Semi-Blind/Blind channel estimation for multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems has received a lot of attention in recent years. A new linear precoder for blind channel estimation is proposed in which only a small number of subcarriers carry symbols that are linearly precoded to effect the inter-symbol correlation needed for the blind channel estimation scheme to function properly. The proposed precoding scheme leaves most of the subcarriers intact, thereby minimizing the number of symbols that have to be jointly estimated via either Maximum Likelihood (ML) or MMSE. An optimal precoder under the sparse structure is developed, which insures that the precoder matrix is well-conditioned to minimize any noise enhancement that may occur in the process of MMSE based joint symbol estimation.
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