tailieunhanh - Báo cáo hóa học: " An Improved Overloading Scheme for Downlink CDMA Frederik Vanhaverbeke"

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: An Improved Overloading Scheme for Downlink CDMA Frederik Vanhaverbeke | EURASIP Journal on Applied Signal Processing 2005 5 604-610 2005 Hindawi Publishing Corporation An Improved Overloading Scheme for Downlink CDMA Frederik Vanhaverbeke Telecommunications and Information Processing TELIN Department Ghent University Sint-Pietersnieuwstraat 41 9000 Gent Belgium Email Marc Moeneclaey Telecommunications and Information Processing TELIN Department Ghent University Sint-Pietersnieuwstraat 41 9000 Gent Belgium Email Received 24 July 2003 Revised 1 March 2004 An improved overloading scheme is presented for single-user detection in the downlink of multiple-access systems based on OCDMA OCDMA O O . By displacing in time the orthogonal signatures of the two user sets that make up the overloaded system the cross-correlation between the users ofthe two sets is reduced. For random O O with square-root cosine rolloff chip pulses the multiuser interference can be decreased by up to 50 depending on the chip pulse bandwidth as compared to quasiorthogonal sequences QOS that are presently part of the downlink standard of CDMA2000. This reduction of the multiuser interference gives rise to an increase of the achievable signal-to-interference-plus-noise ratio for a particular channel load. Keywords and phrases CDMA quasiorthogonal sequences downlink transmission oversaturated channels power control. 1. INTRODUCTION In any synchronized multiple-access system based on code- division multiple access CDMA the maximum number of orthogonal users equals the spreading factor N. In order to be able to cope with overloading of a synchronized CDMA sys- tem . with a number of users K N M N K 2N several schemes have been proposed in literature. Apart from the trivial random spread system PN 1 one can look for signature sets that are as orthogonal as possible. A popular measure for the quasiorthogonality of a signature set is the total squared correlation TSC 2 signature sets that minimize TSC .

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