Pilot assisted synchronization for wireless OFDM systems over fast time varying fading channels

This paper presents a frequency synchronization technique for wireless OFDM communication systems over fast time varying channels. The overall method, known as loop-timing, can be used to synchronize multiple mobile transceivers with a base-station. In this method, the mobiles first achieve downlink synchronization and subsequently derive their uplink timing reference from the recovered downlink clock. To accomplish the former task, a periodic time-frequency pattern of pilot tones is embedded in the transmitted downlink baseband signal. Frequency offsets are estimated and compensated using an approximate maximum likelihood frequency offset estimator. The method can be used to correct for frequency offsets up to half the OFDM symbol rate and is suitable for real time implementation