KR101253175B1

KR101253175B1 - hybrid automatic repeat request method using adaptive mapper and transmitter using the same

Info

Publication number: KR101253175B1
Application number: KR1020060107442A
Authority: KR
Inventors: 박형호; 오민석; 성두현; 최진수; 정재훈; 문성호; 임빈철; 조기형; 강승현
Original assignee: 엘지전자 주식회사
Priority date: 2006-08-07
Filing date: 2006-11-01
Publication date: 2013-04-10
Also published as: KR20080013682A; EP2057772A1; EP2057772A4; KR101299911B1; KR101287272B1; WO2008018742A1; KR20080013662A; KR20080013661A

Abstract

The present invention relates to a method for complex automatic retransmission in a multiple codeword multi-antenna system, the method comprising: transmitting a plurality of transmission symbols for a multiple codeword, receiving a retransmission request signal for the transmission symbols, and retransmitting And transmitting a plurality of retransmission symbols that adaptively remap the plurality of transmission symbols to each other according to a request signal. Adaptive remapping may be performed by exchanging, replacing, and interchanging bit data of a plurality of symbol symbols, or by circularly delaying a plurality of retransmission symbols in a predetermined unit.

Compound Auto Retransmission, Mapper, Diversity, MIMO, HARQ

Description

Hybrid automatic repeat request method using adaptive mapper and transmitter using the same}

1 is a block diagram illustrating a communication system according to an embodiment of the present invention.

FIG. 2 is a flowchart illustrating a composite automatic retransmission method using the communication system of FIG. 1.

3A and 3B are exemplary diagrams illustrating an arrangement of retransmission symbols according to an embodiment of the present invention.

4A and 4B are exemplary diagrams illustrating an arrangement of retransmission symbols according to another embodiment of the present invention.

5A and 5B are exemplary diagrams illustrating an arrangement of retransmission symbols according to another embodiment of the present invention.

6A and 6B are exemplary diagrams illustrating an arrangement of retransmission symbols according to another embodiment of the present invention.

7A and 7B are exemplary diagrams illustrating an arrangement of retransmission symbols according to another embodiment of the present invention.

8A and 8B are exemplary views illustrating a composite automatic retransmission method according to another embodiment of the present invention.

9 is an exemplary view showing a composite automatic retransmission method according to another embodiment of the present invention.

10 is a block diagram showing a transmitter according to another embodiment of the present invention.

11 shows an example of a retransmission symbol.

12 is a block diagram illustrating an embodiment of a transmitter using OFDM.

13 is a block diagram illustrating another embodiment of a transmitter using OFDM.

14 is a block diagram showing a transmitter according to another embodiment of the present invention.

15 shows an example of a retransmission symbol.

FIG. 16 is a signal flowchart illustrating a process of performing complex automatic retransmission of a chase combining method in a multi-codeword multi-antenna system.

FIG. 17 is a signal flow diagram illustrating a process of performing complex automatic retransmission of an IR scheme in a multiple codeword multiple antenna system.

18 is a conceptual diagram illustrating a complex retransmission method using multiple antennas in a multi-user environment.

** Explanation of symbols in main part of drawing **

100: Transmitter

200: receiver

120: adaptive mapper

130: spatial encoder

The present invention relates to a composite automatic retransmission method and a transmitter using the same, and more particularly, to a composite automatic retransmission method using an adaptive mapper and a transmitter using the same.

With the emergence of various multimedia services and high quality services, information communication services are required to guarantee high quality data and differential quality of service (QoS).

Diversity techniques for transmitting the same data repeatedly have been developed to secure communication reliability. If multiple signals are transmitted independently of each other via diversity, even if signals of some paths are received low, signals of the other paths may have large values. Therefore, the diversity technique is to achieve stable transmission and reception by combining a plurality of signals. Types of diversity include frequency diversity for transmitting signals at different frequencies, time diversity for transmitting signals at different points of time, and spatial diversity using a plurality of transmission antennas. diversity).

A system employing spatial diversity is generally referred to as a multiple-input multiple-output (MIMO) system because it includes a plurality of transmit and receive antennas. Types of space diversity include space-time transmit diversity (STTD) and vertical-bell laboratories layered space-time (V-BLAST). The STTD scheme transmits the same data through respective transmit antennas. The V-BLAST scheme transmits different data through respective transmit antennas. Examples of spatial diversity include S. M. Alamouti, A Simple Transmit Diversity Technique for Wireless Communications, IEEE J. Selec. Areas Commun., Vol. 16, pp. 1451-1458, Oct. See 1998.

Meanwhile, another repetitive transmission scheme is an automatic repeat request (ARQ) scheme. The ARQ method retransmits data when an error occurs in the transmitted data. ARQ methods include stop and wait (SAW), go-back-N (GBN), and selective repeat (SR). The ARQ method has a time delay and a poor system efficiency in a poor channel environment. To solve these shortcomings, a hybrid automatic repeat request (HARQ) method combining forward error correction (FEC) and ARQ is proposed. HARQ improves performance by requiring retransmission when the received data contains errors that cannot be decoded.

In general, HARQ can be classified into Type I, Type II, and Type III. Type I discards the data from which an error was detected and requires retransmission of new data. Type II combines retransmitted data with previous data without discarding the data from which an error was detected. The retransmitted data and the previous data may have different code rates or modulation schemes. Type III differs from Type II in that the retransmitted data is a self-decodable code. That is, the retransmitted data can be decoded without combining with previous data.

Alternatively, HARQ may be classified into chase combining and incremental redundancy (IR). Chase combining is a modified method of Type I, which combines the retransmitted data without discarding the data where the error is detected. IR refers to the Type II or Type III scheme. The difference between chase combining and IR is that chase combining retransmits the same data, whereas IR incrementally transmits additional redundant information. Distinguishing between Type II and Type III, Type II is also known as full IR and Type III is partial IR.

For examples of HARQ, see S. Lin, D.J. Costello, M.J. Miller, Automatic repeat request error control schemes, IEEE Communications Magazine, Vol. 22, no. 12, pp. 5-17, Dec. 1984 and D. Chase, Code Combining: A maximum-likelihood decoding approach for combining an arbitrary number of noisy packets, IEEE Trans. on Commun., Vol. 33, pp. 593-607, May 1985.

