时变信道的频率选择性和时变性。系统的输入是一个BPSK信号。系统的时变特性使BPSK信号作为时间的函数，发生衰减和相位旋转。-Time-varying channel frequency selectivity and time variability. Input to the system is a BPSK signal. System is time-varying characteristics make BPSK signal as a function of time, the o