ITERATIVE MULTIUSER RECEIVERS FOR CDMA CHANNELS - AN EM-BASED APPROACH

Maximum-likelihood detection for the multiuser code-division multiple- access (CDMA) channel is prohibitively complex. This paper considers n ew iterative multiuser receivers based on the expectation-maximization (EM) algorithm and related, more powerful ''space-alternating'' algor ithms. The latter algorithms include the SAGE algorithm and a new ''mi ssing parameter'' space-alternating algorithm that alternately updates individual parameter components or treats them as probabilistic missi ng data, Application of these EM-based algorithms to the problem of di screte parameter estimation (i.e., data detection) in the Gaussian mul tiple-access channel leads to a variety of convergent receiver structu res that incorporate soft-decision feedback for interference cancellat ion and/or sequential updating of iterative bit estimates, Convergence and performance analyzes are based on well-known properties of the EM algorithm and on numerical simulation.