Bit-rate maximization for multiuser OFDM systems

In the downlink of multiuser OFDM (Orthogonal Frequency Division Multiplexing) systems, subcarriers of one OFDM symbol can be allocated to multiple users to enable multiplexing. System performance can be enhanced by appropriate subcarrier allocation and bit-loading. In this paper, while guaranteeing a fixed BER performance, we impose a fixed transmitted power constraint on each user to achieve a fair resource allocation. Based on this condition, we propose an algorithm to maximize the sum-rate of the system. This sum-rate optimization is a discrete optimization problem which is hard to solve by conventional methods. We relax the problem into a continuous convex optimization problem so that the subcarrier allocation to each user can be determined numerically. Using the subcarrier allocation for the continuous problem, bits are then loaded to each user. The effectiveness of the proposed method is substantiated by numerical simulations. (c) 2005 Wiley Periodicals, Inc.