KR101718163B1 - Method and apparatus for performing uplink harq in wireless communication system - Google Patents

Abstract

A method and apparatus for performing a hybrid automatic repeat request (HARQ) in a wireless communication system are provided. The terminal receives HARQ configuration information from the base station. Upon receiving the NACK signal for the initial transmission block, the UE adjusts the transmission characteristics of the retransmission block for the initial transmission block based on the HARQ setting information.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for performing uplink HARQ in a wireless communication system,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to wireless communication, and more particularly, to an apparatus and method for performing uplink HARQ (Hybrid Automatic Repeat Request) in a wireless communication system.

As an error compensation scheme for ensuring the reliability of communication, there are a forward error correction (FEC) scheme and an automatic repeat request (ARQ) scheme. In the FEC scheme, an extra error correcting code is added to the information bits, thereby correcting the error at the receiving end. The FEC scheme has an advantage in that there is no time delay and no information is exchanged between the transmitting and receiving ends, but there is a disadvantage in that system efficiency is poor in a good channel environment. Although the ARQ scheme can increase transmission reliability, there is a disadvantage in that time delay occurs and system efficiency drops in a poor channel environment.

Hybrid Automatic Repeat Request (HARQ) is a combination of FEC and ARQ. It checks whether the data received by the physical layer includes errors that can not be decoded, and requests retransmission when an error occurs.

If no error is detected in the received data, the receiver transmits a positive acknowledgment (ACK) signal with a reception acknowledgment to notify the transmitter of the reception success. When an error is detected in the received data, the receiver transmits a negative acknowledgment (NACK) signal to acknowledge the error to the transmitter. The transmitter can retransmit the data when the NACK signal is received.

LTE (Long Term Evolution) based on 3rd Generation Partnership Project (3GPP) TS (Technical Specification) Release 8 is a promising next generation mobile communication standard.

3GPP LTE supports HARQ for both uplink transmission and downlink transmission. The downlink HARQ indicates that when a base station transmits downlink data, the terminal transmits an ACK / NACK signal for the downlink data. The uplink HARQ indicates that the Node B transmits an ACK / NACK signal for the uplink data when the UE transmits uplink data.

Recently, 3GPP LTE-A (LTE-Advanced), an evolution of 3GPP LTE, is under discussion. Representative technologies newly added to the LTE-A system include Carrier Aggregation, Relay, and Multiple Input Multiple Output (MIMO). Carrier aggregation is used to flexibly extend the available bandwidth. Repeaters increase cell coverage, support group mobility, and enable user-centric network deployment. In the uplink MIMO, LTE supports only a single antenna in uplink transmission, while supporting a plurality of antennas to improve a data rate.

In 3GPP LTE-A, which introduces a new technology, a technique for improving HARQ performance is proposed.

SUMMARY OF THE INVENTION The present invention provides a method and apparatus for performing uplink HARQ in a wireless communication system.

It is another object of the present invention to provide a method and apparatus for performing a synchronous / adaptive uplink HARQ in a wireless communication system.

In an aspect, a method for performing an uplink hybrid automatic repeat request (HARQ) in a wireless communication system is provided. The method includes receiving HARQ configuration information from a base station, receiving an uplink resource allocation from the base station, and initializing the uplink data channel on the uplink data channel using the uplink resource allocation from the base station. Block, and the terminal receives an ACK / NACK signal for the initial transmission block from the base station, and a radio resource used for transmission of the ACK / NACK signal is a radio resource used for transmission of the uplink data channel And adjusting transmission characteristics of the retransmission block for the initial transmission block based on the HARQ configuration information when the ACK / NACK signal is a NACK signal, and transmitting the retransmission block to the base station.

The transmission characteristics of the retransmission block may be at least one of a rank, a modulation order, a number of resource blocks, and a transmission power.

The HARQ setting information may be set to lower the rank of the retransmission block than the rank of the initial transmission block.

The HARQ setting information may be set to lower the modulation order of the retransmission block than the modulation order of the initial transmission block.

The retransmission block may be transmitted to the BS in a predetermined HARQ period.

In another aspect, a terminal performing an uplink HARQ (hybrid automatic repeat request) is provided. The UE includes a transmitter for transmitting an initial transmission block or a retransmission block on a Physical Uplink Shared Channel (PUSCH), a receiver for receiving an ACK / NACK signal for the initial transmission block on a Physical Hybrid-ARQ Indicator Channel (PHICH) And a hybrid automatic repeat request (HARQ) entity, wherein the HARQ entity instructs transmission of the retransmission block for the initial transmission block when the ACK / NACK signal is a NACK signal, And the modulation order lower than the rank and the modulation order used for transmission of the initial transmission block.

The transmitting unit may transmit the retransmission block to the BS in a predetermined HARQ period.

