KR20100110753A - Method and apparatus for performing uplink harq in wireless communication system - Google Patents

Abstract

PURPOSE: An apparatus and a method for performing a hybrid automatic repeat request(HARQ) in a wireless communication system are provided to improve the adaptability of the HARQ using a multiple antenna. CONSTITUTION: A terminal receives HARQ setting information from a base station(S710). The base station transmits uplink-resource-allocation to the terminal through a physical downlink control channel(S720). The terminal transmits an initial transmission block through a physical uplink shared channel which is composed of the uplink-resource-allocation(S730). The base station transmits a receipt notification through a physical HARQ by verifying the errors of the initial transmission block(S740). A terminal regulates the transmission characteristic of a re-transmitting block based on the HARQ setting information(S750).

Description

Device and method for performing uplink HARA in wireless communication system {METHOD AND APPARATUS FOR PERFORMING UPLINK HARQ IN WIRELESS COMMUNICATION SYSTEM}

The present invention relates to wireless communication, and more particularly, to an apparatus and method for performing an uplink hybrid automatic repeat request (HARQ) in a wireless communication system.

Error compensation techniques for securing communication reliability include a forward error correction (FEC) scheme and an automatic repeat request (ARQ) scheme. In the FEC scheme, an error at the receiving end is corrected by adding an extra error correction code to the information bits. The FEC method has a low time delay and does not require information to be transmitted and received separately between the transmitter and the receiver, but has a disadvantage in that the system efficiency is poor in a good channel environment. ARQ method can improve the transmission reliability, but it has the disadvantage of incurring time delay and inferior system efficiency in 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 contains an undecodable error, and improves performance by requiring retransmission when an error occurs.

If an error is not detected in the received data, the receiver transmits a positive-acknowledgement (ACK) signal as a reception acknowledgment to inform the transmitter of the reception success. When an error is detected in the received data, the receiver transmits a negative-acknowledgement (NACK) signal as an acknowledgment to notify the transmitter of the error detection. The transmitter may retransmit data when the NACK signal is received.

Long term evolution (LTE), based on the 3rd Generation Partnership Project (3GPP) Technical Specification (TS) Release 8, is a leading next-generation mobile communication standard.

3GPP LTE supports HARQ for both uplink and downlink transmission. The downlink HARQ means that the terminal transmits an ACK / NACK signal for the downlink data when the base station transmits the downlink data. The uplink HARQ means that the base station transmits an ACK / NACK signal for the uplink data when the terminal transmits uplink data.

Recently, a discussion on 3GPP LTE-Advanced (LTE-A), an evolution of 3GPP LTE, is underway. Representative technologies newly added in the LTE-A system include carrier aggregation, relay, and uplink multiple input multiple output (MIMO). Carrier aggregation is used to flexibly expand the available bandwidth. Repeaters increase cell coverage, support group mobility, and enable user-centric network deployment. Uplink MIMO improves the data rate by supporting multiple antennas, whereas LTE supports only a single antenna in uplink transmission.

A technique for improving the performance of HARQ is proposed in 3GPP LTE-A in which a new technology is introduced.

An object of the present invention is to provide a method and apparatus for performing uplink HARQ in a wireless communication system.

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

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

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

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

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

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

In another aspect, a terminal for performing an uplink hybrid automatic repeat request (HARQ) is provided. The terminal includes a transmitter for transmitting an initial transport block or a retransmission block on a physical uplink shared channel (PUSCH), a receiver for receiving an ACK / NACK signal for the initial transport 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 transport block when the ACK / NACK signal is a NACK signal, and rank used for transmission of the retransmission block. And at least one of a modulation order lower than a rank and a modulation order used for transmission of the initial transport block.

The transmitter may transmit the retransmission block to the base station in a predetermined HARQ period.

As multiple antennas are introduced, HARQ can be adaptively performed to increase the efficiency of the system.

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 an asynchronous downlink HARQ in 3GPP LTE.
5 shows an example of channel coding in 3GPP LTE.
6 is a flowchart showing the configuration of a PHICH.
7 is a flowchart illustrating a method of performing synchronous / adaptive uplink HARQ according to an embodiment of the present invention.
8 is a flowchart illustrating a method of performing synchronous / adaptive uplink HARQ according to another embodiment of the present invention.
9 is a flowchart illustrating a method of performing synchronous / 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 illustrating 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 (BS) 11. Each base station 11 provides a communication service for a particular geographic area (generally called a cell) 15a, 15b, 15c. The cell may again be divided into multiple regions (referred to as sectors).

