CN115225202B - Cascade decoding method - Google Patents
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
- H04L1/0056—Systems characterized by the type of code used
- H04L1/0064—Concatenated codes
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
- H04L1/0033—Systems modifying transmission characteristics according to link quality, e.g. power backoff arrangements specific to the transmitter
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
- H04L1/0036—Systems modifying transmission characteristics according to link quality, e.g. power backoff arrangements specific to the receiver
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
- H04L1/0056—Systems characterized by the type of code used
- H04L1/0061—Error detection codes
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
- H04L1/0056—Systems characterized by the type of code used
- H04L1/0071—Use of interleaving
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Abstract
The application provides a cascade coding and decoding method of using an RS code for an outer code and a multilayer coding thought for an inner code by utilizing the characteristic that the lower bit of each transmission symbol is more prone to error than the higher bit after the transmission data is modulated. The outer code of the cascade coding method adopts RS codes, interweaves RS codeword data, divides the interweaved data into preset number groups of bit data, codes each group of bit data by adopting codewords with different code rates, and modulates the preset number groups of multi-layer sub codeword data to obtain modulated data; wherein the lengths of the multi-layer sub-codeword data of each group are consistent, and the multi-layer sub-codeword data respectively correspond to different bits in the modulated data. The cascade coding method realizes higher coding gain by using shorter code length under the condition of a certain code rate; and the cascade decoding uses a low-order decoding result to assist in demodulating and decoding high-order data in channel received data, so that higher decoding performance is obtained, and the decoding performance requirement of the Ethernet above 400Gb/s is met.
Description
Technical Field
The application relates to the technical field of digital communication coding and decoding, in particular to a cascade decoding method.
Background
A source in a digital communication system generates data and transmits the data through a channel. However, the channel may cause interference to the transmitted data, so that the sink cannot correctly receive the transmitted data. The error generated in the transmission is usually corrected by adopting a forward error correction (Forward Error Correction, FEC), that is, the data generated by the source is encoded by the data transmitting end, the data receiving end detects and corrects the error by using a corresponding decoding algorithm, and the decoded data is transmitted to the sink.
According to the ethernet latest standard, two RS codes (Reed-Solomon, inner codes) are applied as FEC schemes in the ethernet sublayer, an RS (528, 514) code corresponding to the KR4 FEC scheme in the ethernet standard and an RS (544, 514) code corresponding to the KP4 FEC scheme in the ethernet standard, respectively.
However, as the transmission rate of ethernet is higher and higher, the ethernet standard above 400Gb/s is being studied, and the decoding performance requirement of the FEC scheme is also higher and higher. On the premise of a certain code rate, in order to increase the coding gain of the FEC scheme, the code length of the code word needs to be increased, but the increase of the code length increases the complexity of the communication system and occupies excessive hardware resources. Therefore, the above-described FEC scheme of a single RS codeword cannot meet the decoding performance requirement of the ethernet application exceeding 400 Gb/s.
Disclosure of Invention
In order to solve the problem that the FEC method of the single code word cannot meet the decoding performance requirement of the Ethernet application exceeding 400Gb/s, the application provides a cascade decoding method by the following aspects.
A first aspect of the present application provides a concatenated coding method comprising:
receiving information source data sent by an information source;
RS encoding is carried out on the information source data to obtain RS codeword data;
interleaving the RS codeword data according to a preset interleaving depth to obtain interleaved data;
grouping the interleaved data to obtain bit data of a preset number of groups; wherein the preset number is the number of bits corresponding to one symbol in the preset modulation mode, and each group of bit data corresponds to different bits in the preset modulation mode;
carrying out multi-layer coding on the bit data of the preset number group to obtain multi-layer codeword data; the multi-layer codeword data comprises a preset number of groups of multi-layer sub-codeword data, and the lengths of each group of multi-layer sub-codeword data are consistent; the length of check bits in the multi-layer sub-codeword data corresponding to the most significant bits in the preset modulation mode is smaller than that of the multi-layer sub-codeword data corresponding to the least significant bits in the preset modulation mode;
And modulating the multi-layer codeword data according to a preset modulation mode to obtain modulation data for channel transmission.
Optionally, when the preset modulation mode is PAM4, the preset number of groups of bit data includes a group of high-order bit data and a group of low-order bit data;
the multi-layer encoding is performed on the bit data of the preset number group to obtain multi-layer codeword data, which comprises the following steps:
encoding the low-order bit data according to a first code rate to obtain low-order multi-layer sub-codeword data;
encoding the high-order bit data according to a second code rate to obtain high-order multi-layer sub-codeword data;
the first code rate is smaller than the second code rate, the high-order multi-layer sub-code word data corresponds to the most significant bit in the PAM4 modulation mode, and the low-order multi-layer sub-code word data corresponds to the least significant bit in the PAM4 modulation mode.
Optionally, when the preset modulation mode is PAM4, the preset number of groups of bit data includes a group of high-order bit data and a group of low-order bit data;
the multi-layer encoding is performed on the bit data of the preset number group to obtain multi-layer codeword data, which comprises the following steps:
encoding the low-order bit data according to a third code rate to obtain low-order multi-layer sub-codeword data;
Directly outputting the high-order bit data without coding to obtain high-order multi-layer sub-codeword data;
the high-order multi-layer sub-codeword data corresponds to the most significant bit in the PAM4 modulation scheme, and the low-order multi-layer sub-codeword data corresponds to the least significant bit in the PAM4 modulation scheme.
A second aspect of the present application provides a concatenated coding method for coding modulated data obtained by a concatenated coding method according to the first aspect of the present application; the cascade coding method comprises the following steps:
executing a first demodulation process on the channel received data according to a preset modulation mode to obtain low-order demodulation data of a first quantity group; decoding the low-order demodulated data to obtain low-order bit data
Using the low-order bit data to assist in processing the channel received data to obtain a second number of groups of high-order bit data; the first number plus the second number are equal to the preset number, and the preset number is the number of bits corresponding to one symbol in a preset modulation mode;
performing de-interleaving treatment on the high-order bit data and the low-order bit data to obtain de-interleaved data;
RS decoding is carried out on the de-interleaving data to obtain RS decoding data;
and sending the RS decoding data to a signal sink.
