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Wireless sensor networks (WSNs) have the potential to radically improve our lives by pervasive environmental monitoring in many applications. However, there are many applications that would be ideal for WSNs, but where reportable events occur with long (days, weeks) or unpredictable durations between occurrences. These uses are hampered by the high energy and latency costs of always-on and periodic wakeup networks, which waste energy on node synchronization and idle monitoring of the RF channel, and exhibit unacceptably high latency for urgent events, e.g., alarms. This thesis proposes, designs, assembles and tests, in a multi-hop WSN test bed, a wakeup receiver (WUR) and associated medium access control (MAC) protocol that can be added to WSNs to make the communications functionality of the network “on-demand”. When not required to communicate, a node’s main radio is shut down, while the wakeup radio remains active, consuming 1.85μW to continuously monitor for wakeup signals. Each node has a transmitter to broadcast the wakeup signal to adjacent nodes and establish communications when required. -40dBm of sensitivity was measured on assembled receiver prototypes, allowing wakeup ranges up to 15 feet with low-power -10dBm 433MHz testing transmitters and a predicted 90 feet with +10dBm transmitters. The WUR prototypes were successfully tested in a multi-hop WSN, becoming the first known example of incorporating fully functional WURs into a multi-hop network. Latency of one second per hop was measured when waking from deep sleep. WSN node energy consumption decreased as much as 1500-fold compared to always-on WSNs, and 15-fold compared to typical periodic wakeup WSNs when 10 hours occurs between wakeup events. At shorter wakeup intervals, the energy improvements are reduced, with performance equivalent to a 1% duty cycle periodic wakeup network at approximately 10 minutes of mean time between wakeup events. The MAC protocol developed to support WSN wake-on-demand allows basic demonstration and performance testing and establishes a foundation for future refinement of wakeup-based MAC protocols.
Advisor: Hamid Sharif-Kashani