Dynamic power and subcarrier allocation for downlink OFDMA systems under imperfect CSI

In this paper, we investigate the joint power and subcarrier allocation for the downlink of orthogonal frequency division multiplexing access systems, with various practical considerations including imperfect estimation of channel state information, a stochastic packet arrival and a time-varying channel. To this end, we formulate the stochastic optimization problem to minimize the time-averaged power consumption, whilst keeping all queues at the base-station stable. The data transmission rate is defined as a function of the transmit power, the assigned subcarrier and the estimation error. With the aid of Lyapunov optimization method, the original problem is transformed into a series of mixed-integer programming problems, which are then solved via the dual decomposition technique. We determine analytical bounds for the time-averaged power consumption and queue length achieved by our proposed algorithm, which depend on the channel estimation error. Moreover, the theoretical analysis and simulation results show that the proposed algorithm reduces the energy consumption at the expense of queue backlog (i.e., achieves a energy-queue tradeoff), and quantitatively strike the energy-queue tradeoff by simply tuning an introduced control parameter V.