Clock Free Data Streams Alignment for Sensor Networks

We develop a data alignment mechanism for sensor networks. The mechanism allows the sensor data streams to be aligned without real-time clocks or virtual clocks. The developed mechanism makes use of the built-in counters on sensors and external synchronization signals to align data streams. The data server broadcasts out-of-channel synchronization signals with constant or variable intervals. The sensor data streams are aligned when received on the server. Only one way communication is used so as to reduce the communication overhead and clock synchronization overhead on sensors nodes. In addition, the developed mechanism is scalable thanks to one way communication. The synchronization error is bounded by the maximum sampling period of the sensors, and is independent of the number of the nodes in the network. Our analysis also shows the required awake time for sensors to tolerate different clock drifts and signal lost.