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.

Wireless sensor networks for factory automation and control will require strict latency and reliability requirements on the order of 1 millisecond end-to-end latency and 10-9total packet error rate. Current wireless sensor networks can achieve up to nine nines (10-9total packet error rate) of reliability, but without tight latency bounds. In order to meet these requirements, wireless sensor networks will require effective modes of network diversity that are also compatible with low-latency time scales. We evaluated the efficacy of time, space, and frequency diversity in cooperative IEEE 802.15.4 wireless networks. We demonstrated a wireless sensor network topology that achieved 99.99999% of reliability bounded by a worst case end - to-end latency of 3 milliseconds.