SCMA场景下的极化码编解码方案改进研究

极化码是目前唯一一种被证明可达到信道容量的编码方式,稀疏码分多址接入(Sparse Code Division Multiple Access,SCMA)可以提高频谱资源的利用率和接入系统的用户接入数量。为了提升SCMA与极化码的联合系统的误码率性能和译码时延,使联合系统的应用越来越广泛,提出了2种降低译码复杂度的方式:简化的左信息更新方式和剪枝译码算法。简化的左信息更新方式对于N=256,N=1024的极化码分别能降低37.6%和44.6%的存储资源占用数;剪枝译码算法在码率为0.5时能降低50%左右的计算复杂度。基于简化的SCAN算法改进了联合检测译码算法,在接收机采用外循环迭代的结构,引入了阻尼机制,选取最优的阻尼方式和最优阻尼值。仿真分析了所提联合检测译码算法与原有联合检测译码算法的误码率性能差异,外迭代接收机性能与内外双循环迭代的接收机性能相同,采用阻尼机制联合接收机的性能比无阻尼接收机的性能高0.8 dB左右,SJIDD的误帧率性能比保留宽度为32的SCLJDD的性能低0.7 dB左右,但能使接收机处理时延降至原来的1/4~1/8。

Research on Improvement of Polar Code Encoding and Decoding Scheme in SCMA Scene

The polarization code is currently the only one that has been proven to achieve channel capacity.Sparse Code Division Multiple Access(SCMA)can improve the utilization of spectrum resources and the number of users accessing the system.In order to improve the bit error rate performance and decoding delay of the joint system of SCMA and polarization code,the joint system is used more and more widely.Two ways for reducing the decoding complexity are introduced,including the simplified left information update method and the pruning decoding algorithm.The simplified left information update method can reduce the storage resource occupancy of 37.6%and 44.6%for the polarization codes of N=256 and N=1024 respectively;the pruning decoding algorithm can reduce the computational complexity by about 50%when the code rate is 0.5.Based on the simplified SCAN(soft-cancellation)algorithm,the joint detection and decoding algorithm is improved.The receiver adopts the structure of outer loop iteration,the damping mechanism is introduced,and the optimal damping method and optimal damping value are selected.The proposed joint detection and decoding algorithm is simulated.Compared with the BER performance of original joint detection and decoding algorithm,the performance of the outer iterative receiver is the same as that of the internal and external two-loop iteration.The performance of the joint receiver using the damping mechanism is about 0.8 dB higher than that of the undamped receiver.The frame error rate performance of SJIDD is about 0.7 dB worse than that of SCL-JDD with a reserved width of 32,but can reduce the receiver processing delay by 4~8 times.