Ranging is one of the most important processes in the mobile worldwide interoperability for microwave access (WiMAX) standard, for resolving the uplink synchronization and near/far problems. In this paper, we focus on the multi-user carrier frequency offset (CFO) estimation in both initial ranging and periodic ranging. After the analysis of some existing ranging methods, we propose two algorithms based on the correlation properties of pseudo noise (PN) sequences in time domain and frequency domain respectively. The root mean square error (RMSE) performance is evaluated in both additive white Gaussian noise (AWGN) channel and multi-path fading channel. Simulation results show that the proposed frequency-domain cross-correlation method performs better than the proposed time-domain cross-correlation method, and is more robust to multi-user interference and residual timing offset. © Copyright 2009 John Wiley & Sons, Ltd.