Optionally, when the preset modulation mode is PAM4, the first number and the second number are both equal to 1; the low-order bit data corresponds to the least significant bit in the modulated data, and the high-order bit data corresponds to the most significant bit in the modulated data;
the processing of the channel received data with the assistance of the low-order bit data to obtain the high-order bit data includes:
when the most significant bit in the modulated data is not coded in the multi-layer coding process, performing a second demodulation process on the most significant bit of the channel received data in a hard decision mode by using the low-order bit data to obtain high-order bit data;
when the most significant bit in the modulated data is encoded in the multi-layer encoding process, performing a third demodulation process by using the low-order bit data to assist in a hard decision mode or a soft decision mode on the most significant bit of the channel received data, and decoding a demodulation result to obtain high-order bit data; when the third demodulation process is executed by adopting hard decision, decoding the demodulation result by adopting a hard decoding mode; and when the third demodulation process is executed by adopting a soft decision mode, decoding the demodulation result by adopting a soft decoding mode.
Optionally, before sending the RS decoding data to the sink, the concatenated decoding method includes:
performing iterative decoding on the RS decoding data to obtain RS iterative decoding data;
transmitting the RS iterative decoding data to a signal sink;
the step of performing iterative decoding on the RS decoding data to obtain RS iterative decoding data includes:
interleaving the RS decoding data to obtain iterative input data; the iteration input data comprise low-order iteration input data and high-order iteration input data;
decoding the low-order iteration input data to obtain low-order iteration bit data;
when the most significant bit in the modulated data is not coded in the multi-layer coding process, performing a second demodulation process on the high-order iteration input data in a hard decision mode by using the low-order iteration bit data to obtain the high-order iteration input data;
when the most significant bit in the modulated data is encoded in the multi-layer encoding process, performing a third demodulation process on the high-order iteration input data in a hard decision mode or a soft decision mode by using the low-order iteration bit data to assist, and decoding a demodulation result to obtain the high-order iteration input data; when the third demodulation process is executed by adopting a hard decision mode, decoding a demodulation result by adopting a hard decoding mode; when the third demodulation process is executed by adopting a soft decision mode, decoding a demodulation result by adopting a soft decoding mode;
Performing de-interleaving treatment on the high-order iteration input data and the low-order iteration bit data to obtain de-interleaving iteration data;
RS decoding is carried out on the de-interleaving iterative data, and RS iterative decoding data are obtained;
and sending the RS iterative decoding data to a signal sink.
Optionally, when the low-order iterative input data is decoded by adopting a hard decoding mode, check bits in the low-order iterative input data are set as check bits in the low-order bit data.
Optionally, when the low-order iterative input data is decoded by adopting a soft decoding mode, the maximum likelihood ratio of the information bit in the low-order iterative input data is set to be the most reliable, and the maximum likelihood ratio of the check bit in the low-order iterative input data is set to be the maximum likelihood ratio in the low-order demodulation data.
Optionally, a hard decision method is adopted when the first demodulation process is executed on the channel received data according to the PAM4 modulation mode, so as to obtain low-order demodulation data;
and (3) adopting a hard decoding mode when decoding the low-order demodulation data to obtain low-order bit data.
Optionally, a soft decision mode is adopted when the first demodulation process is executed on the channel received data according to the PAM4 modulation mode, so as to obtain low-order demodulation data;
and soft decoding is adopted when the low-order demodulation data are decoded, so that low-order bit data are obtained.
The application provides a cascade decoding method. The application provides a cascade coding method of an outer code by adopting an RS code and an inner code by adopting a multilayer coding idea and a corresponding cascade decoding method by utilizing the characteristic that the lower bit of each transmission symbol is more prone to error than the higher bit after the transmission data is modulated. The outer code of the cascade coding method adopts RS codes, interweaves RS codeword data, divides the interweaved data into preset number groups of bit data, codes each group of bit data by adopting codewords with different code rates to obtain preset number groups of multi-layer sub codeword data, and modulates the multi-layer sub codeword data to obtain modulated data; wherein, the lengths of the multi-layer sub-code word data of each group are consistent, and the multi-layer sub-code word data respectively correspond to different bits in the modulated data. The cascade coding method realizes higher coding gain by using shorter code length under the condition of a certain code rate.
When decoding, demodulating and decoding the low order bits in the channel received data to obtain low order bit data; using low-order bit data to assist in processing high-order bits in channel received data to obtain high-order bit data; and de-interleaving the high-order bit data and the low-order bit data, performing RS decoding to obtain RS decoded data, and transmitting the RS decoded data to a signal sink. The FEC scheme using the cascade coding and decoding method provided by the application can meet the decoding performance requirement of Ethernet application exceeding 400 Gb/s.
Drawings
Fig. 1 is a schematic diagram of a communication system using two code sets to form a concatenated code;
fig. 2 is a schematic flow chart of a cascade coding method according to an embodiment of the present application;
fig. 3 is a schematic diagram of a division manner of grouping interleaved data in a cascade coding method according to an embodiment of the present application;
fig. 4 is an exemplary schematic diagram of MLC encoding in a cascade encoding method according to an embodiment of the application;
fig. 5 is an example of a constellation of modulated data in a 16QMA modulation scheme;
FIG. 6 is a schematic flow chart of a cascade decoding method according to an embodiment of the present application;
fig. 7 is a schematic diagram of an MLC encoding and decoding process in a cascade decoding method according to an embodiment of the application;
fig. 8 is a schematic diagram of a process of performing hard decision demodulation on channel received data with assistance of low-order bit data in a cascade decoding method according to an embodiment of the present application;
fig. 9 is a schematic diagram of a process of processing channel received data with assistance of low-order bit data to obtain high-order bit data in a cascade decoding method according to an embodiment of the present application;
FIG. 10 is a comparative schematic diagram of simulation results of decoding performance of experimental group 1, comparative group 1 and comparative group 2;
FIG. 11 is a comparative schematic diagram of decoding performance simulation results of experimental group 2 and experimental group 3;
fig. 12 is a comparative schematic diagram of decoding performance simulation results of experimental group 1, experimental group 4, experimental group 5 and comparative group 1.
