A Robust OFDMA Channel Estimation Against Imperfect Synchronization

Abstract

Orthogonal frequency-division multiplexing(OFDM) has been of major interest for both wireline-based and wireless applications due to its high data rate transmission capability and its robustness to multipath delay spread. However, OFDM systems are much more sensitive to synchronization errors that single carrier systems. Several approaches have been proposed for estimating the time and frequency offset either separately. These separate frequency synchronization methods assume perfect timing synchronization, which may not be guaranteed, and timing estimation errors may affect frequency synchronization. In order to evaluate actual performance, joint timing and frequency synchronization approaches are desirable. Coherent OFDM systems require channel estimation. Previous works on channel estimation assume perfect synchronization. However, this may not be guaranteed and synchronization errors can deteriorate the channel estimation performance. Hence a desirable approach which reflects a more accurate performance is to address synchronization and channel estimation tasks together. The idea of combined timing and frequency synchronization and channel estimation is quite desirable since the synchronization and channel estimation tasks can affect each other. In this paper, we address robust channel estimation in the presence of frequency offset and phase noise. We consider the problem of error propagation in the timing and frequency synchronization steps. The joint estimation of timing offset, frequency offset and channel impulse response is broken down into several stages. At the first stage, timing offset and frequency offset estimator are performed. And then the channel estimation is performed using pilot signal. The simulation results show that the proposed robust channel estimation performs quite well and circumvents the problem of mismatch among individual synchronization tasks.