Timing Synchronization for the Uplink of an OFDMA System

Abstract

This paper deals with a new timing estimator for the uplink of an Orthogonal Frequency-Division Multiple Access (OFDMA) system. The estimator is based on the maximum likelihood (ML) criterion and exploits knowledge of two pilot symbols. Its main advantage is that it provides a feedforward estimate of the timing phase, thus allowing synchronization in only two OFDM blocks. In contrast to other existing schemes, it does not require that the subcarriers of a given user occupy adjacent positions in the signal bandwidth. This makes it possible to interleave subcarriers of different users so as to optimally exploit the frequency diversity of the channel.

Computer simulations are used to assess the performance of the synchronizer. It is found that the symbol error rate of a coherent receiver employing this synchronizer is virtually the same as that of a system with ideal timing.