Channel estimation for OFDM systems with transmitter diversity for a quasi-static fading channel

A simple channel estimation scheme for OFDM systems with transmitter diversity and a quasi-static fading channel is proposed. It is based on the assumption that the channel is highly correlated at nearby subcarriers. For channel estimation, the pilot sequence is given a different circular time shift at each transmitter antenna, which is equivalent to phase modulation in the frequency domain. Then, nearby subcarriers are used to provide an orthogonal subspace to separate channel frequency responses between transmitter antennas and the receiver antenna. The channel estimator is a simple linear filter whose weight vectors can be precalculated. Using this scheme, the system with transmitter diversity can be implemented with a minimal change in structure from the single antenna implementation. The transmitter diversity gain using the proposed channel estimation scheme is demonstrated in the typical WLAN (wireless LAN) environment. Significant improvement in error performance is achieved using a larger number of transmitter antennas when channel frequency coherence between nearby subcarriers is large.