With the introduction of multiple antennas, adaptive HARQ can be performed and the efficiency of the system can be increased.

1 shows a wireless communication system.
2 shows a structure of a radio frame in 3GPP LTE.
3 shows a synchronous uplink HARQ in 3GPP LTE.
4 shows asynchronous downlink HARQ in 3GPP LTE.
5 shows an example of channel coding in 3GPP LTE.
6 is a flowchart showing the configuration of the PHICH.
FIG. 7 is a flowchart illustrating a method of performing a synchronous / adaptive uplink HARQ according to an embodiment of the present invention. Referring to FIG.
8 is a flowchart illustrating a method of performing a synchronization / adaptive uplink HARQ according to another embodiment of the present invention.
9 is a flowchart illustrating a method of performing a synchronization / adaptive uplink HARQ according to another embodiment of the present invention.
10 is a block diagram illustrating a terminal and a base station in which an embodiment of the present invention is implemented.
11 is a block diagram showing an example of a transmission unit of a terminal.

1 shows a wireless communication system. The wireless communication system 10 includes at least one base station 11 (BS). Each base station 11 provides a communication service to a specific geographical area (generally called a cell) 15a, 15b, 15c. The cell may again be divided into multiple regions (referred to as sectors).

A user equipment (UE) 12 may be fixed or mobile and may be a mobile station (MS), a mobile terminal (MT), a user terminal (UT), a subscriber station (SS), a wireless device, (personal digital assistant), a wireless modem, a handheld device, and the like.

The base station 11 generally refers to a fixed station that communicates with the terminal 12 and may be referred to by other terms such as an evolved-NodeB (eNB), a base transceiver system (BTS), an access point have.

Hereinafter, downlink refers to communication from a base station to a terminal, and uplink refers to communication from a terminal to a base station. In the downlink, the transmitter may be part of the base station, and the receiver may be part of the terminal. In the uplink, the transmitter may be part of the terminal, and the receiver may be part of the base station.

2 shows a structure of a radio frame in 3GPP LTE. This can be referred to Section 6 of 3GPP TS 36.211 V8.5.0 (2008-12) "Evolved Universal Terrestrial Radio Access (E-UTRA), Physical Channels and Modulation (Release 8)". A radio frame is composed of 10 subframes indexed from 0 to 9, and one subframe is composed of two slots. The time taken for one subframe to be transmitted is referred to as a transmission time interval (TTI). For example, the length of one subframe may be 1 ms and the length of one slot may be 0.5 ms.

One slot may comprise a plurality of orthogonal frequency division multiplexing (OFDM) symbols in the time domain. OFDM symbols are used to represent one symbol period in the time domain since 3GPP LTE uses orthogonal frequency division multiple access (OFDMA) in the downlink. Limiting the multiple access scheme or name no. For example, an OFDM symbol may be referred to as another name such as a single carrier frequency division multiple access (SC-FDMA) symbol, a symbol period, or the like.

Although one slot includes seven OFDM symbols, the number of OFDM symbols included in one slot may be changed according to the length of a CP (Cyclic Prefix). According to 3GPP TS 36.211 V8.5.0 (2008-12), one subframe in a normal CP includes seven OFDM symbols, one subframe in an extended CP includes six OFDM symbols, do.

A resource block (RB) is a resource allocation unit and includes a plurality of subcarriers in one slot. For example, if one slot includes 7 OFDM symbols in the time domain and the resource block includes 12 subcarriers in the frequency domain, one resource block includes 7 × 12 resource elements (REs) .

A subframe is divided into a control region and a data region in a time domain. The control region includes up to four OFDM symbols preceding the first slot in the subframe, but the number of OFDM symbols included in the control region may be changed. A PDCCH is allocated to the control region, and a PDSCH is allocated to the data region.

As disclosed in 3GPP TS 36.211 V8.5.0 (2008-12), in LTE, a physical channel includes a physical downlink shared channel (PDSCH), a physical uplink shared channel (PUSCH), and a physical downlink control channel (PDCCH) , Physical Control Format Indicator Channel (PCFICH), Physical Hybrid-ARQ Indicator Channel (PHICH), and Physical Uplink Control Channel (PUCCH).

The control information transmitted through the PDCCH is referred to as downlink control information (DCI). The DCI includes a resource allocation (also referred to as a downlink grant) of the PDSCH, a resource allocation of the PUSCH (also referred to as an uplink grant), a set of transmission power control commands for individual UEs in any UE group, and / And activation of VoIP (Voice over Internet Protocol).

The PCFICH transmitted in the first OFDM symbol of the subframe carries a control format indicator (CFI) regarding the number of OFDM symbols (i.e., the size of the control region) used for transmission of the control channels in the subframe. The UE first receives the CFI on the PCFICH, and then monitors the PDCCH.

