Initial uplink synchronization and power control (ranging process) for OFDMA systems
Xiaoyu Fu, Hlaing Minn · 2005
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.