Down-Sampled Impulse Response Least-Squares Channel Estimation for LTE OFDMA

We consider least-squares (LS) downlink channel estimation for LTE OFDMA receivers. The 3GPP Long Term Evolution (LTE) project aims at continuing the competitiveness of the 3GPP standard reached with HSPA. OFDMA was chosen as multiple-access scheme for the downlink and 10 MHz bandwidth is the minimum capability for user equipments (UE). In such a context, an ill conditioning problem of the classical LS approach was found due to the un-excitation of a large portion of available sub-carriers of the LTE OFDMA symbol (due to the guard band). Two methods are investigated and compared to solve this problem: the first solution is regularization and the second one is down-sampling of the channel impulse response. The latter solution proves to perform better and allows some computational savings.