Operation of a forward link acknowledgement channel for the reverse link data

ES 2 324 296 T3

DESCRIPTION

Operation of a forward link acknowledgment channel for reverse link data.

Background

Field

The disclosed embodiments relate generally to the field of communications, and more specifically to procedures and apparatus for operating a forward link acknowledgment channel.

Background

The communications field has many applications including, for example, paging, wireless local loops (WLL), Internet telephony, and satellite communication systems. An exemplary application is a cell phone system for mobile subscribers. Modern communication systems designed to allow multiple users to access a common communication medium have been developed for such cellular systems. These communication systems can be based on code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), or other multiple access techniques known in the art. These multiple access techniques decode and demodulate signals received from multiple users, thereby enabling simultaneous communication between multiple users and allowing a relatively large capacity for communication systems.

In the CDMA system, the available spectrum is efficiently shared among a number of users, and techniques such as soft handoff are employed to maintain sufficient quality to support delay-sensitive services (such as voice) without wasting large amounts of data. power. More recently, systems that improve capacity for data services have also become available. These systems provide data services using higher order modulation, faster power control, faster scheduling, and more efficient scheduling for services that have less stringent delay requirements. An example of such a data service communication system is the High Data Rate (HDR) system that meets the Association's cdma2000 High Data Rate IS-856 Air Interface Specification. of the Telecommunications Industry / Electronic Industries Alliance (TIA / EIA), January 2002 (the IS-856 standard).

In a CDMA system, data transmission occurs from a source device to a destination device. The destination device receives the data transmission, demodulates the signal, and decodes the data. As part of the decoding process, the target device performs the cyclic redundancy code (CRC) check of the data packet to determine if the packet was received correctly. Error detection procedures other than the use of CRC, eg energy detection, may also be used in combination with or instead of CRC. If the packet was received with an error, the destination device transmits a negative acknowledgment (NAK) message on its acknowledgment channel (ACK) to the source device, which responds to the NAK message by retransmitting the packet that was received. with an error.

Transmission errors can be particularly pronounced in applications with low signal quality (for example, low spectral density ratio of bit energy to noise power (E_b/ N_or)). In this situation, a conventional data retransmission scheme, such as automatic repeat request (ARQ), may not meet (or may be designed not to meet) the maximum bit error rate (BER) required for the operation of the device. system. In such a case, combining the ARQ scheme with an error correction scheme, such as a direct error correction (FEC), is often used to improve performance. This combination of ARQ and FEC is generally known as hybrid ARQ (H-ARQ).

After transmitting a NAK, the destination device receives the transmission and retransmission of data, demodulates the signal, and separates the received data into the new packet and the retransmitted packet. The new packet and the retransmitted packet do not need to be transmitted simultaneously. The destination device accumulates the energy of the retransmitted packet received with the energy already accumulated by the destination device for the packet received with an error. The target device then tries to decode the accumulated data packet. However, if the packet frame is initially transmitted with insufficient power to allow successful decoding by the destination device, as described above, and is then retransmitted, the retransmission provides time diversity. As a result, the total transmission energy of the frame (including retransmissions) is lower on average. The combined symbol energy for both the initial transmission and the retransmission (s) of the frame is lower than the energy that would have been required to initially transmit the frame at full power (i.e., at a power level which was sufficient by itself to allow correct decoding by the target device) on average. Thus, the accumulation of the additional energy provided by subsequent retransmissions improves the probability of successful decoding. Alternatively, the destination device may be able to decode the retransmitted packet by itself without combining the two packets. In both cases, the throughput rate can be improved since the packet received in error is retransmitted simultaneously with the transmission of the new data packet. Again, it should be noted that the new packet and the retransmitted packet need not be transmitted simultaneously.

ES 2 324 296 T3

In the reverse link (i.e. the communication link from the remote terminal to the base station), the reverse supplemental channel (RSCH) is used to transmit user information (e.g. packet data) from a remote terminal to the base station. base station, and to support retransmission in the physical layer. The R-SCH may use different encoding schemes for retransmission. For example, a retransmission may use a code rate of 1/2 for the original transmission. The same rate 1/2 code symbols may be repeated for retransmission. In an alternative case, the code behind may be a 1/4 rate code. The original broadcast can use 1/2 of the symbols and the broadcast can use the other half of the symbols. An example of the reverse link architecture is described in detail in US Patent Application No. 2002/0154610, entitled "REVERSE LINK CHANNEL ARCHITECTURE FOR A WIRELESS COMMUNICATION SYSTEM" issued to the assignee of the present application.

