Decision-directed channel estimation for multi-user OFDM environments

Multiple reception antenna assisted space division multiple access (SDMA) techniques designed for wireless OFDM systems have recently drawn wide interest. These techniques facilitate the implementation of effective multi-user detection algorithms at the receiver, such as minimum mean-square error (MMSE) detection, successive interference cancellation (SIC), parallel interference cancellation (PIC) or maximum likelihood (ML) detection. A prerequisite of their operation is the availability of an estimate of the channel's frequency domain transfer function. Decision-directed channel estimation was analysed by Li et al., (1999), in the context of a space-time coded single-user arrangement employing two transmit and two receive antennas. This estimation scheme is also applicable to a multi-user scenario, where each user is equipped with a single transmit antenna. The contribution presented here proposes a decision-directed channel estimator, which invokes only subsets of the available subcarriers in order to reduce the interference between the different users' estimation processes.