Wireless Ad Hoc and Sensor Networks

24 Wireless Ad Hoc and Sensor Networks1.4 Mobile Ad hoc Networks (MANET)The major drawback for cellular networks is the need for a centralizedinfrastructure. Recent technological advancements enable portable computersto be equipped with wireless interfaces, allowing networked communicationeven while mobile. Wireless networking greatly enhances theutility of carrying a computing device. It provides mobile users withversatile and flexible communication between people and continuousaccess to networked services with much more flexibility than cellularphones or pagers.A MANET is an autonomous collection of mobile users communicatingover a relatively bandwidth-constrained wireless link with limitedbattery power in highly dynamic environments. The network topology,due to the mobility in the network is, in general, dynamic and maychange rapidly and unpredictably over time. Hence, the connectivityamong the nodes may vary with time because of node departures, newnode arrivals, and the possibility of having mobile nodes. To maintaincommunication between the nodes in the network, each node in a wirelessad hoc network functions as a transmitter, host, and a router. Themanagement and control functions of the network are also distributedamong the nodes. Moreover, as the network is highly decentralized, allnetwork activity, including discovering the topology, transmitting information,and efficient use of the battery power, must be executed by thenodes themselves.As the users in the MANET communicate over wireless links, they haveto contend with the effects of radio communication, such as noise, fading,shadowing, and interference. Regardless of the application, a MANETneeds efficient distributed algorithms to determine network organization,link scheduling, power control, and routing.A MANET is formed by a cluster of mobile hosts and can be rapidlydeployed without any established infrastructure or centralized administration.Because of the transmission range constraint of transceivers, twomobile hosts can communicate with each other either directly if they areclose enough (peer-to-peer) or (multihop) indirectly by having other intermediatemobile hosts relay their packets. The combination of networkingand mobility will engender new services, such as collaborative softwareto support impromptu meetings, self-adjusting lighting and heating,natural disaster relief operations, and navigation software to guide usersin unfamiliar places and on tours. Protocol standards that were developedfor cellular networks are no longer useful for ad hoc networks because oflack of centralized infrastructure. The standards for ad hoc networks,which are different from those for cellular networks, are presented in thefollowing subsection.