By ATN
Author: Manuel Del Castillo, VP Business Development, Focal Point Positioning
Why is there a need for better GNSS receiver technologies?
Have you ever noticed your satnav playing up when you’re driving through woodland? If so, you’ve experienced one of the technical challenges facing designers of advanced driver-assist systems (ADAS), and one of the engineering roadblocks on the journey to mass-market hands-free driving.
For the continuing evolution of hands-free driving, existing GPS technologies are no longer fit for purpose. Also, there is a greater demand for advanced navigation solutions—such as 3D mapping and predictive analytics—that can help autonomous vehicles (AVs) navigate complex environments more efficiently and safely. To overcome the challenges and restrictions of existing GPS technologies, automotive manufacturers need to overcome a big issue: multipath.
Multipathing can occur in any environment whereby obstacles such as buildings, trees, even mountains can ‘bounce’ GPS signals before reaching the receiver, creating multiple signal paths. This can cause errors in the GPS position calculation, which can be particularly problematic for AVs, where accurate positioning is critical for safe and reliable operation. The receiver may calculate the position based on the wrong set of signals or be unable to determine which signals to use accurately.
To overcome multipathing and the restrictions of GPS in delivering high-level accuracy of location that enables safe, hands-free driving, a reliable, high-precision source of position is required, and Global Navigation Satellite Systems (GNSS) based positioning is the only globally available technology that can provide it. (GNSS includes the original GPS, GLONASS, Galileo, and BeiDou).
A faint signal made even fainter: The challenge of signal attenuation
The problem is that GNSS signals are only as powerful as a 45-watt lightbulb, so any obstruction can make it harder for a receiver to pick them up. Buildings can block them completely, just like the glow from a dim light can be blocked by a blackout curtain. With foliage they can still pass through, but the effect is like a thin curtain making a dim light even dimmer.
Signal attenuation is also an issue when the radio frequency (RF) environment around the receiver is particularly noisy. RF noise can be much stronger than even normal-strength signals, whether it’s noise from other components near the receiver, 4G or 5G cell towers by the roadside, or deliberate interference from GPS signal jammers. Imagine trying to make out a dim light through a thin curtain when you’re in a brightly-lit room, and you get an idea of the challenge.
Receiver sensitivity is a critical consideration for ADAS developers
The problem of signal attenuation must be addressed if hands-free driving is to become safe for use everywhere. Designers and developers of ADAS systems must ensure that the GNSS receiver has the requisite levels of sensitivity, measured in decibel-milliwatts (dBm), to distinguish faint signals.
If the receiver does not have the requisite sensitivity, the positioning system may not always meet the parameters set out in the system’s performance specification, including:
Time to first fix (TTFF): The GNSS receiver in the ADAS system needs to establish where on the Earth’s surface it is, both when the vehicle is first started and when it is exiting from an area with no GNSS coverage, like a garage or underground car park. If there is overhead foliage or noise in the environment, the time to first fix may be longer than set out in the performance specification.
Tracking sensitivity: For hands-free driving, the GNSS receiver needs to maintain a continuous lock on to GNSS signals, even in areas where the signal is attenuated. If the receiver loses lock due to the signals being too faint, the vehicle risks being unable to establish an absolute position until the signal is reacquired.
Position accuracy: In real-world conditions there is often a sliding scale of effects when the vehicle encounters areas of weak signal. Rather than suddenly losing lock and being unable to estimate a position, the weak signals may first cause the receiver to estimate an erroneous position. Such a scenario creates obvious risks that need to be mitigated for hands-free driving.
In response to the demands of automotive OEM’s (original equipment manufacturers), including General Motors, FocalPoint works with the supply chain (including chip makers, ADAS designers etc) to integrate, S-GNSS, powered by Supercorrelation technology – a chipset-level software solution offering improved sensitivity, accuracy, and integrity via its unique capability of determining the angle-of-arrival of satellite signals.
Based on the existing Android open-source interfaces, the S-GNSS API will allow a normal GNSS chipset to run S-GNSS in a separate external host processor. With this additional software added to the GNSS chipset, the overall system can get the performance improvements necessary to upgrade the GNSS receiver to a S-GNSS receiver and offer enhanced positional capabilities.
For more GNSS receiver news, click here.
