CN113612586B - Low-delay channel coding method combining LT code and multiple connections - Google Patents
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Abstract
The invention relates to a low-delay channel coding method combining LT codes and multiple connections, belonging to the technical field of channel coding. The method optimizes the degree distribution function of the LT code, namely, the degree distribution function of the joint degree distribution of the double proportional coefficients is determined, the optimal proportional coefficient is determined according to the channel condition, the optimized degree distribution function is utilized to generate coded symbols, the coded symbols are transmitted through the two links, the coded symbols received in the two links are combined at a receiving end, and confidence hard decision decoding is carried out. The method obtains better performance than HARQ and traditional multi-connection on the indexes of decoding time delay and communication system stability, the error code rate of LT codes after optimizing the degree distribution function is obviously reduced during transmission, and the decoding cost can be lower than 10 when reaching 0.5‑5。
Description
Technical Field
The invention relates to a low-delay channel coding method combining LT codes and multiple connections, belonging to the technical field of channel coding.
Background
Fountain Codes (Fountain Codes) are an effective channel coding method, and include various code patterns such as LT Codes, Raptor Codes, and on-line Fountain Codes. The transmitting end can randomly select d from k information source symbols to carry out XOR operation to generate infinite number of coded symbols, and the receiver can recover the information source symbols from any n coded symbols, wherein n is slightly larger than k. Compared with the traditional channel coding mode with fixed code rate, the code rate of the fountain code can be adaptively changed along with the channel condition, and channel state information does not need to be acquired in advance, so that the fountain code is widely applied to scenes such as multimedia communication, satellite communication, data distribution and the like.
With the progress of technology and the development of the era, communication systems are performing an iterative process of one generation and another. The fifth generation mobile communication system is aimed not only at faster communication but also at Low-Latency high-reliability communication (URLLC) in the new generation mobile communication system. The basic definition of URLLCIn the name, when source symbols are transmitted, the method has the characteristics of low delay and high reliability, but in a communication system, the high reliability and the low delay are always a pair of contradictions. In the near future, various remote operations and intelligent unmanned driving can be stages with huge functions of URLLC, and great convenience is brought to our lives. URLLC has stringent requirements on transmission delay and communication reliability, which are set by the 3GPP, an international standard organization. For the performance index of delay, 0.5ms is the minimum requirement of uplink and downlink delay of the user. For the index of reliability, the requirement of 3GPP for reliability of once transmission of URLLC is: the reliability of transmitting 32 byte packets is 1-10 within 1ms of user plane time delay-5。
However, it has long been a contradiction between ensuring high reliability and shortening the transmission delay of information for the design of communication systems. In order to ensure the reliability of data transmission in the communication system, a Hybrid Automatic Repeat reQuest (HARQ) mode is commonly used in the fourth generation mobile communication system to ensure the reliability of communication. The specific principle of HARQ is: forward error correction coding and automatic retransmission request are combined, namely when channel coding cannot ensure the required reliability, a feedback request sending end retransmits data, the received data are combined, and the transmission reliability is improved in a mode of sacrificing wireless resources and decoding time. Although HARQ can ensure reliability of a communication system when transmitting information source symbols, a large transmission delay is caused by several retransmissions, and the HARQ cannot be applied to a delay sensitive scene. Fountain codes are a promising way to replace HARQ error control. The receiving end of the fountain code only needs to receive a sufficient number of coding symbols, and the decoding accuracy can be ensured, so that the time delay and signaling overhead caused by a feedback retransmission mechanism are avoided.
In the 5G era, as various indexes such as time delay and reliability become more and more severe, the density and the contact ratio of communication sites are being improved at a higher speed, more prominent network heterogeneity, and a terminal multi-system technology has been gradually developed to a mature stage, and a multi-connection technology is proposed again as an important technology for solving mobility, system capacity and reliability. The core content of the multi-connection technology is as follows: the design adopts the idea of separating a user plane and a control plane, so that the terminal working in a radio resource control connection state is simultaneously connected with at least two network nodes. However, the traditional multi-connection technology causes waste of wireless resources, and the combination of the fountain codes and the multi-connection technology can ensure that the communication system can obtain better performance on the stability and low-delay indexes, reduce part of signaling overhead, save the use amount of the wireless resources and obtain better performance than the traditional multi-connection technology.
The invention aims to solve the two problems of huge transmission delay caused by the transmission of an HARQ scheme and larger decoding overhead caused by the transmission of the traditional multi-connection scheme, optimizes the degree distribution function of the traditional LT code, combines the LT code with the multi-connection scheme and obtains better performance than the HARQ and the traditional multi-connection scheme on the indexes of decoding delay and communication system stability.
