Method for effectively transmitting control signal in wireless communication system

Technical field [0001] The present invention relates to wireless communications, and more particularly to a method of efficiently transmitting a control signal in a wireless communication system.

2. Background Art [0002] Next generation mobile communication systems are standardized for the purpose of efficiently connecting to wired and wireless communication networks and integrated services, although previous generation communication systems provide simple wireless communication services. As high-speed and high-bandwidth communication systems are needed, capable of processing and transmitting various types of information, such as video and radio data as well as audio data, it is necessary to develop a technique capable of transmitting a large amount of data that corresponds to the wired capacity communications networks, via a wireless communications network. Accordingly, an appropriate error detection scheme becomes an essential element, which can minimize information loss and increase system transmission efficiency to improve system characteristics.

[0003] Automatic repeat request (ARQ) transmits a positive acknowledgment signal to the transmitter when the receiver receives data correctly and transmits a negative acknowledgment signal to the transmitter, when the receiver is not receiving data correctly. In a hybrid automatic repetition request hybrid automatic repeat request-HARQ), the ACK / NACK signal transmitted by the data receiver is generally represented by a small number of bits.

[0004] To improve the efficiency of data transfer in data processing, HARQ has been proposed corresponding to the ARQ combination and physical layer channel coding. HARQ not only re-transmits data that is not received by the transmitter, but also stores data that is not received by the receiver. When the receiver receives the transmitted data again, the received data is added to the previously stored data to improve efficiency gain.

[0005] As the receiver uses additional feedback radio resources to feed back ACK / NACK signal to the transmitter in HARQ, efficient use of limited radio feedback resources is very important.

[0006] Hereinafter, the downlink represents the communication link from the base station to the user equipment UE and the uplink represents the communication link from the UE to the base station. A downlink is also referred to as a forward link, and an uplink is also referred to as an inverse link. The transmitter may be part of the base station and the receiver may be part of the UE on the downlink. The transmitter may be part of the UE and the receiver may be part of a base station on the uplink.

[0007] A method is needed to distinguish radio resources used for downlink transmission from radio resources in the areas of frequency, time and coding used for uplink transmission. This method is known as duplex. Uplink and downlink can be distinguished from each other in the areas of frequency, time and coding as happens in a multiple access system to identify different users. Duplex is classified in frequency domain duplexing (FDD), which distinguishes uplink and downlink in frequency domain and time domain duplex (TDD), which distinguishes uplink and downlink

EP 2 104 263 B1 according to time.

[0008] The uplink is distinguished from the uplink in the frequency domain in FDD, so data transmission between the base station and UE may be performed continuously in the time domain on each link. While FDD is suitable for a symmetrical service, such as voice communication, because it assigns symmetrically frequencies having the same level to an uplink and a downlink, TDD is suitable for an asymmetrical service, such as internet services, and hence has been active recently research on TDD.

[0009] TDD is suitable for asymmetrical service because it can allocate periods having different lengths to the uplink and to the downlink. In addition, uplink data and downlink data are transmitted and received in TDD in the same frequency band, hence the uplink and downlink channel states match each other. Accordingly, TDD is suitable for matrix antenna technology because the channel status can be immediately evaluated when a signal is received. TDD uses the entire frequency band as an uplink or downlink, distinguishing between an uplink and a downlink in the time domain, uses a frequency band as an uplink for a predetermined time, and uses the frequency band as a downlink for a predetermined time, hence the sending and receiving data between the base station and UE cannot be performed simultaneously.

[0010] When the base station transmits downlink data in the mobile communication system, the UE transmits ACK / NACK signals with respect to the downlink data to the uplink at a predetermined time lapse. If the time used for downlink transmission is longer than the time used for uplink transmission, the number of ACK / NACK signals to be transmitted to the uplink may be limited. That is, a single UE should transmit ACK / NACK signals by using a number of ACK / NACK resources less than N for the received N downlink packets. Accordingly, there is a need for an ACK / NACK signal transmission method capable of minimizing packet loss and maximizing recovery capacity, even when the amount of ACK / NACK signals returned is less than the number of downlink packets.

[0011] In the document "Implications of Solutions for Subframe Bundling; Alcatel-Lucent" 3GPP DRAFT; R1080914, 3rd Generation Partnership Project (3GPP), RAN WG1, Sorrento, Italy, 5.2.2008, the issue of LTE uplink coverage is disclosed. Based on the discussion and characterization study, two solutions are being considered for improving the uplink coverage for LTE. The two proposed solutions use subframe bundling to improve uplink coverage. The document discusses the possible implications of subframe bundling solutions for the standard specification.

[0012] In the document "Combination of ACK / NACKs for TDD; Ericsson" 3GPP DRAFT; R1-080870, 3rd Generation Partnership Project (3GPP), RAN WG1, Sorrento, Italy, 5.2.2008 reveals to TDD that the number of ACK / NACK that could be broadcast in the uplink subframe of a certain EU depends on asymmetry as that there is no one-to-one correspondence between the downlink and uplink subframes as in FDD. In addition, the number of ACK / NACK required in any uplink subframe depends on the use of MIMO mode in DL transmissions. To improve coverage, throughput and simplify construction, it is proposed to consider some forms of multiple ACK / NACK connection. This is also referred to as ACK / NACK compression or bundling.

[0013] Document "UL ACK / NACK for TDD; Motorola" 3GPP DRAFT; R1-080738, 3rd Generation Partnership Project (3GPP), RAN WG1, Sorrento, Italy, 5.2.2008 also applies to bundling a number of downlink subframes intended for a given EU, which compresses the ACK / NACK bits, after

One for each subframe in a bundle, in one bit by AND operation. The ACK / NACK resource indication is associated with the lowest CCE index used to create the downlink scheduling assignment.

SUMMARY OF THE INVENTION [0014] The invention provides a method of performing a HARQ by a user device according to claim 1. 1. [0015] The invention also provides an apparatus for transmitting an ACK / NACK signal using HARQ, according to claim 1. 9.

