To overhear or not to overhear: a dilemma between network coding gain and energy consumption in multi-hop wireless networks

Abstract

Any properly designed network coding technique can result in increased throughput and reliability of multi-hop wireless networks by taking advantage of the broadcast nature of wireless medium. In many inter-flow network coding schemes nodes are encouraged to overhear neighbour's traffic in order to improve coding opportunities at the transmitter nodes.A study of these schemes reveal that some of the overheard packets are not useful for coding operation and thus this forced overhearing increases energy consumption dramatically. In this paper, we formulate network coding aware sleep/wakeup scheduling as a semi Markov decision process (SMDP) that leads to an optimal node operation. In the proposed solution for SMDP, the network nodes learn when to switch off their transceiver in order to conserve energy and when to stay awake to overhear some useful packets. One of the main challenges here is the delay in obtaining reward signals by nodes. We employ a modified Reinforcement Learning (RL) method based on continuous-time Q-learning to overcome this challenge in the learning process. Our simulation results confirm the optimality of the new methodology.

To Code or Not to Code: When and How to Use Network Coding in Energy Harvesting Wireless Multi-Hop Networks

“…In [9], addressing the to-send-or-not-to-send problem, we examined a trade-off between enhancing coding gain on one hand and reducing end-to-end delay on the other. Similarly, in [12], tackling the to-overhear-or-not-to-overhear problem, we investigated a trade-off between increasing coding gain and diminishing energy consumption in multi-hop wireless networks.…”

“…This allows the neighboring nodes to determine the best coding patterns by examining the coding conditions between different packets. An important observation in this context, as highlighted in [12], is that a significant number of these overheard packets do not contribute to improving the coding efficiency in the network.…”

“…In the second decision-making approach, which we separately termed in one of our previous studies To-Overhearor-Not-to-Overhear [12], network nodes aim to gradually learn the best decision between staying awake (and listening to new packets) or going to sleep (and conserving energy). One of the significant issues in employing network coding in wireless networks is that the more a node overhears packets from others, stores these packets in its memory, and reports 1 Efficient Network CODing.…”