Improved High Precision GNSS Positioning with New Satellites and Signals

Nick TalbotResearch Fellow, Trimble Navigation Australia

2013 Surveying ExpoThe Institution of Surveyors, Victoria

Overview

Introduction

GNSS Constellation Status

BeiDou System

CMRx Format

RTK Test Campaign

Test Results

Summary

Introduction Currently 75 GNSS satellites in space

Expect to have 90 GNSS satellites in space by 2015; 120 satellites by 2020

45+ GNSS satellites in view over Asia / Pacific simultaneously by 2020

All GNSS satellites are capable of supporting metre-level and high-precision positioning at centimetre-level

Following presentation describes some of the challenges presented by new satellites and signals

Test results provided to illustrate the benefit of new satellites and signals with latest RTK hardware / firmware

GNSS Constellation StatusSystem Origin Current Future

GPS USA 31 satellites;20 IIA + IIR satellites with L1C/A, L2 PY7 IIR-M satellites with L1C/A, L2C4 IIF satellites with L1C/A, L2C, L5

3-Freq. fully available ~ 2018GPS III ~ 2022

GLONASS Russia 24 satellites;FDMA L1, L2

CDMA signals added in new K-series sats (L1, L2, L5);Planned compatibility with GPS, Galileo

QZSS Japan 1 satellite;Modernized GPS L1, L2, L5+ LEX signal

Planned launch of 3 additional satellites by 2017 (1 GEO)

Galileo EU 4 operational satellites with E1, E5A, E5B, E6(E1 compatible with GPS L1C)

Full constellation (30 sats) ~ 2020

BeiDou China 14 satellites;5 GEO; 6 MEO; 3 Inclined GEOwith B1, B2, B3

Full constellation (35 sats – 5 GEO; 30 MEO) ~ 2020

L5L5L5

L2 LEXL1L1

L5L2 L1G2

G3

G1

E1E5 E6

B1B3

B2RTX /

OmniSTAR

1164

1189

1214

1217

1237

1257

1260

1300

1525

1551

1559

1565

1571

1579

1585

1590

1599

1614

Frequency [MHz]

GPS (US)

Galileo (Europe)

GLONASS (Russia)

InmarSAT

QZSS (Japan)

IRNSS (India)

BeiDou (China)

SBAS (US)

GNSS Spectrum

GNSS antennas and receiver RF components expanded to capture usable signals from E5 to G1 spectrum

Good compatibility between GPS, QZSS and SBAS signal structure

Long term compatibility on L1C and E1 signals with frequency and coding

Galileo-E6; BeiDou-B3; and QZSS-LEX bands are to be regulated (limited access), even though B3 can be tracked and used today for RTK

BeiDou System Three satellite systems

– BeiDou-1 (active ranging system) no Trimble support

– BeiDou-2 (current system) used to be called Compass – subject of this talk

– BeiDou-3 (proposal to move B1 to L1) first MEO satellites may launch in 2014

Current constellation– 5 GEOs / 5 Inclined GEOs / 4 MEOs / More MEOs

in 2014– GEOs are harder to acquire & track due to high

data rate (2ms versus 20ms pre detection interval)

– Multipath errors are constant for static users of GEOs

BeiDou System Signals

– B1, B2 – supported by Maxwell VI ASIC

What’s public– B1 Open Service is “fully” public– B2 is an Open Service – not in the current ICD– B2 is the same signal as B1 so it is supported– B3 is officially a restricted signal – even though current

codes appear to follow a defined polynomial

BeiDou Broadcast Orbit Daily Performance –Based on RTX tracking network

BeiDou dual-frequency code residuals, 7 May, 2013

RTX Station

RM

S [

m]

CMRx Data Format

GNSS corrections need to be transmitted to rover from a reference station or VRS network

Additional satellite observations naturally increases the size of the GNSS correction stream

Many radio solutions have limited bandwidth

CMRx format provides a high level of data compression, with strong resistance to transmission errors

