(A) joint maximum likelihood approach to frame synchronization in presence of frequency offset

Abstract

This thesis investigates a new frame synchronizer that can achieve frame sync in presence of frequency offset. First, a maximum likelihood (ML) algorithm for joint frame synchronization, frequency and channel estimation is developed. Its derivation starts with the assumption of additive white Gaussian noise (AWGN) channels. The modified estimators which are robust to frequency acquisition offset is proposed using grid search of frequency offset and tentative frequency offset estimation. This results is extended to frequency selective channels. In the second part, the proposed frame sync scheme is extended to the systems for multiple transmit antennas. This is a direct extension of the rule in frequency selective channels. When the number of antenna is one, the former rule reduced to the latter. Through computer simulations, in several transmit diversity systems are classified by space time modulation are compared. Periodic training sequences can simplify the implementation of the joint ML frame sync estimator at the expense of performance degradation, To circumvent this problem, modified periodic training sequence is proposed. Finally, the proposed frame sync method is extended to fast fading channel environments. To extend the estimation method to fast fading channels, polynomial time-varying channel model is employed. Through computer simulations, it is shown that the estimation method exhibits robust performance in fast fading channel environments.