AVR2021： AT86RF231 Antenna Diversity

　　AVR2021： AT86RF231 Antenna Diversity

　　天线分集是防止多径衰落的最佳保护。使用它可以大大提高真实网络实现的可靠性。

　　天线分集是一种利用多个天线在不同的传播路径上接收或发送信号以补偿多径干扰的传输方法。

　　由于网络节点间多径传播干扰的影响，接收信号强度可能会发生很大的变化，即使是传播条件的微小变化，也会影响链路质量。这些衰落效应可能导致设备之间的连接错误或楼层丢失增加。

　　在这样的场景中应用天线分集传输技术提高了网络节点之间rf连接的可靠性。

　　本文介绍了使用，设计和布局的at86rf231天线分集，实现如图1所示。提供的信息旨在帮助硬件设计者使用的at86rf231天线分集能力。

　　Wireless communication channel models

　　In wireless communication systems different channel models are used to describe the behavior of the air interface. A simple model is additive white Gaussian noise （AWGN）。 This model assumes a linear addition of wideband noise to the wanted signal with a constant spectral density and a Gaussian distribution of the amplitude.

　　More realistic wireless channel models also consider the impact of multipath propagation. Since a transmitted signal is subject to reflections and refraction on walls， surfaces etc.， the receiving node will see many signals， each differing in phase and amplitude. All signals superpose at the receiving antenna causing an effect called fading.

　　Using more than one antenna allows the evaluation of different multipath scenarios to avoid or reduce the effects of fading or interferences. Assuming that these antennas are independent of each other with respect to the signal propagation paths， the probability that all of them suffer from fading at the same time is significantly reduced.