基於BPSK調變同步訊號之基地台搜尋演算法研究、 化簡與設計

Abstract

在本論文中針對BPSK調變的同步訊號進行基地台搜尋演算法的研究。當同步訊號為BPSK調變時，基地台搜尋將會產生一些特性可以將其複雜度大幅縮減。. 由於BPSK訊號的組成相當簡單，因此在基地台搜尋的過程中會產生大量重覆的運算結果，藉由將這些運算結果事先算出，我們可以將基地台搜尋的複雜度減至一半以上。此外，利用機率的概念，一種新的基地台演算法被提出，此種演算法和傳統的基地台搜尋演算法在數學式上完全等效，但是其複雜度大約只有傳統方法的一半。除了以上兩種演算法，本論文還提出了數種可以降低基地台搜尋的演算法，因此可以有效降低基地台搜尋的複雜度。符元時間偏移和載波頻率偏移的對基地台搜尋的影響在本論文也有一些探討與歸納。

To ensure good transmission quality, a mobile user has to establish connection with a base station before transmitting or receiving any data. Cell search is the procedure that helps a user identify the nearest base station, and then a number of steps will be taken to enter the network via the base station. However, searching all possible base stations to find the nearest one requires high computation complexity as well as the execution time. This thesis focuses on low complexity designs of cell search based on BPSK-modulated signals. There have been a lot of techniques focusing on the same topic as this thesis. Most of them reduce the computation complexity at the price of performance loss. In this thesis, several low-complexity techniques for cell search without performance loss are proposed. The Grouping method and the Level-shifted method are the most important methods among all the proposed methods. In the Grouping method, an efficient multiplexing scheme is derived to achieve low-complexity realizations of the existing cell search methods. In the Level-shifted method, a new metric for cell search is derived by employing the binary characteristic of BPSK-modulated synchronization signals. The effect of timing offset on cell search is also investigated in this thesis. When timing errors exist, the conventional cell search algorithm is robust to timing errors and no performance loss results. If the symbol timing can be acquired to reasonable accuracy, the conventional cell search method can be further simplified.