitted using HCC channel(s).

If the HARQ feedback indicates whether the RS successfully received the codeword (ie, NACK/DTX), the BS may retransmit (not shown). The retransmitted packets will preferably have a different IR version. If the BS receives an ACK from the WTRU, it will move on to transmission of the next message/packet. If the BS and/or RS do not receive an ACK from the WTRU, then both the BS and RS (e.g., using distributed space-time code) wait until the WTRU acknowledges (transmits ACK) or the HARQ retransmissions are exhausted. , will perform a retransmission to the WTRU. Retransmitted packets may have different IR versions. The WTRU combines the received versions to improve decoding of a given packet m. A common identifier is adopted by the BS and RS to enable the WTRU to identify which packet to combine. Such identifiers may be in the form of a HARQ process ID, in the form of a predefined TTI (eg, at TTI # x+y, the RS will transmit the packet it receives from the BS at TTI # x), or any other form of identification. can be The uplink description is similar to the downlink, but the BS and WTRU roles are reversed.

Protocol 1 - Scheme 2 The downlink is shown in FIG. 41 and is largely similar to Scheme 1 with the following differences. A pair of TTIs is used so that HARQ feedback is sent by the WTRU at the end of a later TTI 4410 (as opposed to sending HARQ feedback in each TTI). This can be generalized/extended to a bundle of two or more TTIs instead of a 'pair' TTI. The uplink description is similar to the downlink, but the roles of the BS and WTRU are reversed.

<b><u>Protocol 2 Behavior</u></b>

Protocol 2 - Scheme 1 downlink shown in FIG. 42 describes the HARQ scheme for Protocol 2, which has a full-duplex repeater 4200, i.e., RS can transmit and receive simultaneously (eg, at different frequencies). do. The BS may transmit data to the RS using an MCS suitable for the BS-RS link. In a TTI where the RS is expected to be busy transmitting to the WTRU, the BS may transmit data to the WTRU using the appropriate MCS for the BS-WTRU link. In this example, the RS also receives this transmission 4210 from the BS to the WTRU because of its full-duplex nature. The RS may send data to the WTRU using an MCS suitable for the RS-WTRU link. The WTRU receives up to two codewords (eg, HARQ PDUs). One from the BS, the other from the RS. This can be generalized/extended to more than two codewords if MIMO transmission from BS and/or RS to WTRU is used, or more than one RS is used. Codeword transmission is described/dedicated to the WTRU over the control channel(s) (ie, TCC).

The WTRU may send HARQ feedback (eg, ACK 4220/NACK 4230) to indicate whether each of the two codewords was successfully received. Such feedback may be transmitted using HCC channel(s). The RS may send HARQ feedback (eg, ACK/NACK) to the BS (not shown) to indicate whether the codeword sent by the BS was successfully received by the RS. Such feedback may be transmitted using HCC channel(s). If the HARQ feedback indicates that the RS did not successfully receive the codeword (ie, NACK or DTX), the BS may retransmit (not shown). Retransmitted packets may have different IR versions. If the BS receives an ACK from the WTRU, it will move on to transmission of the next message/packet. If BS receives ACK from RS, BS will move on to transmission of next message/packet. HARQ retransmission may be delegated to the RS. If the RS does not receive an ACK from the WTRU, the RS will perform retransmissions to the WTRU until either the WTRU acknowledges (transmits an ACK) or the HARQ retransmissions are exhausted (limit is reached). The retransmitted packets may have different versions. The WTRU combines the received versions (eg, HARQ combining) to improve decoding of a given packet m. A common identifier is adopted by the BS and RS to enable the WTRU to identify which packet to combine. Such an identifier is (same) HARQ process ID (use of), a predefined TTI (eg at TTI # x+y, RS will transmit the packet it receives from BS at TTI # x), or other It can be any form of identification. If the RS is overloaded with HARQ retransmissions to the WTRU, a flow control signal from RS to BS may be used by the BS to stop new HARQ retransmissions.

The uplink is similar to the downlink, but the BS and WTRU roles are reversed. The description is also similar, only replacing the BS with the WTRU and the WTRU with the BS, as follows. This example is a full-duplex repeater, so RS can transmit and receive simultaneously (eg, on different frequencies). The WTRU sends data to the RS (preferably using an MCS suitable for the WTRU-RS link). In a TTI where the RS is expected to be busy transmitting to the BS, the WTRU may send data to the BS (preferably using an MCS suitable for the WTRU-BS link). The RS may receive such a transmission from the WTRU to the BS because of its full-duplex nature. RS sends data to BS (preferably using MCS suitable for RS-BS link) can be generalized/extended to more than two codewords]. Codeword transmission is described/indicated over the control channel(s) (ie, TCC).

The BS may send HARQ feedback (eg, ACK/NACK) to indicate whether each of the two codewords was successfully received. Such feedback may be transmitted using HCC channel(s). The RS may send HARQ feedback (eg, ACK/NACK) to the WTRU (not shown) to indicate whether the codeword sent by the WTRU was successfully transmitted by the RS. Such feedback may be transmitted using HCC channel(s).

If the HARQ feedback indicates that the RS did not successfully receive the codeword (ie NACK or DTX), the WTRU may retransmit (note: this is not shown in the figure). The retransmitted packets may preferably have different IR versions. If the WTRU receives an ACK from the BS, it will move on to transmission of the next message/packet. If the WTRU receives an ACK from the RS, it will move on to transmission of the next message/packet. HARQ retransmission may be delegated to the RS. If the RS does not receive an ACK from the BS, the RS sends a retransmission to the BS until the BS acknowledges (transmits an ACK) or the HARQ retransmission is exhausted (e.g., a predetermined limit is reached). will perform (take care of) The retransmitted packets may have different versions. The BS combines the received versions (eg, HARQ combining) to improve the decoding of a given packet m. A common identifier is adopted by the WTRU and RS to enable the BS to identify which packet to combine. Such identifiers are (used) the HARQ process ID (use of), a predefined TTI (eg, at TTI # x+y, the RS will transmit the packet it receives from the WTRU at TTI #x), or other It can be any form of identification. When the RS is overloaded with HARQ retransmissions to the BS, a flow control signal from the RS to the WTRU may also be used to stop new HARQ transmissions by the WTRU.

Protocol 2 - Scheme 2 Downlink is generally similar to Scheme 1 and is shown in FIG. 43, with the following differences. In a TTI where the RS is expected to be busy transmitting or retransmitting to the WTRU, the BS may perform some HARQ retransmission to the WTRU using the appropriate MCS for the BS-WTRU link. Whether the BS will take care of performing retransmissions may be based on the ACK/NACK feedback status from the RS and/or the WTRU, and/or the RS load. The uplink diagram and description are similar to the downlink case, but the roles of the BS and WTRU are reversed.

Protocol 2 - Scheme 3 downlink as shown in FIG. 44 is generally similar to Scheme 2, with the following differences. First, a pair of TTIs 4410 is used and HARQ feedback is sent by the WTRU 4420 at the end of a later TTI (as opposed to sending HARQ feedback in each TTI). This can be generalized/extended to a bundle of two or more TTIs instead of a 'pair' TTI. Second, the uplink description is similar to the downlink, but the roles of the BS and WTRU are reversed.

Protocol 2 - Scheme 4 as shown in FIG. 45 is generally similar to Scheme 2, with the following differences. First, HARQ retransmission for certain packets will not be delegated from the BS to the RS (4510). However, HARQ retransmission for some other packets will be delegated from the BS to the RS (4520). Delegation may be based on ACK/NACK feedback status from RS and/or WTRU, and/or RS load. Second, the uplink diagram and description are similar to the downlink case, but switch/relabel BS to WTRU and WTRU to BS.

Protocol 2 - Scheme 5 downlink as shown in FIG. 46 is generally similar to Scheme 1, with the following differences. First, this scheme has a half-duplex repeater so that RS can either receive or transmit, but not simultaneously transmit and receive. Second, HARQ retransmission for certain packets will not be delegated from the BS to the RS (4610). However, retransmission for some other packets will be delegated from the BS to the RS (4620). Delegation may be based on whether the RS has received a packet from the BS (whether the RS is receiving or transmitting because of its half-duplex nature). Other factors such as ACK/NACK feedback status from RS and/or WTRU, and/or RS load may also be considered. Third, the uplink description is similar to the downlink case, but the roles of the BS and WTRU are reversed.

Protocol 2 - Scheme 6 downlink as shown in FIG. 47 is generally similar to Scheme 5, with the following differences. A pair of TTIs 4710 is used and HARQ feedback is sent by the WTRU at the end of a later TTI 4720 (as opposed to sending HARQ feedback in each TTI). This can be generalized/extended to a bundle of two or more TTIs instead of a 'pair' TTI. The uplink description is similar to the downlink, but the roles of the BS and WTRU are reversed.

A physical channel shows and differentiates the various ways in which physical resources are allocated among WTRUs, relay stations, and base stations. A physical channel herein is a specific set of resources associated with a specific terminal (ie, a WTRU), a set of terminals, cells, and the like. More specifically, as appropriate for a particular radio access technology, a physical channel within a cellular system may be defined by direction (uplink UL or downlink DL), carrier frequency, cell or sector of the cellular system, and channelization resources. . Thus, in time division multiple access (TDMA), it is a set of time slots, in frequency division multiple access, it is a set of codes, and in orthogonal frequency division multiple access (OFDMA) it is a set of subcarriers, time division duplex (CDMA) ) (TDD-CDMA), this is a combination of timeslot and code.