BRIEF DESCRIPTION OF THE DRAWINGS [0016]

Fig. 1 shows a wireless communication system.

Fig. 2 is a block diagram of a user equipment (UE).

Fig. 3 shows an example of the construction of a radio frame.

Fig. 4 shows another example of the construction of a radio frame, i.e. a TDD radio frame.

Fig. 5 shows the structure of the downlink subframe.

Fig. 6 shows the structure of the uplink subframe.

Fig. 7 shows ACK / NACK signal transmission in PUCCH.

Fig. 8 shows a method of performing HARQ by bundling ACK / NACK into bundles according to an embodiment of the invention.

Fig. 9 is a flowchart showing a method of performing HARQ in a TDD system according to an embodiment of the invention.

Fig. 10 shows a method of mapping a representative ACK / NACK signal to a radio resource according to an embodiment of the invention.

Fig. 11 shows an ACK / NACK signal transmission method in a TDD system, according to an embodiment of the invention.

Fig. 12 is a flowchart showing an ACK / NACK signal transmission method in a TDD system according to another embodiment of the invention.

DESCRIPTION OF EMBODIMENTS [0017] The invention will now be described more fully with reference to the accompanying drawings, in which embodiments of the invention are shown. However, the invention may be implemented in a variety of forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are presented so that this disclosure is thorough and complete and to fully convey the concept of the invention to those skilled in the art. Drawings emphasize the thickness of layers and regions for clarity. Similar reference numerals in the drawings indicate similar elements.

[0018] Fig. 1 shows a wireless communication system. The wireless communication system can be widely spread to provide various communication services, such as voice, packet data, etc.

[0019] With reference to Fig. 1, the wireless communication system includes a base station BS 10 and at least one user equipment UE 20. BS 10 is generally a stationary station that communicates with UE 20 and may be defined in other terminology, such as B-node, base transceiver (BTS) system, access point, etc. One or more cells are within BS 10 coverage. UE 20 may be fixed or mobile and may be referred to in different terminology

Such as a mobile station (MS), end user device (UT), subscriber station (SS), wireless device, etc.

[0020] The downlink represents the communication link from BS 10 to UE 20 and the uplink represents the communication link from UE 20 to BS 10. On the downlink the transmitter can be part of BS 10 and the receiver can be part of UE 20. W uplink the transmitter may be part of UE 20 and the receiver may be part of BS 10. [0021] For downlink and uplink transmission, various multiple access schemes may be used. For example, downlink multi-access orthogonal frequency division (OFDMA) is used, and uplink multi-access multi-access on a single carrier (SC-FDMA) is used [0022] There is no limit to the multi-access scheme used in a wireless communication system . The multi-access scheme may be based on multi-access coding schemes (CDMA), time-domain multiple access (TDMA), frequency-domain multi-access (FDMA), SCFDMA, OFDMA or other well-known modulation schemes. In these modulation schemes, signals received from many users are demodulated to increase the throughput of the communication system.

[0023] The layers of the radio interface protocol can be classified into the first layer (L1), the second layer (L2) and the third layer (L3) based on the open system joining model (OSI) which is well known in communication systems. Compared to the OSI model, the physical layer (PHY) corresponds to the first layer L1, the medium access control layer (MAC) and the radio link control layer (RLC) correspond to the second layer L2, and the radio resource control layer (RRC) corresponds to the third layer L3. The physical layer provides information transfer services using the physical channel, the MAC layer is connected to the physical layer via a transport channel, and the RRC radio layer is used to control radio resources between the UE and the network.

[0024] Examples of the downlink transport channel include a broadcast channel (BCH) for transmitting system information and a shared downlink channel (DL-SCH) for transmitting user traffic messages or control messages. Downlink user multicast traffic services or broadcast services or control messages may be broadcast on DL-SCH or an additional downlink multicast channel (DL-MCH). The downlink transport channel is mapped to the downlink physical channel.

[0025] Examples of a physical downlink channel include a physical downlink shared channel (PDSCH) mapped to DL-SCH and a physical downlink control channel (PDCCH) for broadcasting control signal.

[0026] Examples of the uplink transport channel include the random access channel (RACH) for initial control messages and the shared uplink channel (UL-SCH) for transmitting user traffic messages or control messages. The uplink transport channel is mapped to the uplink physical channel. Examples of the physical uplink channel include the physical random access channel (PRACH) mapped to RACH, the physical uplink shared channel (PUSCH) mapped to UL.SCH and the physical uplink control channel (PUCCH) for uplink control messages. PUSCH is a physical uplink shared channel and is used when the UE transmits uplink data.

[0027] PDCCH is a physical downlink control channel and transmits control information for PUSCH or PDSCH. An uplink allocation that schedules information for uplink data transmission and a downlink allocation that schedules information for downlink data transmission can be forwarded via PDCCH. Here, scheduling information implies control information, including resource allocation

Radio communication for transmitting downlink data from BS to UE or for receiving uplink data from UE, modulation and coding scheme (MCS), MIMO information, etc.

[0028] Fig. 2 is a block diagram of UE 50. UE 50 includes processor 51, memory 52, RF unit 53, display unit 54 and user interface unit 54. Processor 51 implements the air interface protocol layers and provides the control plane and the user plane. Layer functions are implemented through processor 51. Memory 52 is connected to processor 51 and stores UE control system, applications and general files. The display unit 54 presents UE information and can use well known components such as organic light emitting diodes (OLEDs). The user interface unit 55 may be assembled from a combination of well-known user interfaces, such as a keypad or touch screen. The RF 53 unit is connected to the processor and transmits and / or receives radio signals.

[0029] Fig. 3 shows an example of the construction of a radio frame.

[0030] With reference to Figure 3, the radio frame has ten subframes, and each subframe may contain two slots. The basic data transmission unit corresponds to a subframe, and downlink or uplink scheduling is based on the subframe. A single slot may contain multiple OFDM symbols in the time domain and at least one frequency subcarrier. A single slot may contain six or seven OFDM symbols.

[0031] Fig. 4 shows another example of the construction of a radio frame, i.e. a TDD radio frame.

