A Data Rate Maximization Algorithm for Multiuser OFDM Systems

Abstract

In this paper, we present suboptimal integer bit allocation algorithm that maximizes overall data rate in multiuser orthogonal frequency division multiplexing (OFDM) systems implemented in wireless networks. Assuming knowledge of the instantaneous channel gains for all users, we propose a new multiuser OFDM loading algorithm, with constrains, that maximizes the total data rate in downlink transmission. This is done by solving the maximization problem in two steps. First step provides subcarrier assignment to users based on users' requests on quality of service (QoS) expressed in terms of a minimum signal-to-noise ratio (SNR) on each subcarrier. The second step provides bit and power allocation to subcarriers in order to maximize overall data rate. In order to reduce the computational complexity of the proposed problem we propose a simple method, in the form of a theorem, which assigns subcarriers to users and distributes bits and power among them. We have tested the proposed algorithm in a multiuser environment for various subcarrier SNR values requested by users, and for various levels of interference in the OFDM system. The results show that our loading method obtains a better data rate in some situations than the algorithm described in [5], which states that the data rate of a multiuser OFDM system is maximized when each subcarrier is assigned to only one user. Results show that the total number of bits per OFDM symbol or data rate grows with the number of users in the system.

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