In a CDMA communication system, and specifically in a system adapted for packetized transmissions, congestion and overload can reduce the throughput of the system. Congestion is a measure of the amount of pending and active traffic relative to the nominal capacity of the system. System overload occurs when active and pending traffic exceeds rated capacity. A system can implement a target congestion level to maintain uninterrupted traffic conditions, that is, to avoid overloading and underloading of resources.

A problem with regard to overload is the appearance of delayed transmission responses. An increase in response time often leads to application-level timing limits, in which an application requiring the data waits longer than the application is programmed to allow, resulting in a timing limit condition. The applications will then unnecessarily send messages back into the timing limits, causing more congestion. If this condition continues, the system may reach a condition where it cannot serve users. One solution (used in HDR) for this condition is congestion control. Another solution (used in cdma2000) is proper planning.

The level of congestion in a system can be determined by monitoring active and pending user data rates and the received signal strength required to achieve a desired quality of service. In a wireless CDMA system, the reverse link capability is limited by interference. A measure of cell congestion is the total amount of noise above the thermal noise level at a base station (hereinafter referred to as the "rise over thermal" (ROT)). The ROT corresponds to the reverse link load. A loaded system tries to keep the ROT near a predetermined value. If the ROT is too high, the range of the cell (that is, the distance over which the cell's base station can communicate) is reduced and the reverse link is less stable. The range of the cell is reduced due to an increase in the amount of transmission energy required to provide a target energy level. A high ROT also produces small changes in instantaneous load that result in large excursions in remote terminal output power. A low ROT may indicate that the reverse link is not heavily loaded, thus indicating that the available capacity is potentially wasting.

However, the operation of the R-SCH with H-ARQ may require that the power of the initial transmission of an R-SCH frame not be controlled too tightly to meet ROT constraints. Therefore, the delivered signal-to-noise ratio (SNR) during the initial transmission of an R-SCH frame may be below a sufficient level to allow correct decoding of the received data packet. This condition can result in a NAK message being transmitted on the forward link ACK channel.

As a consequence, from the foregoing discussion, it will be apparent that there is a need in the art for an apparatus and method that enables efficient forward link ACK channel operation.

Summary

One aspect of the invention provides an acknowledgment method in a wireless communication system as set forth in claim 1. Another aspect of the invention provides a transmission method for a remote device in a wireless communication system as set forth in claim 5. Other aspects of the invention provide a remote device and a base station device for a wireless communication system operating an acknowledgment channel as set forth in claims 7 and 8. In a further aspect of the invention there is provided a system communication device operating an acknowledgment channel as set forth in claim 11.

The embodiments disclosed herein address the need for an apparatus and method that enables efficient operation of the forward link ACK channel in conjunction with a packet data channel in a wireless communication system.

In one embodiment, an acknowledgment procedure and wireless communication apparatus includes receiving a reverse supplemental channel (R-SCH) frame at a base station. The base station then transmits an acknowledgment signal (ACK) if the quality of the received R-SCH frame is indicated as good. A negative acknowledgment signal (NAK) is transmitted only if the received data frame is indicated as being bad but has enough energy so that, if combined with energy from retransmission of the data frame, it would be sufficient to allow correct decoding of the data frame.

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In another embodiment, an acknowledgment method and wireless communication apparatus includes transmitting a reverse supplemental channel (R-SCH) frame from a remote terminal to a base station. The base station then transmits a negative acknowledgment signal (NAK) to the remote terminal if the quality of the received R-SCH frame is indicated as being poor. The remote terminal also recognizes that an absence of a received acknowledgment indicates an acknowledgment signal (ACK), such that the quality of the received R-SCH frame is good, indicating a condition in which power of the R-SCH frame is sufficient to allow correct decoding of the frame. The base station, in this regard, is the best base station that provides the least path loss to the remote terminal.

In another embodiment, an acknowledgment channel for a wireless communication system includes a block encoder, a mapper, and a mixer. The block encoder receives an ACK / NAK message that has at least one bit, and operates to encode the ACK / NAK message with a generator array to produce a code word. The mapper maps the codeword into a binary signal. The mixer mixes the binary signal with an orthogonal spreading code such as a Walsh code to produce an encoded ACK / NAK signal.

Other features and advantages of the present invention will be apparent from the following descriptions of the exemplary embodiment, which illustrate, by way of example, the principles of the invention.

