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Performance Evaluation of MultiRate DSCDMA Using FrequencyDomain Equalization in a FrequencySelective Fading Channel
Kazuaki TAKEDA Fumiyuki ADACHI
Publication
IEICE TRANSACTIONS on Communications
Vol.E88B
No.3
pp.11911201 Publication Date: 2005/03/01
Online ISSN:
DOI: 10.1093/ietcom/e88b.3.1191
Print ISSN: 09168516 Type of Manuscript: PAPER Category: Terrestrial Radio Communications Keyword: DSCDMA, frequencydomain equalization, frequencyselective fading,
Full Text: PDF(1.1MB)>>
Summary:
Joint frequencydomain equalization (FDE) and antenna diversity combining is applied to the reception of multirate DSCDMA signals to achieve the frequency diversity effect while suppressing interpath interference (IPI) resulting from the asynchronism of different propagation paths. At a receiver, fast Fourier transform (FFT) is applied for FDE and then inverse FFT (IFFT) is used to obtain a frequencydomain equalized DSCDMA chip sequence for the succeeding despreading operation. An arbitrary spreading factor SF can be used for the given value of FFT window size; an extreme case is the nonspread SC system with SF=1. This property allows a flexible design of multirate DSCDMA systems. Three types of FDE are considered; minimum mean square error (MMSE) equalization, maximalratio combining (MRC) equalization and zeroforcing (ZF) equalization. Matched filter bound analysis for achievable BER performance is presented. The improvement in the BER performance in a frequencyselective Rayleigh fading channel is evaluated by computer simulation. First, we consider the singleuser case and compare the BER performances achievable with MMSE, MRC and ZF equalizations. How the fading rate and the spreading factor affect the BER performance is also evaluated. Furthermore, the BER performance comparison between FDE and rake combining is presented for various values of SF and also performance comparison between DSCDMA and SC signal transmissions, both using FDE, is presented. Finally, we extend our evaluation to the multiuser case. Both downlink and uplink are considered and how the BER performances of downlink and uplink differ is discussed.

