LOS( line of sight) 和 NLOS（not line of sight)从名称上而言，是指的是无线信号的视线传输和非视线传输。简单的使用这两个名词，显然无法将实际上的多样的无线传播环境加以区分，比如水声，比如回波信道等。
而在实际的移动通信的网络规划中，大部分环境都可以分成LOS 和 NLOS.而且，各个标准的接收检测技术在这两种环境中又可以分别做不同的处理。因此，对NLOS 和 LOS的认识，是无线通信人的必修课程。
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