JP2008011146A - Communication method, encoder, and decoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a communication method, an encoder, and a decoder that improve tolerance of a burst error. <P>SOLUTION: The communication method includes a step (S101) wherein the encoder 10 and decoder 20 share state information of a trellis predefined such that a specific bit in an information bit series has a specific state in a state transition table; a step (S102) wherein there are two or more specific bits and the encoder 10 generates a frame such that control bits for control to place the specific bits in the specific state are added before the specific bits; a step (S103) wherein the encoder 10 encodes the generated frame; and a step (S105) wherein the decoder 20 decodes the encoded frame. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a communication method, an encoder, and a decoder.

  In a wireless communication system, an error correction code technique is an indispensable technique for transmitting information. Among them, the turbo code is attracting attention as an encoding / decoding method that approaches the “Shannon limit”, which is the limit of the data transmission rate that can be transmitted without error.

  In the turbo code, of the two convolutional codes, data is once stored in a memory before encoding the second convolutional code. Thereafter, the order of the data is agitated by an interleaver that extracts the data in a different order. When decoding, a decoder corresponding to two convolutional codes is used. At this time, decoding is repeatedly performed while feeding back the result of one decoder.

Thus, the turbo code requires a large amount of calculation for decoding, and at the same time, the calculation amount necessary for decoding and the error correction performance of the code are in a trade-off relationship. That is, in order to improve error correction performance, the amount of calculation required for decoding increases. Therefore, a method of adjusting the amount of calculation necessary for decoding by changing the block size, which is one unit of encoding, has been disclosed (for example, see Non-Patent Document 1).
XLINKS IEEE 802.16e CTC Decoder Core

  However, when the code block size is shortened in order to reduce the computation time required for the turbo decoding described above, the inter-code distance when the encoded data is agitated decreases. That is, as compared with the case where the block size is long, the distance at which each agitated data is dispersed becomes shorter. For this reason, when a part of the block is lost, there is a high possibility that data close to each other before stirring is lost at a time, and there is a problem that resistance to burst errors is reduced.

  Therefore, in view of the above problems, the present invention aims to provide a communication method, an encoder, and a decoder that adjust the amount of calculation required for decoding without changing the block size and improve the tolerance to burst errors. And

  In order to achieve the above object, a first feature of the present invention is that a turbo coding scheme is used to encode an information bit sequence by a method described in a state transition table, and encoded data. A communication method with a decoder for decoding, wherein (a) a predetermined bit in an information bit sequence is defined in advance between an encoder and a decoder as having a specific state in a state transition table A step of sharing trellis shape information, and (b) there are two or more specific bits, and in the encoder, a control bit for controlling a specific bit to be in a specific state is added before the specific bit. Generating a generated frame; (c) encoding the generated frame in the encoder; and (d) decoding the encoded frame using the shape information in the decoder. Including And summarized in that a method.

  According to the communication method according to the first feature, the calculation amount necessary for decoding can be adjusted without changing the block size, and the tolerance to burst errors can be improved.

  Further, in the communication method according to the first feature, when the order of data in the information bit sequence is agitated in the encoding step, the information bit is agitated and decoded so as to change the order of the control bits. When the order of data in the series is stirred, stirring may be performed so that the order of the control bits is changed.

  According to this communication method, since the position of the control bit in the frame does not change before and after stirring, it is possible to control the specific bit to be in a specific state even after decoding.

  A second feature of the present invention is an encoder that encodes an information bit sequence by a method described in a state transition table using a turbo coding method, and (a) decodes encoded data. A specific bit in the information bit sequence with the decoder shares a trellis shape information that predefines that a specific bit in the state transition table has a specific state; and (b) a specific bit There are two or more bits, and a generation unit that generates a frame in which a control bit for controlling a specific bit to be in a specific state is added before the specific bit, and (c) a frame generated by the generation unit The gist of the present invention is that the encoder includes an encoding unit that encodes.

  According to the encoder of the second feature, the calculation amount necessary for decoding can be adjusted without changing the block size, and the tolerance to burst errors can be improved.

  A third feature of the present invention is a decoder that decodes data encoded by an encoder that encodes an information bit sequence by a method described in a state transition table using a turbo coding method. (A) a shape information holding unit that shares shape information of a trellis that predefines that a specific bit in the information bit sequence has a specific state in the state transition table with the encoder; and (b) There are two or more specific bits, and the encoder generates a coded frame generated by adding control bits before the specific bits to control the specific bits to be in a specific state. The gist of the present invention is that the decoder includes a decoding unit that performs decoding using information.

