Time and frequency offset estimation for distributed multiple-input multiple-output orthogonal frequency division multiplexing systems

This study addresses the problem of time and frequency offset estimation in the case of the delays, and the frequency offsets of all the transmitter/receiver pairs are different for distributed multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. A new training structure is designed and an efficient time and frequency offset estimator is proposed. With the symmetric conjugate property of the preamble, the timing metric proposed has an impulse shape, making the time offset estimation accurate. Using the repetition property of the preamble, iterative frequency offset estimation algorithm proposed can acquire a high precision and a wide estimation range. To distinguish different transmit antennas, the preamble is weighted by pseudo-noise (PN) sequences with low cross-correlations. The analysis and the simulation results show that the proposed estimator offers an accurate estimation on the different time delays and frequency offsets caused by the distributed transmitters of the MIMO-OFDM system. This is a situation that the conventional estimators cannot handle as far.