Joint equalization-despreading method for OQAM-CDMA systems

Due to using no guard interval, Orthogonal frequency division multiplexing/offset quadrate amplitude modulation (OFDM/OQAM) systems are more bandwidth efficient than cyclic pre-OFDM (CP-OFDM). In OFDM/OQAM the real-valued symbols are transmitted and at the receiver a real-taking operation is performed to eliminate the pure imaginary intrinsic interference. Another way to eliminate the intrinsic interference of the OFDM/OQAM system is applying code-division multiple access (CDMA) to spread the transmitted symbols across the frequency axis. The resulted system, which is called Complex OQAM-CDMA, has the capability of transmitting complex-valued symbols (instead of real-valued ones) and can provide a transmission rate equal to that of the primer OFDM/OQAM system. At the receiver of the conventional Complex OQAM-CDAM, an equalizer is applied to remove the channel effect and then a despreading process is performed to detect the coded symbols. This detection method suffers from a poor performance in highly dispersive channels because of using two separate stages in the detection process. In this article based on the signal to interference plus noise ratio (SINR) maximization, we propose a novel detection method for the Complex OQAM-CDMA symbols. In the developed method, the equalization and despreading processes are performed jointly to maximize SINR. Simulation results assert that the proposed detection method outperforms the conventional scheme.