[0032] With reference to Fig. 4, the radio frame includes two half-frames. Half frames have the same structure. Each half frame especially contains 5 subframes and 3 fields, i.e. downlink pilot time slot (DwPTS), protection period (GP) and uplink pilot time slot (UpPTS). DwPTS is used for initial cell search, synchronization or channel evaluation in the UE. UpPTS is used to evaluate the channel in the BS and synchronize the UE uplink transmission. GP is used to remove interference that occurs on an uplink due to the multi-path downlink delay signal between the uplink and the downlink.

[0033] Table 1 shows an example of a radio resource configuration. The configuration of the radio frame indicates a special rule by which all subframes are allocated (or reserved) for an uplink or a downlink.

[Table 1]

<td rowspan="2">Configuration</td><td rowspan="2">Periodicity of the switching point</td><td colspan="10">Subframe number</td>

<td> 0</td><td> 1</td><td> 2</td><td> 3</td><td> 4</td><td> 5</td><td> 6</td><td> 7</td><td> 8</td><td> 9</td>

<td> 0</td><td>5 ms</td><td>D</td><td>S</td><td>AT</td><td>AT</td><td>AT</td><td>D</td><td>S</td><td>AT</td><td>AT</td><td>AT</td>

<td> 1</td><td>5 ms</td><td>D</td><td>S</td><td>AT</td><td>AT</td><td>D</td><td>D</td><td>S</td><td>AT</td><td>AT</td><td>D</td>

<td> 2</td><td>5 ms</td><td>D</td><td>S</td><td>AT</td><td>D</td><td>D</td><td>D</td><td>S</td><td>AT</td><td>D</td><td>D</td>

<td> 3</td><td>10 ms</td><td>D</td><td>S</td><td>AT</td><td>AT</td><td>AT</td><td>D</td><td>D</td><td>D</td><td>D</td><td>D</td>

<td> 4</td><td>10 ms</td><td>D</td><td>S</td><td>AT</td><td>AT</td><td>D</td><td>D</td><td>D</td><td>D</td><td>D</td><td>D</td>

<td> 5</td><td>10 ms</td><td>D</td><td>S</td><td>AT</td><td>D</td><td>D</td><td>D</td><td>D</td><td>D</td><td>D</td><td>D</td>

<td> 6</td><td>5ms</td><td>D</td><td>S</td><td>AT</td><td>AT</td><td>AT</td><td>D</td><td>S</td><td>AT</td><td>AT</td><td>D</td>

[0034] In Table 1, "D" means a subframe used for downlink transmission, and "U" means a subframe used for uplink transmission. In addition, "S" means a special subframe that is used for a special purpose, such as frame synchronization or downlink transmission. In the following, the subframe used for downlink transmission is simply referred to as

The downlink subframe, and the subframe used for uplink transmission is simply referred to as the uplink subframe. For each configuration, the position and number of downlink subframes and uplink subframes are different from one radio frame.

[0035] The time point at which the downlink is switched to the uplink or vice versa is defined as the switching point. The periodicity of the switching point represents the period in which the same switching pattern is repeated between the uplink and the downlink. The periodicity of the switching point is 5 ms or 10 ms. For example, in configuration 1, switching occurs in the formula D-&gt; S-&gt; U&gt; U-&gt; U from 0 to the 4th subframe. In addition, from the 5th to the 9th subframe, the switching takes place in the formula D&gt; S-&gt; U-&gt; U-&gt; U in the same formula as the previous switching. As one subframe has 1 ms, the switching periodicity is 5 ms. This means that the periodicity of the switching point is less than the length of one radio frame (i.e. 10 ms) and switching is repeated once within the radio frame. For all configurations, subframes 0 and 5 and DwPTS are used for downlink transmission. The 1st subframe in all configurations and the 6th subframe in configurations 0, 1, 2 and 6 are combined with DwPTS, GP and UpPTS. The time interval for each field varies depending on the configuration. The remaining 8 subframes, other than the 1st and 6th subframes, are composed of 2 slots.

[0036] If the periodicity of the switching point is 5 ms, UpPTS and the 2nd and 7th subframes are reserved for uplink transmission. If the switching point periodicity is 10 ms, UpPTS and the 2nd subframe are reserved for uplink transmission, and DwPTS and the 7th and 9th subframes are reserved for downlink transmission.

[0037] The configuration of Table 1 may be system information known by both BS and UE. The BS may inform the UE that the uplink-downlink allocation status of the radio frame is modified by transmitting only the configuration index, whenever the configuration of the radio frame changes. Configuration is a type of downlink control information. Similar to other scheduling information, the configuration can be transmitted on a downlink physical control channel (PDCCH). Alternatively, the configuration may be control information commonly broadcast on the broadcast channel to all UEs existing in the cell. In addition, the configuration can be included in the system information. The number of half-frames contained in the radio frame, the number of sub-frames contained in the half-frame, and the combination of the downlink subframe and the uplink subframe in the TDD system are shown for purposes of examples only.

[0038] In Table 1, if "S" corresponds to downlink subframes, a single radio frame contains 8 downlink subframes and 2 uplink subframes in configuration 2. That is, the ratio of the number of downlink subframes to the number of subframes uplink is 4: 1. In this case, the UE must receive data via 4 downlink subframes and transmit ACK / NACK signals via a single uplink subframe. When the number of downlink subframes is greater than the number of uplink subframes as described above, the uplink radio resources are insufficient for one-to-one mapping between the subframe (s) for the downlink subframe (s) for ACK / NACK signals. Accordingly, N: 1 mapping between subframe (s) for data and subframe (s) for ACK / NACK signals is performed. In this case, a single ACK / NACK signal is used as feedback HARQ for transmitting multiple PDSCHs for a single UE. This is known as ACK / NACK bundling.

[0039] Fig. 5 shows the structure of a downlink subframe.

