A space-time block coding system with backward compatibility for OFDM-based WLANs

Orthogonal frequency-division multiplexing (OFDM) has been selected as the basis for several standards for high-speed wireless local area networks (WLANs), such as IEEE 802.11a. Increasing the transmission robustness of the SISO (single-input single-output) WLAN system was considered by using the space-time block coding (STBC) scheme with two transmit and one receive antennas. A preamble design for this STBC system was proposed. This preamble is backward compatible with its SISO counterpart as specified by the standards. With this preamble design, a sequential method can be used for the estimation of the channel parameters. Phase tracking and least-squares fitting approaches are discussed to improve channel parameter estimation. A simple soft-detector is also given. Furthermore, a semi-blind channel estimation technique is presented to improve the channel estimation accuracy which leads to improved performance. The approaches given herein are ideally suited for real-time implementations. The effectiveness of this system design and algorithms is demonstrated via numerical examples.