Robust channel estimation for 802.11n (MIMO-OFDM) systems

In a receiver for multiple input multiple output (MIMO) 802.11n system, the residual carrier frequency offset (CFO), after synchronization with training symbols in the preamble of a packet, affects the accuracy of channel estimation. The residual CFO causes inter-carrier interference as well as inter-spatial stream interference. A decision directed algorithm to estimate and correct the residual CFO before channel estimation is presented. A 802.11n packet transmitted with high-throughput mixed mode (HT-MM) packet format has both legacy and high-throughput (HT) training fields. Typically, the channel is estimated only with HT training fields. In this paper, a channel estimation technique which uses both the legacy and high-throughput training field is proposed. Simulation results demonstrating the improvement in channel estimation and packet error rate (PER) performance are also presented.