Turbo synchronization for group-blind multiuser detection

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This proposal considers the problem of synchronization and channel estimation for turbo multiuser detection (MUD) in CDMA systems operating over multipath fading channels.The aim of this project is to investigate using the estimated synchronization and channel parameters in a manner motivated by the general turbo principle. Specifically, we consider the synchronization unit to be another decoder, which will be employed in a turbo scheme. Instead of passing a synchronized signal, the synchronizer passes extrinsic information for each of the coded bits to the next stage.Finally, in this project we propose a receiver structure that takes all the necessary signal processing operations into account simultaneously. In other words, the proposed iterative receiver can jointly perform synchronization, channel estimation, channel equalization, blind/group-blind MUD, and channel decoding. The  proposed  iterative (turbo)  processing  approach  allows  earlier  stages  (or submodules) of a receiver (e.g. the synchronizer and the channel estimator) to refine their processing based on soft information obtained from later stages (e.g., the channel decoder) to provide a refine estimate of some signal parameters.The expected results in this work are as follows: the applicant and his research group can develop a mathematical framework for the design of turbo receivers that can perform jointly synchronization and channel estimation with muliuser detection according to the maximum a posteriori (MAP) criterion, using the expectation-maximization (EM) algorithm or the space alternating generalized expectation and maximization (SAGE) algorithm.The performance of the proposed turbo receivers can be expected to be much better than that of the conventional (or non-iterative) receivers but very close to that of the ideal receiver which assumes perfect knowledge of synchronization and channel parameters as well as all the signatures of active users in the system.