Iterative symbol offset correction algorithm for coherently modulated OFDM systems in wireless communication

Orthogonal frequency division multiplexing (OFDM) system performance remains acceptable under timing synchronisation errors as long as the start of each symbol is determined to lie within a certain length into the cyclic prefix (CP). The Schmidl and Cox algorithm (SCA) is quite robust in estimating the timing and frequency offset synchronisation for systems with large OFDM symbol lengths. It uses two OFDM symbols for training with the first one having two identical halves. The start of the frame is estimated by correlating a received sequence of samples equal to half the OFDM symbol length with the following received samples. The effect of additive white gaussian noise (AWGN) in the estimation process is mitigated only if the number of samples used in the correlation, and hence the OFDM symbol size is large. However to be successfully applied to broadband fixed wireless access (BFWA) systems, OFDM should perform well even with smaller symbol lengths. In this paper we present the iterative symbol offset correction algorithm (ISOCA), which uses the SCA for initial coarse timing synchronisation and follows it with a two stage symbol offset correction algorithm by tracking the phase of the second training symbol. We show through simulation that the ISOCA achieves virtually perfect estimation of the start of frame (SOF), even with very low received SNR.