Adaptive transmission in MIMO systems with limited feedback

Unitary Precoding (UP) and antenna selection have been shown to be effective in improving the bit error rate (BER) performance of multiple-input multiple-output systems. Performance can be further improved by incorporating power control. We propose adaptive transmission schemes for low-rate feedback systems that combine truncated channel inversion (TCI) with UP and antenna selection. Simulations show that, with perfect power control, the proposed scheme achieves a gain of 6.35dB over UP and 3.70dB over Eigenmode Antenna Selection (EAS) at a BER of 10-5. Even with zero bit of power control feedback, the proposed scheme achieves a significant performance gain of about 5.35dB over UP and 2.7dB over the EAS scheme at a BER of 10-5. While the proposed TCI power control algorithms show very good performance in block fading channels, in practice however, channels change continuously over time. Therefore, we also study the performance of the proposed antenna selection algorithms combined with Kalman filtering based channel estimation and tracking over continuously varying channels. Simulations show that this scheme performs better than the existing schemes.