The PHICH carries a positive-acknowledgment (ACK) / negative-acknowledgment (NACK) signal for a hybrid automatic repeat request (HARQ). The ACK / NACK signal for the uplink data transmitted by the UE is transmitted on PHCIH.

3GPP LTE uses synchronous HARQ in uplink transmission and asynchronous HARQ in downlink transmission. The synchronous HARQ means that the retransmission timing is fixed, and the retransmission timing of the asynchronous HARQ is not fixed. That is, the initial transmission and the retransmission are performed in the synchronous HARQ with a constant HARQ cycle.

3 shows a synchronous uplink HARQ in 3GPP LTE.

The UE receives the initial uplink resource allocation on the PDCCH 310 in the n < th > subframe from the BS.

The UE transmits an uplink transmission block on the PUSCH 320 using the initial uplink resource allocation in the (n + 4) th subframe.

The base station sends an ACK / NACK signal for the uplink transport block onto the PHICH 331 in the (n + 8) th subframe. The ACK / NACK signal indicates reception acknowledgment for the uplink transport block, the ACK signal indicates reception success, and the NACK signal indicates reception failure.

NACK signal, the UE sends a retransmission block on the PUSCH 340 in the (n + 12) th subframe.

The base station sends an ACK / NACK signal for the uplink transport block onto the PHICH 351 in the (n + 16) th subframe.

Since retransmission is performed in the (n + 12) th subframe after the initial transmission in the (n + 4) th subframe, the synchronous HARQ is performed with the 8 subframes as the HARQ period.

In 3GPP LTE, eight HARQ processes can be performed, and each HARQ process is indexed from 0 to 7. The above example shows that HARQ is performed in the HARQ process index 4.

4 shows asynchronous downlink HARQ in 3GPP LTE.

The BS transmits the downlink transport block on the PDSCH 412 indicated by the downlink resource allocation on the PDCCH 411 in the n-th subframe.

The UE sends an ACK / NACK signal on the PUCCH 420 in the (n + 4) th subframe. The resource of the PUCCH 420 used for transmission of the ACK / NACK signal is determined based on the resource of the PDCCH 411 (e.g., the index of the first CCE used for transmission of the PDCCH 411).

Even though the base station receives the NACK signal from the UE, it does not necessarily retransmit in the (n + 8) th subframe, unlike the uplink HARQ. Here, it is assumed that the retransmission block is transmitted on the PDSCH 432 indicated by the downlink resource allocation on the PDCCH 431 in the (n + 9) th sub-frame.

The UE sends an ACK / NACK signal on the PUCCH 440 in the (n + 13) th subframe.

According to the asynchronous HARQ, the base station does not necessarily perform the retransmission in a predetermined period even if it receives the retransmission request of the terminal.

5 shows an example of channel coding in 3GPP LTE. This can be referred to in section 5.1 of 3GPP TS 36.212 V8.5.0 (2008-12).

A code block is composed of systematic bits, first parity bits and second parity bits. The code blocks are interleaved through a subblock interleaver. The interleaved code block is stored in a circular buffer of length Kw to form a mother transport block. At this time, the size of the circular buffer can be adjusted according to the buffer size of the terminal. The code block may be rate-matched according to the size of the reception buffer of the terminal.

3GPP LTE uses an Incremental Redundancy (HARQ) type HARQ, and therefore differentiates the redundancy version (RV) at each retransmission. The initial position in the buffer for retransmission is defined according to the RV. The initial transmission block of the HARQ is composed of a data block having a predetermined length with RV0 as a starting point in the parent transport block, and the first retransmission block is composed of a data block having a predetermined length starting from RV1 in the parent transport block.

6 is a flowchart showing the configuration of the PHICH. Since the LTE system does not support Single User-Multiple Input Multiple Output (SU-MIMO) in the uplink, the PHICH carries a 1-bit ACK / NACK signal corresponding to the PUSCH for one terminal.

In step S110, the 1-bit ACK / NACK signal performs channel coding using repetition coding with a code rate of 1/3. In step S120, the ACK / NACK signal coded with a 3-bit codeword is mapped to three modulation symbols through BPSK (Binary Phase Shift Keying) modulation. In step S130, the modulation symbols are spread using an orthogonal sequence with SF (Spreading Factor) N ^PHICH _SF . The number of orthogonal sequences used for spreading is twice the N ^PHICH _SF to apply I / Q multiplexing. 2N _SF ^PHICH orthogonal 2N _SF ^PHICH of PHICH is spread by using the sequences are defined as one PHICH group. PHICHs belonging to the same PHICH group are distinguished through different orthogonal sequences. In step S140, the spread symbols are hierarchically mapped according to rank. In step S250, the hierarchically mapped symbols are mapped to resource elements, respectively.

