A game-theoretic look at simple relay channel

In this paper, we address the problem of communication over the relay channel from the perspective of a stochastic game and evaluate the fundamental tradeoffs between direct communication and relaying through a detailed foray into the questions of throughput, delay and energy-efficiency. We consider a simple wireless ad-hoc network with a transmitter, a relay and a common destination. The relay node not only assists in delivering packets of transmitter but also generates its own packet traffic for destination. Transmitter and relay nodes have conflicting throughput objectives, since all packets transmissions share a single, slotted, classical collision channel, which allows at most one successful transmission per time slot. Relaying packets over an intermediate node might be preferred by transmitter node over direct communication from the energy-efficiency point of view at the expense of increasing energy consumption and decreasing throughput for the relay node. These potential conflicts between interests of transmitter and relay nodes suggest a game-theoretic formulation of communication strategies over simple relay channel. Instead of using external enforcement, we rely on a reward-based mechanism to stimulate cooperation for relaying purposes. In this context, we evaluate the non-cooperative Nash equilibrium by allowing nodes to select their own transmission strategies to optimize individual performance measures, which involve throughput, delay and energy costs. We also formulate the full cooperation of transmitter and relay nodes as a team problem of optimizing total system performance.