Approaching MIMO-OFDM Capacity With Zero-Forcing V-BLAST Decoding and Optimized Power, Rate, and Antenna-Mapping Feedback

This paper studies capacity-approaching transmission schemes for the multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) channel, under the assumption that the channel state information (CSI) is completely known at the receiver but only partially available at the transmitter via a limited-rate feedback channel. A vertical Bell Labs layered space-time (V-BLAST)-based transmission structure is considered, where multiple data streams are independently encoded at the transmitter (i.e., horizontal encoding) and successively decoded at the receiver by the zero-forcing-based generalized decision feedback equalizer. A closed-loop V-BLAST extension is presented whereby transmit powers, rates, and antenna mappings for multiple data streams at different OFDM tones are jointly optimized at the receiver and then returned to the transmitter via the feedback channel. Two low-complexity algorithms for optimization of feedback parameters are proposed: one is based on the Lagrange dual-decomposition method and the other is a greedy algorithm. Antenna and tone grouping techniques by exploiting the MIMO-OFDM channel space-frequency correlations are also proposed to reduce the feedback complexity. Simulation results show that by only a moderate amount of feedback, the proposed closed-loop V-BLAST scheme improves substantially the throughput of the conventional open-loop V-BLAST scheme without feedback and, furthermore, approaches closely the MIMO-OFDM channel capacity achievable by the eigenmode transmission that requires the complete CSI at the transmitter.