  According to the decoder according to the third feature, the calculation amount necessary for decoding can be adjusted without changing the block size, and the tolerance to burst errors can be improved.

  According to the present invention, it is possible to provide a communication method, an encoder, and a decoder that adjust the amount of calculation required for decoding without changing the block size and improve the tolerance to burst errors.

  Next, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic.

(Wireless communication device)
The present invention is applied to communication in a wireless communication apparatus that employs a multicarrier modulation / demodulation method. Examples of the multicarrier modulation / demodulation method include a DMT (Discrete Multi Tone) modulation / demodulation method and an OFDM (Orthogonal Frequency Division Multiplex) modulation / demodulation method. Hereinafter, a base station will be described as an example of a wireless communication device.

  As shown in FIG. 1, the base station 100 according to the present embodiment includes an antenna 1, an RF (Radio Frequency) unit 2, a baseband unit 3 that performs data encoding and decoding, a communication path interface 4, and the like. The control unit 5 is provided.

  The antenna 1 communicates with a wireless terminal through a wireless line. The RF unit 2 performs high-frequency transmission / reception. The communication path interface 4 is connected to other communication devices via the communication network 6. The control unit 5 controls the entire base station.

  The baseband unit 3 includes an encoder 10, a decoder 20, a transmission modulation unit 30, and a reception demodulation unit 31. The reception demodulator 31 performs demodulation processing on the sequence received from the wireless terminal. The decoder 20 performs error correction decoding on the received data based on the packet information. The encoder 10 performs error correction coding on the transmission data. The transmission modulation unit 30 generates a transmission signal for the transmission data.

  The encoder 10 encodes an information bit sequence by a method described in the state transition table using a turbo code method, and the decoder 20 decodes the encoded data.

  As shown in FIG. 2, the encoder 10 includes a first RSC encoder 11, a CTC interleaver 12, a second RSC encoder 13, a multiplexer 14, and a shape information holding unit 15.

  The shape information holding unit 15 holds trellis shape information that predefines that a specific bit in the information bit sequence has a specific state in the state transition table. The trellis shape information is information shared with the decoder 20. The trellis shape information will be described in detail later.

  A first RSC encoder (first recursive systematic convolutional encoder) 11 convolutionally encodes an information bit sequence and outputs redundant bits. At this time, the first RSC encoder 11 generates a frame in which control bits for controlling specific bits to be in a specific state are added before the specific bits, and encodes the generated frame.

  The CTC interleaver 12 agitates the order of the data of the information bit series and replaces it at random. At this time, the CTC interleaver 12 performs agitation so as to change the order of the control bits.

  A second RSC encoder (second recursive systematic convolutional encoder) 13 performs convolutional encoding on the information bit sequence after replacement by the interleaver 12 and outputs redundant bits.

  The multiplexer 14 switches and outputs one input signal from a plurality of input signals.

  FIG. 3 is a diagram showing the internal configuration of the first RSC encoder 11 and the second RSC encoder 13, and the two recursive systematic convolutional encoders are encoders that output only redundant bits, respectively.

  In the encoder 10 configured as described above, simultaneously, the information bit sequence: x1, the redundant bit sequence obtained by encoding the information bit sequence: x1 by the processing of the first RSC encoder 11, x2, and the second RSC. The redundant bit sequence x3 obtained by encoding the information bit sequence after the interleaving process can be output by the process of the encoder 13.

  As shown in FIG. 4, the decoder 20 includes a demultiplexer 21, a first CTC decoder 22, a CTC interleaver 23, a second CTC decoder 24, a CTC deinterleaver 25, and a shape information holding unit. 26. In the following description, received signals: y1, y2, and y3 are signals in which information bit sequence: x1 and redundant bit sequence: x2, x3 are affected by transmission line noise and fading, respectively.

  The demultiplexer 21 switches and outputs a plurality of input signals from one input signal.

  The first CTC decoder 22 calculates a log likelihood ratio from the received signal: y1 and the received signal: y2. Specifically, the first CTC decoder 22 calculates a log likelihood ratio: L (x1k ′) of the estimated information bit: x1k ′ estimated from the received signal: y1k and the received signal: y2k (k is time) Represents). Here, the probability that the information bit: x1k is 1 with respect to the probability that the information bit: x1k is 0 is obtained.

