Design of A Mixed Mode Code Acquisition Scheme for Direct-Sequence Spread Spectrum CDMA Systems

• Main Authors: Hsieh, Chih-Chiang, 謝智強
• Other Authors: Wu, Chwan-Chia
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/57978520366371765475

碩士 === 國立臺灣科技大學 === 電機工程系 === 89 === Matched filters are widely used by receiver design of a direct-sequence spread spectrum (DS-SS) system to achieve despreader of pseudo noise (PN) code. Among various types of Matched filter, serial-parallel architecture yields better trade off in between acquisition speed and circuit complexity. The main purpose of this thesis is to design a fast PN code acquisition detector to rapidly achieve initial synchronization between locally generated PN code and received PN code in a DS-SS system. There are two methods commonly employed in serial search technique: single dwell search and double dwell search. The double dwell search method is superior to single dwell search method in acquisition performance when input SNR is relatively good. While single dwell search method outperforms double dwell search method in acquisition when input SNR is poor. Since input SNR is closely related to the number of users accessing or noise interference the DS-SS system, and it is always pursued fast acquisition in a DS-SS system, it is therefore desired to have a code synchronizer that can achieve rapid code acquisition in both peak and non-peak hours. To this end, the other object of this thesis proposes a mixed mode code synchronizer employing both single and double dwell search methods in which single dwell search is adopted when input SNR is poor while double dwell search is applied when input SNR is relatively good. This thesis also presents the SNR estimation circuit to determine the timing to employ single dwell search or double dwell search.