Channelization resources are allocated as a set of radio resource units (RRUs). A radio resource unit is the smallest specific resource allocation in a specific radio access technology. For example, for Wideband CDMA (WCDMA) HSDPA, 1 RRU = 1 SF16 code * 1 TTI. For Long Term Evolution (LTE), 1 RRU = 1 subcarrier * 1 TTI.

Generally speaking, there are three types of physical channels assigned to terminals (WTRUs), but are not limited thereto. First, a dedicated physical channel is assigned to a particular WTRU for its exclusive use. This allocation may be dynamic and a shared RRU pool may be used, but each RRU is dedicated to a single WTRU. For example, WCDMA HSDPA, originally defined in Release 5 of the UMTS WCDMA standard, is a dedicated assignment. Although the physical HSDPA channel (HS-PDSCH) is shared, each RRU therein is assigned in a dedicated manner. Second, a shared channel is shared between a well-defined set of WTRUs (static or dynamic). Third, a common channel is available to any terminal within a particular cell.

The number of available RRUs depends on how the RRUs are defined and how they are received. These examples apply to all approaches to RRU definition and reception described below.

In general, the RRU may be assumed to be non-coherent or orthogonal (eg, because there are sufficient gap periods or subcarriers of OFDM). Since this guarantees the best performance for each link, the overall system performance is limited by the availability of orthogonal RRUs.

An alternative to this is to allow some small amount of interference between the RRUs and ignore them in the receiver design. This is the case for long-code CDMA in the RAKE receiver. This eliminates RRU availability as a limiting factor in system performance. However, such systems are typically limited by the level of self-interference. Thus, while a large amount of RRUs are available, very few of them can actually be used simultaneously. The actual RRU efficiency of such a system is often similar (and often somewhat less) than that of an orthogonal RRU.

Theoretically-optimal approach is to allow some (limited and controlled) interference between RRUs and use a very powerful receiver to jointly receive all RRUs in the self-interference set. Partial steps in this direction are taken by 3GPP's WTDD TDSCDMA mode.

<b><u>control channels</u></b>

The following control channel architecture may be used in conjunction with Protocol 2 and Protocol 1. Two types of control channels are described here. TCCs are control channels that describe or provide information about the associated (data) transmission. For example, when a transmission occurs, it describes the MCS used, new transmission or retransmission, TR version, etc. HCC is a control channel that describes or provides information on reception status. An example is HARQ ACK/NACK feedback to indicate whether a transmission was successfully received (ACK), unsuccessful (NACK), or not received (DTX; ie, no feedback was sent).

48 shows control channels for DL (4800). The WTRU 4810 monitors a control channel (referred to as TCC1 4830 ) transmitted by the BS 4820 , which signals information regarding transmissions from the BS 4820 . The WTRU 4810 monitors a control channel (referred to as TCC2 4850 ) transmitted by the RS 4840 , which signals information regarding transmissions from the RS 4840 . Alternatively, TCC2 4850 may instead be transmitted by BS 4820 , but still signal information regarding transmission from RS 4840 . TCC1 4830 and TCC2 4850 may be combined into one control channel (ie, a single TCC from the BS).

RS 4840 monitors a control channel (referred to as TCC3 4860 ) transmitted by BS 4820 , which signals information regarding transmissions from BS 4820 . TCC1 4830 and TCC3 4860 may be the same control channel (ie, a single TCC from the BS). The WTRU 4810 sends a HARQ feedback control channel (referred to as HCC1 4870 ) to the BS 4820 . The WTRU 4810 sends a HARQ feedback control channel (referred to as HCC2 4880) to the RS 4840 . RS 4840 sends a HARQ feedback control channel (referred to as HCC3 4890 ) to BS 4820 . HCC1 4870 and HCC2 4880 may be on the same control channel (ie, a single HCC from a WTRU).

49 shows variant A of control channels for UL ( 4900 ). The WTRU 4910 is transmitted by the BS 4920 signaling information regarding transmissions from the WTRU 4910 (ie, instructing the WTRU 4910 when and/or what to transmit to the BS 4920 ). It monitors the assigned control channel (referred to as TCC1 4930). The WTRU 4910 signals information regarding transmissions from the WTRU 4910 (ie, instructs the WTRU 4910 when and/or what to transmit to the RS 4940 ), transmitted by the RS 4940 . It monitors the assigned control channel (referred to as TCC2 4950). Alternatively, TCC2 4950 may be sent by BS 4920 instead. Or, also alternatively, TCC1 4930 and TCC2 4950 may have the same control channel (eg, instructing the WTRU to transmit when and/or what to either or both RS and BS, from BS to WTRU). single TCC).

RS 4940 signals information regarding transmissions from RS 4940 (i.e., instructs WTRU 4940 when and/or what to transmit to BS 4920 and/or WTRU 4910); Monitors the control channel (referred to as TCC3 4960) transmitted by BS 4920. TCC1 4930 and TCC3 4960 may be the same control channel for WTRU 4910 and/or RS 4940 and instructs WTRU 4910 and RS 4940 when and/or what to transmit. . The WTRU 4910 receives a HARQ feedback control channel (referred to as HCC1 4970 ) from the BS 4920 . The WTRU 4910 receives a HARQ feedback control channel (referred to as HCC3 4980 ) from the RS 4940 . RS 4940 receives the HARQ feedback control channel (referred to as HCC3 4990) from BS 4920 . HCC1 4970 and HCC3 4990 may be on the same control channel (single HCC from BS 4920). A UL control channel (TTCx or HCCx) is not necessarily the same as a DL control channel, although the same terminology is used herein.

50 shows variant B of control channels for UL (5000). Variant B describes a WTRU 5010 that transmits to the BS 5020 a control channel (referred to as TCC1 5030 ) signaling information regarding transmissions from the WTRU 5010 . The WTRU 5010 sends a control channel (referred to as TCC2 5050 ) to the RS 5040 signaling information regarding transmissions from the WTRU 5010 . Alternatively, TCC1 5030 and TCC2 5050 may be on the same control channel (ie, a single TCC from WTRU 5010 ).

RS 5040 transmits to BS 5020 a control channel (referred to as TCC3 5060) signaling information about transmission from RS 5040. The WTRU 5010 receives a HARQ feedback control channel (referred to as HCC1 5070 ) from the BS 5020 . The WTRU 5010 receives a HARQ feedback control channel (referred to as HCC2 5080 ) from the RS 5040 . RS 5040 receives a HARQ feedback control channel (referred to as HCC3 5090) from BS 5020. HCC1 5070 and HCC3 5090 may be on the same control channel (ie, a single HCC from BS 5020). The UL control channel (TTCx or HCCx) is not necessarily the same as the DL control channel, although the same terminology is used. Other variations are also possible by combining some aspects from Variant A with other aspects of Variant B.

Several examples are described to improve the downlink performance of a cellular system. These protocols are designed to be built on existing cellular packet air interfaces such as High Speed Packet Access (HSPA) High Speed Downlink Packet Access/High Speed Uplink Packet Access (HSDPA/HSUPA) and Long Term Evolution (LTE). Although these protocols are published in terms of HSPA, the protocols described apply directly to other systems such as LTE and WiMAX.

<b><u>Cooperative repeaters at HSUPA</u></b>

The link between the repeater and the WTRU may be classified as one-to-one or one-to-many. In a point-to-point link, the repeater is dedicated to a single WTRU. In a one-to-many scenario, the repeater receives data from multiple WTRUs. Likewise, the link between the repeater and the BS may be one-to-one, or one-to-many. In the one-to-one scenario, the BS receives data from a single repeater, and in the one-to-many scenario, the base station receives data from a plurality of repeaters. Finally, there is also a direct link between the BS and the WTRU. This link may or may not exist. An architecture can be defined in which the WTRU cannot communicate directly with the BS, ie all communication is through a repeater. However, this will be a restrictive architecture, since the purpose of the repeater is to aid communication between the WTRU and the BS, no repeater is needed, and there may be cases where direct communication between the WTRU and the BS would be beneficial. This link is always defined as one-to-many. Finally, the WTRU may communicate simultaneously with the repeater and the BS.

<tables num="2"><table><tgroup cols="4"><colspec colnum="1" align="center" colname="col1" colwidth="2950" /><colspec colnum="2" align="center" colname="col2" colwidth="2950" /><colspec colnum="3" align="center" colname="col3" colwidth="2950" /><colspec colnum="4" align="center" colname="col4" colwidth="2950" /><tbody><row><entry align="center" namest="col1" nameend="col4">uplink communication</entry></row><row><entry align="center" colname="col1"></entry><entry align="center" colname="col2">WTRU</entry><entry align="center" colname="col3">repeater</entry><entry align="center" colname="col4">BS</entry></row><row><entry align="center" colname="col1">WTRU</entry><entry align="center" colname="col2">NA</entry><entry align="center" colname="col3">One one-to-one or one-to-many</entry><entry align="center" colname="col4">One put </entry></row><row><entry align="center" colname="col1">repeater</entry><entry align="center" colname="col2">One one-to-one or one-to-many</entry><entry align="center" colname="col3">NA</entry><entry align="center" colname="col4">One one-to-one or one-to-many</entry></row><row><entry align="center" colname="col1">BS</entry><entry align="center" colname="col2">One put</entry><entry align="center" colname="col3">One one-to-one or one-to-many</entry><entry align="center" colname="col4">NA</entry></row></tbody></tgroup></table></tables>

For generalization, all links are assumed to be one-to-many. A one-to-one case is a trivial case with one destination.

