1

GLONASS PhaseRange biasesin RTK processing

Gleb ZyryanovAshtech

Workshop on GNSS Biases 2012

Bern, Switzerland

January 18-19, 2012

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Scope

Simplified observation models for GPS

Simplified observation models for GLONASS

FDMA specific: clock and biases

Calibration

GLONASS bias class

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Make life simple

To make everything simple– Zero baseline (two receivers sharing same antenna)– Start with Single Difference.

Benefits:– No ionosphere– No troposphere– No satellite orbit and clock errors– No antenna variations– Multi-path environment is exactly the same

What is left?– Receiver Clock– Biases– Noise

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SD GPS Codes

Simplified observation model for Single Difference GPS Code on a zero baseline

noisec BdtP jGPSba

jGPS

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jGPS

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noisec BdtP jGPSba

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noisec dtP jGPS

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Pdt jGPSba

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SD GPS Carrier Phase

Simplified observation model for Single Difference GPS Carrier Phase on a zero baseline

noisec bNdt jGPS

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noisec bNdt jGPS

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jGPS

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noisec Ndt jGPS

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noiseN ijGPS

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SD GLONASS Codes

Simplified observation model for Single Difference GLONASS Code on a zero baseline

noisec BdtP jGLOba

jGLO

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jGLO

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noisec BdtP jGLOba

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Pdt jGLOba

GLO

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1

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SD GLONASS Carrier Phase (same hw)

Simplified observation model for Single Difference GLONASS Carrier Phase on a zero baseline (same h/w)

noisec bNdt jGLO

ba

jGLO

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jGLO

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jGLO

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jGLO

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noisec bNdt jGLO

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jGLO

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noisec Ndt jGLO

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noisec Ndt ijGLO

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s)frequencieadjacent (for 55621 meters. ms

s)frequencieadjacent (for 80.001876291 meters meter

Pdt jGLOba

GLO

baMean

c ,,,

1

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SD GLONASS Carrier Phase (different hw)

Simplified observation model for Single Difference GLONASS Carrier Phase on a zero baseline (different hardware)

noisec bNdt jGLO

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jGLO

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jGLO

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jGLO

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noisec bNdt jGLO

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jGLO

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Pdt jGLOba

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?,

,b jGLO

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It is observed, that this bias follows linear pattern.

It may be viewed as a small (fraction of a cycle) bias

Or it may be viewed as delta-clock between Code and Carrier.

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Calibration

Bias can be non-linear– Though we have observed only minor variations, but we

clearly see small non-linearity in GLONASS carrier phase after passing low-end filters

Generally bias should be estimated for each GLONASS frequency independently (probably as a variation from linear approximation)

Only GLONASS data should be used for calibration (this mainly concerns proper clock estimation prior to carrier phase bias estimation itself)

Only data from corresponding frequency should be used (i.e. only L2 codes should be used for L2 carrier phase biases calibration)

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What we would like to see happen

Standardized procedure to estimate GLONASS carrier phase biases

Standardized means to specify so call “GLONASS bias class”, which would allow one to apply appropriate biases.

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Absolute calibration vs. Golden-Receiver

At this stage absolute calibration does not seem to be possible.– Even different simulators would introduce their own specific biases.

Selecting Golden-Receiver may offend some vendors.

A relative calibration center could be established– manufacturers submitting their receivers to a single authority (e.g. IGS).

This authority would provide:– estimated GLONASS carrier phase biases for each pair of receivers– raw data samples (recorded from simulator or in real-time)

Any new manufacturer could submit their receivers– to have them calibrated– to have calibration results against other available receivers published– to have corresponding raw data published– to have GLONASS carrier phase bias class name assigned.

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Bias variations

Only High-end hardware may guarantee stable performance and negligible variance in hw biases.

Low-end hardware may introduce noticeable bias variations.

Non-Physical reference stations may not exactly mimic biases of a physical receiver.

There is the need to have GLONASS bias class being accompanied by corresponding standard deviation values.

For physical receivers estimates for these STD could be provided by processing data from not one, but few samples of h/w similarly, as it is done with antennae.

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Final Slide.

Thank you.