Blind adaptive multiuser detection for asynchronous dual-rateDS/CDMA systems

摘要

In this paper, the authors consider an asynchronousndirect-sequence code division multiple access (DS/CDMA) system whereinnusers are allowed to transmit their symbols at one out of two availablendata rates. Three possible access schemes are considered, namely, thenvariable spreading length (VSL), the variable chip rate (VCR), and thenvariable chip rate with frequency shift (VCRFS) formats. Theirnperformance is compared for the case that a linear one-shot multiusernreceiver is employed. It is also shown that detection of the usersntransmitting at the higher rate requires a periodically time-varyingnprocessing of the observables. Moreover, the problem of blind adaptivenreceiver implementation is studied, and a cyclic blindnrecursive-least-squares (RLS) algorithm is provided which is capable ofnconverging to the periodically time-varying high-rate users detectionnstructure. Numerical results show that the proposed receivers arennear-far resistant, and that the VCRFS access technique achieves thenbest performance. Finally as to the adaptive blind receivernimplementation, computer simulations have revealed that the cyclic RLSnalgorithm for blind adaptive high-rate users demodulation outperformsnthe conventional RLS algorithm in most cases of primary importance