Frequency-Interleaved Spread Spectrum with MMSE Frequency-Domain Equalization

Kazuaki TAKEDA  Fumiyuki ADACHI  

IEICE TRANSACTIONS on Communications   Vol.E90-B   No.2   pp.260-268
Publication Date: 2007/02/01
Online ISSN: 1745-1345
DOI: 10.1093/ietcom/e90-b.2.260
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Wireless Communication Technologies
component,  MMSE-FDE,  frequency-interleaving,  

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The use of frequency-domain equalization (FDE) based on minimum mean square error (MMSE) criterion can significantly improve the downlink bit error rate (BER) performances of DS- and MC-CDMA in a frequency-selective fading channel. However, the uplink BER performance degrades due to a strong multi-user interference (MUI). In this paper, we propose frequency-interleaved spread spectrum (SS) using MMSE-FDE, in which the subcarrier components of each user's signal are interleaved onto a wider bandwidth. Then, the frequency-interleaved frequency-domain signal is transformed into a time-domain signal by the inverse fast Fourier transform (IFFT). Frequency-interleaving patterns assigned to different users are orthogonal to each other. The proposed scheme can avoid the MUI completely while achieving frequency diversity gain due to MMSE-FDE. It is shown by computer simulation that the use of frequency-interleaving can significantly improve the uplink performance in a frequency-selective Rayleigh fading channel.