KR101246807B1 - Apparatus and method for hybrid-arq in communication system - Google Patents

Abstract

The present invention relates to an apparatus and method for performing a hybrid automatic repeat request (H-ARQ) in a communication system. The receiver according to the invention uses a buffer to store the decoding result for the previous transmission, a detector for demodulating the received retransmission packet to generate LLR values, the decoding result for the previous transmission and the LLR values from the detector. And a decoder for performing repeated decoding. This invention can significantly reduce the number of iterations of the decoder compared to the same performance.

TC, LDPC, Iterative Decoding, Detector, Iteration Count

Description

Device and method for performing hybrid automatic retransmission request in communication system {APPARATUS AND METHOD FOR HYBRID-ARQ IN COMMUNICATION SYSTEM}

1 is a diagram illustrating an internal configuration of a typical LDPC decoder.

2 is a diagram illustrating a configuration of a transmitter in a communication system using the H-ARQ technique according to an embodiment of the present invention.

3 is a diagram illustrating a configuration of a receiver in a communication system using the H-ARQ technique according to an embodiment of the present invention.

4 is a diagram illustrating an operation procedure of a receiver in a communication system using the H-ARQ technique according to an embodiment of the present invention.

5 is a diagram illustrating an operation procedure of a receiver in a communication system using the H-ARQ scheme according to another embodiment of the present invention.

6 is a diagram illustrating an operation procedure of a receiver in a communication system using the H-ARQ technique according to another embodiment of the present invention.

The present invention relates to an apparatus and method for performing a hybrid automatic repeat request (H-ARQ) in a communication system, and more particularly, to an apparatus and a method for reducing the number of repetitions of a repeater for the same performance.

In the 4th Generation communication system, which is the next generation communication system, active research is being conducted to provide users with services having various Quality of Service (QoS) having a transmission rate of about 100 Mbps. In particular, current 4G communication systems have mobility in a broadband wireless access (BWA) communication system such as a wireless local area network (LAN) system and a metropolitan area network (MAN) system. And researches to support high-speed services in the form of guaranteeing the quality of service are being actively conducted, and representative communication systems are IEEE (Institute of Electrical and Electronics Engineers) 802.16 communication system and IEEE 802.20 communication system.

In general, in wireless data communication, an error may occur in specific data according to a channel state of a radio resource section. Control and recovery techniques for such errors can be largely divided into ARQ (Automatic Repeat ReQuest) and FEC (Forward Error Correction coding).

On the other hand, H-ARQ (Hybrid ARQ) technique is a combination of the ARQ technique and the error correction coding technique. In the ARQ scheme, an error check is performed on a frame received at a receiving end through a cyclic redundancy check (CRC), when an error occurs, a feedback of a retransmission request is sent to the transmitting end, and the transmitting end retransmits the corresponding frame. In addition, the error correction coding scheme is a method in which a transmitter adds additional information (redundancy) to transmission data and transmits an error, and corrects an error using only a frame received at a receiver.

The H-HARQ technique takes advantage of the above-described two techniques, and an error of a predetermined amount or less can be corrected through the FEC, and more errors can be corrected through the ARQ technique. In general, the H-ARQ technique can be roughly divided into a CC (Chase Combining) technique and an IR (Incremental Redundancy) technique. In the CC scheme, when the initial transmission fails, the transmitter retransmits the initial transmission frame, and at the receiver, symbol-combing the initial transmission frame and the retransmission frame to decode the gain, thereby increasing the gain due to an increase in the signal to noise ratio (SNR). You can get it. The IR technique is a technique of transmitting some redundancy data and information data of the encoded data during initial transmission together, and additionally transmitting redundancy data that is not initially transmitted upon retransmission. In other words, an additional coding gain can be obtained by a technique of transmitting at a low code rate during initial transmission and increasing a code rate each time retransmission.

