Date Added: Apr 2010
Wireless Sensor Networks (WSN) is based on small, cheap and energy efficient nodes. Since the largest fraction of the energy used in each node is spent listening to the channel, synchronous networks are employed to reduce such idle listening time. In that case, the receiver predicts the timeslot that the transmitter will use and turns itself off when no incoming signal is expected. The duty-cycle of the receiver can be lower if the timeslot can be predicted with a smaller error, i.e. if a more accurate time reference is available. Accuracies of a few ppm can be achieved by crystal-Controlled Oscillators (XCOs), but since such external components should be avoided to reduce the cost and size of the nodes, accuracy must be given up for the sake of integration.