Although the HARQ scheme uses a retransmission scheme, there is no spatial diversity gain when using one transmit / receive antenna. Therefore, in slow fading in which a channel changes slowly, an error may not be corrected because retransmitted signals undergo similar channels again even when retransmitted.

Since the spatial diversity scheme using multiple antennas is designed under the assumption that the channel does not change during retransmission, inter-symbol interference may occur due to the channel change in fast fading in which the channel changes rapidly. Therefore, a method of increasing the reliability of the communication system is required.

The present invention reflects the above needs, and an object of the present invention is to provide a method for performing complex automatic retransmission through adaptive mapping in a multi-antenna system using multiple codewords and a transmitter supporting the same.

An aspect of the present invention relates to a complex automatic retransmission method in a multi-antenna system, the method comprising: transmitting a plurality of transmission symbols for multiple codewords, receiving a retransmission request signal for the transmission symbols, and retransmitting And transmitting a plurality of retransmission symbols remapping the plurality of transmission symbols with each other according to a request signal.

Another aspect of the present invention relates to a transmitter for supporting complex automatic retransmission in a multi-antenna system, comprising: a plurality of antennas, a modulator connected to the antennas, and a plurality of transmissions for multiple codewords transmitted through the antennas An adaptive mapper that maps symbols to a predetermined modulation scheme and spatially remaps the plurality of transmitted symbols to each other in response to a retransmission request, and is disposed between the modulator and the antennas to cyclically map the transmitted symbols The apparatus may further include a delayed time delay or a phase delayer disposed between the adaptive mapper and the modulator to cyclically delay the phase of the transmission symbol.

In the above two aspects, the remapping is performed by exchanging, replacing, and crossing bit data of the plurality of transmission symbols with each other.

The adaptive mapper may determine the remapping scheme according to the channel quality information fed back from the receiver in the closed loop system, or may arbitrarily determine the remapping scheme in the open loop system.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like reference numerals designate like elements throughout the specification.

The following techniques can be used in various communication systems. The communication system is widely deployed to provide various communication services such as voice, packet data and the like. This technique can be used for downlink or uplink. The downlink means communication from a base station (BS) to a mobile station (MS), and the uplink means communication from a terminal to a base station. A base station generally refers to a fixed station that communicates with a terminal and may be referred to as other terminology, such as a node-B, a base transceiver system (BTS), or an access point. . The terminal may be fixed or mobile and may be referred to by other terms such as user equipment (UE), user terminal (UT), subscriber station (SS), wireless device (wireless device), and the like.

The present invention can be used in single-carrier or multi-carrier communication systems. Multi-carrier systems can utilize orthogonal frequency division multiplexing (OFDM) or other multi-carrier modulation techniques. OFDM divides the overall system bandwidth into multiple orthogonal frequency subbands (or carriers). Single-carrier systems can utilize single-carrier modulation techniques such as single-carrier frequency division multiple access (SC-CDMA) and code division multiple access (CDMA).

Referring to FIG. 1, a communication system includes a transmitter 100 and a receiver 200. Here, the transmitter 100 and the receiver 200 may be referred to as a transceiver that performs both a transmission function and a reception function. However, in order to clarify the description of data retransmission, one of the data transmission and retransmission is called a transmitter, and the other receiving the data and requesting retransmission is called a receiver.

In the downlink, transmitter 100 may be part of a base station, and receiver 200 may be part of a terminal. In the uplink, transmitter 100 may be part of a terminal and receiver 200 may be part of a base station. The base station may include a plurality of receivers and a plurality of transmitters. The terminal may include a plurality of receivers and a plurality of transmitters.

In a communication system using a multiple codeword (MCW) system, the transmitter 100 includes N (N ≥ 1) channel encoders 110-1, ..., 110-N, N adaptations. An adaptive mapper 120-1,..., 120 -N, a spatial encoder 130, a controller 150, and a receive circuitry 180. In addition, the transmitter 100 includes N _t (N _t ≧ 1) antennas 190-1,..., 190 -N _t .

The channel encoders 110-1,..., 110 -N receive N (1 ^st ~ N ^th ) different sets of streams of information bits in parallel and input them in a predetermined coding scheme. By encoding according to the coded data (coded data) is formed. Coding schemes applied to the respective information bits are independent of each other, and different coding schemes may be applied. The information bits can include text, voice, video or other data. The channel encoders 110-1,..., 110 -N may add error detection bits such as a cyclic redundancy check (CRC) to each of the information bits, and add an extra code for error correction. The error correction code may be a turbo code. The turbo code is a structural code that includes information bits as structural bits. In the case of turbo codes with a code rate of 1/3, two parity bits are allocated to one structural bit. However, the technical concept of the present invention can be applied to an LDPC (low density parity check code) or other convolutional codes as well as the error correction code.

The adaptive mapper 120-1,..., 120 -N modulates the coded data of each information bit stream according to a predetermined modulation scheme to provide modulation symbols. Each of the encoded data is mapped to symbols representing positions according to amplitude and phase constellation by corresponding adaptive mappers 120-1, ..., 120-N. The modulation scheme is not limited, and may be m-quadrature phase shift keying (m-PSK) or m- quadrature amplitude modulation (m-QAM). For example, m-PSK may be BPSK, QPSK, or 8-PSK. The m-QAM may be 16-QAM, 64-QAM, or 256-QAM. In the case of the QPSK scheme, the adaptive mapper 120-1,..., 120 -N maps the coded data into modulation symbols composed of 2 bits. In the case of the 16-QAM scheme, the adaptive mapper 120-1,..., 120 -N maps the coded data into modulation symbols composed of 4 bits.

In addition, the adaptive mapper 120-1,..., 120 -N adaptively modulates the coded data according to the retransmission request signal of the controller 150. This will be described later.

The spatial encoder 130 processes according to a space-time code coding scheme so that it can transmit from a block of modulation symbols through a plurality of antennas 190-1,..., 190 -N. The space-time code coding scheme of the spatial encoder 130 will be described later with reference to the adaptive mapper 120-1,..., 120 -N. The set of symbols transmitted in one period (or one time slot) by the output of the spatial encoder 130 is hereinafter referred to as transmit symbol.

The modulators 140-1, ..., 140-N modulate the transmission symbols output from the spatial encoder 130 in accordance with a multiple access modulation scheme to each antenna 190-1, ..., 190-N). There is no limitation on the multiple access modulation scheme, and a single-carrier modulation scheme such as well-known CDMA scheme or a multi-carrier modulation scheme such as OFDM scheme can be adopted.

