多使用者多輸入多輸出系統中X架構前置編碼

Abstract

多使用者多輸入多輸出(MU-MIMO)系統近期被廣泛的研究，此系統中最主要的問題為基地台傳送給一個使用者的訊號，會被傳送給其他使用者的訊號所干擾，因此MU-MIMO前置編碼為一個解決此問題的有效方法，在這種方法中，不同使用者之間的干擾會在傳送端預先消除。現有的前置編碼器主要利用強制歸零(ZF)或是最小均方誤差(MMSE)的準則設計，然而其效能是有限的。本論文旨在研究由最大似然(ML)準則設計的MU-MIMO前置編碼，我們提出使用新開發的X架構前置編碼方法於MU-MIMO系統中。首先，我們利用區塊對角方(BD)方法消除多使用者干擾，MU-MIMO系統會轉變成多個平行的單使用者多輸入多輸出(SU-MIMO)系統，接著我們針對每個SU-MIMO系統做X架構前置編碼，且對所有SU-MIMO系統做功率分配。由模擬數據結果顯示，我們提出的方法明顯地超越現有的MU-MIMO前置編碼方法。

Multiuser multiple-input-multiple-output (MU-MIMO) systems have been extensively studied recently. The main problem in the system is that the transmitted signal from a basestation to one user is interfered by the signals to other users. MU-MIMO precoding has been proposed as an effective way to solve the problem. In the approach, the interference between the different users is pre-canceled at the transmitter. Existing precoders mainly designed with zero-forcing (ZF) or minimum mean-square-error (MMSE) criteria and the performance is limited. This thesis aims to investigate MU-MIMO precoding with the maximum likelihood (ML) criterion. We propose using a newly developed X-structured precoding scheme in the MU-MIMO system. First, we use block diagonal schemes to cancel the multi-user interference such that the MU-MIMO system can be transferred to a set of parallel single-user MIMO (SU-MIMO) systems. Then, we conduct the X-structured precoding for each SU-MIMO system, and power allocating for all SU-MIMO systems. Numerical results show that the proposed method significantly outperforms the existing MU-MIMO precoding methods.