International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 4
Number 1
March 2010
41
The following article provides a overview of the per-
formance of EGNOS SIS (PRN 120) as observed at
EGNOS 7 days over a period of 168 hours from 19
of November 00:00 until 26 of November 23:59
with a Septentrio PolaRx 2 receiver, during the ob-
served period of 168 hours at EGNOS CHELM.
Smoothing was set to 100 seconds.
This First Glance Report is generated with Pega-
sus 4.2 and presents the following performance
characteristics:
− Sample validity: Valid samples are all the sam-
ples that are present in the data and are not con-
sidered to be affected due to logging or pro-
cessing tool problems
− Accuracy statistics: calculated for horizontal and
vertical positioning errors separately.
− For the measured accuracy, the samples are
taken directly from the horizontal and vertical
errors as computed by PEGASUS.
− For the scaled accuracy, every sample is scaled
with a ratio of AL/PL(i) before taking the 95th
percentile.
− User Availability percentiles for the different PA
operations: determined by dividing the number of
samples that are available for an operation by the
total number of valid samples
− Number of discontinuity events within the peri-
od: the total number of discontinuity events for a
given operation.
− Number of Integrity events within the period: the
total number of integrity events. The Misleading
Information (MI) events are determined based on
samples with XPE>XPL. The Hazardous MI
(HMI) are counted according to XPE>XAL>XPL
for each operation.
All values that exceed a certain required threshold
are presented in red.
For more information refer to the FGA Perfor-
mance algorithms document.
The Implementation of the EGNOS System to
APV-I Precision Approach Operations
A. Fellner
Silesian University of Technology, Gliwice, Poland
K. Banaszek
Polish Air Navigation Services Agency, Warsaw, Poland
P. Trominski
GNSS-Consortium, Poland
ABSTRACT: First in the Poland tests of the EGNOS SIS (Signal in Space) were conducted on 5th October
2007 on the flight inspection with SPAN (The Synchronized Position Attitude Navigation) technology at the
Mielec airfield. This was an introduction to a test campaign of the EGNOS-based satellite navigation system
for air traffic. The advanced studies will be performed within the framework of the EGNOS-APV project in
2009. The implementation of the EGNOS system to APV-I precision approach operations, is conducted ac-
cording to ICAO requirements in Annex 10. Definition of usefulness and certification of EGNOS as SBAS
(Satellite Based Augmentation System) in aviation requires thorough analyses of accuracy, integrity, continui-
ty and availability of SIS (Signal in Space). Also, the project will try to exploit the excellent accuracy perfor-
mance of EGNOS to analyze the implementation of GLS (GNSS Landing System) approaches (Cat I-like ap-
proached using SBAS, with a decision height of 200 ft). Location of the EGNOS monitoring station Chelm,
located near Polish-Ukrainian border, being also at the east border of planned EGNOS coverage for ECAC
states is very useful for SIS tests in this area. According to current EGNOS programmed schedule, the project
activities will be carried out with EGNOS system v2.2, which is the version released for civil aviation certifi-
cation. Therefore, the project will allow demonstrating the feasibility of the EGNOS certifiable version for
civil applications.
42
Table 1. SIS Analyze .
Site
[ANALYZE] EGNOS CHELM 7 days
Date
27/11/2008
Location
51.130
Lon:
23.480
Alt:
254.70
Receiver
Septentrio PolaRx 2
Soft-
ware
Pegasus 4.2300150
PRN
120
Data set
Start
Stop
Expected
Total
SBAS Msg
Valid
Valid(%)
1 Hz
00:00
23:59
604800
604788
604285
604428
99.94%
Results per operation
APV-I
APV-II
CAT-I
40 / 50
40 / 20
40 / 12
Accuracy (m)
Meas.
Scaled
Req.
Meas.
Scaled
Req.
Meas.
Scaled
Req.
