A wireless ad hoc network is an autonomous, self-organized, distributed, peer-to-peer network of fixed, nomadic, or mobile users that communicate over bandwidth-constrained wireless links. There is no preexisting infrastructure. Wireless ad hoc networks can be relay, mesh, or star networks comprising special cases. When the nodes are connected in mesh topology, the network is also known as a wireless mesh network. It is known as a mobile ad hoc network (MANET), when the nodes are mobile.
A wireless ad hoc network has a mutlihop relaying of packets, as shown in Fig. 22.1. It can be easily and rapidly deployed, and expensive infrastructures can be avoided. Without an infrastructure, the nodes handle the necessary control and networking tasks by themselves, generally by distributed control. Typical applications are wireless PANs for emergency operations, civilian, and military use. The wireless ad hoc network is playing an increasing role in wireless networks, and wireless ad hoc networking mode has been or is being standardized in most IEEE families of wireless networks.
MANETs and wireless sensor networks (WSNs) are the two major types of wireless ad hoc networks. They both are distributed, multi-hop systems. A MANET is an autonomous collection of mobile routers (and associated hosts) connected by wireless links. Each node is an information appliance, such as a personal digital assistant (PDA), equipped with a radio transceiver. The nodes are fully mobile.