WO2018225364A1

WO2018225364A1 - Wireless communication method and wireless communication system

Info

Publication number: WO2018225364A1
Application number: PCT/JP2018/014518
Authority: WO
Inventors: 敬亮山本; 矢野　隆
Original assignee: 株式会社日立国際電気
Priority date: 2017-06-06
Filing date: 2018-04-05
Publication date: 2018-12-13
Also published as: JPWO2018225364A1; JP6812546B2

Abstract

A demodulator demodulates a wireless signal and outputs first bit information; an interleave processing unit performs de-interleave processing on the first bit information to return bits that were exchanged with interleave processing to their original sequence and outputs second bit information; a decoder decodes the second bit information and outputs third bit information; a de-interleave processing unit performs interleave processing, which is the reverse process to the de-interleave processing, on the third bit information and generates fourth bit information, and performs a decoding process repeatedly by inputting the fourth bit information as advance information to the demodulator; a first code optimization processing unit generates control information for redundant bits on the basis of a combination of two pieces of likelihood information of repeated input and output of the decoding process; and a transmitting device uses at least one code word for which the free distance differs on the basis of the generated control information and transmits additional redundant bits.

Description

Wireless communication method and wireless communication system

Import by reference

This application claims the priority of Japanese Patent Application No. 2017-111439, which was filed on June 6, 2017, and is incorporated herein by reference.

The present invention relates to a wireless communication method for transmitting and receiving data via a wireless propagation path.

Hybrid-ARQ (HARQ) is widely known as background technology in this technical field. HARQ is a method combining ARQ and an error correction code, and is a technique for improving error correction capability at the time of retransmission by using a previous retransmission result at the time of decoding. For example, Non-Patent Document 1 discloses a HARQ scheme using a turbo code having excellent error correction capability. In the method disclosed in Non-Patent Document 1, the encoded parity sequence is punctured and transmitted, and when an error occurs, the punctured parity sequence is sequentially added and transmitted for each retransmission.

Also, a technique called BICM-ID (Bit Interleaved Coded Modulation with Iterative decoding) has been proposed. For example, as described in Patent Document 1 and Non-Patent Document 2, in BICM-ID, excellent characteristics can be obtained by repeating demodulation processing for modulation and decoding processing for encoding. The characteristics of the BICM-ID are determined not by the characteristics of the demodulator and the decoder but by their matching. For this reason, it is possible to analyze a convergence characteristic using EXT (Extrinsic Information Transfer) analysis and design a demodulator and a decoder that realize excellent characteristics (see, for example, Non-Patent Document 3). In Non-Patent Document 4, encoding is performed with a code based on a repetitive code, which is a simple code, and multi-level modulation using non-Gray mapping and extended mapping is performed to reduce transmission rate loss. Disclosed is a method for providing BICM-ID with a small processing capacity.

JP 2010-124367 A

The conventional HARQ system performs error-free communication by changing the coding rate of an error correction code based on an effective signal-to-noise power ratio (SNR) and an estimated value of channel capacity. However, when HARQ is applied to the BICM-ID required in the present invention, the performance of the BICM-ID is determined by the convergence characteristics of the demodulator and the decoder. For this reason, even if the SNR and channel capacity are the same, the convergence characteristics of the demodulator differ depending on the propagation path characteristics and the modulation method, and the characteristics of the decoder that matches the convergence characteristics of the demodulator differ. Therefore, in the code configuration determined based on the SNR and the channel capacity, inappropriate redundant bits are used for retransmission, and there may occur a situation where communication is more error-prone when larger than necessary redundant bits.