[0040] Referring to FIG. 5, the 3 previous OFDM symbols of the first downlink subframe slot correspond to the control region to which PDCCH is assigned, and the remaining OFDM symbols correspond to the data region to which PDSCH is assigned. Control channels other than

EP 2 104 263 B1

PDCCHs, such as PCFICH and PHICH, can be assigned to the control region. The UE may decode control information transmitted via PDCCH to read data information transmitted via PDSCH. Here, the number of OFDM symbols contained in the control region in the subframe is not limited to 3 and can be known through PCFICH.

[0041] The control region consists of a set of control channel elements (CCE). The CCE file is the CCE file that builds the control region in a single subframe. CCE corresponds to many groups of resource elements. For example, CCE may correspond to 9 groups of resource elements. The resource element group is used to define the mapping of control channels to resource elements. For example, a single group of resource elements can consist of 4 resource elements.

[0042] Within the control region, multiple multiplied PDCCHs may be transmitted for many UEs. The PDCCH provides control information such as scheduling assignment. PDCCH is transmitted on aggregation of individual CCEs or several continuous CCEs. Hereinafter, the number of CCEs used to transmit PDCCH is referred to as the CCE aggregation level. For example, the CCE aggregation level can be elements of the set {1,2, 4, 8}. The CCE aggregation level corresponds to the number of CCEs used to transmit PDCCH and is the CCE unit for PDCCH lookup. The amplitude of the CCE aggregation level is defined by the number of continuous CCEs. The level of CCE aggregation may vary depending on the EU. For example in fig. 4, the aggregation level of CCE of the 2nd and 4th user devices UE2, UE4 and UE6 is 1, the aggregation level of CCE of the 3rd and 5th user devices UE3 and UE5 is 2, and the aggregation level of 1st and the 7th user device UE1 and UE7 is 4.

[0043] Fig. 6 shows the structure of the uplink subframe.

[0044] Referring to Fig. 6, the uplink subframe may be divided into a control region to which the PDCCH is allocated which transmits uplink control information in the frequency domain and a data region to which the PUSCH is allocated which transmits user data . [0045] PUCCH for a single UE is assigned to a resource block (RB) pair in the subframe, and RBs belonging to the RB pair respectively have different subcarriers in two slots. This means that the RB pair allocated to PUCCH performs frequency hopping at the slot boundary.

[0046] PUCCH can support multiple formats. This means that PUCCH can transmit uplink control information having different numbers of bits for subframes according to a modulation scheme. The following table shows the PUCCH format, modulation scheme and number of bits that are supported according to 3GPP TS 36.211 V8.2.0.

[Table 2]

<td>PUCCH format</td><td>Modulation scheme</td><td>Number of bits per subframe, M</td>

<td> 1</td><td>N / D</td><td>N / D</td>

<td>1a</td><td>BPSK</td><td> 1</td>

<td>1b</td><td>QPSK</td><td> 2</td>

<td> 2</td><td>QPSK</td><td> 20</td>

<td>2a</td><td>QPSK, BPSK +</td><td> 21</td>

<td>2b</td><td>QPSK + QPSK</td><td> 22</td>

[0047] The 1 PUCCH format is used to send SR scheduling requests, the 1a / 1b PUCCH format is used to transmit a representative ACK / NACK signal, the 2 PUCCH format is used to transmit CQI, and the format 2a / 2b

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PUCCH is used to transmit CQI and a representative ACK / NACK signal.

[0048] The 1a / 1b PUCCH format is used when a representative ACK / NACK signal is transmitted as the only one in any subframe, and the 1 PUCCH format is used when only SR scheduling requests are transmitted. PUCCH formats for transmitting control information have been described above. The allocation patterns and amount of allocation of radio resources used to broadcast control information may vary, depending on the PUCCH format.

[0049] Fig. 7 shows ACK / NACK signal transmission on a PUCCH channel.

[0050] Referring to Fig. 7, the RS reference signal is loaded in 3 SC-FDMA symbols among the 7 SC-FDMA symbols contained in a single slot, and a representative ACK / NACK signal is loaded in the remaining SC-FDMA symbols. The SC reference signal is loaded in 3 continuous SC-FDMA symbols in the middle of the slot.

[0051] To transmit the ACK / NACK signal, the 2-bit representative ACK / NACK signal is modulated by QPSK to generate a single modulation symbol d (0). The modulated m (n) sequence is generated based on the modulation symbol d (0) and the cyclically shifted sequence r (n, a). "A" is the amount of cyclic shift (CS). It is possible to multiply the cyclically shifted sequence r (n, a) by the modulation symbol to generate the modulated y (n) sequence according to equation 1.

Equation 1 Xn) = rf (o) r (n, a) [0052] The cyclically shifted sequence r (n, a) may have different CS sizes or the same CS size for the corresponding SC-FDMA symbols. Although the sizes CS 0, 1, 2 and 3 are sequentially set for 4 SC-FDMA symbols in a single slot in this case, this is just an example.

[0053] Furthermore, although a single modulation symbol is generated by QPSK modulation of the 2 bit ACK / NACK signal in the current embodiment, it is also possible to modulate the BPSK of the 1 bit ACK / NACK signal to generate a single modulation symbol. The number of ACK / NACK signal bits, the modulation scheme and the number of modulation symbols are exemplary and do not limit the invention.

[0054] In addition, the modulated sequence can be spread using an orthogonal sequence to increase UE throughput. The sequences shown in Table 3 can be used as orthogonal sequences wi (k) (and is a sequence index, 0 &lt;k &lt;K-1) having a spreading factor of K = 4.

[Table 3]

<td>Sequence index</td><td>[in (0), in (1), in (2), in (3)]</td>

<td> 0</td><td> [+1 +1 +1 +1]</td>

<td> 1</td><td> [+1 -1 +1 -1]</td>

<td> 2</td><td> [+1 -1 -1 +1]</td>

[0055] Otherwise, the sequences shown in Table 4 can be used as orthogonal sequences wi (k) (and is a sequence index, 0 &lt;k &lt;K-1) having a spreading factor of K = 3.

