Final Report Summary - PRECISIO (Professional Receiver via Software Radio)
PRECISIO is a collaborative research project that has received funding from the European Union’s Seventh Framework Programme (FP7/2007-2013) under grant agreement number 247683 (PRECISIO). The project is being conducted by a consortium of European organisations: Nottingham Scientific Ltd, GMV Aerospace and Defence, M3 Systems, JAST, Helios and the University of Nottingham. Originally a two year programme of work, the project started in January 2010. However, the project was extremely ambitious and numerous technical challenges were encountered. Two extensions were required with the eventual end date being in April 2013.
The PRECISIO concept is for a GNSS receiver to meet the challenges of today’s users which are:
• Sufficiently high-end to meet the needs of users.
• Multi-constellation capable.
• Multi-frequency capable.
• Upgradeable and flexible for new GNSS signals and services.
The approach to deliver such a receiver is to follow a Software Defined Radio (SDR) implementation, differing from a conventional GNSS receiver in that a minimum amount of hardware is required. The GNSS signals are collected by the antenna and sent to a radio frequency front end that digitises the received signal. All other receiver operations are performed by software which is either directly hosted on a processor in implemented within an FPGA. This SDR approach has the potential to deliver several key benefits to users and operators:
• ‘Future proof’ equipment against the uncertainty in GNSS signals and services.
• Reconfigurable and upgradeable equipment that can take advantage of future signals and services as they becomes available.
• Longer lifetime for installed equipment.
• Allowing for dynamic reconfiguration to an always-optimal processing chain in constrained environments.
• Dramatically reduced receiver costs.
• Potential for shared infrastructure for disparate markets and operations.
It was not possible to create an end-to-end prototype due to technical difficulties in all components. However, the project has been successful and extremely beneficial to all contributing parties. The major outputs are listed.
1. A detailed analysis of the markets and user requirements for a professional grade GNSS receiver based on software defined radio.
2. A comprehensive business plan and roadmap for the exploitation of a professional grade GNSS receiver.
3. The RF front end as two boards, an RF and digital. Comprehensive analysis of the performance, not only through the results but also through the re-examination of the designs to provide explanation. A series of lessons learned and future design and implementation recommendations has been produced.
4. The software defined receiver implemented on FPGA. Comprehensive testing of the data output from the system has taken place and operational validation. Again, a series of lessons learned and future design and implementation recommendations has been produced.
5. A multi-frequency conical spiral antenna has been built by a company new to the GNSS industry (with satellite communications experience). This has been tested in the laboratory and in the field where it has been compared against commercial alternatives. The results are particularly important for a new entrant into the GNSS market.
6. A Receiver Validation Tool capable of post-processing the RF front end output to provide data files for all of the major GNSS signals and frequencies. This provides an excellent test harness for the validation of future systems.
7. A comprehensive dissemination of the project, the technical challenges and obstacles, and the findings to the GNSS community. This included presentations at conferences in the UK, in Europe and in the United States.
Project Context and Objectives:
THE RATIONALE BEHIND THE PROJECT
PRECISIO concerns the development of a satellite navigation receiver capable of receiving and processing signals from multiple existing and future GNSS (eg GPS, GLONASS, Galileo, Compass). The project focused on technical risk reduction activities associated with the development of a software receiver. The ever increasing amount of processing power available in the next generation micro-processors enable computationally intensive signal processing algorithms to be performed in software where previously Application Specific Integrated Circuits (ASIC) would have been required. The rationale behind the SDR approach is make use of the emerging commercial of the shelf (COTS) processor hardware. The innovation is focussed on developing new signal processing algorithms, exploiting the flexibility afforded by a software approach compared to simply replicating existing hardware designs in software.
Software radio (“software receiver”) technology is state-of-the-art technology. It has the potential to revolutionise satellite navigation services. Software receivers enable satellite navigation services to be readily upgraded with a simple firmware upload, moving the industry and associated market from being product driven based on the sales of electronic devices, to being service oriented focussed on the provision of applications. Software receivers facilitate revenue generating value added commercial services making use of integrated satellite navigation, telecommunications and other services. As well as enabling service provision, it also allows services to be offered to users according to their location, reception environment, their context of operation and the services they have subscribed to. There are three governing reasons for initiating this work:
• The market for software-based receivers that can be reconfigured through firmware updates and software directives is well established in the Satellite TV domain, the same cognitive solutions are emerging in the 3rd generation mobile phone sector. The PRECISIO project team wish to gain the early starter initiative in the “GNSS” market. In particular the professional GNSS sector is already shifting toward service oriented business models as opposed to product sales or application sales. This is notable with the recent award for the UK DGNSS Recapitalisation Project which has been awarded on an installation and maintenance/support contract as opposed to a conventional product procurement.
• The GNSS applications currently being developed by PRECISIO team members are currently constrained by the functionality and performance of the existing hardware receiver platforms. Access to next generation cognitive software receiver technology will enable new applications to be developed and implemented by the project team without waiting for new receiver technology to appear from the traditional hardware receiver manufacturers.
• The increasing use of GNSS for high-performance demanding applications in more and more constrained environments (eg urban canyons, multipath environments, interference) raise the need for flexible receivers allowing to dynamic reconfiguration to always optimal processing chain (eg to provide short acquisition time for given applications, or very high accuracy, or even providing specific interference mitigation techniques).
Four of the project partners, NSL, M3 Systems, JAST and GMV wish to extend their capability in this technology for commercial reasons. The University of Nottingham wish to do so in an academic context and for HELIOS gain business knowledge of this new technology entrant.
The overarching objective of the PRECISIO project was to define, design, develop, validate and demonstrate a multi-constellation, multi-frequency, high-end prototype GNSS software receiver targeting the professional application markets. This PRECISIO high-end prototype will be based on software receiver technology and shall be a capable of receiving and processing signals from Galileo, GPS, GLONASS, Beidou/Compass and SBAS in real-time. These claims shall be confirmed through a validation and demonstration campaign.
