Use of space time block codes and spatial multiplexing using TDLS channel estimation to enhance the throughput of OFDM based WLANs

HIPERLAN/2, 802.11a, 802.11g and HiSWANa wireless local area networks (WLANs) employ coded orthogonal frequency division multiplexing (COFDM) and provide data rates of up to 54 Mbps in a 20 MHz bandwidth. In this paper, space-time block coding (STBC) and spatial multiplexing MIMO techniques are considered as a means of enhancing the performance of COFDM WLANs. To perform channel estimation for multiple transmit and receive antennas, it is necessary to make transmitted pilot signals orthogonal in space and time. In this paper, this was achieved using a Hadamard design. A time domain least square channel estimator was used to achieve high performance. Packet error rate (PER) performance results for the case of 2Tx and 2Rx antennas are presented and throughput enhancements are evaluated. It is observed that STBC doubles the link throughput for low SNR values. As expected, multiplexing achieves significant throughput enhancements at high SNR values at the expense of additional complexity.