An Iterative Algorithm for Joint Demodulation in Multicarrier CDMA Systems

A multiuser demodulation algorithm for the uplink of an asynchronous multicarrier code division multiple access (MC-CDMA) based wireless communication system is derived. The estimation of the multipath channel parameters and the symbol detection are incorporated in a joint demodulation scheme which employs a space-alternating generalized expectation-maximization (SAGE) algorithm for the iterative maximization of the log-likelihood function. Two different approaches to initialize the parameter estimates are presented based on the transmission of preambles as well as on a blind acquisition scheme. The performance of the algorithm is investigated in Monte Carlo simulations. The bit-error rates indicate that the scheme is robust in near-far situations as opposed to conventional demodulation and is thus particularly suited for systems without a tight power control.