<b><u>HSUPA Serving Grant Methodology</u></b>

The HSUPA channel is an Enhanced Dedicated Physical Channel (EPDCH). The BS controls the allocation of E-DPCH between all WTRUs, and this controlled scheduling is based on a set of rules on how the WTRUs should behave with respect to certain signaling.

The BS sends a resource indication on the downlink called a Scheduling Grant (SG). This SG indicates to the WTRU the maximum amount of uplink resources available. When issuing a scheduling grant, the BS may use QoS related information provided by the SRNC and coming from the WTRU in the scheduling request.

The scheduling grant has the following characteristics: The scheduling grant controls the maximum allowed E-DPDCH/DPCCH power ratio, and the scheduling grant can be transmitted once per TTI or slower. There are two types of Grant.

Absolute grants provide an absolute limit on the maximum amount of UL resources that a WTRU can use. The second grant is a status grant, which instructs the WTRU to increase or decrease the resource limit compared to the previously used value. The absolute grant is transmitted by the serving E-DCH cell. This is valid for one WTRU, or for a group of WTRUs, or for all WTRUs in a cell. This is done by the UTRAN assigning the same identity to a group of WTRUs by assigning up to two identities (called "primary" and "secondary") for each WTRU. Relative grants may be sent by serving and non-serving Node Bs as a supplement to absolute grants. WTRU behavior is exactly the same for one WTRU, a group of WTRUs, and relative grants for all WTRUs. The relative grant from the serving E-DCH RLS can have one of three values: "up", "hold", or "down". A relative grant from a non-serving E-DCH RL can take one of two values: "hold" or "down".

The following information is provided to the BS by the WTRU to assist with grant allocation scheduling. This information is provided in the scheduling information (SI). The logical channel ID of the highest priority channel with data in the buffer unambiguously identifies the highest priority logical channel with data available and QoS information associated with this indicated logical channel. Some examples of information in the SI include: WTRU buffer occupancy (in bytes), total buffer status, buffer status for the highest priority logical channel with data in the buffer as part of the total reported buffer, WTRU power headroom (UPH). The UPH field indicates the ratio of the maximum WTRU transmit power to the corresponding DPCCH code power.

<b><u>HSUPA Serving Grant Functions in Collaborative Networks</u></b>

Notably, the purpose of the serving grant is to provide significant improvements in terms of user experience (throughput and latency) and capacity. Therefore, it is important to ensure that the serving grant function and purpose are valid when HSUPA is used in a collaborative environment. Furthermore, the grant is a function of the required QoS as well as the channel conditions.

Note that the UPH is a function of the channel conditions between the WTRU and the BS. If this condition is not favorable, too much power is consumed on the DPCCH and too little power is left on the EDPCH. This is important because it means that the grant between the WTRU and the BS may not necessarily be suitable for communication between the WTRU and the relay.

<b><u>Link between BS and relay</u></b>

One important part of communication is the link between the repeater and the BS. For example, if the bandwidth available for communication between the relay-BS link is lower than the bandwidth available for communication between the relay and the WTRUs, the system becomes unbalanced and the relay cannot forward the WTRU packets to the BS, so that the It will start queuing and possibly dropping WTRU packets.

Some signaling messages between the relay and the BS are defined in the table below.

<tables num="3"><table><tgroup cols="3"><colspec colnum="1" align="justify" colname="col1" colwidth="3597" /><colspec colnum="2" align="justify" colname="col2" colwidth="3597" /><colspec colnum="3" align="justify" colname="col3" colwidth="3597" /><tbody><row><entry align="justify" colname="col1">direction</entry><entry align="justify" colname="col2">message</entry><entry align="justify" colname="col3">Explanation</entry></row><row><entry align="justify" colname="col1">BS -&gt; repeater</entry><entry align="justify" colname="col2">measurement request</entry><entry align="justify" colname="col3">Channel measurement requests along with specific reporting criteria (eg, periodic, triggered events), these measurements include UL DPCCH received power, total power, interference, etc. for a particular WTRU.</entry></row><row><entry align="justify" colname="col1">repeater -&gt; BS</entry><entry align="justify" colname="col2">measurement report</entry><entry align="justify" colname="col3">Response to "Measurement Request" message. These measurements include UL DPCCH received power, total power, interference, etc. for a particular WTRU.</entry></row><row><entry align="justify" colname="col1">BS -&gt; repeater</entry><entry align="justify" colname="col2">repeater polling</entry><entry align="justify" colname="col3">Request status of the repeater</entry></row><row><entry align="justify" colname="col1">repeater -&gt; BS</entry><entry align="justify" colname="col2">Polling response</entry><entry align="justify" colname="col3">Response to "Relay Polling" message. The response indicates that the repeater is "in service".</entry></row><row><entry align="justify" colname="col1">BS -&gt; repeater</entry><entry align="justify" colname="col2">load request</entry><entry align="justify" colname="col3">Request the number of WTRUs associated with that relay, along with specific reporting criteria (eg periodic, triggered events)</entry></row><row><entry align="justify" colname="col1">repeater -&gt; BS</entry><entry align="justify" colname="col2">load response</entry><entry align="justify" colname="col3">Response to "Load Request" message. This message contains the number of WTRUs associated with the repeater and possibly the buffer occupancy of each of these WTRUs.</entry></row></tbody></tgroup></table></tables>

The purpose of these messages is to help the BS perform assignments for WTRUs associated with a single repeater, assignments for communication between each repeater and the BS, and balancing assignments between WTRUs associated with different repeaters.

<b><u>Example 1: WTRU communicates only with repeaters.</u></b>

<b><u>Centralized Scheduling</u></b>

In centralized scheduling, the BS allocates a scheduling grant (SG) to each WTRU and this SG is transmitted from the BS to the WTRU through a repeater. The repeater will simply forward the assignment to the WTRUs.

Because the WTRU communicates directly with the repeater, the SI transmitted by the WTRU reflects the link between the WTRU and the repeater, and the BS can use that information to perform grant assignments. However, the BS also needs to consider the fact that the repeater needs to transmit data from all associated WTRUs to the BS. Thus, there is no advantage in providing a large grant to a WTRU if there is not enough bandwidth between the repeater and the BS.

To explain this, we will introduce "repeater SI" which will reflect the capacity of the repeater. Together with the higher layer signaling messages defined above, the "relay SI" may be used to control the bandwidth allocated to the BS-repeater channel as well as the SG allocation to WTRUs.

51 is an exemplary frame structure diagram 5100 for SI. Referring to FIG. 51 , a frame structure for an SI reported from a repeater to a BS includes a repeater SI 5110 , at least one WTRU ID 5120 , and at least one SI 5130 .

<b><u>Hierarchical Scheduling</u></b>

In hierarchical scheduling, the BS allocates a grant to a repeater, which then, based on the received grant, SI received from the WTRU, and any other QoS information related to the WTRU, to other WTRUs associated with that repeater. Allocate Grant Note that, in this case, control of serving grant allocation to the WTRU is given to the repeater.

In order to ensure that the BS allocates enough grants to the repeaters, the repeaters need to send a "combined SI" containing the combined SIs from all WTRUs.

<b><u>Difference between "Combined SI" and "Repeater SI"</u></b>

It should be noted that the above "coupled SI" and "repeater SI" differ from each other in that they serve different purposes.

Since "repeater SI" is used to reflect the capacity of the repeater, it includes information such as how full the repeater buffer is, and the channel condition between the repeater and the BS. The BS then uses that information in conjunction with the SI of the WTRU.

"Combined SI" includes information related to buffers and channel conditions for all WTRUs combined so that the BS can allocate sufficient resources to the BS. The BS then distributes this resource among the WTRUs. In that case, the BS uses the "joined SI" (not the WTRU SI) to allocate the serving grant to the repeater.

It should be noted that in the case of hierarchical scheduling, the repeater may transmit "repeater SI" information to the BS. In this case, the BS may use both the "combined SI" and the "repeater SI" to perform grant assignment to the repeater.

That is, "repeater SI" contains information necessary to control communication between the repeater and the BS (used for both centralized and hierarchical cases). "Combined SI" simply replaces the SIs of WTRUs by combining information for all WTRUs into one SI (used only in the hierarchical case).

<b><u>Example 2: WTRU communicates with repeater and BS simultaneously</u></b>

If the WTRU communicates with both the repeater and the BS, the scheme will become more complex. The WTRU may receive the grant from the BS or directly from both the BS and the repeater. Using the same grant for both links (WTRU-repeater and WTRU-BS) may not be optimal because the channel conditions are different. One option is to use a combined approach in which the WTRU receives the grant for both the repeater and the BS and uses a lower value than the received value. Another option is for the WTRU to transmit an SI that reflects the most conservative case (lower power headroom). However, this option may not be optimal, as grants limit the ETFC (amount of data to be transferred) to be used and thus may limit throughput.