Brief description of the drawings

Figure 1 is a diagram of an exemplary wireless communication system that supports a number of users and can implement various aspects of the invention;

Figure 2 is a simplified block diagram of one embodiment of a base station and remote terminal of the communication system of Figure 1;

Figure 3 illustrates an exemplary forward link ACK channel in accordance with the acknowledgment scheme discussed herein;

Figure 4 illustrates an exemplary forward link ACK channel operating on an assumption that the remote terminal recognizes which base station is the best base station;

Figures 5A through 5C illustrate a flow chart of an exemplary procedure for implementing an acknowledgment scheme operating on a direct link ACK channel ; and Figure 6 is a block diagram of an exemplary F-CPANCH.

Detailed description

The detailed description set forth below in connection with the accompanying drawings is intended to be a description of exemplary embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced. The term "exemplary (s)" used throughout this description means "serving as an example, case, or illustration", and should not necessarily be construed as preferred or advantageous over other embodiments. The detailed description includes specific details in order to provide a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention can be practiced without these specific details. In some cases, well-known structures and devices are shown in block diagram form to avoid confusing the concepts of the present invention.

In recognition of the need for an apparatus and method that enables efficient operation of the forward link ACK channel discussed above, this description describes exemplary embodiments for efficiently allocating and utilizing reverse link resources. In particular, a reliable acknowledgment scheme and an efficient retransmission scheme, which can improve reverse link utilization and allow data frames to be transmitted at lower transmission power, are described in detail below.

Although various aspects of the present invention will be described in the context of a CDMA communication system, those skilled in the art will appreciate that the techniques for providing efficient forward link ACK channel operation described herein are equally suitable for its use in various other communication environments including communication systems based on TDMA, FDMA, SDMA, PDMA, and other multiple access techniques known in the art, and communication systems based on AMPS, GSM, HDR, and various CDMA standards, and other communication standards known in the art. As a consequence, any reference to a CDMA communication system is intended only to illustrate the inventive aspects of the present invention, with the understanding that such inventive aspects have a wide range of applications.

FIG. 1 is a diagram of an exemplary wireless communication system 100 that supports a number of users and that may implement various aspects of the invention. Communication system 100 provides communication for a series of cells, each cell being served by a corresponding base station 104

ES 2 324 296 T3 (BS). Various remote terminals 106 are scattered throughout the system 100. Individual remote terminals or base stations will be identified by a letter suffix such as 104a or 106c. It will be understood that references to 104 or 106 without a letter suffix refer to base stations and remote terminals in the general sense.

Each remote terminal 106 can communicate with one or more base stations 104 on the forward and reverse links at any particular time, depending on whether the remote terminal is active or not and whether it is in soft handoff or not. Forward link refers to transmission from a base station 104 to a remote terminal 106, and reverse link refers to transmission from a remote terminal 106 to a base station 104. As shown in FIG. 1, base station 104a communicates with remote terminals 106a, 106b, 106c, and 106d, and base station 104b communicates with remote terminals 106d, 106e, and 106f. Remote terminal 106d is in a soft handoff condition and simultaneously communicates with both base stations 104a and 104b.

In wireless communication system 100, a base station controller (BSC) 102 communicates with base stations 104 and may further communicate with a public switched telephone network (PSTN). Communication with the PSTN is typically achieved through a mobile switching center (MSC), which is not shown in Figure 1 for simplicity. The BSC can also communicate with a packet network, which is typically achieved through a packet data serving node (PDSN) that is also not shown in Figure 1. The BSC 102 provides coordination and control for stations 104 base. The BSC 102 further controls the routing of telephone calls between the remote terminals 106, and between the remote terminals 106 and users communicating with the PSTN (for example, conventional telephones) and with the packet network, through the stations 104 base.

Figure 2 is a simplified block diagram of one embodiment of a base station 104 and a remote terminal 106, which can implement various aspects of the invention. For a particular communication, voice data, packet data, and / or messages can be exchanged between base station 104 and remote terminal 106. Various types of messages can be transmitted such as messages used to establish a communication session between the base station and the remote terminal and messages used to control a data transmission (e.g., power control, data rate information, acknowledgment receipt, etc.). Some of these message types are described below. In particular, the implementation of the reverse link data acknowledgment using the forward link ACK channel is described in detail.