The receiving circuit 180 receives the signal transmitted from the receiver 200 through the antennas 190-1,..., 190 -N. The receiving circuit 180 digitizes the received signal and sends the received signal to the controller 150.

The controller 150 controls the overall operation of the transmitter 100. The controller 150 extracts information from the signal received from the receiving circuit 180. Extracting information includes general demodulation and decoding. The extracted information may include a retransmission request signal. The controller 150 sends a retransmission request signal to the adaptive mapper 120-1,..., 120 -N to prepare a retransmission symbol.

The information extracted from the signal received from the receiving circuit 180 may include channel quality information (CQI). The CQI may be referred to as information that the receiver 200 feeds back to the transmitter 100 about a channel environment, a coding scheme, and a modulation scheme. Through the CQI, the controller 150 controls the channel encoders 110-1, ..., 110-N or the adaptive mapper 120-1, ..., 120-N, so that each channel encoder 110 is controlled. The coding scheme of -1, ..., 110-N) or the modulation scheme of each adaptive mapper 120-1, ..., 120-N can be adaptively changed.

Meanwhile, the receiver 200 includes a spatial decoder 220, a demapper 230-1, ..., 230-M, a channel decoder 250-1, ..., 250-M, And an error detector 260-1, ..., 260-M, a controller 270, and a transmit circuitry 280. In addition, the receiver 200 includes M _t antennas (M _t ≥ 1) 290-1,... 290 -M _t .

The signal received from the antennas 290-1,..., 290 -M _t is demodulated by the demodulator 210-1,..., 210 -M and input to the spatial decoder 220. The spatial decoder 220 recovers the transmission symbol according to the decoding control signal provided from the controller 270. The decoding control signal controls decoding based on the space-time coded coding scheme of the receiver 100. The decoding control signal may be preset in a memory (not shown) of the controller 270. Alternatively, the decoding control signal may be received from the transmitter 100.

The demappers 230-1,..., 230 -M demap each modulation symbols back into the coded data according to the demapping control signal provided from the controller 270. The demapping control signal controls the demapper 230-1,..., 230 -M based on the modulation scheme in the adaptive mapper 120-1,..., 120 -N of the transmitter 100. do. The demapping control signal may be preset in a memory (not shown) of the controller 270. Alternatively, the demapping control signal may be received from the transmitter 100.

The receiver 200 may include a combiner 240-1,..., 240 -M for combining the retransmitted symbols with the previous symbols. That is, in the case of HARQ of the chase combining or IR method, the combiner 240-1,..., 240 -M combines the previous symbols with the retransmitted symbols. The combining method may use an equal gain combining method in which weights of the previous data and the retransmitted data are equal to each other and combined through an average value. Alternatively, an MRC (maximum ratio combining) method may be used to weight each data. There is no limit to the coupling method, and various other methods can be used.

However, the present invention is not limited to the chase combining or the IR method, and can be applied to the Type I method which performs channel decoding only through the retransmitted symbols without combining with the previous symbol. In this case, the coupling unit 240-1,..., 240 -M may be excluded from the receiver 200.

The channel decoders 250-1, ..., 250-M decode the coded data according to a predetermined decoding scheme. The error detectors 260-1, ..., 260-M detect whether there is an error in the decoded data bits through a CRC check or the like.

The controller 270 controls the overall operation of the receiver 200 and provides a retransmission request signal or the like to the transmitting circuit 280. To this end, the controller 270 may perform general channel encoding, modulation, and the like.

The controller 270 receives an error status from the error detectors 260-1, ..., 260-M and determines whether to request retransmission. The controller 270 may generate a positive acknowledgment (ACK) signal if no error is detected and a negative acknowledgment (NACK) signal if an error is detected. The ACK signal or the NACK signal becomes a retransmission request signal.

In addition, the controller 270 may provide a CQI signal by measuring channel quality from the transmitted signal. This becomes a feedback signal to the transmitter 100 regarding channel quality such as signal-to-noise ratio (SNR) and error rate. In order to measure channel quality, the transmission symbol transmitted from the transmitter 100 may further include a pilot symbol.

The transmitting circuit 280 receives a retransmission request signal from the controller 270 and transmits the same through the antennas 290-1,..., 290 -M.

Hereinafter, a hybrid retransmission method according to an embodiment of the present invention will be described using the communication system of FIG. 1. For clarity, the following description assumes two transmit antennas (N = 2), and transmit symbols are s1 and s2 for each antenna. However, an embodiment of four transmission antennas is additionally provided for a clear understanding of the present invention. In this case, transmission symbols are s1, s2, s3, and s4 for each antenna. Those skilled in the art will be able to apply the technical spirit of the present invention to a communication system having one or more antennas as well as two or four antennas. Here, the subscripts of the transmission symbols s ₁ ¹ , s ₂ ¹ , s ₃ ¹ , and s ₄ ¹ indicate the transmitting antenna, and the superscript means the number of retransmissions. For the sake of explanation, it is assumed that transmission is performed in symbol units (symbol-by-symbol), but may be performed in groups of symbols. Alternatively, the transmission may be performed in whole or in part of the data block, or may be in whole or in part of the data packet.

Referring to FIG. 2, the transmitter 100 transmits s ₁ , s ₂ (s ₃ , s ₄ ) (S110). The symbol s ₁ is transmitted through the first antenna 190-1, the symbol s ₂ is transmitted through the second antenna 190-2, and when there are four transmission antennas, the third antenna 190-3 is transmitted. The symbol s ₃ is transmitted, and the symbol s ₄ is transmitted through the fourth antenna 190-4.

The receiver 200 performs time-space decoding on the received symbols s ₁ and s ₂ (s ₃ and s ₄ ) and performs channel decoding to determine whether an error occurs (S120). If no error is detected, an ACK signal is transmitted to the transmitter 100, and the transmission for the next transmission symbols is waited. However, it is assumed here that the receiver 200 detects an error and transmits a NACK signal as a retransmission request signal (S130).