The user equipment (UE) 12 may be fixed or mobile, and may include a mobile station (MS), a mobile terminal (MT), a user terminal (UT), a subscriber station (SS), a wireless device, and a PDA. (personal digital assistant), wireless modem (wireless modem), a handheld device (handheld device) may be called other terms.

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

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

2 shows a structure of a radio frame in 3GPP LTE. It may 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 consists of 10 subframes indexed from 0 to 9, and one subframe consists of two slots. The time it takes for one subframe to be transmitted is called a transmission time interval (TTI). For example, one subframe may have a length of 1 ms and one slot may have a length of 0.5 ms.

One slot may include a plurality of orthogonal frequency division multiplexing (OFDM) symbols in the time domain. Since OFDM symbols use orthogonal frequency division multiple access (OFDMA) in downlink, the OFDM symbols are only intended to represent one symbol period in the time domain, and the limitation on the multiple access scheme or name is not limited. no. For example, the OFDM symbol may be called another name such as a single carrier frequency division multiple access (SC-FDMA) symbol, a symbol period, and the like.

Although one slot includes seven OFDM symbols as an example, the number of OFDM symbols included in one slot may vary according to the length of a cyclic prefix (CP). According to 3GPP TS 36.211 V8.5.0 (2008-12), one subframe includes 7 OFDM symbols in a normal CP and one subframe includes 6 OFDM symbols in an extended CP. 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). It may include.

The subframe is divided into a control region and a data region in the 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. PDCCH is allocated to the control region and PDSCH is allocated to the data region.

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

Control information transmitted through the PDCCH is called downlink control information (DCI). DCI may include resource allocation of PDSCH (also called downlink grant), resource allocation of PUSCH (also called uplink grant), collection of transmit power control commands for individual UEs in any UE group, and / or It may include the activation of Voice over Internet Protocol (VoIP).

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

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

3GPP LTE uses synchronous HARQ in uplink transmission and asynchronous HARQ in downlink transmission. Synchronous HARQ means that retransmission timing is fixed, and asynchronous HARQ does not have fixed retransmission timing. That is, in the synchronous HARQ, initial transmission and retransmission are performed at a constant HARQ period.

3 shows a synchronous uplink HARQ in 3GPP LTE.

The terminal receives an initial uplink resource allocation on the PDCCH 310 in the nth subframe from the base station.

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

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

The terminal receiving the NACK signal transmits a retransmission block on the PUSCH 340 in the n + 12th subframe.

The base station transmits an ACK / NACK signal for the uplink transport block on the PHICH 351 in the n + 16th subframe.

After initial transmission in the n + 4th subframe, since retransmission is performed in the n + 12th subframe, synchronous HARQ is performed using 8 subframes as the HARQ period.

Eight HARQ processes may be performed in 3GPP LTE, and each HARQ process is indexed from 0 to 7. The above example shows that HARQ is performed at HARQ process index 4.

4 shows an asynchronous downlink HARQ in 3GPP LTE.

The base station transmits a downlink transport block to the UE on the PDSCH 412 indicated by downlink resource allocation on the PDCCH 411 in the nth subframe.

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

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

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

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

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

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

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

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

In step S110, the 1-bit ACK / NACK signal performs channel coding using repetition coding at a code rate 1/3. In step S120, the ACK / NACK signal coded with a 3-bit codeword is mapped to three modulation symbols through Binary Phase Shift Keying (BPSK) modulation. In step S130, modulation symbols are spread using a Spreading Factor (SF) N ^PHICH _SF and an orthogonal sequence. 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 section 6.9 of 3GPP TS 36.211 V8.5.0 (2008-12), the PHICH resource corresponding to the PUSCH is assigned to the lowest Physical Resource Block (PRB) index I ^{lowest _ index} _{PRB _ RA} and the PUSCH of the resource used for the PUSCH. It is defined using the cyclic shift n _DMRS of the data demodulation reference signal used. The demodulation reference signal refers to a reference signal used for demodulation of data transmitted on the PUSCH. More specifically, PHICH resources are known by index pairs (n ^group _PHICH , n ^seq _PHICH ). n ^group _PHICH is a PHICH group number, n ^seq _PHICH is an orthogonal sequence index in the PHICH group, and is given as follows.

