Energy Efficient Reliable Communication for Multi-hop Wireless Networks

Current algorithms for minimum-energy routing in wireless networks typically select minimum-cost multi-hop paths. In scenarios where the transmission power is fixed, each link has the same cost and the minimum-hop path is selected. In situations where the transmission power can be varied with the distance of the link, the link cost is higher for longer hops; the energy-aware routing algorithms select a path with a large number of small-distance hops. In this paper, we argue that such a formulation based solely on the energy spent in a single transmission is not able to find minimum energy paths for end-to-end reliable packet transmissions. The proper metric should include the total energy (including that expended for any retransmissions necessary) spent in reliably delivering the packet to its final destination. We first study how link error rates affect this retransmission-aware metric, and how it leads to an efficient choice between a path with a large number of short-distance hops and another with a smaller number of large-distance hops. Such studies motivate the definition of a link cost that is a function of both the energy required for a single transmission attempt across the link and the link error rate. This cost function captures the cumulative energy expended in reliable data transfer, for both reliable and unreliable link layers. Through detailed simulations, we show that our schemes can lead to upto 30-70% energy savings over best known current schemes, under realistic environments. Use of minimum energy paths for packet transmission may not always maximize the operational lifetime of multihop wireless networks. In the latter part of this paper, we define a new power-aware routing algorithm, called MRPC, that can be used to increase the operational lifetime of the network. MRPC integrates a node-specific metric, (residual battery power) and our proposed link-specific metric to select a path with the largest packet capacity at the ‘critical’ node. Finally, we also present, CMPRC, a conditional variant of MRPC that switches from minimum energy routing to MRPC only when the packet forwarding capacity of nodes falls below a threshold and through simulations we quantify the benefits of these schemes. Index Terms Low-power protocols, Wireless ad-hoc networks, Energy-efficiency, Reliable