Time Keeping Ability of Crystal-Free Radios

The Internet-of-Things (IoT) promises one trillion wireless sensors in the next 10 to 15 years. To enable this scale, we present the experimental results on the time-keeping ability of crystal-free radios to lower the cost of the wireless sensors. We propose a network referenced frequency lock loop and demonstrate a one sigma mean frequency accuracy of 47 p/min, post calibration. We also extend this concept to calibrate the on-chip RF local oscillator by exploiting the network time synchronization for frequency calibration. This timing accuracy is sufficient to create a scalable wireless mesh network up to 10 hops deep with a 1 ms guard time interval. The impact of time synchronization on the average power consumption of the wireless sensor node is negligible and especially true for environments with mobility and high data traffic. We envision these emerging microsystems to be embedded into everyday objects and discuss the tradeoff of mobility with the average power consumption.