Where 'mod' represents a modulo operation.

n ^group _PHICH has a value between 0 and (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.

Orthogonal sequences used in the 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 control signaling overhead. Second, the complexity of performing HARQ can be reduced.

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

Adaptive HARQ is a method 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 can be adaptively retransmitted according to channel conditions, thereby increasing the probability of success in retransmission.

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

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

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

In step S730, the terminal transmits an initial transmission block (initial transmission block) to the base station on the PUSCH configured by the uplink resource allocation.

In step S740, the base station determines whether the initial transport block is an error, and sends an acknowledgment on the PHICH. The resource used for transmission of the PHICH is determined from the resources of the PUSCH as described above. In this case, it is said that an error of the initial transport block occurs and sends a NACK signal.

In step S750, the terminal adjusts the transmission characteristics of the retransmission block (retransmission block) based on the HARQ configuration information. The adjusted transmission characteristics may be rank, modulation order, resource block size, 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 transport block and the retransmission block is transmitted in a constant HARQ period. For example, the HARQ period may be 8 subframes. When the initial transport block is transmitted in the nth subframe, the retransmission block is transmitted in the n + 8th subframe.

Here, although one retransmission is described, up to M (M> 1) retransmissions may be performed when a NACK signal is received. For each retransmission, transmission specification may be adaptively adjusted based on HARQ configuration information.

Adaptive HARQ is set via a semi-static message, such as a higher layer message. HARQ retransmission can be applied to reduce signaling overhead and to allow the receiver to have better decoding performance.

Now, the proposed adaptive HARQ scheme will be described. For synchronous / adaptive uplink HARQ, the following adaptive scheme may be considered.

Adaptive HARQ is to change the transmission characteristics in retransmission compared to the initial transmission. The changed transmission characteristic includes 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, no change is taken into account for channel coding for the retransmission block. That is, it is assumed that the structural bits and parity bits of the code block are not changed even when retransmitted. However, if higher coding gain is required, then a change in channel coding may be considered.

First Example : Rank  Down method ( rank down scheme )

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

Since the existing 3GPP LTE only considers a single transmission antenna in the uplink, only a rank 1 is possible, and therefore, the same rank must always be applied. If uplink transmission uses antennas of multiple transmissions, the rank may be changed.

High rank is vulnerable to channel variation. The lower the rank, the lower the transmission rate but the higher the transmission reliability. In addition, the rank down scheme may be efficient because the rank down method is not affected by the channel change even if the retransmission is greatly delayed due to the relatively long HARQ period in the synchronous HARQ.

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

Supported rank Initial transfer Resend first Second resend 3rd resend 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 terminal may adjust the rank according to the rank supported. For example, when supporting the rank 2 and the HARQ configuration information is set to 0 as the rank adjustment index, (2, 2, 2, 1) of Table 2 is used. If the rank 3 is supported and the HARQ configuration information is set to 2 as the rank adjustment index, (3, 2, 2, 2) of Table 2 is used. If the rank 4 is supported and the HARQ configuration information is set to 2 as the rank adjustment index, (4, 3, 3, 3) of Table 2 is used.

2nd Example : Modulation change method ( modulation change scheme )

Modulation order may be considered as a transmission characteristic adjusted during retransmission. The modulation change scheme is to apply a lower modulation order to the retransmission block than the initial transport block.

Only parity bits of the code block may be included in the retransmission block according to RV in the HARQ of the IR scheme. Since the parity bits generally operate more robustly during the channel decoding process, the transmission reliability of the parity bits can be improved by lowering the modulation order of the retransmission block.

The following table shows an example of the modulation change method.

index Initial transfer Resend first Second resend 3rd resend 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 above shows exemplary modulation change schemes for Quadrature Phase Shift Keying (QPSK), 16-Quadrature Amplitude Modulation (16QAM), 64QAM, but lower modulation orders (e.g., Binary Phase Shift Keying (BPSK), etc.) Alternatively, higher modulation orders (eg, 256QAM, etc.) may be combined.

