Study On Downlink Synchronization And Cell Search Technology For BroadBand Wireless Communication System

With the rapid development of Internet, telecommunication industry pays more and more attention to broadBand wireless communication. At present, OFDM technology is preferred in broadBand wireless communication system, for the advantages that it can effectively combat the multi-path effect, eliminate internal symbol interferences, and it has high frequency efficiency. The 802.16E standard, representative of broadBand wireless system, chooses OFDM as its PHY layer framework. This paper mainly focuses on downlink synchronization and cell search scheme of 802.16E system.There are two main aspects about OFDM synchronization technologies: symbol timing synchronization and carrier frequency synchronization. In this paper, the performance of symbol timing synchronization algorithm based on auto-correlation characteristic of PN sequence is analyzed theoretically, factors that affect its performance are summarized, and we propose an improved algorithm to better its performance. For carrier frequency synchronization techniques, we study performance of classical Moose carrier frequency offset estimation algorithm and time domain frequency estimation algorithm based on CP. After that, we propose carrier frequency synchronization schemes about continual OFDM system and packet OFDM system.In this paper, the characteristics of 802.16E preamble are presented. We propose whole cell search and downlink synchronization scheme for 802.16E system including frame detection, coarse timing synchronization and coarse frequency offset estimation, integer frequency offset estimation and cell index identification, fine timing synchronization and fine frequency offset estimation. And these algorithms are validated by simulation. After that, two network organization mode called same frequency network mode and different frequency network mode are presented. In same frequency network mode, the classical frame detection algorithm is noneffective in cell edge. Several algorithms are proposed to solve this problem. Simulation and analysis prove that they are efficient in this case. At last a frequency tracking algorithm is proposed to avoid impact of interference from adjacent cell/sector.