Initial uplink synchronization and power control (ranging process) for OFDMA systems

We address the initial ranging process in OFDMA systems such as IEEE 802.16a. The proposed ranging method includes three main tasks - timing estimation, multi-user ranging code detection, and power estimation. All tasks are performed based on a bank of correlators corresponding to ranging codes. The timing estimation scheme is based on the peak of correlator outputs. The multi-user ranging code detection is based on the correlator outputs and an adaptive threshold. A novel adaptive threshold setting is proposed. A simple user-power estimator is derived based on the correlator outputs. A scheme of initial power adjustment at the random access users is also proposed which brings in a significant improvement in ranging code detection performance. The simulation results show that the proposed method works well even in the presence of several simultaneous random-access users and is robust to other data-users' interference. The simplicity of the proposed method is also quite appealing.