LTE-Advanced系統之低複雜度細胞搜尋技術

Abstract

無線寬頻存取很重要的一個步驟，是下行鏈路(Downlink)剛建立時用戶端(UE)所必須做的訊號偵測、初始時間與載波頻率的同步以及搜尋目前所屬基地台(eNodeB)的物理層細胞識別碼(physical layer cell identity , Cell Identity)，這一連串的動作就是所謂的初始細胞搜尋(initial cell search)。一般要完成以上動作，基地台會傳送額外的引導符元(preamble)用來做基地台的辨認，而在3GPP LTE系統利用的是兩個同步訊號，包含主同步訊號(Primary Synchronization Signal, PSS)與副同步訊號(Secondary Synchronization Signal, SSS)來完成初始細胞搜尋的動作。而3GPP LTE系統的初始細胞搜尋還包含了符元循環字首長度和雙工模式的辨識。 本論文主要是基於在3GPP LTE下行鏈路規格所提出的一種快速同步與低複雜度細胞搜尋的方法。利用主同步訊號之相位差來同時偵測整數部份載波頻率偏移(Integer Carrier Frequency Offset ,ICFO)和細胞分區識別碼(Sector Identity)。利用副同步訊號來求得子訊框指標(sub-frame index)和細胞分群識別碼(Group Identity)。本論文以降低主、副同步訊號的處理的複雜度為主，我們根據3GPP LTE下行鏈路規格找出主、副同步訊號一些特別的性質並且利用這些性質來有效降低初始細胞搜尋的複雜度，並且保持偵測性能在可容忍的範圍之內。

The most important procedure of wireless access is signal detection,initial time acquisition,carrier frequency synchronization and eNodeB identification when UE want to establish a link with eNodeB. The fallowing behavior is so called the initial cell search. In order to achieve the above information , eNodeB has to send the additional preamble to recognizethemselves. However, 3GPP LTE systems use two dedicated synchronization signals: Primary Synchronization Signal(PSS) and Secondary Synchronization Signal(SSS) to searching the serving cell identity. The initial cell search also has to identifyof CP length and duplex mode. In this thesis, we propose a low complexity method to identify the cell identity as soon as possible.First we explain the procedure of synchronization and cell search, and use the phase difference of the PSS to joint detect the sector identity and integral part of the carrier frequency offset.And we also use the SSS to get the information of group identity and sub-frame index. This thesis aim to decrease the complexity of the PSS and SSS detection.According to the standard of 3GPP LTE , we find some special propertiesof synchronization. And make use of those propertiesto decrease the complexity of initial cell search, also maintain the detection performance is in the tolerable range.