Detailed Description
For the convenience of explanation of the technical scheme of the application, the concept of cascade coding related to the application is briefly introduced.
The concatenated code is composed of two or more simple codes, and fig. 1 illustrates a schematic structure of a communication system in which two codes compose the concatenated code. As shown in fig. 1, the concatenated code comprises an outer code (typically non-binary) and an inner code (typically binary), which are two independent codes that are transmitted serially over a channel. The method comprises the steps of firstly carrying out outer code coding on data sent by an information source, then carrying out inner code coding after interleaving, then transmitting through a channel, and carrying out inner code decoding, de-interleaving and then outer code decoding by adopting a two-stage decoding mode on a decoding end by cascade codes.
Referring to fig. 2, a schematic flow chart of a cascade coding method according to a first embodiment of the present application is provided. The concatenated coding method comprises steps 11 to 16.
And step 11, receiving the source data sent by the source. The source is the source and sender of data in a communication system, converting various messages into the original electrical signals, referred to herein as source data.
And step 12, performing RS coding on the information source data to obtain RS codeword data.
In this embodiment, the outer code uses an RS codeword. In the latest ethernet standards, two RS codewords are used to encode source data. The RS code is transmitted in symbol form, one is RS (528, 514) code, corresponding to KR4 FEC scheme in ethernet standard; wherein one RS codeword has 528 symbols and 514 information symbols in total. The other is an RS (544, 514) code, where one RS codeword has 544 symbols, 514 information symbols in total; corresponding to KP4 FEC schemes in the ethernet standard. 1symbol is 1symbol (symbol number), 1 symbol=10 bits.
And step 13, interleaving the RS codeword data according to a preset interleaving depth to obtain interleaved data.
And performing symbol-level row-column interleaving on the RS codeword data, wherein the preset interleaving depth is I, and the I can be any positive integer. However, the delay increases with the increase of I, and in practical application, an appropriate I is configured according to the requirements of delay, throughput rate, and the like.
And 14, grouping the interleaved data to obtain bit data of a preset number of groups. The preset number is the number of bits corresponding to one symbol in the preset modulation mode, and each group of bit data corresponds to different bits in the preset modulation mode.
Step 15, carrying out multi-layer coding on bit data of a preset number of groups to obtain multi-layer codeword data; the multi-layer codeword data comprises a preset number of groups of multi-layer sub-codeword data, and the lengths of each group of multi-layer sub-codeword data are consistent; the check bit length in the multi-layer sub-codeword data corresponding to the most significant bit in the preset modulation scheme is smaller than the check bit length in the multi-layer sub-codeword data corresponding to the least significant bit in the preset modulation scheme.
In this embodiment, the implementation of steps 14-15 is described using RS (544, 514) codes for the outer codes in PAM4 (4 Pulse Amplitude Modulation, fourth pulse amplitude modulation) modulation. In PAM4 modulation, two bits are modulated into one symbol, and the preset number is equal to 2. The interleaved data is first divided into N parts, each part containing 2k bit data, and the 2k bit data is divided into high bit data (k in total 1 Individual) and low-order bit data (total k 2 Individual). Wherein 2k=k 1 +k 2 ，k 1 ＞k 2 The method comprises the steps of carrying out a first treatment on the surface of the I.e. the interleaved data is divided into 2 groups, the first group comprising N parts of k 1 A second group of bits corresponding to the data on the most significant bit (Most Significant Bit, MSB) in PAM4 modulation, the second group containing N parts of k 2 And a bit data corresponding to data on the least significant bit (Least Significant Bit, LSB) in PAM4 modulation.
In practice, there are various ways to divide 2k bit data into higher bit data (k total 1 Individual) and low-order bit data (total k 2 And (c) a). Fig. 3 shows the embodiment of dividing 2k bit data into higher bit data (k total 1 Individual) and low-order bit data (total k 2 And a) one division example. As shown in fig. 3, for the first 2k of the 2 k-bit data 1 The bit data is divided according to odd-even sequenceThe number is high-order bit data, and the even number is low-order bit data; rear (k) 2 -k 1 ) The data is high order bit data. In other examples, the divisions may also be made in other orders, provided 2k=k is satisfied 1 +k 2 And k is 1 ＞k 2 The present application is not limited to the method of division.
Multi-level coding (MLC) is performed on the high-order bit data and the low-order bit data, resulting in Multi-level codeword data (referred to as MLC codeword data in the present application). In this embodiment, taking PAM4 as an example of a preset modulation scheme, the multi-layer codeword data includes two groups of MLC sub codeword data. The constituent codes of MLC codes select BCH codes, namely, the BCH codes with different code rates are adopted for encoding high-order bit data and low-order bit data, and two groups of MLC sub codeword data with consistent lengths are obtained; wherein, the length of one MLC sub code word data is n, and the length of one MLC sub code word data is 2n.
Referring to fig. 4, an exemplary MLC coding is shown in this embodiment. As can be seen from the calculation formula of the code rate (code rate=information bit length/code length), when the code rate and the code length are fixed, the bit data length of the information bit is also fixed. In FIG. 4, k is k 1 And k 2 Average value of (2). In practical application, according to the design requirement of practical communication system, the code rate and code length 2n of MLC code word are combined to derive the information bit length 2k of MLC code word, and further derive the proper k 1 And k 2 。
In one implementation, the low-order bit data is encoded by using a BCH code of a first code rate in MLC encoding, and the high-order bit data is encoded by using a BCH code of a second code rate, so as to obtain low-order multi-layer sub-codeword data and high-order multi-layer sub-codeword data respectively, wherein the first code rate is smaller than the second code rate, i.e. the error correction capability of the low-order multi-layer sub-codeword data is higher than that of the high-order multi-layer sub-codeword data. Illustratively, the low bit data is encoded using a BCH (360,320) code with an error correction capability of 4; the high bit data is encoded using BCH (360, 340) codes with error correction capability of 2. Correspondingly, n=360, k 1 ＝320，k 2 ＝340。
In another implementation, the low-order bit data is encoded by using a BCH code of a third code rate in MLC coding to obtain low-order multi-layer sub-codeword data; and the high-order multi-layer sub-codeword data is directly output without coding the high-order bit data, namely the high-order multi-layer sub-codeword data has no error correction capability. Illustratively, low order bit data is encoded using a BCH (360,320) code, corresponding to k 1 ＝320，k 2 ＝360，n＝360。
In this embodiment, since the outer code and the inner code are different in code length, the interleaved data is divided into N parts, and each part is encoded. N is determined according to the data length of the RS code word, the preset interleaving depth and the length of the information bit of the code word selected by the multi-layer coding in the step 15. By way of example only, and not by way of limitation,wherein, the preset interleaving depth is set to 2, the outer code adopts RS (544, 514) code, the data length of the MLC code word of the inner code is equal to 360 (no error correction capability corresponding to high bit data) +320 (4 error correction capability corresponding to low bit data), and the BCH (360, 320) code is adopted.