A typical example of the invention disclosed in the present application is as follows. That is, a wireless communication method for transmitting data from a transmission device to a reception device, wherein the reception device demodulates a radio signal and outputs bit information; a decoder that decodes the bit information; An interleave processing unit for switching the bit order of bit information, a deinterleaving processing unit for switching the bit order of the bit information, and a first code optimization processing unit for generating redundant bit control information, Performs coding using a convolutional code having at least two types of free-distance codewords, wherein the demodulator demodulates a radio signal using prior information and outputs first bit information. And the interleaving unit performs a dein that restores the order of the bits exchanged in the interleaving process for changing the order of the bits with respect to the first bit information. Performs a leave process, outputs second bit information, the decoder decodes the second bit information, outputs third bit information, and the deinterleave processing unit outputs the third bit information. The bit information is subjected to an interleaving process that is an inverse process of the deinterleaving process, the fourth bit information is generated, and the fourth bit information is input to the demodulator as the prior information, thereby repeatedly. The decoding process is performed, and the first code optimization processing unit generates redundant bit control information based on a combination of two pieces of likelihood information of the input and output of the iterative decoding process, and the generated control information To the transmitter, and the transmitter transmits an additional redundant bit using at least one of the codewords having different free distances based on the generated control information.

According to the representative embodiment of the present invention, communication can be performed while suppressing an increase in redundant bits due to retransmission. Problems, configurations, and effects other than those described above will become apparent from the description of the following embodiments.

It is a figure which shows the structure of the radio | wireless communications system of this invention. It is a figure which shows the resending procedure of the resending method of this invention. FIG. 3 is a diagram showing iterative decoding processing in the retransmission method of the present invention, FIG. 3A is a diagram showing a receiving side iterative decoding processing unit in this embodiment, and FIG. 3B is an EXIT analysis at the time of initial transmission FIG. 3C is a diagram showing the results of EXIT analysis after N times of transmission. It is a figure which shows an example of a structure of the encoding modulation process part using the resending method of this invention. It is a figure which shows an example of a structure of the encoder used with the retransmission method of this invention. It is a figure which shows an example of a structure of the encoder used with the retransmission method of this invention. It is a figure which shows an example of a structure of the encoder whose constraint length used by this invention is 7. It is a figure which shows an example of the characteristic of the code | symbol used with the resending method of this invention. It is a figure which shows an example of the encoding process using the resending method of this invention. It is a figure which shows an example of the convergence characteristic of the decoder in the resending method of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing a configuration of a wireless communication system according to an embodiment of the present invention.

The wireless communication system of the present embodiment includes an encoder 10, an interleaver 11, a modulator 12, a transmitter having a code optimization processing unit 19 and an antenna 13, and an iterative decoding processing unit 18, a code optimization processing unit 21 and an antenna 22. It is comprised by the receiver which has. The transmitter and the receiver are connected via a radio propagation path 14.

In the transmitter, the encoder 10 encodes information bits, the interleaver 11 switches the bit order in the codeword output from the encoder 10, the modulator 12 modulates, and the antenna 13 outputs it.

The iterative decoding processing unit 18 of the receiver includes a demodulator 15, a deinterleaver 16, a decoder 17, and an interleaver 20. In the receiver, a signal is received via the radio propagation path 14, the demodulator 15 demodulates the received signal, a deinterleaver 16 that performs reverse processing of the interleaver 11 returns the bit order, and a decoder 17 decodes the signal. To do. The decoding result is input to the demodulator 15 via the interleaver 20, and the demodulator 15 refers to the decoding result of the decoder 17 and outputs a further highly accurate demodulation result. In the wireless communication system of this embodiment, the transmitter performs encoding and modulation using the encoder 10, the interleaver 11, and the modulator 12, and the receiver uses the demodulator 15, the deinterleaver 16, the decoder 17, and the interleaver. The BICM-ID is configured by performing iterative decryption processing using 20.