The main objectives of this project were:
• Definition of the user requirements for the application.
• Definition of system requirements.
• Development of a system prototype.
• Demonstration/validation of the prototype by means of an extensive test campaign.
• Demonstration that the safety requirements for the application can be met by the system, by means of simulations, tests, modelling, etc.
• Development of roadmap and business case for the future implementation of the technology into the professional markets
The system prototype was to be developed from first principles with three main components, an RF front end, a software receiver and an antenna, being developed. Each of these had specific objectives, which were:
• Prototyping of a multipath suppression antenna element. This is a priority requirement for professional grade GNSS antenna/receiver equipment
• Prototyping of a multi-constellation, flexible multi-frequency RF Front end
• Prototyping of a multi-constellation, multi-frequency high-end software receiver
• Prototyping of a Receiver Validation Tool
The one objective that was not met during the project was the development of a system prototype due to difficulties encountered in the three main elements. They all faced unforeseen operational challenges that ultimately delayed the project and meant that the validation and testing campaigns had to be modified. However, extensive analysis took place and has been documented, with the findings being invaluable to the three technology providers (NSL, M3 Systems and JAST) in their future exploitation of the technologies. Some of the deliverables are also invaluable for future development, marketing and product placement. This includes the market analysis, user requirement gathering, a validation strategy against the full user requirements and the implementation plan.
The programme of work to develop the PRECISIO prototype has followed a classical engineering cycle and consisted of a series of seven major technical activities which cover the definition, research, design, development, validation and demonstration of the PRECISIO prototypes. These activities have been supported by three additional management, coordination and dissemination tasks which cover all matters that concern project coordination and control. The project also included a dedicated activity covering the development of an implementation plan. The work packages defined in the programme of work are:
WP1: User Analysis: Analysis of the user segment/target market and capture of the technical requirements for this market.
WP2: Technology Research: Architecture trade-offs for the hardware, software, algorithms and implementation components of the complete system.
WP3: Prototype Requirements: Determination of the Functional, Performance and Interface requirements to elaborate the prototype system specification.
WP4: Prototype Design: Developing the Architectural and Detailed design from the prototype requirements.
WP5: Prototype Development: Component part selection, procurement and acceptance, development, coding and testing, assembly, integration and test.
WP6: Prototype Validation: Component Integration and Validation testing, including simulation, laboratory, controlled and field trials. There is a feedback loop to the development phase in order to optimise the PRECISIO solution.
WP7: Implementation Plan: Determination of target users and markets, development of a business plan, pricing models and implementation roadmap.
WP8: Dissemination and Awareness: Promotion of PRECISIO at workshops, conferences, and demonstrations, development of web portal.
WP9: Coordination: Project coordination and interaction, providing support to the EC/GSA and others.
WP10: Management: Contractual, technical, risk and project management activities of the consortium.
DESCRIPTION OF WORK ACTIVITIES AND RESULTS FOR EACH WORK PACKAGE
WP1: USER ANALYSIS
WP1 was a three month activity led by HELIOS and involving NSL, GMV and the University of Nottingham. The output from this work package is ‘D3 - User Requirements and User Segment Analysis Document’.
The initial activity was to capture the user requirements for the fixed infrastructure markets. Led by the GNSS business consultancy experts, Helios, the activity involved all partners. The work drew on consortium knowledge and recent reports to isolate a set of specific markets for fixed infrastructure receivers and to determine a set of initial user requirements. The following markets were identified and analysed:
1. National reference networks: Set up by commercial companies or national mapping agencies providing realtime services for RTK-type survey operations.
2. International public infrastructure: Permanent receiver stations widely spread all over the world producing numerous different products, such as accurate GNSS satellite ephemeris and clocks, station geocentric coordinates, Earth rotation parameters, atmospheric products. For instance, IGS and EUREF fall into this category.
3. Global commercial service networks: Set-up by commercial companies proving real-time precise navigation typically through PPP techniques. The market is dominated by Fugro, Subsea-7 and C&CT/Navcom.
4. GNSS infrastructure: The backbone of the various worldwide GNSS systems, the ground infrastructure is funded and operated by the public and/or private sector.
5. Maritime DGNSS: The International Association of Lighthouse Authorities (IALA) maintains a network of stations to provide DGNSS services to maritime users as a navigation service. IALA organisations are typically government agencies or government-owned organisations.
6. Meteorology: Users in this market are typically the official national meteorological offices and institutes in each country and they often make use of the GNSS International public infrastructure.
7. Metrology networks: There are around 40 timing laboratories around the world that employ GNSS receivers for timing services They are almost exclusively public entities and/or national agencies.
8. Interference monitoring: Currently a military market, this is foreseen as a future civil market with the increasing reliance on GNSS receivers within government related applications (road charging, as an example).
9. Ionospheric monitoring: Typically Government initiatives, or international bodies using a collection of contributions from public and academic institutions. Two different objectives were identified; to monitor the Total Electron Content (TEC) and to monitor the rapid scintillation of radio waves as they pass through the ionosphere.
10. Payload/signal validation: Required by the owners and operators of GNSS, the receivers are used to validate satellite transmissions both from space and in testing environments.
11. Survey: This has been classified as the commercial operation that utilises reference stations on a temporary basis, typically for RTK-style surveying.
12. Rail: Train-borne equipment and not a primary market for PRECISIO but considered for future evolutions as the equipment requires a long refresh rate (10-15 years) and therefore ideally suited to SDR.
13. Automotive: Again a dynamic application so not of primary focus to PRECISIO, but considered for future evolutions due to the emerging requirements and their reliance on positioning technologies.
