Multi-access interference suppression in canonical space-time coordinates: A decentralized approach

We propose a decentralized space–time multiuser detection scheme based on the notion of canonical space–time coordinates (CSTCs) for representing the received signal. The CSTC representation provides a natural framework for decentralized multi-access interference (MAI) suppression in lower dimensional subspaces that results in complexity reduction relative to existing chip rate filtering schemes. The framework is based on a partitioning of the signal space into active and inactive CSTCs. The active CSTCs contain the signal of the desired user, facilitate maximal diversity exploitation and minimal complexity interference suppression. The inactive CSTCs only contain MAI and can be included progressively to attain a desired level of MAI suppression at the cost of increased complexity. We develop CSTC-based linear coherent multiuser detectors using the linearly constrained minimum variance (LCMV) criterion. We characterize the set of inactive coordinates and analyze the performance of the LCMV receiver as a function of the number of inactive CSTCs. Channel estimation and detector sensitivity to channel estimation errors are discussed. We demonstrate that the low-complexity adaptive receivers designed via the CSTC framework are more robust to channel estimation errors than existing chip-domain filtering schemes.