Distributed Synchronization

The goal of this research line is to analyze the possible options for network synchronization in dense sensor networks, and to design a power efficient and robust synchronization scheme. The considered scenario is characterized by a large set (up to thousands) of wireless nodes communicating by means of short-distance links. In order to reduce both the overall cost of deployment of the system and the size of the single device, the standard node is not equipped with a quartz crystal, and depends thus on an external reference for clock generation. Such external reference is provided by a small set of nodes, referred to as Reference Clocks, which provide the neighboring nodes with a time reference in the form of a periodic sequence of pulses.
Nodes that are within reception range from a reference clock lock themselves to the sequence of pulses by means of a Phase Lock Loop (PLL) circuit. An example of the scenario is presented in Figure 1.

In our research we compare two different classes of network synchronization algorithms:

• deterministic algorithms, based on the application of a procedure which leads the nodes to a TDMA-based organization, with clock signals originating in Reference Clocks and propagated to all other nodes by means of hop-to-hop retransmissions;
• biology-inspired algorithms, based on the convergence of multiple independent clocks to a common reference by means of a feedback effect. This effect, observed in several biological systems, was proposed for communication systems based on coupled oscillators in [1], and was further investigated in [2], [3] (among others).

References

[1]

R. E. Mirollo and S. H. Strogatz, "Synchronization of pulse-coupled biological oscillators," SIAM J. Appl. Math., Vol. 50, No. 6, pp. 1645-1662, December 1990.

[2]

F. Tong and Y. Akaiwa, "Theoretical analysis of interbase-station synchronization systems," IEEE Trans. Commun., Vol. 46, No. 5, pp. 590-594, May 1998.

[3]

M. Cremaschi, O. Simeone and U. Spagnolini, "Distributed timing synchronization for sensor networks with coupled discrete-time oscillators," International Workshop on Wireless Ad Hoc and Sensor Networks (IWWAN2006), New York, NY, June 28-30 2006.