For the reverse link, at the remote terminal 106, messages (eg, from a controller 230) and voice and / or packet data (eg, from a data source 210) are provided to a transmit data processor 212 (TX), which formats and encodes data and messages with one or more encoding schemes to generate encoded data. Each encoding scheme can include any combination of cyclic redundancy check (CRC), convolutional, Turbo, block, and other encoding, or no encoding at all. Typically, voice data, packet data, and messages are encoded using different schemes, and different types of message can also be encoded differently.

The encoded data is then provided to a modulator 214 (MOD) and further processed (eg, covered, spread with short PN sequences, and encrypted with a long PN sequence assigned to the user terminal). The modulated data is then provided to a transmitter unit 216 (TMTR) and conditioned (e.g., converted to one or more analog signals, amplified, filtered, and quadrature modulated) to generate a reverse link signal. . The reverse link signal is routed through a duplexer 218 (D) and transmitted through an antenna 220 to base station 104.

At base station 104, the reverse link signal is received by an antenna 250, routed through a duplexer 252, and provided to a receiver unit 254 (RCVR). Receiver unit 254 conditions (eg, filters, amplifies, downconverts, and digitizes) the received signal and provides samples. A demodulator 256 (DEMOD) receives and processes (eg, de-spreads, discovers, and pilot demodulates) the samples to provide recovered symbols. The demodulator 256 may implement a comb receiver that processes multiple instances of the received signal and generates combined symbols. A receive (RX) data processor 258 then decodes the symbols to retrieve the data and messages transmitted on the reverse link. The recovered voice / packet data is provided to a data sink 260 and the recovered messages may be provided to a controller 270. Processing by demodulator 256 and RX data processor 258 is complementary to that performed at remote terminal 106. The RX demodulator 256 and data processor 258 may further be operated to process multiple transmissions received over multiple channels, eg, a reverse fundamental channel (R-FCH) and a reverse supplemental channel (R-SCH). Also, transmissions can be received simultaneously from multiple remote terminals, each of which can transmit on a reverse fundamental channel, a reverse supplemental channel, or both.

Over the forward channel, at base station 104, voice and / or packet data (eg, from a data source 262) and messages (eg, from data source 262) are processed (eg, formatted and encoded). controller 270) by a transmit (TX) data processor 264, are further processed (for example, covered and spread) by a modulator 266 (MOD), and conditioned (for example, converted to analog signals, amplify, filter, and are quadrature modulated) by a transmitter unit 268 (TMTR) to generate a forward link signal. The forward link signal is routed through duplexer 252 and transmitted through antenna 250 to remote terminal 106.

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At remote terminal 106, the forward link signal is received by antenna 220, routed through duplexer 218, and provided to a receiver unit 222. Receiver unit 222 conditions (eg, downconverts, filters, amplifies, quadrature demodulates, and digitizes) the received signal and provides samples. The samples are processed (eg, de-spread, discovered, and pilot demodulated) by a demodulator 224 to provide symbols, and the symbols are further processed (eg, decoded and checked) by a data processor 226 reception, to retrieve the data and messages transmitted over the direct link. The retrieved data is provided to a data sink 228, and the retrieved messages may be provided to the controller 230.

The reverse link has some characteristics that are very different from the direct link. In particular, the data transmission characteristics, soft handoff behaviors, and fading phenomena are normally very different between forward and reverse links. For example, the base station usually does not know a priori which remote terminals have packet data to transmit, or how much data it has to transmit. Thus, the base station can allocate resources to remote terminals whenever requested and as available. Due to the uncertainty in user demands, utilization on the reverse link can fluctuate widely.

Apparatus and procedures are provided for efficiently allocating and utilizing reverse link resources in accordance with exemplary embodiments of the invention. Reverse link resources can be allocated via a supplementary channel (eg, R-SCH) that is used for packet data transmission. In particular, a reliable acknowledgment scheme and an efficient retransmission scheme are provided.

A reliable acknowledgment scheme and an efficient retransmission scheme must consider several factors that control communication between base stations and a remote terminal. One of the factors to consider includes the fact that base stations with path losses that are approximately a few dB greater than those of a base station with the least path loss to the remote terminal (for example, the base station that is the most close to the remote terminal), but are in the active set of the remote terminal, they have relatively few opportunities to correctly receive reverse supplementary channel (R-SCH) frames.

