JP2008211489A - Mapping method, decoding method, and communicating system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a mapping method capable of suppressing an error rate of a decoding result in multivalued modulation where an influence degree to a decoding characteristic is used for mapping and an error rate on a communication path is changed by a bit to be mapped, and to provide a decoding method, and a communication system. <P>SOLUTION: This invention relates to the mapping method in the communication system using the multivalued modulation where a convolution code and the information of not less than three bits per one symbol are assigned, and also where the bit with the smallest influence on the decoding result is assigned to a position of the bit with the largest error rate compared with the other bit. Especially, the bit which can be omitted in a punctured encoding system is assigned as the bit with the smallest influence on the decoding result. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a mapping method, a decoding method, and a communication system, and more particularly, to a mapping method, a decoding method, and a communication system for multi-level modulation.

  The convolutional coding method is called a punctured coding method, which is a technique that easily realizes a high coding rate by omitting a part of the codeword and transmitting it, and is often used in actual systems. (For example, refer nonpatent literature 1). In this punctured coding method, bits omitted in the codeword are determined to be the bits with the least deterioration in the error rate after decoding when they are sent without transmission. Which bits are omitted to determine the least deterioration in characteristics is examined by computer search or the like, and frequently used coding rates are generally well known.

  From these facts, it can be seen that the degree of influence on the decoding characteristics varies depending on each bit of the codeword. The punctured encoding method uses various influences on the decoding characteristics for each bit, and transmits various other bits easily by transmitting only other bits without transmitting a part of the code word. The characteristic deterioration is minimized while realizing the coding rate.

G. Begin et al., “High-Rate Punctured Convolutional Codes: Structure Properties and Construction Technique”, IEEE Transactions on Communications, VOL. 37, NO. 12, December 1989

  In multi-level modulation, the error rate on the communication path varies depending on the bit to be mapped. In multilevel modulation, a plurality of bits mapped to one signal point have different immunity to noise added on the communication path for each bit. Therefore, conventionally, a method such as interleaving has been used so that codeword bits mapped to bits that are vulnerable to noise and have a high error rate are not consecutive during decoding, but are basically input to the modulator. Since the mapping is performed in the order of the data, the influence on the decoding characteristics of each bit of the codeword has not been considered at all. Therefore, if a codeword bit that has a large influence on decoding characteristics is assigned to a codeword bit that is mapped to a bit that is vulnerable to noise and has a high error rate, the overall error rate characteristic of the decoding result will be high. There was a problem.

  The present invention has been made to solve such a problem, and uses a degree of influence on decoding characteristics for mapping, and a mapping method and decoding method capable of suppressing an error rate of a decoding result in multilevel modulation to a low level And to obtain a communication system.

  The present invention relates to a mapping method in a communication system using multilevel modulation that allocates convolutional codes and information of 3 bits or more per symbol, and in the multilevel modulation, the bit having the highest error rate among the bits. This is a mapping method in which mapping is performed by allocating bits having the least influence on decoding results to positions.

  The present invention relates to a mapping method in a communication system using multilevel modulation that allocates convolutional codes and information of 3 bits or more per symbol, and in the multilevel modulation, the bit having the highest error rate among the bits. Since this mapping method assigns bits with the least influence on the decoding result to the position and performs mapping, the degree of influence on the decoding characteristics is used for mapping, and the error rate on the communication path changes depending on the bits to be mapped. In multi-level modulation, the error rate of the decoding result can be kept low.

Embodiment 1 FIG.
In the present invention, on the assumption that all bits are transmitted, the degree of influence on the decoding characteristics is used for mapping, and in the multilevel modulation in which the error rate on the communication path changes depending on the bit position to be mapped, A method for reducing the error rate will be described.

  1 is a block diagram showing a communication system according to Embodiment 1 of the present invention. As shown in FIG. 1, in the communication system according to the first embodiment, an encoder 10 that performs error correction or detection encoding of data to be transmitted to the transmission side, importance at the time of decoding the encoded data, and the like And a modulator 12 that modulates the encoded data using the codeword information 11 and transmits the data to the receiving side. The transmission side and the reception side are connected via a communication path 13 that transmits the modulated data. Further, the receiving side includes a demodulator 14 that receives and demodulates received data transmitted through the communication path 13 and a decoder 15 that decodes the demodulated received data.

  Next, the operation will be described. In the configuration of FIG. 1 described above, the communication system according to the first embodiment first encodes data to be transmitted by the encoder 10, and then uses the codeword information 11 by the modulator 12, The encoded data is modulated and transmitted. On the receiving side, the received data is demodulated by the demodulator 14 and decoded by the decoder 15. In the following description, the encoder 10 is a convolutional encoder, the decoder 15 is a Viterbi decoder, and the modulator 12 is 16 DAPSK (16 Differential Amplitude Phase Shift Keying) by differential modulation.

