OFDM Amplify-and-Forward Two-Way Relaying for MIMO Multiuser Networks

We consider a wireless relay network where two pairs of nodes exchange information with their partners through a single amplify-and-forward two-way relay with each node equipped with multiple antennas. We propose a new relaying scheme employing OFDMA for the multiple access transmission in the first time slot and OFDM/SDMA for the broadcast transmission in the second time slot to improve the sum rate of the network. To fully utilize spatial diversity, we design the relay beamforming matrices according to two methods respectively, i.e., signal to leakage and noise ratio (SLNR) and block diagonalization based zero-forcing (BDZF), on per subcarrier basis. We also derive the upper bound on the capacity region of this two-way relay network by using cut-set theory. Simulation results show that the proposed scheme outperforms three other relaying schemes in terms of sum rate and can approach the upper bound of capacity region.