Estimation of Time and Frequency Offset in OFDM Systems

We present the joint maximum likelihood (ML) symbol-time and carrier-frequency offset estimator in orthogonal frequency-division multiplexing (OFDM) systems. Redundant information contained within the cyclic prefix enables this estimation without additional pilots. Simulations show that the frequency estimator may be used in a tracking mode and the time estimator in an acquisition mode.

ORTHOGONAL frequency-division multiplexing (OFDM) systems have recently gained increased interest. OFDM is used in the European digital broadcast radio system and is being investigated for other wireless applications such as digital broadcast television and mobile communication systems, as well as for broadband digital communication on existing copper networks. We address two problems in the design of OFDM receivers. One problem is the unknown OFDM symbol arrival time. Sensitivity to a time offset is higher in multicarrier systems than in single-carrier systems and has been discussed in [3] and [4]. A second problem is the mismatch of the oscillators in the transmitter and the receiver. The demodulation of a signal with an offset in the carrier frequency can cause a high bit error rate and may degrade the performance of a symbol synchronizer
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