Broadcasting in Mobile Ad Hoc Networks

Mobile ad hoc networks (MANETs) are self-organizing and the constituent mobile nodes communicate with each other as autonomous hosts in the absence of a fixed infrastructure. Recently, MANETs are deployed to places where the network is required to be promptly established such as military operations and disaster relief. However, the mobile nodes merely operate with limited resources such as processing, communication, and energy. The nodes further have the characteristic of high mobility. Thus, MANET has the properties of frequently route breakage and unpredictable topology changes. Clearly, these properties make the transmission methods widely used in fixed infrastructures inappropriate for MANET. Broadcasting is an alternative which is a one-toall transmission method, namely a packet or a message generated by a node, called the source, is sent to all other nodes in the network. Moreover, broadcasting is an important operation in applications performing route discovery (Johnson & Maltz, 1996; Park & Corson, 1997; Pearlman & Haas, 1999; Perkins & Royer, 1999), updating the network knowledge, or sending an alarm signal. However, it seems greedy and excessive in aspect of resource limitation, especially energy which is a major concern in MANET, since the nodes transmit packets in a multi-hop communication manner. Therefore, the energy cost of broadcast packet transmission (i.e., the number of transmissions) should be minimized to conserve the energy of the mobile nodes. Blind flooding is the most straightforward approach to broadcasting. Specifically, every node in the network forwards the broadcast packet exactly once. It ensures the full coverage of all the network: all the nodes in the network are guaranteed to receive the broadcast packet in case that the network is static and the occurrence of collision and error is not considered during propagation. However, flooding may generate excessive redundant transmissions which cause a critical problem, referred to as the broadcast storm problem (Ni et al., 1999), introducing communication contention and collision due to sharing wireless resources and overlapping coverage areas among nodes. The broadcast storm problem can be readily avoided by reducing the number of retransmissions. In order to alleviate the broadcast storm problem, probability-based, areabased, and neighbor knowledge approaches control the amount of traffic, that is, each node determines whether or not to retransmit the broadcast packet. The probability-based approach controls message flood with a predefined probability or received packet count. Obviously, it resembles blind flooding when the probability that a node retransmits the