Joint channel and Frequency Offset estimation in MIMO-OFDM systems with insufficient Cyclic Prefix

A Maximum Likelihood joint channel and Frequency Offset estimator is addressed for Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing systems in the presence of Inter Symbol Interference and Inter Carrier Interference due to an insufficient Cyclic Prefix. The use of known Pseudo Noise based Symmetric Sequences to perform the joint estimation is proposed. The periodicity of the cost function for the Frequency Offset estimator has been analytically derived. It has been found that the proposed Pseudo Noise based Symmetric Sequences achieve an acquisition range for normalized Frequency Offset within the interval ±0.5, while previously proposed symmetric sequences are limited to ±0.25. The performance of Frequency Offset and channel estimators has been evaluated by the Cramér–Rao Bound and the theoretical Mean Squared Error. Also, the analytical Mean Squared Error for channel estimation in case of an imperfect estimation of Frequency Offset has been developed to analyze its impact in the performance. Moreover, we have proven that the estimation with the second half of the symmetric preamble performs better than with the whole preamble.