多輸入多輸出無線通信頻道之盲判別

Abstract

本論文針對多輸入多輸出頻率選擇衰減之無線通信頻道，利用不同的編碼方式，提出了三種通道盲蔽判別的方法。判別的方法是利用所估測出來的接收信號協方差矩陣，先計算出通道乘積矩陣，再對一個由通道乘積矩陣所形成的厄米特矩陣取特徵分解，即可求出通道脈衝響應矩陣。我們分別考慮了以下三種不同的編碼方式: (1) 週期性編碼， (2) 週期性編碼加補零 ，(3) 補零。 對應於上述三種編碼方式，通道乘積矩陣可分別由: (1) 一系列經解耦過的過定線性系統方程組求得， (2) 一個下三角線性系統方程式求得，(3) 執行一些簡單的減法所求得。對於前兩種判別方法，我們也設計了相對應的最佳週期編碼序列來減少通道雜訊以及數值誤差的影響，以提高通道估測的準確度。與子空間的方法比較起來，我們所提出的方法較為簡單，同時判別條件也較為寬鬆。此外我們的方法還可適用於發射器數目多於、少於、或等於接收器數目的情況。數值模擬的結果顯示我們所提出的方法對通道階數過估的情況具有相當的強健性。

We propose three blind identification algorithms for multiple-input multiple-output (MIMO) frequency selective fading wireless communication channels based on different precoding. The algorithms compute the channel product matrices from the estimated covariance matrix of the received data and then determine the channel impulse response matrix via an eigen-decomposition. Three precoding are considered: (i) periodic precoding, (ii) periodic precoding plus zero padding, and (iii) zero padding alone. As a result, for each of the three cases, the computation required to determine the channel product matrices are also different. The computations required are respectively (i) to solve a decoupled group of overdetermined linear systems of equations, (ii) to solve a lower triangular linear system, and (iii) to carry out a number of simple subtractions. For the first two algorithms, we also discuss the optimal design of the precoding sequences to minimize the effects of additive channel noise and numerical error, so as to increase the accuracy of channel estimation.

The algorithms are simple, in terms of the amount of computations required, as compared with subspace methods; they allow a more relaxed identifiability condition and are applicable to MIMO channels with more transmitters or more receivers. Simulation results show that they are reasonably robust with respect to channel order overestimation.