Disclosure of Invention
The invention aims to solve the problems that a plurality of retransmissions bring huge transmission delay in HARQ transmission and a plurality of connections cause great wireless resource waste in multi-connection transmission, and provides a low-delay channel coding method combining LT codes and multiple connections.
In order to achieve the purpose, the invention adopts the following technical scheme:
the low-delay channel coding method combining the LT code and the multiple connections comprises the following steps:
step 1: optimizing the degree distribution function of the LT code, determining the degree distribution function of the joint degree distribution of the double proportion coefficients, and determining the optimal proportion coefficient according to the channel condition, which specifically comprises the following substeps:
step 1.1, adopting sliding robust arc sub-distribution, optimized Poisson distribution and ideal arc sub-distribution to form double-proportion coefficient joint degree distribution, optimizing a degree distribution function of the LT code, and determining the degree distribution function;
σ(i)＝αP′(i)+βρ(i)+(1-α-β)μ′(i)
wherein, σ (i) represents a joint degree distribution function of the double proportionality coefficients, and i represents a coding symbolic value; alpha and beta are proportionality coefficients;
p '(i) represents an optimized Poisson distribution, ρ (i) represents an ideal soliton distribution, and μ' (i) represents a sliding robust soliton distribution;
wherein the content of the first and second substances,
wherein the content of the first and second substances,
wherein λ is a parameter;
wherein, R is c · ln (k/δ) · k, c ∈ (0, 1), δ ∈ (0, 1), in the above formula, c and δ are two parameters that affect decoding performance, and n is a first peak point; b is a first crest factor with a magnitude of (0, 1);
step 1.2: after the degree distribution function form is determined, according to the channel condition, Monte Carlo simulation is carried out on two proportional coefficients in the dual proportional coefficient joint degree distribution, and the optimal proportional coefficient is determined by the number of recovery information source symbols of the receiving end under different proportional coefficients;
wherein the two proportionality coefficients refer to α and β;
step 2: generating a random number between (0, 1), obtaining the degree of a coding symbol by using a dichotomy according to a degree distribution function, randomly selecting a plurality of information source symbols with degrees, putting the information source symbols into an encoder for half-sum operation, and obtaining a corresponding coding symbol, wherein the method specifically comprises the following steps: obtaining the degree d of a coding symbol by using a dichotomy degree distribution function, then randomly selecting d information source symbols from k information source symbols, and putting the randomly selected d information source symbols into an encoder by a transmitting end for half-sum operation to obtain a corresponding coding symbol;
and step 3: transmitting the coded symbol through two binary erasure channels with different erasure probabilities;
and 4, step 4: after receiving the coded symbols, the receiving end combines the coded symbols received in the two links, and recovers the coded symbols lost in the transmission process of the other link by using the coded symbols correctly transmitted in one link so as to reduce the decoding overhead in the subsequent transmission process;
and 5: the decoder searches for the code symbol with the moderate degree of 1 in the received code symbol, if the code symbol is found, the decoder jumps to the step 6 to carry out decoding, otherwise, the decoder jumps to the step 2;
step 6: carrying out confidence hard decision decoding;
to this end, from step 1 to step 6, a low-latency channel coding method combining LT codes and multiple connections is completed.
Advantageous effects
The invention provides a low-delay channel coding method combining LT codes and multi-connection, which has the following beneficial effects compared with an HARQ scheme and a traditional multi-connection method:
1. when the number of recovered source symbols is the same during control transmission, the decoding overhead required by the HARQ is higher, that is, the transmission delay of combining the LT code and the multiple connections is lower than that of the HARQ;
2. combining LT codes with multiple connections saves a retransmission mechanism, decoding cost required during transmission is lower than that of the traditional multiple connections, and the quantity of consumed wireless resources is reduced;
3. the LT code after optimizing the degree distribution function obtains obvious reduction of error code rate during transmission, and can be lower than 10 when the decoding overhead reaches 0.5-5。
Drawings
Fig. 1 is an implementation flowchart of a low latency channel coding method combining LT codes and multiple connections according to the present invention;
fig. 2 is a schematic diagram of determining an optimal scaling factor α in step 1 according to an embodiment 1 of a low-latency channel coding method combining LT codes and multiple connections;
fig. 3 is a schematic diagram of determining an optimal scaling factor β in step 1 of the LT code and multi-connection combined low-latency channel coding method according to the embodiment 1 of the present invention;
FIG. 4 is a schematic diagram showing the bit error rate comparison between an optimized degree distribution function and a conventional degree distribution function in embodiment 1 of the LT code and multi-connection combined low-delay channel coding method of the present invention;
fig. 5 is a diagram of comparing transmission delays of LT codes combined with multiple connections and HARQ in step 7 according to an embodiment 1 of the low-delay channel coding method combining LT codes with multiple connections;
fig. 6 is a diagram of a comparison of the number of wireless resources consumed by the transmission of LT codes combined with multiple connections in step 8 in step 1 of a low-latency channel coding method combining LT codes and multiple connections according to the present invention.
