SNR-based channel pairing design in multichannel TDBC-based two-way relaying

We consider two-way amplify-and-forward relaying in a multichannel system with two terminal nodes and one relay nodes, where the time-division broadcast (TDBC)-based two-way relaying strategy is used. Given power alloation, we investigate the design of subchannel pairing at the relay to maximize the sum rate of the system. With broadband systems of large number of subchannels, our focus is on designing efficient subchannel pairing strategies. We first show that, unlike in the one-way case, there exists no explicit SNR-based pairing strategy leading to sum-rate maximization. Instead, we formulate the pairing optimization as an axial 3-D assignment problem which is NP-hard, and propose an iterative optimization method to solve it with complexity O(N³). Based on SNR over each subchannel, we also propose sorting-based algorithms for scenarios with and without direct link, with a low complexity of O(N logN). The simulation results also show the proposed algorithm offers the performance very close to the iterative optimization method.