MMLD Algorithm for Power Estimation in OFDMA System

Initial uplink synchronization is an integral part of wireless communication systems especially in Orthogonal Frequency Division Multiple Access (OFDMA) system and enables the base station to detect new subscriber stations willing to commence communication. Ranging enables the base station to estimate the uplink channel parameters of the subscriber stations. Accurate estimation of channel parameters is crucial as they ensure the uplink signals from all the subscriber stations reach the base station synchronously at similar power levels. However the detection performance and estimation problem turns out to be very challenging when multiple users initiate the synchronization procedure at the same time. The existing Successive Interference Cancelation (SIC) based algorithms suffer both the impacts of channel estimation errors as well as uncancelled Multiple Access Interference (MAI). For this Moment Maximum Likelihood Detection (MMLD) algorithm is proposed that reduces or cancels the reconstructed MAI from the received signal with the help of expectation maximization algorithm by iteratively constructing objective function. The simulation results show that the MMLD method significantly improves the performance of power estimation in this paper.