What do asset trackers, pet finders, fitness wearables, cycling computers, and smartphones have in common? One similarity is that they all use GNSS for positioning and navigation. Another is that they can’t support positioning and navigation when their battery is dead.
Hence the challenge for device OEMs, which must balance the need for timely location information with the need for long battery life. One option is duty cycling. Instead of running the GNSS receiver continuously, this technique powers it on only at specific intervals based on the application requirements.
For example, an asset tracker on a shipping container might be configured to power on the GNSS receiver once a hour, while a fitness wearable might be once every 10 seconds. If the device has an accelerometer, then a related option is intelligent duty cycling, which powers up the GNSS receiver only when a significant amount of motion is detected. Intelligent duty cycling can be a good fit for pet trackers because cats are motionless much of the day, sleeping an average of 12-16 hours.
Assisted-GNSS (A-GNSS) is another option. By using a small amount of cellular data to download current satellite almanac and ephemeris data, the receiver can get a “hot start,” thus reducing its Time-To-First-Fix (TTFF) from ~30 seconds to 1-2 seconds. This allows for shorter, more power-efficient fix attempts.
How to Power-Optimize Your GNSS Antenna Selection and Integration
A high-performance GNSS antenna arguably is the most powerful option for balancing battery life and granularity. In fact, a GNSS antenna complements duty cycling and A-GNSS by ensuring that whenever the receiver is on, it has high-quality signals to work with. That means the receiver doesn’t have to work as hard and thus doesn’t have to draw as much power.
But some GNSS antennas maximize these benefits. When comparing antennas, the top three specs to focus on are:
- Efficiency: A highly efficient antenna delivers more of the received power, meaning the receiver’s Low-Noise Amplifier (LNA) doesn’t need as much gain (and thus, power) to achieve the same signal level.
- System Noise Figure: A well-designed RF front-end (antenna + filter + LNA) with a low noise figure improves the Signal-to-Noise Ratio (SNR). A better SNR can allow the receiver to operate reliably in weaker signal conditions without increasing transmission power.
- Interference Rejection: Interference from transceivers (e.g., cellular) on or near the device forces the GNSS receiver to use more power to decipher the signal it needs. Integrating filters directly into the antenna module is a proven method to reduce this power drain.
Power-Efficient GNSS Chipsets and Cloud Offload
Not all GNSS receivers are created equal. Many newer chipsets are designed specifically for IoT applications that require ultra-low power modes:
- Acquisition vs. Tracking Current: Power consumption is highest during the satellite acquisition phase. Look for chipsets with low current in both modes.
- Power Save Modes: Many modern ICs offer a “supervised” or “trickle-power” mode where most of the receiver is shut off, but a tiny portion remains active to keep the oscillator warm. This drastically reduces TTFF on the next wake-up cycle.
Cloud/edge computing is another option. This offloads the task of processing location data to the cloud so the device doesn’t have to use its power, thus extending battery life. The device can be configured to collect raw GNSS data (pseudoranges) and send small packets of this data to the cloud for position calculation.
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