在陆地移动通信这种瑞利信道上，比特差错经常是成串发生的。这是由于持续时间较长的深衰落谷点会影响到相继一串的比特。(In the land mobile communication the Rayleigh channel, bit error is often occurred in clusters. This is because the bit deep decline will affect the point of sowing have a longer duration.)