A Random Beamforming Technique for Broadcast Channels in Multiple Antenna Systems

A random beamforming technique is proposed for broadcast channels in multiple antenna systems. In the proposed scheme, a random weight vector, corresponding to a random pattern, is imposed on each communication resource in time-frequency domain, with a resulting average of the random patterns on all resources to be isotropic. We proved that, the capacity of such a system is upper bounded by that of a single antenna system, on the premise of same power budget. The design criteria and detailed design of random patten sequence are presented. We propose a basic random beamforming and Alamouti enhanced scheme, and a structure of the transmitter and receiver. The performance of the proposed scheme is verified by numerical simulation. It is also observed that it is robust to calibration errors and failures of radio frequency chains.