Performance of multicode DS/CDMA with noncoherent M-ary orthogonal Modulation in multipath fading channels

TitlePerformance of multicode DS/CDMA with noncoherent M-ary orthogonal Modulation in multipath fading channels
Publication TypeJournal Article
Year of Publication2004
AuthorsIskander, C. - D., and P. T. Mathiopoulos
JournalWireless Communications, IEEE Transactions on
Pagination209 - 223
Date Publishedjan.
Keywords3G mobile communication, aperiodic cross correlation functions, BER, bit-error rate, cdma2000, closed loop systems, closed-loop power control algorithm, code division multiple access, code transmission, data transfer, direct-sequence code-division multiple-access, equal-gain combining, error probability, error statistics, fading coefficients, Gaussian approximation, Gaussian channels, hard handoff, interference terms, IS-95B, lognormal fading channels, matrix algebra, mobile user, modulation, multicode DS/CDMA, multipath channels, multipath fading channels, Nakagami fading channels, noncoherent combining loss, noncoherent M-ary orthogonal modulation, power control, probability density function, radio receiver, radio receivers, radiofrequency interference, receiver decision matrices, reverse link, Rician channels, Rician fading channels, single-cell system, spread spectrum communication, transceiver, transceivers, video communications

This paper presents the performance analysis and simulation of a multicode direct-sequence code-division multiple-access system with noncoherent M-ary modulation, in a multipath fading environment. This type of transceiver is specified for the reverse link of the IS-95B and cdma2000 (radio configurations 1 and 2) systems and is intended to serve high-rate applications such as data transfer and video communications. While previous studies considered the analytical error performance of coherent multicode systems, little attention has been devoted in the literature to the noncoherent case. We provide concise and useful expressions for the interference terms as a function of the commonly used aperiodic cross correlation functions. After a statistical characterization of these terms, we make use of the Gaussian approximation (GA) in order to obtain the bit-error rate (BER). However, unlike some other analyses (for coherent detection) relying on the GA, in our derivation, we take into account the fact that all the codes transmitted by a mobile user fade in unison. As demonstrated via computer simulations, this fact is crucial to obtain a reliable estimate of the BER, especially when equal-gain combining (EGC) is used at the receiver. The analysis is also extended to include a simple closed-loop power control algorithm and hard handoff between multiple cells. In particular, we verify-for the multicode case-previous observations that the use of EGC allows improvement only for a certain range of values of the total interference seen at the receiver: When either the number of interfering users is too large, or too many codes are assigned to the high-rate user, the noncoherent combining loss becomes such that the use of many diversity branches can decrease the performance as compared to a system with little or no diversity.


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