In recent years, error correction coding techniques are frequently used as low density parity check (LDPC) codes and turbo codes. In general, the receiving end uses an iterative decoder to decode the LDPC code and the turbo code. The iterative decoder refines the LLR (Log-likelihood Ratio) value, which is a soft decision value for each bit, through iterative decoding. For example, in the case of a turbo code, an encoder of a transmitting end performs encoding using two component encoders, and a repeating decoder of a receiving end repeats that two component decoders exchange LLR values for each bit with each other. Perform decoding.

In the case of the LDPC code, as shown in FIG. 1, decoding is performed by repeating the exchange of LLR values between check nodes and variable nodes. Specifically, the initial LLR values from the detector are stored in variable nodes. Each check node updates its LLR value using the LLR values of variable nodes connected to it, and each variable node updates its LLR value using the LLR values of the check nodes. By repeating this process, the accuracy of the LLR value is increased. As the number of iterations increases, such an iterative decoder improves error correction performance.

According to the prior art, the H-ARQ technique uses only the LLR value generated from the detector in the previous transmission and does not use the LLR value generated in the decoder when detecting and decoding the retransmitted data. That is, the H-ARQ technique performs decoding by combining the LLR value obtained in the initial transmission and the LLR value obtained in the retransmission, wherein the combined LLR value is the LLR value generated by the detector. That is, even though there is a more refined LLR value through the decoder, the LLR value generated by the detector is used for symbol combining. In the case of the iterative decoder, the error correction capability increases as the number of iterations increases, but there is a problem that the number of iterations cannot be sufficiently increased due to problems such as latency and complexity. If the iterative decoder starts decoding with a more refined LLR value, the number of iterative decodings for the same performance may be significantly reduced.

Accordingly, an object of the present invention is to provide an apparatus and method for reducing the number of iterative decoding of an iterative decoder in a system using the H-ARQ technique.

Another object of the present invention is to provide an apparatus and method for reducing the number of iterative decoding for the same performance in a system using the H-ARQ technique.

Another object of the present invention is to provide an apparatus and method for reducing the number of retransmissions in a system using the H-ARQ technique.

It is still another object of the present invention to provide an apparatus and method for combining and decoding an LLR obtained from a decoder at a previous transmission and an LLR obtained from a detector at a retransmission in a system using the H-ARQ technique.

It is still another object of the present invention to provide an apparatus and method for using the last state values of a decoder for a previous transmission in retransmission decoding in a system using the H-ARQ technique.

According to an aspect of the present invention for achieving the above object, in a communication system using a hybrid automatic repeat reQuest (H-ARQ) method, in a receiver, a buffer for storing a decoding result for the previous transmission, and a received retransmission packet And a detector for generating LLR values by demodulating, and a decoder for performing repeated decoding using the decoding result of the previous transmission and the LLR values from the detector.

According to another aspect of the present invention, in a communication method using a hybrid automatic repeat reQuest (H-ARQ) method, a method for storing a decoding result of the previous transmission, and demodulating the received retransmission packet LLR value And repeating decoding using the decoding result of the previous transmission and the LLR values of the retransmission packet.

Hereinafter, the operation principle of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. The following terms are defined in consideration of the functions of the present invention, and may be changed according to the intentions or customs of the user, the operator, and the like. Therefore, the definition should be based on the contents throughout this specification.

Hereinafter, the present invention proposes a method for using the LLR value and the final state value obtained by the repeat decoder in the previous transmission in a communication system using a hybrid automatic repeat reQuest (H-ARQ) technique for retransmission decoding. Here, the LLR value obtained in the iterative decoder indicates the final LLR value of the iterative decoder after decoding is completed. In addition, the final state value represents a state value stored in an internal check node and a variable node after decoding completion, assuming the LDPC decoder as shown in FIG. 1.

 Meanwhile, the HARQ scheme includes various schemes such as chase combing and incremental redundancy, but the following description will focus on the chase combining scheme for retransmitting the same packet. However, the present invention is not limited thereto and may be equally applied to other HARQ schemes.

2 illustrates a configuration of a transmitter in a communication system using the H-ARQ technique according to an embodiment of the present invention.

As shown, the transmitter comprises an encoder 202, a modulator 204, a baseband processor 206, an RF transmitter 208, a buffer 210, and an H-ARQ controller 200.

