WO2008149261A2 - Method and apparatus for hybrid automatic repeat request in a multiple antenna system - Google Patents

Method and apparatus for hybrid automatic repeat request in a multiple antenna system Download PDF

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Publication number
WO2008149261A2
WO2008149261A2 PCT/IB2008/052096 IB2008052096W WO2008149261A2 WO 2008149261 A2 WO2008149261 A2 WO 2008149261A2 IB 2008052096 W IB2008052096 W IB 2008052096W WO 2008149261 A2 WO2008149261 A2 WO 2008149261A2
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WIPO (PCT)
Prior art keywords
signals
base
transmit antennas
repeat request
multiplying
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Application number
PCT/IB2008/052096
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French (fr)
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WO2008149261A3 (en
Inventor
Jia Zhu
Gang Wu
Xun Fan
Ni Ma
Qi Zhou
Xiaobo Zhang
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Koninklijke Philips Electronics N.V.
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Publication of WO2008149261A2 publication Critical patent/WO2008149261A2/en
Publication of WO2008149261A3 publication Critical patent/WO2008149261A3/en

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413—MIMO systems
    • H04B7/0417—Feedback systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
    • H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
    • H04B7/0619—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal using feedback from receiving side
    • H04B7/0621—Feedback content
    • H04B7/0623—Auxiliary parameters, e.g. power control [PCB] or not acknowledged commands [NACK], used as feedback information
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
    • H04B7/0667—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of delayed versions of same signal
    • H04B7/0671—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of delayed versions of same signal using different delays between antennas
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
    • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
    • H04L1/18—Automatic repetition systems, e.g. Van Duuren systems
    • H04L1/1812—Hybrid protocols; Hybrid automatic repeat request [HARQ]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/02—Arrangements for detecting or preventing errors in the information received by diversity reception
    • H04L1/06—Arrangements for detecting or preventing errors in the information received by diversity reception using space diversity
    • H04L1/0618—Space-time coding
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2626—Arrangements specific to the transmitter only
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/0001—Arrangements for dividing the transmission path
    • H04L5/0014—Three-dimensional division
    • H04L5/0023—Time-frequency-space

