PRECISIO – a multi-constellation, multi-frequency software receiver

William Roberts, NSL

ENC GNSS 2010

20 October 2010

Braunschweig

Slide 2

Develop a GNSS receiver ... to meet the challenges of today’s users

Sufficiently high-end to meet the needs of users.

Multi-constellation capable.

Multi-frequency capable.

Upgradeable and flexible for new GNSS signals and services

that is designed to Provide differentiators over other solutions.

Be scalable to a user production product and potential further markets.

that will be tested and validated In operational environments ensuring it meets users’

requirements for fixed infrastructure receivers

Slide 3

Adopting a SDR approach

Delivers 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.

Slide 4

The Precisio Team

Slide 5

Slide 6

Slide 7

Authors

1Nottingham Scientific Ltd, Loxley House, Tottle Road, Nottingham NG2 1RT, UK

4M3 Systems, 26 rue du soleil levant, 31410 Lavernose, France

2GMV Aerospace and Defence SA, Isaac Newton, 11 P.T.M. Tres Cantos, 28760 Madrid, Spain

1William Roberts, Michele Bavaro, Mark Dumville

4Fabrice Legrand3Stefano Vaccaro,5Stuart Mitchell, Andy Sage, Daniel Kominak

2Enrique Domínguez Tijero, Manuel Toledo-López

6Chris Hill, Terry Moore

3JAST SA, PSE-C, Lausanne, CH-1015, Switzerland

5Helios, 29 Hercules Way, Aerospace Boulevard, AeroPark, Farnborough, GU14 6UU, UK6IESSG, The University of Nottingham, University Park, Nottingham, NG7 2RD, UK

Slide 8

Project Structure and Timeline

Now

WP1

User

Analysis

WP2

Tech.

Research

WP3

Req.

Consol.

WP4

Design

WP5

Development

WP6 Validation & Trials

WP7 Implementation Plan

WP8 Dissemination & Awareness

WP9 Coordination & Support to GSA

WP10 Management

Project DurationT0 T0 + 24m

Slide 9

Initial user requirements

Initial user requirements

Market analysis

Indentify and characterise market segmentsSupply chain and purchasing analysisCurrent and emerging applications

Capturing the User Requirements

Non-GNSS requirements

Technical (GNSS) user requirements

D1: User Requirements and User Segment Analysis Document

Market 1:

Application 1A

Initial user requirements

Recent reportsInternal project knowledge

Target stakeholdersfor consultation

User requirements consultation

Classify critical functionality for competitive advantage

Slide 10

Market Analysis to User RequirementsMarket segments

National reference networksInternational public infrastructureGlobal commercial service networksGNSS infrastructureMaritime DGNSSMeteorologyMetrology networksInterference monitoringIonospheric monitoring (TEC)Ionospheric monitoring (Scintillation)Payload/signal validation toolSurveyRailAutomotive

GNSS requirements

Non GNSS requirements

Market analysis

Market characterisation:Users and ApplicationsCompetitive environmentMarket EvolutionPurchasing behaviourReceiver technology:Technical & commercial prioritiesCurrent issues/limitationsImplications and needs for a SDRSpecific requirements

Consultation

Slide 11

Precisio Product Rollout

+6 months

End of project prototype

+12 months

+18 months

Slide 12

Subset of User requirements Track code, phase, doppler observables for

all in view satellites for all received frequencies in all GNSS (GPS, Glonass, Galileo, Compass) includes GPS L2C & L2P

Upgradable to all future GNSS (on publication of ICD) Compass, Glonass CDMA, Galileo PRS, CS

Receive WAAS, EGNOS and MSAS

72 channels 220 for 2nd generation

20Hz to 100Hz sampling frequency

No smoothing is applied to the observables as standard phase smoothing optional

Carrier/code phase 0.2/20 mm rms

Receiver hardware delay extremely stable

Synchronize with GPS time < ± 1 ms

Timing accuracy should be 1ns or better

Support RTCM, RTCM-HP, BINEX, RINEX v3, NMEA and 1pps outputs

Remote operation, configuration, and diagnostics Inc acquisition and tracking settings