According to the section 6.9 of 3GPP TS 36.211 V8.5.0 (2008-12), PHICH resources corresponding to the PUSCH is the lowest PRB resources (Physical Resource Block) index I ^lowest _PRB ^{index _} _{_ RA} and the PUSCH to be used in the PUSCH It is defined using cyclic shift n _DMRS of the reference signal for data demodulation used. The reference signal for demodulation refers to a reference signal used for demodulating data transmitted on the PUSCH. More specifically, the PHICH resource is known by an index pair (n ^group _PHICH , n ^seq _PHICH ). n ^group _PHICH is the PHICH group number, and n ^seq _PHICH is the orthogonal sequence index in the PHICH group, and is given by:

Here, 'mod' denotes a modulo operation.

n ^group _PHICH has a value from 0 to (N ^group _PHICH -1), and the number of PHICH groups N ^group _PHICH is given as follows.

Here, N _g ∈ {1/6, 1/2, 1, 2} is given in the upper layer.

The orthogonal sequences used in PHICH are shown in the following table.

Sequence index
n ^seq _PHICH Orthogonal Sequence Normal CP, N ^PHICH _SF = 4 Extended CP, N ^PHICH _SF = 2 0 [+1 +1 +1 +1] [+1 +1] One [+1 -1 +1 -1] [+1 -1] 2 [+1 +1 -1 -1] [+ j + j] 3 [+1 -1 -1 +1] [+ j-j] 4 [+ j + j + j + j] 5 [+ j - j + j - j] 6 [+ j + j - j - j] 7 [+ j-j-j + j]

As described above, the uplink HARQ of the 3GPP LET is synchronous. Synchronous HARQ has the following advantages over asynchronous HARQ.

First, there is no need to send HARQ process indexes, which reduces the control signaling overhead. Second, the complexity due to HARQ performance can be reduced.

However, according to the existing PHICH structure, it is a non-adaptive HARQ that can be used for transmission of a 1-bit ACK / NACK signal and can not additionally change a transmission attribute.

Adaptive HARQ is a scheme that can change the transmission characteristics used for each retransmission compared to the initial transmission. Adaptive HARQ requires additional signaling to change transmission characteristics, but adaptive retransmission according to channel conditions is possible, thereby increasing the probability of success in retransmission.

FIG. 7 is a flowchart illustrating a method of performing a synchronous / adaptive uplink HARQ according to an embodiment of the present invention. Referring to FIG.

In step S710, the terminal receives HARQ configuration information from the base station. The HARQ setup information is information for performing a synchronous / adaptive uplink HARQ. The HARQ setup information may be broadcast as part of the system information or transmitted through a UE-specific message. The UE-specific message may be an RRC message or a MAC message. Through the HARQ setup information, the UE can determine the HARQ operation mode and / or the adaptation information. The HARQ operation mode may indicate whether to perform synchronous HARQ and / or whether to perform adaptive HARQ. The adaptation information indicates a change in the transmission characteristics of the initial transmission contrast retransmission when performing the adaptive HARQ. More details will be described later.

In step S720, the BS transmits an uplink resource allocation (or an uplink grant) to the UE on the PDCCH.

In step S730, the MS transmits an initial transmission block to the BS on the PUSCH configured with the uplink resource allocation.

In step S740, the base station determines whether the initial transmission block is erroneous and sends an acknowledgment to the PHICH. The resources used for the transmission of the PHICH are determined from the resources of the PUSCH as described above. Here, it is assumed that an error occurs in the initial transport block and a NACK signal is sent.

In step S750, the UE adjusts a transmission characteristic of a retransmission block based on HARQ setting information. The transmission characteristics to be adjusted can be a rank, a modulation order, a size of a resource block, a transmission power, and the like, which will be described later.

In step S760, the terminal transmits a retransmission block on the PUSCH. At this time, the initial transmission block and the retransmission block are transmitted with a constant HARQ cycle. For example, the HARQ period may be 8 subframes. When the initial transmission block is transmitted in the nth subframe, the retransmission block is transmitted in the (n + 8) th subframe.

Here, although retransmission is described once, a maximum M (M > 1) retransmission can be performed when a NACK signal is received. The transmission specification can be adaptively adjusted based on HARQ setting information for each retransmission.

Adaptive HARQ is set up through a semi-static message such as an upper layer message. The HARQ retransmission can be applied so that the signaling overhead is reduced and the receiver has better decoding performance.

The proposed adaptive HARQ scheme will now be described. For the synchronous / adaptive uplink HARQ, the following adaptation scheme can be considered.

Adaptive HARQ is to change the transmission characteristics in retransmission compared to the initial transmission. The changed transmission characteristics include at least one of a resource block allocation, a MIMO mode, a modulation and coding scheme, a transport block size, and a duration of retransmission. The MIMO mode includes at least one of a rank, a Precoding Matrix Indicator (PMI), a spatial multiplexing mode, and a spatial diversity mode.