Definitions

  • the invention relates to a radio communication technology, and more particularly, to a method and apparatus for hybrid automatic repeat request in a multiple antenna system.
  • a Multiple (antenna) Input Multiple (antenna) Output (MIMO) wireless communication system can provide a greater channel capacity.
  • Cyclic Delay Diversity CDD is a relatively simple transmitting diversity technology which provides spatial diversity by transmitting copies of the cyclic delayed data stream via different transmit antennas.
  • the CCD technology may be used in a coded Orthogonal Frequency Division Multiplexing (OFDM) system with multiple transmit antennas, where the spatial diversity is converted into frequency diversity, which may be used by an error correction decoder.
  • OFDM Orthogonal Frequency Division Multiplexing
  • Fig. 1 is a schematic block diagram of a transmitter of a coded CDD-OFDM system with multiple transmit antennas #l ⁇ #n, where the OFDM signals on each transmit antenna branch are delayed by a different cyclic delay A 1 , except for the branch of the first transmit antenna
  • the transmitter shown in Fig. 1 includes the following modules: a Forward Error Correction (FEC) coder 101, an interleaver 102, a modulator 103 and a OFDM processing unit 104. It can be seen from the diagram that the transmitter of such a CDD-OFDM system has a structure substantially the same as that of the transmitter of a traditional SISO OFDM system, with the exception that it additionally comprises multiple transmit antennas and cyclic delay processing.
  • FEC Forward Error Correction
  • the receiver of a CDD-OFDM system may have a structure substantially the same as that of a SISO OFDM system.
  • a typical structure of such a receiver is shown in Fig. 2, where the signal from the receive antenna is processed by a synchronization unit 201, an OFDM unit 202, a channel estimation unit 203, a demodulator 204, a de-interleaver 205 and an FEC decoder 206.
  • the cyclic delay A 1 should be greater than the Channel Impulse Response (CIR).
  • CIR Channel Impulse Response
  • N sub indicates the number of sub-carriers in an OFDM symbol
  • n is the number of transmit antennas, 0 ⁇ i ⁇ n — 1.
  • the Hybrid Automatic Repeat reQuest is an efficient error control technology that combines the Automatic Repeat reQuest (ARQ) and the FEC, which can be used in a coded CDD-OFDM system.
  • Chase combining is one of the HARQ solutions using diversity reception, which implements diversity reception by weighted combination of different copies of a Codeword received.
  • time diversity can be obtained at the receiver. This requires that the interval between two transmissions of the same codeword should be long enough, such that the transmission channel conditions of the two transmissions are different. But in the environment of a slow-fading channel, the transmission delay brought by such a long interval is not acceptable.
  • Another HARQ solution proposes to change the Bit-interleaving mode for different retransmissions (?), so that a signal constellation and frequency diversity can be obtained even if the retransmission channels remain unchanged.
  • a HARQ solution increases the system complexity and cost, because it requires additional read and write control in order to recover the corresponding codeword at the receiver according to an error correction sequence.
  • An object of the invention is to provide a method and apparatus for hybrid automatic repeat request in a multiple antenna system, which provide different and complementary channel conditions in initial transmission and subsequent retransmissions to achieve time diversity.
  • a method of hybrid automatic repeat request for a multiple antenna system comprising the steps of: a) performing base-band processing on signals; b) multiplying the base-band processed signals with a group of predetermined symbols, and initially transmitting the multiplied signals via different transmit antennas; and c) if a repeat request is received, multiplying the base-band processed signals with another group of predetermined symbols, and retransmitting the multiplied signals via the different transmit antennas, such that the signals in the two transmissions have different channel conditions at a receiver.
  • An apparatus for hybrid automatic repeat request for a multiple antenna system comprising: a base-band processing module for base -band processing on signals; and a multiplying module for multiplying the base -band processed signals with a group of predetermined symbols and initially transmitting the multiplied signals via different transmit antennas and, after a repeat request is received, for multiplying the base-band processed signals with another group of predetermined symbols and retransmitting the multiplied signals via the different transmit antennas, such that the signals in the two transmissions have different channel conditions at a receiver.
  • the hybrid automatic repeat request method of the multiple antenna system according to the present invention can obtain different and complementary channel conditions in different transmissions by adding simple multiplication processing, which improves system performance effectively, and which may be used more simply in practical systems due to easy changes in the current structure.
  • Fig.l illustrates a schematic block diagram of a transmitter in a coded CDD-OFDM system of the prior art
