Feedback in Coded Wireless Packet Networks

In this paper we propose an end-to-end feedback mechanism for intra-session random linear network coding with opportunistic routing in wireless packet networks with lossy links. We focus on bidirectional network coding, i.e., forward and reverse flows between two nodes are coded together, which is key for efficient utilization of the wireless medium as it allows intermediate nodes to relay traffic in both directions with a single transmission. We analyze the performance in terms of decoding and acknowledgement times in a three-node network when nodes are fully backlogged. The results are compared to the theoretic lower bound obtained by solving the network's flow formulation. In addition, we derive symmetric injection rates from the these results which the network should be able to sustain. The evolution of source backlogs and decoding/acknowledgement over time are simulated, demonstrating that backlogs remain bounded. The insight gained will help in developing a generalized feedback model for coded wireless mesh networks, which is to the best of our knowledge an open problem.