ION GNSS 2012
Session A3: Geodesy, Surveying & RTK for Civil Applications

Title: A Comparison of a GNSS Software Defined Radio Receiver and Hardware Receivers within Reference Networks
Author(s): W. Roberts, R. De Lezaeta, NSL, UK; E. Dominguez Tijero, GMV, Spain; C. Hill, University of Nottingham, UK; I. Fernandez Hernandez, European Commission
Room: 103/104 (NCC)

GNSS is entering into a period of intense change over the next 5-10 years which will impact on users and operators of high-end GNSS equipment. For many years, GPS and GLONASS existed as the only systems. However, all is set to change with the advent of new global and regional systems (Galileo, Compass, IRNSS, GINS and QZSS), augmentation services and test satellites offering combined new and improved performance. Furthermore, GPS and GLONASS are also going through their own phases of modernisation with the GPS III programme and the GLONASS M and K programmes.
With such a diverse range of developments and future possibilities it is difficult to see how the traditional hardware receiver solutions can keep pace with the speed of changes demanded by users and operators. The PRECISIO project is aiming to address this challenge by developing a high-end prototype multi-constellation, multi-frequency receiver based on a Software Defined Radio (SDR) approach and suitable for a wide range of professional applications.

PRECISIO is a collaborative project under the European Commission 7th Framework Programme being conducted by a consortium of European organisations: Nottingham Scientific Ltd, GMV Aerospace and Defence, M3 Systems, JAST, Helios and the University of Nottingham. The project started in January 2010 and, at the time of this conference, will be near completion having completed the user requirements capture, the design, component development and integration, and testing of a prototype receiver for professional markets requiring fixed infrastructure receivers.

PRECISIO has designed and developed an end-to-end prototype GNSS receiver comprising an antenna, RF front end, and software receiver. The antenna implements a hybrid structure, resulting from the combination of a helix antenna and a spiral antenna, guaranteeing good performance at low elevation angles, wide bandwidth and symmetrical geometry. The Front-end is based on RF sampling directly across all RNSS bands (GPS L1/L2C/L5, Galileo E1/E5/E6/GIOVE, GLONASS G1/G2 and COMPASS B1, B2) in real-time and in a form suitable to the software receiver component.. The Software Receiver is built using a hybrid mixed architecture of FPGA and general purpose microprocessor. The GNSS signal processing algorithms are capable of optimally processing both legacy and new signals including those of the new BOC family (BOC, MBOC and ALTBOC) with a high quality level.

The performances of the PRECISIO prototype along with its capability to seamlessly integrate into current infrastructure will be evaluated and validated. The process will use existing GNSS processing software and networks, actual signals from space and simulated signals from a GPS, Galileo and GLONASS full constellation simulator. The validation demonstrations focus on analysing the performances and capabilities of PRECISIO across a range of different applications by embedding the PRECISIO prototype into different sets of existing GNSS infrastructure networks. The networks target different geodetic user communities and therefore the tests are aimed at determining the suitability of PRECISIO within that particular domain.

GMV´s magicGNSS will be used as the validation platform operating on the PRECISIO receiver´s raw GNSS observables in RTCM-HP and RINEX v3 formats. magicGNSS can execute different algorithms (PPP and ODTS) and is able to compute precise user coordinates, clock and tropospheric delays, user integrity, etc. All civil GNSS signals from PRECISIO will be processed using static Precise Point Positioning (PPP) algorithms in order to evaluate performances . Using Orbit Determination and Time Synchronization (ODTS) algorithms, magicGNSS will process PRECISIO data alongside data from a subset of the IGS network to test its integration capability into existing station networks and the PRECISIO´s applicability within international GNSS services, ionospheric studies and orbit determination. The fundamental acceptance criteria is whether magicGNSS will accept PRECISIO alongside the existing GNSS receiver types, or whether PRECISIO will be flagged as an outlier and rejected from the network solution.

Following a successful initial validation phase, the PRECISIO prototype will be subject to a series of application demonstrations using signals acquired in a range of scenarios including nominal, demanding and extreme environments. In-field demonstrations will take place in different locations and infrastructures in the UK. BIGF is the University of Nottingham-operated British Isles continuous GNSS Facility that collects data from continuously operating receivers, processes, and provides scientifically valuable products such as station velocities, and tropospheric estimates. Incorporating PRECISIO data will determine the suitability within geodetic and meteorology applications. A second trial aimed at determining PRECISIO´s suitability within geodesy, surveying and mapping applications will be performed using a RTK reference network. Again hosted and operated by the University of Nottingham, the Real-Time Kinematic GPS research testbed is founded on Leica´s Spider software, the same platform used in Leica´s national SmartNet commercial RTK network. PRECISIO will be included as a reference station providing data for networked RTK corrections for field users.

This paper provides a high level description of the project and the receiver that has been developed, before concentrating on the validation, testing and demonstrations. These process the raw GNSS observables and resulting positions to determine the suitability of PRECISIO to serve as a professional receiver capable of generating GNSS data at the required output rate and quality, and in the required formats, for use in research and commercial services. Direct comparisons to existing hardware-based geodetic receivers will be made concluding with an assessment of the current, and projection of the future, capability for a software defined radio geodetic receiver.

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