[Table 4]

<td>Sequence index</td><td>[in (0), in (1), in (2)]</td>

<td> 0</td><td> [1 1 1]</td>

<td> 1</td><td>[1 eHi ^]</td>

<td> 2</td><td> [1</td>

[0056] Here, the scattering operation of the sequence modulated by the orthogonal sequence wi (k) having a scattering factor K = 4 for 4 SC-FDMA symbols contained in a single slot for a representative ACK / NACK signal is described.

[0057] Fig. 8 shows a method of performing HARQ by bundling ACK / NACK in bundles according to an embodiment of the invention. Fig. 8 shows that a UE that has received downlink data transmits ACK / NACK signals to an uplink in a TDD system in which the number of subframes used for downlink transmission is greater than the number of subframes used for uplink transmission. . However, the invention is applied not only to the TDD system but also to the FDD system where the ACK / NACK signals for multiple downlink subframes are transmitted by a single uplink subframe. [0058] With reference to Fig. 8, the UE transmits data corresponding to 3 continuous downlink subframes or a single ACK / NACK signal corresponding to PDSCH via a single uplink subframe. This means that the ratio of ACK / NACK signals to data (or PDSCH) is 3: 1. When multiple subframes are allocated to a particular UE for downlink transmission in a TDD system, ACK / NACK signals are transmitted including downlink data transmitted as a single HARQ packet.

[0059] Hereinafter, the ACK / NACK signal transmitted through a single uplink subframe according to the ACK / NACK bundling is referred to as the representative ACK / NACK signal. In contrast, among many downlink subframes associated with a single uplink subframe, at least one downlink subframe through which data is transmitted for a certain UE is referred to as downlink subframes enclosed in a bundle. Each subframe contained in bundled downlink subframes is referred to as a downlink subframe enclosed in a bundle.

[0060] The UE determines the representative ACK / NACK signal as an ACK or NACK signal according to the following method.

[0061] The UE performs decoding for the codeword that the US has received in the bundled downlink subframe and performs the logical AND operation of the ACK signals or NACK signals for the downlink subframes bundled to generate at least one representative ACK / NACK signal . That is, the UE transmits the ACK signal only when it sequentially receives all the code words received in the bundled subframes, and transmits the NACK signal when the receipt of any of the code words fails. Or, when multiple representative ACK / NACK signals are generated, the UE divides the code words that are transmitted on the bundled downlink subframes into multiple groups of code words. Thus, the UE may transmit the ACK / NACK signal for each group of code words.

[0062] There is a rule for determining the ACK or NACK signal taking into account downlink data compiled from multiple code words as single data. Here, the code word is a unit of data transmitted for each bundled downlink subframe and may be referred to as a transport block. [0063] Still, the set of code words corresponding to the decision base in generating the representative ACK / NACK signal is referred to as a downlink data packet. Accordingly, it is believed that the UE sequentially receives a downlink data packet when the ACK / NACK signal is an ACK signal and it is considered that the downlink data packet received by the UE fails when the representative ACK / NACK signal is a signal NACK.

[0064] If the UE fails to decode the downlink data packet, it is natural for the UE to send the NACK signal to the BS. The BS re-transmits the downlink data packet to the UE. However, if the UE leaves the scheduling information (or PDCCH) and cannot detect the existence of the skipped data contained in the downlink subframe bundle, the UE should perform the HARQ only based on the remainder of the bundled frame (s)

Downlinks except for the omitted, bundled downlink subframe. It is not important whether the UE is expected to send a NACK signal because the BS may resend the downlink data. However, if UEs are likely to send ACK signal, data for the missed downlink bundle will be lost and cannot be recovered. Therefore, BS or UE must know which bundled downlink subframe corresponds to the representative ACK / NACK signal.

[0065] In Fig. 8, although it is assumed that the UE is the entity that transmits the ACK / NACK signal, the BS can also transmit the ACK / NACK signal in the same manner.

[0066] Fig. 9 is a flowchart showing a method of performing HARQ in a TDD system according to an embodiment of the invention.

[0067] Referring to Fig. 9, BS transmits the bundling rate to the UE in step S100. The bundling indicator is control information that indicates the bundled downlink subframes associated with a single uplink subframe to transmit a representative ACK / NACK signal. The bundling indicator can be the number of bundled downlink subframes or the command to send bundled downlink subframes. The bundling indicator is included in the scheduling information and can be transmitted via PDCCH. Otherwise, the bundling indicator may be included in the bundled data packets and transmitted. The bundling indicator will be described in more detail later.

[0068] The BS transmits the downlink data packet to the specified UE via the bundled downlink subframe in step S110. Bundled downlink subframes can be continuous subframes or discontinuous subframes. The downlink data packet is transmitted via PDSCH, which is the physical channel in each downlink subframe. When the bundling indicator is included in the bundled data packet, the bundling indicator and the bundled downlink data packet can be transmitted simultaneously.

[0069] The UE detects the bundled downlink subframe in step S120. The UE specifies that there is no skipping of the bundled downlink subframe when all the bundled downlink subframe indicated by the bundling indicator is successfully received. In contrast, the UE specifies that the bundled downlink subframe is skipped when the receipt of any bundled downlink subframe fails. For example, the UE detects only two downlink subframes, although the bundling indicator indicates that there are three downlinked subframes. The UE determines that the bundled downlink subframe is omitted and generates a representative NACK signal to report that the UE failed to detect one bundled downlink subframe. Of course, the UE specifies that a receive error occurs when it fails to receive any of the two downlink subframes.

[0070] The UE transmits a representative ACK / NACK signal to the BS in the step S130. The UE transmits a representative ACK / NACK signal via the predetermined uplink subframe. A representative ACK / NACK signal can be transmitted via PUCCH, which is the PUSCH control channel, which is the uplink data channel. The uplink radio resources used to transmit the representative ACK / NACK signal will be described in more detail below.

[0071] The BS transmits HARQ again when the representative ACK / NACK signal is the NACK signal and transmits new data when the representative ACK / NACK signal is the ACK signal in step S140.

