Inter-Code Interference and Optimum Spreading Sequence in Frequency-Selective Rayleigh Fading Channels on Uplink MC-CDMA

Takashi SHONO  Tomoyuki YAMADA  Kiyoshi KOBAYASHI  Katsuhiko ARAKI  Iwao SASASE 

Publication
IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences  Vol.E87-A  No.8  pp.1981-1993
Publication Date: 2004/08/01
Online ISSN: 
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on Digital Signal Processing)
Category: Signal Processing for Communications
Keyword: 
MC-CDMA,  OFDM,  inter-code interference,  desired-to-undesired signal power ratio,  spreading sequence, 

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Summary: 
In uplink multicarrier code division multiple access (MC-CDMA), the inter-code interference (ICI) caused by the independent and frequency-selective fading channel of each user and the inter-carrier interference caused by the asynchronous reception of each user's OFDM symbols result in multiple access interference (MAI). This paper evaluates the ICI in frequency-selective Rayleigh fading channels for uplink MC-CDMA. We derive theoretical expressions for the desired-to-undesired signal power ratio (DUR) as a quantitative representation of ICI, and validate them by comparison with computer simulations using a Walsh-Hadamard (WH) code. Based on the analytical results, we obtain the optimum spreading sequence that minimizes the ICI (in short, maximizes the multiplexing performance); this sequence appears to be orthogonal. Three equalization combining methods are examined; equal gain combining (EGC), orthogonality restoring combining (ORC), and maximum ratio combining (MRC).