A multicode space-frequency RAKE receiver

In order to realize spatial multiplexing and multipath diversity in broadband MIMO systems with N_Tx transmit and N_Rx receive antennas, we study a multicarrier code division multiplex approach. Since the guard interval acts as a natural boundary in the underlying OFDM system, the optimal maximum-likelihood sequence estimator has moderate complexity, but it may not be feasible with multiple codes. So we consider a linear receiver. The initial stage is the novel space-frequency RAKE (where the optimal combining and despreading are done in reversed order, compared to the space-time RAKE). It is followed by a linear MMSE space-code interference cancellation removing all spatial and code interference. The receiver realizes most of the spatial and multipath diversity in the channel up to high system load.