Transmit antenna-switched receive diversity for bi-directional beamforming in two-way communications

This paper investigates an attempt to improve reliability in two-way communication through the bi-directional use of spatial resources when time selectivity exists and instantaneous channel information is not available at the transmitter. The system, which uses spatial resources bi-directionally and employs beamforming, is called a `bi-directional beamforming (BBF)´ system. The use of full bandwidth and the reciprocity between time and frequency allow the BBF system to reduce the symbol duration. Focusing on this reduction in symbol duration, we propose a transmit antenna-switched receive diversity for BBF (TAS-BBF) scheme designed to improve reliability in time selective environments. The resulting TAS-BBF scheme with N antennas can achieve diversity order of 2(N-1) in fast fading environments without channel state information at the transmitter, whereas conventional schemes are only able to achieve a diversity order of N in this environment.