We propose new channel-based or covariance-based closed-loop space-time signal processing schemes that combines transmit beamforming and spatial multiplexing in Rayleigh frequency-flat fading channel. We assume that the number of transmit antennas is greater than the number of receive antennas. To implement the proposed schemes, we use the following three maximization criterions: signal-to-noise ratio (SNR) maximization criterion, mutual information maximization criterion, and signal-to-interference-plus-noise ratio (SINR) maximization criterion. The proposed schemes achieve the multiplexing gain by spatial multiplexing and the antenna gain by beamforming.
The achievable SNR and mutual information are shown according to each criterion. Bit error rate (BER) with ML (Maximum Likelihood) and MMSE (Minimum Mean-Squared Error) nulling and cancelling detection algorithm are given for spatial multiplexing, TAA (Transmit Antenna Array) beamforming, double-STTD (Space-Time Transmit Diversity) or D-STTD, and proposed schemes in Rayleigh frequency-flat fading channel with Monte-Carlo simulation. We show that the proposed schemes have lower BER than the other schemes. We show that the channel-based scheme is adaptive to slowly varying channel environment and covariance-based scheme is adaptive to fast varying channel environment.