Each of the markets was characterised in terms of the users, the current equipment suppliers and the competitive environment within which they operate, the anticipated evolution of the market and, most importantly, the purchasing behaviour/characteristics of the customer. The particular GNSS technical priorities, non-technical considerations and commercial price points were identified, leading to a set user requirements. The content of this characterisation was enforced and verified through consultations with national mapping, maritime, commercial, rail and timing agencies and organisations.
The user requirements were consolidated into over 110 separate requirements, each mapped into the markets to which they apply. Individually there are too many to fully describe, but they can be summarised under the following general categories.
• Capable: Requirements concerning the GNSS and SBAS systems and signals that must be tracked.
• Flexible: The ability to upgrade to new and developing systems as the ICD becomes publically available
• Transparent: The use of accepted and open measurement processes and characteristics
• High quality: Stringent definitions for the quality of the main sub-components, for instance the antenna phase centre stability and the RMS of code and carrier measurements.
• Reconfigurable: The ability to reconfigure the major aspects of the receiver, for instance the correlation procedures, internal multipath mitigations and the tracking loops,
• Stable: To ensure that the receiver is stable with a long mean time between failure and a high availability. This is particularly important for the acceptance of the software receiver.
• Useful: The receiver must support the output formats required by the targeted markets, for instance RTCM (and RTCM-HP), RINEX v3 and 1pps outputs
• Viable: The receiver must compete in terms of price against the existing hardware counterparts which are becoming increasingly affordable. Commercial hardware equivalents are currently priced from $8,000.
The user requirements capture led to an initial rollout roadmap detailing the target markets and the requirements to be addressed in the prototype, subsequent production and future generation products. Due to the requirements (both technical and non-technical) and purchasing behaviour of the customer, the International Public Infrastructure, National Reference Networks, and Meteorology were identified as the most suited for the first PRECISIO production product. Further refinements of the product would later address the more specific markets that use specialised geodetic receivers tailored to individual applications or for qualification, and a second generation product would address the markets that are not using geodetic receivers but are able to use more standard professional receivers.
WP2: TECHNOLOGY RESEARCH
WP was a 3 month activity commencing at the end of WP1. Led by GMV, the work involved all partners apart from HELIOS. There was two parts to WP2, firstly a state of the art and gap anlaysis followed by an investigation, analysis and recommendation of a series of core technologies to be deployed within each component of the PRECISIO prototype. A brief summary of the findings from each of the six deliverables under this work package is provided below.
D4 The State of the Art and Gap Analysis
This study has been carried out in order to determine the capabilities and offerings of different suppliers in terms of hardware receivers and software defined receiver technology. This study addresses what is available and what is planned as compared to the requirements and the technological capabilities. In particular it analyses features, capabilities, limitations and expectations with respect to current products and technologies.
The report outlines the opportunity for PRECISIO to provide functionality and performances that address real world requirements and thereby create a real differentiator for the eventual product in the marketplace.
D5.1 Feasibility Study and Technology Trade-offs, Advanced Antenna Technology
The study has been completed examining a number of antenna solutions and multipath rejection techniques that can be used for navigation. All solutions have been assessed with respect to the User Requirements from WP1.
D5.2 Feasibility Study and Technology Trade-offs, Flexible RF Front End
The study examined the PRECISIO front-end requirements and then proposes three viable technical approaches to meet those requirements. From a commercial point of view, to guarantee minimum price, the alternative technical approaches made use of COTS sub-components.
D5.3 Feasibility Study and Technology Trade-offs, SW Receiver
The study looked at various alternative technologies for implementing the SW receiver culminating in best options recommendations for the various components
- Receiver core technologies:
- HW mapping best candidate:
- HW platform best candidates:
- Interface best candidates:
D5.4 Feasibility Study and Technology Trade-offs, Advanced Observables
The study resulted in a comprehensive document that focussed on new low-level observables (outputs from Correlators) and new observables from frequency combinations.
The first strand is the creation and application of new observables through access to the GNSS data at the correlators. For example, this includes new quality flags, Interference and jamming detection, multipath flags and/or ionospheric scintillation detection (important feature for monitoring the approaching solar maximum). The most promising candidates emerging from this study shall be implemented in the signal validation tool.
The second strand of this activity will include an assessment of advanced observable processing algorithms (eg new narrow lane, ionospheric free and wide lane observables) aiming primarily to obtain higher-order ionospheric delay estimates and improved ambiguity resolution. The results of this work will inform the receiver validation tool, however the implementation of the results in PRECISIO prototype will depend on whether these observables can be generated from the data received from the other GNSS receivers used within the validation and demonstration activities.
D5.5 Feasibility Study and Technology Trade-offs, Integration into Infrastructures
This study consolidated the user requirement has been filtered to exclude performance related requirements leaving those relevant to interface and integration into the various infrastructure networks. Additional requirements not explicitly mentioned in the D3 document, but which are relevant for interface and integration are also listed and discussed
WP3: PROTOTYPE REQUIREMENTS
WP3 was a two month activity led by M3 Systems and also including NSL, GMV and JAST. The purpose was to define the system requirements grouped under the following categories:
• Technical (functional, performance, interfaces)
• System & Operations (Size, Form and fixture, Parts, EMC , Vibration, Temperature, Power, Isolation, Accessibility, Downtime/reboot, Processing speeds/times)
• Product (quality, reliability, usability, efficiency, maintainability, portability, reusability)
• Implementation (Delivery, Documentation, Standards, Support, warranty)
• Security – (accessibility, vulnerabilities, hazards)
• Safety – (materials, disposals, special procedures)
• Verification – describing the means, methods and mechanisms for verifying compliance with the requirements.
As well as the categories, each technical requirement was given a full description, linked to the appropriate user requirement, prioritised, and given a target product phase.
D6 - PRECISIO Technical Requirement
The deliverable from the work package is ‘D6 - PRECISIO Technical Requirements’.