In the wireless communication system of the present embodiment, the code optimization processing unit 19 of the transmitter has a function of controlling a redundant bit generation method based on likelihood information obtained by iterative decoding processing with BICM-ID. In the receiver, when an error remains as a result of the repetition process of BICM-ID, the external information (Extrinsic Information) output from the demodulator 15 and the prior information (A Priori Information) input to the demodulator 15 are estimated. Control information (redundant bit information or likelihood information) for determining additional redundant bits to be retransmitted from the transmitter is used as the degree information. The receiver feeds back control information (redundant bit information or likelihood information) to the transmitter together with the retransmission request. Based on the control information from the receiver, the transmitter determines additional redundant bits to be retransmitted and controls the encoder 10. Likelihood information used for code optimization is equivalent before and after the interleaver 20 and the deinterleaver 16, and either of them may be used. The likelihood information used by the code optimization processor 19 is based on a combination of likelihood information of demodulator external information or decoder prior information and likelihood information of demodulator prior information or decoder external information. A retransmission code is determined.

FIG. 2 is a diagram showing a retransmission procedure according to the present embodiment.

First transmission is performed from the transmitter (24), and when an error is detected at the receiver, a retransmission request and code optimization information are fed back from the receiver to the transmitter (25). The transmitter generates a code to be used for retransmission based on the fed back code optimization information, adds a redundant bit, and performs the second transmission (26). The receiver repeats the decoding process by combining the received signal at the first transmission stored in the buffer and the redundant bit added for the second time. If an error remains, the receiver again sends it from the receiver to the transmitter. A retransmission request and code optimization information are fed back (27). Thereafter, the retransmission process is repeated until there is no error at the receiver or the upper limit of the number of retransmissions is reached (28), and when the decoding process is completed without error at the receiver, a reception confirmation response is fed back to the transmitter. (29) The communication process is terminated.

Note that the overhead required for retransmission may be reduced by not explicitly notifying the receiver of the redundant bit configuration designed by the code optimization processing unit 19 of the transmitter. In this case, the decoder 17 uses the algorithm for determining the same redundant bits in the code optimization processing unit 19 of the transmitter and the code optimization processing unit 21 of the receiver, and the decoder 17 performs redundancy from the code optimization processing unit 21 of the receiver. The bit configuration is obtained and the decoding process is performed.

FIG. 3A is a diagram illustrating the iterative decoding processing unit 18 of the receiver in the present embodiment, and FIG. 3B is a diagram illustrating an EXIT analysis result at the time of initial transmission, and FIG. These are figures which show the EXIT analysis result after N times transmission.

As the likelihood information exchanged between the demodulator and the decoder using BICM-ID, a log-likelihood ratio (LLR: Log Likelihood Ratio) in units of bits is generally used. LLR is a logarithmic expression of the ratio between the probability that the bit b is 0 and the probability that it is 1, and is expressed by Equation (1).

In Equation (1), P (b = 0) indicates the probability that b is 0, and P (b = 1) indicates the probability that b is 1.

The convergence characteristics of the BICM-ID iterative decoding process can be analyzed by EXT (Extrinsic Information Transfer) analysis described in Non-Patent Document 3. In the EXIT analysis, the input / output characteristics of the decoder and demodulator are displayed in the form of the mutual information amount Im of the bit expressed by Equation (2), and the characteristics of both are overlapped and plotted on one chart for repeated decoding. The amount of information obtained by processing can be analyzed.

The mutual information amount in Equation (2) is an average of the entire code word of the mutual information amount of bits, and is expressed by a value of 0 to 1, and the closer to 1, the greater the bit likelihood of the entire code word.

Prior information _{I A demodulator, DEM} and the decoder of the external information _{I E,} the _DEC on the horizontal axis, the demodulator of the external information _{I E, DEM,} prior information _{I A decoder,} taking the vertical axis to _DEC, The mutual information amount increases along each characteristic by the iterative decoding process. In the EXIT analysis result 30 at the time of initial transmission shown in FIG. 3B, the increase in the mutual information amount is stopped at the point where the characteristics of the two intersect, and errors remain in the decoding result. By changing the characteristics of the decoder from the mutual information amount at the intersection so that the value of the external information when the prior information of the coordinates of the intersection is given becomes larger, the intersection becomes closer to 1. That is, by changing the additional information bits due to retransmission and changing the characteristics of the decoder so that the intersection is closer to 1, residual errors in iterative decoding after retransmission can be reduced. By repeating this process, as shown in FIG. 3C, the characteristics of the decoder are changed so that the convergence characteristics of the demodulator and the decoder do not intersect in the EXIT analysis result 31 after N transmissions. It is possible to obtain no results.

