INTERNATIONAL TELECOMMUNICATION UNION
RADIOCOMMUNICATION
STUDY GROUPS
AMCP WF7/WP15
Document 8D/TEMP/148-E
31 October 2001
English only
Working Party 8D
WORKING DOCUMENT TOWARDS A DRAFT NEW RECOMMENDATION
Protection criteria for telemetry systems in the aeronautical mobile service and
mitigation techniques to facilitate sharing with geostationary mobile-satellite
services in the frequency band 1 518-1 525 MHz
The ITU Radiocommunications Assembly,
considering
a)
that the World Radiocommunication Conference (Istanbul, 2000) adopted Resolution 226
inviting the ITU-R to study, as a matter of urgency, sharing between the MSS and aeronautical
mobile telemetry in the band 1 518-1 525 MHz, taking into account, inter alia,
Recommendation ITU-R M.1459;
b)
that ITU-R has established that, so as to meet projected MSS requirements in the frequency
range 1-3 GHz, spectrum of the order of two times 123 MHz will be required by 2005 and of the
order of two times 145 MHz will be required by 2010;
c)
that the frequency band 1 492-1 525 MHz is allocated to the MSS (space-to-Earth) in
Region 2 on a primary basis, except in the United States;
d)
that the frequency band 1 518-1 525 MHz is allocated to the fixed service on a primary
basis in all three Regions, to the mobile service on a primary basis in Regions 2 and 3, and to the
mobile, except aeronautical mobile, service on a primary basis in Region 1;
e)
that in a number of countries the band 1 429-1 535 MHz is allocated to the aeronautical
mobile service on a primary basis exclusively for the purposes of aeronautical telemetry within their
national territories under the provisions of No. S5.342;
f)
that, in Region 2, the use of the band 1 435-1 535 MHz by the aeronautical mobile service
for telemetry has priority over other uses by the mobile service under the provisions of No. S5.343;
g)
that Recommendation ITU-R M.1459 contains threshold values to determine the need to
coordinate between the mobile service and aeronautical mobile service for telemetry operating in
the band 1 452-1 525 MHz;
h)
that these coordination threshold values are necessarily stringent as they are based on some
worse-case assumptions in determining the potential for interference into aeronautical telemetry
receivers;
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j)
that Recommendation ITU-R M.1459 invites for further studies to be introduced in the
ITU-R for determining the probability of interference to telemetry stations in the aeronautical
mobile service which could lead to less stringent protection values,
further considering
a)
that Recommendation ITU-R M.1459 proposes a number of interference mitigation
techniques that could be implemented to achieve successful sharing with the MSS;
b)
that the principle of site diversity could effectively resolve MSS interference problems in
the case of MSS satellites subtending high elevation angles (> 5 degrees) at all aeronautical
telemetry stations,
recommends
1
that the values needed for protection of the aeronautical mobile service for telemetry
systems considering site and antenna diversity in the 1 518-1 525 MHz band shared with
geostationary satellites in the MSS, should be determined by the following (see NOTE 1):
–
for geostationary satellites visible to any aeronautical telemetry receiving station, the
protection value corresponds to a pfd at the telemetry receiving station in any 4 kHz band
for all methods of modulation:
–181.0
dB(W/m2)
for
0    4
–190.75 + 2.44 
dB(W/m2)
for
4 <   20
–188.3 + 35.6 log 
dB(W/m2)
for
20 <   60
–125.0
dB(W/m2)
for
60 <   90
where  is the angle of arrival (degrees above the horizontal plane);
2
that the calculation methods given in Annex 1 (see NOTE 2) may be used, as applicable,
for determining the probability of interference to telemetry systems in the aeronautical mobile
service.
NOTE 1 - The pfd limits shown have been derived on the basis of a number of essential facts and
assumptions that are reflected within the sharing study in Annex 1.
NOTE 2 - The sharing analysis in Annex 1 is primarily based on the interference model and
characteristics of telemetry stations available within Recommendation ITU-R M.1459 and some
other contributions to ITU-R meetings.
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ANNEX 1
A proposal for the sharing of the frequency band 1 518-1 525 MHz
by the geostationary MSS and the national aeronautical
telemetry mobile service
1
Introduction
In this paper a proposal is developed for the sharing of the frequency band 1 518-1 525 MHz by the
geostationary MSS and the national aeronautical mobile services.