[0072] The bundling indicator will now be explained in detail. In one embodiment, the bundling index may correspond to the number of bundled downlink subframes. The bundling index is, for example, 3 in Fig. 8. The bundling index can be transmitted

Through all bundled downlink subframes or some of the bundled downlink subframes. The UE counts the number of bundled downlink subframes that the UE detects. The UE then compares the beam capture indicator with the meter. If the bundling indicator is different from the UE counter, the UE transmits a representative NACK signal to BS or does not perform any operation and operates in the mode of discontinuous transmission (DTX). If the number of downlink subframes actually counted by the UE is 2, while the bundling index is received for example equal to 3, this means that the UE failed to receive a single downlink subframe, hence the UE transmits a representative NACK signal to BS or not does nothing.

[0073] In another embodiment, the bundling indicator may indicate the order of transmission of the bundled downlink subframes or the order of PDSCH transmission with respect to the specific UE. The UE counts the number of downlink subframes it itself detects. For example, if 4 downlink subframes are associated with a single uplink subframe for a representative ACK / NACK signal, then 3 of the 4 downlink subframes are bundled downlink subframes for a particular UE. The bundling indicators 1, 2 and 3 can be increasingly assigned to the three bundled subframes of the downlink in order. The determined UE increases the counter each time the UE detects the bundled downlink subframe. For example, this happens when the specified UE only detects the bundled downlink subframe, corresponding to, for example, the bundling indicators 1 and 3. The counter is 1 when the specified UE detects the 1st bundled downlink subframe. Detection of the 2nd bundled downlink subframe by the specified UE fails, therefore the counter is still 1. When the specified UE detects the 3rd bundled downlink subframe, the counter is 2, although the bundling indicator is 3. The bundling indicator does not correspond to the meter, hence it may be known that the specified UE failed to detect the PDCCH of the 2nd bundled downlink subframe corresponding to the bundling indicator 1. In this case, the specified UE may generate a representative NACK signal or not perform any operation in DTX mode.

[0074] An example in which the UE determines the existence of a reception error is represented as follows. [Mathematical figure 2] No. of bundling index # (Ndai-1) mod (a) +1 [0075] Here, Ndai denotes the number of bundled downlink subframes successfully detected by the UE, and mod (a) represents the modulo operation. When the bundling indicator is information about (ceiling [log2 (a)]) bits, the transmission order begins with 1 when the bundling indicator becomes larger than the maximum transmission order a, hence the modulo operation is performed. In this way, the UE may correctly transmit a representative ACK / NACK signal. Here, the bundling index can also be referred to as downlink assignment index (DAI).

[0076] The information indicated by the bundling indicator itself may vary, depending on the DCI format. For example, when the DCI format is 0, the bundling indicator simply indicates the number of PDSCH transmissions associated with the uplink subframe that transmits the representative ACK / NACK signal for the specified UE. When the DCI format is 1 / 1A / 1B / 1D / 2 / 2A, which is used for downlink scheduling information, the bundling indicator shows the increasing number of PDSCH transmissions for a specific UE and can be updated every subframe.

[0077] The radio resources used for the UE to transmit the representative ACK / NACK signal will now be explained. In bundling ACK / NACK, a single uplink subframe is used to transmit ACK / NACK signals for bundled downlink subframes. According

In addition, radio resources that will transmit ACK / NACK signals with respect to a plurality of bundled downlink subframes must be allocated to the uplink subframe. If downlink data is transmitted to different UEs via 4 downlink subframes, when the ratio of the number of downlink subframes to the number of uplink subframes is for example 4: 1, the UEs should be able to transmit ACK / NACK signals through this the uplink subframe itself. Accordingly, a radio resource for ACK / NACK signals, which is four times the radio resource required when the ratio of the number of downlink subframes to the number of uplink subframes is 1: 1, must be allocated to each uplink subframe.

[0078] In contrast, when downlink data is transmitted to a single UE via a bundled downlink subframe, the radio resource for a representative ACK / NACK signal corresponding to the bundled downlink subframes will not be used by other UEs. Accordingly, a single UE may transmit a representative ACK / NACK signal by using one radio resource allocated to the ACK / NACK signals.

[0079] According to the invention, the UE transmits a representative ACK / NACK signal using a radio resource for ACK / NACK signals, and the radio resources for ACK / NACK signals are allocated for the last bundled downlink subframe among the bundled downlink subframes. This gives the criterion in which BS determines whether or not PDSCH of bundled downlink subframes is successfully transmitted. For example, if the UE omits the last downlinked subframe (s) from among the downlinked subframes, the UE transmits a representative ACK / NACK signal using the radio resource assigned to the penultimate downstream subframe. In this case, the BS may conclude that the last bundled downlink subframe (s) is omitted by the radio resource used to transmit the representative ACK / NACK signal.

[0080] Fig. 10 shows a method of mapping a representative ACK / NACK signal to a radio resource according to an embodiment of the invention. Here, a representative ACK / NACK signal is transmitted via PUCCH.

[0081] Referring to Fig. 10, a single uplink subframe is allocated to transmit the ACK / NACK signal for 4 downlink subframes. The specific position of the bundled subframe (s) corresponding to the uplink subframe for a representative ACK / NACK signal is defined in the table below.

[Table 5]

<td>Configuration</td><td colspan="10">Subframe</td>

<td></td><td> 0</td><td> 1</td><td> 2</td><td> 3</td><td> 4</td><td> 5</td><td> 6</td><td> 7</td><td> 8</td><td> 9</td>

<td> 0</td><td> -</td><td> -</td><td> 6</td><td> -</td><td> 5</td><td colspan="3"> 6</td><td colspan="2"> 4</td>

<td> 1</td><td> -</td><td> -</td><td> 7, 6</td><td> 4</td><td> -</td><td> -</td><td> -</td><td> 7, 6</td><td> 4</td><td> -</td>

<td> 2</td><td> -</td><td> -</td><td> 8, 7, 6, 4</td><td> -</td><td> -</td><td> -</td><td> -</td><td> 8, 7, 6, 4</td><td> -</td><td> -</td>