It should be noted that, in the above example, the MLC code uses a BCH code as a constituent code, and other codewords may also be used as constituent codes, for example, LDPC codes or Polar codes are used as constituent codes of the MLC code.
And step 16, modulating the multi-layer codeword data according to a preset modulation mode to obtain modulated data for channel transmission. In this embodiment, taking PAM4 modulation scheme as an example, the corresponding bits of the upper multi-layer sub-codeword data (corresponding to the MSBs in the modulated data) and the lower multi-layer sub-codeword data (corresponding to the LSBs in the modulated data) are modulated into one symbol bit in the modulated data by PAM 4. Table 1 shows the correspondence between the multi-layer codeword data and the modulation data in the PAM4 modulation scheme.
Table 1: modulating multi-layer codeword data according to PAM4
| (MSB，LSB) | (0,0) | (0,1) | (1,0) | (1,1) |
| PAM4 modulation after | -3 | -1 | 1 | 3 |
As can be seen from the data format of PAM4 modulated data in table 1, when the modulated data is smaller than 0, the corresponding highest bit is 0, and when the modulated data is larger than 0, the highest bit is 1. It can be seen that the highest bit has the greatest effect on the value of the modulated data. Therefore, in the encoding process, the bit data corresponding to the least significant bit and the most significant bit are encoded by adopting different code rate encoding modes. In the decoding process, even if the least significant bit is decoded in error, the value corresponding to the most significant bit can be judged only according to whether the modulation data is greater than 0 or less than 0.
For example, referring to fig. 5, a schematic diagram of an example constellation diagram of 16QAM modulated data is shown. Taking the example of two-bit decoding of 00 without coarsening, the low-order auxiliary high-order demodulation process is shown in table 2.
Table 2:16QAM low order auxiliary high order demodulation process (taking low order as 00 as an example)
| Two digits 00 without thickening | Re<1,Im>-j | Re<1,Im<-j | Re>1,Im>-j | Re>1,Im<-j |
| Coarsening the two-bit demodulation result | 10 | 11 | 00 | 01 |
It should be noted that, when modulating data, gray codes are generally used to reduce the possibility of errors and improve the decoding performance. However, in the encoding method provided by the present application, if the gray code is used for modulation at the time of modulation, when the low-order bit data is used for assisting in demodulating and decoding the high-order bit data, even if the low-order bit data is decoded correctly, the high-order bit data is highly likely to be in error. So in order to make the decoding result of the high-order bit data as reliable as possible, the modulation process does not use gray codes when the cascade coding method of the present application is used for designing the communication system.
The embodiment provides a cascade coding method, which comprises the steps of receiving information source data sent by an information source; RS encoding is carried out on the information source data to obtain RS codeword data; interleaving the RS codeword data according to a preset interleaving depth to obtain interleaved data; grouping the interleaved data to obtain bit data of a preset number of groups; wherein the preset number is the number of bits corresponding to one symbol in the preset modulation mode, and each group of bit data corresponds to different bits in the preset modulation mode; carrying out multi-layer coding on the bit data of the preset number group to obtain multi-layer codeword data; the multi-layer codeword data comprises a preset number of groups of multi-layer sub-codeword data, and the lengths of each group of multi-layer sub-codeword data are consistent; the length of check bits in the multi-layer sub-codeword data corresponding to the most significant bits in the preset modulation mode is smaller than that of the multi-layer sub-codeword data corresponding to the least significant bits in the preset modulation mode; and modulating the multi-layer codeword data according to a preset modulation mode to obtain modulation data for channel transmission.
The cascade coding method utilizes the characteristic that the lower bits of each transmission symbol are more prone to error than the higher bits after the transmission data are modulated, the lower bits and the higher bits of the modulation symbols respectively adopt the inner codes with different error correction capacities, different error correction capacities are provided for different bits of the modulated symbols, and under the condition of a certain code rate, higher coding gain is realized by using shorter code length.
In the first embodiment, PAM4 is exemplified as the preset modulation scheme. The preset modulation method in the cascade coding method provided in the foregoing embodiment may also be other modulation methods.
For example, when the preset modulation mode is 16QAM, one symbol in the 16QAM modulated data corresponds to four bits, and the interleaved data is grouped to obtain four sets of bit data, where one set of bit data corresponds to one bit in the 16QAM modulated data. Corresponding to the order of modulating data from high order to low order, constituent codes in MLC codeword can select BCH (360,350), BCH (360,350), BCH (360,330), BCH (360,330), BCH (360,350), BCH (360, 340), BCH (360,330) respectively. As long as the following two conditions are satisfied: after MLC encoding, the lengths of the MLC sub codeword data are consistent, and the error correction capability of the MLC sub codeword data corresponding to the least significant bit is higher than that of the MLC sub codeword data corresponding to the most significant bit.
The application also provides an embodiment of a cascade decoding method corresponding to the embodiment of the cascade coding method. Referring to fig. 6, a schematic workflow diagram of a cascade decoding method according to a second embodiment of the application is provided. The concatenated coding method includes steps 21-26.
And step 21, executing a first demodulation process on the channel received data according to a preset modulation mode to obtain a first number group of low-order demodulation data. The channel received data refers to the modulated data obtained by the cascade coding method provided by the first embodiment of the present application, which is transmitted through a channel, and added with a channel noise signal.