  • Fig.2 illustrates a schematic block diagram of a receiver in a coded CDD-OFDM system of the prior art
  • Fig.3 illustrates a general schematic block diagram of the transmitter in a coded CDD-OFDM system utilizing the HARQ solution of the present invention
  • Fig.4 illustrates a schematic block diagram of a dual antenna transmitter in a coded CDD-OFDM system utilizing the HARQ solution of the present invention
  • Fig. 5 illustrates a schematic block diagram of a four antenna transmitter in a coded CDD-OFDM system utilizing the HARQ solution of the present invention.
  • Fig.3 illustrates a general schematic block diagram of a transmitter in a coded CDD-OFDM system utilizing the HARQ solution of the present invention, where the cyclic delay A 1 is suitably selected to obtain complete spatial diversity and remains unchanged during retransmission.
  • the OFDM signals to be transmitted corresponding to different transmitting antennas are multiplied with different symbols n, where the symbol n is "-1" or "+1".
  • the transmitter of the coded CDD-OFDM system utilizing the HARQ solution of the present invention employs a group of multiplying units 105, which is used to multiply the OFDM signals with different symbols n.
  • Fig.4 illustrates a schematic block diagram of a dual antenna transmitter in a coded CDD-OFDM system utilizing the HARQ solution of the present invention, where, in the initial transmission, symbols multiplied in the multiplying units 105 corresponding to the antennas #1 and #2 are (+1, -1) respectively; thus, the present invention has the same implementation effect as the prior art.
  • a NAK signal When the received data cannot be recovered correctly at the receiver, a NAK signal will be fed back to the transmitter to request a retransmission, and then part of or all the initial data will be retransmitted such that the receiver may implement Chase combination to recover the data.
  • the retransmitted data signal will be assigned to a same sub-carrier with the initial transmission signal, and the cyclic delay ⁇ ; remains unchanged. In this case, symbols multiplied in the multiplying units 105 corresponding to antennas #1 and #2 are
  • antenna #1 still transmits a same signal as the output of the OFDM processing unit, while antenna #2 transmits a signal which is generated by the output signal of the OFDM processing unit multiplying "-1" and is (?) then
  • a 1 can be a value — — according to the equation (1), and also
  • n may be one of four possible cases, i.e. (+1, +1), (-1, -1), (+1, -1) and (-1, +1), where the combination (+1, +1) and (-1, -1) has no benefit to the present invention since it has a same effect as in the prior art, and (+1, -1) has an effect equivalent to (-1, +1). Therefore, for a dual antenna transmitter, (+1, -1) and (-1, +1) are all applicable in the initial transmission and the retransmission.
  • Fig. 5 illustrates a schematic block diagram of a four antenna transmitter in a coded CDD-OFDM system utilizing the HARQ solution of the present invention.
  • #2, #3 and #4 are (+1, +1, +1, +1) respectively, which has the same implementation effect as in the prior art.
  • a NAK signal When the receiver cannot recover the received data correctly, a NAK signal will be fed back to the transmitter to request a retransmission, and part or all of the initial data will be retransmitted such that the receiver can implement the Chase combination to recover the data.
  • the retransmitted data signal will be assigned to a same sub-carrier as the initial transmission signal, and the cyclic delay ⁇ ; remains unchanged.
  • symbols multiplied in the multiplying units 105 corresponding to antennas #1, #2, #3 and #4 are (+1, -1, +1, -1) respectively, and if a second retransmission is necessary, it is the symbols (+1, +1, -1, -1) that are to be multiplied.
  • a 1 - A 3 CaH be the values
  • symbol n may be one of sixteen possible cases, where half of the cases have the same implementation effect as the other half.
  • using (+1, -1, +1, -1) and (+1, +1, -1, -1) respectively for the first retransmission and the second retransmission is based on the condition that the transmission channels change slowly to make the retransmission channel and the initial transmission channel complementary to the greatest possible extent.
  • other combinations of symbol n may also be used.
  • the present invention multiplies different symbols with signals on different antenna branches, such that a different and complementary channel condition can be obtained in different transmissions even in an environment of a flat/slow fading channel, which can contribute to the improvement of system performance. Since, compared with the prior art, the present invention only adds a group of multiplying units 105 to the transmitter, and the single antenna receiver of the prior art shown in Fig.
  • the present invention can obtain a better performance improvement without making notable changes to the hardware of the prior art.
  • a multiple antenna receiver may also be used.
  • the multiplying units 105 are located before the cyclic delay, the multiplying units 105 can also be located after the cyclic delay without this leading to a different effect.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Radio Transmission System (AREA)
  • Radar Systems Or Details Thereof (AREA)