The 16 antenna technical requirements that were defined included
• The antenna must cover the L1 frequency band at 1575.42 MHz
• The antenna must cover the L2 frequency band at 1227.60 MHz
• The antenna must cover the L5a frequency band at 1176.45 MHz
• The antenna must cover the L5b frequency band at 1207.14 MHz
• The antenna performance must be guaranteed over the temperature range –30°C to +40°C
• The antenna performance must be guaranteed for any elevation angle between 0° to 90° and for any azimuth position
• The antenna polarization should be RHCP within each band listed in requirements
• The antenna RF interface must consist of an SMA connector
• The antenna power must be supplied with a 12 V DC interface
19 requirements were defined for the front end which included:
• The front-end should work with any external active antenna (including choke-ring)
• The front-end should be able to receive signals from all constellations, all frequencies
• The front-end should be future-proof against new signals and modulations coming in the GNSS spectrum
• The front-end should exhibit very small and very stable hardware delay
• The front-end should have a very good out-of-band rejection capability
• The receiver should provide very accurate phase measurements
• The front-end must allow a high accuracy of the time counter and a good timing stability
• The front-end should have low power consumption
The majority of requirements (143) were attributed to the software receiver subsystem. They were grouped according to the following:
• GNSS SIGNAL PROCESSING CAPABILITIES
• RAW MEASUREMENT PERFORMANCES
• SBAS INTEGRITY AND CORRECTIONS
• INTERFERNCE EFFECTS MITIGATION
• MULTIPATH EFFECTS MITIGATION
• TIME TO FIRST FIX
• INTERFACES (PHYSICAL / PROTOCOLS)
• OBSERVABLES / OUTPUT MEASUREMENTS
• SYSTEM AND OPERATIONS
• USER INTERFACE / CONFIGURABILITY
• AGNSS - ETERNAL AIDING
• PRECISE POSITIONNING
• DATA LOGGING
Many of these requirements were implicitly linked to another sub-system (ie antenna and/or front end) and therefore an additional field was populated to describe this link.
WP4: PROTOTYPE DESIGN
WP4 is the design definition for the three sub-components resulting in an architectural design document and design justification document for each. The three month activity was led by M3 Systems and also involved JAST and NSL.
D7.1 and 8.1 EBB Preliminary Design and Test Plan
For the antenna, the effort of this preliminary design phase was focused on the choice and the evaluation of the performance of the antenna element. Given the technical requirements and the outcome of the last meeting, the critical functions to be fulfilled by this element are as follows:
Guarantee the coverage of the frequency bands of interest – L1, L2, L5a and L5b bands – as well as providing a possibility to easily upgrade to new bands, depending on future market evolution – e.g. the E6 band.
Guarantee the coverage for elevation angles ranging from horizon to zenith – 0° to 90°.
Provide a phase centre stability allowing adequate performance of the system for all bands and elevation angles listed above.
Two possible candidates were presented during the last meeting, both with advantages and disadvantages: the helix and the Archimedean spiral antenna. The effort was thus put on combining the performance of these two structures to achieve optimal performance.
The design stage create a complete 3D model of the structure that could be fully parameterized for progressively modifing the antenna from a standard Archimedean spiral antenna to a conical spiral antenna with the desired performance. The parameters were optimised for the application through theoretical performance analysis. The architecture was given, alongside a test plan.
D7.2 Design Justification File Flexible RF Front End
D8.2 ADD for Flexible RF Front End
For the RF Front End, the work package concentrated on the selection of the component parts that make up the front end. Two separate boards were used, the RF side containing the filter block and amplifiers, and the digital board that contained the ADC, clock, FPGA and I/Os. Alternatives for each of these components were considered and a final selection made.
The architectural design provided a detailed description/design of the data flow, the sub-system and system interfaces, the physical design and test methodologies.
D7.3 Design Justification File for the Software Receiver
D8.3 Architectural Design Document for the Software Receiver
The Design Justification File of the SW Receiver sub-system took as inputs the System Requirements for the PRECISIO prototype developed as part of the WP3 of the project, coupled with the constraints and innovations identified within the Technology Research activities as part of WP2.
The architectural design detailed the Functional Architecture Definition, Algorithm, Software and Hardware Specifications, and the Interface Definition.
WP5: PROTOTYPE DEVELOPMENT
WP5 was planned to be a 7 month activity, led by NSL and also involving M3 Systems and JAST. The deliverables were the sub-system prototypes and a report deliverable (D12.4) on the signal validation tool.
WP5 took much longer than expected with all component parts experiencing several difficulties. It also proved to be a rather iterative work package, in that the component parts were built but during sub-system testing, errors were identified that meant a re-design or, due to risk mitigation, an alternative approach found. Two extensions were requested during this work package which ultimately lasted 25 months.
The consortium antenna specialists, JAST, have analysed various antenna characteristics through the examination of a number of antenna solutions that have been used for navigation. There are a large variety of elements (including a turnstile, vertical monopole, patch, spiral, and helix), many of which are suitable for PRECISIO when considered in terms of quality of polarisation; bandwidth (for multiband applications), radiation pattern shape, and suitability for use in an antenna array. The most flexible element is the microstrip patch, but this is somewhat misleading since ‘microstrip patch’ covers a large variety of designs: two different patch designs might be more different in behaviour than a flat spiral and a quadrifilar helix are, for example. The best intrinsic properties are offered by the various kinds of helices.
The main multipath rejection techniques that have been considered are: 1) specially designed ground planes, 2) vertical (endfire) array with fixed beamshaping, and 3) digital (adaptive) beamforming. The latter has been ruled out because of complexity, lack of integration with the receiver and uncertain phase characteristics that may place an extraordinary burden on calibration.
Any of the aforementioned element designs may in principle be fitted with a choke ring or other multipath-rejecting ground plane. This offers great flexibility, but the addition of a ground plane is never a straight improvement; it modifies the phase and polarization properties of the element and so the new assembly requires a complete, separate characterization.
