Analysis of MC-DS-CDMA systems in doubly spread channels

Thad B. Welch, Rodger E. Ziemer

Research output: Contribution to conferencePaperpeer-review

2 Scopus citations

Abstract

Kondo and Milstein introduced and analyzed the performance of a system that combined multicarrier modulation (MCM) with direct-sequence spread spectrum (DSSS) in late 1993. Their system and similar systems are called MC-DS-CDMA systems. The dramatic performance improvement of this system (as compared to a single carrier system operating in a flat fading channel) is due, in part, to the use of coherent modulation/demodulation and perfect knowledge of the complex channel gains for each of the independent channels associated with every subcarrier. In this paper we investigate the performance degradation associated with a more easily realized system. Our system employs differentially coherent modulation/demodulation with an equal gain combiner (EGC) at the receiver. We investigate the performance of this system operating in a doubly spread (Doppler and delay spread) channel. In a doubly spread channel, any system which does not account for the rapid variations in channel phase will exhibit an irreducible bit error probability. This phenomenon exists even for the single user case. A system utilizing an EGC is analyzed for the single user case and in the presence of multiple access interference (MAI). The MC-DS-CDMA single user system, with Eb/N0 = 18.5 dB, can achieve a BEP of 10-6 in a doubly spread channel (fdT = 0.08 and a channel delay spread, τ0 = 1 μs), while a single carrier DPSK system operating at the same Eb/N0 and under the same channel conditions would achieve a BEP of 0.037. The multi-user system with 50 active users would achieve a BEP of 0.008 as compared to a BEP of 0.07 for a single carrier system.

Original languageEnglish
Pages757-761
Number of pages5
StatePublished - 1998
EventProceedings of the 1998 IEEE Military Communications Conference. Part 1 (of 3) - Bedford, MA, USA
Duration: 19 Oct 199821 Oct 1998

Conference

ConferenceProceedings of the 1998 IEEE Military Communications Conference. Part 1 (of 3)
CityBedford, MA, USA
Period19/10/9821/10/98

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