In the following, changes are not considered in the channel coding for the retransmission block. That is, it is assumed that the systematic bits and parity bits of the code block are not changed even if they are retransmitted. However, if a higher coding gain is required, a change in channel coding may be considered.

1st Example : Rank  Down method ( rank down scheme )

A rank may be considered as the transmission characteristic adjusted at retransmission. The rank-down scheme is to apply a lower rank to the retransmission block than the initial transmission block.

Since the conventional 3GPP LTE considers only a single transmission antenna in the uplink, only the rank 1 can be used, so that the same rank always has to be applied. If an antenna of a plurality of transmissions is used in the uplink transmission, the rank can be changed.

The high rank is vulnerable to channel variation. The lower the rank, the lower the transmission rate, but the higher the transmission reliability. Also, the rank-down scheme can be efficient because it is not affected by the channel change even if the retransmission is greatly delayed due to a relatively long HARQ period in the synchronous HARQ.

The following table shows an example of a rank-down scheme according to the rank supported by the UE.

Supported ranks Initial transmission First retransmission Second retransmission Third retransmission One One One One One 2 2 2 2 One 2 2 One One 2 One One One 3 3 3 3 2 3 3 2 2 3 2 2 2 3 3 2 One 3 2 2 One 3 2 One One 4 4 4 4 3 4 4 3 3 4 3 3 3 4 4 3 2 4 3 3 2 4 3 2 2 4 3 2 One 4 4 4 2 4 4 2 2 4 2 2 2 4 4 2 One 4 2 One One 4 2 2 One 4 4 4 One 4 4 3 One 4 3 One One

The rank-down of Table 2 is merely an example, and other combinations are possible. In addition, some elements may be missing, or other elements may be added.

The UE can adjust the rank according to the supported rank. For example, when the rank 2 is supported and the HARQ setting information is set to 0 as the rank adjustment index, (2, 2, 2, 1) in Table 2 is used. (3, 2, 2, 2) of Table 2 are used when the HARQ setting information supports the rank 3 and the HARQ setting information sets 2 as the rank adjustment index. 4, and (4, 3, 3, 3) of Table 2 are used when the HARQ setting information sets 2 as the rank adjustment index.

Second Example : Modulation modulation method ( 변조 change scheme )

The modulation order can be considered as the transmission characteristic adjusted at retransmission. The modulation scheme is to apply a lower modulation order to the retransmission block than the initial transmission block.

Only the parity bit of the code block may be included in the retransmission block according to the RV in the IR scheme HARQ. Since the parity bits generally operate more robust in the channel decoding process, it is possible to lower the modulation order of the retransmission block and increase the transmission reliability of the parity bits.

The following table shows an example of modulation modulation scheme.

index Initial transmission First retransmission Second retransmission Third retransmission 0 QPSK QPSK QPSK QPSK One 16QAM 16QAM 16QAM QPSK 2 16QAM 16QAM QPSK QPSK 3 16QAM QPSK QPSK QPSK 4 64QAM 64QAM 64QAM 16QAM 5 64QAM 64QAM 16QAM 16QAM 6 64QAM 16QAM 16QAM 16QAM 7 64QAM 64QAM 16QAM QPSK 8 64QAM 16QAM 16QAM QPSK 9 64QAM 16QAM QPSK QPSK

The table shows exemplary modulation schemes for Quadrature Phase Shift Keying (QPSK), 16-Quadrature Amplitude Modulation (16QAM), and 64QAM, but a lower modulation order (e.g., Binary Phase Shift Keying (BPSK) Or a combination of higher modulation orders (e.g., 256QAM, etc.).

The UE can adjust the modulation order based on the HARQ setting information. For example, if the HARQ setting information sets 0 as the modulation change index, (QPSK, QPSK, QPSK, QPSK) in Table 3 is used. When the HARQ setting information is set to 7 as the modulation change index, (64QAM, 64QAM, 16QAM, QPSK) shown in Table 3 is used.

Third Example : Rank  Down and modulation change method

The rank and the modulation order can be simultaneously considered as the transmission characteristics adjusted at the time of retransmission. This scheme applies a lower rank and / or lower modulation order to the retransmission block than the initial transmission block.

If the rank is lowered, the SNR (Signal-to-Noise Ratio) operating range may be excessively changed. The modulation order is defined to represent the granularity of the operating point. If the modulation order is reduced by one level (e.g., from 16QAM to QPSK), the effective operating range is reduced by 3 dB. This lowers the target BLER (Block Error Rate) and affects the decoding probability of the receiver. Lowering the rank by one may result in a change in the operating range that is much larger than the modulation order being lowered by one level. Therefore, a gain can be obtained by simultaneously considering the change of rank and modulation order.