In this embodiment, the first demodulation process is performed using a preset modulation scheme corresponding to the cascade coding method. The first demodulation process refers to demodulating low-bit data in channel received data to obtain low-bit modulation data. When the preset modulation mode in the cascade coding method uses PAM4 modulation, demodulation is also performed according to the PAM4 modulation mode in the corresponding first demodulation process, the first number is equal to 1, and the low-order demodulation data corresponds to the least significant bit in the PAM4 modulation data; when the preset modulation mode in the cascade coding method uses 16QAM modulation, demodulation is also performed according to the 16QAM modulation mode in the corresponding first demodulation process, the first number is equal to 2, and the low-order demodulation data corresponds to the least significant bit and the second least significant bit in the 16QAM modulation data.
In step 21, the low-order demodulated data corresponds to multi-layer sub-codeword data of a low-order portion of the multi-layer codeword data in the concatenated coding method. For example, when the preset modulation mode is 16QAM, the low-order demodulation data corresponds to two sets of low-order multi-layer sub-codeword data, and when the preset modulation mode is PAM4, the low-order demodulation data corresponds to one set of multi-layer sub-codeword data corresponding to the least significant bit.
And step 22, decoding the low-order demodulation data to obtain low-order bit data.
In one implementation, the first demodulation process may be performed on PAM4 modulated data in a hard decision manner, resulting in low-order demodulated data. Correspondingly, the low-order demodulation data are decoded in a hard decoding mode to obtain low-order bit data.
In another implementation manner, a first demodulation process may be performed on PAM4 modulated data according to a soft decision manner, to obtain low bit data; correspondingly, the low-order demodulation data are decoded according to a soft decoding mode, and low-order bit data are obtained.
The soft decision and soft decoding mode has good decoding performance, low error rate, but high complexity, and needs the channel to provide soft information. The complexity of the hard decision and hard decoding mode is low, the decoding performance is lower than that of the soft decision and soft decoding mode, but the soft message is not required to be provided by a channel, so that the power consumption of the equalizer is greatly reduced. In practical application, different decision modes can be selected to execute the first demodulation process according to the requirements of specific application scenes.
In this embodiment, when the BCH code is selected by the constituent codes of the MLC code in the concatenated coding method, correspondingly, when the concatenated coding is performed, the hard coding of the BCH code may use a BM (Berlekamp-Massey) algorithm, and when the soft coding may use a Chase-II algorithm.
Step 23, using the low-order bit data to assist in processing the channel received data to obtain a second number of groups of high-order bit data; the first number plus the second number are equal to a preset number, and the preset number is the number of bits corresponding to one symbol in the preset modulation mode.
In this embodiment, the channel reception data is demodulated with the high order bits assisted by the low order decoding result of the channel reception data. Referring to fig. 7, a schematic diagram of an MLC encoding and decoding process is shown. As shown in fig. 7, taking PAM4 modulation mode as an example, low-order demodulation is performed on channel received data to obtain low-order demodulated data, and then the low-order demodulated data is decoded to obtain low-order bit data; and demodulating the channel received data with the assistance of the low-order bit data to obtain high-order demodulated data, and decoding the high-order demodulated data to obtain high-order bit data. Wherein the AWGN channel in fig. 7 refers to a gaussian additive white noise channel, which is used to simulate real channel noise.
Referring to fig. 8, a schematic diagram of a process of demodulating the modulated data with the assistance of low-order bit data is provided, and the demodulation method provided in fig. 8 adopts a hard decision mode to demodulate to obtain binary high-order demodulation data; in fig. 8, noise_symbol represents modulation data received by a channel. When the low-order bit data is 0 and the channel receiving data is larger than-1, the corresponding high-order demodulation data is 1; when the low-order bit data is 0 and the channel receiving data is smaller than-1, the corresponding high-order demodulation data is 0; when the low-order bit data is 1 and the channel receiving data is greater than 1, the corresponding high-order demodulation data is 1; when the low bit data is 1 and the channel reception data is less than 1, the corresponding high bit demodulation data is 0.
When the low-order bit data is used to assist in demodulating the channel received data in a soft decision manner, the obtained high-order demodulated data is soft information, and the specific assisting process is similar to that of fig. 8, and will not be repeated here.
In practical application, when the low-order bit data is used for assisting in demodulating the channel received data by adopting hard decision, binary high-order demodulation data is obtained, and correspondingly, a hard decoding mode is adopted when the high-order demodulation data is decoded. When the low-order bit data is used for assisting in demodulating the channel receiving data by adopting soft decision, the high-order demodulation data of soft information is obtained, and correspondingly, a soft decoding mode is adopted when the high-order demodulation data is decoded.
Referring to fig. 9, taking PAM4 modulation as an example, a workflow diagram of processing channel received data to obtain high-order bit data with the assistance of low-order bit data is given according to whether the most significant bit in the modulated data is encoded in the multi-layer encoding process.
When the most significant bit in the modulated data is not coded in the multi-layer coding process, the decoding is not needed in the cascade decoding process, and the high-order demodulation data is directly output. The above-mentioned uses the low-order bit data to assist and adopts the way of the hard decision when demodulating the channel received data, the binary high-order demodulation data obtained is outputted directly into the high-order bit data. In the present embodiment, the above-described demodulation process is referred to as a second demodulation process. At this time, as shown in FIG. 9, step 23 further includes step 231-1, step 232-1, and step 233.
In step 231-1, the low-order bit data is used to assist in demodulating the channel received data in a hard decision manner, so as to obtain binary high-order demodulated data. The specific demodulation process is shown in fig. 8.
Step 232-1, directly outputting binary high-order demodulation data.
Step 233, obtaining high-order bit data.
When the most significant bit in the modulated data is encoded in the multi-layer encoding process, then the high-order demodulated data needs to be decoded in the cascade decoding process. In the present embodiment, a demodulation process to obtain high-order demodulated data to be decoded is referred to as a third demodulation process.
And when the third demodulation process is executed in a hard decision mode, decoding the obtained high-order demodulation data in a hard decoding mode. At this time, as shown in FIG. 9, step 23 further includes step 231-2, step 232-2, and step 233.