Detailed Description
The low-latency channel coding method combining LT code and multiple connections according to the present invention will be further illustrated and described in detail with reference to the accompanying drawings and embodiments.
Example 1
The invention relates to a low-delay channel coding method combining LT codes and multiple links, which optimizes a degree distribution function of the LT codes, namely, determines a degree distribution function of the joint degree distribution of double proportionality coefficients, determines an optimal proportionality coefficient according to channel conditions, generates coded symbols by using the optimized degree distribution function, transmits the coded symbols through two links, combines the coded symbols received in the two links at a receiving end, and performs confidence hard decision decoding. The method obtains better performance than HARQ and traditional multi-connection on the indexes of decoding time delay and communication system stability, the error code rate of LT codes after optimizing the degree distribution function is obviously reduced during transmission, and the decoding cost can be lower than 10 when reaching 0.5-5。
In the specific implementation, two vehicles A and B are assumed to be carriedWith a mobile terminal TAAnd TB. Now TANeed to go to TBAnd transmitting a source symbol with the length k being 1000, and transmitting under a binary erasure channel. In an automobile communication scene, on one hand, the requirement on time delay is high, on the other hand, the high mobility in the automobile communication can lead the channel state to change continuously, and the accurate channel state information is difficult to obtain, and the LT code can replace an HARQ mechanism, so that the time delay is reduced; and the decoding overhead can be reduced by combining the LT codes with multiple connections, and the quantity of the used wireless resources is saved. Therefore, the rateless code has better application potential in an automobile communication scene, and the method obtains better performance than that of the HARQ and the traditional multi-connection on the indexes of decoding time delay and communication system stability;
the operation of each step under specific parameter conditions is specifically set forth below:
step 1: the degree distribution function of the LT code is optimized. The invention optimizes the LT code by adopting the double-scale coefficient joint degree distribution formed by the sliding robust arc sub distribution, the optimized Poisson distribution and the ideal arc sub distribution.
Let c be 0.2, δ be 0.7, n be 3, b be 0.7, λ be 2, the number of monte carlo simulations be 1000, the erasure probability of the binary erasure channel be 0.2, and the optimal scaling factor is determined when the source symbol length k is 500 and 1000, respectively.
Controlling two proportional coefficients alpha and beta to take values between (0, 1) according to the modes of 0, 0.1, 0.2, … and 1, carrying out 1000 Monte Carlo simulations after each group of proportional coefficients is determined, and calculating at a receiving end TBAnd determining the number of the recovered source symbols so as to determine the optimal proportionality coefficient combination. The simulation results are illustrated by fig. 2 and 3. Finally, it can be determined that the optimal scaling factor α is 0.2 and β is 0.5 for this channel.
The deletion probabilities of the two links for transmission in step 3 are 0.2 and 0.3, respectively, and the determination of the optimal proportionality coefficient in the link with the deletion probability of 0.3 is the same as that in step 1.
Step 2: after the optimal proportionality coefficient is determined, a random number between (0, 1) is generated, the degree d of a coding symbol is obtained by a dichotomy degree distribution function, wherein d is less than or equal to 1000, then d source symbols are selected from the 1000 source symbols in a random manner, and the transmitting end carries out XOR operation on the randomly selected d source symbols to obtain a corresponding coding symbol.
And step 3: and after a coded symbol is obtained, the coded symbol is transmitted through two binary erasure channels with different erasure probabilities. The deletion probabilities are 0.2 and 0.3, respectively.
And 4, step 4: after receiving the coded symbols, the receiving end combines the coded symbols received in the two links, and recovers the coded symbols lost in the transmission process of the other link by using the coded symbols correctly transmitted in one link, so that the decoding overhead in the subsequent transmission process can be reduced.
