Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Spreading Sequence Design and Theoretical Limits for Quasisynchronous CDMA Systems | EURASIP Journal on Wireless Communications and Networking 2004 1 19-31 2004 Hindawi Publishing Corporation Spreading Sequence Design and Theoretical Limits for Quasisynchronous CDMA Systems Pingzhi Fan Institute of Mobile Communications Southwest Jiaotong University Chengdu 610031 China Email Received 4 November 2003 Revised 1 March 2004 For various quasisynchronous QS CDMA systems such as LAS-CDMA system which emerged recently in order to reduce or eliminate the multiple access interference and multipath interference it is required to design a set of spreading sequences which are mutually orthogonal within a designed shift zone called orthogonal zone. For traditional orthogonal sequences such as Walsh sequences and orthogonal Gold sequences the orthogonality can only be achieved at the inphase point in other words the orthogonality is destroyed whenever there is a relative shift between the sequences that is their orthogonal zone is 0. In this paper new concepts of generalized orthogonality GO and generalized quasiorthogonality GQO for spreading sequence design in both direct sequence DS QS-CDMA systems and time frequency hopping TH FH QS-CDMA systems are presented. Besides selected GO GQO sequence designs and general theoretical periodic and aperiodic limits together with several applications in QS-CDMA systems are also reviewed and analyzed. Keywords and phrases sequences design generalized QS-CDMA. 1. INTRODUCTION In a typical direct sequence DS code division multiple access CDMA system all users use the same bandwidth but each transmitter is assigned a distinct spreading sequence 1 . The importance of the spreading sequences to spread spectrum CDMA is difficult to overemphasize for the type of sequences used its length and its chip rate set bounds on the capability of the system that can be changed only by changing the spreading sequences 2 3 . The well-known binary Walsh sequences or variablelength orthogonal sequences have perfect .