When the NACK signal is received, the transmitter 100 transmits retransmission symbols s ₁ ¹ , s ₂ ¹ (s ₃ ¹ , s ₄ ¹ ) (S140). The retransmission symbol s ₁ ¹ is transmitted through the first antenna 190-1, the retransmission symbol s ₂ ¹ is transmitted through the second antenna 190-2, and when there are four transmit antennas, the retransmission symbol s ₃ ¹ is The third antenna 190-3 is transmitted and the retransmission symbol s ₄ ¹ is transmitted through the fourth antenna 190-4. When the NACK signal is received, the controller 150 spatially remaps the transmission symbols s ₁ , s ₂ (s ₃ , s ₄ ) through the adaptive mapper 120-1,..., 120 -N. The retransmission symbols s ₁ ¹ , s ₂ ¹ (s ₃ ¹ , s ₄ ¹ ) are configured. The spatial remapping method used in retransmission may have various methods, which will be described later with reference to FIG. 3.

The receiver 200 performs time-space decoding on the received retransmission symbols s ₁ ¹ and s ₂ ¹ (s ₃ ¹ and s ₄ ¹ ) and determines whether an error is performed by channel decoding. At this time, the combiner (240-1, ..., 240-M) is the previous symbols s ₁ , s ₂ (s ₃ , s ₄ ) and retransmission symbols s ₁ ¹ , s ₂ ¹ (s ₃ ¹ , s) ₄ ¹ ) can be combined. In general chase combining, the log-likelihood ratio (hereinafter referred to as LLR) values of retransmission symbols and the LLR values of previous symbols are combined and combined.

If no error is detected, the receiver 200 transmits an ACK signal to the transmitter 100 and waits for transmission of the next transmission symbols. However, it is assumed here that the receiver 200 detects an error and transmits a NACK signal as a retransmission request signal (S160).

When the NACK signal is received, the transmitter 100 transmits remapped retransmission symbols s ₁ ¹ and s ₂ ¹ (s ₃ ¹ and s ₄ ¹ ) again (S170). The retransmission symbol s ₁ ² is transmitted through the first antenna 190-1, the retransmission symbol s ₂ ² is transmitted through the second antenna 190-2, and when there are four transmit antennas, the retransmission symbol s ₁ ³ is The third antenna 190-3 is transmitted, and the retransmission symbol s ₂ ⁴ is transmitted through the fourth antenna 190-4. Adaptive mapper 120-1, ..., 120-N spatially remaps transmitted symbols s ₁ , s ₂ (s ₃ , s ₄ ), thereby retransmitting symbols s ₁ ² , s ₂ ² ( s ₃ ² , s ₄ ² ).

The receiver 200 performs time-space decoding on the received retransmission symbols s ₁ ² and s ₂ ² , and performs channel decoding to determine whether there is an error (S180). At this time, the combiner 240-1, ..., 240-M is the previous symbols s ₁ , s ₂ (s ₃ , s ₄ ) and the retransmission symbols s ₁ ² , s ₂ ² (s ₃ ² , s). ₄ ² ) can be combined.

The receiver 200 transmits an ACK signal or a NACK signal to the transmitter 100 according to whether an error is detected (S190). When the ACK signal is transmitted, retransmission for the corresponding symbols ends. The retransmission request by the NACK signal may be made up to the n th repetition number (n ≧ 1). If the error is still detected by the nth retransmission, the retransmission process can be reset and transmission for the next symbols can be started. Or transmission may be done again from the beginning for the current symbols.

Hereinafter, the adaptive mapping in the adaptive mapper 120-1, ..., 120-N will be described. For clarity, transmission symbols in the case of two transmission antennas s ₁ = {a ₁ , a ₂ , a ₃ , a ₄ }, s ₂ = {b ₁ , b ₂ , b ₃ , b ₄ , b ₅ , b ₆ }, and transmission symbols added when four transmission antennas are s ₃ = {c ₁ , c ₂ }, s ₄ = {d ₁ , d ₂ , d ₃ , d ₄ }. Here, a, b, c, and d are bit data constituting a transmission symbol, and subscripts indicate arbitrary bit data, but the order and contents thereof are not limited. The transmission symbols are modulation symbols modulated by m-PSK or m-QAM. Although the transmission symbols s ₁ , s ₂ , s ₃ , and s ₄ are composed of four bit data, this is only an example and the number of bit data included in the transmission symbol may vary.

Retransmission symbols are formed by remapping data bits between transmission symbols s ₁ , s ₂ or bit data between s ₁ , s ₂ , s ₃ , s ₄ . Since the transmitted symbols are modulated symbols, remapping of bit data of the transmitted symbols may be referred to as remapping of signal constellations. Remapping of bit data may include the exchange or replacement of bit data. Hereinafter, bit-mapping remapping will be described. However, in the case of a packet-taking transmission of a plurality of symbols, it may be referred to as remapping of a symbol unit.

If the transmission symbols s ₁ , s ₂ or s ₁ , s ₂ , s ₃ , s ₄ are transmitted through different antennas, remapping them may be said to be spatially remapped. Spatial means that data sent through each antenna is associated with each other.

3A and 3B, a retransmission symbol may be formed by exchanging bit data of transmission symbols with each other.

Referring to Figure 3a, in the first retransmission (T2) for the first transmission (T1), the retransmission symbols s ₁ ¹ and s ₂ ¹ is bit data (a _1, a ₄₎ and the bit data of s ₂ of s ₁ (b ₁ , b ₆ ) are formed by exchanging each other and rearranging bit data in a symbol.

Also, according to FIG. 3B, in the first retransmission T2 for the first transmission T1, the retransmission symbols s ₁ ¹ and s ₂ ¹ are the bit data a ₁ , a ₄ of s _{1 and} the bit data of s ₂ . (b ₁ , b ₆ ) are formed by exchanging each other and rearranging bit data in a symbol. The retransmission symbols s ₃ ¹ and s ₄ ¹ exchange the bit data c ₂ of s ₃ and the bit data a ₄ of s ₁ with each other and rearrange the bit data in the symbol to form the same. That is, retransmission symbols s ₁ ¹ , s ₂ ¹ , s ₃ ¹ , and s ₄ ¹ spatially exchange bit data of transmission symbols s ₁ , s ₂ , s ₃ , and s ₄ , and convert the bit data within the symbol. Form by rearranging.

