Iterative Semi-Blind Blue Estimation of Channel State Information for the Asynchronous GMAC with Memory

In this paper we propose an iterative algorithm for estimating the semi-blind BLUE of the channel impulse response with respect to each source transmitter in an asynchronous scalar Gaussian multiple access channel (GMAC) with complex-valued intersymbol interference (ISI). We examine the case for the two-user GMAC where user 1's training arrives during the data portion of user 2. We demonstrate the algorithm with simulation results and contrast these results with other known channel estimation techniques such as correlation and least squares. We prove convergence of the algorithm under certain conditions for which we can realize the iterations as separate contraction mappings. We also give approximate versions of the algorithms which are more suited to real time applications.