| 5. | We can reduce the isi and noise by elaborately designing transmitting filter and the receiving filter when the channel is known and unaltered . however , the factual channel is time - varying and not known entirely . so the isi is always existent 在信道特性已知且恒定的情况下,通过精心设计发送和接收滤波器就可以消除码间干扰和使噪声的影响最小,但实际信道既不可能完全知道,也不可能恒定不变,系统码间干扰总是存在。 |