Performance of asynchronous long-code multicarrier CDMA systems in the presence of frequency offsets and correlated fading

The effects of frequency offsets and aperiodic random spreading sequences on the performance of asynchronous multicarrier code division multiple access (CDMA) systems with correlated fading are investigated in this research. Random parameters including asynchronous delays, correlated Rayleigh fading and spreading sequences are averaged to determine the covariance matrix of the interference-plus-noise vector. An analytic expression for the average signal-to-interference-plus-noise ratio (SINR) is obtained. Furthermore, average bit error probability (BEP) based on the Gaussian approximation is also derived. We show that the system degrades significantly if the frequency offset of the desired user is present, while the system is insensitive to interferers´ frequency offsets. In consequence, it is crucial to estimate and compensate the desired user´s synchronization imperfection. Finally, design tradeoff among the number of subcarriers, fading correlations, and inter-carrier interference (ICI) are presented in simulation results.