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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。
In the master alphabet system, the difference of each tone brings about a difference of modulation coefficients, which in turn leads to a high bit error rate of tone demodulation with a higher frequency than a frequency with the same signal-to-noise ratio. To solve this problem, the pre-emphasis method is applied, that is, the signal quality is improved by allocating the same modulation factor to different frequencies without changing the modulation frequency offset of the system. Theoretical analysis, software simulation and equipment measurement show that this method can raise the energy of single tone with high frequency and reduce the bit error rate and bit error rate of receiver. According to the deduced approximate expression of the variation of signal-to-noise ratio of the primary letter before and after the application of this method, the engineering value can be used to calculate the specific value.