PEDAMACS protocol operates in three phases: topology learning, topology collection and scheduling phases. In the topology learning phase, each node identifies its neighbors, its interferers, and its parent node in the routing tree rooted at the AP obtained according to some routing metric. In the topology collection phase, each node sends this (local) topology information to the AP so, at the end of this phase, the AP knows the full network topology. At the beginning of the scheduling phase, the AP broadcasts a schedule. Each node then follows the schedule: In particular, the node sleeps when it is not scheduled either to transmit a packet or to listen for one.

We had implemented a random access protocol and PEDAMACS by using the TinyOS operating system, and conducted Monte Carlo simulations of the two protocols in TOSSIM, the TinyOS simulation framework, over 10 different random configurations. The figure below compares the delay of random access and PEDAMACS schemes assuming that every node generates one packet at the beginning of the schedule. As the number of nodes increases, the delay in both schemes increases. The ratio of the delay experienced in random access scheme to that in PEDAMACS scheme is about six.

The power-consuming operations in a sensor node are transmission and reception of a packet, listening to the channel, sampling, and running the microprocessor. The figure below gives the lifetime estimates for random access and PEDAMACS schemes for a 30-second packet generation period at each node, 50 kbps transmission rate, assuming that each node has a pair of AA batteries, which can supply 2200 mAh at 3 V. The lifetime of a random access network is about ten days whereas that of a PEDAMACS network is about 600 days.

Please refer to the publication for more details:

Coleri, S. and P. Varaiya. PEDAMACS: Power efficient and delay aware medium access protocol for sensor networks. California PATH Working Paper UCB-ITSPWP-2004-6, 2004.