HNSE
(95%)
1.71
6.92
16
1.72
7.03
16
1.72
7.72
16
VNSE
(95%)
1.69
5.46
20
1.63
2.23
8
1.53
1.60
4
Availability (%)
Valid
EGNOS
Solutions
597696
510339
62104
Minimum Required
99%
99%
na
Availability
98.886%
84.433%
10.275%
Continuity
Events
345
3120
7838
Integrity
HMI APV-I
HMI APV-II
HMI CAT-I
Total
0
0
0
Horizontal
0
0
0
Vertical
0
0
0
Table 2. PL and APV-I statistics .
Protection level statistics
99%
95%
50%
mean
std deviation
HPL
34.81
22.99
10.24
11.89
5.21
VPL
35.66
24.43
15.40
16.39
4.67
APV-I Position error statistics
Samples
Mean
RMS
95%
std deviation
HPE
597696
1.10
1.16
1.71
0.35
VPE
597696
0.76
0.92
1.69
0.51
1 SIGNAL IN SPACE ANALYSIS
Figure 1. Message Distribution by time.
1.1 Message Types Distribution
Table 3. Message type counter .
.
PRN 120 PRN 126
SBAS MT number % number %
MT 0 150905 24.97 150839 24.97
MT 1 9396 1.55 9393 1.56
MT 2 0 0.00 0 0.00
MT 3 150865 24.97 150806 24.97
MT 4 0 0.00 0 0.00
MT 5 0 0.00 0 0.00
MT 6 590 0.10 585 0.10
MT 7 9397 1.56 9392 1.55
MT 9 9396 1.55 9393 1.56
MT 10 9396 1.55 9393 1.56
MT 12 3764 0.62 3762 0.62
MT 17 3764 0.62 3763 0.62
MT 18 18819 3.11 18814 3.11
MT 24 150869 24.97 150807 24.97
MT 25 550 0.09 550 0.09
MT 26 82811 13.70 82772 13.70
MT 27 3763 0.62 3763 0.62
MT 28 0 0.00 0 0.00
MT 62 0 0.00 0 0.00
MT 63 0 0.00 0 0.00
Total 604285 100.00 604032 100.00
1.2 Message Type 6 Analysis
This figure shows the number of occurrences for
consecutive MT6 broadcasts (1, 2, 3, 4 or more repe-
titions). A normal alert consists of four consecutive
MT6 messages, while single occurances indicate
CPF switch-overs.
Table 4. Message type 6 repetitions.
Message Type 6 repetitions
single
double
3 x 4 x
> 5x
PRN 120 1 0 1 145 1
PRN 126 1 0 1 145 0
2 POSITION SOLUTION ANALYSIS
2.1 Position errors and Protection levels
All plots have fixed scales that represent nominal
behaviour. When the performance does not fit
properly within these scales further detailed investi-
gations are needed.
43
2.2 Position solution plots.
Figure 2,3. Horizontal and vertical Error, Protection Level and
NSV over time.
Figure 4. Scatter plot of horizontal deviation from reference
position.
Figure 5, 6. Horizontal and Vertical Stanford graphs.
2.3 APV-I Statistics
Figure 7,8. Horizontal and Vertical position error distributions
(epochs when APV-I available).
44
Figure 9,10. Horizontal and Vertical protection level distribu-
tions (epochs when APV-I available).
Figure 11,12. Horizontal and Vertical Safety Index distribu-
tions (epochs when APV-I available).
2.4 Integrity
In case of a (potential) Misleading Information situa-
tion, this section will provide a list of all the epochs
where there was an xPE/xPL ratio of more than 1
(real MI) or more than 0.75 (near MI).
2.4.1 Integrity events
There are no Integrity events in the data. The
maximum Horizontal PL/PE ratio is 0.397273 and
the maximum Vertical PL/PE ratio is 0.455981
The following table represents the most extreme
epochs: Highest xPE/xPL ratio, Lowest xPL values
and Highest xPE values.
