放大傳遞之合作式系統在服務品質限制下聯合

Abstract

在放大傳遞協定多輸入多輸出中繼傳輸系統中，傳統前置編碼器設計通常是在總功率限制下討論如何去改善連線品質。在本論文中，我們從不同觀點來看此問題，我們考慮在服務頻質限制下如何讓總傳輸功率最小。因多輸入多輸出中繼傳輸系統包含兩條路徑（中繼路徑和直線路徑）和兩個前置編碼器（發送端前置編碼器和中繼端前置編碼 器），要直接導出此問題的最佳解有很大的困難。藉在目的端使用最小方均差接收器，我們首先將此設計的問題轉化成有限制條件的最佳化問題。不過我們發現這最佳化問題的成本函數是前置編碼器的非線性函數直接求取這問題的解仍然困難。我們因此提議一新設計方法來解決這問題。主要想法是使用一最小均方差上限當做成本函數以及使用一限制型的前置編碼器結構。在我們的方法下，這前置編碼器設計問題可以被轉變成一個功率分配的問題，因而能顯著地簡化最佳解的推導。模擬解果顯示相較於傳統非合作式多輸入多輸出傳輸系統我們所提出的方法可以大幅的減少傳輸功率。

Conventional precoder designs for amplify-and-forward (AF) multiple-input multiple-output (MIMO) relay systems often consider how to improve the link quality under a total power constraint. In this thesis, we consider the design problem from a different perspective by minimizing the total transmission power under a quality of service (QoS) constraint. The problem is difficult since the MIMO relay system involves two links, the relay and direct links, and two precoders, the source and relay precoders. Using the minimum mean-square-error (MMSE) receiver at the destination, we first formulate the design problem as a constrained optimization problem. It is found, however, that the cost function is a highly nonlinear function of the precoders, and it is not feasible to solve the problem directly. We then propose a new design method to remedy the problem. The main idea is to replace the MSE with an upper bound, and apply a constrained structure for the precoders. Using our approach, the precoders design problems can be translated into a power allocation problem, significantly simplify the solution derivation. Simulations show that the proposed methods can dramatically reduce the required transmission power compared to the conventional non-cooperative MIMO systems.