Abstract

The present invention proposes a method and apparatus for hybrid automatic repeat request in a multiple antenna system, which improve the system.

Description

method and apparatus for Hybrid automatic repeat request in A Multiple antenna System
Field of the Invention The invention relates to a radio communication technology, and more particularly, to a method and apparatus for hybrid automatic repeat request in a multiple antenna system.
Background of the Invention
Compared with a Single (antenna) Input Single (antenna) Output (SISO) wireless communication system, a Multiple (antenna) Input Multiple (antenna) Output (MIMO) wireless communication system can provide a greater channel capacity. In a MIMO system, Cyclic Delay Diversity (CDD) is a relatively simple transmitting diversity technology which provides spatial diversity by transmitting copies of the cyclic delayed data stream via different transmit antennas. The CCD technology may be used in a coded Orthogonal Frequency Division Multiplexing (OFDM) system with multiple transmit antennas, where the spatial diversity is converted into frequency diversity, which may be used by an error correction decoder. Because it is relatively simple in use, the CDD technology has been taken into consideration as a reference transmit diversity scheme, to be used in a unicast downlink data channel of 3GPP LTE standard. Fig. 1 is a schematic block diagram of a transmitter of a coded CDD-OFDM system with multiple transmit antennas #l~#n, where the OFDM signals on each transmit antenna branch are delayed by a different cyclic delay A1 , except for the branch of the first transmit antenna
#1. To avoid interference between symbols, to each of the OFDM modulated signals should be added a Cyclic Prefix (CP) of a certain length. The transmitter shown in Fig. 1 includes the following modules: a Forward Error Correction (FEC) coder 101, an interleaver 102, a modulator 103 and a OFDM processing unit 104. It can be seen from the diagram that the transmitter of such a CDD-OFDM system has a structure substantially the same as that of the transmitter of a traditional SISO OFDM system, with the exception that it additionally comprises multiple transmit antennas and cyclic delay processing. Since CDD converts a MIMO channel into an equivalent Single (antenna) Input Multiple (antenna) Output (SIMO) channel, the receiver of a CDD-OFDM system may have a structure substantially the same as that of a SISO OFDM system. A typical structure of such a receiver is shown in Fig. 2, where the signal from the receive antenna is processed by a synchronization unit 201, an OFDM unit 202, a channel estimation unit 203, a demodulator 204, a de-interleaver 205 and an FEC decoder 206. To obtain maximum spatial diversity, the cyclic delay A1 should be greater than the Channel Impulse Response (CIR). When the CIR is unknown, one option is:
N
A, = -**- i (1) n where Nsub indicates the number of sub-carriers in an OFDM symbol, and n is the number of transmit antennas, 0 ≤ i ≤ n — 1.
The Hybrid Automatic Repeat reQuest (HARQ) is an efficient error control technology that combines the Automatic Repeat reQuest (ARQ) and the FEC, which can be used in a coded CDD-OFDM system. Chase combining is one of the HARQ solutions using diversity reception, which implements diversity reception by weighted combination of different copies of a Codeword received. When the transmission channels for different copies change significantly, time diversity can be obtained at the receiver. This requires that the interval between two transmissions of the same codeword should be long enough, such that the transmission channel conditions of the two transmissions are different. But in the environment of a slow-fading channel, the transmission delay brought by such a long interval is not acceptable. To solve the above problem, another HARQ solution proposes to change the Bit-interleaving mode for different retransmissions (?), so that a signal constellation and frequency diversity can be obtained even if the retransmission channels remain unchanged. But such a HARQ solution increases the system complexity and cost, because it requires additional read and write control in order to recover the corresponding codeword at the receiver according to an error correction sequence.
Summary of the Invention
An object of the invention is to provide a method and apparatus for hybrid automatic repeat request in a multiple antenna system, which provide different and complementary channel conditions in initial transmission and subsequent retransmissions to achieve time diversity. A method of hybrid automatic repeat request for a multiple antenna system according to the present invention, comprising the steps of: a) performing base-band processing on signals; b) multiplying the base-band processed signals with a group of predetermined symbols, and initially transmitting the multiplied signals via different transmit antennas; and c) if a repeat request is received, multiplying the base-band processed signals with another group of predetermined symbols, and retransmitting the multiplied signals via the different transmit antennas, such that the signals in the two transmissions have different channel conditions at a receiver.
An apparatus for hybrid automatic repeat request for a multiple antenna system according to the present invention, comprising: a base-band processing module for base -band processing on signals; and a multiplying module for multiplying the base -band processed signals with a group of predetermined symbols and initially transmitting the multiplied signals via different transmit antennas and, after a repeat request is received, for multiplying the base-band processed signals with another group of predetermined symbols and retransmitting the multiplied signals via the different transmit antennas, such that the signals in the two transmissions have different channel conditions at a receiver.
Compared with the prior art, the hybrid automatic repeat request method of the multiple antenna system according to the present invention can obtain different and complementary channel conditions in different transmissions by adding simple multiplication processing, which improves system performance effectively, and which may be used more simply in practical systems due to easy changes in the current structure.
Other objects and attainments together with a better understanding of the present invention will become apparent and appreciated by referring to the following descriptions and claims taken in conjunction with the accompanying drawings.
Brief Description of the Drawings
A more detailed description of the invention will be given with reference to the drawings, where:
Fig.l illustrates a schematic block diagram of a transmitter in a coded CDD-OFDM system of the prior art;
Fig.2 illustrates a schematic block diagram of a receiver in a coded CDD-OFDM system of the prior art; Fig.3 illustrates a general schematic block diagram of the transmitter in a coded CDD-OFDM system utilizing the HARQ solution of the present invention;
