Overlaid or time-multiplexed pilots for channel estimation in iterative MIMO receivers

We consider the use of overlaid pilots for multiple input multiple output (MIMO) channel estimation in the context of single-user and single-carrier modulation. Imposing no loss in spectral efficiency, overlaid pilots are potentially of special interest, notably in relatively fast fading channels. However, when channel is to be estimated over short sequences, estimation errors can be important, due to the non-zero cross-correlation of data and pilot sequences. We show how these estimation errors limit the performance of the receiver, when iterative data detection and channel estimation is performed. Also, for the case of iterative detection at receiver, we compare the performances of the overlaid and the time-multiplexed pilot schemes.