Research On LDPC Codes And Cooperative Communication Technology And Its Application

With the rapid development of wireless communication and the increasing demand for information transmission quality,the cooperative communication technology is an effective anti-channel fading method,which obtains the spatial diversity gain to improve the transmission performance of wireless communication.Thus being widely concerned.Amplify and forward protocol,decode and forward protocol,compress and forward protocol and quantize and forward protocol are four common cooperative protocols.Among them,quantize and forward protocol is a research hotspot because of its low complexity and high performance.LDPC code,as an effective anti-jamming channel coding technology,has the characteristics of approaching the Shannon limit,and we combine it with cooperative communication technology and apply it to wireless communication system to ensure the transmission reliability.In this paper,the LDPC code and cooperative communication technology and application are studied in depth.In view of the complexity of LDPC code decoding algorithm,the error of quantize and forward and the application scenario,the related design method and cooperative transmission scheme are put forward.The main research work as follows:(1)In order to solve the problem of high complexity of LLR-BP iterative decoding algorithm,the LLR-BP algorithm is optimized in this paper.In the process of updating the check node,a linear approximation of the hyperbolic tangent function and the hyperbolic arc tangent function is carried out by using the error linear approximation method.At the same time,the variable node is dynamically selected according to the reliability of the variable node.The simulation results show that the complexity of the optimized LLR-BP algorithm is much lower than that of the LLR-BP algorithm in the case where the decoding performance loss is small.(2)In order to solve the problem that the relay has a certain quantization error when the received signal is directly quantized in the quantize and forward scheme,based on the three-node cooperative transmission model,this paper designs a cooperative transmission scheme of LDPC codes and quantize and forward.The relay first evaluates the reliability of the received signal,and evaluates the 2-bit quantization to satisfy the reliability requirement according to the evaluation result,and then transfers the quantization information to the target node after LDPC encoding.The simulation results show that the BER performance of the designed transmission scheme is improved compared with the reference quantization scheme and DF Protocol,and as the distance of source to relay increasing,the BER performance enhancement of the design transmission scheme is more obvious.(3)Based on multiple access relay scene,LDPC codes and quantize and forward cooperative transmission scheme is designed,there are two schemes.Scheme 1 uses LDPC encoding on the relay channel,and scheme 2 does not use LDPC encoding onthe relay channel.The relay nodes of the two schemes need to evaluate the reliability of the two source information,and according to the evaluation results to meet the reliability requirements of the two source information for the soft domain network coding,and then 2-bit quantify the mixed information.The simulation results show that the BER performance of the two transmission schemes is improved compared with the reference scheme and the DF protocol.With the increase of the source to the relay distance,the BER performance of the two designed transmission schemes improves more obvious.