And 5: the decoder searches the received code symbol with the moderate degree of 1, if the code symbol is found, the decoding process continues, otherwise, the decoding is finished. The decoder selects a degree-1 code symbol. Since the encoding degree is 1, and its value is actually equal to the original source symbol participating in encoding, the decoding of the original information is completed, and the check node corresponding to the encoding symbol on the tanner graph and the edge connecting to the variable node are deleted. The variable node corresponding to the original information source symbol and all check nodes connected with the variable node with edges are subjected to the primary modulo two summation, the result is the updated value of the corresponding check node, and the primary modulo two summation is performed on the original information source symbol after the original information source symbol participates in the coding process of the corresponding coding symbol, which is equivalent to the effect of removing the original information source symbol from the coding symbol. This variable node and all its edges are then deleted on the graph.
Step 6: and (5) continuously repeating the step (2) to the step (5) until the receiving end finishes decoding.
And 7: and independently transmitting the same number of coding symbols between the two mobile terminals by adopting an HARQ scheme, and calculating the time delay required by decoding.
And 8: and independently transmitting the same number of coding symbols between the two mobile terminals by adopting a traditional multi-connection scheme, and calculating the number of the wireless resources consumed when decoding is completed.
In the whole transmission process, the number of information source symbols recovered under different decoding overheads and the size of the error rate can be obtained by controlling the number of coding symbols received by a receiving end, namely controlling the size of decoding overheads.
FIG. 4 is a schematic diagram showing bit error rate comparison between an optimized degree distribution function and a conventional degree distribution function in embodiment 1 of the low-delay channel coding method combining LT codes and multiple links according to the present invention; fig. 5 and 6 illustrate the advantages of the present invention compared to HARQ and conventional multi-connection.
The above detailed description is intended to illustrate the objects, aspects and advantages of the present invention, and it should be understood that the above detailed description is only exemplary of the present invention and is not intended to limit the scope of the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (3)
1. A low-delay channel coding method combining LT codes and multiple connections is characterized in that: the method comprises the following steps:
step 1: optimizing the degree distribution function of the LT code, determining the degree distribution function of the joint degree distribution of the double proportion coefficients, and determining the optimal proportion coefficient according to the channel condition;
step 1, specifically comprising the following substeps:
step 1.1, a dual-scale coefficient joint degree distribution is formed by adopting sliding robust arc sub-distribution, optimized Poisson distribution and ideal arc sub-distribution, a degree distribution function of the LT code is optimized, and the degree distribution function is determined as follows:
σ(i)＝αP′(i)+βρ(i)+(1-α-β)μ′(i)
wherein, σ (i) represents a joint degree distribution function of the double scale coefficients, and i represents a coding sign degree value; alpha and beta are proportionality coefficients;
p '(i) represents an optimized Poisson distribution, ρ (i) represents an ideal soliton distribution, and μ' (i) represents a sliding robust soliton distribution;
wherein，
Wherein the content of the first and second substances,
wherein λ is a parameter;
wherein, R ═ c · ln (k/δ) · k, c ∈ (0, 1), δ ∈ (0, 1), in the above formula, c and δ are two parameters affecting decoding performance, and n is a first peak point; b is a first crest factor with a magnitude of (0, 1);
step 1.2: after the degree distribution function form is determined, carrying out Monte Carlo simulation on two proportional coefficients in the dual proportional coefficient joint degree distribution according to the channel condition, and determining the optimal proportional coefficient by recovering the number of information source symbols at the receiving end under different proportional coefficients;
step 2: generating a random number between (0, 1), obtaining the degree of a coding symbol by using a dichotomy according to a degree distribution function, and randomly selecting a plurality of information source symbols with degrees to be placed in an encoder to carry out half-sum operation to obtain a corresponding coding symbol;
and step 3: transmitting the coded symbol through two binary erasure channels with different erasure probabilities;
and 4, step 4: after receiving the coded symbols, the receiving end combines the coded symbols received in the two links, and recovers the coded symbols lost in the transmission process of the other link by using the coded symbols correctly transmitted in one link so as to reduce the decoding overhead in the subsequent transmission process;
and 5: the decoder searches for the code symbol with the moderate degree of 1 in the received code symbol, if the code symbol is found, the decoder jumps to the step 6 to carry out decoding, otherwise, the decoder jumps to the step 2;
step 6: and carrying out confidence hard decision decoding.
2. The method of claim 1, wherein the LT code and the multiple connections are combined to form a low-latency channel coding method, and the method comprises: in step 1.2, the two proportionality coefficients refer to α and β.
3. The method of claim 1, wherein the LT code and the multiple connections are combined to form a low-latency channel coding method, and the method comprises: step 2, specifically: and obtaining the degree d of a coded symbol by using a dichotomy according to a degree distribution function, then randomly selecting d information source symbols from the k information source symbols, and putting the randomly selected d information source symbols into an encoder by a transmitting end for half-sum operation to obtain a corresponding coded symbol.
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