Low-power sensor data over power lines

Researchers at the University of Washington and Georgia Tech have designed small ultra-low-power 27 MHz sensor nodes that transmit data to a receiver by coupling over the powerline. The sensor nodes consume less than 1 mW when transmitting (65 μW gets consumed in a custom CMOS transmitter). The researchers claim this is the lowest power transmitter to date compared to those found in traditional whole-home wireless systems.

In their SNUPI system (for Sensor Nodes Utilizing Powerline Infrastructure), only the base station receiver is wired directly to the powerline (i.e, plugged into an outlet). Each node in the sensor network transmits wireless signals that couple to nearby powerlines, creating signals that travel through the infrastructure to the base station receiver. This way, the sensor nodes can transmit at much lower power because signals only need to propagate to the nearest powerline.
The SNUPI wireless sensing platform includes an ultra-low-power 16-bit microcontroller, a 16-bit ADC, and a custom 27 MHz, 9.6 kbps frequency-shift-keying (FSK) wireless transmitter which consumes less than 1 mW. A custom transmit-only radio accounts for just 65 μW of the 1 mW, rendering its power consumption negligible when compared to the microcontroller.

The prototype of the SNUPI sensor node measures 3.8x3.8x1.4 cm and weighs 17 gm including the battery and antenna. A SNUPI node with a simple light sensor beaconing once per minute will dramatically outlive the 10 year shelf-life of its small 225 mAh coin-cell battery, researchers say.

To keep down power dissipation in the transmitter circuitry, researchers implemented the transmitter oscillator on a single silicon die using a 0.13 μm CMOS process, which resulted in only 65 μW of power for whole-home range.

Researchers say they tested their system for interference with other emerging powerline communication systems, such as HomePlug, and found no problems. They aim to commercialize the base technology, which they believe could be used as a platform for a variety of sensing systems. One area of particular interest is in health care. Medical monitoring needs a compact device that can sense pulse, blood pressure or other properties and beam the information back to a central database, without requiring patients to replace the batteries.

The researchers delivered a paper on their development at the Ubiquitous Computing conference in Copenhagen, Denmark: http://sockeye.cs.washington.edu/research/pubs/Cohn_SNUPI_ubicomp10.pdf