New Quasi-Synchronous Sequences for CDMA Slotted ALOHA Systems

Masato SAITO  Takaya YAMAZATO  Masaaki KATAYAMA  Akira OGAWA  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E81-A   No.11   pp.2274-2280
Publication Date: 1998/11/25
Online ISSN: 
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on Spread Spectrum Techniques and Applications)
CDMA slotted ALOHA system,  QS-sequences,  access timing error,  orthogonal Gold sequences,   flat fading channel,  

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One of unique features of CDMA slotted ALOHA (CDMA S-ALOHA) is that user must synchronize his transmission to given slot. Thus orthogonal sequence as spreading sequence would achieve ideal throughput if each of packets accomplish perfect synchronization. In the presence of any ambiguity in synchronizations, however, quasi-synchronous (QS) sequences suit well with CDMA S-ALOHA system. In this paper, we introduce new QS-sequences obtained from the orthogonal Gold sequences and discuss their performance when applying to CDMA S-ALOHA systems. As a result, withstanding to access timing error, good performance is ensured with this sequence under the environment of AWGN, MAI (multiple access interference) and frequency non-selective fading, that is, micro or pico cellular systems and indoor wireless LANs.