Estimation and compensation of frequency offset in DAC/ADC clocks in OFDM systems

A frequency offset between the clocks in the digital-to-analog-converters (DAC´s) in the transmitter and the analog-to-digital-converters (ADC´s) in the receiver would severely impact the performance of an OFDM communication system. The effect of the frequency offset can be approximated as a phase rotation for each sample of an OFDM symbol, where the amount of the rotation is proportional to the sub-channel index. In this paper, an algorithm for the compensation of such a frequency offset is proposed which uses the pilot tones present in each OFDM symbol. The required phase corrections for samples in all sub-carriers are determined and applied. The proposed algorithm is tested on an OFDM communication system whose parameters are selected based on IEEE 802.11a standard for wireless local area networks (WLAN). Simulation results show that the algorithm works quite effectively even with large amounts of frequency offsets.