Topology control

Abstract

Networks of wireless units, communicating with each other via radio transceivers, typically along multihop paths, are generally known as wireless ad hoc networks (WANETs). WANETs can be used wherever a wired infrastructure is infeasible and/or economically inconvenient. For example, in order to provide communications during emergencies, special events (such as conferences, expos, concerts, etc.), or in hostile environments, WANETs are extremely useful (Santi 2005a). Wireless sensor networks (WSNs) are a special class of WANETs where network nodes are wireless sensors (which may be mobile in some cases). Sensor nodes collect the data of interest (e.g., temperature, pressure, soil makeup, etc.), and wirelessly transmit them, possibly compressed and/or aggregated with those of neighboring nodes, to other nodes. WSNs can be used to monitor remote and/or hostile geographical regions, to trace animal movement, to improve weather forecast, and so on. WSNs are envisioned to be an integral part of our lives in future, more so than the present day cell-phones or PCs (Akyildiz et al. 2002). A protocol stack, used by the sensor nodes in WSNs, is suggested in Fig. 6.1 (Akyildiz et al. 2002). It follows the conventional 5-layer model of TCP/IP stack with some modifications. For example, this protocol stack combines power and routing awareness, integrates data with networking protocols, communicates power efficiently through the wireless medium, and promotes cooperative efforts of sensor nodes. Several energy-conserving methods have been proposed at various layers of the protocol stack of WSN. These range from design of low power CMOS circuitry to energy aware applications. All these energy-conserving methods together constitute the power management plane of the WSN architecture (Fig. 6.1), which manages how a sensor node uses its power, Due to similarity in concept, realisation of WSN applications requires WANET techniques to be handy in the first place. But, although many protocols and algorithms have been proposed for traditional WANETs, they are not well suited for the unique features and application requirements of WSNs (Akyildiz et al. 2002). For instance, unlike wired networks, each node in a multi-hop WSN can potentially change its set of one-hop neighbors and subsequently the overall network topology, by changing its transmission power. Without proper TC algorithms in place, a randomly connected multi-hop WSN may suffer from poor network utilisation, high end-to-end delays, and short network lifetime. Interestingly, the topology also depends on several uncontrollable factors, such as node mobility, weather, interference, noise, along with controllable parameters, such as transmit power and antenna direction. © Springer-Verlag Berlin Heidelberg 2007.