衰落是由于发射机与接收机之间空间位置的微小变化引起的，描述小范围内接收信号场强中瞬时值的快速变化特性，是由多径传播和多普勒频移两者共同作用的结果，包括由多径效应引起的衰落和信道时变性引起的衰落，具有信号的多径时延扩展特性和信道的时变特性-Fading is caused due to a slight change of the position of the space between the transmitter and the receiver, the characteristics of the receiving signal field strength, the instantaneous value of the rapid changes in the descr iption within, by multipath propagation and Doppler frequency shift of the joint action of botha result, time-varying fading caused by multipath effects and channel fading due to multipath delay spread characteristics and channel time-varying characteristics of the signal