FIG. 4 is a diagram illustrating an example of a configuration of a coded modulation processing unit using a convolutional code according to the present embodiment.

Since the encoded modulation processing unit shown in FIG. 4 uses a convolutional code, the encoder 10 is composed of a convolutional encoder 40. In addition, a puncture processing unit 41 that punctures codes is provided between the convolutional encoder 40 and the interleaver 11.

It is known that the error correction capability of a convolutional code is determined by the free distance of the code with respect to the constraint length (corresponding to the circuit scale), and a code with a large (preferably maximum) free distance with respect to the constraint length is generally used. Used. For example, it is known that a generator polynomial (133, 171) has a maximum free distance in a convolutional code with a constraint length of 7 and an encoding rate of 1/2 (the number of branches is 2) and is generally used. . On the other hand, the convolutional code of this embodiment is characterized by having a generator polynomial having at least two types of free distances. That is, in general, by using a generator polynomial having a small free distance that is not used due to poor error correction capability, code design at the time of retransmission can be made according to the characteristics of the demodulator, and good iterative decoding can be realized.

FIG. 5 is a diagram illustrating an example of a convolutional encoder according to the present embodiment.

First, the information bits are input to the shift register 50 having a memory length with a constraint length of −1, and a convolutional code is formed by the logical operation of the output extracted from the tap of the shift register. The convolutional encoder of this embodiment is characterized by having at least two branches having different free distances d. Even if the free distance is the same, but the generator polynomials are different, the convergence characteristics of the decoder are not completely the same, and therefore, a plurality of branches having the same free distance may be included.

FIG. 6 is a diagram illustrating an example in which the convolutional code according to the present embodiment is configured by separating memories for different branches with different free distances and generator polynomials.

In the convolutional encoder shown in FIG. 5, branches having different free distances are generated from the output of one large shift register tap. However, the convolutional encoder shown in FIG. 6 is divided into a plurality of shift registers. Also good.

FIG. 7 is a diagram illustrating an example of an encoder having a constraint length of 7. In this encoder, in a convolutional code with a constraint length of 7, a code Ca of a generator polynomial (133, 171) with a degree of freedom distance of 10 and a code Cb of a generator polynomial (5, 7) with a free distance of 5 Have By selecting and puncturing the codes having different free distances and designing the codes and retransmission codes, the retransmission codes when HARQ is applied to the BICM-ID are optimized.

FIG. 8 is a diagram illustrating an example of the convergence characteristics of the convolutional code decoder according to the present embodiment.

FIG. 8 shows a convergence characteristic 80 of a convolutional code decoder with a free distance of 3 and a coding rate of 1/2, and a convergence characteristic 81 of a convolutional code decoder with a free distance of 10 and a coding rate of 1/2. It shows. Since the

convergence characteristics

80 and 81 have the same coding rate but different convergence characteristics, it is possible to realize iterative decoding with good characteristics by designing the code according to the characteristics of the demodulator.

FIG. 9 is a diagram illustrating an example of a retransmission method using a convolutional code according to the present embodiment.

In FIG. 9, the encoder 10 (convolutional encoder 40, puncture processing unit 41) shown in FIG. 9A is used to puncture a code Ca having a free distance d0 and a code Cb having a free distance d1. The case where the encoder which processes and produces | generates an output code is shown is shown.

First, the information bits are encoded, two code words having different free distances are generated, a part of the code words 90 are extracted by puncturing, and the first transmission is performed. When a retransmission request is received from the receiver after the initial transmission, an additional redundant bit is selected from among the punctured codes based on the code optimization information fed back, and the additional redundant bit (91 after the second time) , 92). The convergence characteristic of the decoder is controlled according to which free distance is used to select additional redundant bits. The receiver stores all codewords from the first transmission until it is confirmed that decoding can be performed without error, and repeatedly performs decoding processing using all the stored codewords.

