AVR2021： AT86RF231 Antenna Diversity

　　天線分集是防止多徑衰落的最佳保護。使用它可以大大提高真實網絡實現的可靠性。

　　天線分集是一種利用多個天線在不同的傳播路徑上接收或發送信號以補償多徑干擾的傳輸方法。

　　由于網絡節點間多徑傳播干擾的影響，接收信號強度可能會發生很大的變化，即使是傳播條件的微小變化，也會影響鏈路質量。這些衰落效應可能導致設備之間的連接錯誤或樓層丟失增加。

　　在這樣的場景中應用天線分集傳輸技術提高了網絡節點之間rf連接的可靠性。

　　本文介紹了使用，設計和布局的at86rf231天線分集，實現如圖1所示。提供的信息旨在幫助硬件設計者使用的at86rf231天線分集能力。

　　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.