In particular, in the second retransmission T3, the retransmission symbols s ₁ ² and s ₃ ² may be formed by exchanging bit data a ₄ of s ₁ and bit data c ₂ of s ₃ with each other. The retransmission symbols s ₂ ² and s ₄ ² are the bit data of s ₂ (b ₁ , b ₄ ) and s ₄ . It can be formed by exchanging the bit data (d ₂ , d ₃ ) with each other. That is, retransmission symbols s ₁ ² , s ₂ ² , s ₃ ² , and s ₄ ² may be formed by spatially exchanging bit data of transmission symbols s ₁ , s ₂ , s ₃ , and s ₄ .

In the above, it is preferable that the number of bit data exchanged with each other is smaller than or equal to (number of bits / 2) of a symbol having a smaller number of bits among two symbols to be exchanged. This is to ensure minimum spatial diversity for data transmitted through each symbol. However, the present invention is not limited thereto, and there is no limitation on the number of bit data exchanged and the order or manner of exchange.

In the first retransmission T2, the bit data of transmission symbols are spatially exchanged and retransmitted, and in the second retransmission T3, the bit data of the transmission symbols is newly exchanged spatially and retransmitted. Diversity gain can be obtained by the exchange of bit data of transmission symbols. In this case, only the second retransmission is described as an example. However, the third retransmission and subsequent retransmissions may retransmit retransmission symbols that spatially remap transmission symbols.

Referring to FIG. 4A, retransmission symbols s ₁ ¹ and s ₂ ¹ in the first retransmission T2 spatially transmit the bit data of the transmission symbols s ₁ and s ₂ like the retransmission symbols in the first transmission of FIG. 3A. They are exchanged with each other and formed by rearranging bit data in a symbol.

In the second retransmission T3, bit data between transmission symbols s ₁ and s ₂ may be replaced with each other. That is, the retransmission symbols s ₁ ² and s ₂ ² exchange bit data between transmission symbols s ₁ and s ₂ , and then replace LSB (least significant bit) and MSB (most significant bit) with their complement. to be.

Referring to FIG. 4B, the retransmission symbols s ₁ ¹ , s ₂ ¹ , s ₃ ¹ , and s ₄ ¹ in the first retransmission T2 are transmitted symbols s ₁ like the retransmission symbols in the first transmission of FIG. 3B. The bit data of, s ₂ , s ₃ , and s ₄ are spatially exchanged with each other, and rearranged in the symbol to form the bit data. Also, in the second retransmission T3, the LSB and MSB of transmission symbols s ₁ , s ₂ , s ₃ , s ₄ can be replaced by their complement.

The substitution of the bit data is not limited to the LSB and the MSB, and can be independently replaced with the complement of the LSB and the MSB. Alternatively, the bit data of a predetermined part may be replaced with a complement.

In general, the LSB and the MSB are set in the indication data such as the TFCI information or the CQI information, and the LSB and the MSB may be differently defined according to the mapping method used in the communication system. In this embodiment, the bit strongest in channel change is defined as the MSB, and the bit weakest in channel change is defined as the LSB. Specifically, a ₁ , b ₁ , c ₁ , and d ₁ are designated as MSB in the initial transmission (T1). And define a ₄ , b ₆ , c ₂ , and d ₄ as LSB.

Diversity gain can be obtained by exchanging and replacing bit data of such transmission symbols.

Referring to FIG. 5A, in the first retransmission T2, the retransmission symbols s ₁ ¹ and s ₂ ¹ spatially exchange bit data of the transmission symbols s ₁ and s ₂ , rearrange the bit data, and then reconstruct the bit data with the LSB. It forms by replacing MSBs with their complement.

In the second retransmission T3, the retransmission symbols s ₁ ² and s ₂ ² spatially exchange bit data of the transmission symbols s ₁ and s ₂ , rearrange the bit data and then reconstruct the bit data of the middle portion. It is formed by replacing with a complement. That is, the retransmission symbols s ₁ ² and s ₂ ² are formed by substituting different bit data with the substituted bit data of the first retransmission symbols s ₁ ¹ and s ₂ ¹ .

Referring to FIG. 5B, in the first retransmission T2, retransmission symbols s ₁ ¹ , s ₂ ¹ , s ₃ ¹ , and s ₄ ¹ represent bit data of transmission symbols s ₁ , s ₂ , s ₃ , and s ₄ . They are formed by exchanging spatially with each other, rearranging the bit data, and substituting the LSB and MSB for their complement. In the second retransmission T3, the retransmission symbols s ₁ ² , s ₂ ² , s ₃ ² , and s ₄ ² spatially exchange bit data of transmission symbols s ₁ , s ₂ , s ₃ , and s ₄ . After rearranging the bit data, the bit data of the middle part is replaced by its complement. That is, the retransmission symbols s ₁ ² , s ₂ ² , s ₃ ² , s ₄ ² are different bits from the replaced bit data of the first retransmission symbols s ₁ ¹ , s ₂ ¹ , s ₃ ¹ , s ₄ ¹ . It is formed by replacing data.

In the first retransmission T2, the bit data of the transmission symbols are spatially replaced with each other and retransmitted. In the second retransmission T3, the bit data of the transmission symbols are newly replaced with the spatial data. Diversity gain can be obtained through remapping by replacement of bit data of transmission symbols.

Referring to FIG. 6A, in the first retransmission T2, retransmission symbols s ₁ ¹ and s ₂ ¹ spatially exchange bit data of transmission symbols s ₁ and s ₂ and rearrange the positions of the bit data. It is formed by substituting LSB and MSB for their complement.

In the second retransmission T3, bit data between transmission symbols are exchanged with each other. That is, the retransmission symbols s ₁ ² and s ₂ ² are formed by spatially exchanging bit data of the transmission symbols s ₁ and s ₂ and rearranging positions of the bit data in the symbol.

Referring to FIG. 6B, in the first retransmission T2, retransmission symbols s ₁ ¹ , s ₂ ¹ , s ₃ ¹ , and s ₄ ¹ represent bit data of transmission symbols s ₁ , s ₂ , s ₃ , and s ₄ . It is formed by exchanging spatially with each other, rearranging the positions of the bit data, and replacing the LSB and the MSB with their complements. In the second retransmission T3, the bit data between transmission symbols are exchanged with each other. That is, the retransmission symbols s ₁ ² , s ₂ ² , s ₃ ² , s ₄ ² spatially exchange bit data of transmission symbols s ₁ , s ₂ , s ₃ , s ₄ , and bit data within the symbol. Form by rearranging the position of.

