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Quasi-Synchronous Time Division Duplex CDMA
IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences
Publication Date: 1995/09/25
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on Information Theory and Its Applications)
code division multiple access, quasi-synchronous, time division duplex, co-channel interference,
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A quasi-synchronous (QS) code division multiple access (CDMA) system is proposed for mobile communications. In the proposed method, which uses the time division duplex (TDD) mode of transmission, a mobile receiver can measure propagation delay changes. It then accordingly adjusts its transmission time so its signal can arrive at base station synchronously with other mobile units. A simple control unit is used at the mobile unit in order to reduce any error due to the propagation delay changes. The system operates as follows. At the start of a call, a mobile unit is quasi-synchronised through feedback control from the base station. The mobile unit then maintains synchronous status without any further base station feedback. The degree of the quasi-synchronous accuracy is determined by a clock in mobile units. This paper shows performance results based on using a clock rate of ten times faster than the spreading rate. Orthogonal codes are used for spreading the signals. The results demonstrate that the reverse link CDMA multiuser interference is to a great degree removed.