预加重技术在主字母体制中的应用

Implementation of Pre-Emphasis in High Alphabet Systems

在主字母体制中,各单音的差异带来调制系数的差异,进而引起在相同的信噪比条件下,频率高的单音比频率低的单音解调的误码率高。针对这个问题,应用预加重方法,即不改变系统的调制频偏,而通过对不同的频率分配相同的调制系数的方法来改善信号质量。经理论分析、软件仿真及设备实测,其结果证实此方法能够适当提高频率高的单音的能量,降低接收机的误码及漏码率。依据推导出的应用此方法前后主字母单音信噪比变化近似计算表达式,可利用工程参数计算具体数值。

The modulation index is different for different tones in the high alphabet system and, as a result, the BER （Bit Erro Rate） of higher frequency tones is higher than the BER of other frequency tones at the same SNR （Signal to-Noise Ratio）. A pre emphasis method is proposed to solve the problem. While maintaining modulation offset of the system, the same modulation index is assigned to different frequencies to improve signal quality. Theoretical a nalysis, software simulation and equipment testing show that the proposed method increases the energy of high fre- quency tones and lowers the BER and dropout rate of the receiver. Accurate values can be computed with engineer- ing parameters using the approximation equations derived from the change of SNR of the high alphabet tones before and after application of the method.