One of the biggest challenges for satellite based positioning is mitigating the effects of multipath interference and non-line-of-sight (NLOS) signals, particularly in urban environments.
The Supercorrelation technology developed by UK-based Focal Point Positioning, already described in the pages of InsideGNSS, confronts the problem by performing long coherent integration, wherein the receiver antenna is moved in a complex way, boosting sensitivity towards line-of-sight (LOS) signals while suppressing unwanted signals.
Speaking at a presentation of the NAVISP-funded project ‘Real-time S-GNSS Receiver’, Focal Point Vice President Business Development Miguel del Castillo said, “The value of Supercorrelation is not about improving the minimum receiver sensitivity, i.e. tracking really low power signals, but decreasing the codephase and doppler error of signals mildly attenuated, either by a concealed antenna or by foliage, or by a sound wall, and therefore improving line-on-the-map accuracy.”
For the ‘Real-time S-GNSS Receiver’ project, Focal Point used a new S-GNSS receiver to assess the performance benefits of Supercorrelation in driving trials conducted in a deep urban canyon setting, specifically in London’s Canary Wharf, using a purpose-built hardware-and-software platform. The tests revealed significant accuracy improvements in measurement, including pseudorange and Doppler, and in position and velocity.
Focal Point also demonstrated its new Skyscan technology, which enables signals received via a single-element antenna to be decomposed into LOS and NLOS components and mapped onto an azimuth and elevation plot, thereby revealing the signal strength and directions-of-arrival of the various signal components.
In situ trials
“With GNSS, in cities, reflected signals dominate or interfere with the true line-of-sight (LOS) signals,” said Focal Point Technical Project Lead Javier Garcia, “and receivers cannot rely on power level to distinguish between LOS and NLOS. We developed a complete S-GNSS receiver, which is designed to get around these problems, and then evaluated its performance, using live data recordings, captured using a custom-built trials system.”
The test hardware setup comprised a Novatel PwrPak7 OEM7720 GNSS Receiver, Novatel SPAN IMU ISA-100C (200 Hz), two Novatel GNSS-850 antennas and the FocalPoint S-GNSS Receiver. The multi-band, multi-constellation u-blox F9T was also used as a reference commercial GNSS receiver.
“Our live data results demonstrated significant improvements in terms of raw measurements and PVT accuracy provided by Supercorrelation,” said Garcia. “With S-GNSS, positioning accuracy was within less than one meter of ground truth, all along a complex route at Canary Wharf, while the non-S-GNSS solution was 5-plus meters off on that same route.”
“S-GNSS potentially solves the complexities of accurate and safe GNSS positioning in challenging environments,” said Castillo, “including in demanding autonomous car applications. And with our results we also see that S-GNSS can provide resilience against RF interference or spoofing attacks, enhancing cyber-security.”
‘Real-time S-GNSS Receiver’ was funded under the European Space Agency’s NAVISP program, aimed at advancing GNSS- and non-GNSS-based positioning, navigation and timing solutions in participating member states.