<b><u>Centralized Scheduling</u></b>

One approach is for the BS to allocate the grant based on the combined information of the WTRU and the relay. The modified SI information may be provided by the WTRU, which reflects the UPH related to the channel between the WTRU and the BS and the WTRU and the repeater. This information may be provided by the repeater along with an indication of channel conditions such as received power and interference level between the repeater and its associated WTRUs. Knowledge of the conditions of the link between the repeater and the BS may be provided.

<b><u>Hierarchical Scheduling</u></b>

Another approach is for the BS to allocate a grant to the WTRU for communication between the WTRU and the relay. This, in turn, allocates a grant to the WTRU for communication between the WTRU and the repeater. The WTRU will then have to deal with the grants from both the BS and the repeater and coordinate them to some extent. The method for coordination depends on whether the WTRU should use the same or different ETFC for each link (WTRU-BS and WTRU-repeater). If a different ETFC can be used, the WTRU can apply the grant independently. Otherwise, the WTRU will need to merge the grant, and the weakest link will dominate the transmission. This issue is discussed below.

<b><u>Choice between Example 1 and Example 2</u></b>

Where different ETFCs may be used to transfer data between the WTRU and the BS and between the WTRU and the repeater, different grants may be applied to each link. If the same ETFC needs to be used to transmit data from the WTRU to the BS and from the WTRU to the repeater, the same grant must be applied to both links. This will limit throughput performance. If the link between the WTRU and the repeater is much better than the link between the WTRU and the BS, and if the grant will be limited due to poor communication between the WTRU and the BS, then the WTRU communicates through only the repeater instead of through both the repeater and the BS. It may be more preferable to choose to do so. In this case, the WTRU can take advantage of good channel conditions between the WTRU and the repeater, and can maximize its throughput. This is illustrated in Example 1 above.

<b><u>LTE and cooperative networks</u></b>

In LTE, channel allocation in the uplink is also done through the use of grants. Although the details of the procedure for grant allocation are still being developed into a standard, it is clear that the problems presented in this specification and the proposed approach are also important and are applicable to LTE with the appropriate modifications required for channel allocation in LTE. do. It should also be noted that in LTE, the uplink transmission is always transmitted on a shared channel (with the use of grant assignments), in which case the problem discussed here is more and more important for LTE operation in cooperative networks. becomes important

52 is an exemplary synchronization diagram of BS and RS DL transmissions to a WTRU using a timing adjustment procedure 5200 . Referring to FIG. 52 , the BS signals the RS ( 5210 ) and estimates the BS-&gt;RS propagation delay ( 5220 ). Then, the BS signals the timing adjustment value to the RS (5230). Then, the RS may adjust the DL transmission timing (5240).

Although features and elements of the present invention have been described in preferred embodiments in particular combinations, each feature and element, alone or in combination with other features and elements of the present invention, without the other features and elements of the preferred embodiment. Or without them, it can be used in various combinations. The methods or flowcharts provided in the present invention may be implemented in a computer program, software, or firmware, tangibly embodied in a computer-readable storage medium for execution by a general-purpose computer or processor. Examples of computer-readable storage media include read-only memory (ROM), random access memory (RAM), registers, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and CDs. -Includes optical media such as ROM disks and DVDs.

Suitable processors include, for example, general purpose processors, special purpose processors, conventional processors, digital signal processors (DSPs), multiple microprocessors, one or more microprocessors in conjunction with DSP cores, controllers, microcontrollers, application specific integrated circuits (ASICs) , field programmable gate array (FPGA) circuits, and any other type of integrated circuit, and/or state machine.

A processor in association with software may be used to implement a radio frequency transceiver for use in a wireless transmit/receive unit (WTRU), user equipment (UE), terminal, base station, radio network controller (RNC), or any host computer. WTRUs include cameras, video camera modules, videophones, speakerphones, vibrators, speakers, microphones, television sets, hands-free headsets, keyboards, Bluetooth modules, frequency modulated (FM) radio units, liquid crystal display (LCD) units, organic light emitting devices. implemented in hardware and/or software, such as a diode (OLED) display unit, digital music player, media player, video game player module, internet browser, and/or any wireless local area network (WLAN) or ultra-wideband (UWB) module It can be used in conjunction with existing modules.

implementations

One. A method for wireless communication comprising transmitting and receiving data signals using a relay station (RS).

2. The method of implementation 1, wherein a single RS assists a wireless transmit/receive unit (WTRU).

3. The method of implementation 1 wherein more than one RS assists the WTRU.

4. The method as in any one of embodiments 1-3, wherein the WTRU communicates with a base station (BS) strictly via RS.

5. The method of implementations 1 or 2, wherein the WTRU communicates with the BS directly and via RS.

6. The method of embodiment 4, wherein a single RS assists a single WTRU.

7. The method of embodiment 4 wherein a single RS assists more than one WTRU.

8. The method of implementation 7 wherein separate BS-RS channels are used for WTRUs.

9. The method of embodiment 7, wherein one BS-RS channel is shared between WTRUs.

10. The method of embodiment 6, wherein the BS broadcasts information for the RS.

11. The method of embodiment 10, wherein the RS broadcasts the information.

12. The method as in any of embodiments 6-11, wherein the BS receives information regarding how the WTRU selects an RS and associates itself with the selected RS.

13. The method of embodiment 7 wherein the BS receives and pools data to be transmitted to a plurality of WTRUs and transmits the pooled data to a single RS.

14. The method of embodiment 13, wherein the BS receives data from a plurality of WTRUs assembled by an RS.

15. The method of embodiment 5 comprising the use of diversity techniques.

16. The method of embodiment 15, wherein a single RS assists a single WTRU.

17. The method of embodiment 15, wherein a single RS assists more than one WTRU.

18. The method of embodiment 13 wherein separate BS-RS channels are used for WTRUs.

19. The method of embodiment 17, wherein one BS-RS channel is shared between WTRUs.

20. The method of embodiment 16, wherein the BS broadcasts information for the RS.

21. The method of implementation 16, wherein the RS broadcasts information.

22. The method as in any of embodiments 16-21, wherein the BS receives information regarding how the WTRU selects an RS and associates itself with the selected RS.

23. The method of embodiment 17, wherein the BS receives and aggregates data to be transmitted to a plurality of WTRUs and transmits the aggregated data to a single RS.

24. The method of embodiment 23, wherein the BS receives data from a plurality of WTRUs assembled by an RS.

25. The method of implementation 3, wherein the base station receives transmissions from a plurality of RSs operating in parallel to assist one WTRU.

26. The method of implementation 25 comprising at least one of a diversity technique and a spatial multiplexing technique.

27. The method of embodiment 25 or 26, wherein the RS serves one WTRU.

28. The method of implementations 25 or 26, wherein the RS serves a plurality of WTRUs.

29. The method of any one of embodiments 25-28, wherein the RS serves as a forwarding repeater.

30. The method of any one of embodiments 25-28, wherein the RS serves as a diversity repeater.

31. The method of implementation 3, wherein the base station receives transmissions from a plurality of RSs operating in series to assist one WTRU.

32. The method of any one of embodiments 3 and 25-31, wherein each RS is dynamically associated with a different BS.

33. The method of implementation 32, wherein a repeater is associated with more than one relay station.

34. The method of any one of implementations 1, 2, 4, 5, or 10-12, comprising implementing a WTRU protocol stack down to a physical layer (PHY) level.

35. The method of embodiment 34, wherein the PHY processing comprises

amplification, and forwarding at the RF level;

demodulation, re-modulation, and forwarding;

Decoding, re-encoding, and forwarding

A method for wireless communication comprising at least one of.

36. The method of implementations 34 or 35, wherein the RS-WTRU link may use a different frequency or different code as compared to the BS-RS link.

37. The method of any one of embodiments 34-36, wherein the modulation on the RS-WTRU link may be different from the modulation on the BS-RS link.

38. The method of any one of embodiments 34-37, wherein the error protection codes are different on the RS-WTRU and BS-RS links.

39. The method of any one of implementations 1, 2, 4, 6, or 10-12, comprising implementing a WTRU protocol stack down to a physical (PHY) layer.

40. The method of any one of implementations 1, 2, 4, 6, or 10-12, comprising implementing a WTRU protocol stack up to a medium access control (MAC) layer.

41. The method of any one of implementations 1, 2, 4, 6, or 10-12, comprising implementing a WTRU protocol stack up to a radio link control (RLC) layer.

42. The method of embodiment 41, wherein the protocol stack operates in a mode that is one of an acknowledgment mode, a no acknowledgment mode, a transparent mode, and a persistent mode.

43. The method of embodiment 41 or 42, wherein the RLC protocol modes between the BS and the RS and between the RS and the WTRU are different.

44. The method as in any one of implementations 34-43, comprising the transmission of data packets between a BS and a WTRU via RS.

45. The method of embodiment 44,

forward the packet to the RLC processor of the BS;

forwarding at least one RLC block to the MAC processor of the BS;

forwarding the at least one MAC block to the PHY processor of the base station;

sending at least one PHY block to the receiving PHY processor of the RS.

