Layered space-time equalization for wireless MIMO systems

In this paper we investigate layered space-time equalization (LSTE) architectures for multiple-input-multiple-output (MIMO) frequency selective channels. At each layer or stage of detection, a MIMO delayed decision feedback sequence estimator (MIMO-DDFSE) is used to tentatively detect a group of selected data streams, among which a sub-group of data streams are output and are canceled from the received signals. With the proposed architectures, the number of the tentatively detected and output data streams can be different at different LSTE stages, while the MIMO-DDFSE can also reduce to the special cases of multiple-input-single-output decision feedback equalizer (MISO-DFE), MISO-DDFSE and MIMO-DFE, allowing tradeoffs between performance and complexity. We also derive the equalizer coefficients, discuss timing recovery and consider channel estimation. Simulation results demonstrate the performance of the proposed LSTE structures, and the tradeoffs between performance and complexity of the multistage structure and the single-stage version. We also demonstrate the impact of imperfect channel estimation, imperfect interference cancellation, the number of receive antennas, filter length, and oversampling on performance.