基于无率纠错码和高阶QAM调制的收端速率自适应方案

现有的自适应解调方案中调制阶数最高仅限于16,且方案分析和设计中没有考虑信道编码的译码环节.本文研究适用于高阶QAM的自适应解调算法,并结合无率纠错码提出一种收端速率自适应方案.接收端有多种解调模式,每种解调模式删除一个符号中不同数量的、似然比绝对值最低的几个比特,以提高解调比特的可靠度和平均互信息.从互信息分析的角度,得到在满足要求的译码误码性能时,译码所需要的码字长度的理论结果,进一步给出在译码复杂度约束条件下解调模式的选择方案.以256-QAM调制星座和Raptor码为例对方案进行了仿真,验证了理论分析的正确性和方案的有效性.

Rate Adaptive Scheme at Receiver Based on Rateless Error Correcting Codes and High Order QAM

The order of the modulation used in existing adaptive demodulation schemes is no higher than 16,and the decoding of channel codes is not taken into consideration in the analysis and design.In this paper,an adaptive demodulation algorithm is studied.It includes multiple demodulation modes and can be applied to higher order quadrature amplitude modulations.A rate adaptive scheme at receiver is proposed which combines this algorithm and rateless error correcting codes.The bits whose absolute values of the log-likelihood ratio are the smallest in one symbol are deleted and the number of deleted bits varies in different demodulation modes,so the reliability and the average mutual information of demodulated bits can be boosted.From the perspective of mutual information analysis,the theoretical results of the required codeword length which meet the requirements of error performance are obtained.Moreover,the selection of the demodulation mode under a decoding complexity constraint is given.A sample scheme employing 256-QAM modulation constellations and Raptor codes is provided,and the simulation results of this sample are consistent well with those of the theoretical analysis,which confirms the effectiveness of the scheme.