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

Författare

Nafiseh Seyed Mazloum

Summary, in English

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 significantly
reduce idle listening energy cost. In this thesis such a scheme is introduced and it is called DCW-MAC, an acronym for
duty-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 idealized
conditions. This analysis show that DCW-MAC has the potential to significantly reduce energy costs, compared to two
established reference schemes based only on low-power wake up receivers or duty-cycled listening. Findings motivate
further investigations and more detailed analysis of energy consumption. We do this in two separate steps, first concentrating
on the energy required to transmit wake-up beacons and later include all energy costs in the analysis. The more complete
analysis 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, energy
can 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 average
delays, making it possible to quickly evaluate how a different wake-up receiver characteristic influences what is possible to
achieve 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 many
low-power analog front-ends in literature. We also propose a a simple frame-work for comparing the relative merits of
analog front-ends for wake-up receivers, where we use the experiences gained about DCW-MAC energy consumption to
provide a simple relation between wake-up receiver/analog front-end properties and energy consumption for wide ranges of
scenario parameters. Using this tool it is possible to compare analog front-ends used in duty-cycled wake-up schemes, even
if 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 comprehensive
analysis of many of its important properties.

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