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随着无线接入系统的工作频段越来越高,传输带宽越来越宽,非视距(Non Light Of Sight,NLOS)传输的限制就越来越大。研究非视距传播环境下抗衰落技术,对解决非视距无线接入条件下系统的可靠性和有效性,提高工程应用能力具有重要意义。非视距传输的关键实际上是抗多径衰落技术,包括OFDM、收发分集、子信道化、智能天线和自适应调制等技术。在分析非视距传播的条件和影响的基础上,对解决非视距传输问题的几个关键技术进行讨论,并对其在象WiMAX这样的宽带无线接入中的应用优势和影响进行了分析。
With the increasing frequency band of the wireless access system and the widening transmission bandwidth, the limitation of non-line of sight (NLOS) transmission becomes larger and larger. Studying the anti-fading technology in non-line-of-sight propagation environment is of great significance to solve the reliability and effectiveness of the system under non-line-of-sight wireless access conditions and improve the engineering application ability. The key to non-line-of-sight transmission is actually anti-multipath fading techniques, including OFDM, receive and transmit diversity, sub-channelization, smart antennas and adaptive modulation techniques. Based on the analysis of the conditions and impact of NLOS, several key technologies to solve the problem of NLOS transmission are discussed, and their application advantages and impact in broadband wireless access like WiMAX are analyzed .