Low-Power RF Integrated Circuits for Wireless Sensor Network Synchronization and Communication

Abstract

Society has been witness to and participant in an on-going computing revolution as new classes of computing technology have displaced older technologies as the dominant market force--from mainframes decades ago to smartphones today. The rise of each new class of computing technology has brought about even smaller and more ubiquitous systems. As this trend continues, wireless sensor networks (WSNs) are widely perceived as the new frontier of computing technology for a variety of applications, including environmental, infrastructure, and health monitoring. Many of these applications, however, require sensor nodes with both long lifetimes and small volumes, resulting in highly energy-constrained systems. Because energy sources, such as a battery and solar cell, have been slow to improve, energy must instead be conserved through better circuit design and systems analysis. While significant progress has been made in low-power processors and timers, wireless synchronization and communication remain the highest energy tasks in a wireless sensor node.

In this dissertation, the design of three RF integrated circuits is presented to address challenges associated with synchronization and communication in WSNs. Two of these circuit designs demonstrate a new type of receiver for harvesting a digital clock from ambient wireless signals for the synchronization of a WSN. The first receiver extracts a clock from the GSM standard while the other extracts a clock from the CDMA standard. Both receivers are designed with a low-power sleep-state so they can be duty-cycled to further conserve synchronization energy. Several other wireless standards also are investigated for their potential as a harvested-clock source.

The third circuit design demonstrates a 10GHz IR-UWB receiver for cubic-mm sensor nodes based on a new communication protocol which is also presented. The protocol enables the duty-cycled operation of a communication radio in severely energy-constrained systems and takes into account system-level challenges like battery limitations and clock accuracy. Based on this analysis, a receiver architecture was developed that satisfies all of the constraints for a cubic-mm system.