Fig.4 illustrates a schematic block diagram of a dual antenna transmitter in a coded CDD-OFDM system utilizing the HARQ solution of the present invention; and Fig. 5 illustrates a schematic block diagram of a four antenna transmitter in a coded CDD-OFDM system utilizing the HARQ solution of the present invention.
Throughout the drawings, same labels refer to same, similar or corresponding features or functions.
Detailed Description of the Invention
Fig.3 illustrates a general schematic block diagram of a transmitter in a coded CDD-OFDM system utilizing the HARQ solution of the present invention, where the cyclic delay A1 is suitably selected to obtain complete spatial diversity and remains unchanged during retransmission. In initial transmission and subsequent retransmissions, the OFDM signals to be transmitted corresponding to different transmitting antennas are multiplied with different symbols n, where the symbol n is "-1" or "+1". It can be seen that, compared with the prior art, the transmitter of the coded CDD-OFDM system utilizing the HARQ solution of the present invention employs a group of multiplying units 105, which is used to multiply the OFDM signals with different symbols n. Since MIMO solutions configured with dual transmit antennas and four transmit antennas are mainly considered in 3GPP LTE, the present invention is illustrated in detail by taking transmitters with dual antennas and four antennas as examples. Of course, using the present invention in a system with other numbers of transmit antennas is also feasible and effective. Fig.4 illustrates a schematic block diagram of a dual antenna transmitter in a coded CDD-OFDM system utilizing the HARQ solution of the present invention, where, in the initial transmission, symbols multiplied in the multiplying units 105 corresponding to the antennas #1 and #2 are (+1, -1) respectively; thus, the present invention has the same implementation effect as the prior art. When the received data cannot be recovered correctly at the receiver, a NAK signal will be fed back to the transmitter to request a retransmission, and then part of or all the initial data will be retransmitted such that the receiver may implement Chase combination to recover the data. To achieve complementary channel conditions in the initial transmission and the subsequent retransmission, the retransmitted data signal will be assigned to a same sub-carrier with the initial transmission signal, and the cyclic delay Δ; remains unchanged. In this case, symbols multiplied in the multiplying units 105 corresponding to antennas #1 and #2 are
(+1,-1) respectively when retransmitting, that is, antenna #1 still transmits a same signal as the output of the OFDM processing unit, while antenna #2 transmits a signal which is generated by the output signal of the OFDM processing unit multiplying "-1" and is (?) then
cyclically delayed. Herein, A1 can be a value — — according to the equation (1), and also
can be other values that can result in the largest spatial diversity.
In the environment of dual transmit antennas, the symbol n may be one of four possible cases, i.e. (+1, +1), (-1, -1), (+1, -1) and (-1, +1), where the combination (+1, +1) and (-1, -1) has no benefit to the present invention since it has a same effect as in the prior art, and (+1, -1) has an effect equivalent to (-1, +1). Therefore, for a dual antenna transmitter, (+1, -1) and (-1, +1) are all applicable in the initial transmission and the retransmission.
Fig. 5 illustrates a schematic block diagram of a four antenna transmitter in a coded CDD-OFDM system utilizing the HARQ solution of the present invention. In the initial transmission, symbols multiplied in the multiplying units 105 corresponding to antennas #1,
#2, #3 and #4 are (+1, +1, +1, +1) respectively, which has the same implementation effect as in the prior art.
When the receiver cannot recover the received data correctly, a NAK signal will be fed back to the transmitter to request a retransmission, and part or all of the initial data will be retransmitted such that the receiver can implement the Chase combination to recover the data.
Because of the same reason as described above in the embodiment of the dual transmit antennas, the retransmitted data signal will be assigned to a same sub-carrier as the initial transmission signal, and the cyclic delay Δ; remains unchanged. In this case, in the first retransmission, symbols multiplied in the multiplying units 105 corresponding to antennas #1, #2, #3 and #4 are (+1, -1, +1, -1) respectively, and if a second retransmission is necessary, it is the symbols (+1, +1, -1, -1) that are to be multiplied. Herein, A1 - A3 CaH be the values
— N sub_ ^ — N sub_ an(j — 3N Sjώ_ respectively according to the equation (1), or they can be other
values that can result in complete spatial diversity. In the environment of four transmit antennas, symbol n may be one of sixteen possible cases, where half of the cases have the same implementation effect as the other half. In the above embodiment, using (+1, -1, +1, -1) and (+1, +1, -1, -1) respectively for the first retransmission and the second retransmission is based on the condition that the transmission channels change slowly to make the retransmission channel and the initial transmission channel complementary to the greatest possible extent. However, depending on the actual environment, other combinations of symbol n may also be used.
For a four antenna transmitter, when more than two data retransmissions are necessary, the benefit of the present invention will be more obvious since there are more combinations of symbol n that may be selected to obtain complementary transmission channels. Therefore, in the initial transmission and the subsequent retransmissions using (?) the HARQ procedure, the present invention multiplies different symbols with signals on different antenna branches, such that a different and complementary channel condition can be obtained in different transmissions even in an environment of a flat/slow fading channel, which can contribute to the improvement of system performance. Since, compared with the prior art, the present invention only adds a group of multiplying units 105 to the transmitter, and the single antenna receiver of the prior art shown in Fig. 2 can still be used as the receiver of the present invention, the present invention can obtain a better performance improvement without making notable changes to the hardware of the prior art. Of course, in order to obtain a better effect, a multiple antenna receiver may also be used. Additionally, it should be noted that although the multiplying units 105 are located before the cyclic delay, the multiplying units 105 can also be located after the cyclic delay without this leading to a different effect.
It should be noted that the above embodiments are intended to be illustrative rather than limiting, and it is to be understood by those skilled in the art that various improvements and modifications may be made to the disclosed hybrid automatic repeat request method of the multiple antenna system and the apparatus thereof without departing from the basis of the invention. Therefore, the scope of the present invention is defined by the attached claims. Moreover, the reference numerals in the claims should not be understood as limiting the scope of the claims.

