Under ideal conditions, satellite signals from a Global Navigation Satellite System (GNSS) arrive at an antenna without any loss of integrity, providing the perfect position measurement. Increasing amount of wireless communication infrastructure on the ground and in space, however, create interference environments and impact the GNSS’s signal tracking and positioning capabilities.
Reference station operators or users trusting GNSS for reference station and monitoring applications need to rely on reliable continuous GNSS operation. Monitoring networks and reference stations cannot be easily moved around to avoid negative impact from RF interference.
To reliably operate in areas of interference, users need the right tools at hand to identify if and what kind of interference might be present to mitigate signal interference and jamming.
Public sector, private land surveying, asset collection and resource management professionals require receivers that are maximally resistant to interference to continue offering their data and services with no – or just minor- degradation.
Eliminating interference impact
If interference is present, users need their equipment to detect when interference is present and a solution to mitigate it. Unlike any other reference station receiver, the Leica GR/GM-Series with RefWorx 4.20 can effectively mitigate signal interference ensuring continuous and reliable service operation, even in demanding radio frequency (RF) environments.
Leica Geosystems RefWorx 4.20, with new functionality for RF spectrum analysis and interference mitigation for the GR/GM-Series, allows station operators to provide continued Real Time Positional Services at a performance level the community expects and have improved performance for the CORS Real Time Network.
Gaining insights into the frequency spectrum
For any application in though environments, professionals need insights on the frequency power spectrum, including all desired as well as undesired signals. Companies looking for undesired behaviours and limited performance with their reference stations can easily troubleshoot interference problems instead of bringing external equipment and spending time and money investigating potential reasons and analysing raw data.
With the new Leica RefWorx Interference ToolBox users can easily determine if there is an interference signal within the GNSS signal band with graphically displayed (plotted) information. The enhanced Leica SmartTrack+ technology now continually measures the radio frequency (RF) spectrum within and around the GNSS signal bands observed by the GNSS receiver. The solution, furthermore, is designed to automatically detect and alert the user about potential signal interference.
The Interference ToolBox allows real-time remote connection to the GNSS receiver, from anywhere at any time. Customers can easily share frequency spectrum information for post-processing with other colleagues, scientists or Leica Geosystems support team for assistance.
Figure 1 – The image shows the Interference ToolBox desktop software for spectrum analysis with real-time remote receiver connectivity and integrated logging and replay for post-analysis capability. The graph shows L1-Band spectrum (pre-decimation) with GPS L1 signal spectrum (post-decimation), with no interference present and no filters applied.
Figure 2 – The picture shows the power spectrum on the GPS L1 band. The top plot is showing the full spectrum, and the bottom plot is showing a pass band around GPS L1 frequency, i.e. 1575.42 MHz. It can be clearly seen that there is an interference signal around 1578.7 MHz. This is very close to the GPS L1 frequency and can have severe consequences on the tracking performance of the receiver. This interference also impacts GAL E1 signal, because it transmits at the same frequency as GPS L1. In this case, the interference signal was not transmitted all the time, it appears for some period then disappears.
Figure 3 – Same GPS L1 data plot, with a notch filter applied. The two pictures show the notch filter on the L1 band wideband Itop) and around GPS L1 passband (bottom). RefWorx Interference Toolbox allowed to detect that there was a strong interference near GPS L1. With the new Interference Mitigation capabilities enabled, the tracking performance increased by 12,5%, the number of loss lock decreased by 24%, and SNR on GPS L1 increased by an average of almost 4 dB.
Mitigating interference signals
To further reduce or eliminate the impact on GNSS tracking, the new solution offers industry-unique High Dynamic Range (HDR) mode, as well as programmable Bandpass and Notch filters.
The HDR mode is a powerful mitigation tool, allowing the receiver to perform equivalently under interference as it does when no interference is present. It increases the signal power and linearity specific to a selected band. When applied, a centimetre level RTK solution can become available, when no solution at all was possible in the case of an out of band wideband interferer without enabling HDR mode. Whilst, in case of in-band CW (continuous wave) interference, the flexible combination of the notch filter and HDR mode allows high-performance levels. The notch filter alone is useful when the CW interferer is weak, but when the interferer is strong enough to cause distortion across the pass band, the increased linearity provided by HDR mode is key for the notch filter to be able to cleanly suppress the CW interferer. The bandpass filter effectively eliminates disruptive impacts of near-band interferers.
Full GNSS positioning solution
The new RefWorx 4.20 solution maintains continuous GNSS multi-frequency operation even in challenging RF environments with SmartTrack+. The Interference Toolbox provides insights on the frequency power spectrum as is seen by the receiver, including all desired as well as undesired signals, allowing users to easily identify and remove manually potential interference signals or enable automatic intelligent interference detection and mitigation.
With an effective RF interference mitigation solution:
- Users deliver high quality and continuous data to his application or service.
- There is no need to build on-site physical protection (stealth/shielding) against local interferes.
- There is no need to move the station to another location in case the source of interference cannot be identified and stopped or protection be built up against it.
The outlined benefits save time and cost, maximising performance and efficiency, positioning navigation and timing.
Join SmartTrack+ Interference Mitigation & Toolbox Webinar on May 29th 2018, 13:30-14:30 CEST time. Click to register!
Pache Frank
Senior product manager for GNSS infrastructure solutions at Leica Geosystems