October 2012
Intermediate to advanced
160 pages
2h 49m
Chinese
Content preview from 802.11n技術手冊
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第四章
波束成形的類型
可以用來增加接收器訊雜比（SNR）的相關技術中，波束成形為其中之一。本書所使用
的
波束成形
一詞，僅指透過多重天線陣列以主動導引傳輸的技術。如果你的傳送器不是
使用天線陣列中的多個元件以導引波束，那麼它就不是波束成形技術。例如，一個靜態
指向型天線的陣列無法進行波束成形。也許可以透過使用高增益的指向型天線來增加範
圍，但僅是靜態的使用指向型天線。為了成為真正的波束成形設備，無論是無線電晶片
或是天線都必須做些什麼，以改變離開天線的傳輸，並且是採用逐個訊框（Frame-by-
frame）的基礎。
無論是在無線電晶片或是天線陣列上實作，波束成形在無線電訊號的傳送上，是應
用一種數學的轉換以改變訊號傳送的方式。在數學上，轉換通常是表示成一個矩陣
（Matrix），以將傳入的訊號進行預先波束成形（Pre-beamforming），並將其對映至一些
輸出上。
3
於晶片上實作的波束成形，其矩陣的維度為時空串流的數量，即其輸入與傳送
鏈路數。在一個三串流並具備三個輸出的系統中，該矩陣將會是方形，對映著每個輸入
與輸出的組合。當波束成形實作於天線陣列時，矩陣的大小也會是輸出與輸入的數量。
一個天線陣列也仍然可以將三串流傳輸作為其輸入，但不同於將它們對映至三條傳送鏈
路，天線陣列可能將三個輸入對映至十個或更多的輸出元件。
用以描述轉換由時空串流至傳送能量的矩陣，稱為導引矩陣（Steering Matrix）。在圖
3-7 的一個 802.11n 介面區塊圖中，其空間對映器使用導引矩陣以改變傳送資料 ...
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