g. stienne * s. reboul j.-b. choquel m. benjelloun
DESCRIPTION
SPACE REFLECTO 2013. Ground-Based Altimetry Using a Single-Receiver Single-Frequency GNSS Phase Ambiguity Resolution Technique. G. Stienne * S. Reboul J.-B. Choquel M. Benjelloun. Overview. System geometry Software receiver Signal processing architecture - PowerPoint PPT PresentationTRANSCRIPT
Ground-Based Altimetry Using a Single-Receiver Single-Frequency GNSS Phase
Ambiguity Resolution Technique
G. Stienne*S. ReboulJ.-B. ChoquelM. Benjelloun
SPACE REFLECTO 2013
System geometry Software receiver- Signal processing architecture- Phase processing in open loops
Altimetry measurement Ambiguity resolution Experiments Conclusion, prospectives
2
Overview
System geometry: ground-based applications
3
is the path difference between the direct and the reflected signal
4
Receiver architecture
Code generator Carrier replica (frequency)
Phase processing(POL)
Code generator Carrier replica (frequency, phase)
Code and phase processing (DLL-POL)
DirectsignalRHCP
ReflectedsignalLHCP
Sam
e os
cilla
tor f
or th
e di
gitiz
ing
Pse
udor
ange
var
iatio
ns
In open loops, phase measurements are angular
Additional code delay(s)
Filter defined as the Kalman filter but with the Circular Normal von Mises distribution
Prediction step:
Update step:
Phase tracking: circular filter (linear evolution case)
with
11
with
and
6
Phase tracking: circular change estimatorWhen a cycle slip occurs (high dynamics, low Signal to Noise Ratios), it can be detected and its amplitude estimated via a GLR change estimator defined following the von Mises distribution.
The estimations of (cycle slip position)and (cycle slip amplitude) are based on the inversion of (filter innovation)
7
Ranging: code vs phaseBoth the code and the phase of a GNSS signal are periodic
C/A code period: Phase period:
Range periods:
GNSS codes are square signals. The observed code delays are piecewise constant. The sampling frequency defines the measurements resolution. Ranging precision: several meters.
The carrier is continuous, and so the phase delays. Ranging precision: centimeter.
Phase ambiguity
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Phase pseudorangingPseudorange variations
Received signal frequency
Replicated signal frequency
Phase delay between the received signal and its replica
Pseudorange at t=0 ambiguity
Local oscillator noises
9
Phase altimetry
Direct signal:
Reflected signal:
Choosen common Common for a GNSS-R receiver
Same receiver clock errors, atmospheric errors, orbit errors on both signals
10
Pseudorange at t=0The pseudorange at t=0 is obtained by dating the code using the data message
1 ms
Known emission date (TLM)
Received code
Known reception date
The telemetry word emission is dated, so the emission of each code period can be dated with the precision of the satellite atomic clock.
The first code delay, , has to be precisely estimated in order to get a precise datation at t=0.
11
Precise estimation of
Code delays
Phase variations applied to each code delay
Principle : averaging the code delays obtained over the whole acquired signalMethod : Bring each delay back to the origin using the estimated phase variations
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Experiments : principle
Graduations for accurately known height modifications
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Experiments : principle
Constant height for thereflecting water
Several acquisitions (7 seconds)Precisely known variations on the antenna height between two acquisitions
The variations of should be observed
Observation of several satellite footprints => same measured heights
First test:
Second test :
Experiments : observed footprints
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Experiments : results
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The height is constant over time: good estimation of the phase
The results on satellites 21 and 25 differ by up to 2 meters: wrong estimation of or with the signal of the satellite 21 or occurrence of a parasitic multipath
On satellite 25, the water level variations differ by up to 20 centimeter from what was expected
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Conclusion & prospectives
Development of a mobile GNSS reflectometer Short signal durations, no double difference Robust and precise height variations estimations with 1 millisecond of coherent integration Still imprecisions on altimetry measurements linked to the phase ambiguity resolution Need for more experiments in order to find the limits of the proposed ambiguity resolution technique Airborne experiments
Thank you for your attention
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GPS L1 signal structure
Emitted signal :
Received signal:
Code delay Phase delay
L1 carrier
C/A code
Data message
Modulation
Multiplexing
Emitted signal