In step 231-2, the low-order bit data is used to assist in demodulating the channel received data in a hard decision manner, so as to obtain binary high-order demodulated data. The demodulation process is shown in fig. 8.
In step 232-2, the binary high-order demodulated data is decoded by hard decoding.
Step 233, obtaining high-order bit data.
And when the third demodulation process is executed in a soft decision mode, decoding the obtained high-order demodulation data in a soft decoding mode. At this time, as shown in FIG. 9, step 23 further includes step 231-3, step 232-3, and step 233.
And 231-3, using the low-order bit data to assist in demodulating the channel received data in a soft decision mode to obtain high-order demodulated data of the soft information.
And step 232-3, decoding the high-order demodulation data of the soft information in a soft decoding mode.
Step 233, obtaining high-order bit data.
In the present embodiment, the execution process of steps 21 to 23 is referred to as MLC decoding process. When the first demodulation process in step 21 adopts a soft decision mode, it is called MLC soft decoding. Further, MLC soft decoding involves using low bit data to assist in demodulating channel received data in both hard decisions and soft decisions. When the first demodulation process in step 22 employs a hard decision mode, it is referred to as MLC hard decoding. Further, MLC hard decoding involves using low-order bit data to assist in demodulating channel received data in both hard and soft decisions. That is, MCL soft decoding includes two forms of low-order soft decision demodulation+high-order soft decision demodulation and low-order soft decision demodulation+high-order hard decision demodulation; the MLC hard decoding includes two forms of low hard decision demodulation+high hard decision demodulation and low hard decision demodulation+high soft decision demodulation.
And step 24, performing de-interleaving treatment on the high-order bit data and the low-order bit data to obtain de-interleaved data.
And step 25, performing RS decoding on the de-interleaved data to obtain RS decoded data.
And step 26, transmitting the RS decoding data to a signal sink.
And de-interleaving the MLC decoding result, reducing the MLC decoding result into the sequence of RS code words, performing RS decoding, and transmitting the obtained RS decoding data to a signal sink. In this embodiment, the RS decoding adopts a hard decoding method.
In this embodiment, the performance of the cascade decoding method may also be increased by an iterative decoding manner, that is, after RS hard decoding is completed, the MLC decoding and the RS decoding are performed again by using the RS decoding data as iterative input data, and the obtained iterative decoding result is sent to the sink. Specifically comprising steps 31-36.
Step 31, interleaving the RS decoding data to obtain iterative input data. After interleaving the RS decoding data, the interleaved data is directly used as input data of iterative decoding without encoding, and is used as input of MLC decoding process again. The iteration input data comprises low-order iteration input data and high-order iteration input data.
And step 32, decoding the low-order iteration input data to obtain low-order iteration bit data. Taking a PAM4 modulation mode as an example, the low-order iteration input data is directly decoded to obtain low-order iteration bit data. Because the RS decoded data has no information of check bits, the discarded check bits need to be processed in the iteration input data obtained after interleaving the RS decoded data. In one implementation, the low-order iteration input data is decoded in a hard decoding mode, and check bits in the iteration input data are set as check bits of the data after the first low-order decoding, namely check bits in the low-order bit data; in another implementation, the low-order iterative input data is decoded by adopting a soft decoding method, the maximum likelihood ratio of information bits in the low-order iterative input data is set to be the most reliable, and the maximum likelihood ratio of check bits in the low-order iterative input data is set to be the maximum likelihood ratio in the low-order demodulation data.
And step 33, processing the high-order iteration input data with the assistance of the low-order iteration bit data to obtain the high-order iteration input data. Step 33 further includes steps 331 and 332, depending on whether the most significant bit in the modulated data is encoded during the multi-layer encoding process.
And step 331, when the most significant bit in the modulated data is not coded in the multi-layer coding process, performing a second demodulation process on the high-order iteration input data in a hard decision mode by using the low-order iteration bit data to obtain the high-order iteration input data.
And step 332, when the most significant bit in the modulated data is encoded in the multi-layer encoding process, performing a third demodulation process on the high-order iterative input data in a hard decision mode or a soft decision mode with the assistance of the low-order iterative bit data to obtain high-order demodulation iterative data, and decoding the high-order demodulation iterative data to obtain the high-order iterative input data. Further, when the third demodulation process is executed by adopting a hard decision mode, decoding the high-order demodulation iteration data by adopting a hard decoding mode; and when the third demodulation process is executed by adopting a soft decision mode, decoding the high-order demodulation iteration data by adopting a hard decoding mode.
In this embodiment, steps 32 to 33 are referred to as an MLC iterative decoding process, where when the low-order iterative input data is decoded by hard decoding, the process is referred to as an MLC hard iterative decoding process; when the low-order iterative input data is decoded by adopting a soft decoding mode, the method is called an MLC soft iterative decoding process. Further, the MLC hard iterative decoding process includes two forms of low-order iterative hard decoding, high-order iterative hard decoding, and low-order iterative hard decoding, high-order iterative soft decoding, and the MLC soft iterative decoding process includes two forms of low-order soft decoding, high-order iterative soft decoding, and low-order soft decoding, high-order iterative hard decoding.
And step 34, performing de-interleaving treatment on the high-order iteration input data and the low-order iteration bit data to obtain de-interleaving iteration data.
And 35, performing RS decoding on the de-interleaving iterative data to obtain RS iterative decoded data. In this embodiment, the hard decoding method is adopted when RS decoding is performed on the deinterleaved iterative data.
Step 36, the RS iterative decoding data is sent to the sink.
It should be noted that, when the first demodulation process is performed on the channel received data transmitted by the channel in a hard decision manner to obtain low-order demodulated data, an iterative decoding manner is required to be adopted, so that the obtained decoded data can meet the performance requirement of the ethernet with the speed of more than 400 Gb/s. That is, when the first demodulation process is performed by the hard decision method, the flow of the concatenated decoding method includes MLC hard decoding+rs decoding+mlc hard iterative decoding+rs decoding.
When the first demodulation process is performed on the modulated data transmitted by the channel in a soft decision mode to obtain low-order demodulated data, the cascade decoding method flow can comprise a non-iterative mode, namely MLC soft decoding+RS decoding; the iterative decoding mode can also be adopted, and comprises two modes, namely MLC soft decoding, RS decoding, MLC soft iterative decoding, RS decoding and MLC soft decoding, RS decoding, MLC hard iterative decoding, RS decoding.