CMRx Data Format vs RTCM 3.x

0100200300400500600700

by

tes

/se

c

4 6 8 10 12

48

12

GPS Glo

nass

RTCM 3.1GPS (L1, L2) + GLONASS (L1, L2)

9600 baud with 1 repeater (426 bytes/s)

CMRx Data Format vs RTCM 3.x

CMRxGPS (L1, L2, L5) + GLONASS (L1, L2) + BeiDou (B1, B2)

9600 baud with 1 repeater (426 bytes/s)

0100200300400500600700

by

tes

/se

c

4 6 8 10 12

48

12

GPS Glo

nass

GLONASS +

BeiD

ou

4 / 4

8 / 8

12 / 12

RTK Test Campaign A test campaign was run in several regions around the world

where GPS, GLONASS, BeiDou, QZSS and Galileo satellites are currently visible, including China, Australia and New Zealand

Data collected on baselines from 2km – 22km in a variety of environments:

Most in high multipath, trees, significantly masked environments

Some in relatively benign environments

15 different baselines

Most data collected in China

22km line from Perth Australia

6km line from Christchurch New Zealand

RTK Test Campaign Tests conducted with Trimble R10; NetR9 receiver + Zephyr

Geodetic 2 antenna, hardware

Real-time system testing performed in the field

PC version of RTK processor used to process logged GNSS data and analyze performance with various satellite systems enabled / disabled

Truth computed using post-processed RTX

Collective Results – Vertical 95%

Christchurch, New Zealand

Collective Results – Horizontal 95%

RTK Example – Moderate Environment (Xi’an)

Data collected using R10 GNSS receiver in China– Supports GPS/GLONASS/Galileo/QZSS/BeiDou

Processed using a PC build of the real-time RTK engine– Operates in the same mode as real-time, no backward processing– Radio latency modeled– Operating mode set to kinematic– Data reprocessed with/without BeiDou

Environment was moderately difficult

Baseline length approximately 5km– Data collected in Xi’an

R10 GNSSBase Receiver

Moderate Environment (Xi’an) – Base Station (not a recommended setup)

R10 GNSSRover Receiver

Moderate Environment (Xi’an) – Rover

Moderate Environment (Xi’an) – Satellite Tracking

Moderate Environment (Xi’an) – PDOP

Moderate Environment (Xi’an) – Height Error

Moderate Environment (Xi’an) – Horizontal Position Error

Galileo RTK• Galileo satellites are currently unhealthy• Trimble firmware is Galileo capable/ready.• Modify firmware to force the satellites to report they

are healthy and hence are used in the RTK solution• Evaluate the RTK performance

– 2-hour period with 3 Galileo satellites.– 2 identical rovers on an 8.9km line – real time test

• Common antenna• Located in Melbourne Australia• RX1 = GPS+GLN+QZSS+BDS+Galileo• RX2 = GPS+GLN+QZSS+BDS

Number of satellites in RTK

Height Error

Summary Current BeiDou constellation nearly doubles the

number of visible satellites over Asia Additional satellites improve accuracy of position

estimates Tests show addition of BeiDou improved 95%

position errors by:– 5-75% horizontal– 8-68% vertical

Additional satellites help to reduce the overall impact of measurement noise and multipath errors

Summary Similar incremental improvements in position

accuracy noted with Galileo satellites in RTK solution

Additional satellites lead to increases in RTK correction bandwidth

CMRx format designed for increased satellite counts

CMRx roughly 55% smaller than RTCM v3.x

Expect to see significant improvements in position availability and accuracy when BeiDou, QZSS, Galileo constellations fully populated

Questions?

Acknowledgements:

Stuart Riley and Sunnyvale TeamEric Leroy (QA)App Firmware TeamHCC/Survey/Infra/InTech H/W TeamTimo Allison, Markus Glocker (Terrasat)TNZ & Westminster field testingXi’an China teamDave Vanden Berg & InTech Beijing