FIG. 10 is a diagram illustrating an example of convergence characteristics of a decoder in a retransmission method using a convolutional code. FIG. 10 shows a convergence characteristic 101 at the first transmission, a convergence characteristic 102 at the second transmission, a convergence characteristic 103 at the third transmission, and a convergence characteristic 100 of the demodulator.

For the sake of explanation, the number of additional redundant bits to be transmitted in one retransmission is assumed to be 1/4 the size of the codeword at the time of initial transmission, and the redundant bits can be arbitrarily controlled by the 1/4 size of the codeword. To do. Further, a convolutional code having a code rate of 1/4 and a coding rate of 1/4 is used as an encoder.

In FIG. 10, codes having 50% puncture of codewords having free distances of 3 and 10 at the time of initial transmission are used, and the convergence characteristics 91 of the decoder at the time of initial transmission are the convergence characteristics 100 of the demodulator, It intersects at the point of the horizontal axis 0.013 and the vertical axis 0.16, and an error has occurred in the decoding result.

* Based on the coordinates of this intersection, the method of generating additional redundant bits used for the second transmission is controlled, and additional redundant bits are selected. An additional redundant bit option is either a punctured untransmitted codeword of codewords with a free distance of 3, 10 and there are two methods. The external information output by the encoder when retransmitted in each method is 0.038 and 0.022, respectively. For this reason, the method of transmitting puncture bits with a free distance of 3 increases the external information when providing prior information of the decoder at the intersection. Thereafter, the same procedure is repeated, and the output of the demodulator reaches 1 in the convergence characteristic 103 of the decoder after the third transmission. For this reason, an iterative decoding result without error can be obtained.

As described above, according to the embodiment of the present invention, since the code generation method is controlled according to the convergence characteristics of the demodulator, the BICM-ID whose characteristics cannot be determined only by the signal-to-noise power ratio and the communication capacity is used. Even in the existing systems, communication can be performed while suppressing an increase in redundant bits due to retransmission.

Further, since the value based on the likelihood information obtained by the iterative decoding process is notified as control information from the receiving apparatus to the transmitting apparatus, the amount of information fed back from the receiving apparatus to the transmitting apparatus can be reduced. In addition, the code optimization processing unit 21 of the receiving apparatus and the code optimization processing unit 19 of the transmitting apparatus use the same algorithm, and are necessary for retransmission when the configuration of redundant bits is not explicitly notified to the receiver. Overhead can be reduced.

Also, in the case where the code configuration determined based on the likelihood information obtained by the iterative decoding process is notified as control information from the reception device to the transmission device, an algorithm for determining the configuration of redundant bits on the transmission side is provided. This is unnecessary, and the processing amount on the transmission side can be reduced.

Also, when the configuration of redundant bits is explicitly notified to the receiver, it is not necessary to have an algorithm for determining the configuration of redundant bits on the receiving side, and the processing amount on the receiving side can be reduced.

The present invention is not limited to the above-described embodiments, and includes various modifications and equivalent configurations within the scope of the appended claims. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and the present invention is not necessarily limited to those having all the configurations described. A part of the configuration of one embodiment may be replaced with the configuration of another embodiment. Moreover, you may add the structure of another Example to the structure of a certain Example. In addition, for a part of the configuration of each embodiment, another configuration may be added, deleted, or replaced.

In addition, each of the above-described configurations, functions, processing units, processing means, etc. may be realized in hardware by designing a part or all of them, for example, with an integrated circuit, and the processor realizes each function. It may be realized by software by interpreting and executing the program to be executed.

Information such as programs, tables, and files that realize each function can be stored in a storage device such as a memory, a hard disk, and an SSD (Solid State Drive), or a recording medium such as an IC card, an SD card, and a DVD.

Also, the control lines and information lines indicate what is considered necessary for the explanation, and do not necessarily indicate all control lines and information lines necessary for mounting. In practice, it can be considered that almost all the components are connected to each other.