For example, in order not to cause a change in the excessive operation range, the degree of modulation is increased simultaneously when the rank is lowered. Alternatively, the first retransmission may only lower the modulation order, the second retransmission may only lower the rank, and the third retransmission may lower both the modulation order and the rank. This can reduce the rapid change of the operating range.

The following table shows an example of a rank-down and modulation variation scheme.

index Initial transmission First retransmission Second retransmission Third retransmission 0 Rank 2, QPSK Rank 1, 16QAM Rank 1, QPSK Rank 1, QPSK One Rank 2, 16QAM Rank 2, QPSK Rank 1, 16QAM Rank 1, QPSK 2 Rank 2, 64QAM Rank 2, 16QAM Rank 1, 64QAM Rank 1, 16QAM 3 Rank 2, 64QAM Rank 2, 16QAM Rank 1, 16QAM Rank 1, QPSK 4 Rank 3, QPSK Rank 2, 16QAM Rank 2, QPSK Rank 2, QPSK 5 Rank 3, 16QAM Rank 3, QPSK Rank 2, 16QAM Rank 2, QPSK 6 Rank 3, 16QAM Rank 3, 16QAM Rank 2, 16QAM Rank 2, QPSK 7 Rank 3, 64QAM Rank 3, 16QAM Rank 2, 64QAM Rank 2, 16QAM 8 Rank 3, 64QAM Rank 3, 16QAM Rank 2, 16QAM Rank 1, 16QAM 9 Rank 4, QPSK Rank 4, QPSK Rank 3, 16QAM Rank 2, 16QAM 10 Rank 4, 16QAM Rank 4, QPSK Rank 3, 16QAM Rank 3, QPSK 11 Rank 4, 16QAM Rank 4, 16QAM Rank 3, 16QAM Rank 3, QPSK 12 Rank 4, 16QAM Rank 4, QPSK Rank 3, QPSK Rank 2, QPSK 13 Rank 4, 64QAM Rank 4, 16QAM Rank 3, 64QAM Rank 3, 16QAM 14 Rank 4, 64QAM Rank 4, 16QAM Rank 3, 16QAM Rank 2, 16QAM 15 Rank 4, 64QAM Rank 4, 16QAM Rank 3, 64QAM Rank 2, 64QAM 16 Rank 4, 64QAM Rank 4, 64QAM Rank 3, 16QAM Rank 2, 16QAM

Those skilled in the art will appreciate that the above table is exemplary only and that various ranks (1, 2, 3, 4 ...) and various modulation orders (BPSK, QPSK, 16QAM, 64QAM, 256QAM, Modulation scheme can be constructed.

Fourth Example : Radio resource / transmission power change

Radio resources and / or transmission power may be considered as the transmission characteristics adjusted at the time of retransmission. The HARQ configuration information may include information on a change in radio resources and / or a change in transmission power.

The change in radio resources is to change the amount of radio resources allocated for retransmission. For example, the number of resource blocks allocated to the PUSCH used for retransmission is changed compared to the PUSCH used for the initial transmission. If the modulation order of retransmission is low and a larger number of resource blocks are needed, the number of resource blocks allocated for retransmission can be increased. The HARQ configuration information may include information indicating the number of resource blocks that are changed at the time of retransmission.

The change of the transmission power is to adjust the transmission power according to the retransmission. If the previous transmission failed, the transmission power of the previous transmission may not be appropriate. Therefore, the UE increases the level of the transmission power during retransmission. Alternatively, the receiver may reduce the level of transmission power upon retransmission, assuming that it attempts to decode the retransmission block in combination with the previous transmission. This can be expressed as P _tx = P _init + P _delta . P _tx is the transmission power level, P _init is the initial transmission power level, and P _delta is the retransmission power offset, which may be a negative or positive value. The HARQ setup information may indicate P _delta .

Fifth Example : re-send Diversity

Diversity can be considered as transmission characteristics adjusted at retransmission. As a method for obtaining the diversity effect, constellation rearrangement, subcarrier mapping, and interleaving can be used. The HARQ setup information may include information indicating a scheme for obtaining a diversity effect.

The constellation rearrangement rotates or rearranges the constellation used in the initial transmission so that the same constellation bits in the constellation are mapped to different modulation symbols during retransmission. For example, in BPSK modulation, if bits are mapped onto the constellation I axis during initial transmission, bits are mapped onto the constellation Q axis during retransmission. Each constellation bit may have a different error rate. Therefore, decoding performance can be improved through constellation rearrangement.

Alternatively, UEP (Unequal Error Probability) can be applied to the structural bits and parity bits of the code block. Mapping architectural bits to more reliable storages in the constellation, and mapping parity bits to more reliable storages compared to the structured bits. Alternatively, it is possible to map the structural bits on constellations to more reliable low-cost stores and to map parity bits to more reliable stores in comparison to the structured bits.

