Adaptive time reversal beamforming in dense multipath communication networks

In this paper, we study the transmit time reversal beamforming in rich scattering environments in a multi-user wideband communication network. We consider the downlink time reversal transmission where a base station communicates with many users. The base station has multiple antennas and the user has a single antenna. Due to the presence of scatterers, conventional transmit beamforming suffers from crosstalk caused by nearby users. We design a wideband beamformer that focuses on the intended user while minimizing its interference to other users subject to the constraint of the sum rate capacity. We also show that the proposed beamformer is equivalent to time reversal focusing and nulling and yields higher sum data rate than the conventional delay line wideband beamformer. We verify our results using realistic scattering channels simulated by finite-difference time-domain modeling of the scattering environment.