In the first embodiment, the modulation method is assumed to be 16 DAPSK. FIG. 2 shows an example of 16 DAPSK signal points and mapping. In FIG. 2, each bit at each signal point (a0, a1, a2, a3) is a bit assigned by a0 to a2 to a phase term, and a3 shows a bit assigned to an amplitude term. Thus, in 16 DAPSK, information of 3 bits is mapped (assigned) to the phase term and 1 bit to the amplitude term. At this time, it is generally known that 1 bit assigned to the amplitude term has the highest error rate compared to 3 bits assigned to the phase term. Mapping amplitude term, as in FIG. 2, when the case of selecting a circle outside and inside by a signal to be transmitted, the bits allocated to amplitude term at time t and C _t, when assigning as: There are two ways.

When C _t = C _t−1 Amplitude a _t = a _t−1
When C _t ≠ C _t−1 Amplitude a _t ≠ a _t−1

  In 16 DAPSK, 1 bit out of 4 bits is particularly prone to error. Therefore, in the first embodiment, by assigning 1 bit that seems to have the least influence on the overall characteristics to the amplitude term, Even if one of the bits is wrong, it is possible to improve the overall performance.

  The code word information 11 shown in FIG. 1 is information indicating which one bit is allocated to the amplitude term, or a value obtained by quantifying the influence of each bit on the decoding characteristics. 11 makes it possible to determine which bit should be assigned to a bit position having a high error rate.

  In the example of the first embodiment, when the coding rate of the encoder 10 composed of the convolutional encoder is halved, one of the four bits of the code word is assigned to the amplitude term having poor characteristics. It is done. In the case of an encoder with a constraint length K = 7, the puncture pattern of the punctured coding method for generating a code with a coding rate of 3/4 by omitting 1 bit in 4 bits of the codeword is 2 × 2 in FIG. Represented by a matrix. That is, in this example, the fourth bit is the bit that has the least influence on the decoding characteristics. Therefore, the fourth bit is modulated as a bit assigned to the amplitude term. On the receiving side, by performing demodulation and decoding in a normal general procedure, it is possible to minimize the influence of the error rate of the amplitude term on the overall performance.

  Further, in the decoder 15, in the demapping of the bit mapped to the bit position having a high error rate, the possibility of transmitting 1 or 0 is almost the same (for example, determination of 1 and 0) In the vicinity of the boundary (for example, when the reception signal point is near the boundary), decoding may be performed without taking into account the information of this bit obtained from this signal point.

  Here, the case of 16 DAPSK has been described. However, the present invention is not limited to this. For example, other modulation schemes such as 8 PSK (8 Phase Shift Keying), 16 QAM (16 Quadrature Amplitude Modulation), and 64 QAM (64 Quadrature Amplitude Modulation) may be used. As long as the modulation method has a difference in error characteristics for each bit, the first embodiment can be similarly applied, and the number of bits of information allocated per signal is not limited to four. In addition, the convolutional code having a constraint length of 7 and a coding rate of 1/2 has been described as an example. However, the constraint length and the coding rate are not limited to this, and the same idea can be applied even if the encoder used in the system is a punctured code Applicable. For example, when a punctured code with a coding rate of 2/3 is used as a system and modulation is performed with 16 DAPSK, an allocation bit to an amplitude term may be determined with reference to a puncture pattern with a coding rate of 8/9. If the puncture pattern is unknown, a bit having a small influence on the decoding characteristic is obtained in advance by computer search or the like, and the bit assigned to the amplitude term is determined.

  As described above, in the first embodiment, in the communication system using multilevel modulation in which the modulation scheme is 16 DAPSK and the convolutional code and 4 bits of information per signal are allocated, other bits are used in the multilevel modulation. In comparison, the bit rate (amplitude term), which can be generally omitted in the punctured code, is assigned to the codeword bits that are weak against noise and have to perform the weakest mapping from errors. Can be reduced. As a result, the overall error rate characteristic can be kept low.

Embodiment 2. FIG.
In the second embodiment, another example of the same system as in FIG. 1 will be described. In the second embodiment, a case will be described in which a convolutional encoder with a coding rate of 1/2 and 16QAM are used. Since the configuration of the communication system is basically the same as that of FIG. 1, reference is made to FIG. 1, and detailed description thereof is omitted here.

  The 16QAM mapping is as shown in FIG. In this case, 2 bits out of 4 bits assigned to one signal point are vulnerable to errors. If the coding rate is 1/2 and 2 bits out of 4 bits are vulnerable to errors, the coding rate of the target puncture pattern will be 1 when trying to refer to the punctured code. is there. Therefore, in this case, without assigning bits that can be omitted in the punctured coding method, the degree of influence on the decoding of each codeword bit is determined by computer search or computer simulation in advance, and the modulated signal The bit having the least influence on the decoding is assigned to the bit position where error is likely to occur.