In order for soft handoff to work and the overall remote terminal transmit power to be reduced, the remote terminal needs to receive indications for these lost or bad R-SCH frames. Since the remote terminal is going to receive significantly more negative acknowledgments than positive acknowledgments, an exemplary acknowledgment scheme is configured (see Figure 3), so that the base station (BS) sends to a terminal ( Remote RT) an acknowledgment (ACK) for a good frame and a negative acknowledgment (NAK) for a bad frame only if the received bad R-SCH frame has enough power so that, if combined with energy from the retransmission of the R-SCH frame, it would be sufficient to allow a correct decoding of the frame by the base station. Bad frames that have insufficient energy (even when combined with retransmission energy) to allow correct decoding of the frame by the base station will not receive a NAK signal. Thus, when the remote terminal does not receive an ACK or NAK signal, the remote terminal will assume that the bad frame received at the base station did not have enough power to allow a correct decoding of the frame. In this case, the remote terminal will need to retransmit the frame with a sufficient default transmission level to allow correct decoding. In one embodiment, this default transmission level may be predetermined to enable correct decoding by the base station. In another embodiment, this default transmission level can be determined dynamically according to a transmission condition of the wireless CDMA system.

Figure 3 illustrates an exemplary forward link ACK channel in accordance with the acknowledgment scheme discussed above. In the illustrated embodiment, the remote terminal sends an R-SCH frame to the base station (s). The base station receives the R-SCH frame and sends an ACK signal if the received R-SCH frame is recognized as being a "good" frame.

In one embodiment, recognition of the quality of the received R-SCH frame (ie, as being "good" or "bad") can be performed by observing the reverse link pilot signal, or, equivalently, based on the power control bits sent from the remote terminal. Therefore, if the reverse link pilot signal includes enough power to allow correct decoding of the frame by the base station, the frame is considered to be "good". Otherwise, if the reverse link pilot signal includes insufficient energy to allow correct decoding of the frame by the base station, the frame is considered to be "bad".

The base station's exemplary forward link ACK channel sends a NAK signal with a delta ratio (T / P) traffic to pilot if the received R-SCH frame is recognized as being a "bad" frame but has enough power to combine with the retransmission. This condition occurs when the received bad R-SCH frame has sufficient energy, so that, if combined with energy from retransmission of the R-SCH frame, it would be sufficient to allow correct decoding of the frame by the base station.

The ratio (T / P) traffic to pilot can be computed by measuring the ratio between the energy level of the reverse traffic channel (eg R-SCH) and the reverse pilot channel. Thus, in this embodiment, this ratio is used for R-SCH power control and compared to the total energy level sufficient to allow correct decoding of the R-SCH frame by the base station. The difference between the initial transmission T / P value and the total energy level sufficient to allow correct decoding of the R-SCH frame provides a parameter referred to as a T / P delta. In general, the total energy level is the energy level

ES 2 324 296 T3 required to maintain a certain quality of service (QoS), which depends on speed, channel condition, and other QoS related parameters. As a consequence, the T / P delta provides a differential energy value that must be delivered by the remote terminal during retransmission to compensate for the lack of power during the initial transmission, and allow the base station to correctly decode the R-SCH frame. on the reverse link. The calculated T / P delta can be transmitted to the remote terminal over the direct ACK channel along with acknowledgment signals. In case there are two or more base stations in the remote terminal's active set, and both base stations send NAK signals with different T / P deltas in response to bad R-SCH frames, the remote terminal should choose that one. with the lowest T / P delta, so that at least one base station is allowed to correctly decode the packet.

Also, the base station will not send a NAK signal (ie NULL data) when the received bad R-SCH frame, combined with retransmission power, has insufficient power to allow correct decoding of the frame by the base station. The remote terminal must recognize this "NULL" condition as a signal from the base station to the remote terminal to retransmit the R-SCH frame with a sufficient default transmission level to allow correct decoding.

The acknowledgment scheme illustrated in Figure 3 can be further optimized if the remote terminal can detect or determine which base station has the least path loss to the remote terminal (ie, the best base station). In one embodiment, a pattern of power control commands from the base station to the remote terminal is used to determine which base station is the best base station. For example, the base station can measure the power gap of the actually received frame relative to the power control target (as is done in closed loop power control) to determine which base station is the best base station. By averaging the lack of power over many frames, the base station can determine if it is the best base station or not. This information can be transmitted to the remote terminal. As another example, the base station can measure the power control increase / decrease bit pattern to determine which base station is the best.

