Robust 2-D Channel Estimation for Staggered Pilot Grids in Multi-Carrier Systems: LTE Downlink as an Example

The paper extends the recently proposed concept of finite dimensional robust 2-D MMSE channel estimation to the staggered pilot grids in multi-carrier systems. The proposed scheme is particularly useful once the receiver has no knowledge of the channel correlation function and it intends to pursue the MMSE channel estimation for improved performance. We build a minimax optimization setup, as a function of the pilot grid structure, that leads to the Least Favourable (LF) channel correlation sequence, which is then employed by the receiver to obtain the maximally robust channel estimation coefficients guaranteeing the best worst-case performance. For staggered pilot grid, such as the one found in LTE Downlink specifications, we present three implementation variants for the maximally robust 2-D MMSE channel estimation and compare their performance in terms of coded BER.