Interaction of transmit diversity and proportional fair scheduling

In evolving 3G systems, the proportional fair packet scheduling algorithm promises an attractive trade-off between average cell capacity and user fairness by exploiting multi-user selection diversity in time-shared channels. However, in these systems the option of antenna transmit diversity already exist, whose performance benefit is dependent on the considered scheduling strategy. This study focusses on the interaction between proportional fair packet scheduling and open or closed-loop transmit diversity techniques. The basic interaction is studied by using an analytical model. Additionally, Monte Carlo simulations are conducted to study the effect of scheduling delays. In the low mobility Rayleigh fading case, the potential average cell capacity gain with proportional fair scheduling, compared to a simple round robin in time approach, is on the order of 60% for single-antenna transmission. It reduces, however, to around 35% when dual antenna transmit diversity is additionally deployed. Comparing the performance of the different transmit diversity schemes to single-antenna transmission, conditioned on proportional fair scheduling, it is found that the closed-loop schemes provide a benefit over a wide range of terminal speeds, whereas open-loop space-time block coding exhibits limited performance and in some cases even a loss.