The subcarrier mapping used for the initial transmission and the subcarrier mapping used for the retransmission can be different. It is possible to obtain different frequency characteristics depending on the positions of the subcarriers to be allocated. Depending on the number of retransmission attempts, a frequency first or a time first mapping may alternatively be performed. When one resource block includes 7 × 12 resource elements, the frequency-priority mapping maps the 12 frequency subcarriers in the first OFDM symbol to the subcarriers in the next OFDM symbol. The time-aided mapping maps to the first subcarrier of each of the seven OFDM symbols first, and then to the next subcarrier of each of the seven OFDM symbols.

Also, the location of the radio resource may be changed during retransmission. It is possible to define a pattern in which resource blocks allocated at the time of retransmission are arranged and allocate allocated resource blocks according to a pattern defined for each retransmission. The time / frequency diversity gain can be obtained by arranging them in different time or frequency regions for each retransmission according to the pattern of the resource block. The HARQ setting information may include information indicating a pattern of radio resources.

The five embodiments for the above-described adaptive HARQ can be implemented independently of each other, or can be implemented in combination. For example, a rank-down scheme can be applied with a change in transmit power.

8 is a flowchart illustrating a method of performing a synchronization / adaptive uplink HARQ according to another embodiment of the present invention.

In step S810, the BS transmits uplink resource allocation and HARQ setup information to the UE on the PDCCH. Compared to the embodiment of FIG. 7, the HARQ setup information is dynamically transmitted on the PDCCH. Accordingly, the UE can perform the synchronous / adaptive uplink HARQ based on different HARQ configuration information for each HARQ process. A new DCI format may be defined for transmission of HARQ setup information.

In step S820, the MS transmits an initial transmission block to the BS on the PUSCH configured with the uplink resource allocation.

In step S830, the base station determines whether the initial transmission block is erroneous and sends an acknowledgment to the PHICH. The resources used for the transmission of the PHICH are determined from the resources of the PUSCH as described above. Here, it is assumed that an error occurs in the initial transport block and a NACK signal is sent.

In addition to the ACK / NACK signal, the base station may transmit an uplink resource allocation for retransmission to the UE on the PDCCH. At this time, the base station can change the adaptive HARQ setting by transmitting HARQ setting information together. Uplink resource allocation for retransmission may be sent at a different period than PHICH. For example, a base station that receives an initial transmission block in an nth subframe may send an ACK / NACK signal in an n + kth subframe and an uplink resource allocation for retransmission in an n + k + pth subframe have. n is the subframe number used for the initial PUSCH transmission. k is the subframe offset used for the PHICH transmission, and k > 1. p is a subframe offset used for uplink resource allocation for retransmission, and p > = 0.

In step S840, the UE adjusts the transmission characteristics of the retransmission block based on the HARQ setting information.

In step S850, the UE transmits a retransmission block on the PUSCH. At this time, the initial transmission block and the retransmission block are transmitted with a constant HARQ cycle. For example, the HARQ period may be 8 subframes. When the initial transmission block is transmitted in the nth subframe, the retransmission block is transmitted in the (n + 8) th subframe.

Adaptive HARQ is set via dynamic messages. The transmission characteristics can be changed dynamically, and the performance of the adaptive HARQ can be enhanced.

9 is a flowchart illustrating a method of performing a synchronization / adaptive uplink HARQ according to another embodiment of the present invention.

In step S910, the BS transmits an uplink resource allocation to the UE on the PDCCH.

In step S920, the MS transmits an initial transmission block to the BS on the PUSCH configured with the uplink resource allocation.

In step S930, the base station determines whether the initial transmission block is erroneous and sends an acknowledgment to the PHICH. The resources used for the transmission of the PHICH are determined from the resources of the PUSCH as described above. Here, it is assumed that an error occurs in the initial transport block and a NACK signal is sent.

In step S940, the UE adjusts a transmission characteristic of a retransmission block based on HARQ setting information. Compared with the embodiments of FIGS. 7 and 8, the HARQ setting information is not previously notified to the UE but is specified in advance between the Node B and the UE. For example, when the rank-down scheme is used, the initial transmission is designated between the base station and the terminal in advance, such as rank 4, the first retransmission is rank 3, and the second retransmission is rank 2. [ This does not require additional signaling and has the advantage of utilizing the existing structure as it is.

In step S850, the UE transmits a retransmission block on the PUSCH. At this time, the initial transmission block and the retransmission block are transmitted with a constant HARQ cycle. For example, the HARQ period may be 8 subframes. When the initial transmission block is transmitted in the nth subframe, the retransmission block is transmitted in the (n + 8) th subframe.

10 is a block diagram illustrating a terminal and a base station in which an embodiment of the present invention is implemented.

The terminal 1600 includes an HARQ entity 1610 and a physical entity 1620. The physical entity 1620 includes a transmission unit 1621 and a reception unit 1622.

