基于EXIT函数的自适应OFDM LDPC调制编码方案设计*

推导了瑞利衰落信道下,LDPC迭代译码的互信息公式,采用数值积分的方法计算校验节点外部信息,避免了信噪比较低时校验节点的LLR服从高斯分布的不精确假设带来的误差.分析了该编码系统的EXIT函数,以EXIT误差函数为代价函数,提出了自适应OFDM-LDPC编码方案.该方案与传统自适应方案相比,不需要确定切换门限,数值计算简单,而且避免了计算子信道信噪比带来的误差,适用于高速通信系统.最后在802.16e协议的仿真平台上进行了仿真验证.

Design of LDPC codes for adaptive OFDM modulation and coding system based on EXIT function

This paper proposed an adaptive channel coding and modulation scheme based on EXIT function for OFDM transmission over Rayleigh fading channel. And studied mutual information of LDPC code in Rayleigh fading channel. Mutual information of check node was got by numerical integral. It made the analysis more accurate, particularly for fading channel where the messages from check nodes were far from Gaussian at low SNR. Also studied the EXIT charts for this system and presented an adaptive OFDM-LDPC scheme with EXIT error function as cost function. Compared to traditional one, this method achieved best scheme with low complexity and had no use of getting switch threshold, This design method was suitable for high rate transmission. Finally, given simulation results and analysis based on 802.16e standard.