Beamforming Only Based on Specular Component for Downlink Massive MIMO Systems

Abstract

In this paper, we are concerned with a multiuser downlink massive MIMO system operating over Ricean fading channels where each user can be equipped with one or multiple antennas. We present a beamforming (BF) transmission scheme that is only based on the specular component, which can reduce efficiently the heavy overhead for channel estimation. For the individual achievable rates, we particularly analyze their power-scaling law when the transmit power per user is scaled down by the number of antennas at the base station (BS). It is found that the individual rates of the proposed BF can be higher than the corresponding rates of the BF based on the scattered and specular components if the specular component is relatively strong. In addition, it is shown that each user can asymptotically achieve the same rate as in the single-user case when both the numbers of BS antennas and the user terminals go to infinity with a fixed ratio. Thus we conclude that the massive MIMO systems may be more suitable to be deployed in Ricean fading rather than Rayleigh fading.