GNSS Galileo Code Receiver

Ref-Nr: TDO0014

Technology abstract

A Portuguese Aerospace Engineering company delivers advanced design solutions and turn-key space SW systems. The company offers Galileo Code Receiver - an advanced GNSS receiver targeting cost effective, high navigation accuracy (down to 20cm) requirements. The company is open to set up technology licensing agreements with end users and system integrators (OEM and Value Added Resellers) willing to take advantage of early access to the technology for new applications or improved systems.

Technology Description

Urban environments have rich GNSS reflected signals from buildings, trees, bridges and other objects multipath) which can contaminate Code and Carrier observables requiring the use of additional sensors, increasing costs and complexity. For surveying applications, existing high accuracy RTK receivers rely on carrier phase measurements, which under harsh environments can be a major difficulty due to cycle-slips. 
 
The navigation algorithms will use code measurements of the dual frequency receiver and extract the ionosphere effects using an innovative concept using the low noise properties of E5 AltBOC and combined with the with E1 MBOC signal to estimate the ionospheric delay. Such combination preserves the low noise properties of E5 AltBOC for use in the navigation solution and uses precise or broadcast RT orbits and clocks allows a RT high accuracy and robust positioning (7cm - 14 cm).
 
The following receiver characteristics can be highlighted:
- Fully configurable FPGA-based (Xilinx Virtex-6) 16-channel Galileo/GPS receiver (up to 160 real correlators)
- Embedded micro-processor 
- BPSK/BOC/CBOC/AltBOC signal processing: Galileo E1 CBOC, Galileo E5 AltBOC, GPS L1 C/A, GPS L1C and GPS L5
- Interfaces: PCIe, Ethernet, CAN, UART, JTAG, GPIO (FMC and header pins), SMA
- Supports both single and dual frequency RF front-end
- Digital IF/baseband signals with up to 4-bits
- Includes a software package (receiver monitoring and control, measurement post-processing, navigation)
 
Laboratory results so far indicate that the system could be used in applications requiring high accuracy positioning (few centimetre level) using code measurements instead of the traditional carrier phase measurements. Hence the name of the receiver: Galileo Code Receiver. This is possible thanks to an innovative combination of Galileo signals (more specifically AltBOC modulation in the E5 band with low noise characteristics and high robustness to multipath environments typical of urban environments) and dedicated navigation algorithms. The latter explores the low noise properties of the Galileo AltBOC code measurements combining then with Galileo signals on the E1 band for estimation of the ionospheric delays.
 
The receiver, today implemented in a FPGA, is currently undergoing tests with live Galileo signals (a total 4 satellites have already been launched out of a total of 30 in the complete constellation) and has already been successfully demonstrated in laboratory conditions using a hardware mock-up.
 
The current receiver mock-up can be made available for testing in the desired applications and its integration in the end-user platform requires simple physical mounting, an Ethernet port, an antenna and power supply.

Innovations & Advantages

GPS satellite navigation technologies has been powerful enabler of new products/applications and drivers of productivity gains in many economic activities. Still, high precision, real time dependable applications are still limited by the error prone GPS in many contexts, therefore making the use of GPS receivers either practically complex (and expensive) or even impossible. 
 
With the advent of GALILEO, the possibilities will greatly increase. The company developed a GPS/GALILEO receiver that brings navigation accuracy to the centimetre level. The innovative technology is able to extract from the GALILEO signal an extremely robust and precise navigation solution, even in demanding environments.
 
The receiver uses the Galileo E5 signal AltBOC modulation, offering ultra-low noise and multipath robust Code observables (versus Carrier phase observables, prone to discontinuities - cycle-slips - especially in urban environments). 
 
If real-time (RT) navigation is desired, the solution may involve expensive bulky high grade inertial sensors, ultra-sonic sensors, cameras or barometers. Otherwise, the solution involves post-processing techniques for smoothing navigation outputs.
 
These RT and non-RT solutions are suboptimal because:
• Unmanned Aerial Vehicles need to be cheap and light to operate in urban environments and with RT requirements, thus requiring a robust and accurate navigation solution. For infrastructure inspections using UAV (power lines, windpower generator rotor blades, etc.) we need to fly close to the monitored object;
• Even if RT capability is not required, existing GPS receiver manufacturers do not recommend the use of high precision GPS in urban environments or close to trees, thus the use of high quality inertial sensors for post-processing.

Further Information

Several technical publications can be made available upon request:
· Ismael Colomina  et al, “The Accuracy Potential of Galileo E5/E1 Pseudoranges for Surveying and Mapping”, Proceedings of the ION GNSS 2011
· Pedro Silva et al “Galileo AltBOC Signal Processing for Precise Positioning - Experimental Results”, Proceedings of the ION GNSS 2012

Current and Potential Domains of Application

Applications outside space:
DEIMOS Engenharia developed a TT project with this technology (for inspection of difficult to reach sites - building structures, windpower generators, high voltage electric towers), funded by the National Technology Transfer Initiative in Portugal (ptti.ipn.pt), though the transfer was already under study by the company. This Tech Description looks to support the TT and present the technology potential to other non-space applications.
 
GNSS high accuracy positioning for
- Guidance and control applications (UAV and other unmanned vehicles)
- Inspection of difficult to reach sites such as building structures, windpower generators, high voltage electric towers
- Agriculture imaging
- Surveillance autonomous missions in defined areas;
- Civil protection (Search & Rescue)
- Autonomous agro/forest equipment (tractors, cutters, lawnmowers, (e.g. golf courses, stadiums), etc)
- GNSS surveying in harsh environments (urban, dense forestry, remote rural settings)
 
Applications in space:
GNSS Reflectometry involves taking measurements from the reflections from the Earth of signals transmitted by GNSS satellites. It has been already demonstrated using GPS and allowing to measure moisture, snow dept and wave motion and windspeed of oceans. These applications can also benefit from more accurate measurements present in the E5 band. This is currently investigation by DEIMOS under a Portuguese national research initiative (POR-QREN) project called SARGO.