多使用者多輸入多輸出系統中湯林遜哈洛希瑪與X架構混合前置編碼

Abstract

在多使用者多輸入多輸出(MU-MIMO)系統中主要有兩種干擾訊號來源：用戶內干擾(ITA) 和用戶間干擾(IUI)。前置編碼已被視為一個解決此干擾問題的有效方法。其中，湯林遜哈洛希瑪前置編碼(THP)可將這些干擾在傳送端預先消除，然而，當它用於MU-MIMO前置編碼時，ITA和IUI皆被預先消除，故其效能並不是最佳的。本論文旨在研究應用於MU-MIMO系統中之THP的新方法。首先，我們使用區塊性THP(BTHP)來預先消除IUI，如此一來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(XP)，而在每個使用者的接收端處使用最大似然(ML)偵測器來解回自己的MIMO訊號。然而，傳統的THP方法不能直接適用於我們所提出之BTHP方法，於是我們提出兩種新的方法來解決此問題。由模擬結果顯示，我們提出的方法明顯優於現有的MU-MIMO前置編碼方法。

Two kinds of interferences arise in multi-user MIMO (MU-MIMO) systems, intra-user interference (ITA) and inter-user interference (IUI). Precoding has been proposed as an effective way to mitigate the interference problem. Tomlinson-Harashima precoding (THP), pre-canceling interference at the transmitter, is known to be effective in MIMO precoding. However, when it is used in MU-MIMO precoding, both ITA and IUI are pre-canceled, leading to a suboptimum performance. This thesis aims to develop new methods for THP in MU-MIMO systems. First, a block THP (BTHP) is developed such that only IUI is pre-canceled, transforming the MU-MIMO system to single-user MIMO (SU-MIMO) systems. Then, a X-structured precoding (XP) scheme is applied for each SU-MIMO system. At the receiver of each user, a maximum likelihood detector is used for its own MIMO signal. However, the conventional decoding scheme of THP cannot be used in that of BTHP. We then propose two new methods to solve the problem. Simulations with an OFDM system show that the propose methods significantly outperform existing MU-MIMO precoding methods.