With the emergence of location tracking devices used to keep tabs on vaccines or many other critical supplies, there’s a need to keep energy requirements low.
The problem is that it takes plenty of energy for a device to receive location information in the Global Navigation Satellite System (GNSS) of which GPS is a part.
Now there are strategies that can reduce the energy needed by GNSS by 10 times or more, according to JP Norair, principal radio and firmware engineer at PCH International.
“GPS can be used in 2021 on devices that need to last months or years on a battery,” Norair told Fierce Electronics. He also spoke at a virtual forum as part of the Low Power Technologies Summit and his keynote video is here:
Norair has built energy designs for smartphones and other devices and has devised these three low-power strategies for design engineers:
- Rely on assisted GPS ephemeris data as part of a system architecture, if possible. It’s the best way to improve energy efficiency of a GPS/GNSS system, although the most involved. (Ephemeris data gives calculated positions of celestial objects, including GPS satellites, at regular intervals.)
- Without ephemeris data, it may be possible to store almanac data in a large flash memory chip. Predicted satellite orbitals can be stored for months or years.
- New vertical integration devices from vendors offer features that merge Wi-Fi access point detection with GPS. However, the device cost can be high and there may be lock-in to a cloud service provider.
Norair’s tips rely on reducing the time the receiver in a device spends searching for satellites, a period known as time to first fix (TTFF). It is the difference between when the receiver is activated and when the satellite information comes into it.
“Fortunately, there are ways to improve TTFF dramatically,” he said. Using ephemeris data, downloadable from the internet, can reduce a 30 to 60 second satellite discovering process down to 1 to 5 seconds, resulting in a big energy savings, he said. In one example, Norair suggested using a state-of-the-art receiver such as the mBlox M10 (20 mW active) or Sony CXD5610 (10 mW active).
The ephemeris data is only available for two to four hours on each download from a satellite, so each device must download the data on a regular basis.
Using ephemeris data in a low power wide area network (LP-WAN) requires planning for system and network requirements, which is not always possible, Norair said.
As his second tip, Norair said it is possible to obtain almanac data, basically tables of satellite locations--some calculated for years into the future. The satellite discovery process can be reduced to 2 to 10 seconds, still a big energy savings.
Norair’s third option is to use an edge device such as the Semtech LoRa-Edge GNSS+Wi-Fi location engine or one of several white label products also available. One disadvantage is that location is only known in the cloud, not on the device.
More solutions are emerging for low-power GNSS. Do not assume GNSS is too power-hungry for an application, Norair advised. “You can do GNSS on a coin cell. You can optimize your architecture,” he said.
Trackers for the supply chain will benefit from low-power approaches. “Supply-chain management isn’t new. I was building tech for the military supply chain 15 years ago,” Norair said. “But now there’s a big push towards commercial supply chain management. Now, the supply chain and IIoT are demanding a use case of ‘on demand’ location” where a query or a sensor event can trigger a device to acquire its location. Such events tend to be infrequent and Norair said he usually targets 10 events a day.
Commercial supply chain management use cases require a different approach than GPS for wearables, but engineers have begun addressing them recently, he added.
JP Norair’s low-power insights are part of his keynote and a panel discussion featured in the Low Power Technologies Summit, Feb. 16-17. Registration is free for the virtual event.
RELATED: How low can IoT power go? Good question.
As IoT devises proliferate, more eyes are on energy harvesting