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QS-CDMA: A potential air interface candidate for 4G wireless communications

: Stanczak, S.; Boche, H.


Nassar, C.R.:
Emerging Technologies for Future Generation Wireless Communications : Boston, Monday 29 July 2002
Bellingham, WA: SPIE, 2002 (Proceedings of SPIE 4869)
ISBN: 0-8194-4648-3
Emerging Technologies for Future Generation Wireless Communications <2002, Boston>
Conference Paper
Fraunhofer HHI ()

The paper addresses the problem of constructing signature sequences for quasi-synchronous CDMA systems. The major feature of QS-CDMA is that the duration of any signature waveform is significantly longer than the maximal signal delay with respect to a common clock. In contrast to completely asynchronous CDMA systems for which all aperiodic correlations must be taken into consideration, in case of quasi-synchronous CDMA, it is sufficient to focus on a small window around the zero shift, the so-called interference window. This simplifies sequence design and allows us to reduce both the inter-symbol interference and multiple access interference drastically, thereby enhancing the system performance tremendously. This is all the more important since construction of sequences for completely asynchronous CDMA systems is a notoriously difficult problem and no such sequence sets are known. Consequently, random sequences must be used that are known to induce a significant capacit y loss. In this paper, we present two possible methods for obtaining sequences with small aperiodic correlation sidelobes in the vicinity of the zero shift. We discuss advantages and disadvantages of QS-CDMA and W-CDMA, the major air interface for third generation mobile communications systems. Some simulation results are presented.