Performance Evaluation of Asynchronous MC-DS-CDMA under Random Spreading and Correlated Fading

The effects of inter-carrier interference (ICI) and aperiodic random spreading sequences on the performance of asynchronous multicarrier code division multiple access (CDMA) systems with correlated fading among sub-carriers are investigated in this research. To obtain the maximal ratio combining (MRC) filter, random parameters including asynchronous delays, correlated Rayleigh fading and spreading sequences are averaged to find the unconditional covariance matrix of the interference-plus-noise vector. We demonstrate that the ICI in the system proposed by Kondo and Milstein can be mitigated by assigning a common random spreading sequence over all sub-carriers for each user, rather than using a set of distinct spreading sequences. Moreover, the analytic expression for the bit error probability (BEP) can be obtained with the Gaussian approximation. Simulation results are used to demonstrate the accuracy of our analysis. Finally, various design tradeoffs including the number of sub-carriers, fading correlations. ICI and multipath effect are also presented in simulation.