AVR2021： AT86RF231 Antenna Diversity

　　AVR2021： AT86RF231 Antenna Diversity

　　天線分集是防止多徑衰落的最佳保護(hù)。使用它可以大大提高真實網(wǎng)絡(luò)實現(xiàn)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(fā)送信號以補償多徑干擾的傳輸方法。

　　由于網(wǎng)絡(luò)節(jié)點間多徑傳播干擾的影響，接收信號強度可能會發(fā)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(zhì)量。這些衰落效應(yīng)可能導(dǎo)致設(shè)備之間的連接錯誤或樓層丟失增加。

　　在這樣的場景中應(yīng)用天線分集傳輸技術(shù)提高了網(wǎng)絡(luò)節(jié)點之間rf連接的可靠性。

　　本文介紹了使用，設(shè)計和布局的at86rf231天線分集，實現(xiàn)如圖1所示。提供的信息旨在幫助硬件設(shè)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.