Belgrade University Faculty of Civil Engineering Department of Geodesy and Geoinformatics TESTING THE STABILITY OF GPS OSCILLATORS WITHIN SERBIAN PERMANENT GPS STATIONS NETWORK Vukan Ogrizović, Violeta Vasilić, Siniša Delčev, Jelena Gučević
Jun 25, 2015
Belgrade UniversityFaculty of Civil Engineering
Department of Geodesy and Geoinformatics
TESTING THE STABILITY OF GPS OSCILLATORS WITHIN SERBIAN PERMANENT GPS STATIONS NETWORKVukan Ogrizović, Violeta Vasilić,Siniša Delčev, Jelena Gučević
Belgrade UniversityFaculty of Civil Engineering
Department of Geodesy and Geoinformatics
AGROS
34 stations in Serbian permanent GPS network
Trimble receivers (4000, 5700 & NetRS) Monitoring center Mostly used by surveyors m to mm accuracy
Belgrade UniversityFaculty of Civil Engineering
Department of Geodesy and Geoinformatics
Periodical tests of AGROS
ReceiverReceiverfeaturesfeatures
accuracyaccuracy
PhasePhasecentercenter
OscillatorOscillatorstabilitystability
Belgrade UniversityFaculty of Civil Engineering
Department of Geodesy and Geoinformatics
Testing of oscillator stability
RINEX data from 30 stations downloaded from monitoring centre
Observables - Phase L1 measurements for the reference SV
24-hour long session - all referred to the same date
Allan’s variance and PSD calculated
Analysis of obtained graphs
Belgrade UniversityFaculty of Civil Engineering
Department of Geodesy and Geoinformatics
Measure of frequency stability
Alan’s variance
2 122
1
22 1
2
1 0
1ˆ ( )
2 2 1
21
2 2 1
N n
y k n kk
N nk n k n k
k
y yN n
x x x
N n n
213 1
222 2
1
22 2
1mod ( ) 2
2 3 1
( ) mod ( )3
j nN n
y i n i n ij i j
x y
x x xn N n
Modified Alan’s variance
Belgrade UniversityFaculty of Civil Engineering
Department of Geodesy and Geoinformatics
Type of random process
Averaging interval
Single-sided spectral density
2 ( ) ~ ( ) ~y y
22 1 0 1 2
2 1 0 1 22
( )yS f h f h f h f h f h f h f
1
Belgrade UniversityFaculty of Civil Engineering
Department of Geodesy and Geoinformatics
Block diagram of the VI
Belgrade UniversityFaculty of Civil Engineering
Department of Geodesy and Geoinformatics
Front panel layout
Belgrade UniversityFaculty of Civil Engineering
Department of Geodesy and Geoinformatics
Allan variance
0
0.05
0.1
0.15
0.2
1 4 16 64 256
1024
4097
1638
7
s
Typical graph for 5700 type receiver
0.01
3.01
6.01
9.01
1 4 16 65 259
1037
4149
1659
4
(s)
[ns/
s] However, several stations showed different characteristics, due to environmental conditions
Belgrade UniversityFaculty of Civil Engineering
Department of Geodesy and Geoinformatics
Analysis for station LOZN
Correct Allan variance graph
0
0.5
1
1.5
1 4 16 64 256 1024 4096 16384
(s)
[ns
/s]
PSD graph indicated periodical disturbances of an unknown source with the period of 15-30 min
but
Belgrade UniversityFaculty of Civil Engineering
Department of Geodesy and Geoinformatics
Results
Functional characteristics of noise processes
# of FFM ( = 0): 17 # of RWFM ( = +1): 13
Belgrade UniversityFaculty of Civil Engineering
Department of Geodesy and Geoinformatics
Conclusions and remarks
Older types of receivers showed larger Allan’s variances
Environment affects the results of modern receivers, also
Only FFM and RWFM occur in results
Calibration of GPS receivers is a must
Receivers with 1PPS output are recommended
Belgrade UniversityFaculty of Civil Engineering
Department of Geodesy and Geoinformatics
The work on this paper was supported by Serbian Ministry of Science and
Technological Development