Claims

What is claimed is:
1. A method of hybrid automatic repeat request for a multiple antenna system, comprising the steps of: a) performing base -band processing on signals; b) multiplying the base-band processed signals with a group of predetermined symbols, and initially transmitting the multiplied signals via different transmit antennas; and c) if a repeat request is received, multiplying the base-band processed signals with another group of predetermined symbols, and retransmitting the multiplied signals via the different transmit antennas, such that the signals in the two transmissions have different channel conditions at a receiver.
2. The method according to claim 1, wherein the different channel conditions in step c) are complementary channel conditions.
3. The method according to claim 2, wherein the values of the predetermined symbols are "+l" and "-l".
4. The method according to claim 1, wherein the base-band processing in step a) comprises the processes of forward error correction coding, interleaving, modulation and orthogonal frequency division multiplexing.
5. The method according to claim 1, wherein step b) and step c) further comprise the step of cyclic delaying and adding a cyclic prefix of a certain length to the signals before the signals are transmitted via the transmit antennas.
6. An apparatus for hybrid automatic repeat request for a multiple antenna system, comprising: a) a base-band processing module for base -band processing on signals; and b) a multiplying module for multiplying the base-band processed signals with a group of predetermined symbols and initially transmitting the multiplied signals via different transmit antennas and, after a repeat request is received, for multiplying the base-band processed signals with another group of predetermined symbols and retransmitting the multiplied signals via the different transmit antennas, such that the signals in the two transmissions have different channel conditions at a receiver.
7. The apparatus according to claim 6, wherein the different channel conditions are complementary channel conditions.
8. The apparatus according to claim 7, wherein the values of the predetermined symbols are "+l" and "-l".
9. The apparatus according to claim 6, wherein the base -band processing module comprises the following processing units: a forward error correction coder, an interleaver, a modulator and an orthogonal frequency division multiplexer.
10. The apparatus according to claim 6, further comprises a cyclic delay processing module for cyclically delaying and adding a cyclic prefix of a certain length to the signals before the signals are transmitted via the transmit antennas.
PCT/IB2008/052096 2007-06-06 2008-05-29 Method and apparatus for hybrid automatic repeat request in a multiple antenna system WO2008149261A2 (en)

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CN200710109939 2007-06-06

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