<td> 3</td><td> -</td><td> -</td><td> 11,7, 6</td><td> 6, 5</td><td> 5, 4</td><td> -</td><td> -</td><td> -</td><td> -</td><td> -</td>

<td> 4</td><td> -</td><td> -</td><td> 12, 11,8,7</td><td> 7, 6, 5, 4</td><td> -</td><td> -</td><td> -</td><td> -</td><td> -</td><td> -</td>

<td> 5</td><td> -</td><td> -</td><td>subject to determination</td><td> -</td><td> -</td><td> -</td><td> -</td><td> -</td><td> -</td><td> -</td>

<td> 6</td><td> -</td><td> -</td><td> 7</td><td> 7</td><td> 5</td><td colspan="3"> 7</td><td> 7</td><td> -</td>

[0082] In table 5, the subframe n is an uplink subframe indicator. The bundled down subframe corresponding to the nth subframe (uplink subframe) is referred to as nk. That is, the downlink subframe enclosed in the bundle is indicated as the subframe before the nth subframe by k. Here k

EP 2 104 263 B1 is an indicator that defines the downlink framed in a bundle and belongs to the set K, containing M elements {k0, k.1, ..., kM-1}. The position of the downlink bundled subframe is determined by the subframe and configuration.

[0083] For example, if a representative ACK / NACK signal is transmitted by the 2nd subframe (n = 2) when the radio frame is determined by configuration 2, when n = 2 the bundling indicator corresponds to the set K = {8.7, 6.4}. Accordingly, the bundled downlink subframes covered by the representative ACK / NACK signal correspond to the 4th, 5th, 6th and 8th subframes before the 2nd subframes at 8, 7, 6 and 4. This is because the bundled downlink subframes occur before the uplink subframe that transmits the representative ACK / NACK signal.

[0084] Each downlink subframe consists of PDCCH and PDSCH, and PDCCH is divided into 4 sections. A section may be referred to as a certain radio resource region (i.e., resource block (RB)). This split is an example and the interval and number of divided sections can be changed. The UE decodes PDCCH through the CCE and then decodes PDSCH according to the PDCCH downlink allocation. The UE receives data from the PDSCH, and the data receiving region can be composed of resource blocks, which are radio resource units. [0085] Radio resources of ACK / NACK signals for a specific PDCCH may be determined by a resource index. Here, radio resources are PUCCH radio resources. For example, the 0th downlink subframe uses radio resources corresponding to indexes 1, 2, 3 and 4 in the uplink subframe to transmit ACK / NACK signals, and the 1st downlink subframe uses radio resources corresponding to indexes 5, 6, 7 and 8 in the uplink subframe to transmit ACK / NACK signals. That is, the radio resources used to transmit ACK / NACK signals through a single uplink subframe can be classified by their respective downlink subframes. Alternatively, to limit the amount of radio resources for ACK / NACK signal broadcasting, it may be considered that ACK / NACK signal resources for a certain downlink subframe may be duplicated using a different downlink subframe.

[0086] If the specified UE receives the code word through the 0th, 1st and 3rd downlink subframes among the 4 bundled downlink subframes, the specified UE decodes the PDCCH section 3 of the 0th downlink subframe and reads PDSCH indicated by section 3. In addition, the specified UE decodes section 6 PDCCH of the first downlink subframe and reads the PDSCH indicated by section 6. In addition, the specified UE decodes the section 13 PDCCH of the 3rd downlink subframe and reads the PDSCH indicated by section 13. [0087] The determined UE transmits a representative ACK / NACK signal according to whether the UE successfully receives the PDSCH or whether receiving the PDSCH fails. Here, the UE specified does not use radio resources with indexes 3 and 6 and transmits a representative ACK / NACK signal using only radio resources with indexes 13, corresponding to the last section 13 that was last received by the UE.

[0088] The radio resource of the bundled subframe (s) that the UE detects as the newest (or closest to the uplink n subframe) is used to transmit a representative ACK / NACK signal. The bundled downlink subframe (s) is contained in the downlink subframe associated with the uplink n subframe.

[0089] For example, it is assumed that a representative ACK / NACK signal is transmitted in uplink subframe 2 in configuration 2. The bundled downlink subframes are 4th, 5th, 6th and 8th subframes . If the UE detects 4th, 5th and 8th subframes, a representative ACK / NACK signal is transmitted using the radio resource according to the downlink 8th subframe received last. This is done when k = 4. That is, when the downlink subframe by the smallest number is specified

For elements that belong to the set K, the radio resource used to transmit the representative ACK / NACK signal is determined according to the downlink subframe.

[0090] This is a method for determining radio resources that transmit a representative ACK / NACK signal. The method for determining whether the representative ACK / NACK signal corresponds to the ACK signal or the NACK signal has been described above.

[0091] The specified UE cannot read the PDSCH indicated by section 13 unless the UE detects the PDCCH section 13 of the 3rd downlink subframe. Accordingly, the specified UE will transmit a representative ACK / NACK signal according to the radio resource index corresponding to the last received section 6. In contrast, BS expects to receive a representative ACK / NACK signal according to the radio resource index 13 because the BS transmits downlink data according to section 13. However, the BS receives a representative ACK / NACK signal according to radio resource index 6, hence the BS may recognize that the downlink data transmission recently transmitted in accordance with section 13 has failed. Accordingly, BS may perform the HARQ retransmission even if the ACK / NACK signal is a representative ACK / NACK signal.

[0092] If the radio resource selection method for the ACK / NACK signal is combined with the method of detecting the bundled down link subframe with the bundling indicator as described above, it is possible to detect the skipped, bundled down frame subframe (s) independently whether the position of the omitted, included in the downlink subframe (s) bundle lies in the middle or last. For example, it is assumed that the specified UE does not detect section 6 PDCCH of the first downlink subframe and detects section 13. The bundle tracing indicator in section 3 PDCCH is 1, the bundle tracing indicator in section 6 PDCCH is 2, and the indicator the bundle in section 13 PDCCH is 3. UE fails to detect section 6, hence the UE counter when the UE detects section 13 PDCCH still indicates 2. Here, the UE does not transmit a representative ACK / NACK signal according to the radio resource corresponding to section 13 and operates in DTX mode. BS expects to receive a representative ACK / NACK signal according to index 13 of the radio resource, since BS transmits downlink data according to section 13. However, BS does not receive any representative ACK / NACK signal, hence BS can retransmit HARQ.