The HARQ entity 1610 performs the operations of the UE for the synchronous / adaptive HARQ in the embodiments of FIGS. 7 to 9 described above. The HARQ entity 1610 adjusts the transmission characteristics of the retransmission based on the HARQ setting information, and instructs the physical entity 1620 to adjust the transmission characteristics.

The transmitting unit 1621 transmits the transmission block, and the receiving unit 1622 receives the acknowledgment ACK / NACK signal for the transmission block. Based on the acknowledgment, the HARQ entity 1610 may instruct the physical entity 1620 to retransmit the transport block.

The base station 1700 includes an HARQ entity 1710 and a physical entity 1720. The physical entity 1720 includes a transmission unit 1721 and a reception unit 1722. The HARQ entity 1710 performs the operations of the base station for the synchronous / adaptive HARQ in the embodiments of FIGS. 7 to 9 described above. The receiving unit 1722 receives the transmission block, and the transmitting unit 1721 transmits the acknowledgment ACK / NACK signal to the transmission block. Based on the acknowledgment, the receiver 1722 may receive the retransmission of the transport block.

The HARQ entities 1610 and 1710 and the physical entities 1620 and 1720 may be implemented in hardware or may be a protocol implemented by a processor (not shown). The protocol is stored in memory (not shown) and is executed by the processor.

11 is a block diagram showing an example of a transmission unit of a terminal. The transmitting unit 1621 supports multiple antennas.

The transmitter 1621 includes a channel encoder 1801, a mapper 1802 and a layer mapper 1803, a precoder 1804 and a signal generator 1805-1 to 1805- . Nt is the number of antenna ports.

The channel encoder 1801 encodes input information bits according to a predetermined coding scheme to generate a transmission block. A mapper 1802 maps each transmission block to a modulation symbol according to a modulation scheme and maps the transmission symbols to modulation symbols having a complex value. The layer mapper 1803 maps the modulation symbols to each layer. The layer may be an information path input to the precoder 1804, and the number of layers corresponds to a value of a rank. The precoder 1804 processes the mapping symbols mapped to the respective layers by a MIMO scheme according to the plurality of antenna ports 1806-1, .., 1806-Nt to output antenna specific symbols. The signal generators 1805-1, ..., 1805-Nt convert the antenna specific symbols into transmission signals and the transmission signals are transmitted through the respective antenna ports 1806-1, ..., 1806-Nt. The signal generators 1805-1, ..., 1805-Nt can perform OFDM modulation.

In the above-described exemplary system, the methods are described on the basis of a flowchart as a series of steps or blocks, but the present invention is not limited to the order of the steps, and some steps may occur in different orders . It will also be understood by those skilled in the art that the steps shown in the flowchart are not exclusive and that other steps may be included or that one or more steps in the flowchart may be deleted without affecting the scope of the invention.

The above-described embodiments include examples of various aspects. While it is not possible to describe every possible combination for expressing various aspects, one of ordinary skill in the art will recognize that other combinations are possible. Accordingly, it is intended that the invention include all alternatives, modifications and variations that fall within the scope of the following claims.

Claims (12)

A method for performing a hybrid automatic repeat request (HARQ) in a wireless communication system,
The UE receiving HARQ configuration information from the base station;
The UE receiving first information on uplink radio resource allocation from the base station;
The UE transmitting an initial transmission block on an uplink data channel using first information on the uplink radio resource allocation from the base station;
Wherein the UE receives an ACK / NACK signal for the initial transmission block on a downlink control channel from the base station, wherein downlink radio resources used for receiving the ACK / And determining from the uplink radio resource used for transmission,
Receiving HARQ setup information updated by the UE from the BS when the received ACK / NACK signal is a NACK signal, and transmitting the updated HARQ setup information together with second information on uplink radio resource allocation Being;
Adjusting a transmission characteristic of a retransmission block for the initial transmission block based on the HARQ configuration information when the received ACK / NACK signal is a NACK signal; And
And transmitting the retransmission block to the base station using second information on the uplink radio resource allocation,
The step of adjusting the transmission characteristics of the retransmission block
Wherein at least one of a rank and a modulation order of retransmission blocks is lower than a rank or modulation order for the initial transmission block according to the number of retransmissions of the initial transmission block. delete delete delete 2. The method of claim 1, wherein the retransmission block is transmitted to the base station in a pre-specified HARQ period. The method of claim 1, wherein the HARQ setup information is received through system information or a Radio Resource Control (RRC) message. The method of claim 1, wherein the HARQ setup information is received together with the uplink resource allocation. The method of claim 1, wherein the uplink data channel is a Physical Uplink Shared Channel (PUSCH) and the downlink control channel is a PHICH (Physical Hybrid-ARQ Indicator Channel). delete delete delete delete

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