高阶QAM调制下基于对数似然比门限的自适应解调方案  

Adaptive Demodulation Scheme of High Order QAM Based on Log-likelihood Ratio Threshold

作　　者：雷维嘉[1] 宋海娜[1] 谢显中[1] 

机构地区：[1]重庆邮电大学移动通信技术重庆市重点实验室,重庆400065

出　　处：《电子与信息学报》2017年第6期1305-1312,共8页Journal of Electronics & Information Technology

基　　金：国家自然科学基金(61471076);重庆市基础与前沿研究计划(cstc2015jcyj A40047);长江学者和创新团队发展计划(IRT1299);重庆市科委重点实验室专项经费(CSTC)~~

摘　　要：现有的自适应解调方案中采用的调制星座阶数最高仅限于16,且方案分析和设计中没有考虑信道编码的译码环节。该文研究适用于高阶QAM调制的自适应解调算法,并结合无率纠错码提出一种收端速率自适应方案。收端将符号中每个比特的对数似然比绝对值与设定的解调门限值比较,大于该解调门限值的比特解调,否则删除。无率码译码码字长度固定,通过调整解调门限达到误码性能要求。在解调比特的平均互信息分析的基础上,给出不同信噪比下达到期望的译码误码性能要求的解调门限值及解调比例的计算方法。以256-QAM星座和Raptor码为例给出方案设计实例并进行仿真,仿真结果验证了理论分析的正确性和方案的有效性。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 used for higher order Quadrature Amplitude Modulation （QAM） is studied. A rate adaptive scheme at receiver is proposed which combines this algorithm and rateless error correcting codes. The bits in received symbols with absolute log-likelihood ratio value higher than demodulation threshold are demodulated, otherwise, deleted. In the scheme, the length of the codeword for the rateless codes decoding is fixed, and error performance is achieved by adjusting the demodulation threshold. Based on the analysis of the average mutual information of the demodulation bits, the calculation method is given of the log-likelihood ratio demodulation threshold and demodulation bits ratio under different signal-to-noise ratio. A sample design scheme employing 256-QAM 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.

关 键 词：自适应解调 正交幅度调制 速率自适应 对数似然比 互信息 无率编码 

分 类 号：TN919.3[电子电信—通信与信息系统]