非理想相干解调时网格编码调制系统的性能分析

Performance Evaluation of Trellis-Coded Modulation on Imperfect Coherent Detection

在理想相干检测的情况下,8相相移键控(8-PSK)方式的网格编码调制(TCM)与QPSK方式相比,可以得到较高的编码功率增益,且不会增加系统所需的带宽.然而,就相同的载噪比C/N,8-PSK方式对于相干载波相位偏移的灵敏度要比QPSK方式大得多,将会引入较多的误码.为了分析非理想相干检测的影响,首先导出相干载波相移θ时上述两系统信码判决间的等效距离.然后分别用系统模拟和解析方法求出在给定各种条件下的事件错误率及其上限.显然,编码功率增益将随相干载波相位偏移的上升而下降.最后给出在不同载噪比时上述两系统平均事件错误率和平均信息比特错误率的求解方法及其计算结果.从所得的计算结果中可以看出,要得到较高的TCM编码功率增益,降需要一对载噪比较高的相干载波.在一般情况下,这个条件较难满足.

Trellis-coded modulation(TCM)in 8 phase-shift keying(8-PSK) scheme is more power efficient than uncoded quaternary phase- shift keying(QPSK)at the same spectral efficiency in the case of perfect coherent detection.However it seems that for the same signal-to-noise ratio(SNR)of phase reference,the sensitivity to phase offset for 8-PSK is more serious than for uncoded QPSK.To analyse the effect of imperfect coherent detection,the equivalent distances under some recovered carrier phase offsets are derived.Then the conditional event error probability and it's upper bound with respect to recovered carrier phase offset are taken into account.The computing methods and results for the average event and bit error probabilities of the 4-state 2/3-TCM and uncoded QPSK schemes with noisy phase reference are given.