Distributed Power Control for Energy Efficient Routing in Ad Hoc Networks Pierpaolo Bergamo, Alessandra Giovanardi, Andrea Travasoni, Daniela Maniezzo, Gianluca Mazzini, and Michele Zorzi Dipartimento di Ingegneria, Universit` a di Ferrara E-mail: pbergamo,agiovanardi,atravasoni,dmaniezzo,gmazzini,mzorzi @ing.unife.it Abstract In this paper, distributed power control is proposed as a means to improve the energy efficiency of routing algorithms in ad hoc networks. Each node in the network estimates the power necessary to reach its own neighbors, and this power estimate is used both for tuning the transmit power (thereby reducing interference and energy consumption) and as the link cost for minimum energy routing. With reference to classic routing algorithms, such as Dijkstra and Link State, as well as more recently proposed ad hoc routing schemes, such as AODV, we demonstrate by extensive simulations that in many cases of interest our scheme provides substantial trans- mit energy savings while introducing limited degradation in terms of throughput and delay. 1 Introduction In the recent literature, ad hoc networks have gained much attention, due to the convenience of building mobile wireless networks without any need for a pre-existing infrastructure. An ad hoc network is a collection of wireless mobile hosts which are able to cooperatively establish communications, using no fixed infrastructure or centralized administration. In such an environment, each host acts as a router and forwards packets to the next hop in order to reach, through multiple hops, the final destination. Many issues need to be addressed in ad hoc networking, one of the most relevant being the packet route selection [32]. A number of algorithms which can be used to find convenient routes have been presented in the past literature, e.g., in [18] [20] [28] [29]. In proactive routing protocols [18] [28], paths towards all destinations are periodically refreshed even if not used. Normally, these protocols require nodes to broadcast information about their neighbors, and, based on this infor- mation, each node in the network computes the minimum path to every possible destination. In reactive routing pro- tocols [20] [29] the path to reach a destination is discovered This work was supported by ALCATEL and by the European Commis- sion under the EYES project (IST-2001-34734). only when needed by means of a procedure called route dis- covery. With this procedure, the source finds more than one path and selects the “shortest” (usually in terms of number of hops). Note that routing algorithms need to know the net- work topology, so a given amount of control traffic overhead is always present and should be minimized in order to in- crease the useful data throughput and to decrease the packet delivery time and the energy consumption. Most of these proposals are based on the intuitive goal of choosing the shortest paths, i.e., minimizing the number of hops. In view of another primary concern in ad hoc net- works, namely energy consumption [21] [31], selecting the shortest path is not the best choice in general, since a num- ber of short hops usually results in less energy consumption compared to fewer longer hops. A few papers have recently appeared, in which various routing strategies are compared in terms of energy consumption, i.e., based on the amount of energy which is spent in correctly delivering a packet to its final destination. A simulation study in [9] compares several routing protocols with respect to energy consumption, with- out proposing any improvement to those protocols to achieve better energy efficiency. Another study of the energy con- sumption of traditional ad hoc routing protocols has been done in [16]. In [42], two algorithms for routing in energy- constrained, ad hoc, wireless networks are presented, which work on top of existing on-demand ad hoc routing protocols. [35] and [36] propose new metrics to be minimized in finding the routing path. Those metrics are power-aware, that is their target is to maximize energy efficiency (e.g., by finding the lowest energy routing path) and/or the lifetime of the whole network (e.g., by balancing traffic). [10] proposes a new path cost for a static network which can be used with any exist- ing algorithm. The objective is to find the link cost function which will lead to the maximization of the system lifetime. Energy efficient location based routing is studied in [44]. As an alternative (or in addition) to the minimization of the energy cost of delivering a packet, the energy status of intermediate nodes is also a concern, as it directly affects the network lifetime. Several papers have considered rout- ing metrics which explicitly include residual node energy [2] [39] [41]. Specific battery characteristics are used to devise 1