A method for wireless communication, comprising:

46. The method of embodiment 44,

forward the PHY block to the transmit PHY processor of the RS;

sending the PHY block to the WTRU's PHY processor.

A method for wireless communication comprising a.

47. The method of embodiment 44,

forward at least one MAC block to a MAC processor of the WTRU;

apply automated repeat request (ARQ) between the BS MAC processor and the WTRU MAC processor;

forward at least one RLC block to an RLC processor of the WTRU;

apply automated repeat request (ARQ) between the BS RLC processor and the WTRU RLC processor;

Forwarding packets out of the WTRU RLC processor

A method for wireless communication comprising a.

48. The method of any one of embodiments 44-47, wherein the PHY processing in the RS comprises:

amplification, and forwarding at the RF level;

demodulation, re-modulation, and forwarding;

Decoding, re-encoding, and forwarding

and at least one of the options of

49. The method of any one of embodiments 44-48, wherein the RS comprises adaptively switching between the options of implementation 45.

50. The method of any one of implementations 44-49, wherein the RS-WTRU link may use a different frequency or different code as compared to the BS-RS link.

51. The method of any one of embodiments 44-49, wherein the modulation on the RS-WTRU link is different from the modulation on the BS-RS link.

52. The method of any one of embodiments 44-49, wherein the error protection codes are different on the RS-WTRU and the BS-RS link.

53. The method of embodiment 44,

forward the packet to the RLC processor of the BS;

forwarding at least one RLC block to the MAC processor of the BS;

forwarding the at least one MAC block to the PHY processor of the base station;

sending at least one PHY block to the receiving PHY processor of the RS.

A method for wireless communication comprising a.

54. The method of embodiment 44,

forwarding the at least one MAC block to the MAC processor of the RS;

applying HARQ between the MAC processor of the BS and the MAC processor of the RS;

forward the block to a second PHY processor of the RS;

sending at least one PHY block to the WTRU's PHY processor;

A method for wireless communication, comprising:

55. The method of embodiment 44,

forward at least one MAC block to a MAC processor of the WTRU;

apply HARQ between the RS MAC processor and the WTRU MAC processor;

forward at least one RLC block to an RLC processor of the WTRU;

apply ARQ between the BS RLC processor and the WTRU RLC processor;

Forwarding packets out of the WTRU RLC processor

A method for wireless communication, comprising:

56. The method as in any one of embodiments 53-44, comprising retransmitting the packet multiple times if the RS acknowledges (ACK) the packet to the BS and transmission of the packet to the WTRU is unsuccessful.

57. The method of embodiment 56, wherein upon the event of a buffer overflow in RS MAC,

keep guesses about the state of the buffer;

periodically communicate the buffer occupancy status to the BS;

Incorporate the buffer occupancy status into the feedback received by the BS;

send a negative acknowledgment (NACK) to indicate that the buffer is full;

send an acknowledgment (ACK) to indicate that the buffer is almost full;

Sending a delayed ACK/NACK to report whether the delivery of a particular packet was successful

A method for wireless communication comprising performing at least one of:

58. The method of implementation 57, wherein maintaining a guess about the state of the buffer comprises obtaining the maximum number of attempts the RS makes and the time taken to transmit the data.

59. The method of implementation 57, wherein maintaining a guess about the state of the buffer comprises using an average time to pass a packet from the RS to the BS.

60. The method of embodiment 44,

forward the packet to the RLC processor of the BS;

forwarding at least one RLC block to the MAC processor of the BS;

forwarding the at least one MAC block to the PHY processor of the base station;

sending at least one PHY block to the receiving PHY processor of the RS.

A method for wireless communication, comprising:

61. The method of embodiment 44,

forwarding the at least one MAC block to the MAC processor of the RS;

apply HARQ between the BS MAC processor and the RS MAC processor;

forwarding the at least one RLC block to the RLC processor of the RS;

apply ARQ between the BS RLC processor and the RS RLC processor;

forward the block to the second RS MAC processor;

forward the block to the second RS PHY processor;

sending at least one PHY block to the WTRU PHY processor.

A method for wireless communication comprising a.

62. The method of embodiment 44,

send at least one MAC block to the WTRU MAC processor;

perform HARQ between the WTRU MAC processor and the RS MAC processor;

forward at least one RLC block to the WTRU RLC processor;

perform ARQ between the WTRU RLC processor and the RS RLC processor;

Forwarding packets out of the WTRU RLC processor

A method for wireless communication comprising a.

63. The method of any one of embodiments 1-62, wherein WTRUs that communicate directly with the BS are grouped together.

64. The method as in any one of embodiments 1-63, wherein WTRUs communicating with a BS via a single RS are grouped together, wherein the group each corresponds to a respective RS.

65. according to embodiment 63 or 64,

distinguish between WTRUs at the center of the cell and WTRUs at the edge of the cell;

put the central WTRUs in a group in direct contact with the BS;

Splitting the edge WTRUs into groups that communicate with the BS via a single RS

A method for wireless communication, comprising:

66. according to embodiment 63 or 64,

the RS monitors the communication between the WTRU and the BS and the reported channel metrics;

the RS uses information from the monitoring to determine whether communication with the WTRU is improved over the RS;

When the RS determines that communication will be improved, the RS establishes a connection between the WTRU and the BS.

A method for wireless communication, comprising:

67. The method of embodiment 63 or 64, comprising periodically transmitting a beacon signal that allows WTRUs to determine whether they would benefit from using the RS and communicates this determination to the RS.

68. The method of embodiments 63-68 comprising each WTRU periodically updating its location, wherein the location is used to determine a group to which the WTRU should belong.

69. According to embodiments 63-68,

aggregating transmissions from multiple WTRUs into one transmission;

Separating the aggregated transmissions from RS

A method for wireless communication, comprising:

70. The method according to any one of embodiments 63-69,

generate a single ACK/NACK;

Forwarding the ACK/NACK to the BS or MAC-WTRU in the network

A method for wireless communication comprising performing hybrid automatic repeat request (HARQ) by

71. The method as in any one of embodiments 63-69, comprising performing hybrid automatic repeat request (HARQ) by generating a separate ACK/NACK for each data packet.

72. The method of any one of embodiments 63-69, wherein the WTRU communicates with more than one RS.

73. The method of any one of embodiments 1, 2, 5, 15, 16 and 20-22, wherein the RS protocol stack comprises:

physical layer (PHY);

a media access control (MAC) layer; and

Radio Link Control (RLC) Layer

terminating in one of the following.

74. The method of embodiment 73, wherein the PHY processing in the RS comprises:

amplification, and forwarding at the RF level;

demodulation, re-modulation, and forwarding;

decoding, re-encoding, and forwarding;

Compression and Forwarding

A method for wireless communication comprising at least one of.

75. The method of implementation 74, wherein processing the PHY at the RS comprises adaptively switching between the options of implementation 64.

76. The method of any one of embodiments 73-75, wherein the RS-WTRU link may use a different frequency or different code compared to the BS-RS link.

77. The method of any one of embodiments 73-75, wherein the modulation on the RS-WTRU link may be different from the modulation on the BS-RS link.

78. The method of any one of embodiments 73-75, wherein the error protection codes are different on the RS-WTRU and BS-RS links.

79. The method of any one of embodiments 73-78, comprising the transmission of data packets between a BS and a WTRU via RS.

80. The method according to any one of embodiments 73-79,

forward the packet to the RLC processor of the BS;

forwarding at least one RLC block to the MAC processor of the BS;

forwarding the at least one MAC block to the PHY processor of the base station;

send at least one PHY block to the receiving PHY processor of the RS and the PHY processor of the WTRU;

forward the block from the receiving PHY processor of the RS to the transmitting PHY processor of the RS;

sending at least one PHY block to a second PHY processor of the WTRU.

A method for wireless communication, comprising:

81. The method according to any one of embodiments 63-69,

forward at least one MAC block to a MAC processor of the WTRU;

perform HARQ between the MAC processor of the BS and the MAC processor of the WTRU;

forward the at least one RLC block to an RLC processor of the WTRU;

perform ARQ between the BS RLC and the WTRU RLC processor;

Forwarding packets out of the WTRU RLC processor

A method for wireless communication, comprising:

82. The method of any one of embodiments 73-81, wherein the RS is scheduled to transmit in the same transmission time interval (TTI) as the BS.

83. The method of any one of embodiments 73-81, wherein the RS is scheduled to transmit in a different transmission time interval (TTI) than the BS.

84. The method of embodiment 82 or 83, comprising scheduling direct RS transmission.

85. The method of embodiment 82 or 83, wherein the RS continues to listen for retransmissions even when no further retransmissions are needed.

86. The method as in embodiments 82 or 83, comprising notifying the RS which packets the BS is still transmitting or when the BS has stopped transmitting packets.

87. The method according to any one of embodiments 80-86,

A method for wireless communication, comprising: a repeater initiating a transmission by transmitting after each BS transmission what is determined by the protocol until it successfully decodes the data.

88. The method of any one of embodiments 80-86, wherein the repeater comprises waiting for the repeater to initiate transmission until the accumulated information is above a quality threshold or has received a minimum number of transmissions.

