Channel estimation for a new high performance MIMO STC-OFDM WLAN system

A novel MIMO STC-OFDM technique has been developed that achieves both high spectral efficiency and high performance over frequency selective channels. This is accomplished by a combination of MIMO OFDM, group coded transmit signals and antennas, array processing at the receiver for interference suppression on a per carrier basis, and a new decoding scheme. It also incorporates frequency diversity by pairing, for STC purposes, subcarriers that are K/2 apart, where K is the total number of FFT frequencies. This paper discusses a channel estimation scheme for this new 4×4 MIMO WLAN system. Time domain matrix-vector formulation leads to estimates that have an SNR on the order of 48 dB when just one block of high power QPSK symbols per transmitter is used, while the receiver AWGN SNR is 19 dB or higher. The final 4×2 equivalent channel matrix, for each of the two component subsystems, is shown to have a corresponding SNR of 37 dB. Most importantly, the loss in system BER performance due to the channel estimation process (compared to the known channel case) is found to be negligible. At 19 dB signal SNR, this new scheme achieves a BER of 3×10⁴, without the need for coding or interleaving. The data rate achieved, over a bandwidth of 20 MHz, is 144 Mbps with a corresponding spectral efficiency of 7.2 bits/s/Hz.