In the first retransmission T2, the bit data of the transmission symbols are spatially replaced and retransmitted, and in the second retransmission T3, the bit data of the transmission symbols are spatially exchanged with each other and retransmitted. Diversity gain can be obtained through remapping by exchange and replacement of bit data of transmission symbols.

Referring to FIG. 7A, a retransmission symbol is formed by exchanging bit data of transmission symbols with each other. Retransmitting symbols s ₁ ¹ and s ₂ ¹ has, but the bit data (a _1, a ₂₎ and bit data (b _3, b ₅₎ of s ₂ on s ₁ exchange, the bits are formed so as to be arranged to cross each other .

Referring to Figure 7b, but Figure 7a similarly to retransmit symbols s ₁ ¹ and s ₂ ¹ is exchanging bits of data (a _1, a ₂₎ and bit data (b _3, b ₅₎ of s ₂ of s ₁ with each other, The bits are formed to be arranged to cross each other. Furthermore, retransmitting symbols s ₃ ¹ and s ₄ ¹ are but a bit data (d ₃₎ of s _3-bit data (c ₁₎ and s ₄ of the exchange, the bit data of s ₃ ¹ are formed are arranged to intersect each other, .

According to the present invention, replacement and rearrangement of bit data in one symbol may be performed in various other ways as long as bit data is exchanged between symbols.

8A and 8B are exemplary diagrams illustrating an arrangement of retransmission symbols according to another embodiment of the present invention.

8A and 8B, retransmission symbols are formed by exchanging bit data of transmission symbols with each other. This embodiment assumes that only the transmission symbols for antenna 2 109-2 perform retransmission and the transmission symbols for the remaining antennas transmit new data in the secondary transmission T2. In addition, the modulation scheme is changed and applied during retransmission. In this case, it is preferable to change a symbol having an error in the initial transmission to a modulation method having a low coding rate and to retransmit to improve transmission reliability. Meanwhile, when the present embodiment is a closed loop multiple codeword system supporting AMC, the controller 150 determines an MCS level (eg, a coding rate and / or a modulation order) according to the CQI information fed back from the receiver, and accordingly A new modulation scheme may be applied to each symbol during retransmission, and in the present embodiment, the open loop multi-codeword system may uniformly set a modulation scheme such that a transmission reliability is relatively high for a symbol to be retransmitted. .

According to FIG. 8A, 16QAM and 64QAM are applied to each symbol S1 and S2 at the initial transmission T1, but are changed to 64QAM and QPSK at retransmission T2. When the symbol 2 is transmitted with 64QAM for the antenna 109-2, but an error occurs due to a poor channel condition, the retransmission is modulated with 16QAM to increase transmission reliability. On the other hand, the first antenna 109-1 succeeded in the initial transmission, and the state of the corresponding channel was determined to be better based on the feedback information. In the second transmission (T2), the modulation scheme is changed to 64QAM so that the new symbol is changed. Send the data. Of course, in the open loop system, the first antenna 109-1 may perform retransmission while maintaining 16QAM in the same manner as in the initial transmission.

Meanwhile, according to FIG. 8B, 16QAM, 64QAM, QPSK, and 16QAM were applied to each symbol S ₁ , S ₂ , S ₃ , and S ₄ at the initial transmission (T1), but at the time of retransmission (T2), 64QAM, 16QAM, Changed to 16QAM and 16QAM respectively. Here, only the transmission symbol of the antenna 109-2 is retransmitted. Specifically, the retransmission is changed to 16QAM having a lower coding rate than 64QAM. Some of the remaining antennas 190-1 and 190-3 succeeded in initial transmission and changed to a modulation scheme having a high coding rate in the second transmission, and the other part 190-4 was maintained as it is.

9 is an exemplary view showing a composite automatic retransmission method according to another embodiment of the present invention. For clarity, the following description assumes two transmit antennas (N = 2), and transmit symbols are s ₁ and s ₂ for each antenna.

Referring to FIG. 9, an orthogonal space-time block code (STBC) may be used as the space time code scheme. As is well known, in a communication system with two transmit antennas, Alamouti's STBC is shown in Table 1 below.

First antenna Second antenna First transfer s ₁ s ₂ Second transfer -s ₂ ^* s ₁ ^*

Here, s ₁ ^* and s ₂ ^* are complex conjugates of s ₁ and s ₂ , respectively. Using Alamouti code can greatly reduce the complexity of the encoder. The retransmission method using STBC will be described below.

First, through the first antenna (190-1) transmits the transmission symbols s ₁ and s ₂ first transmits the transmission symbols via a second antenna (190-2).

When an error is detected in the transmitted symbols and a NACK signal is transmitted, a retransmission symbol -s ₂ ^* is transmitted through the first antenna 190-1 during the first retransmission (T2), and the second antenna 190- Send retransmission symbol s ₁ ^* through 2).

The error is detected by the retransmission symbols when the NACK signal is transmitted by mapping the re-transmission symbols s ₁ and s _2, constitutes a retransmission symbols s ₁ 'and s _2'. Retransmission symbols s ₁ ′ and s ₂ ′ may be configured by exchanging bit data with each other between transmission symbols s ₁ and s ₂ . First retransmission when (T3) is to transmit a first retransmission symbols through an antenna (190-1) s ₁ 'transmission, the second antenna ₂ through the retransmitted symbol s (190-2) to ".

When an error is detected and a NACK signal is transmitted, retransmission symbols s ₁ ^* and -s ₂ ^* are remapped to form retransmission symbols s ₁ ' ^* and -s ₂ ' ^* . The retransmission symbols s ₁ ^* and -s ₂ ^* exchanging bits of data between each other may constitute a retransmission symbols s ₁ ^'* and -s _2' ^*. In the first retransmission T3, the retransmission symbol-s ₂ ' ^* is transmitted through the first antenna 190-1, and the retransmission symbol s ₁ ' ^* is transmitted through the second antenna 190-2.

Although a system having two antennas has been described above, the technical idea of the present invention may be applied to a system having three or more antennas as it is. In addition, not only STBC but also the space-time trellis code may be applied to the technical idea of the present invention. On the other hand, since the present invention assumes a multiple codeword system, in the present embodiment, a predetermined space-time coding scheme is applied and a different coding rate and / or modulation scheme may be further applied to each symbol.

