分碼多工無線通訊系統下鏈波束形成及發射機前置編碼技術之研究

Abstract

本篇論文中，吾人考慮同步分碼多工系統在多路徑衰減通道中之下鏈運作(基地台到行動台)。吾人將介紹發射機和接收機聯合最佳化法，發射機前置編碼法，和下鏈波束合成法。發射機前置編碼法表示一種在發射機對發射訊號的線性轉換，而聯合最佳化法則在每個發射及接收端對訊號做線性轉換。在本篇論文中，發射機前置編碼法將搭配耙狀接收器使用。雖然聯合最佳化法的性能較發射機前置編碼法好，但是後者比前者更易於實現，且需較低之計算量。根據下鏈波束合成原理，吾人可利用線性化最小功率法計算發射陣列的權值，藉此使所有使用者都可在給定訊號干擾雜訊比下接收訊號，達到空間多工之目的。最後，吾人以電腦模擬證實發射機前置編碼及下鏈波束合成兩者的結合為改善通訊品質之一適當方案。

In this thesis, we consider a synchronous code division multiple access (CDMA) system operating in a multipath fading downlink channel (basestation-to-mobile). We will introduce the joint transmitter-receiver optimization, transmitter precoding, and downlink beamforming techniques. The transmitter precoding technique represents a linear transformation of the transmitted signals at transmitter, and the joint optimization technique performs a linear transformation of signals at both the transmitter and receiver. In this thesis, transmitter precoding will be equipped with the RAKE receiver. Although the performance of joint optimization is better than that of transmitter precoding, the latter is simpler to implement and requires a lower computational complexity. Based on downlink beamforming, we can use the power minimizer to calculate array weights, so that all users receive their signals with a given signal-to- interference-and-noise (SINR). This leads to spatial division multiple access (SDMA). At last, we demonstrate by computer simulations that combining transmitter precoding with downlink beamforming is an adequate scheme for improving the communication quality.