Inter-Code Interference and Optimum Spreading Sequence in Frequency-Selective Rayleigh Fading Channels on Uplink MC-CDMA(Signal Processing for Communications)(<Special Section>Digital Signal Processing)

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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).
2004-08-01