10 is a block diagram showing a transmitter according to another embodiment of the present invention. 11 shows an example of a retransmission symbol. This may be a transmitter using a cyclic delay diversity technique.

10 and 11, the transmitter 400 includes a channel encoder 410-1,..., 410 -N, an adaptive mapper 420-1,..., 420 -N, a spatial encoder 430. ), A controller 450 and a receiving circuit 480. Transmitter 400 also includes N (N> 1) antennas 490-1, ..., 490-N and modulators 440-1, ..., 440-N.

The embodiment of FIG. 10 differs from the embodiment of FIG. 1 in that delayers between modulators 440-1, ..., 440-N and antennas 190-1, ..., 190-N. (470-1, ..., 470- (N-1)) was added. Other operations are the same as in the embodiment of FIG. Delays 470-1, ..., 470- (N-1) cyclically transmit the transmission symbols transmitted by respective antennas 190-1, ..., 190-N. Can be delayed. The time Δ ₁ , ..., Δ _N-1 delayed by the delayers 470-1, ..., 470- (N-1) may have different values depending on the user, and the receiver The feedback can be adjusted from the information.

The operation of the transmitter 400 is as follows. First, (T1) transmit symbol s1 is repeatedly transmitted by cyclically delaying through all antennas 190-1,..., 190 -N _t . When an error is detected in the transmitted symbol and a NACK signal is transmitted, at the first retransmission (T2), the retransmission symbol s ₁ ¹ remapped through the adaptive mapper 420 is transmitted to all antennas 190-1,... , 190-N _t ) through a cyclic delay to transmit. The retransmission symbol s ₁ ¹ may be configured by remapping between cyclically delayed transmission symbols s ₁ . If an error is also detected by the retransmission symbols s ₁ ¹ and a NACK signal is transmitted, the retransmission symbols s remapped through the adaptive mapper 420-1, ..., 420-N even at the second retransmission (T3). ₁ ² is cyclically delayed and transmitted through all antennas 190-1,..., 190 -N _t .

Cyclic delay diversity is a technique for implementing spatial diversity by transmitting the same data through a plurality of antennas and at the same time ensuring frequency diversity through time delay. An additional retransmission gain can be obtained by remapping the retransmission symbols.

12 is a block diagram illustrating an embodiment of a transmitter using OFDM. This is implemented in the OFDM scheme in the embodiment of FIG.

Referring to FIG. 12, the symbols output from the spatial encoder 530 are converted into time-domain samples by an inverse fast Fourier transform unit (540-1, ..., 540-N _t ). CPs are inserted into the samples by cyclic prefix (CP) insertion units 545-1, ..., 545-N _t and transmitted by antennas 590-1, ..., 590-N _t . do. Delays 570-1, ..., 570- (between the IFFT section 540-1, ..., 540-N _t ) and the CP insertion section 545-1, ..., 545-N _t ) N _t -1)) is arranged to cyclically delay the samples.

In another embodiment, the arrangement of the retarders 470-1, ..., 470- (N _t -1) and the CP inserts 545-1, ..., 545-N _t may be interchanged. have. That is, the CP may insert the symbol after delaying the symbol, but may also delay the symbols after inserting the CP.

13 is a block diagram illustrating another embodiment of a transmitter using OFDM. This is the shift in the frequency domain of the retarder in the embodiment of FIG.

13, a space encoder 630 and the IFFT unit (640-1, ..., 640-N t) the phase delay unit (670-1, ..., 670- (N t -1 between) ) Is arranged to cyclically delay the phase of the symbols. The time delay in the time domain and the phase delay in the frequency domain are due to the duality.

Meanwhile, since the present invention assumes a multiple codeword system, a predetermined time delay scheme or a phase delay scheme may be applied to the present embodiment, and a different coding rate and / or modulation scheme may be further applied to each symbol.

In addition, the communication system according to the technical concept of the present invention may be applied to a system having one transmission antenna as well as a plurality of transmission antennas. That is, the communication system according to the present invention is not only a multiple-input multiple-output (MIMO) system or a multiple-input single-output (MISO) system, but also a single-input single-input. It may be a single-output (SISO) system or a single-input multiple-output (SIMO) system. A MIMO system uses multiple transmit antennas and multiple receive antennas. The MISO system uses multiple transmit antennas and one receive antenna. The SISO system uses one transmit antenna and one receive antenna. The SIMO system uses one transmit antenna and multiple receive antennas.

14 is a block diagram showing a transmitter according to another embodiment of the present invention. 15 shows an example of a retransmission symbol.

Referring to Figures 14 and 15, transmitter 800 includes channel encoders 810-1, ..., 810-N, adaptive mapper 820-1, ..., 820-N, parallel / serial converters. 830, a modulator 840, a controller 850, and a receiving circuit 860. However, unlike the previous embodiment, the transmitter 800 includes one antenna 890.

The operation of the transmitter 800 is as follows. First, each symbol (s1, s2, s3) for multiple codewords is a channel encoder (810-1, ..., 810-N) and adaptive mapper (820-1, ..., 820-N) And then serialized via the bottle / serial converter 830. The transmission symbols s ₁ , s ₂ , and s ₃ are transmitted in the initial transmission T1. In one embodiment, multiple symbols may be sent at one time. In this case, transmission is performed in a packet unit, and thus transmission symbols s ₁ , s ₂ , and s ₃ may be referred to as one packet. In another embodiment, a plurality of symbols may be sequentially transmitted in one time slot. There is no limit on the number of symbols to be transmitted, and may be two or more. Here, since the present invention assumes a multiple codeword system, each symbol may have a different coding rate and / or modulation scheme applied thereto. For example, coding rates 1/2 and QPSK modulation may be applied to s1 and s2, and coding rates 3/4 and 16QAM modulation may be applied to s3.

When an error is detected in the transmitted symbol and a NACK signal is transmitted, at the first retransmission (T2), retransmission symbols s ₁ ¹ , remapped through the adaptive mapper 820-1, ..., 820-N. Send s ₂ ¹ , s ₃ ¹ . Retransmission symbols s ₁ ¹ , s ₂ ¹ , and s ₃ ¹ may be configured by exchanging bit data between transmission symbols s ₁ , s ₂ , and s ₃ . If an NACK signal is also transmitted due to an error detected by the retransmission symbol, the retransmission symbol s ₁ ² , remapped by the adaptive mapper 820-1,..., 820 -N even during the second retransmission (T3). Send s ₂ ² , s ₃ ² . In this case, different coding rates and / or modulation schemes may be applied to each of the retransmitted symbols with reference to the fed back information.

