Space-Time Coding and Beamforming Using Noisy Rate-Limited Feedback

We combine space-time coding and transmit beamforming over quasi-static block fading MISO channels, using quantized channel feedback. Our goal is to preserve diversity and besides, to provide additional array gain (SNR gain) compared to conventional space-time codes. In practice, the transmitter channel state information is degraded by bandwidth limitation and noise in the feedback link. The imperfect and impaired feedback leads to drastic performance degradation unless the system is robustly designed against low-resolution and erroneous feedback information. Therefore, combining coding and beamforming must be optimized for low-rate and erroneous feedback conditions. In this work, the combining is performed using a class of constellation sets inspired from orthogonal designs and precoded STBCs which is called partly precoded orthogonal designs (PPODs). PPODs provide full-diversity with any feedback rate, any number of transmit antennas, and any amount of feedback error. The attractive property of our scheme is that it converges to conventional space-time coding with low-rate and highly erroneous feedback and to pure beamforming with high rate and error-free feedback. Moreover, our scheme shows desirable robustness against design mismatch with respect to feedback channel specifications.