Margin adaptive resource allocation in downlink OFDMA system with outdated channel state information

Most of existing works on resource allocation in TDMA and OFDMA systems assume the availability of perfect channel state information (CSI) at the transmitter. The availability of only a noisy estimate of the channel and the feedback delay are the problems which are faced more often. In this paper, we study the effect of feedback delay on resource allocation in a downlink OFDMA system. We approach the problem by using convex optimization framework and get the optimal solution with zero optimality gap. By considering the probability distribution function of the current CSI conditioned on outdated CSI in the resource allocation framework, we propose an algorithm that minimizes the total transmit power of the system subject to strict constraints on users´ conditional expected capacities. Results show that the system performance is sensitive to feedback delay and provide guidelines for system dimensioning and design.