89. The method of any one of embodiments 73-88, wherein the BS continues transmitting packets until an ACK is received or a maximum number of transmissions is exceeded.

90. The method of any one of embodiments 73-89, wherein the RS initiates a transmission when it has successfully decoded a BS transmission.

91. The method of any one of embodiments 73-90, wherein the RS initiates transmission when it has accumulated a sufficient amount of information to pass a predefined threshold.

92. The method according to any one of embodiments 73-91, wherein every frame comprises a reserved distributed radio resource unit (RRU) for a repeater.

93. The method of any one of embodiments 73-92, wherein the RS is signaled to be ready to transmit when a NACK is received.

94. The method of any one of embodiments 73-93, wherein the RS transmits its ready-to-send status using an ACK message associated with a particular HARQ process.

95. The method as in any one of embodiments 73-94, comprising using direct signaling to tell a repeater which packet should be transmitted in which RRU.

96. The method of implementations 94 or 95, further comprising scheduling repeater transmissions by scheduling in the same RRU, thereby maximizing MIMO efficiency.

97. The method as in embodiments 94 or 95, further comprising scheduling transmissions in relay by scheduling at different RRUs, thereby maximizing time diversity and minimizing interference.

98. The method according to any one of embodiments 73-97,

tracking the quality of WTRU-BS and WTRU-RS channels;

selectively sending NACK transmission to RS or BS or both

A method for wireless communication, comprising:

99. The method of embodiment 98, wherein the selectivity is based on a WTRU-BS or WTRU-RS channel.

100. The method of embodiment 98 or 99 comprising performing selective transmission at a PHY layer or higher layers.

101. A method for wireless communication, comprising determining a direction of transmission for a communication message.

102. The method of embodiment 101,

receive a communication message;

decode the communication message;

re-encoding the decoded message

Further comprising, a method for wireless communication.

103. The method of implementation 101, wherein the message is re-encoded based on channel quality.

104. The method of any one of embodiments 101-103, comprising transmitting the re-encoded message.

105. The method of any one of implementations 101-104, wherein the determining is based on at least one throughput.

106. The method of implementation 105, further comprising using a time division duplex relay protocol.

107. The method of implementation 106, comprising determining a transmission path to a wireless transmit/receive unit based on maximizing data throughput.

108. The method of any one of embodiments 101-107, further comprising determining a transmission time interval (TTI) for transmission.

109. The method of implementation 108, wherein the TTI is determined based on a scheduling function.

110. The method of implementation 109, wherein the scheduling function uses the decision variable as an input.

111. The method of implementation 110, wherein the scheduling function further utilizes a buffer occupancy or fairness option.

112. The method of implementation 111, wherein for hybrid automatic repeat request (HARQ) scheduling, the decision variable is based on a channel quality condition.

113. The method of any one of embodiments 101-111, wherein the channel condition is reported using feedback.

114. The method of implementation 113, wherein feedback from a plurality of wireless transmit/receive units (WTRUs) is aggregated into one transmission when reported by a repeater.

115. The method of any one of embodiments 111-114, wherein the acknowledgment/negative-acknowledgment (ACK/NACK) is sent directly via the repeater.

116. The method of embodiment 115 wherein different ACK/NACKs are aggregated across WTRUs and TTIs.

117. The method of implementation 105, further comprising using a parallel transmit duplex relay (PTDR) protocol.

118. The method of embodiment 117, wherein the transmission is split into two sub-TTIs (steps).

119. The method of embodiment 118, wherein the base station transmits to the repeater during step 1.

120. The method of embodiment 119, wherein the transmission includes information that repeaters intend to communicate to the WTRU.

121. The method as in any one of embodiments 117-120, wherein the repeater and the base station transmit concurrently to the WTRU during step 2.

122. The method of implementation 121, wherein the scheduling in each step is performed according to a scheduling process.

123. The method of any one of embodiments 120-122, wherein HARQ scheduling is performed independently by the base station and by each repeater.

124. The method of implementation 123, wherein the base station aggregates WTRUs having the same repeater into one transmission in step 1.

125. The method of implementation 124, wherein the repeater knows the quality of the repeater to WTRU channel to perform the scheduling.

126. The method of any one of embodiments 122-125, wherein step 1 and step 2 require separate ACK/NACK.

127. The method of any one of embodiments 101-105, further comprising using a Superposition Time Division Duplexed Relaying (STDDR) protocol.

128. The method of implementation 127, wherein the base station schedules different WTRUs based on their respective needs and channel conditions.

129. The method of embodiment 128 wherein the request and channel conditions are reported to the base station via a repeater or directly from a WTRU.

130. The method as in any one of embodiments 127-129, wherein the base station transmits simultaneously to the repeater and to the WTRUs using overlap coding in step 2.

131. The method of implementation 130, wherein the repeater takes over a portion of the communication to forward received data to the aggregated WTRU, while the base station continues to serve those WTRUs scheduled on the direct link at full power. Way.

132. The method according to any one of embodiments 127-131, further comprising determining an achievable data rate between the base station BS and the relay station RS, and between the base station BS and the first WTRU UE1.

133. The method of implementation 132, further comprising determining an achievable data rate between the BS and the WTRU UE1 and between the repeater RS and the second WTRU UE2.

134. The method of implementation 132, wherein HARQ scheduling is performed independently by the base station and each repeater.

135. The method of implementation 134, wherein channel state feedback is sent to the repeater.

136. The method of implementation 135, wherein the plurality of WTRUs are aggregated into one transmission when fed back from the WTRUs to the base station via a repeater.

137. The method as in any one of implementations 127-135, further comprising using a separate ACK/NACK process to determine throughput for each WTRU.

138. The method of embodiment 137, wherein the ACK/NACK is sent from the repeater to the base station and from the WTRU directly to the base station.

139. The method of embodiment 138, wherein the ACK/NACK is sent from a WTRU to a transmitter, including a repeater or a base station.

140. The method of implementation 139, wherein the repeater forwards the WTRU ACK/NACK to the base station.

141. The method of implementation 139, wherein the repeater does not forward the WTRU ACK/NACK to the base station.

142. The method of any one of embodiments 101-105, further comprising using a Fountain Extended Time Division Duplex Relaying (FTDDR) protocol.

143. The method of embodiment 142, wherein fountain encoding is used at each transmitter.

144. The method of implementation 143, wherein the fountain code refers to a code type capable of driving an outage probability to zero without channel state information from a source.

145. The method of implementation 144, wherein the transmitter encodes data into an infinite length code stream.

146. The method of implementation 145, wherein the receiver gathers information until it completely recovers the data.

147. The method of implementation 146, wherein the source data may be recovered from any set of sufficiently encoded packets.

148. The method of embodiment 147, wherein the data comprises: <img file="KR20100109984A_D0072.tif" />transmitted directly from the base station to the WTRU, or with the aid of a repeater, depending on whether <img file="KR20100109984A_D0073.tif" />denotes the achievable data rate between BS and RS, <img file="KR20100109984A_D0074.tif" />represents the data rate directly achievable between the base station and the WTRU.

149. The achievable throughput between the WTRU and the WTRU of embodiment 148 is:

<img file="KR20100109984A_D0075.tif" />when, <img file="KR20100109984A_D0076.tif" />

150. The method of implementation 149, wherein the base station broadcasts information to both the repeater and the WTRU.

151. The method of embodiment 150, wherein the repeater <img file="KR20100109984A_D0077.tif" />receiving certain new information at a time.

152. In implementation 151, the new information is broadcast from the base station and received by the repeater, <img file="KR20100109984A_D0078.tif" />information that is not received by the WTRU in

153. The method of embodiment 152, wherein maximizing over a selection of all L repeaters, <img file="KR20100109984A_D0079.tif" />here, <img file="KR20100109984A_D0080.tif" />is the achievable throughput.

154. The method of implementation 153, wherein the base station does not pre-dedicate a repeater.

155. The method of implementation 154, wherein only repeaters send an ACK to the base station.

156. The method of implementation 155, wherein a first relay ACKing may be selected for scheduling.

157. The method of implementation 156, wherein the base station allows time observation frames to collect sufficient repeater ACKs and select among them according to selected criteria.

158. The method of implementation 157, wherein more than one repeater is selected and the repeaters may be scheduled using a typical cellular scheduler.

159. The method of implementation 158, wherein more than one WTRU is served by one repeater, and data to these WTRUs may be aggregated in one transmission or scheduled separately.

160. The method of implementation 159, wherein the codes used are rateless and thus channel state feedback is not required.

161. The method of implementation 160, wherein repeaters need only send an ACK to the base station to allow for further scheduling.

162. The method of embodiment 161, wherein the WTRU ACK/NACK need only be available at the base station.

163. The method of embodiment 162, wherein the ACK/NACK is forwarded either directly in the uplink or via a repeater.

164. The method of any one of embodiments 127-163, wherein the method comprises Fountain &amp; A method for wireless communication, wherein the method is a superposition coding time division duplex relay (FSTTDR) protocol.

165. The method of implementation 164, wherein the WTRUs do not need to be delivered via a repeater, and the transmission is scheduled at the beginning of the communication.