  The CTC interleaver 23 rearranges the signals so that the received signal: y1k and the external information: Le (x1k) are matched with the time of the received signal: y3.

  The second CTC decoder 24 calculates a log likelihood ratio from the received signal: y1 and the received signal: y3. Specifically, like the first CTC decoder 22, the second CTC decoder 24 is based on the received signal: y1, the received signal: y3, and the previously calculated external information: Le (x1k). The log likelihood ratio: L (x1k ′) is calculated.

  The CTC deinterleaver 25 rearranges the external information and feeds it back to the first CTC decoder 22 as prior information: La (x1k). At this time, the CTC deinterleaver 25 performs agitation so as to change the order of the control bits.

  The shape information holding unit 26 holds trellis shape information that predefines that a specific bit in the information bit sequence has a specific state in the state transition table. The shape information is information shared with the encoder 10.

(Communication method)
First, trellis shape information according to the present embodiment will be described.

  The decoder 20 calculates a state transition probability when decoding received data. Specifically, as shown in FIG. 5, the probability βk + 1 (S1) that the state of k + 1 bits is S1 is that the state of k-1 bits is S1, and the state of k bits is S0. , The product of the probabilities that the state of k + 1 bits is S1, and is expressed as αk−1 (S1) × γk (S1, S0) × γk + 1 (S0, S1). When all transition states are considered in this way, the state transition table shown in FIG. 6 is obtained. The decoder 20 calculates the state of each bit using such a state transition table and outputs the state with the highest probability.

  In this embodiment, the encoder 10 and the decoder 20 share the trellis shape information that predefines that a specific bit in the information bit sequence has a specific state in the state transition table. For example, as shown in FIG. 7, shape information specifying that the i-bit state is S0 and the j-bit state is S0 is shared.

  Next, the communication method according to the present embodiment will be described with reference to FIG. Here, it is assumed that communication is performed between the first wireless communication apparatus including the encoder 10 on the transmission side and the second wireless communication apparatus including the decoder 20 on the reception side.

  First, between the encoder 10 and the decoder 20, a specific bit in the information bit sequence shares trellis shape information that predefines that it has a specific state in the state transition table (S101). As the shape information to be shared, for example, as shown in FIG. 9, it is assumed that 1 bit, m bit, and n bit in the information bit sequence are defined as the state S0. The shape information may be determined in advance between the first wireless communication device and the second wireless communication device. The shape information is added to the control signal before the communication and the second information is transmitted from the first wireless communication device to the second wireless communication device. May be transmitted to the other wireless communication apparatus.

  Next, the encoder 10 of the first wireless communication apparatus sets a control bit for controlling a specific bit (l bit, m bit, n bit) to be in a specific state (all S0). A previously added frame is generated (S102). That is, in FIG. 9, several bits before l bit, m bit, and n bit are control bits. The number of control bits is a number necessary for setting each specific bit to a specific state, and depends on the product of the number of combinations of states and the number of specific bits.

  Next, the encoder 10 of the first wireless communication apparatus encodes the generated frame (S103). At this time, the encoder 10 stirs and encodes the order of the data in the information bit sequence, but stirs so that the order of the control bits is changed. For example, when there are two specific bits, there are two positions where control bits are arranged as shown in FIG. 10 (shaded area in FIG. 10), and there are 3 specific bits as shown in FIG. If there are two, as shown in FIG. 11, there are three positions where control bits are arranged (shaded portions in FIG. 11).

  Next, the first wireless communication device transmits the encoded frame information to the second wireless communication device (S104).

  Next, the decoder 20 of the second wireless communication apparatus decodes the encoded frame using the shape information shared with the encoder 10 (S105). At this time, the decoder 20 agitates the order of the data in the information bit series, but agitate so that the order of the control bits is changed, and return to the original order.

(Function and effect)
According to the communication method, the encoder 10 and the decoder 20 according to the present embodiment, by using the trellis shape information, the calculation amount necessary for decoding is adjusted without changing the block size which is one unit of encoding. can do. That is, as the number of specific bits increases, the number of state transitions predicted by the decoder 20 decreases, and the calculation amount necessary for decoding can be adjusted.

  Further, since it is not necessary to reduce the block size, the interleaving distance is widened, and the resistance to burst errors can be improved.

