1

Flying™ RTK Solution as Effective Enhancement of Conventional Float RTK

Dmitry Kozlov, Gleb ZyryanovMagellan, Russia

ION GNSS 2007

Session D1: Algorithms and Methods 1

September 26,2007

2

Scope (18 slides)

•Summary

•Float and Fixed RTK

•Flying RTK

•Magellan products with Flying RTK

•Convergence performance

•Concluding remarks

•Acknowledgment

3

Flying RTK algorithm: Summary

We present new RTK algorithm which:

•Can be positioned between standard Float and Fixed RTK

•Has all the external attributes of Float RTK

•Uses internally some ideas of Fixed RTK

•Insures convergence performance better than Float RTK

•Integrated into 2 latest Magellan productsOEM DG14 RTK boardHandheld ProMark3 Surveyor

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Float and Fixed RTK: difference

Float RTK Fixed RTK

Receiver type Usually L1 only Typically L1&L2

Accuracy level Meter to decimeter Centimeter

Dependence on baseline length

Not so dramatical Noticeable (working distance is usually less than 50 km)

Initialization time Decimeter after 3-10 minutes

Centimeter after some convergence time depending on baseline

Treating DD ambiguity

As float unknown value

As known integer value

5

Float and Fixed RTK: commonality

Float RTK Fixed RTK

Core processing engine

Kalman Filter or similar recurrent estimator

Kalman Filter or similar recurrent estimator

Input data Receiver raw observations and external reference RTK data

Receiver raw observations and external reference RTK data

Treating ambiguity Ambiguity is processed as float all the time

Ambiguity is processed as float initially

Behavior at star up Slow convergence Same convergence until ambiguity fix

Fixing ambiguity to integer

Not appled Applied, but by quite a separated search and validation procedure

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Float and Fixed RTK: tentative diagram

KF update

KF project

data X,P

X,P

X,P

KF update Valid?

KF project

Ambiguity fixand X,P

modification

Integer searchdata X,P

YES

NO

X,P

X,P

Float RTK

Fixed RTK

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Flying RTK: backlog

•Actual DD is unknown integer (finite number of alternatives)

•There is theoretical foundation how to treat it

•Optimal multi-channel algorithm is too complicated

•Let us use Float RTK scheme

•Let us process DD ambiguity as unknown float, but consider as unknown integer

•Let us use DD ambiguity search results to generate Flying RTK correction to Float RTK solution

8

Fixed and Flying RTK: tentative diagram

KF update Valid?

KF project

Ambiguity fixand X,P

modification

Integer searchdata X,P

YES

NO

X,P

X,P

KF update

KF project

Flying RTK correction

Integer search

data X,P

X,P

Smoothing

X,P

Fixed RTK

Flying RTK

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RTK slogans

•Float RTK: always process DD ambiguity as unknown float variable

•Fixed RTK: first process DD ambiguity as unknown float variable, then (after fix) as known integer value

•Flying RTK: always process DD ambigity as unknown float variable, but always consider as unknown integer

10

Different RTK: typical convergence tubes

Error in time, example

0

0.2

0.4

0.6

0.8

1

time

erro

r, m

FlyingFloatFixed (correctly)Fixed (incorrectly)

Flying RTK convergence is as flat as Float RTK convergence

Flying RTK converges faster than Float RTK

Flying RTK never fixes wrong ambiguity as it can be with Fixed RTK

Flying RTK steady state accuracy can be as good as cm

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Flying RTK implementation: DG14 RTK

•L1 GPS+SBAS RTK OEM board (base and rover)•Fixed and Flying RTK

•RTCM-2.3 (base and rover)•RTCM-3.0 and Magellan proprietary (rover)

•20 Hz Raw data •10 Hz RTK (with extrapolated base) position•5 Hz synchronized (matched tags) RTK position

•OTF Fixed RTK initialization•RTK with moving base•Heading function

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Flying RTK implementation: ProMark3 RTK

•L1 GPS+SBAS RTK handheld (base and rover)•Real time and post-processed Surveying and Mobile Mapping functions•Fixed and Flying RTK

•RTCM-3.0 (base and rover)•RTCM-2.3,3.0 and Magellan proprietary (rover)•Compatibility with VRS, FKP and MAC Networks

•NTRIP&DIP rover (with external GPRS module)•External license free radio (base and rover)

•OTF Fixed RTK initialization•Initialization of known point•Initialization on kinematics bar

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Flying RTK performance: evaluation principles

•Apple to apple comparison•PC version of RTK•Static data but kinematics processing•RTK auto-reset each 10 minutes•Statistically sufficient estimates•CEP convergence pattern

•Cases:DG14 data (base and rover)Zmax data (base and rover, L1 portion only)ProMark3 data (against Ntrip Network)

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Flying RTK: Convergence with DG RTK data

CEP convergence pattern

0

0.1

0.2

0.3

0.4

0.5

0 200 400 600

tracking time,sec

erro

r, m

FloatRTKFlyingRTK

DG14 base and rover

24 full days data at different times and locations

Baselines from few meters to 10 km

Open sky to partly shaded sky environment

Kinematics processing

15

Flying RTK: convergence with Zmax data (L1 only)

CEP after 180 sec

0.1

0.15

0.2

0.25

0.3

0 10 20 30 40 50 60

baseline, km

erro

r, m

Float RTK Flying RTK Zmax data: base and rover

L1 CA portion only

Open sky baselines

Baselines from 7 to 52 km

>48 hours for each baseline

Accuracy after 3 minutes

Kinematics processing

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Flying RTK: convergence with ProMark3 data

CEP convergence pattern

0

0.1

0.2

0.3

0.4

0.5

0 200 400 600

tracking time,sec

erro

r, m

FloatRTKFlyingRTK

ProMark3 data (rover)

Orpheon NTRIP Network, France

10 km baseline

Open sky

48 hours

Kinematics processing

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Conclusions

Many GNSS users want decimeter accuracy

Standard DGPS can deliver only sub-meterOne of the choices is RTK

L1/L2 RTK with fixed ambiguity can be too expensive

Alternative is much cheaper Float L1 RTK

L1 RTK Float convergence is not always fast

Flying RTK algorithm shows improvement compared to classic Float RTK ‘in the same box’

Flying L1 RTK is good compromise for these users

18

Acknowledgments

Magellan System Test group:for their careful testing and validation efforts with release DG14 RTK and ProMark3 RTK

Yves Le Pallec, Eugeny Sunitsky (all Magellan), and Bill Cottrell (Cottrell Navigation Services):for help with data collection

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Final slide

Flying™ RTK Solution as Effective Enhancement of Conventional Float

RTK

THAHK YOU FOR YOU ATTENTION

QUESTIONS?