  In the computer search and computer simulation in this case, for example, a combination of 2 bits with the smallest decoding error rate is searched for and selected with 2 bits out of 4 bits in the codeword.

  As described above, the method of finding bits to be assigned to bit positions with poor characteristics by computer search and computer simulation can be applied regardless of the coding rate, and the puncture pattern is not used in the example of the first embodiment. It is also possible to find by the above method.

  Here, 16QAM has been described as an example. However, the present invention is not limited to this, and the same method can be applied when using a modulation method having different error rate characteristics depending on the bit position of mapping.

  As described above, in the second embodiment, in a communication system using multilevel modulation in which a modulation scheme is 16QAM and a convolutional code and 4 bits of information per symbol are allocated, other bits are used in multilevel modulation. Compared to the codeword bits that are weak to noise and have to be mapped from error to weak, the bit that has the least influence on decoding that has been searched in advance by computer simulation etc. is assigned. The rate can be reduced. As a result, the overall error rate characteristic can be kept low.

Embodiment 3 FIG.
FIG. 5 is a block diagram showing a communication system according to the third embodiment. As shown in FIG. 5, in the communication system according to the third embodiment, an encoder 10 that performs error correction or detection coding on data to be transmitted and an interleaved rearranged data after interleaving are performed on the transmission side. A leaver 16a and a modulator 12 that modulates encoded data after interleaving using codeword information 11 such as importance at the time of decoding the encoded data and transmits the encoded data to the receiving side are provided. It has been. In addition, the transmission side and the reception side are connected via a communication path 13. On the receiving side, a demodulator 14 that receives and demodulates the reception data transmitted through the communication path 13, a deinterleaver 17a that deinterleaves and rearranges the demodulated reception data and returns the original arrangement order, And a decoder 15 for decoding the demodulated received data after deinterleaving.

  Next, the operation will be described. In the communication system according to the third embodiment, in the configuration of FIG. 5 described above, first, on the transmission side, data to be transmitted is encoded by the encoder 10, and the encoded data is rearranged by the interleaver 16a. The data after the rearrangement is modulated by the modulator 12 in consideration of the word information 11 and transmitted. Next, on the receiving side, the transmission data transmitted through the communication path 13 is received, the received data is demodulated by the demodulator 14, the data order is rearranged by the deinterleaver 17 a, and decoded by the decoder 15. To do. As described above, in the third embodiment, the encoded data is rearranged by the interleaver 16a on the transmitting side, and the original order is restored by the deinterleaver 17a on the receiving side. Unlike the above-described first embodiment, the other operations are the same as those of the first embodiment, and thus the description of the same operations is omitted here.

  In the third embodiment, for example, as in the first embodiment, the encoder 10 is a convolutional encoder, the decoder 15 is a Viterbi decoder, and the modulator is 16 DAPSK by differential modulation. The interleaver 16a needs to output in the order in which the bits to be assigned to the amplitude terms are correctly assigned to the amplitude terms. Therefore, as shown in FIG. 6, two interleavers 16aa and 16ab are provided, and bits to be assigned to the amplitude term and other bits are interleaved by different interleavers. That is, the bits to be assigned to the bit position (here, the amplitude term) having a high error rate are interleaved by the interleaver 16aa, and other bits are interleaved by another interleaver 16ab. In this way, since the bit with a high error rate and the other bits are interleaved separately, the bit to be assigned to the amplitude term is correctly and automatically mapped (assigned) to the amplitude term.

  Similarly, two deinterleavers (not shown) are provided for the deinterleaver 17a so that the bit to be assigned to the amplitude term and the other bits are deinterleaved by another deinterleaver. However, the present invention is not limited to this, and deinterleaving may be performed by one deinterleaver.

  As described above, in the third embodiment, basically, as in the first embodiment, in a communication system using multilevel modulation that assigns convolutional codes and information of 4 bits per symbol, multilevel modulation is performed. In comparison with other bits, the bit rate that is generally susceptible to being omitted in the puncture code is assigned to the codeword bits that are vulnerable to noise and have to be mapped from error to weakness. Can be reduced. As a result, the overall error rate characteristic can be kept low. In addition, since the encoded data is provided with an interleaver 16a that divides the data into a bit with a high error rate and other bits and interleaves them separately, the bit with a high error rate is correctly and automatically used as an amplitude term. Can be mapped.

