Generalized Orthogonal Sequences and Their Applications in Synchronous CDMA Systems

Pingzhi FAN  Li HAO  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E83-A   No.11   pp.2054-2069
Publication Date: 2000/11/25
Online ISSN: 
Print ISSN: 0916-8508
Type of Manuscript: INVITED PAPER (Special Section on Spread Spectrum Techniques and Applications)
orthogonality,  generalized orthogonality,  spreading codes,  ZCZ sequences,  LCZ sequences,  synchronous CDMA,  

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In synchronous CDMA system, the orthogonal spreading sequences are employed to reduce the multiple access interference. However, as the frequency selectivity of the propagation channel strengthens, the orthogonality among different users tends to diminish because of increasing inter-path interference. In this paper, various binary and nonbinary orthogonal sequences are discussed. In order to maintain the orthogonality among different users, a new concept of generalized orthogonality is defined and the corresponding sequences are presented, including binary, quadriphase and nonbinary code sequences. Based on a simplified synchronous CDMA system model, the related system performance is also analyzed and compared for different orthogonal and generalized orthogonal spreading sequences. Our analytical and simulation results show that the generalized orthogonal code sequences are indeed more robust in the multipath propagation channels, compared with the traditional orthogonal code sequences.