The exchange, replacement, crossover, change in modulation scheme, and delay of the retransmission symbols as described above may be divided into cases where an error occurs in all initial transmission symbols and an error occurs in some initial transmission symbols. If an error occurs in all initial transmitted symbols, bits are reordered between symbols to be retransmitted.However, if an error occurs in some symbols, a bit rearrangement is performed between the symbols to be retransmitted and a new symbol to be transmitted through an error free antenna. Perform.

In addition, the retransmission symbols as described above may be remapped at every retransmission, or may be remapped for only one retransmission. Each remapping can have a different remapping scheme, or the same remapping scheme can be used.

There is no limit to the criteria for determining the remapping method. In an embodiment, the controllers 150, 450, and 850 may appropriately determine the remapping scheme according to the situation in an open-loop manner. As a parameter for determining the remapping scheme, the maximum Doppler frequency and the delay spread may be referred to. In another embodiment, as described above, the controllers 150, 450, and 850 may determine the remapping scheme according to the channel quality fed back from the CQI signal in a closed-loop manner.

Since the above-described embodiments form a retransmission symbol by remapping the transmission symbols, it may be referred to as a composite automatic retransmission using a Type I or chase combining method. FIG. 16 is a signal flowchart illustrating a process of performing automatic retransmission by using an adaptive mapper in a multiple codeword multi-antenna system, but performing complex automatic retransmission by a chase combining method.

That is, when an error occurs in a specific symbol among the symbols (or streams or packets) transmitted in the initial T1, and a NACK is received from the receiver, the same symbol as the corresponding symbol is retransmitted, but each data bit of the corresponding symbol is displayed. Adaptive mapping and retransmission are performed so that they are exchanged, replaced or crossed with the data bits of the symbol. The receiving end calculates the LLR value of the encoded bits by using a demapping method for a retransmission previously promised with the transmitting end, and increases the transmission reliability of the data by adding the calculated LLR value with the LLR value of the previously encoded coded bits.

On the other hand, the technical idea of the present invention can be applied to the complex automatic retransmission of the IR method as it is. FIG. 17 is a signal flow diagram illustrating a process for performing automatic retransmission using an adaptive mapper in a multiple codeword multi-antenna system, but performing complex automatic retransmission using an IR scheme.

In FIG. 17, when an error occurs in a specific symbol among symbols (or streams or packets) that have been initially transmitted (T1), a partial IR that transmits systematic bits and punctured parity bits during retransmission, as in antenna 1 partial IR) may be used, or full IR may be used to additionally transmit parity bits in retransmission as in antenna 2. FIG. In this case, instead of retransmitting the transmission symbols, redundancy symbols are retransmitted, and an additional retransmission gain can be secured by spatially remapping the extra symbols.

In addition, in the present invention, a multi-user environment may be considered when applying a complex retransmission method using multiple antennas. 18 is a conceptual diagram illustrating a complex retransmission method using multiple antennas in a multi-user environment.

Even when symbols transmitted through one or more transmit antennas are transmitted to receiver 1 and receiver 2, if an error occurs in a symbol transmitted to a specific receiver, symbol-to-symbol exchange, substitution, transition, Additional complex automatic retransmission gain can be secured by retransmission by applying a signal property rearrangement such as a modulation scheme change.

The present invention considers symbols transmitted through different antennas when mapping retransmission symbols. Therefore, by implementing mapping diversity through remapping between symbols, an additional retransmission gain can be secured.

The present invention may be implemented in hardware, software, or a combination thereof. (DSP), a programmable logic device (PLD), a field programmable gate array (FPGA), a processor, a controller, a microprocessor, and the like, which are designed to perform the above- , Other electronic units, or a combination thereof. In the software implementation, the module may be implemented as a module that performs the above-described function. The software may be stored in a memory unit and executed by a processor. The memory unit or processor may employ various means well known to those skilled in the art.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention. You will understand. Therefore, the present invention is not limited to the above-described embodiment, and the present invention will include all embodiments within the scope of the following claims.

As described above, according to the present invention, retransmission is performed according to a mapping scheme suitable for a channel environment during retransmission. In particular, when performing retransmission according to a transmission error in a multiple codeword system, a diversity gain can be additionally secured by spatially remapping a symbol for each codeword, thereby minimizing retransmission requests and improving communication quality. have.

Claims

In the Hybrid Automatic Repeat Request method,

Transmitting a first symbol to which constellation mapping has been applied;

Receiving a retransmission request signal for the first symbol; And

And transmitting a second symbol to which constellations are applied according to the retransmission request signal.

The method of claim 1,

And repositioning the constellation changes the modulation scheme of the first symbol.

3. The method according to claim 1 or 2,

And the constellation relocation exchanges bit data of the first symbol.

3. The method according to claim 1 or 2,

And the constellation reposition replaces bit data of the first symbol.

The method of claim 1,

And the first symbol is encoded with a space-time block code.

The method of claim 1,

And cyclically delaying the second symbol by a predetermined time unit.

The method of claim 1,

And cyclically delaying the phase of the second symbol by a predetermined unit.

In the transmitter for performing a hybrid automatic repeat request (Hybrid Automatic Repeat Request),

An antenna for transmitting and receiving wireless signals;

A modulator coupled to the antenna; And

The first symbol to which constellation mapping is applied is transmitted through the antenna, the retransmission request signal for the first symbol is received through the antenna, and the second symbol to which constellation relocation is applied according to the retransmission request is performed. Transmitter comprising a control unit for transmitting through.

9. The method of claim 8,

And the constellation reposition changes a modulation scheme of the first symbol.

10. The method according to claim 8 or 9,

And the constellation relocation exchanges bit data of the first symbol.

10. The method according to claim 8 or 9,

And the constellation reposition replaces bit data of the first symbol.

9. The method of claim 8,

And the constellation relocation is determined based on channel quality information fed back from the receiver.

9. The method of claim 8,

And a time delay for cyclically delaying the first symbol.

delete

9. The method of claim 8,

The modulator is a transmitter for performing an inverse fast Fourier transform (IFFT).