A Unified Analysis for Direct-Sequence CDMA in the Downlink of OFDM Systems

This paper presents a unified analysis for the downlink BER performance of convolutionally coded and single-user detected MC-CDMA, MCDS-CDMA and TFL-CDMA. As a special case, an analysis is obtained also for OFDMA. The intra-cell interference is analyzed under the assumption of Hadamard spreading codes and a correlated frequency-selective Rayleigh-fading channel. The presented results assume error-free channel estimates and a perfectly synchronized receiver. It is concluded that the compared schemes achieve essentially the same performance for low system loads. For high loads, and especially in a near-far scenario, OFDMA is found to outperform the others. Index Terms Code division multiaccess, spread spectrum communication, orthogonal frequency-division multiplexing, fading channels, convolutional codes.