In an alternative embodiment, the best base station can be easily determined if the remote terminal is operating in a data / voice (DV) mode of a 1xEv-DV system. In this mode, both the base station and the remote terminal need to know which base station is the best base station. Thus, the remote terminal uses the Reverse Channel Quality Indicator (R-CQICH) channel to indicate to the base station the channel quality measurements of the best base station.

However, using any of the embodiments described above, there may still be a period of time when the two sides (the base station and the remote terminal) are not necessarily in sync about which base station is the best base station. As a consequence, in one embodiment, during the period when there is a conflict between the two sides, the base station that is designated and deallocated as being the best base station is configured to send both ACK signals (when the frame is good) and NAK (when the frame is bad), so the remote terminal will not be baffled.

Figure 4 illustrates an exemplary forward link ACK channel operating on an assumption that the remote terminal recognizes which base station is the best base station. Thus, in the illustrated embodiment, the remote terminal sends R-SCH frames to the best base station and the secondary base station (s). Since the best base station will be receiving many more "good" frames than "bad" frames, the acknowledgment scheme from the best base station is biased towards not sending ACK signals for "good" frames, but sending ACK signals. nAk for "bad" frames. The secondary base station will be biased in reverse, as it will be receiving many more "bad" frames than "good" frames. Thus, the acknowledgment scheme from the secondary base station is biased towards sending ACK signals for "good" frames, but not sending NAK signals for "bad" frames.

As a consequence, in response to receiving the R-SCH frame from the remote terminal, the exemplary forward link ACK channel of the best base station does not send an ACK signal (i.e., NULL data) if the R-SCH received is recognized as being a "good" frame. The remote terminal must recognize this "NULL" condition as a signal from the best base station that the transmitted R-SCH frame was received with sufficient energy to allow correct decoding and that there is no need for retransmission of the frame. If the received R-SCH frame is recognized as being a "bad" frame but has enough power to combine with the retransmission, the best base station sends a NAK signal with a delta of T / P. This condition occurs when the received bad R-SCH frame has enough energy, so that, if combined with energy from retransmission of the R-SCH frame, it would be sufficient to allow correct decoding of the frame by the best base station. The best base station sends a NAK signal without a T / P delta if the received bad R-SCH frame, combined with retransmission power, has insufficient power to allow correct decoding of the frame by the best base station. Thus, the remote terminal retransmits the R-SCH frame with a sufficient default transmission level to allow correct decoding.

However, the exemplary forward link ACK channel of the secondary base station, in response to receipt of the R-SCH frame from the remote terminal, sends an ACK signal if the received R-SCH frame is recognized as which is a "good" plot. If the received R-SCH frame is recognized as being a "bad" frame but has enough power to combine with the retransmission, the secondary base station sends a NAK signal with a delta of T / P. This condition occurs when the received bad R-SCH frame has enough energy so that, if combined with energy from retransmission of the R-SCH frame, it would be sufficient to allow a

ES 2 324 296 T3 correct decoding of the frame by the secondary base station. The secondary base station does not send a NAK signal (ie NULL data) when the received bad R-SCH frame, combined with retransmission power, has insufficient power to allow correct decoding of the frame by the base station. The remote terminal must recognize this "NULL" condition as a signal from the secondary base station to the remote terminal to retransmit the R-SCH frame with a sufficient default transmission level to allow correct decoding.

An exemplary method for implementing an acknowledgment scheme described above, operating on a forward link ACK channel, is illustrated in a flow chart shown in Figures 5A through Figure 5C. In frame 500, a determination is made as to whether the remote terminal under a condition where the terminal has knowledge about which base station has the least loss of path to the remote terminal (ie, the best base station). As described above, this can be determined by measuring the energy gap of the actually received frame relative to the power control target. By averaging the lack of power over a sufficient number of frames, the base station can determine whether it is the best base station or not. This information can be transmitted to the remote terminal. If the remote terminal is operating in a data / voice (DV) mode of a 1 xEv-DV system, both the base station and the remote terminal must know which base station is the best base station. Thus, in DV mode, there is no need to determine which base station is the best base station.

If the remote terminal cannot determine which base station is the best base station in box 500, a result of "No", then a base station that received the R-SCH frame sends an ACK signal (in box 504) if the received R-SCH frame is recognized as being a "good" frame. Recognition of the quality of the received R-SCH frame (ie, as being "good" or "bad") can be performed according to the process described above.