The terminal may adjust the modulation order based on the HARQ configuration information. For example, if HARQ configuration information is set to 0 as a modulation change index, (QPSK, QPSK, QPSK, QPSK) shown in Table 3 is used. If HARQ configuration information is set to 7 as the modulation change index, (64QAM, 64QAM, 16QAM, QPSK) shown in Table 3 is used.

The third Example : Rank  Down and modulation change scheme

Rank and modulation order may be considered simultaneously as transmission characteristics adjusted for retransmission. This approach is to apply a lower rank and / or a lower modulation order to the retransmission block than the initial transport block.

If the rank is lowered, the signal-to-noise ratio (SNR) operating range may be excessively changed. The modulation order is defined to represent the granularity of the operating point. When the modulation order is one level lower (eg from 16QAM to QPSK), the effective operating range is reduced by 3dB. This lowers the target block error rate (BLER), which affects the decoding probability of the receiver. If the rank is lowered by one, it can cause a change in the operating range that is much larger than the modulation order is lowered by one level. Therefore, a gain can be obtained by considering the change in rank and modulation order simultaneously.

For example, in order not to bring about an excessive change in the operating range, the modulation order is increased at the same time as the rank is lowered. Alternatively, only the modulation order may be lowered for the first retransmission, the second retransmission may lower only the rank, and the third retransmission may lower both the modulation order and the rank. This can reduce the sudden change in the operating range.

The following table shows an example of the rank down and modulation change scheme.

index Initial transfer Resend first Second resend 3rd resend 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

The above table is merely an example, and those skilled in the art can combine various ranks (1, 2, 3, 4 ...) with various modulation orders (BPSK, QPSK, 16QAM, 64QAM, 256QAM, ...) for various rank down and Modulation changes can be configured.

Fourth Example : Radio resource / transmission power change

Radio resources and / or transmission power may be considered as transmission characteristics adjusted for retransmission. The HARQ configuration information may include information about a change in radio resources and / or a change in transmit 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 a PUSCH used for retransmission is changed compared to a PUSCH used for initial transmission. If the modulation order of the retransmission is lowered and a larger number of resource blocks are required, the number of resource blocks allocated to the retransmission may be increased. The HARQ configuration information may include information indicating the number of resource blocks that are changed during retransmission.

The change in transmit power is to adjust the transmit power according to retransmission. If the previous transmission failed, the transmission power of the previous transmission may not be suitable. Therefore, the terminal increases the level of transmission power during retransmission. Or, assuming the receiver attempts to decode the retransmission block in combination with the previous transmission, the level of transmit power may be reduced upon retransmission. This can be expressed as P _tx = P _init + P _delta . P _tx is a transmit power level, P _init is an initial transmit power level, P _delta is a retransmission power offset, and may be negative or positive. HARQ configuration information may indicate P _delta .

5th Example : re-send Diversity

Diversity may be considered as a transmission characteristic adjusted during retransmission. As a method for obtaining the diversity effect, constellation rearrangement, subcarrier mapping, and interleaving may be used. The HARQ configuration information may include information indicating a method for obtaining diversity effect.

Constellation rearrangement is to rotate or rearrange constellations used for initial transmission, such that constellation bits of the same constellation are mapped to different modulation symbols upon retransmission. For example, in the case of BPSK modulation, when the bit is mapped to the I axis of the constellation during initial transmission, the bit is mapped to the Q axis of the constellation upon retransmission. Each constellation bit may have a different error rate. Therefore, constellation rearrangement can improve decoding performance.

Alternatively, Unequal Error Probability (UEP) may be applied to structural bits and parity bits of a code block. It is to map structural bits to more reliable constellation points in the constellation and to map parity bits to more reliable constellation points than structural bits. Alternatively, structural bits may be mapped to more reliable constellation points in the constellation, and parity bits may be mapped to more reliable constellation points than structural bits.

