Carrier frequency offset estimation in OFDMA systems based on averaging over successive blocks

An uplink OFDMA systems is considered. Different users use different transmit antennas, thus, each user contributes a different carrier frequency offset (CFO) at the receiver. The multiple CFOs introduce intercarrier interference, thus impeding user separation and transmit signal recovery. A low complexity CFO estimation approach is proposed for estimating multiple CFOs. The proposed approach relies on one or more pilot symbols per user which are placed far from each other and each one carries the same symbol over a number of successive blocks. A user´s CFO is obtained based on averaging over consecutive OFDM blocks of the symbols corresponding to the pilot tones of that user. Simulation results suggest that accurate CFOs estimation is possible with a very small amount of averaging, which makes the method applicable to the case of slowly varying channels. The proposed approach does not require channel state information, which is important as channel state information cannot be easily obtained before CFO correction.