  In this embodiment, the order of data in the information bit sequence is stirred when encoding, but stirring is performed so that the order of control bits is changed. Similarly, the order of data in the information bit series is stirred when decoding, but stirring is performed so that the order of the control bits is changed. That is, in the conventional agitation processing, the control bits are dispersed in the frame as shown in FIG. 12, but in this embodiment, the order of the control bits is changed as shown in FIGS. To stir. As described above, since the position of the control bit in the frame does not change before and after stirring, it is possible to control the specific bit to be in a specific state even after decoding.

(Other embodiments)
Although the present invention has been described according to the above-described embodiments, it should not be understood that the descriptions and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  For example, in the present embodiment, the case where a specific bit is in the state S0 has been described as an example of the trellis shape information, but the state is not limited to S0 and may be in another state. Further, there are a plurality of specific bits, but it is not necessary that all the specific bits are in the same state, and a specific state may be defined in advance for each bit.

  Furthermore, in the present embodiment, the base station has been described as an example of the wireless communication apparatus according to the present invention, but it is needless to say that a wireless terminal such as a PC or a mobile phone may be used.

  As described above, the present invention naturally includes various embodiments not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

It is a block block diagram of the radio | wireless communication apparatus which concerns on this embodiment. It is a block block diagram of the encoder which concerns on this embodiment. It is a block block diagram of the RSC encoder of FIG. It is a block block diagram of the decoder which concerns on this embodiment. It is a figure for demonstrating the state transition probability which concerns on this embodiment (the 1). It is a figure for demonstrating the state transition probability which concerns on this embodiment (the 2). It is a figure which shows the shape information of the trellis which concerns on this embodiment (the 1). It is a sequence diagram which shows the communication method which concerns on this embodiment. It is a figure which shows the shape information of the trellis which concerns on this embodiment (the 2). It is a figure which shows before and after stirring of the flame | frame which concerns on this embodiment (the 1). It is a figure which shows before and after stirring of the flame | frame which concerns on this embodiment (the 2). It is a figure which shows before and after stirring of the conventional flame | frame.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Antenna 2 ... RF part 3 ... Baseband part 4 ... Communication path interface 5 ... Control part 6 ... Communication network 10 ... Encoder 11 ... 1st RSC encoder 12 ... CTC interleaver 13 ... 2nd RSC encoder 14 ... Multiplexer 15 ... Shape information holding unit 20 ... Decoder 21 ... Demultiplexer 22 ... First CTC decoder 23 ... CTC interleaver 24 ... Second CTC decoder 25 ... CTC deinterleaver 26 ... Shape information holding unit 30 ... Transmission modulation Unit 31 ... Reception demodulation unit 100 ... Base station

Claims (4)

A method of communicating between an encoder that encodes an information bit sequence and a decoder that decodes the encoded data by a method described in a state transition table using a turbo coding scheme,
Sharing, between the encoder and the decoder, trellis shape information that predefines that a particular bit in the information bit sequence has a particular state in the state transition table;
There are two or more specific bits, and the encoder generates a frame in which control bits for controlling the specific bits to be in the specific state are added before the specific bits;
Encoding the generated frame in the encoder;
And a step of decoding the encoded frame using the shape information in the decoder. In the encoding step, when stirring the order of the data in the information bit series, stirring so as to change the order of the control bits,
2. The communication method according to claim 1, wherein in the decoding step, when the order of the data in the information bit series is stirred, stirring is performed so that the order of the control bits is changed. An encoder that encodes an information bit sequence by a method described in a state transition table using a turbo coding method,
A specific bit in the information bit sequence shares trellis shape information preliminarily defined as having a specific state in the state transition table with a decoder that decodes the encoded data. A shape information holding unit;
There are two or more specific bits, and a generation unit for generating a frame in which a control bit for controlling the specific bits to be in the specific state is added before the specific bits;
An encoder comprising: an encoding unit that encodes the frame generated by the generation unit. A decoder that decodes data encoded by an encoder that encodes an information bit sequence by a method described in a state transition table using a turbo coding scheme,
A shape information holding unit that shares shape information of a trellis that predefines that a specific bit in the information bit sequence has a specific state in the state transition table with the encoder,
There are two or more specific bits, and the encoder generates and encodes a control bit that controls the specific bits to be in the specific state before the specific bits. And a decoding unit that decodes the received frame using the shape information.

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