2, in the initial transmission, the encoder 202 encodes the transmission data to generate an encoded packet. In addition, the encoder 202 stores the encoded packet for the initial transmission in the buffer 210. For example, the encoder 202 may use a Turbo Code (TC), a Low Density Parity Check (LDPC) code, or the like.

The modulator 204 modulates the encoded packet from the encoder 200 in a predetermined modulation scheme to generate modulation symbols. For example, the modulator 204 may use QPSK, 16QAM, 64QAM, and the like.

The baseband processor 206 takes the data from the modulator 204 and performs the remaining baseband processing to output. For example, in a CDMA system, the baseband processor 206 spreads and modulates data from the modulator 204 using an orthogonal code. As another example, in the case of an OFDM system, the baseband processor 206 calculates and outputs inverse fast fourier transform (IFFT) data from the modulator 204.

The RF transmitter 208 converts the sample data from the baseband processor 208 into an analog signal, and converts the analog signal into a signal of an RF band that can be actually transmitted.

After the initial transmission, the HARQ controller 200 monitors a response signal (ACK / NACK) fed back from the receiver, and determines whether to retransmit according to the response signal. If the ACK signal is received from the receiver, the encoder 202 generates and outputs a new encoded packet according to the initial transmission under the control of the HARQ controller 200. If the NACK signal is received from the receiver, the encoder 202 controls the HARQ controller 200 to read a previous transmission coded packet buffered in the buffer 210 and outputs the same to the modulator 204. . According to the HARQ technique, the previous transmission coded packet may be retransmitted as described above, and as another example, some redundancy data of the coded packet may be transmitted.

3 illustrates a configuration of a receiver in a communication system using the H-ARQ technique according to an embodiment of the present invention.

As shown, the receiver comprises an RF receiver 300, a baseband processor 302, a detector 304, a decoder 306, a CRC checker 308, a HARQ controller 310 and a buffer 312. do.

Referring to FIG. 3, first, the RF receiver 300 converts a signal of an RF band received through an antenna into a baseband signal, and converts the baseband signal into sample data and outputs the sampled data.

The baseband processor 302 baseband processes and outputs sample data from the RF receiver 300. For example, in a CDMA system, the baseband processor 302 despreads and demodulates the sample data from the RF receiver 300 using a known orthogonal code in advance. As another example, in the case of an OFDM system, the baseband processor 302 performs FFT (Fast Fourier Transform) operation on the sample data from the RF receiver 300 and outputs the sample data.

The detector 304 demodulates (or detects) the data from the baseband processor 302 according to a known modulation scheme, and outputs an LLR value of each code bit. In the initial transmission, the decoder 306 iteratively decodes and outputs the LLR values from the detector 304. Here, it is assumed that the decoder 306 is an iterative decoder that decodes a turbo code or an LDPC code. Meanwhile, according to the present invention, the decoder 306 buffers at least one of the LLR values input from the detector 204, the final LLR values of the decoder 306, and the final state values of the decoder 306. ).

The CRC checker 308 performs an error check (CRC check) on the decoded data from the decoder 306 and provides the result to the HARQ controller 310. The HARQ controller 310 generates a response signal (ACK or NACK) according to the error check result and feeds it back to the transmitter. In addition, the HARQ controller 310 informs the decoder 306 whether to request a retransmission.

The present invention proposes three methods for decoding a retransmission packet.

First, the final state value of the decoder 306 for the previous transmission is used for retransmission packet decoding. When the reception of the initial transmission packet fails, the decoder 306 stores the final status values in the buffer 312, and upon receiving a subsequent retransmission packet, the decoder 306 receives the status values for the previous transmissions stored in the buffer 312. Set them to internal memories. Thereafter, the decoder 306 receives LLR values from the detector 306 and performs repeated decoding. If the number of repetitions of the decoder in the first transmission was N _R , the number of repetitions in one retransmission becomes 2N _R , and the number of repetitions in two retransmissions becomes 3N _R. That is, the number of repetitions of the decoder increases according to the number of retransmissions. The first method will be described in detail later with reference to FIG. 4.