Recommendation ITU-R M.1459, adopted by the 2000 Radiocommunication Assembly, sets forth
"Protection criteria for telemetry systems in the aeronautical mobile service and mitigation
technologies to facilitate sharing with geostationary broadcasting-satellite and mobile-satellite
services in the frequency bands 1 452-1 525 MHz and 2 310-2 360 MHz".
2
Proposed constraint to the geostationary MSS
The constraints on pfd recommended for all satellite networks are given in Recommendation ITU-R
M.1459 and are:
TABLE 2A
List of constraints on the power flux-spectral density of MSS emissions within
the service area of the aeronautical telemetry service
Elevation angle
Power flux-spectral density
Degrees
dBW/(4 kHz/m2)
0.5 < Elevation < = 4
–181
4 < Elevation < = 20
–193 + 20*log (Elevation)
20 < Elevation < = 60
–213.3 + 35.6*log (Elevation)
Elevation > 60
–150 dBW
The aeronautical telemetry receiving ground station has a very high sensitivity to interference
–181 dB(W/(4 kHz/m2)) at zero degrees elevation which corresponds to the maximum aircraft range
of about 320 kilometres and altitude of 20 kilometres. The characteristic of interference power
flux-spectral density versus aircraft elevation angle as given in Recommendation ITU-R M.1459 is
shown in Figure 2 below.
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Graph of maximum recommended power flux spectral density versus elevation angle of aircraft
Maximum recommended power flux spectral density dBW/(4
kHz*square metre)
-145
-150
-155
-160
-165
-170
-175
-180
-185
1
10
100
Elevation angle of aircraft (degrees)
FIGURE 2
Recommendation ITU-R M.1459
It is shown in Section 3 below that the constraints that apply to non-geostationary satellites are not
applicable to geostationary satellites and the Table 2A values may be restricted to interference from
non-geostationary networks. The values given in Table 2A may be replaced with the values given in
Table 2B below when interference from geostationary networks is considered.
TABLE 2B
List of constraints on the power flux-spectral density of geostationary MSS
emissions within the service area of the aeronautical telemetry service
Elevation angle
Power flux-spectral density
Degrees
dBW/(4 kHz/m2)
0  Elevation  4
–181
4 < Elevation  20
–190.75 + 2.44* (Elevation)
20 < Elevation  60
–188.3 + 35.6*log (Elevation)
60 < Elevation  90
–125 dBW
This set of pfd limits corresponds to satisfactory operation of MSS satellites over coverage area
with 20 degrees satellite elevation angle of more.
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3
Principles on which the proposal is based and development of the formula
3.1
Elevation versus azimuth angles for a geostationary satellite
At every location on the Earth there are just two azimuth bearings at 0 degrees elevation that point
directly at the geostationary orbit. In the case of Belarus the two bearings are  78.8 degrees wrt to
due south. In the case of Andrews Air Force Base, United States the two bearings are  83 wrt due
south.
The two cases are illustrated in the graphs below.
Plot of geostationary satellite elevation angles versus satellite azimuth angles from latitude 39
degrees (Andrews Air Force Base, USA)
60
Satellite longitudes in steps of 10 degrees
Satellite inclination angles in steps of 1 degree
Satellite elevation angle in degrees
50
40
30
20
10
0
-10
-100
-80
-60
-40
-20
0
20
40
60
80
100
Azimuth angle wrt due north (southern hemisphere) or due south (northern hemisphere) in degrees
FIGURE 3.1A
Andrews Air Force Base, United States
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Plot of geostationary satellite elevation angles versus satellite azimuth angles from latitude 52.4
degrees (Belarus)
50
Satellite longitudes in steps of 10 degrees
Satellite inclination angles in steps of 1 degree
Satellite elevation angle in degrees
40
30
20
10
0
-10
-100
-80
-60
-40
-20
0
20
40
60
80
100
Azimuth angle wrt due north (southern hemisphere) or due south (northern hemisphere) in degrees
FIGURE 3.1B
Belarus
3.2
Interference margins of multibeam mobile-satellite services
The interference margin can be calculated from the spreadsheet given in Document 8D/30 called
"Working document towards draft CPM text - Contribution In response to Resolution 226
(WRC-2000)".
In reviewing the calculations given in the spreadsheet of Document 8D/30 the following alternative
values for the parameters listed in the table below were used.
