Optimal user pairing in cooperative wireless network coding with constrained power minimization

In this paper, we consider a network-coded cooperative wireless network, where users mutually pair among themselves to realize network coding. We consider a multi-user environment, where users transmit to a common destination, without engaging the idle users into cooperation. Two nodes constituting a pair periodically swap the roles of source and relay to mutually achieve spatial diversity. As such, conditioned on the successful detection of the source´s packet, a network coded packet is formed at the relay by a linear combination of its own packet and the source´s packet. A single transmission of this network coded packet therefore helps both nodes to achieve diversity gain. We address the problem of finding the optimal user pairing which maximizes the network capacity. Using this optimal capacity pairing, we subsequently solve a constrained optimization problem to minimize the transmission power, such that the network performance constraint in terms of the maximum average outage probability per user is met.