The cascade decoding method provided by the second embodiment of the present application is used for decoding the modulated data obtained by using the cascade coding method provided by the first embodiment of the present application, and the cascade decoding method includes performing a first demodulation process on the channel received data according to a preset modulation mode to obtain low-order demodulated data; decoding the low-order demodulation data to obtain low-order bit data; using low-order bit data to assist in processing channel received data to obtain high-order bit data; performing de-interleaving treatment on the high-order bit data and the low-order bit data to obtain de-interleaved data; RS decoding is carried out on the de-interleaving data to obtain RS decoding data; and sending the RS decoding data to a signal sink. The cascade decoding method uses low-order bit data to assist in processing high-order bits in the modulated data to obtain high-order bit data, ensures decoding performance, reduces complexity of a system and reduces time delay.
In order to further embody the performance advantages of the cascade coding method and the cascade decoding method provided by the application, a comparative experiment is carried out by taking a PAM4 modulation mode as an example.
In comparison experiment 1, experiment group 1 uses the cascade coding method of RS code+mlc code provided by the first embodiment of the application, specifically, the outer code adopts RS (544, 514, t=15), that is, KP4 FEC scheme, the lower bit data is coded by BCH (360,320) code in the constituent codes of the inner code MLC code, the error correction capability is 4, the higher bit data is not coded, no error correction capability exists, and the preset interleaving depth i=2. Where the interleaving depth i=2 has great potential to be compatible with the PCS (Physical Coding Sublayer ) of existing ethernet. Decoding is carried out by using the cascade decoding method of MLC soft decoding and RS decoding provided by the second embodiment of the application, specifically, in the MLC soft decoding process, the channel received data is demodulated by adopting a soft decision mode to obtain low-order demodulated data, and the low-order demodulated data is decoded by using a Chase-II algorithm to obtain low-order bit data; wherein the number of flip bits in the Chase-II algorithm is set to 3; demodulating the channel received data in a hard decision mode by using low-order bit data assistance, and directly outputting a demodulation result to obtain high-order bit data; and de-interleaving the high-order bit data and the low-order bit data to obtain de-interleaved data, and performing RS hard decoding to obtain an RS decoding result.
A cascade coding method of RS codes plus BCH codes is used for the comparison group 1; specifically, the outer code uses RS (544, 514, t=15) code, i.e. KP4 FEC scheme, and the inner code uses BCH (360, 340) code. The code rate of the cascade codes in experimental group and comparative group 1 is the same, and gray codes are used in the PAM4 modulation process in comparative group 1. Comparative group 2 used KP4 FEC scheme.
The decoding performance corresponding to the three sets of encoding methods in comparative experiment 1 is shown in fig. 10. Wherein, experiment group 1 corresponds to 2rs+mlc_flip3 in fig. 10, comparison group 1 corresponds to 2rs+bch360 (t=2) gray code_flip3 in fig. 10, and comparison group 2 corresponds to RS (544,514) in fig. 10. As can be seen from fig. 10, when the output BER (Bit Error Ratio) index reaches 1E-15, the SNR (Signal-Noise Ratio) of the experimental group and the comparative group 1 is improved by more than 1dB compared with that of the comparative group 2, and the decoding performance of the experimental group is improved by about 0.05dB compared with that of the comparative group 1. Where flip in fig. 10 refers to the least reliable bit (flip) number at BCH soft decoding.
Comparative experiment 2 verifies whether iterative decoding is required when MLC is hard decoded. In the cascade coding method of experiment group 2, the preset interleaving depth i=4, and the rest settings are the same as those of the cascade coding method of experiment group 1 in comparative experiment 1. Experiment group 2 used a cascade decoding method of MLC hard decoding+rs decoding. The cascade coding method of the experimental group 3 is consistent with that of the experimental group 2, and the iterative decoding mode of MLC hard decoding, RS decoding, MLC hard iterative decoding and RS decoding is used for decoding.
The decoding performance corresponding to the two test groups in the comparative test 2 is shown in fig. 11, wherein the FER (Frame Error Rate) of the test group 2 corresponds to FER-sim 4kp4 iter1 in fig. 11, the BER (bit Error Rate) of the test group 2 corresponds to BER-sim4kp4 iter1 in fig. 11, the FER (Frame Error Rate) index of the test group 3 corresponds to FER-sim 4kp4 iter2 in fig. 11, and the BER index of the test group 3 corresponds to BER-sim4kp4 iter2 in fig. 11. The performance requirement of the Ethernet above 400Gb/s is that the output BER is E-15 when the raw-BER is 2E-3. As can be seen from fig. 11, the decoding scheme of experiment group 2 requires a channel condition of about 1.8E-3 to meet the output BER of E-15, and cannot meet the performance requirement of ethernet; the decoding scheme of experiment group 3 can meet the requirement under the channel condition of about 2.8E-3, which is far more than the performance requirement of the Ethernet.
As can be seen from comparative experiment 2, when the modulated data transmitted from the channel is subjected to the first demodulation process in a hard decision mode to obtain low-order demodulated data, an iterative decoding mode is required, and the obtained decoded data can meet the performance requirement of the ethernet with the speed of more than 400 Gb/s.
Comparative experiment 3 the decoding performance of experimental group 1, experimental group 4 and experimental group 5 and comparative group 1 were compared. The cascade coding method of experiment group 4 is the same as experiment group 1, and the cascade coding method adopts an iterative coding mode of MLC soft coding+RS coding+MLC soft coding+RS coding, wherein, high bit data is not coded in coding, so that in the MLC soft coding process, a low bit coding result is used for assisting in hard decision demodulation of high bits, and the high bit data is directly output. The cascade coding method of the experimental group 5 is the same as the experimental group 1, and the cascade coding method adopts an iterative coding mode of MLC soft coding, RS coding, MLC hard iterative coding and RS coding.