In table 506, a determination is made as to whether the received bad R-SCH frame has enough energy, so that, if combined with energy from retransmission of the R-SCH frame, it would be sufficient to allow a correct decoding of the frame by the base station. If this is the case, the base station's exemplary forward link ACK channel sends a NAK signal with a delta of T / P, in frame 508. Otherwise, the base station will not send a NAK signal (ie NULL data) for the bad R-SCH frame, in box 510. The remote terminal must recognize this "NULL" condition as a signal from the station. base to the remote terminal to retransmit the R-SCH frame with a sufficient default transmission level to allow correct decoding.

If the remote terminal can determine which base station is the best base station in box 500, a result of "Yes" in box 500, then the source of an ACK / NAK signal is determined, at 502, as being or either the "best" base station or a "secondary" base station. If the source is the "best" base station, then the exemplary forward link ACK channel of the best base station does not send an ACK signal (ie, NULL data) in response to a "good" frame, in the frame 512. The remote terminal will recognize this "NULL" condition as a signal from the best base station that the transmitted R-SCH frame was received with enough power to allow correct decoding and that there is no need for retransmission of the frame.

In table 514, a determination is made whether the received bad R-SCH frame has enough energy, so that, if combined with energy from the retransmission of the R-SCH frame, successful decoding can be performed. of the frame by the base station. If this is the case, the exemplary forward link ACK channel of the best base station sends a NAK signal with a delta of T / P, in frame 516. Otherwise, the best base station sends a NAK signal without a T / P delta, at 518. Thus, the remote terminal retransmits the RSCH frame with a default transmission level sufficient to allow correct decoding.

If the source of an ACK / NAK signal (at table 502) is determined to be the secondary base station, then the exemplary forward link ACK channel of the secondary base station sends an ACK signal, at table 520, in response to a "good" plot. In table 522, a determination is again made as to whether the received bad R-SCH frame has enough energy, so that, if combined with energy from the retransmission of the R-SCH frame, it would be sufficient to allow correct decoding of the frame by the base station. If this is the case, the exemplary forward link ACK channel of the secondary base station sends a NAK signal with a delta of T / P, at frame 524. Otherwise, if the received bad R-SCH frame, combined with retransmission power, has insufficient power to allow correct decoding of the frame by the base station, then the secondary base station does not send a NAK signal (i.e. , NULL data), in table 526. The remote terminal must recognize this "NULL" condition as a signal from the secondary base station to the remote terminal to retransmit the R-SCH frame with a sufficient default transmission level to allow correct decoding.

As described above, negative acknowledgments (ACKs) and negative acknowledgments (NAKs) are transmitted by the base station for data transmission over the R-SCH. Furthermore, the ACK / NAK can be transmitted using a direct common packet acknowledgment channel (F-CPANCH). Figure 6 is a block diagram of an exemplary F-CPANCH.

In one embodiment, ACK and NAK are transmitted as n-bit ACK / NAK messages, each message being associated with a corresponding data frame transmitted on the reverse link. Thus, each ACK / NAK message can include 1,2, 3, or 4 bits (or possibly more bits), with the number of bits in the message depending on the number of

ES 2 324 296 T3 reverse link channels in service configuration. The n-bit ACK / NAK message can be block coded for increased reliability or transmitted without coding. To improve reliability, the ACK / NAK message for a particular data frame can be retransmitted in a subsequent frame (eg, 20 milliseconds later) to provide time diversity for the message. The time diversity provides more reliability, or it may allow the reduction in power used to send the ACK / NAK message while maintaining the same reliability. The ACK / NAK message may use error correction encoding as is well known in the art. For retransmission, the ACK / NAK message can repeat the exact same codeword or it can use increased redundancy. The encoding approach is described in more detail below.

In the illustrated embodiment of Figure 6, the F-CPANCH input for MAC ID = j, and k bits every 20 milliseconds, where k = 1, 2, 3, or 4, are provided to a block encoder 602 (6 , k). In general, the (n, k) block codes are specified in terms of their generating matrices. The encoder output code word, y = [i and_1K Y_n-1], is equal to y = uG, where u = [u_oror₁ K u_k-1] is the input sequence, u₀ is the first input bit, and₀is the first bit of output, and G is the generator matrix kx n.

The generating matrix for the F-CPANCH (6, 1) code is

G = [1 1 1 1 1 1].

