Blind channel estimation in MIMO OFDM systems with multiuser interference

This paper proposes a blind channel estimation method in the context of a multiuser orthogonal-frequency-domain-multiplexing (OFDM) system, where each user transmits utilizing all available subcarriers. A linear nonredundant block precoding scheme is applied at the input of the OFDM system. The precoding spreads the symbols of each user over all subcarriers, thus increasing multipath diversity. At the same time, it introduces a structure to the transmitted symbols, which is exploited at the receiver to estimate the channel in a blind fashion. The proposed channel estimation approach employs computationally simple cross-correlation operations and yields the channel up to a diagonal ambiguity. It does not require channel length information and is not sensitive to additive stationary noise. The precoding does not increase transmission power and maintains even distribution of power between OFDM blocks. A general description of precoding matrices is provided as well as analytical expressions of symbol error probability and signal-to-interference ratio, which could be used to obtain optimum precoding schemes.