Wireless Ad Hoc and Sensor Networks

Optimized Energy and Delay-Based Routing 383Sensor nodes play the dual role of data collection and routing and thereforeneed energy to perform. Malfunctioning of a few nodes, due tohardware or lack of energy, in the network will cause significant topologychanges, leading to greater consumption of energy and rerouting of packets.Therefore, energy efficient schemes and communication protocols arebeing designed for WSNs.One of the requirements for a protocol is scalability, meaning that theaddition of more nodes to the existing network should not affect thefunctionality of the network with the protocol. Therefore, the communicationprotocols for the WSNs should take into consideration their limitedresources such as battery power, memory, and bandwidth, and be able tofunction in the face of topology changes due to node mobility as well asguaranteeing scalability.Available routing protocols for sensor networks are classified as datacentric,location based, quality of service (QoS) aware, and hierarchicalprotocols. Data-centric protocols (Esler et al. 1999) such as SPIN (Heizelmanet al. 1999), directed diffusion (Intanagonwiwat et al. 2003), and GRAB(Ye et al. 2003, 2005) consolidate redundant data when routing from sourceto destination. Location-based routing protocols such as GPSR (Hill et al.2000), GEAR (Zhang et al. 2004), and TTDD (Luo et al. 2002) require GPSsignals to determine an optimal path so that the flooding of routingrelatedcontrol packets is not necessary. From Chapter 1, sensor nodes arenot supposed to have GPS devices and therefore such protocols havelimited use. On the other hand, QoS aware protocols such as SPEED(He et al. 2003) address various requirements such as energy efficiency,reliability, and real-time requirements. Finally, the hierarchical protocolssuch as LEACH (Heinzelman et al. 2002), TEEN (Manjeshwar et al.2001), APTEEN (Manjeshwar et al. 2002), and PEGASIS (Lindsey andRaghavendra 2002) form clusters and CHs to minimize the energy consumptionboth for processing and transmission of data.In LEACH, the CH function is rotated among the nodes to reduce theenergy consumption because only the CHs communicate to the BS eventhough the placements of CHs are not uniform. Nodes in TEEN andAPTEEN are designed to respond to sudden changes in the sensedattribute when the attribute exceeds a user-defined threshold. On the otherhand, PEGASIS is a chain-based protocol in which rather than multipleCH sending data, only one node in the chain is selected to transmit to theBS. LEACH, TEEN, APTEEN, and PEGASIS assume that the position ofthe BS is fixed and every node in the sensor network can directly communicateto it. This assumption is not always valid in larger networks,because the BS could be out of range with some of the CHs making amultihop routing protocol a necessity.AODV is an on-demand routing protocol that discovers routes on an“as-needed” basis for wireless ad hoc networks. It uses traditional routing