Constrained Resource Allocation in OFDMA Downlink Systems with partial CSIT

Adaptive resource allocation algorithms based on perfect channel state information at the transmitter (CSIT) improve the performance of OFDMA systems. However, perfect CSIT is rarely possible due to channel estimation errors and channel feedback delay. In this paper, we consider practical subchannel assignment and power allocation strategies for downlink multiuser OFDMA systems, where the base station has imperfect CSI. The goal is to maximize the expected weighted sum rate while satisfying users´ minimum data rate and system fairness requirements under total power constraint. We use the Lagrange dual decomposition framework to derive an algorithm that efficiently finds the optimal allocation. Simulation results show the impact of the channel estimation error on the performance of the system and illustrate the trade-off between maximized expected weighted sum rate and the constraints.