具有低相位偏差敏感度的异步双层QAM调制

An Asynchronous Double Layered QAM with Lower Sensitivity to Phase Errors

高阶QAM(Quadrature Amplitude Modulation)调制是提高频谱效率的一个有效途径,但它对相位偏差容忍度较差.文章提出了一种异步双层QAM调制方法,可在发射端用较低的调制阶数实现和传统高阶QAM调制相当的频谱效率,并分别针对提出的异步双层QAM调制和传统QAM调制,推导了平坦瑞利块衰落信道下固定相位偏差的误符号率闭合解析表达式.理论分析与计算机仿真结果吻合,研究表明,误符号率为10-1时,异步双层256-QAM调制在相位偏差为0.9度的误符号率性能与无相位偏差情况比较,差异仅为0.3d B;而传统高阶4096-QAM调制的差异为11d B.

High order quadrature amplitude modulation （QAM） can improve spectral efficiency effectively, but it is very sensitive to phase errors. An asynchronous double layered modulation format is proposed to achieve nearly the same spectral effi- ciency as conventional high order QAM but with lower modulation orders in transmitter and lower sensitivity to phase errors. A closed-form formula for the symbol error rate （SER） of the proposed asynchronous double layered QAM format together with con- ventional QAM format is derived under flat Rayleigh block fading channel at fixed phase error.Both the theoretical analysis and the simulation results show that the performance degradation of the proposed asynchronous double 256-QAM format is just 0.3 dB at the SER of 10^-1 as the phase error increased from 0 degree to 0.9 degree.In contrast,the performance degradation of the conventional 4096-QAM format is up to 11 dB.