Effect of frame synchronization errors on pilot-aided channel estimation in OFDM: analysis and solution

Channel estimation in orthogonal frequency division multiplexing (OFDM) systems requires transmission of pilot tones, especially in a high delay spread environment. The number of pilot tones needed exceeds the maximum length of the channel delay (normalized to the symbol period) by one. The best estimate of the channel values in between pilots can be acquired by an IFFT, zero padding and an FFT. Such an estimator gives perfect estimate of the channel in the absence of noise and synchronization errors. However, in the presence of frame synchronization errors, its performance degrades, especially for timing offsets to the right. In this paper, we analyze the sensitivity of such channel estimator to frame synchronization errors, explaining how it is more affected by timing offsets to the right than those to the left. Then through utilizing this sensitivity, we propose a low complexity method to correct frame synchronization errors, which can improve the performance considerably without a need for added training overhead.