Second, combine the LLR values of the detector 304 for the previous transmission and the LLR values of the detector 304 for the retransmission, and retransmit the combined LLR values and the final state value of the decoder 306 for the previous transmission. This is the method used for decoding. If the reception of the initial transmission packet fails, the decoder 306 stores the LLR values of the detector 304 and the final state values of the decoder 306 for the previous transmission in the buffer 312, and then receives the retransmission packet. The decoder 306 sets the state values for previous transmissions stored in the buffer 312 in internal memories. The decoder 306 then combines the LLR values of the detector 304 for the previous transmission and the LLR values for the retransmission, and performs iterative decoding with the combined LLR values. The second method will be described in detail later with reference to FIG. 5.

Third, the method combines the LLR values of the decoder 306 for the previous transmission and the LLR values of the detector 304 for the retransmission, and uses the combined LLR values for decoding. The decoder 306 stores the final LLR values in the buffer 312 when it fails to receive the initial transport packet. Upon receiving the retransmission packet, the decoder 306 combines the LLR values of the decoder 306 for the previous transmission with the LLR values of the detector 304 for the retransmission, and performs repetitive decoding with the combined LLR values. The third method will be described in detail later with reference to FIG. 6.

On the other hand, when the receiver supports the above-described three modes, decoding may be performed by selecting one of the three modes according to a predetermined criterion.

In the following description of the detailed operation according to the present invention, it is assumed that initial transmission fails.

4 illustrates an operation procedure of a receiver in a communication system using the H-ARQ scheme according to an embodiment of the present invention.

Referring to FIG. 4, the receiver first checks whether a retransmission packet is received in step 401. When the retransmission packet is received, the receiver acquires an LLR value using a detector in step 403. In step 405, the receiver reads the final state values of the decoder for the previous transmission (or the initial transmission) from the buffer and sets them in the internal memory of the decoder.

In step 407, the receiver inputs the LLR values from the detector to the decoder loaded with the final state values for the previous transmission, and obtains decoded date for the retransmitted packet through repeated decoding of the decoder. .

In step 409, the receiver performs an error check (CRC check) on the decoded data. In operation 411, the receiver determines whether an error occurs in the retransmission packet from the error check result. If no error exists in the retransmission packet, the receiver proceeds directly to step 415. On the other hand, if there is an error in the retransmission packet, the receiver proceeds to step 413 and stores the final state values of the decoder in the buffer and proceeds to step 415.

In step 415, the receiver generates a response signal (ACK or NACK) according to the error check result and feeds it back to the transmitter.

5 illustrates an operation procedure of a receiver in a communication system using the H-ARQ scheme according to another embodiment of the present invention.

Referring to FIG. 5, the receiver first checks whether a retransmission packet is received in step 501. When the retransmission packet is received, the receiver acquires an LLR value using a detector in step 503. The receiver then combines the LLR values of the detector for the previous transmission (or the initial transmission) with the LLR values of the detector for the retransmission in step 505. In step 507, the receiver reads the final state values of the decoder for the previous transmission (or the initial transmission) from the buffer and sets them in the internal memory of the decoder.

In step 509, the receiver inputs the combined LLR values into the decoder loaded with the final state values for the previous transmission, and generates decoded data for the retransmission packet through repeated decoding of the decoder.

In step 511, the receiver performs an error check (CRC check) on the decoded data. In operation 513, the receiver determines whether an error occurs in the retransmission packet from the error check result. If no error exists in the retransmission packet, the receiver proceeds directly to step 517. On the other hand, if an error exists in the retransmission packet, the receiver proceeds to step 515 and stores the combined LLR values and final state values of the decoder in the buffer and then proceeds to step 517.

In step 517, the receiver generates a response signal (ACK or NACK) according to the error check result and feeds it back to the transmitter.

6 illustrates an operation procedure of a receiver in a communication system using the H-ARQ technique according to another embodiment of the present invention.