Table 5, 6. Highest xPE/xPL ratio, Lowest xPL values and
Highest xPE values.
extremes
Epoch
HPE
HPL
HPE/
HPL
VPE
VPL
VPE/VPL
max
normHor
175329
3.59359
9.04564
0.39727
1.51378
10.8631
0.13935
max
normVer
175331
0.16034
8.86431
0.01809
5.03754
11.0477
0.45598
max
HPE
565906
6.07277
60.2411
0.10081
-
1.57755 35.1706
0.04485
max
VPE
385129
4.89637
52.9584
0.09246
-
12.6208 140.124
0.09007
min
HPL
78769
1.22757
6.67681
0.18386
0.71793
11.5757
0.06202
min
VPL
287957
0.97835
6.78061
0.14429
0.06461
10.0249
0.00645
HPE
HPL
HPE/HPL
VPE
VPL
VPE/VPL
extremes
6.07277
6.67681
0.397273
-
12.6208 10.0249
0.455981
2.5 Cumulative Density Function
The Cumulative Density Function (CDF) gives a
good indication of the quality of the data in terms of
over-bounding. Especially the trend towards lower
probabilities becomes clear. The graphs should be
read as follows:
− The Red dashed line indicates the ideal trend
− The vertical axis indicates the probabilities, the
more data is available, the lower the graphs con-
tinue
− The horizontal axis indicates the quality of over-
bounding.
45
− The data points are strictly not allowed to exceed
the red-dashed line.
− However at the start they normally tend to ex-
ceed it, and this is acceptable as long as this is
only for a small area at the beginning
− The steeper the trend of the data-points, the bet-
ter.
− A clear downward trend gives confidence that
the over-bounding is sufficient.
− A clear trend towards exceeding the reference
(red-dashed) line is an indication of non over-
bounding.
− In case the trend is parallel and close to the ref-
erence, further investigation such as EVT is
recommended.
− A change(s) of the trend suggests that multiple
system modes are present in the data. For de-
tailed analysis these should be separated.
Figure 13. Horizontal and Vertical Position over-bounding in
CDF.
2.6 Continuity
This section will provide a list of all the discontinui-
ty events. In case there are more than 20 discontinui-
ty events the tables are filtered to a maximum table
length of 20. In case there still too many independ-
ent events, the table will not be displayed and further
investigation is recommended.
The following table presents the discontinuity
performance in more detail.
− All discontinuities regardless of duration (same as
in firstglance)
− Long discontinuities lasting 3 or more seconds
− Independent discontinuities, lasting 3 or more se-
conds and after continuously available period of
15 or more seconds
− P(disc.): Continuity Risk determined by multiply-
ing the continuity risk per epoch with 15 seconds
− P(slide): Continuity Risk determined with sliding
window of 15 seconds
Table 7. Discontinuity in detail.
Discontinuity events
Valid APV-1 APV-2 CAT-1 APV-35m
All
10
345
3120
7838
745
Long
9
40
173
257
49
Independent
7
27
103
67
27
P(disc.)
0.00017
0.00068
0.00303
0.01618
0.00069
P(slide)
0.00021
0.00206
0.01723
-9.35643
0.00371
2.7 Discontinuity events for Position Solution
Table 8. The following table presents all Position discontinuity
events.
Position discontinuity events
#
Epoch
duration
stable period
1
379453
34
33493
2
387656
219
8169
3
387879
25
4
4
416940
160
29036
5
484425
171
67325
6
484600
84
4
7
70570
160
28709
8
109514
1
38784
9
201129
44
4466
10
242862
160
41689
3 RANGE DOMAIN ANALYSIS
3.1 Signal quality and PRN Status
Figure 14, 15. Signal to Noise ratio.
46
Figure 16. PRN Noise and Status.
3.2 Normalised range error
Figure 17, 18. Normalised range errors.
Figure 19, 20. Normalised range errors histogram and CDF.
4 CONCLUSION
From a GNSS applications point of view (GPS as-
sisted in Europe by EGNOS) special importance pa-
rameters recorded by the receiver are: availability
and continuity. Carried out measuring session shows
that the EGNOS system in the current development
phase isn't meeting requirements put for air applica-
tions. The preliminary assessment of the EGNOS
system doesn't let categorize it as meeting APV re-
quirements at the border of the EGNOS service.