Adaptive Transmission Using Channel Inversion for Multiple-Antenna Systems

Abstract

Adaptive modulation often achieves a significantly higher capacity than nonadaptive modulation in multiple-antenna wireless communication systems, particularly when the transmit antennas outnumber the receive antennas. Adaptive modulation generally involves varying signal power, constellation and coding in response to changing channel conditions, which adds considerable system complexity. This thesis examines simpler adaptive transmission schemes based on channel inversion (CI) and truncated channel inversion (TCI) in combination with multi-dimensional eigen-beamforming. Optimal CI and TCI schemes for multiple-antenna systems are derived and it is shown that these schemes suffer a small loss in capacity relative to optimal adaptive modulation, even for relatively small antenna arrays. This thesis also considers a practical coding scheme, turbo trellis-coded modulation (TTCM) in conjunction with CI. The results indicate that this scheme can perform within 4 dB of the optimal adaptive capacity.