Ad hoc wireless networks enable new and exciting applications, but also pose significant technical challenges. In this article we give a brief overview of ad hoc wireless networks and their applications with a particular emphasis on energy constraints. We then discuss recent advances in the link, multiple access, network, and application protocols for these networks. We show that cross-layer design of these protocols is imperative to meeting emerging application requirements, particularly when energy is a limited resource. ad hoc [Latin.] a. For this purpose, to this end; for the particular purpose in hand or in view. b. attrib. or as adj. Devoted, appointed, and so on, to or for some particular purpose. Oxford English Dictionary, 2nd Edition An ad hoc wireless network is a collection of wireless mobile nodes that self-configure to form a network without the aid of any established infrastructure, as shown in Fig. 1 . Without an inherent infrastructure, the mobiles handle the necessary control and networking tasks by themselves, generally through the use of distributed control algorithms. Multihop connections, whereby intermediate nodes send the packets toward their final destination, are supported to allow for efficient wireless communication between parties that are relatively far apart. Ad hoc wireless networks are highly appealing for many reasons. They can be rapidly deployed and reconfigured. They can be tailored to specific applications, as implied by Oxford's definition. They are also highly robust due to their distributed nature, node redundancy, and the lack of single points of failure. These characteristics are especially important for military applications, and much of the groundbreaking research in ad hoc wireless networking was supported by the (Defense) Advanced Research Projects Agency (DARPA) [1][2][3]. Despite much research activity over the last several decades on wireless communications in general, and ad hoc wireless networks in particular, there remain many significant technical challenges in the design of these networks. In this tutorial we describe some of these technical challenges and possible approaches to solving them, with a special emphasis on how finite node energy impacts each layer of the network protocol stack. The lack of infrastructure inherent to ad hoc wireless networks is best illustrated by contrast with the most prevalent wireless networks today: cellular systems and wireless local area networks (WLANs). In cellular telephone networks the geographic area of interest is divided into regions called cells. A mobile terminal located in a given cell communicates directly with a base station located at or near the center of each cell, as shown in Fig. 2 . Thus, there is no peer-to-peer communication between mobiles. All communication is via the base station through single-hop routing, although recent work indicates that multihop routing to the base station can significantly improve performance [4] [5] [6] ). Each base station is connected by a high-speed link (typically wired) to a mobile switching center (MSC) that in turn is connected to the public switched telephone network (PSTN). The base stations and MSC perform all control and networking functions, including authentication, call routing, and handoff. The mobile units that constitute the wireless portion of this network depend entirely on the base station/MSC/PSTN infrastructure for connectivity and centralized control. Most WLANs have a similar centralized single-hop architecture: mobile nodes communicate directly with a centralized access point that is connected to the backbone Internet, and the access point performs all networking and control functions for the mobile nodes. In contrast, an ad hoc wireless network has peer-to-peer communication, distributed networking and control functions among all nodes, and multihop routing. This discussion should not be taken to mean that ad hoc wireless networks are completely flat; that is, cannot have any infrastructure or
Power aware protocols in ad hoc networks are discussed in REF .
Design challenges for energy-constrained ad hoc wireless networks
IEEE Wirel. Commun.
IEEE Wirel. Commun.
Computer Science