About the Event
We consider a class of sensor networks with two special characteristics. First, the nodes periodically generate data for transfer to a distinguished node called the access point. Second, the nodes are (transmit) power and energy limited, but the access point, which communicates with the ‘outside world’, is not so limited. Such networks might be used for instance when traffic on a freeway or at an urban street intersection is periodically sensed for purposes of control. We propose a medium access control scheme, called PEDAMACS, for this special class of networks.
PEDAMACS uses the high-powered access point to synchronize the nodes and to schedule their transmissions and receptions. The protocol first enables the access point to gather topology (connectivity) information. A polynomial-time scheduling algorithm then determines when each node should transmit its data, and the access point announces the transmission schedule to the other nodes.
Because PEDAMACS schedules node transmissions, its performance is much better than that of protocols designed for more general contention (or random access) networks in terms of power consumption, delay, fairness, and congestion control. The comparison is based on simulations in TOSSIM, a simulation environment for TinyOS, the operating system for the Berkeley sensor nodes. For our traffic application, the power consumption of a PEDAMACS network is 100 times lower than a contention network, making sensor network technology economically viable.