Most of the elements are not suitable as elements in a vertical endfire array. In the examples found in the literature study, turnstile elements and specially folded dipoles have been used; these can be considered as dipoles with different feeding arrangements. Flat spirals also seem suitable in principle, if mechanically less flexible. The design of such an array requires that the design of the elements be an integral part of it.
The selected design consists of a single antenna element featuring broadband characteristics and improved low elevation performance. 3D optimization of the structure of the antenna has been carried out to guaranteed regularity and symmetry in the radiation pattern.
The design of the antenna makes it possible to work with and without its choke ring ground plane, which will be easily removable when size and weight constraints are to be considered with respect to intrinsic performance. Indeed, the absence of choke ring penalizes performance at low elevation angle (multi-path rejection and polarization) whereas it has no impact of on performances at higher elevation angles.
The PRECISIO RF FE was built by NSL. The role of the RF FE is to isolate, amplify and digitise the lower and upper RNSS bands so to include GPS L1/L2C/L5, Galileo GIOVE/IOV/FOC, GLONASS G1/G2 and COMPASS B1, B2 signals. Within PRECISIO different architectures have been considered, the multi-channel super-heterodyne, multi-channel homodyne (direct conversion) and the direct band-pass sampling method. When examining all options, it is essential from commercial point of view, that COTS components are used to guarantee minimum price.
The heterodyne and homodyne methods were discounted as they require multiple narrow band FEs which may prove difficult to tune, their poor power consumption, the lack of availability of components capable of covering Galileo E5 AltBOC signals, and the general difficulty and complexity of the design. The preferred method is the use of direct band-pass sampling that uses one RF chain for all GNSS frequencies. The method also presents the best trade-off between cost of the materials and elegance of the solution.
The front-end was composed of two separate PCB boards to be stacked on top of each other and enclosed into a RF shielded enclosure. The RF board carries all the RF chain, comprising COTS amplifiers/attenuators and bespoke dual band-pass filters. Tuning of the RF chain with spectrum and network analyzers will be done to ensure good amplification linearity and stability, as well as rejection of the out-of-band signals.
The digital board includes a high-speed ADC, a low noise clock synthesizer and distribution chip, a low-cost FPGA for signal conditioning and logic level translation, and various interfaces to the external modules (GigE, USBHS, LVDS). The sampling frequency selected for Precisio is 540 MHz which is a good trade-off between band separation guarding, ease of generation using the selected clock synthesis devices and the data rate supported by the FPGA device performing the digital signal conditioning.
In order to ensure that the proposed design is viable and to ensure that the out-of band-rejection does not fold into the digitised bands, an iterative design, prototype build and evaluate process has been undertaken.
The design considerations for the software receiver have been undertaken by the topic experts, M3 Systems. A trade-off between the use of general purpose microprocessor-based, DSP-based and FPGA-based architectures has been made to ensure the most appropriate solution for PRECISIO. The digital signal processing for this type of product is complex as it must accommodate all GNSS signals and provide optimal processing architectures for BOC, MBOC and ALTBOC modulated signals. Added to this, the software receiver must consider the required high level of performance and robustness/stability in terms of interference robustness and mitigation, multipath mitigation, integrity capabilities, complete re-configurability and upgradability capabilities, and the support of various interfaces.
The functional architecture of the receiver is built around the following main functional blocs:
1. the signal processing functional blocs, composed by:
• the Channel Switching and Data formatting stage, consisting in formatting the raw data flow coming from the Front-End;
• the Interference Mitigation stage, including time and frequency domains signal processing techniques aiming at mitigate performance deteriorations due to the presence of interference signals into the GNSS frequency bandwidths;
• the signal Detection and Acquisition stage, implementing massive parallel FFT-based correlators leading to very quick signal acquisition time;
• the signal Tracking stage, implementing several channels of DLL, FLL and PLL in order to provide raw phase measurements on each received signals
• the Navigation Data Demodulation stage, aiming at extracting the raw data but also navigation message parameters
• the PVT module, providing a GPS PVT solution in order to date the raw measurements and to provide a 1_PPS signal to the user
2. the raw observables recorder, capturing the receiver observables including at least :
• code phase measurements (smoothed or unsmoothed),
• carrier phase measurements (accumulated Doppler from satellite acquisition),
• signal C/N0 ratio
• code carrier phase coherency indicator
• Receiver channel status
• Raw measurement time
• Constellation and Satellite ID
3. the I/O controller, including physical and software drivers needed to interface the Receiver with :
• local and global networks via ETHERNET
• USB devices (keyboard and mouse for HMI, external data storage units)
• a screen (HDMI interface) for HMI
• standard RS232 devices
4. the receiver main controller, which implements the main sequencer and all the control / command functions of the receiver;
5. the User interface application, which aims at providing the application to interface with the User, including local control and command capabilities.
Following the design analysis, a preferred implementation option has been proposed that mixes the various architectural solutions within a multi-board approach. The two boards are:
1. Mother board:
• Microprocessor implementing PVT, enhanced processing applications, HMI, communication drivers, data formatting functions for I/O standard
• Memory ressources implementing the executable code, the PRN and secondary codes sequences, the default configuration parameters of the receiver, and storage
• Peripherals providing standard communication means with the external world such as Ethernet, RS232, USB and Video interface ports
2. Signal Processing boards:
• FPGA implementing pre-processing functions, correlators, FFT-coprocessor for acquisition
• Microprocessor (FPGA implemented) implementing extended correlation processes, tracking loops, data and navigation message demodulation functions, raw measurements formatting
The Carrier Board interfaces with 2 GNSS Processing Modules, but several GNSS Processing modules can be implemented and chained together thanks to a dedicated high-speed serial link in order to improve the signal processing capabilities of the system, providing a high level of modularity and expendability to the Receiver.