The generating matrix for the F-CPANCH (6, 2) code is

<img file="ES2324296T3_D0001.tif" />

The generating matrix for the F-CPANCH (6, 3) code is

<img file="ES2324296T3_D0002.tif" />

The generating matrix for the F-CPANCH (6, 4) code is

1110 0 0

1110 0

0 1110

0 0 1 1 1

The output of encoder 602 is then mapped to signal points in a mapper 604, so that a 0 is a + 1 and a 1 is a -1. The resulting signal is mixed by a 606 mixer with a Walsh code, such as a 128-ary Walsh code (W¹²⁸). The use of a Walsh code provides channelization and resistance to phase errors at the receiver. It should be noted that, for other CDMA systems, other orthogonal or quasi-orthogonal functions may be substituted for Walsh code functions (eg, OVSF for WCDMA).

To improve reliability, the ACK / NAK message for a particular data frame can be retransmitted in a subsequent frame (eg, 20 milliseconds later) to provide time diversity for the message. Retransmission is implemented by inserting a block 612, which provides a sequence delay of one frame of 20 milliseconds, and a mapper 614 (substantially similar to mapper 604) and a mixer 616 (substantially similar to mixer 606). However, mixer 616 is mixed with a Walsh code starting at 65 and ending at 128.

The outputs of mixers 606 and 616 are combined by an adder element 618. The output of adder element 618 is then demultiplexed by a demultiplexer 620 to produce an ACK / NAK signal having 384 symbols every 20 milliseconds (19.2 ksps) appropriate for forward link transmission.

ES 2 324 296 T3

Table 1 provides the properties of the F-CPANCH code.

TABLE 1

F-CPANCH code properties

<td rowspan="2">Code (n, k)</td><td rowspan="2">Best d_m¡n possible</td><td rowspan="2">d_m¡n got</td><td colspan="2">Code words</td>

<td>Weight</td><td>Number</td>

<td> (6, 1)</td><td> 6</td><td> 6</td><td> 0 6</td><td> 1 1</td>

<td> (6, 2)</td><td> 4</td><td> 4</td><td> 0 4</td><td> 1 3</td>

<td> (6. 3)</td><td> 3</td><td> 3</td><td> 0 3 4</td><td> 1 4 3</td>

<td> (6, 4)</td><td> 2</td><td> 2</td><td> 0 2 3 4 6</td><td> 1 3 8 3 1</td>

An efficient and reliable acknowledgment scheme can improve reverse link utilization, and can also allow data frames to be transmitted at lower transmission power. For example, without retransmission, a data frame needs to be transmitted at a higher power level (Pi) required to achieve a one percent frame error rate (1% FER). If retransmission is used and is reliable, a data frame can be transmitted at a level (P₂) of lower power required to achieve FER of 10%. The 10% erasure of frames can be retransmitted to achieve an overall 1% FER for transmission (ie 10% x 10% = 1%). In addition, retransmission provides time diversity, which can improve performance. The retransmitted frame can also be combined with the initial transmission of the frame at the base station, and the combined power from the two transmissions can also improve performance. Recombination can allow an erased frame to be retransmitted at a lower power level.

Those skilled in the art will understand that process steps can be interchanged without departing from the scope of the invention. Those skilled in the art will also understand that information and signals can be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and code elements that may be referred to throughout the above description may be represented by voltages, intensities, electromagnetic waves, magnetic fields or particles, fields or particles. optical, or any combination thereof.

Those of skill will further appreciate that the various illustrative logic blocks, modules, circuits, and steps of a technique described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, and steps have been generally described above in terms of their functionality. Whether such functionality is implemented as hardware or software depends on the particular application and design constraints imposed on the overall system. Those skilled in the art may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be construed as leading to departure from the scope of the present invention.

The various illustrative logic blocks and modules described in connection with the embodiments disclosed herein may be implemented or realized with a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field programmable gate arrangement (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor can be a microprocessor, but alternatively, the processor

ES 2 324 296 T3 can be any conventional processor, controller, microcontroller, or state machine. A processor can also be implemented as a combination of computing devices, for example, a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The steps of a method or technique described in connection with the embodiments disclosed herein can be performed directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module can reside in a RAM memory, a flash memory, a ROM memory, an EPROM memory, an EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium. known in the art. An exemplary storage medium is coupled to the processor so that the processor can read information from; and write information to the storage medium. Alternatively, the storage medium can be integrated with the processor. The processor and storage medium can reside in an ASIC. The ASIC can reside in a subscriber station. Alternatively, the processor and storage medium can reside as discrete components in a subscriber station.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the scope of the invention.