Subcarrier mapping used for initial transmission and subcarrier mapping used for retransmission may be different. This is because different frequency characteristics can be obtained depending on the position of the allocated subcarriers. Depending on the number of retransmission attempts, frequency first or time first mapping may be alternately performed. When one resource block includes 7 × 12 resource elements, frequency first mapping is to first map to 12 subcarriers in the first OFDM symbol and then to subcarriers of the next OFDM symbol. The time-first mapping is to first map to the first subcarrier of each of the seven OFDM symbols and then to the next subcarrier of each of the seven OFDM symbols.

In addition, the position of the radio resource may be changed during retransmission. A pattern in which allocated resource blocks are allocated in retransmission may be defined, and an allocated resource block may be arranged according to a defined pattern for each retransmission. According to the pattern of the resource block, time / frequency diversity gain can be obtained by disposing in different time or frequency domains for each retransmission. The HARQ configuration information may include information indicating a pattern of radio resources.

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

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

In step S810, the base station transmits uplink resource allocation and HARQ configuration information to the terminal on the PDCCH. In comparison with the embodiment of FIG. 7, HARQ configuration information is dynamically delivered on the PDCCH. Accordingly, the UE may perform synchronous / adaptive uplink HARQ based on different HARQ configuration information for every HARQ process. A new DCI format may be defined for transmission of HARQ configuration information.

In step S820, the terminal transmits an initial transmission block (initial transmission block) to the base station on the PUSCH configured by the uplink resource allocation.

In step S830, the base station determines whether the initial transport block is an error, and sends an acknowledgment on the PHICH. The resource used for transmission of the PHICH is determined from the resources of the PUSCH as described above. In this case, it is said that an error of the initial transport block occurs and sends a NACK signal.

In addition to the ACK / NACK signal, the base station may transmit uplink resource allocation for retransmission to the terminal on the PDCCH. At this time, the base station may change the adaptive HARQ configuration by sending the HARQ configuration information. Uplink resource allocation for retransmission may be sent in a different period from the PHICH. For example, the base station receiving the initial transport block in the n-th subframe may send an ACK / NACK signal in the n + k-th subframe, and uplink resource allocation for retransmission in the n + k + p-th subframe. have. n is a subframe number used for initial PUSCH transmission. k is a subframe offset used for PHICH transmission and k> 1. p is a subframe offset used for uplink resource allocation for retransmission, and p> = 0.

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

In step S850, the terminal transmits a retransmission block on the PUSCH. At this time, the initial transport block and the retransmission block is transmitted in a constant HARQ period. For example, the HARQ period may be 8 subframes. When the initial transport block is transmitted in the nth subframe, the retransmission block is transmitted in the n + 8th subframe.

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

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

In step S910, the base station transmits uplink resource allocation to the terminal on the PDCCH.

In step S920, the terminal transmits an initial transmission block to the base station on the PUSCH configured with the uplink resource allocation.

In step S930, the base station determines whether the initial transport block is an error, and sends an acknowledgment on the PHICH. The resource used for transmission of the PHICH is determined from the resources of the PUSCH as described above. In this case, it is said that an error of the initial transport block occurs and sends a NACK signal.

In step S940, the terminal adjusts the transmission characteristics of the retransmission block based on the HARQ configuration information. In comparison with the embodiments of FIGS. 7 and 8, the HARQ configuration information is specified in advance between the base station and the terminal rather than the base station notifying the terminal. 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 a separate signaling, there is an advantage that can use the existing structure as it is.

In step S850, the terminal transmits a retransmission block on the PUSCH. At this time, the initial transport block and the retransmission block is transmitted in a constant HARQ period. For example, the HARQ period may be 8 subframes. When the initial transport block is transmitted in the nth subframe, the retransmission block is transmitted in the n + 8th 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 object 1620 includes a transmitter 1621 and a receiver 1622.

The HARQ entity 1610 performs an operation of a terminal for synchronous / adaptive HARQ in the above-described embodiment of FIGS. 7 to 9. The HARQ entity 1610 adjusts the transmission characteristics of the retransmission based on the HARQ configuration information and indicates this to the physical entity 1620.

The transmitter 1621 transmits a transport block, and the receiver 1622 receives an ACK / NACK signal that is an acknowledgment for the transport block. Based on the acknowledgment, the HARQ entity 1610 can instruct the physical entity 1620 to retransmit the transport block.