As part of the WP, NSL also developed the signal validation tool which is known as GALACTIC which provides the means for a quick and reliable validation of the samples produced by the RF front-end in study. It allows to perform different tasks such as acquisition, tracking and visualisation that ensure the quality of the IF samples and of the signals within them. GALACTIC is written in Matlab having a visual GUI and the capability of outputting various statistical functional plots.
GALACTIC presents the user with a number of parameters for processing and validation the signals, controlling, for example, the intermediate and sampling frequencies, real and IQ data formats, acquisition settings, output options, etc. The tool has the capability of producing RINEX data files along with a navigation solution and can process the following signals:
• E1B (Single Freq)
• E5a (Single Freq)
• E5b (Single Freq)
• E5 (AltBOC)
• E1B - E5a (Dual Freq)
• E1B - E5b (Dual Freq)
• EGNOS L1 (Single Freq)
• GPS L1 (Single Freq)
• GPS L5 (Single Freq)
• GPS L2C (Single Freq)
The Signal Validation Tool includes a series of different functionalities to help the user to determine the validity of the samples and signals in study. Each option will be explained separately in detail.
The acquisition is the first task in every GNSS receiver and assures that the signal is present in the samples processed. The architecture implemented consists of a serial search in frequency combined with a parallel search in code by circular correlation with FFTs. Both data and pilot (if available) channel/signals are used in the acquisition process. The combination is made in a non-coherent way which involves a gain of 1.5 dB.
The local replicas generated are fully compliant with each of the systems SIS ICDs, but for Galileo E1 especially, the acquisition is performed with the BOC(1,1) component only and not with the full CBOC. This involves a loss of less than 0.4 dB.
The frequency search space is determined by the admissible maximum shift and the length of the coherent integration period which sets the size and number of the frequency bins and thus the maximum error in the estimation. The longer the coherent integration time is, the shorter the bins will be, and finally the smaller the frequency error will become.
The parameters for acquisition as well as the general parameters should be set properly to acquire the signal chosen, or otherwise the function will fail to detect the signals even though they might be present. It is a very common mistake to chose the wrong sample format or, sampling or IF frequencies, therefore special attention should be dedicated to these points.
The user then selects which satellites to acquire via a sub menu with all the possible combinations for GPS/GALILEO/GIOVE and EGNOS satellites. Once the acquisition task is being performed the evolution is shown in the command window of Matlab, where the details of the operation are shown.
The tracking is performed as a continuation of the acquisition process to refine the estimations and follow the variations of the signal so that measurements can be generated and the navigation message decoded. The tracking routine implemented involves 3 stages: pull-in, tracking and re-acquisition, and a control module to change from one to the other.
The RINEX generation involves several different operations to extract the information from the navigation message (demodulation and decoding), and perform the measurements.
The PVT computation is a single-frequency snapshot solution based on Least Squares. It takes as inputs the RINEX files generated previously and produces a single “.kml” file that can be seen with Google Earth.
The outputs from this work package are the prototype component parts and the receiver validation tool.
WP6: PROTOTYPE VALIDATION
Prototype validation was delayed due the technical difficulties within the previous WP.
D9 – Validation Strategy and Test Plan
The validation strategy and test plan was developed based on a single end-to-end prototype being developed. It therefore can be used as an excellent resource for future receiver developments. However, within PRECISIO, it was not possible to produce this end-to-end prototype and therefore some of the tests were not directly applicable.
Due to this, initiated by NSL the consortium examined each validation test and identified those that can be performed as initially intended, those that can be carried out with some modifications/compromises and those that are not possible or sensible to do in current conditions. This document is made available alongside the project deliverables.
D10 – Validation Test Report
Due to the problems encountered during the development of the PRECISIO FE (WAVE FE) and hence the inability to fully integrate the PRECISIO receiver, the prototype validation cases described in D9 could not be carried out as planned. Therefore a modified approach has been followed to validate the PRECISIO prototype consisting on validating each element separately: antenna, FE and SW receiver.
The antenna and the FE separated validations add new tests to the validation approach, while the current status of the SW receiver does not allow performing all the prototype validation cases already described in D9 but a reduced subset.
In order to validate the antenna it is placed in a known location, alongside a commercial geodetic antenna, each one feeding one of a pair of identical receivers. Antennas might be swapped over after the first 24 hours in case there are differences between the sites/receivers. Finally the antenna performance will be checked by looking at the positioning capability and the measurement quality and multipath performance.
The WAVE FE was connected to a signal simulator and the samples will be processed by a SW receiver (different from the PRECISIO one). Finally the measurements generated by the SW receiver will be checked looking at the positioning capability, the measurement quality and the clock behaviour.
SW Receiver Validation
As the PRECISIO receiver could not be completely integrated, the SW Receiver will be validated separately running a subset of the D9 tests planned for the whole PRECISIO receiver prototype (the demonstration trials have been removed from the list) and reducing the duration of some of the tests and avoiding some steps (i.e. bands not covered by the STEREO FE that were planned to be covered by the WAVE FE).
In order to fill the gap left by the PRECISIO FE (WAVE FE) another FE was used instead, the STEREO FE provided by NSL. Regarding the antenna, a commercial off-the shelf antenna will be used for the tests.
D11 – Performance Assessment
The purpose of the Performance Assessment document is to complement D10 by providing the performance assessment of PRECISIO prototype based on the precision validation test results provided in D10. Also, D12 will provide reference values of the performance achieved by the geodetic HW receivers, which can be used to compare the ones provided in this document.
Due to the problems encountered during the development of the PRECISIO FE, PRECISIO receiver could not be fully integrated and hence, each element of the PRECISIO prototype is being validated separately: antenna, FE and SW receiver. In such situation, this performance assessment becomes more important as it highlights each element results that will impact on the PRECISIO prototype.
D12.4 – Receiver Validation Tool
The receiver validation tool(s) is the platform used to test the PRECISIO receiver validating its performance requirements. The PRECISIO receiver validation platform consists on a set of tools/applications developed/upgraded within the frame of PRECISIO project, with different functionalities and capabilities that will be used through the validation process that will follow the validation steps described in the validation strategy described in D9.
