Late last year (2017), Broadcom - a manufacturer of GPS chipsets introduced the first dual frequency Global Navigation Satellite System (GNSS) chipset. This dual frequency receiving chip has the potential of improving consumer GPS accuracy from 5m to 30cm.
A Quick Background.
Consumer GPS and other GNSS rely on receiving a signal from orbiting satellites using a frequency known as the L1 Signal - 1575.42 MHz (10.23 MHz × 154).
Your GPS receiver uses this satellite signals to fix its distance from each satellite based on how long it takes the signal to go from satellite to receiver. It receives a minimum of three different satellite signals then computes your terrestrial position.
This is the frequency that GPS has operated on for over 2 decades. The addition of the L5 frequency band is part of the modernization of the GPS system.
This newer generation L5 frequency broadcasts consists of more complex signal at a different frequency and will be broadcast in conjunction to the legacy L1 signal. The L5 frequency has a higher transmission power, wider bandwidth and improved signal structure.
The L5 frequency will not only be used by the GPS system, but also by other GNSS in orbit - the European Galileo, and the Indian IRNSS and Japanese QZSS satellite systems.
OK. So now what?
Currently when a satellite's L1 signal is being received by a GPS receiver, the signal can reach the receiver directly, or indirectly by bouncing off buildings or canyons. The receiver calculates it's position based on the time that these signal took to reach the receiver from the satellite. As the direct and bounced signals arrive at different times and overlap, it results in lower accuracy as the receiver is looking for the peak of the signal to fix the signal arrival time. See the image below.
The newer dual frequency L1/L5 receiver will first lock on to the L1 signal, and then refine its positional computation using the L5. The L5 signal is so sharp that L5 signals don’t overlap with their reflections, so receivers can easily find the signal that arrives first. The receiver chip can effectively ignore any L5 signals after the first one it receives.
Why is this a thing now?
Up to now, there haven't been enough L5 capable satellites in orbit. 2015/2016 saw the addition of several L5 frequency capable satellites to earth's orbit. While the dual-frequency GPS has been used in commercial/industural applications such as in the oil and gas exploration industry, it hasn't been adopted in consumer based devices.
However, now there are enough orbiting satellites sending the both the L1 and L5 frequency (about 30 in orbit), with around 6-7 being visible at a position on a large portion of the globe, that it will be sufficient for mass market use.
What does this mean?
- Greater accuracy - Using the L5 signal, it can mean that accuracy can be improved to around 30cm compared with the current 3-5 meters with the L1 Signal
- Improved accuracy in cities, canyons and open areas - The L5 signal is less prone to reflections on buildings and other objects, so using both the L1 legacy signal and the L5 signal will greatly improve accuracy here.
- Improved battery life - as a result of improved accuracy "searching" for satellites, the receiver should consume less battery power in achieving a GPS lock. Broadcom are indicating that their dual frequency GNSS chipset will use less than half the power of their previous GNSS receivers. "current consumption during GNSS tracking can be lower than 5 mA,” claims Broadcom.
Hopefully some phones and devices will start sporting dual frequency GPS chips later in 2018. For the big phone brands, they are predominantly using integrated SoC (System on Chip) designs which incoporate the GNSS with the CPU (central processing unit) and GPU (Graphics Processing Unit). But hopefully it dual frequency GNSS will feature in newer models.
For dedicated GPS manufacturers like Garmin it might take a while to incorporate this into their receivers. They have been outpaced by smartphones for a while now. The consumer handheld GPS receiver market seems to be a fairly small market segment, and manufacturer's focus appears to be on their GPS watch range and their auto products. I still hold out hope that they incorporate these features into their devices sooner than later.