Beamforming, Doppler compensation, and differential space-time coding

We consider the design of two beams, formed at the base station, that will serve as the two channels for differential space-time block coding in a high-mobility outdoor scenario. The mobile is assumed to have one omnidirectional antenna. In one approach, we consider selecting assuming no interference, the two most powerful beams produced by an RF beamformer. In the other approach, we make a compromise between power and Doppler spectrum partitioning. One channel is a beam that points directly at the mobile. The other beam is the difference of left and right beams, symmetric about the mobile. These left and right beams are Doppler compensated prior to forming their difference. Using computer simulation, we find that selecting beams based on power is more effective than selecting beams based on Doppler partitioning. We also find that using the two most powerful beams formed from eight antenna elements yields 7 dB and 8 dB SNR improvements, at 1.9 GHz and 5.8 GHz, respectively, relative to spatial diversity with two omnidirectional antennas.