Fairness-based resource allocation in OFDMA downlink with imperfect CSIT

OFDMA is one of the promising technologies which can provide high speed wireless data with high spectral efficiency. This paper focuses on the efficient management of resources - power, rate and subcarriers on the OFDMA downlink. A novel approach of considering three factors together for OFDMA resource allocation - imperfect Channel State Information at Transmitter (CSIT), outage, and fairness is presented in this paper. The resource allocation scheme is split into two steps - rate & power allocation step, and subcarrier allocation step. To reduce complexity, equal power allocation is assumed and optimal rate to be allocated on each link to maximise throughput is determined. Then in the second step, heuristic strategies are proposed for subcarrier allocation which will incorporate fairness. We consider methods to ensure both short-term and long-term fairness and also inclusion of fairness among users with different rate requirements. The effectiveness of the proposed scheme is demonstrated through simulations. In terms of throughput, the proposed scheme bridges the gap between perfect and imperfect CSIT, and achieves high value of Jain´s fairness index. At the same time, there is minimal degradation in throughput in comparison to the performance of throughput-maximising schemes. Thus the proposed resource allocation scheme achieves a good balance between throughput and fairness at low complexity under conditions of imperfect CSIT.