[0093] The BS may distinguish between successful or unsuccessful transmission of bundled downlink subframes with a radio resource for a representative ACK / NACK signal transmitted from the UE. In contrast, the UE may distinguish whether the downlink subframe (s) included in the bundle has been omitted by comparing the bundling rate with the number of downlink subframes detected in the bundle.

[0094] The ACK / NACK signal transmission method will now be explained by using the radio resources used to transmit downlink data. When the UE simultaneously transmits the uplink data together with the transmission of the ACK / NACK signal to the uplink subframe, the radio resource allocated to the transmission of the ACK / NACK signal may not be a radio resource for transmitting general control information. That is, the UE may transmit the ACK / NACK signal by using the radio resource in PUSCH without using the radio resource in PUCCH. Here, the ACK / NACK signal can be multiplied with general uplink data.

[0095] The UE transmits a NACK signal with respect to downlink data that are not recognized or not intended for this UE, as well as downlink data whose successful receipt is evaluated by the UE. The NACK signal formally transmitted for downlink data is referred to as the NACK sample signal. When a test NACK signal is transmitted, the BS can recognize whether the UE is properly receiving downlink data and whether the ACK / NACK signals transmitted from the UE are true.

[0096] Fig. 11 shows a method of transmitting an ACK / NACK signal in a TDD system, according to an embodiment of the invention.

[0097] With reference to Figure 11, there are 4 downlink subframes No. 0, No. 1, No. 2 and No. 3 and uplink subframe No. n for transmitting ACK / NACK signals corresponding to 4 downlink subframes No. 0, No. 1, No. 2 and No. 3. Only the downlink subframe No. 0 transmits downlink data for UE A. Accordingly, the UE decodes the downlink subframe No. 0 and transmits the ACK / NACK signal to the subframe No. 0 through resource utilization. radio "a" PUSCH subframe n uplink. In addition, the UE transmits 3 NACK signals as ACK / NACK signals with respect to downlink subframes 1, 2 and 3 by using radio resources "b", "c" and "d" PUSCH of the uplink subframe n. The UE transmits all ACK / NACK signals with respect to downlink subframes 1, 2 and 3 even though downlink data for UE A is not forwarded in downlink 1, 2 and 3 subframes . This means that the UE transmits 4 ACK / NACK signals.

[0098] Although in Fig. 11 the radio resources a, b, and c are continuous, the radio resources for transmitting ACK / NACK signals can be spread in PUSCH. In addition, the method of mapping ACK / NACK signals to radio resources a, b, and c may be different from the method of mapping radio resources for ACK / NACK signals in PUCCH. In addition, the ACK / NACK signal can be independently transmitted or multiplied with uplink data and transmitted.

[0099] The ACK / NACK signal can be transmitted as needed via PUCCH. In this case, a representative ACK / NACK signal is transmitted as described above. The system can freely choose whether the representative ACK / NACK signal is transmitted by PUCCH or whether the NACK (dummy NACK) test signal is transmitted by PDSH. In addition, the ACK / NACK signal can be dynamically transmitted when switching to PUCCH and PUSCH.

[0100] Transmitting the same amount of ACK / NACK signals with a maximum number of downlink subframes or data for a UE causes a overhead problem because the amount of feedback increases. The following describes how to limit feedback.

[0101] Fig. 12 is a flowchart showing an ACK / NACK signal transmission method in a TDD system according to another embodiment of the invention.

[0102] Referring to Fig. 12, the BS configures the bundled downlink subframes with Nd downlink subframes and forwards the data to the UE via the bundled subframes at step S200. Downlink data is transmitted by PDSCH enclosed in a downlink subframe bundle. The UE transmits a representative ACK / NACK signal to the BS in step S210. The method of generating a representative ACK / NACK signal is described with reference to Fig. 8. The UE transmits data by counting the Nc information to the BS in step S220. Nc is the number of bundled downlink subframes that the UE detects. Thus, ND = Nc + N omitted. Here, Nominated means the number of downlink subframes that are bundled that are not detected (or recognized) by the UE.

[0103] The number of data count information bits is ceiling [log2 (max (ND))] if the data count information is expressed in an independent information bit stream. The UE must provide ceiling information [log2 (max (ND)]] + 2 bits via the uplink subframe if the representative ACK / NACK signal is 2 bits. Therefore, it is more desirable in terms of signaling overhead to use both the representative ACK / NACK signal and data counting information than to transmit 2xKmax (ND) bit ACK / NACK signals. A representative ACK / NACK signal and data counting information are transmitted via PUSCH.

[0104] BS determines whether HARQ retransmission is performed, or new data is transmitted according to the representative ACK / NACK signal and data counting information in step S230. This determination is made by comparing Nd and Nc by BS. An embodiment in which the UE detects all bundled downlink subframes, Npominated = 0, and Nc = Nd. That is, BS may be aware that no downlinked subframes are omitted based on the data counting information. Therefore, BS performs HARQ retransmission or transmission of new data according to a representative ACK / NACK signal.

In another embodiment, in which the UE omits at least one of the bundled downlink subframes, N omitted # 0, and Nc # Nd. Therefore, BS may be aware that the UE omitted the bundled downlink subframes. Then the BS can perform HARQ retransmission, even if the BS receives a representative ACK signal from the UE.

[0106] The aforementioned functions may be performed by processors such as microprocessors, controllers, microcontrollers, application-specific integrated circuits (ASICs), and so on, according to software or program codes encoded to perform functions. The design, development and implementation of these codes are obvious to those skilled in the field.

[0107] While the invention has been shown and described especially with reference to embodiments thereof, persons skilled in the art will understand that various changes in form and detail can be made therein without departing from the scope of the invention as defined by the following claims.