Connect the Dots: Low Power Makes GPS for Assets and Wearables, Bearable

Create: 09/18/2017 - 19:10

Mobile World Congress started in Barcelona way back in the early days of cellular communications and was and remains the go-to event for everything to do with smartphones, from semiconductors to software and hard technology to soft-touch partnership building. It is now also consumed (and conflated) with the IoT.

At its inaugural U.S. event in San Francisco last week, both 5G and IoT were dominant themes, with demonstrations of IoT-based ideas, and major announcements by carriers of their pursuit of long-range cellular-based IoT technologies such as NB-IoT and LTE-M.

The event was somewhat eclipsed by Apple’s little affair a few miles south in The Valley, but both had a common IoT theme: low-power wearables. In Apple’s case it still comes in the form of the Apple Watch, but that’s a narrow interpretation of what form-factor wearables will take as the power required by specific functions falls, dramatically (Figure 1).

Figure 1: The form factor and utility of wearables is tied to power consumption. Adding geo-tracking just got easier. (Image source: u-blox)

As power consumption for data communication, information processing and data gathering falls, wearable devices can either do more, take smaller forms, or both. One parameter that haunts designers of wearables, and any IoT device or sensor, is getting an accurate location while they are constantly moving, without sucking all the battery power.

In many respects, cellular operators have an advantage in that they can use their networks to provide pretty accurate location sensing through triangulation over longer distances than say, LoRaWAN, Sigfox, Wi-Fi or Zigbee. Bluetooth doesn’t really count, unless it’s for ultra-short distances, a matter of meters, using beacons.

The ultimate outdoor location-tracking technology is GPS, or global navigation satellite service (GNSS). Alas, that tends to consume more power than most wearables or remote IoT sensing devices can tolerate, or at least it used to.

GNSS Sucks Power. Or Does It?

The figures on GNSS power consumption are hard to nail down, as it’s such a competitive environment. Just ask Broadcom, Telit or u-blox. Power consumption is also dependent upon many variables, including the type of GNSS used, duty cycle, sensitivity requirements and whether or not it uses assisted-GPS techniques.

This is why it was so refreshing to see u-blox actually put a figure on power consumption for its new ZOE-M8B GNSS system-in-package (SiP) announced last week (Figure 2). In its Super-Efficient (Super-E) mode, it consumes 12 mW, in a package that measures 4.5 x 4.5 x 1.0 mm.

Figure 2: The ZOE-M8B SiP brings low-power, small-footprint geo-tracking to IoT and wearable applications. (Image source: u-blox)

Targeting fitness monitors and trackers, the ZOE-M8B helps fill the need for multi-purpose health monitors that can do all the monitoring of heart rate, ambient condition, calories burned of a typical monitor, while also being able to add precise location information.

While accelerometers can help track relative position and give a good estimate of distance travelled based on motion, only a GNSS-based tracking system can return users to a given location, log hiking or biking trips, and give geographical context. As interesting as these features may be, designers have been reluctant to add GNSS capability due to the power and space these devices consume. That’s why u-blox is happy to discuss the power consumption figure: 12 mW is low, up to 2.5x lower than the company’s previous M8 generation.

That said, an IoT solution provider needs to be careful to look at the conditions under which that low power consumption is achieved (Figure 3).

Figure 3: The M8B operates with the popular GPS technologies, but when comparing, look for support features such as data batching. (Image source: u-blox)

For example, 12 mW is when it is operated with concurrent GNSS reception in full power mode at 1 Hz. The average power over a typical 30-minute track, will be as low as 25 mW, using AssistedNow Offline data and industrial antenna with moderate-to-low signal levels.

Power management functionality features are also critical, and the M8B supports data batching, which gathers data without having to constantly run the main controller, so it can be sent when needed.

Cellular and Absolute Positioning Add to IoT’s Utility

Adding absolute positioning capability to IoT devices using GPS is not as prohibitive as it used to be, thanks to devices such as u-blox’s M8B, but there is still a trade-off that needs to be accounted for in terms of cost and complexity, along with additional space and power. However, the ability to provide absolute position information to any remote device, wearable or asset based, may now be worth giving GNSS a second look. 

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Patrick Mannion
Patrick Mannion is an independent writer and content consultant who has been working in, studying, and writing about engineering and technology for over 25 years.

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