Congratulations to student Wu Xiaoxiao who received the Postgraduate Research Output Award 2014 at the 78th Congregation for the Conferment of Degrees!
Below is her sharing:
Over the last decade, transmit beamforming has been extensively studied and recently, widely applied as an efficient transmit scheme in multiple-input single-output (MISO) physical-layer multicast systems. Therein, beamforming based on semidefinite relaxation (SDR) has been shown to be promising, but its performance may degrade as the number of users increases. Our work proposes two innovative transceiver strategies, both of which subvert traditional fixed beamforming philosophy and can serve large-scale systems. Specifically, the first strategy, called stochastic beamforming (SBF), randomizes the beamformer in a per-symbol time-varying manner. We prove that their multicast achievable rate gaps with respect to the MISO multicast capacity must be no worse than 0.8314 bits/s/Hz, irrespective of any other factors such as the number of users. The second strategy combines transmit beamforming and the Alamouti space-time code, and it is shown to exhibit a better multicast rate scaling than SDR-based beamforming. Moreover, we further the work by combining SBF and the beamformed Alamouti scheme, wherein an improved constant rate gap of 0.39 bits/s/Hz is proven. These proposed beamforming schemes are tested under a channel-coded, many user setting, and yield significant SNR gains over many existing beamforming designs. Hence, they are practical and may reform beamforming systems with a low complexity payout.