The decoding performance results of comparative experiment 3 are shown in fig. 12; wherein, comparative group 1 corresponds to 2rs+bch360 (t=2) gray code_flip 3 in fig. 12, experimental group 1 corresponds to 2rs+mlc_flip3 in fig. 12, experimental group 4 corresponds to 2rs+mlc two soft iterations_flip 3 in fig. 12, and experimental group 5 corresponds to 2rs+mlc soft and hard iterations_flip 3 in fig. 12. As can be seen from fig. 12, when the interleaving depth is 2, the decoding performance curve is fit-extended, and when the output BER is equal to 1E-15, the decoding performance of experiment group 4 is improved by about 0.28dB compared with experiment group 1, and the decoding performance of experiment group 5 is improved by about 0.12dB compared with experiment group 1. From the above analysis, it can be seen that the decoding performance of the concatenated decoding method can be increased by means of iterative decoding.
The above-provided embodiments are only examples under the general inventive concept and do not constitute limitations on the scope of the application. Any other embodiments which are extended according to the solution of the application without inventive effort fall within the scope of protection of the application for a person skilled in the art.
Claims (6)
1. The cascade decoding method is characterized by being used for decoding the modulated data obtained by the cascade coding method; a concatenated coding method comprising:
Receiving information source data sent by an information source;
RS encoding is carried out on the information source data to obtain RS codeword data;
interleaving the RS codeword data according to a preset interleaving depth to obtain interleaved data;
grouping the interleaved data to obtain bit data of a preset number of groups; wherein the preset number is the number of bits corresponding to one symbol in the preset modulation mode, and each group of bit data corresponds to different bits in the preset modulation mode;
carrying out multi-layer coding on the bit data of the preset number group to obtain multi-layer codeword data; the multi-layer codeword data comprises a preset number of groups of multi-layer sub-codeword data, and the lengths of each group of multi-layer sub-codeword data are consistent; the check bit length in the multi-layer sub-codeword data corresponding to the most significant bit in the preset modulation mode is smaller than the check bit length in the multi-layer sub-codeword data corresponding to the least significant bit in the preset modulation mode;
modulating the multi-layer codeword data according to the preset modulation mode to obtain modulation data for channel transmission;
the cascade coding method comprises the following steps:
executing a first demodulation process on the channel received data according to a preset modulation mode to obtain low-order demodulation data of a first quantity group;
Decoding the low-order demodulation data to obtain low-order bit data;
using the low-order bit data to assist in processing the channel received data to obtain a second number of groups of high-order bit data; the first number plus the second number are equal to a preset number, and the preset number is the number of bits corresponding to one symbol in the preset modulation mode;
de-interleaving the high-order bit data and the low-order bit data to obtain de-interleaved data;
RS decoding is carried out on the de-interleaving data to obtain RS decoding data;
transmitting the RS decoding data to a signal sink;
when the preset modulation mode is PAM4, the first number and the second number are both equal to 1; the low-order bit data corresponds to the least significant bit in the modulated data, and the high-order bit data corresponds to the most significant bit in the modulated data;
the processing the channel received data with the assistance of the low-order bit data to obtain high-order bit data includes:
when the most significant bit in the modulated data is not coded in the multi-layer coding process, the low-order bit data is used for assisting in performing a second demodulation process on the most significant bit of the channel received data in a hard decision mode, so that the high-order bit data is obtained;
When the most significant bit in the modulated data is encoded in a multi-layer encoding process, performing a third demodulation process on the most significant bit of the channel received data in a hard decision mode or a soft decision mode by using the low-order bit data to obtain high-order demodulated data, and decoding the high-order demodulated data to obtain the high-order bit data; when a third demodulation process is executed by adopting hard decision, decoding the high-order demodulation data by adopting a hard decoding mode; and when the third demodulation process is executed by adopting a soft decision mode, decoding the high-order demodulation data by adopting a soft decoding mode.
2. The concatenated decoding method of claim 1, wherein prior to the transmitting of the RS decoded data to the sink, the concatenated decoding method comprises:
performing iterative decoding on the RS decoding data to obtain RS iterative decoding data;
performing iterative decoding on the RS decoding data to obtain RS iterative decoding data, including:
interleaving the RS decoding data to obtain iterative input data; the iteration input data comprise low-order iteration input data and high-order iteration input data;
Decoding the low-order iteration input data to obtain low-order iteration bit data;
when the most significant bit in the modulated data is not coded in the multi-layer coding process, performing a second demodulation process on the high-order iteration input data in a hard decision mode by using the low-order iteration bit data to obtain the high-order iteration input data;
when the most significant bit in the modulated data is encoded in a multi-layer encoding process, performing a third demodulation process on the high-order iteration input data in a hard decision mode or a soft decision mode by using the low-order iteration bit data in an auxiliary mode, and decoding a demodulation result to obtain the high-order iteration input data; when the third demodulation process is executed by adopting a hard decision mode, decoding a demodulation result by adopting a hard decoding mode; when the third demodulation process is executed by adopting a soft decision mode, decoding a demodulation result by adopting a soft decoding mode;
and performing de-interleaving treatment on the high-order iteration input data and the low-order iteration bit data to obtain de-interleaving iteration data.
3. The concatenated decoding method of claim 2, wherein when the low-order iterative input data is decoded in a hard decoding manner, check bits in the low-order iterative input data are set as check bits in the low-order bit data.
4. The cascade decoding method according to claim 2, wherein when the low-order iterative input data is decoded by soft decoding, a maximum likelihood ratio of information bits in the low-order iterative data is set to be most reliable, and a maximum likelihood ratio of check bits in the low-order iterative input data is set to be a maximum likelihood ratio in the low-order demodulated data.
5. The concatenated decoding method of claim 3, wherein the low-order demodulated data is obtained by a hard decision method when a first demodulation process is performed on the channel received data in accordance with a PAM4 modulation scheme;
and the low-order bit data is obtained by adopting a hard decoding mode when the low-order demodulation data is decoded.
6. The cascade decoding method according to any one of claims 1, 3, 4, wherein the low-order demodulated data is obtained by adopting a soft decision method when performing a first demodulation process on the channel received data according to PAM4 modulation method; and soft decoding is adopted when the low-order demodulation data are decoded, so that the low-order bit data are obtained.
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