The base station 1700 includes a HARQ entity 1710 and a physical entity 1720. The physical object 1720 includes a transmitter 1721 and a receiver 1722. The HARQ entity 1710 performs an operation of a base station for synchronous / adaptive HARQ in the above-described embodiment of FIGS. 7 to 9. The receiver 1722 receives a transport block, and the transmitter 1721 transmits an ACK / NACK signal that is an acknowledgment for the transport block. Based on the acknowledgment, the receiver 1722 may receive 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 protocols implemented by a processor (not shown). The protocol is stored in memory (not shown) and executed by a processor.

11 is a block diagram illustrating an example of a transmission unit of a terminal. The transmitter 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, ..., 1805-Nt. It includes. Nt is the number of antenna ports.

The channel encoder 1801 generates a transport block by encoding input information bits according to a predetermined coding scheme. The mapper 1802 maps each transport block into constellations according to a modulation scheme and maps them to modulation symbols having complex values. The layer mapper 1803 maps modulation symbols to each layer. The layer may be referred to as an information path input to the precoder 1804, and the number of layers corresponds to a rank value. The precoder 1804 processes the mapping symbols mapped to each layer by a MIMO method according to the plurality of antenna ports 1806-1,..., 1802-Nt, and outputs 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 each antenna port 1806-1,. The signal generators 1805-1,..., 1805-Nt may perform OFDM modulation.

In the exemplary system described above, the methods are described based on a flowchart as a series of steps or blocks, but the invention is not limited to the order of steps, and certain steps may occur in a different order or concurrently with other steps than those described above. Can be. In addition, those skilled in the art will appreciate that the steps shown in the flowcharts are not exclusive and that other steps may be included or one or more steps in the flowcharts may be deleted without affecting the scope of the present 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)

In the method for performing uplink hybrid automatic repeat request (HARQ) in a wireless communication system,
The terminal receives the HARQ configuration information from the base station,
The terminal receives an uplink resource allocation from the base station,
The terminal transmits an initial transport block on an uplink data channel by using the uplink resource allocation from the base station,
The terminal receives an ACK / NACK signal for the initial transport block from the base station, the radio resources used for the transmission of the ACK / NACK signal is determined from the radio resources used for the transmission of the uplink data channel,
When the ACK / NACK signal is a NACK signal, adjust transmission characteristics of a retransmission block for the initial transport block based on the HARQ configuration information, and
Transmitting the retransmission block to the base station. The method of claim 1, wherein the transmission characteristic of the retransmission block is at least one of rank, modulation order, number of resource blocks, and transmission power. The method of claim 2, wherein the HARQ configuration information is set to lower the rank of the retransmission block than the rank of the initial transport block. The method of claim 2, wherein the HARQ configuration information is set to lower a modulation order of the retransmission block than a modulation order of the initial transport block. The method of claim 1, wherein the retransmission block is transmitted to the base station in a predetermined HARQ period. The method of claim 1, wherein the HARQ configuration information is received through system information or a Radio Resource Control (RRC) message. The method of claim 1, wherein the HARQ configuration 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 Physical Hybrid-ARQ Indicator Channel (PHICH). In the terminal for performing an uplink HARQ (hybrid automatic repeat request),
A transmitter for transmitting an initial transport block or a retransmission block on a physical uplink shared channel (PUSCH);
A receiver configured to receive an ACK / NACK signal for the initial transport block on a Physical Hybrid-ARQ Indicator Channel (PHICH); And
Include a hybrid automatic repeat request (HARQ) object,
The HARQ entity indicates the transmission of the retransmission block for the initial transport block when the ACK / NACK signal is a NACK signal, and at least one of a rank and a modulation order used for transmission of the retransmission block is included in the initial transport block. A terminal lower than the rank and modulation order used for transmission. The terminal of claim 9, wherein the transmitter transmits the retransmission block to the base station in a predetermined HARQ period. 10. The terminal of claim 9, wherein the transmitter transmits a plurality of retransmission blocks, the HARQ entity lowers the modulation order of the first retransmission block, and lowers the rank of the second retransmission block. The terminal of claim 9, wherein the HARQ entity adjusts at least one of a number of resource blocks and a transmission power used for transmission of the retransmission block.

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