166. The method of implementation 165, wherein the WTRUs do not wait for a repeater to complete service.

167. The method of implementation 166, wherein all data streams are fountain-type encoded.

168. The method of implementation 167, wherein the communication at each TTI is in two phases.

169. The method of implementation 168, wherein the repeater and the N WTRUs are scheduled concurrently in step 1.

170. The method of implementation 169, wherein the repeater schedules and serves the M WTRUs, while the other N WTRUs are continuously served by the base station at higher power in step 2.

171. The method of embodiment 170, wherein the repeater sends only an ACK to the base station to allow for further scheduling.

172. The method of implementation 171, wherein ACK/NACK is only available at the base station, which may be forwarded or transmitted directly via a repeater in the uplink.

173. A method for transmitting data to a wireless transmit/receive unit (WTRU) in a cell having base stations, the method comprising using at least one repeater to improve performance of a downlink channel.

174. The method of embodiment 173, wherein cells have N dedicated repeaters.

175. The method as in embodiments 173 or 174, further comprising estimating a signal-interference-to-noise ratio (SINR) under a particular power cell and interference assumption.

176. The method according to any one of embodiments 173-175, further comprising determining under which conditions the cellular system is interference limited.

177. The method as in any one of embodiments 173-176, further comprising determining a repeater power and location in the cell.

178. The method according to any one of embodiments 173-177, further comprising determining a set of parameters that maximize a minimum SINR level provided throughout the cell.

179. The method as in any one of embodiments 173-178, further comprising using a decision protocol based on maximizing a resulting throughput for the WTRU.

180. The method as in any one of embodiments 173-179, further comprising evaluating a SINR cumulative density function (CDF) using the plurality of random WTRU positions and channel propagation parameters.

181. The method according to any one of embodiments 173-180, wherein the repeater is disposed along the SINR line of 3 dB.

182. The method according to any one of embodiments 173 to 181, wherein the maximum interference is determined, and only the strongest interfering transmitter in each of the plurality of outer cells is considered active to represent a worst-case scenario, wherein the SINR is the base station transmit power P_B, the channel between the base station and the WTRU <img file="KR20100109984A_D0081.tif" />, and repeater transmit power P_Rwhich depends on the data transmission method.

183. The method of embodiment 182, wherein SINR is

<img file="KR20100109984A_D0082.tif" />

A data transmission method, which is given by .

184. The method according to any one of embodiments 173-181, wherein random interference is determined, a random transmitter is selected between a base station and N relay stations (RSs), outer cells are considered, and SINR is the base station transmit power P_B, the channel between the base station and the WTRU <img file="KR20100109984A_D0083.tif" />, and repeater transmit power P_Rwhich depends on the data transmission method.

185. The method of embodiment 184, wherein SINR is:

<img file="KR20100109984A_D0084.tif" />

A data transmission method, which is given by

186. A method for evaluating the gains associated with the use of repeaters in high-speed downlink packet access (HSDPA), wherein the transmit power of a base station (BS) is set to a predetermined value, each cell having only one wireless transceiver (WTRU) , a method for evaluating gains.

187. The WTRU as in any one of embodiments 173-181, or 186, wherein to evaluate throughput in HSDPA communication, a two-hop scheme is used, and the base station continues until the relay station fully decodes the bits and initiates transmission, and the WTRU transmitting the information bits (b) to the selected relay station until α decodes the information bits.

188. The method of embodiment 187, wherein the effective throughput is

<img file="KR20100109984A_D0085.tif" />

is given, where, <img file="KR20100109984A_D0086.tif" />ego <img file="KR20100109984A_D0087.tif" />and T_RSis the time it takes for the repeater to completely decode b information bits during the first phase of communication, T_Uis the additional time it takes the WTRU to decode the b bits during the second phase of communication.

189. The method of any one of embodiments 173-181, or 186, for implementation in HSDPA communication:

use a rateless two-hop scheme;

the WTRU decodes information bit b received from the base station during a first phase of communication;

the WTRU decoding information received from the relay station during the second phase of communication

wherein the second stage bits are residual bits that the WTRU did not decode in the first stage.

190. The method of embodiment 189, wherein the effective throughput is

<img file="KR20100109984A_D0088.tif" />

is given by

here, <img file="KR20100109984A_D0089.tif" />ego, <img file="KR20100109984A_D0090.tif" />and T_RSis the time it takes for the repeater to completely decode b information bits, T_Uis the additional time it takes the WTRU to decode the b bits.

191. The method of any one of embodiments 173-181, or 186, for implementation in HSDPA communication:

using a distributed antenna scheme, wherein the WTRU simultaneously receives different bits of information from a base station and a relay station;

the WTRU uses successive interference cancellation to differentiate between different information signals transmitted by the base station and the relay station;

The achieved decoding rate at the WTRU is subject to the following conditions:

[<img file="KR20100109984A_D0091.tif" />, here, <img file="KR20100109984A_D0092.tif" />is the transmission rate of the BS, and RRS-U is the transmission rate of the signal received from the relay station]

Further comprising satisfying the, gain evaluation method.

192. The method of implementation 191, wherein non-rateless coding is used by the transmission source, b information bits are multiplexed between RS and BS, and the effective throughput is:

<img file="KR20100109984A_D0093.tif" />

The gain evaluation method, which is given by

193. In implementation 191, a rateless code is used, the BS and RS split only the bits that the WTRU did not recover when the RS has fully decoded all information bits, and the effective throughput is:

<img file="KR20100109984A_D0094.tif" />

The gain evaluation method, which is given by

194. A method for wireless communication implemented by a wireless transmit/receive unit (WTRU) comprising: sending a transmission to a base station via a cooperative repeater.

195. The method of implementation 194, further comprising receiving a transmission from a base station via a cooperative repeater.

196. The method of implementations 194 or 195, wherein the repeater is a forwarding repeater.

197. The method of any one of embodiments 194-196, wherein the repeater is a distributed-MIMO repeater.

198. The method of any one of embodiments 194-197, further comprising sending the transmission to a plurality of cooperative repeaters.

199. The method of any one of embodiments 194-198, further comprising receiving transmissions from a plurality of cooperative repeaters.

200. The method of embodiments 198 or 199, wherein a plurality of cooperative repeaters are shared.

201. The method of any one of embodiments 194-200, further comprising using a PHY layer cooperative transmission, wherein the WTRU and the repeater listen for the base station transmission in a first phase of transmission, and the WTRU listens to the base station transmission during the second phase of the transmission. and receiving transmissions from both.

202. The method of implementation 201, further comprising using rateless coding.

203. The method of any one of implementations 194-202, further comprising using distributed beamforming for transmission.

204. The method of any one of implementations 194-203, wherein the WTRU has a cooperative PHY layer that communicates with cooperative MAC layers of a base station and a repeater.

205. The method of any one of implementations 194-204, wherein the WTRU has a cooperative MAC layer that communicates with cooperative MAC layers of a base station and a repeater.

206. The method of any one of implementations 194-205, wherein the WTRU has a cooperative RLC layer that communicates with cooperative MAC layers of base stations and repeaters.

207. The method of embodiment 206 or 206, wherein the MAC layer performs the cooperative HARQ function in a distributed, decentralized, or hierarchical manner.

208. The method of implementation 207, wherein the MAC layer performs each of the cooperative channel access function and the cooperative resource allocation function in a distributed, decentralized, or hierarchical manner.

209. The method of any one of embodiments 194-208, wherein the transmission is in TDM mode.

210. The method of any one of embodiments 194-209, wherein a two-hop transmission is performed.

211. The method of any one of embodiments 194-210, wherein the transmission is in FDM mode.

212. The method of any one of implementations 209-211, wherein the WTRU transmits to the repeater only data that has not yet been transmitted to the base station.

213. The method of implementation 211, wherein the WTRU continuously transmits data on a first frequency and forwards the data to a base station on a second frequency.

214. A WTRU comprising a processor configured to perform the method according to any one of implementations 194-213.

215. The method of any one of implementations 194-214, further comprising synchronizing transmissions to a repeater by timing adjustments.

216. The method of implementation 215, further comprising the repeater to receive a timing adjustment based on the estimate of the downlink propagation delay, and the repeater to adjust the downlink transmission timing.

217. A cooperative repeater comprising a cooperative MAC layer, a cooperative PHY layer, configured to present the WTRU MAC and PHY protocols to a base station and present the base station MAC and PHY protocols to the WTRU.

218. The cooperative repeater of embodiment 216, further configured to present the WTRU RLC protocol to the base station and present the base station RLC protocol to the WTRU.

219. The cooperative repeater of embodiments 216 or 217, wherein the repeater is a two-hop forwarding repeater.

220. The cooperative repeater of embodiment 216, wherein the repeater is a distributed MIMO repeater.

221. The cooperative repeater of embodiment 216, wherein the repeater is a shared repeater that presents the WTRU MAC protocol and the repeater MAC protocol to the base station.

222. The cooperative repeater as in implementations 216 or 219, wherein the repeater is a shared repeater that presents base station MAC scheduling functionality to WTRUs sharing the repeater.

223. Step 1 A method for cooperative multiplexing of data comprising receiving a message m1 from a first station in time period T1.

224. The method according to embodiment 223, further comprising receiving message m1' from the relay station in step 2 time interval T2.