Claims

A wireless communication method for transmitting data from a transmitting device to a receiving device,
The receiving device is:
A demodulator that demodulates a radio signal and outputs bit information;
A decoder for decoding the bit information;
An interleave processing unit for changing the bit order of the bit information;
A deinterleave processing unit for changing the bit order of the bit information;
A first code optimization processing unit for generating redundant bit control information,
The transmitter performs encoding using a convolutional code having at least two types of free-distance codewords,
The method
The demodulator demodulates the radio signal using prior information and outputs first bit information;
The interleave processing unit performs deinterleaving processing for returning the order of the bits replaced in the interleaving processing for replacing the order of bits to the first bit information, and outputs second bit information,
The decoder decodes the second bit information and outputs third bit information;
The deinterleave processing unit performs an interleave process on the third bit information, which is a reverse process of the deinterleave process, generates fourth bit information, and converts the fourth bit information to the prior information. As an input to the demodulator to perform an iterative decoding process,
The first code optimization processing unit generates redundant bit control information based on a combination of two likelihood information of input and output of the iterative decoding process, and transmits the generated control information to the transmission device. Notify
The wireless communication method, wherein the transmitting device transmits an additional redundant bit using at least one of codewords having different free distances based on the generated control information.
The wireless communication method according to claim 1,
The transmission device includes a second code optimization processing unit,
The control information notified from the receiving device to the transmitting device is a value based on likelihood information obtained by the iterative decoding process,
The wireless communication method according to claim 1, wherein the first code optimization processing unit and the second code optimization processing unit have the same algorithm for determining a code configuration based on the control information.
The wireless communication method according to claim 1,
The wireless communication method characterized in that the control information notified from the receiving device to the transmitting device has a code structure determined based on likelihood information obtained by the iterative decoding process.
The wireless communication method according to claim 1,
The transmission device includes a second code optimization processing unit,
The second code optimization processing unit transmits a configuration of redundant bits transmitted by the transmission device to the reception device.
A wireless communication system for transmitting data from a transmitting device to a receiving device,
The receiving device is:
A demodulator that demodulates a radio signal and outputs bit information;
A decoder for decoding the bit information;
An interleave processing unit for changing the bit order of the bit information;
A deinterleave processing unit for changing the bit order of the bit information;
A first code optimization processing unit for generating redundant bit control information,
The transmitter performs encoding using a convolutional code having at least two types of free-distance codewords,
The demodulator demodulates the radio signal using prior information and outputs first bit information;
The interleave processing unit performs deinterleaving processing for returning the order of the bits replaced in the interleaving processing for replacing the order of the bits to the first bit information, and outputs second bit information,
The decoder decodes the second bit information and outputs third bit information;
The deinterleave processing unit performs an interleave process on the third bit information, which is a reverse process of the deinterleave process, generates fourth bit information, and converts the fourth bit information to the prior information. As an input to the demodulator to perform iterative decoding processing,
The first code optimization processing unit generates redundant bit control information based on a combination of two likelihood information of input and output of the iterative decoding process, and transmits the generated control information to the transmission device. Notify
The wireless communication system, wherein the transmitting device transmits an additional redundant bit using at least one of codewords having different free distances based on the generated control information.
The wireless communication system according to claim 5,
The transmission device includes a second code optimization processing unit,
The control information notified from the receiving device to the transmitting device is a value based on likelihood information obtained by the iterative decoding process,
The wireless communication system, wherein the first code optimization processing unit and the second code optimization processing unit have the same algorithm for determining a code configuration based on the control information.
The wireless communication system according to claim 5,
The wireless communication system, wherein the control information notified from the receiving device to the transmitting device has a code configuration determined based on likelihood information obtained by the iterative decoding process.
The wireless communication system according to claim 5,
The transmission device includes a second code optimization processing unit,
The wireless communication system, wherein the second code optimization processing unit transmits a configuration of redundant bits transmitted by the transmission device to the reception device.