Embodiment 4 FIG.
In the fourth embodiment, an example in which an interleaver is configured by a block interleaver 16b as shown in FIG. 7 in the same communication system as in the third embodiment described above will be described. When trying to assign the fourth bit of the encoder's output 4 bits to the amplitude term, normally writing horizontally and reading vertically, and modulating the output of the interleaver 16b in sequence, the 4th bit becomes I do n’t know if it ’s assigned to the amplitude term. Therefore, as shown in FIG. 7, the memory in the interleaver 16b is divided in advance into an address for writing a bit to be assigned to a bit position (in this case, an amplitude term) with a high error rate and an address for writing other bits. The bit to be assigned to the amplitude term is set so that the output after the rearrangement by the interleaver 16b is sequentially written in a predetermined address group set in advance as the address of the memory assigned to the amplitude term. By reading normally in order, it is mapped correctly to the amplitude term. In FIG. 7, each numeral indicates the order of writing, and the address for writing a bit to be assigned to a bit position with a high error rate is a group of addresses that are hatched (hatched), and the other bits The address to which is written is a group of addresses not hatched. FIG. 7 shows a state in which each fourth bit is sequentially written to a predetermined address group that is hatched. Since other operations are the same as those in the first and third embodiments, description thereof is omitted here.

  Here, the case of the block interleaver has been described. Similarly, in other interleavers such as a random interleaver, a bit to be assigned to a bit position having a high error rate can be assigned to a bit position having a high error rate in the interleaver. By confirming the memory location first and sequentially writing the output bits in accordance with a certain order, the characteristics of the code word and the mapping characteristics can be matched to improve the characteristics of the entire system. Further, although the case of 16 DAPSK has been described here, the present invention can be applied to other schemes as long as the modulation scheme changes the error rate characteristics at the mapping position.

  As described above, in the present embodiment, as in Embodiments 1 and 3, in a communication system using multilevel modulation that assigns a convolutional code and 4-bit information per symbol, Compared to other bits in modulation, bits that are generally noiseless and have a weak mapping from error to weak mapping are assigned to bits that are generally omissible in puncture codes. The rate can be reduced. As a result, the overall error rate characteristic can be kept low. In addition, since the interleaver 16b is provided that interleaves the encoded data and distinguishes bits having a high error rate from other bits and stores them at a predetermined address, the data is normally read from the interleaver 16b. Thus, a bit with a high error rate can be correctly and automatically mapped to an amplitude term.

It is the block diagram which showed the structure of the communication system which concerns on Embodiment 1 of this invention. It is explanatory drawing which showed an example of the 16 DAPSK signal point and mapping in the communication system which concerns on Embodiment 1 of this invention. It is explanatory drawing which showed an example of the puncture pattern of the punctured encoding in the communication system which concerns on Embodiment 1 of this invention. It is explanatory drawing which showed an example of the 16QAM signal point and mapping in the communication system which concerns on Embodiment 2 of this invention. It is the block diagram which showed the structure of the communication system which concerns on Embodiment 3 of this invention. It is the block diagram which showed the structure of the interleaver in the communication system which concerns on Embodiment 3 of this invention. It is the block diagram which showed the structure of the interleaver in the communication system which concerns on Embodiment 4 of this invention.

Explanation of symbols

  10 encoder, 11 information, 12 modulator, 13 channel, 14 demodulator, 15 decoder, 16a, 16aa, 16ab, 16b interleaver, 17a deinterleaver.

Claims (5)

A mapping method in a communication system using multilevel modulation that assigns convolutional codes and information of 3 bits or more per symbol,
In the multi-level modulation, a mapping method characterized in that mapping is performed by allocating a bit having the least influence on a decoding result to a bit position having the highest error rate in each bit.   2. The mapping method according to claim 1, wherein a bit that can be omitted in the punctured coding scheme is assigned as a bit that has the least influence on the decoding result.   The bit having the smallest influence on the decoding result is determined in advance by computer search or computer simulation, and the bit is assigned as the bit having the smallest influence on the decoding result. The mapping method described in 1.   When mapping by the mapping method according to any one of claims 1 to 3, 1 is transmitted or 0 is transmitted in demapping of a bit mapped to a bit position having the highest error rate A decoding method characterized by performing decoding without taking into account the information of the bits when decoding is possible. Encoding means for error correction or detection encoding of data to be transmitted;
Modulation means for modulating the encoded data and transmitting it to the receiving side;
A communication means for transmitting the transmitted data;
Demodulation means for receiving and demodulating the data transmitted from the transmission side by the communication means;
Decoding means for decoding the demodulated data,
The modulation means allocates the bit having the least influence on the decoding result to the bit position having the highest error rate in each bit in multilevel modulation in which convolutional code and information of 3 bits or more per symbol are allocated. A communication system characterized by performing mapping.

Images