225. The method according to embodiment 224, wherein m1' is based on a version of m1 received by the relay station from the base station in step 1.

226. The method according to embodiments 224 or 225, wherein time interval T2 comes after time interval T1.

227. The method of any one of embodiments 224-226, wherein T2 is discontinuous with T1.

228. The method of any one of embodiments 224-226, wherein T2 is contiguous with T1.

229. The method according to any one of embodiments 223-228, wherein the transmission medium is slotted into fixed size transmission time intervals (TTIs).

230. The method according to any one of embodiments 223-229, further comprising receiving message m2 from the first station in step 2 .

231. The method according to any one of embodiments 223-230, wherein the receiving is using an optimal multi-user detector.

232. The method of embodiment 231, wherein the optimal multi-user detector is a sequence interference cancellation (SIC) receiver.

233. The method according to any one of embodiments 223-232, further comprising combining received versions of a message to improve decoding of the message.

234. The method of embodiment 233, wherein the combining is a hybrid automatic repeat request (HARQ) combining.

235. The method according to any one of embodiments 223-234, further comprising generating two messages v1 and v2.

236. The method according to embodiment 235, wherein the two messages v1 and v2 are medium access control (MAC) packet data units (PDUs).

237. The method according to any one of embodiments 235-236, further comprising sending in step 1 a message v1 to the relay station and the second station.

238. The method according to embodiment 237, further comprising sending message v2 to the second station in step 2 .

239. The method of any one of embodiments 223-238, wherein the first station is a wireless transceiver (WTRU).

240. The method according to any one of embodiments 223-239, wherein the first station is a user equipment (UE).

241. The method according to any one of embodiments 223-240, wherein the first station is a base station.

242. The method as in embodiments 237 or 238, wherein the second station is a base station.

243. The method as in embodiments 237 or 238, wherein the second station is a wireless transmit/receive unit (WTRU).

244. The method as in embodiments 237 or 238, wherein the second station is a user equipment (UE).

245. The method according to any one of embodiments 223-244, further comprising in step 1 sending a message m to the relay station and the second station.

246. The method according to embodiment 245, further comprising sending a message m to the second station in step 2, wherein the message is sent by the relay station in or in step 2.

247. The method according to any one of embodiments 223-246, further comprising using a control channel TCC.

248. The method according to any one of embodiments 223-247, further comprising using a control channel HCC.

249. The method according to any one of embodiments 223-248, further comprising monitoring control channel TCC1.

250. The method according to any one of embodiments 223-249, further comprising monitoring control channel TCC2.

251. The method according to embodiment 249 or 250, wherein TCC1 signals information about transmission from a base station and TCC2 signals information about transmission from a relay station.

252. The method according to any one of embodiments 249-251, wherein the TCC1 is received from a base station.

253. The method according to any one of embodiments 249-252, wherein the TCC2 is received from a base station.

254. The method according to any one of embodiments 249-252, wherein the TCC2 is received from a relay station.

255. The method as in any one of implementations 249-254, further comprising transmitting a HARQ feedback control channel HCC1 to the base station.

256. The method as in any one of embodiments 249-255, further comprising sending a HARQ feedback control channel HCC2 to the relay station.

257. The method as in any one of implementations 249-256, further comprising transmitting a HARQ feedback control channel HCC3 to the base station.

258. The method of any one of implementations 249-257, further comprising receiving a HARQ feedback control channel HCC1 from a base station.

259. The method as in any one of embodiments 249-258, further comprising receiving a HARQ feedback control channel HCC2 from the relay station.

260. The method of any one of implementations 249-259, further comprising receiving a HARQ feedback control channel HCC3 from a base station.

261. The method as in any one of embodiments 223-260, further comprising transmitting a control channel TCC1.

262. The method as in any one of embodiments 223-261, further comprising transmitting a control channel TCC2.

263. The method of embodiment 262, wherein TCC1 is transmitted to a base station.

264. The method as in embodiments 262 or 263, wherein the TCC2 is transmitted to the base station.

265. The method according to any one of embodiments 262-264, wherein the TCC2 is sent to the relay station.

266. The method as in any one of embodiments 223-265, further comprising receiving up to two codewords in a transmission time interval (TTI).

267. The method of implementation 266, wherein one codeword is received from a relay station and the other codeword is received from a base station.

268. The method of implementation 266, wherein one codeword is received from a relay station and another codeword is received from a wireless transmit/receive unit (WTRU).

269. The method according to any one of embodiments 266-268, wherein in the case of multiple-input multiple-output transmissions more codewords are received.

270. The method as in any one of embodiments 266-269, further comprising transmitting HARQ (ACK/NACK) feedback to indicate whether each of the two codewords was successfully received. .

271. The method of implementation 270, wherein the feedback is transmitted using HCC.

272. The method according to any one of embodiments 266-271, further comprising combining the received versions to improve decoding of packet m.

273. The method of implementation 272, further comprising using common identifiers such as HARQ process ID and predefined TTI.

274. The method of any one of embodiments 266-273, further comprising using a flow control signal.

275. The method of any one of embodiments 266-277, further comprising receiving an ACK.

276. The method of implementation 275, further comprising sending a next message.

277. The method as in any one of embodiments 266-274, further comprising retransmitting the message if an ACK is not received.

278. The method of any one of embodiments 223-277, further comprising a full duplex relay allowing simultaneous transmission and reception.

279. The method as in any one of embodiments 223-278, further comprising delegating HARQ retransmissions.

280. The method according to embodiment 279, wherein HARQ retransmission is delegated from the base station to the relay station.

281. The method of implementation 279, wherein HARQ retransmission is delegated from a base station to a wireless transmit/receive unit (WTRU).

282. The method as in any one of embodiments 223-281 for cooperative multiplexing of data for uplink transmission.

283. The method according to any one of embodiments 223-282, for cooperative multiplexing of data for downlink transmission.

284. The method according to any one of embodiments 223-282, wherein step 1 refers to a step in time during which the source communicates with the relay station.

285. The method according to any one of embodiments 223-283, wherein step 2 indicates a time at which both the source and relay station communicate with the destination.

286. The method of embodiment 285, wherein R_BS-RS= link base station (BS) - rate on relay station (RS); R_BS-U = rate on link BS-WTRU in step 1; R_BS-U(2) = rate on link BS-WTRU in step 2; R_RS-Uis the rate on the link RS-WTRU in step 2; wherein T1 = the temporal length of step 1 and T2 is the temporal length of step 2;

287. The method of embodiment 286, wherein b_BS, and from the relay station b_RSto receive - b = b_BS + b_RS- A method for cooperative multiplexing of data, further comprising:

288. The method of embodiment 287,

<img file="KR20100109984A_D0095.tif" />and canceling interference from the BS on the RS-WTRU link to obtain

289. The method of embodiment 288, wherein the rate achieved in this second step is <img file="KR20100109984A_D0096.tif" />A method for cooperative multiplexing of data, which may be denoted as

290. The method of embodiment 287 or 288, wherein the interference cancellation uses SIC.

291. The method of any one of embodiments 285-290, further comprising recovering the b1 bit in a first step and recovering the b2 bit in a second step,

<img file="KR20100109984A_D0097.tif" />ego,

At the end of phase 1, in the WTRU <img file="KR20100109984A_D0098.tif" />is achieved.

292. The method of embodiment 291, <img file="KR20100109984A_D0099.tif" />The method for cooperative multiplexing of data further comprising determining that RS is a valid candidate only if .

293. The method of embodiment 291, <img file="KR20100109984A_D0100.tif" />The method for cooperative multiplexing of data further comprising determining that RS is a valid candidate only if .

294. The method as in any one of embodiments 284-293, further comprising receiving only a portion of message b.

295. The method of embodiment 294, wherein receiving only part of message b is from a base station.

296. The method according to embodiment 294, wherein receiving only part of message b is from a relay station.

297. The method as in any one of embodiments 283-296, further comprising dividing b bits at the MAC or PHY layer.

298. The method according to embodiment 297, wherein in step 1 b_RSsend b = b to user equipment in step 2_BS + b_RSA method for cooperative multiplexing of data, further comprising transmitting

299. The method of embodiment 298, <img file="KR20100109984A_D0101.tif" /> or <img file="KR20100109984A_D0102.tif" />A method for cooperative multiplexing of data.

300. The method of implementation 299 further comprising forwarding successfully decoded bRS bits at a rate RRS-U to the WTRU, wherein: <img file="KR20100109984A_D0103.tif" />ego,<img file="KR20100109984A_D0104.tif" />, the BS transmits bBS bits simultaneously at the rate RBS-U(2).

301. A base station comprising at least one transmitter, at least one receiver, at least one processor, each configured to operate according to any one of implementations 1-300.

302. A relay station comprising a processor, configured to operate according to any one of embodiments 1-300.

303. A wireless transmit/receive unit comprising at least one transmitter, at least one receiver, and at least one processor, each configured to operate according to any one of implementations 1-300.

110: forwarding relay architecture 120: Multiple WTRU-Serving-Relay Architecture 130: cooperative relay architecture 140: multi-BS-shared-relay architecture 150: WTRU 160: relay station (RS) 165: transmitter 170: receiver 175: processor 180: transmitter 185: receiver 190: processor 195: base station (BS)