Wireless Ad Hoc and Sensor Networks

Distributed Fair Scheduling in Wireless Ad Hoc and Sensor Networks 3397.6 Energy-Aware MAC Protocol for WirelessSensor NetworksSensor networks are an important emerging area of wireless networking.They originated from ad hoc networks; however, the application requirementsare different from an ad hoc network perspective. Because of thehardware and application considerations, the sensor networks areresource-limited. The main objective of a sensor network is to collect andforward sampled information about the environment. Normally, a sensorgenerates data only when there is an unusual event with long idle periodsbetween when no data are collected. However, during transmission ofdata from the unusual event, a particular sensor node can generate anintense traffic. To minimize redundancy and network congestion, thetraffic is aggregated within groups of sensors called clusters in which asensor node acts as a CH. Thus, a cluster topology is normally used. A largeamount of data is typically forwarded through the whole sensor networkvia the CHs toward the BS where it is tagged for further analysis. In certainsensor network applications, for example military and planetary exploration,QoS requirements, in terms of finite end-to-end delay, low loss ininformation along with high throughput have to be met in the presenceof fading channels to make useful decisions with the data. In these applications,energy efficient protocols that can render satisfactory QoS arenecessary to extend the life time of the sensor nodes.Sensor nodes are energy constrained because they run on batteries.Hence, it is desirable to conserve energy even with long idle periodsbetween transmissions. It was shown in Reghunathan et al. 2002 thatenergy consumption while listening or receiving is significant (similar asin transmission mode). Thus, a large amount of energy can be saved byturning off the RF circuitry during these idle periods. Rigorous work inthis area has been in place (Woo and Culler 2001, Ye et al. 2002, Singh andRaghavendra 1998) for asynchronous protocols. PAMAS (Singh andRaghavendra 1998) and S-MAC (Ye et al. 2002) save energy by periodicallyplacing the nodes into a sleep mode. However, they still require nodes tolisten to the radio channel for a significant amount of time, and energyconservation is moderate. On the other hand, LEACH protocol (Heinzelmanet al. 2002) uses time division multiple access (TDMA) to reduce thetime spent on radio communication. The nodes are assigned time slotsfor the transmission and the reception of data. These nodes sleep for therest of the TDMA cycle. Hence, an improvement in energy is observedwhen compared to an asynchronous protocol. However, maintaining synchronizationthroughout the network is difficult, and TDMA protocols areinflexible and not dynamic in the allocation of radio resources.