Duty-cycled Wake-up Schemes for Ultra-low Power Wireless Communications

Sammanfattning: In sensor network applications with low traffic intensity, idle channel listening is one of the main sources of energy waste.The use of a dedicated low-power wake-up receiver (WRx) which utilizes duty-cycled channel listening can significantlyreduce idle listening energy cost. In this thesis such a scheme is introduced and it is called DCW-MAC, an acronym forduty-cycled wake-up receiver based medium access control.We develop the concept in several steps, starting with an investigation into the properties of these schemes under idealizedconditions. This analysis show that DCW-MAC has the potential to significantly reduce energy costs, compared to twoestablished reference schemes based only on low-power wake up receivers or duty-cycled listening. Findings motivatefurther investigations and more detailed analysis of energy consumption. We do this in two separate steps, first concentratingon the energy required to transmit wake-up beacons and later include all energy costs in the analysis. The more completeanalysis makes it possible to optimize wake-up beacons and other DCW-MAC parameters, such as sleep and listen intervals,for minimal energy consumption. This shows how characteristics of the wake-up receiver influence how much, and if, energycan be saved and what the resulting average communication delays are. Being an analysis based on closed form expressions,rather than simulations, we can derive and verify good approximations of optimal energy consumption and resulting averagedelays, making it possible to quickly evaluate how a different wake-up receiver characteristic influences what is possible toachieve in different scenarios.In addition to the direct optimizations of the DCW-MAC scheme, we also provide a proof-of-concept in 65 nm CMOS,showing that the digital base-band needed to implement DCW-MAC has negligible energy consumption compared to manylow-power analog front-ends in literature. We also propose a a simple frame-work for comparing the relative merits ofanalog front-ends for wake-up receivers, where we use the experiences gained about DCW-MAC energy consumption toprovide a simple relation between wake-up receiver/analog front-end properties and energy consumption for wide ranges ofscenario parameters. Using this tool it is possible to compare analog front-ends used in duty-cycled wake-up schemes, evenif they are originally designed for different scenarios.In all, the thesis presents a new wake-up receiver scheme for low-power wireless sensor networks and provide a comprehensiveanalysis of many of its important properties.