Choke ring or multi-element antenna as multipath mitigation system

Phase centre repeatability +/- 0.5mm in the horizontal and +/- 1mm in the vertical

The receiver MTBF > 57000 hours

Rx availability > 99.999%

Low cost

Slide 13

Subset of User requirements Track code, phase, doppler observables for

all in view satellites for all received frequencies in all GNSS (GPS, Glonass, Galileo, Compass) includes GPS L2C & L2P

Upgradable to all future GNSS (on publication of ICD) Compass, Glonass CDMA, Galileo PRS, CS

Receive WAAS, EGNOS and MSAS

72 channels 220 for 2nd generation

20Hz to 100Hz sampling frequency

No smoothing is applied to the observables as standard phase smoothing optional

Carrier/code phase 0.2/20 mm rms

Receiver hardware delay extremely stable

Synchronize with GPS time < ± 1 ms

Timing accuracy should be 1ns or better

Support RTCM, RTCM-HP, BINEX, RINEX v3, NMEA and 1pps outputs

Remote operation, configuration, and diagnostics Inc acquisition and tracking settings

Choke ring or multi-element antenna as multipath mitigation system

Phase centre repeatability +/- 0.5mm in the horizontal and +/- 1mm in the vertical

The receiver MTBF > 57000 hours

Rx availability > 99.999%

Low cost

Capable,Flexible,

Transparent,High quality,

Reconfigurable, Stable, Useful,

Low cost

Slide 14

Interference detectionAntenna beamformingPush to fix applications

Multipath detectionSignal Quality Monitoring

Professional applicationsGNSS augmentations

Mobiles, car navigation, LBS, tracking, etc

Example Applications

Functional Blocks of a GNSS Rx

Output

Slide 15

Sub-component outputs available internally (eg used for multipath/interference mitigation)Limited outputsLimited applications

Comments

Hardware GNSS Rx

“Har

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Slide 16

Software Defined Radio GNSS Rx

Outputs available for different applicationsFlexible RF settingsFlexible correlation and acquisition & tracking functions/routines

CommentsSD

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cess

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ign

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TS

Slide 17

Antenna Considerations

Selection criteria Radiation pattern properties

Amplitude: multipath rejection

Phase: phase centre variation, errors

Polarization: multipath rejection, G/T

Form factor

Weight, encumbrance

Height, standard radomes

Interface: 1 or 2 ports

Other antenna properties

Bandwidth

Efficiency

User acceptance

Slide 18

Different candidates have been evaluated and traded-off against main requirements

Turnstile, Dipoles

Spiral, Conical Helix, Quadrifilar Helix

Patches

Trade-off results suggest patches or planar elements like spirals offer the highest performance, flexibility and integratability with multipath mitigation strategy (Choke rings, array)

Antenna Radiating elements

Slide 19

Multipath rejection features

Multipath rejection techniques Vertical array

Phase-cancelling configurations

Reactive ground planes

Absorbing ground planes

Digital beamforming

Passive structures (e.g chockerings) have been selected as the most suitable multipath rejection technique.

Slide 20

RF Front End Design Capture all GNSS Frequencies & Digitise to suitable resolution

Maintain a reasonable form factor, power consumption, & cost

Lower RNSS Band (1150-1300 MHz) High RNSS Band (1550-1610 MHz)

Slide 21

Architectural solutions (limited to COTS)

• Multiple narrow band F/Es are difficult to tune equally

• Power consumption an issue

• Not many COTS components would do E5 AltBOC

• Chaotic RF and digital design hard to maintain

Multi-channel super-heterodyne Multi-channel homodyne (direct conversion)

Slide 22

Preferred RF FE solution

ADVANTAGES

• One RF chain for all GNSS frequencies

• Very elegant solution

• Commercially feasible now

Direct band-pass sampling front-end

RF board, Isolates & amplifies GNSS frequencies

Digital Board,ADC and digital band tuning

DISADVANTAGES

• Need high gain at RF

• Needs very careful filtering of the signal

Slide 23

Prototype RF FE solution

RF

chain

Antenna

GNSS

SDR Receiver

Validation I/F

FPGA

digital

downconverter

digital

downconverter

FIFO buffer

digital

downconverter

FIFO buffer

FIFO buffer

GB Ethadapter

ADC

GNSS ch1

GNSS chN

GNSS ch2

GNSS ch1

GNSS ch2

GNSS chN

LVDS

parallel

Interface FPGA

partner

Serialiser

Slide 24

FE Spectrum Response

1st iteration had poor out-of-band rejection

2nd iteration dual band filters have good response, with minimal noise folding in the digital domain.

