了解和實現(xiàn)MIMO射頻鏈路

　　多年來，作為一種理論方法和學(xué)術(shù)課題，多輸入多輸出（MIMO）收發(fā)系統(tǒng)正受到關(guān)注和支持組件的重大設(shè)計。該技術(shù)已經(jīng)通過了最新的4G一代和下一代LTE（長期演進(jìn)）蜂窩標(biāo)準(zhǔn)，提供吞吐量和性能的需要，以及在Wi-Fi的IEEE 802.11n標(biāo)準(zhǔn)。

　　MIMO方法的原理是在基站甚至用戶手持機上使用多個半獨立天線和發(fā)送/接收信道，以克服不可避免的信號路徑問題，例如噪聲、衰落和多徑。實際上，對這些問題多“柔術(shù)”翻轉(zhuǎn)；采用先進(jìn)的硬件和軟件將他們從以前被認(rèn)為是無線的弱點轉(zhuǎn)化為顯著的長處和優(yōu)點。

　　MIMO versus diversity systems

　　MIMO is much more sophisticated and complex than diversity antenna systems. Using multiple antennas for better signal coverage is a well-established technique; usually this is done at the receiver but it can also be done at the transmitter， which may not be co-located. （Note that to avoid confusion， the industry is now referring to basic single-antenna systems as single input， single output， or SISO.）

　　In a basic antenna diversity-receiver design， two or more antennas are used， spaced at least one-quarter wavelength apart. Each antenna‘s signal goes to an RF low-noise amplifier （LNA）， and then the signals are combined. This combining can be done is different ways， with an increasing scale in complexity， cost， and benefit.