Transmit beamforming for a large reconfigurable antenna array

Abstract

Many space-time transmission schemes have been proposed recently to exploit the high channel capacity from the MIMO communication systems. However, algorithms for a large antenna array (LAA) remain an open research problem. The standard channel estimation and space-time modulation schemes are not practical for LAAs due to high implementation complexity. In this paper, we propose a novel transmit beamforming scheme based on a reconfigurable LAA. Compared to the traditional schemes, our new scheme requires a much smaller number of radio frequency (RF) chains, yet it still enjoys the high performance offered from the LAA. Based on a reconfigurable LAA, we present a pilot assisted round robin channel estimation algorithm. With this estimation algorithm, the tracking of the fading channel is significantly simplified at the mobile station. We then introduce an adaptive transmit beamforming algorithm based on relative channel phase feedback at the transmitter. For a time varying Rayleigh fading channel, we investigate the system SNR as a function of the latency of the round robin channel estimation and derive the optimal training duration for given mobile speed. Finally, numerical simulations show that the proposed scheme accomplishes superior performance for various kinds of time varying Rayleigh fading channels. Overall, the proposed system enjoys good performance, high flexibility, low cost as well as low power consumption at both the base station and mobile station