Marketable low cost product, available now

RF

bo

ard

Dig

ital

Bo

ard

Slide 25

The Software Receiver

Digital signal processing complexity analysis : High level of complexity due to :

The capability to process all GNSS signals : complexity of the baseband signal processing vs. signal modulation schemes Optimal processing architectures for BOC, MBOC and ALTBOC signal processing

High level of performance and robustness : Interference robustness and mitigation capabilities

Multipath effect mitigation capabilities

Precise positioning capabilities

Autonomous integrity capabilities

Hybridization with external sensors capabilities

Complete re-configurability and upgradability capabilities

Support of standard interfaces

Slide 26

General purpose microprocessor-based architecture Pros: Generic platform, standard C/C++ source codes Cons: Limited performances in term of integration capabilities (amount of

channels, advanced signal processing techniques), limited input signal bandwidth)

DSP-based architecture Pros: improved signal processing performances Cons: device-dedicated C source codes, limited performances in term of

integration capabilities (amount of channels)

FPGA-based architecture Pros: high integration capability (amount of channels), high input signal

bandwidth, Cons: limited performances of VHDL-based or integrated processors

Mixed Proc-DSP-FPGA architecture Preferred solution for high performance and high integration capability for the

targeted multi-constellation and multi-frequency receiver

Architecture options

Slide 27

Mother board:

Microprocessor implementing :

PVT, enhanced processing applications, HMI, communication drivers, data formatting functions for I/O standard

FLASH memory implementing :

the executable code, the PRN and secondary codes sequences, the default configuration parameters of the receiver

Storage

Signal Processing boards: FPGA implementing :

pre-processing functions, correlators, FFT-coprocessor for acquisition

Microprocessor (ASIC or FPGA implemented) implementing :

extended correlation processes

tracking loops;

data and navigation message demodulation functions

raw measurements formatting

Mixed Proc-DSP-FPGA architecture

Slide 28 2010/09/24 Page 28PRECISIO PROTOTYPE VALIDATION

Precisio Validation

Precisio target market: GNSS infrastructures and services

The project prototype will be validated Within existing GNSS networks

Signals in space, simulated signals

magicGNSS will be used as the receiver validation platform A web application for GNSS data processing, featuring high precision and

integrity

Calculates precise user coordinates, clock and tropospheric delay, etc

Calculate suser receiver integrity

Oriented to precision applications

Will Precisio deliver performances comparable with the hardware receiver devices currently deployed in international GNSS networks?

Slide 29 2010/09/24 Page 29PRECISIO PROTOTYPE VALIDATION

Tested within 4 Networks

1. UK, British Isles continuous GNSS Facility - BIGF.

2. UK, RTK reference network..

3. Spain, IGS Network within the IGS Real Time Pilot Project)

4. UK, alongside a COMPASS tracking station (dependent on ICD)

Slide 30

In Summary User requirements identified

Initial target markets

National reference networks, international public infrastructure, meteorological services

Requirements: capable, flexible, transparent, high quality, reconfigurable, stable, useful .... & low cost (meets IGS Super Rx)

Antenna, RF Front End and SDR Rx are currently at the design stage RF Front End following a iterative design process

Prototype will be validated in real-world networks (IGS, UK national/regional, COMPASS*)

using simulated signals

Using test/initial transmissions

Slide 31

Workshop Announcement

Workshop on State of the Art SDR GNSS Technologies

2-day event, 14-15 April, 2011

Hosted by GRACE, sponsored by industry & EC projects

Day 1 – Invited speakers, technology specialists

Day 2 – EC project presentations

Technology demonstrations throughout

Using GPS + Galileo full constellation simulator

Dynamic positioning test track

Signal “log and replay” devices

Thank youwilliam.roberts@nsl.eu.com

www.precisio.org