Referring to FIG. 6, the receiver first checks whether a retransmission packet is received in step 601. When the retransmission packet is received, the receiver acquires an LLR value using a detector in step 603. The receiver then combines the LLR values of the decoder for the previous transmission (or the initial transmission) with the LLR values of the detector for retransmission in step 605.

In step 607, the receiver inputs the combined LLR values into a decoder, and generates decoded data for a retransmission packet through repeated decoding of the decoder.

In step 609, the receiver performs an error check (CRC check) on the decoded data. In operation 611, the receiver determines whether an error occurs in the retransmission packet from the error check result. If no error exists in the retransmission packet, the receiver proceeds directly to step 615. On the other hand, if there is an error in the retransmission packet, the receiver proceeds to step 613 to store the final LLR values of the decoder in the buffer and proceeds to step 615.

In operation 615, the receiver generates a response signal (ACK or NACK) according to the error check result and feeds it back to the transmitter.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but is capable of various modifications within the scope of the invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the following claims, but also by those equivalent to the scope of the claims.

As described above, the present invention has the effect of significantly reducing the number of repetitions of the decoder for the same performance by using the LLR values of the decoder calculated in the previous transmission and the final state values of the decoder for the previous transmission in retransmission packet decoding. . That is, the capacity of the system can be improved by increasing the decoding performance of the decoder, thereby reducing the number of packet retransmissions.

Claims (14)

A receiver in a communication system using a hybrid automatic repeat request (H-ARQ) technique, A buffer that stores the decoding result of the previous transmission, A detector for demodulating the received retransmission packet to produce LLR values; And a decoder for performing repeated decoding using the decoding result of the previous transmission and the LLR values from the detector. The method of claim 1, And the buffer stores at least one of the LLR values of the detector for the previous transmission, the final LLR values of the decoder for the previous transmission, and the final state values of the decoder for the previous transmission. The method of claim 1, And the decoder is a decoder for decoding a turbo code or a Low Density Parity Check (LDPC) code. The method of claim 1, And the decoder sets the final state values of the decoder for the previous transmission in internal memory and performs repeated decoding as input to the LLR values from the detector. The method of claim 1, The decoder sets the final state values of the decoder for the previous transmission in internal memory, combines the LLR values of the detector for the previous transmission with the LLR values of the detector for the retransmission, and inputs the combined LLR values. And repeating decoding. The method of claim 1, And the decoder combines the final LLR values of the decoder for the previous transmission and the LLR values of the detector for the retransmission and performs repeated decoding as input to the combined LLR values. The method of claim 1, An error checker that performs an error check on the decoded data from the decoder; And a HARQ controller for feeding back a response signal according to an error check result of the error checker to a transmitter. In a reception method in a communication system using a hybrid automatic repeat reQuest (H-ARQ) method, Storing the decoding result of the previous transmission; Demodulating the received retransmission packet to generate LLR values; Performing iterative decoding using the decoding result of the previous transmission and the LLR values of the retransmission packet. 9. The method of claim 8, And the decoding result is at least one of the LLR values of the detector for the previous transmission, the final LLR values of the decoder for the previous transmission, and the final state values of the decoder for the previous transmission. 9. The method of claim 8, And the iterative decoding is decoding for a turbo code or a low density parity check (LDPC) code. The method of claim 8, wherein the decoding process, Setting final state values of the decoder for the previous transmission in the internal memory of the decoder; And performing a repetitive decoding on the decoder by inputting the generated LLR values. The method of claim 8, wherein the decoding process, Setting final state values of the decoder for the previous transmission in the internal memory of the decoder; Combining the LLR values of the detector with the generated LLR values for the previous transmission, And performing a repetitive decoding on the decoder by inputting the combined LLR values. The method of claim 8, wherein the decoding process, Combining the final LLR values of the decoder for the previous transmission with the generated LLR values, And performing a repetitive decoding on the decoder by inputting the combined LLR values. 9. The method of claim 8, Performing an error check on the decoded data; And feeding back a response signal according to the error check result to the transmitter.

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