• Matlab scripts have been developed as pre-validation checks of measurement data
• GMV's software, magicGNSS has been tailored to provide a dedicated test and validation capability in order to assess the performance of the PRECISIO prototype against GNSS data from other IGS receivers. PPP has been developed for the position analysis and comparison and ODTS (orbit determination and time synchronisation) is to check if PRECISIO can provide ODTS products
D12.4B – Signal Validation Tool
The signal validation tool, GALACTIC has been described under the section related to the previous WP. GALACTIC was used as part of the WAVE Front End validation process and the acquisition profiles and tracking results of selected signals have been produced (those sharing frequencies were not selected). This was carried out using signals from space and those generated within a Spirent simulator.
A detailed analysis of the results, including a lessons learned section has been provided within the deliverable.
WP 7 IMPLEMENTATION PLAN
WP7 was a 21 month activity led by Helios with the responsibility of producing the Implementation and Business Plan. The Implementation and Business Plan has been updated on 3 occasions during the project’s lifetime.
D13 - Implementation and Business Plan
This document develops the Implementation Plan for the future PRECISIO product with the objective to ensure a robust and viable business is established on the basis of the PRECISIO prototype.
Its role therefore will be as a reference guide of the necessary commercial issues which should be taken into account during the evolution of the PRECISIO product.
In particular the document analyses and evaluates the potential addressable markets within which to launch PRECISIO and assesses the various options for commercialisation in the identified target markets. Specific recommendations are provided for the future product in order to maximise its penetration and ensure its commercial success.
The business and implementation plan are founded upon a comprehensive assessment of the opportunities across the above mentioned markets.
This includes consideration of the standalone opportunity itself (i.e. the specific value proposition of the product in question and its potential market generating value) as well the breadth of factors influencing its realisation. This encompasses different factors having varying impact both on an environmental and customer specific level. Throughout this the underlying technological, commercial and regulatory trends within each market are considered.
WP 8 DISSEMINATION AND AWARENESS
WP8 continued throughout the length of the project. All dissemination was carried out by the WP leaders, NSL, although contributions were supplied by all partners.
The project was disseminated within 10 events in the UK, Europe and the United States. This included workshop representation, oral presentations at conferences, exhibiting at conferences and paper submissions with proceedings. The feedback from the events was very positive with potential clients interested to see if a front end and software defined radio solution could compete on a technical footing with the established hard-based commercial receivers.
D14 - Dissemination and Awareness Plan, Documentation and Materials
This document describes the planned intentions for dissemination, the actual activities that were carried out and is accompanied by all the materials that have been produced.
WP9 COORDINATION AND WP10 MANAGEMENT
The management related activities were carried out by NSL. A major discrepancy with the WP descriptions is that the planned workshop did not take place and therefore the deliverable D15 (D15 – Project Workshop (and report)) has not been produced.
GRACE at the University of Nottingham planned for and advertised a GNSS SDR Workshop/Symposium EU GNSS Receiver Workshop on the 14th-15th April 2011. The workshop was to provide the forum for multiple SDR projects and PRECISIO, and the ATENEA project were going to be sponsors. However, the conference failed to attract enough delegates to make it viable and a decision was made to cancel the event.
Due to the technical difficulties that were being experienced by PRECISIO, no further attempt was made to participate in a workshop. Becasue of this and the extensive dissemination that has occured within the project, it was agreed that the D15 deliverable should not be produced.
Project status was regularly updated to the GNSS community through presentations at conferences and exhibiting at international GNSS conferences. The exhibits had PRECISIO advertising material and hardware (RF front end) on show.
The project management activities (WP10) have implemented appropriate mechanisms to complete the project on time, with the required quality and making the best possible use of available resources, as well as to maintain the appropriate level of coordination with other related activities.
The following deliverables were produced:
D1 - Project Plan (Management, Administrative, Financial)
This provided information on the scope of the project, the scope and schedule of the work, contact information for the partners and the client, document management instructions and financial information.
D2.x – Periodic Progress Reports
These have been produced at the end of the reporting periods and are submitted online.
D16 - Final Project Report (internal)
This document, internal version
D17 - Final Project Report (public)
This document, external version
The following information has been provided by the beneficiaries. It demonstrates the value of the PRECSIO contract as it has resulted in a number of exploitable opportunities. Although the project has proved problematic, valuable lessons have been learnt for future exploitation and these have also been listed.
NOTTINGHAM SCIENTIFIC LTD
Work done and results achieved within the scope of the PRECISIO project has created several exploitation avenues for NSL. These benefits could not have occurred without the knowledge and experience gained from PRECISIO.
Signal validation Tool (GALACTIC)
As part of the PRECISIO activity, NSL developed a signal validation tool which was used within the project to validate the Rf front end. This tool has been further developed with extended functionality and enhanced performance to become a core asset within NSL. The signal validation tool (GALACTIC) is now being used to support several GNSS programmes and to support product development at NSL.
• Galileo PRS – GALACTIC has been adapted and extended to provide the means to assess the performance of different acquisition strategies for Galileo PRS signals. This has resulted in the creation of new IP in this domain.
• EGNOS – GALACTIC has been instrumental in supporting the EGNOS V3 projects at Phase A, Ax+B1. GALACTIC will also be used within the pending EGNOS V3 Phase B2 contract.
• PROSBAS – GALACTIC will be utilised within the PROSBAS study which is defining the EGNOS V3 Signal-in-space. GALACTIC shall assess options and analyse alternative strategies.
• ESA Mobile Land User testbed – GALACTIC has most recently been extended to provide a unique capability to receive and process commercial service messages at E6 frequency to support the Emergency Service concept within the ESA MLU testbed project.
