Testing the Stability of GPS Oscillators within Serbian Permanent GPS Stations Network

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



AGROS

34 stations in Serbian permanent GPS network

Trimble receivers (4000, 5700 & NetRS) Monitoring center Mostly used by surveyors m to mm accuracy



Periodical tests of AGROS

ReceiverReceiverfeaturesfeatures

accuracyaccuracy

PhasePhasecentercenter

OscillatorOscillatorstabilitystability



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



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



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



Block diagram of the VI



Front panel layout



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



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



Results

Functional characteristics of noise processes

# of FFM ( = 0): 17 # of RWFM ( = +1): 13



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



The work on this paper was supported by Serbian Ministry of Science and

Technological Development

Testing the Stability of GPS Oscillators within Serbian Permanent GPS Stations Network

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