Interference subspace rejection in wideband CDMA: Modes for high data-rate operation

This paper extends our study on a multi-user receiver structure for base-station receivers with antenna arrays in multicellular systems. The receiver employs a beamforming structure with constraints that nulls the signal component in appropriate interference subspaces. Here we introduce a new mode, ISR-D (diversities), which finds and suppresses the subspace of the identified paths of all known interferers. A frame extension technique is proposed which can be applied to all available ISR modes to increase the dimensionality of the observation space and thereby avoid noise amplification as a result of subspace suppression, as well as allow asynchronous transmission. Performance differences arise between the modes due to different sensitivities to channel identification and data detection errors. For homogeneous high data-rate situations ISR-DX manifests the best performance. However, due to its reduced complexity, ISR-TRX appears to offer the best complexityperformance tradeoffs.