In a bi-directional relay channel, a pair of nodes wish to exc hange independent messages over a shared wireless half-duplex channel with the help of relays. Recent work has mostly considered information theoretic limits of the bi-directional relay channel with t wo terminal nodes (or end users) and one relay. In this work we consider bi-directional relaying with one base station, multiple terminal nodes and one relay, all of which operate in half-duplex modes. We assume that each terminal node communicates with the base-station in a bi-directional fashion through t he relay and do not place any restrictions on the channels between the users, relays and base-stations; t hat is, each node has a direct link with every other node. Our contributions are three-fold: 1) the introd uction of four new temporal protocols which fully exploit the two-way nature of the data and outperform simple routing or multi-hop communication schemes by carefully combining network coding, random binning and user cooperation which exploit over-heard and own-message side information, 2) derivations of inner and outer bounds on the capacity region of the discrete-memoryless multi-pair two-way network, and 3) a numerical evaluation of the obtained achievable rate regions and outer bounds in Gaussian noise which illustrate the performance of the proposed protocols compared to simpler schemes, to each other, to the outer bounds, which highlight the relative gains achieved by network coding, random binning and compress-and-forward-type cooperation between terminal nodes.
We consider a multiuser two-way relay network where multiple pairs of users communicate with their pre-assigned partners, using a common intermediate relay node, in a two-phase communication scenario. In this system, a pair of partners transmit to the relay sharing a common spreading signature in the first phase, and the relay broadcasts an estimate of the XORed symbol for each user pair in the second phase employing the relaying scheme termed jointly demodulate-and-XOR forward (JD-XOR-F) in [1]. We investigate the joint power control and receiver optimization problem for this multiuser two-way relay system with JD-XOR-F relaying. We show that the total power optimization problem decouples into two subproblems, one for each phase. We construct the distributed power control and receiver updates in each phase which converge to the corresponding unique optimum. Simulation results are presented to demonstrate the significant power savings of the multiuser two-way relay system with the proposed iterative power control and receiver optimization algorithms, as compared to the designs with a iquestone-wayiquest communication perspective.