Through the PRECISIO activity, NSL has now access to software receiver technology capable of processing signals from all constellations, at all frequencies and all services (incl PRS). Clearly, an important part of the NSL business is to customise their software receiver technology to specific applications, operating environments and dynamics. Access to a complete library of capability enables NSL to serve the needs of more customers.
RF front end (WAVE)
The PRECISIO project resulted in the development of the WAVE RF front end. WAVE consists of 2 boards: analogue RF and the digital board. The analogue RF has been plagued with challenges. As a result the RF board will not be commercialised. However, the digital board (ADC, FPGA) has proven to be a powerful platform for signal processing. This has resulted in NSL pursuing a completely new product which utilises their existing RF front end (STEREO) with a new digital digital processing board to create a very powerful software defined radio receiver suitable for multi-constellation and multi-frequency processing. This new product (internally named SUMMIT) is being utilised in the following projects and ventures:
• EGNOS V3 – the Rf front end has supported work on the receiver aspects of the EGNOS V3 system design. NSL is contracted to provide a software receiver to ASTRIUM as part of EGNOS V3 Phase B2 experimentation. The prototype will utilise technology developed within PRECISIO.
• LYNX – NSL is currently working within a UK project to develop a GPS/Galileo L1/E1 high end reference receiver for GNSS performance monitoring. The receiver is based on the integration of GALACTIC within the RF FE processing from PRECISIO.
1.- Lessons learned:
The PRECISIO project has globally permitted to improve the M3 SYSTEM’s skills in the field of GNSS receiver manufacture and design, which will be very useful for the M3’s future products developments. Such improvements have been performed in many fields, such as:
- Hardware design and production: a complete product quality level hardware platform has been designed and developed, including two FPGA-based configurable GNSS signal processing board, a carrier board with general purpose application and communication capabilities, and a professional level enclosure;
- GNSS signal processing algorithms: our GNSS signal processing skills have been improved, either concerning the algorithms required to process the modernized GNSS signals modulations, but also for the processing of the existing GPS P-Code for which an original semi-codeless technique has been designed to perform phase measurements of the L2 carrier.
- Real-time system development: the knowledge of M3S in the field of embedded complex real-time systems has been significantly improved, either for the design of the complex multi-processor and mixed hardware-software architecture required by a GNSS receiver, but also for the general knowledge of the required development tools (specifically the XILINX tools).
An original semi-codeless algorithm has been designed for the processing of the GPS P-Code to provide carrier phase measurements on the L2 carrier. It was initially decided to patent such original technique, but the idea was abandoned due to the close future availability of the civil L2C GPS signal that will become the main source for the L2 carrier phase measurements for the multi-frequency receivers. Anyway, the designed semi-codeless technique has been integrated the internal Company’s intellectual property portfolio of algorithms.
Recommendation for future implementations:
The main recommendations to achieve the initial objectives of the PRECISIO project are:
- to upgrade the GNSS Processing Module with another FPGA technology in order to be have enough resources to implement the required 36 channels per GNSS module; this could be achieve using bigger FPGA component (VIRTEX as an example)
- to upgrade the GNSS Processing Module with another FPGA technology in order to be able to manage the integrated real-time constrained processor with a higher clock frequency to fit with the 36 channels per module requirements; this could be achieve using bigger FPGA component such as VIRTEX, or new SOC component including programmable logic resources and hard integrated micro-processors such as the new ZINQ components from XILINX.
1) JAST got closer to the GNSS market, after few modification and a proper antenna calibration we will be able to introduce the PRECISIO antenna on the market at a competitive price. Since the market is growing there are many opportunities for our company in this field.
2) The antenna concept used for the PRECISIO project is under evaluation for multiband aeronautical applications where to the SATCOM communication is added to standard ones in order to improve the air traffic control.
3) The PRECISIO antenna model can be used in the future for different applications including antennas for the space segment where a precise phase center calibration is required.
4) Thanks to PRECISIO project JAST got many useful contacts in the GNSS field market that are precious for innovative cooperation in the present and in the coming future
Thanks to the PRECISIO project, GMV enhanced the magicGNSS portfolio (http://magicgnss.gmv.com/). GMV pre-existing tools magicGNSS/ODTS and magicGNSS/PPP, which form part of PRECISIO Receiver Validation Platform, were improved to process GPS&GLONASS and GPS&GALILEO double frequency measurements allowing the performance assessment of multi-constellation geodetic-type receivers by analysing the receiver clock and the pseudorange and phase measurement residuals. The magicGNSS/ODTS tool was also intended to be used to demonstrate the production product receiver capability of being integrated into a GNSS network providing multi-constellation ODTS products.
Although the problems with the PRECISIO FE blocked the progress of the project and prevented the analysis of the PRECISIO receiver data from being as expected, one of the objectives of the project from GMV point of view was to enhance magicGNSS portfolio, and this has been completely achieved as the improved magicGNSS tools were tested using real measurements from IGS and MGEX stations, decoupling them from the project problems. Also the analysis of PRECISIO data allowed GMV to increase its already established experience analysing receiver measurements.
From GMV side, the magicGNSS products (ODTS and PPP) associated to already existing IPs were enhanced during the project.
Recommendation for future implementations:
In projects aiming to integrate different elements the dependencies between them are critical and should be taken into account in the risk analysis. In the view of what has happened with the PRECISIO FE, one recommendation for future implementations is to try to develop, test and validate each element in a separate way, thus, all the elements could be completed independently, even if there is a problem with one of them or if they cannot be properly integrated and tested, and this would also minimize the impact of a delay in one of the elements. A second recommendation is to try to have a backup solution for each element whenever possible, this backup solution would not satisfy all the requirements and would limit the scope of the project, but the integration could be completed in case of problems allowing to accomplish some of the objectives of the project.
List of Websites:
The following web site was made available for the duration of the project, www.precisio.org.
This is a cloaked mirror of the web site, www.nsl.eu.com/precisio/. This site will be kept open after the project has completed.