Design of spreading codes with high diversity gain for multicarrier CDMA systems

The paper proposes a designing guideline for the spreading codes of the multicarrier code division multiple access (MC-CDMA) systems based on the evaluation of the performance of the maximum-likelihood multi-user detection (ML-MUD) in the frequency selective fading channels. Two parameters of the spreading codes, the minimum Hamming distance and the minimum product distance, are found to bound the performance of the system. According to this, a new kind of spreading codes, which are constructed by offsetting the phase of conventional orthogonal codes, is proposed to maximize the diversity gain. Simulation results show that full diversity order can be obtained even for full loaded systems. The proposed spreading codes can also improve the performance of single-user detectors. Copyright (C) 2007 John Wiley & Sons, Ltd.