中文摘要：

现代通信系统中,软译码可有效提升译码性能,高阶调制如MQAM和MPSK能够在不增加带宽的同时获得高的传输速率。但高阶调制解调模式下软信息的精确求解过于复杂,目前已有的近似算法性能损失过大。针对软输入技术,结合16QAM和32PSK 2种高阶调制方式,对软信息计算作进一步分析,提出了采用数值逼近的方法对16QAM的最小距离软信息计算公式进行修正和采用旋转坐标转换软信息量度方案的方法对32PSK的软信息计算公式进行修正的2种算法。结合LDPC码的仿真结果表明,算法在不增加计算复杂度的前提下,其性能仍能进一步逼近理论算法。

英文摘要：

The soft decision technique has been proved to be an efficient way to improve decoding performance in modem communication systems. The high-order modulation such as M-ary QAM and M-ary PSK can achieve high transmission rate without increasing the bandwidth. However, the accurate calculation expression of soft output algorithms via the log-sum approximation is of high computational complexity and traditional approximate algorithm has a great loss in performance. A low-complexity soft decision technique is proposed for two kinds of gray mapping modulation schemes,including 16QAM and 32PSK. Compared with the traditional method, the proposed algorithm is closer to the theoretical value under the simulation system with LDPC codes.