October 2012
Intermediate to advanced
160 pages
2h 49m
Chinese
Content preview from 802.11n技術手冊
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第二章
MIMO 與 802.11n 實體層
划呀、划呀，划著你的小船，
輕輕順著溪流而下…
―划呀、划呀、划著你的小船（
Row, Row, Row Your Boat
），經典童謠
要提升網路的速度，可以採用兩種方式。首先，協定設計者可以嘗試增加原始速度（即
為量測的傳輸速率），這可以稱為「跑更快（Go faster）」的方法。增加傳輸速率已經
成為大幅提升無線區域網路速度的主要工具，它使原先 802.11 標準的 1 Mbps 提升至
802.11a 與 802.11g 的 54 Mbps。第二種方法，協定設計者可以透過增加協定的效率，以
增加使用者所感受到的速度。這可以透過在給定的時間內傳送更多的位元資料來達成，
可稱之為「效率（Efficiency）」的方法。雖然 802.11n 同時採用了這兩種方法，但大部
分的增益來自於資料速率的大幅提升。在「跑更快」方法的核心關鍵技術中，802.11n
採用了 MIMO。早期的 802.11n 可以達到 150 Mbps 的資料傳輸速率，而標準也規劃了
一個明確的路徑，以讓資料速率能夠提升至 600 Mbps。而這些速率唯有透過 MIMO 技
術的應用方能實現。
大構想：MIMO 與資料串流
在 MIMO 技術發展之前，802.11 使用的是單資料串流，一個傳送器使用一支天線，而接
收器也使用一支天線。
1
pre-802.11n 設備的傳輸鏈結可以用它的兩個元件來進行描述，
其一被稱為單一輸入（Single-Input），因為接收器只用了一支天線，而另一個被稱為單
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.