Channel estimation and training design for MIMO-OFDM two-way relay systems

In this paper we consider two-way relaying systems consisting of two end users, N₁ and N₂, which exchange their information with the help of a relay, R. The three terminals are equipped with multiple antennas. The information exchange process between N₁ and N₂ are divided into two phases. Both N₁ and N₂ send their information to R at the first phase. The relay will amplify its received signals and transmit the resultant signals back to N₁ and N₂ at the second phase. The end users estimate the necessary channel coefficients to decode the signals; therefore, the processing burden on the relay is reduced. In this paper, a least-squared based estimation method is proposed to estimate those coefficients. Optimal pilot vectors are also proposed to minimize the mean-square-error (MSE) of channel estimation. Furthermore, the proposed training signals has the peak-to-average-power ratio (PAPR) of 1.