TABLE 3.2
Comparison list of parameters' values used in Document 8D/30
and values adopted in this study
Parameter
Units
8D/30 values
Alternative
values
3
2
Antenna gain of handset MES
dBi
MSS link noise temperature referred to the input port of
the LNA of the MES (unfaded)
Kelvin
290
140
MSS link noise temperature referred to the input port of
the LNA of the MES (faded)
Kelvin
290
290
Threshold MSS carrier-to-noise ratio
dB
7
6
Forward link fade margin
dB
15
12
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The reasons for each revised value are:
•
Antenna gain of handset MES: (2 dBi)
This value of handset gain is also applicable to antennas placed pointing at zenith on yachts
and vehicles and is typical of antenna gain values of handset MESs currently in use. With
digital systems there is little change in voice quality with carrier-to-noise ratio to enable the
listener to optimize the pointing of the handset antenna manually.
•
MSS link noise temperature referred to the input port of the LNA of the MES (unfaded):
(140 Kelvin)
This value is needed to calculate the maximum MSS satellite PFD equivalent to a specified
fade margin.
•
Threshold MSS carrier-to-noise ratio: (6 dB)
Values of 4 dB and 6 dB are applicable to existing L-band networks.
•
Forward link fade margin: (12 dB)
This value of fade margin is approximately the maximum value, if the fade margins of the
forward and return links are to be the same and the diameter of the MSS satellite antenna is
a maximum of 12 metres.
With these assumptions the plot of interference deficit or required satellite antenna discrimination
for the MSS versus MSS satellite elevation angle within the aeronautical service area can be
prepared and is given in Figure 3.3 below. The required MSS satellite e.i.r.p. density is also shown.
MSS satellite interference deficit and required MSS satellite EIRP spectral density as a function of
satellite elevation angle within the affected aeronautical service area
33.6
33.4
50
33.2
40
33.0
30
32.8
Interference deficit
32.6
20
32.4
EIRP spectral density
Mobile satellite EIRP sprctral density
(dBW/4kHz)
MSS satellite antenna discrimination needed or
interference defiicit (dB)
60
10
32.2
0
32.0
0
10
20
30
40
50
60
70
Satellite elevation angle within the affected aeronautical service area (degrees)
FIGURE 3.3
MSS interference margin deficits to the aeronautical telemetry service
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It can be seen from the figure above that when the antenna of the aeronautical receiving ground
station points directly at the MSS geostationary satellite at zero degrees elevation the interference
margin is –51 dB if a common service area is in use. There are only two azimuth angles at which
this can happen as shown in Figures 3.4A and 3.4B below.
3.3
Introduction of FEC to the aeronautical telemetry service
The values of threshold carrier-to-noise ratio given in Recommendation ITU-R M.1459 are between
9 and 15 dB implying that the telemetry data is not protected by forward error correction (FEC). If
FEC was applied to the aeronautical link data stream, this would increase the link margin by 5 dB.
3.4
Diversity of telemetry ground station sites
Now suppose the aircraft follows a track that is exactly on the line of sight between an aeronautical
telemetry ground station site north of the equator and every possible visible geostationary satellite
position to the south i.e. the contour shown in Figures 3.1A and 3.1B by the thick black line.
Suppose that the aircraft whilst completing the flight patterns is at the maximum range (i.e. up to
320 kilometres or 200 miles) or, if not at the maximum range, at the maximum altitude. What will
the locus of the aircraft be and what will be the azimuth and elevation angles of the aircraft as
viewed from a second telemetry ground station site precisely 30 kilometres (Belarus) and
18 kilometres (Andrews Air Force Base, United States) due south of the first telemetry ground
station site? The outcome is shown in Figures 3.4A and 3.4B below.
Plot of geostationary satellite elevation angles versus satellite azimuth angles from latitude 39
degrees (Andrews Air Force Base, USA) and pointing angles to an aircraft from two telemetry
ground stations 18 kilometres apart
0 degrees inclination
Aircraft as seen from telemetry station 18 kilometres to the south
90
80
< Locus of same aircraft from a second
ground station site 18 kilometres to the south
70
Satellite elevation angle in degrees
Satellite inclination angles in steps of 1 degree
Satellite longitudes in steps of 10 degrees
60
50
40
< Locus of aircraft from first telemetry
ground station corresponds exactly to the
pointing angles of the geostationary arc
30
20
10
0
-10
-100
-80
-60
-40
-20
0
20
40
60
80
100
Azimuth angle wrt due north (southern hemisphere) or due south (northern hemisphere) in degrees
FIGURE 3.4A
Andrews Air Force Base, United States
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Plot of geostationary satellite elevation angles versus satellite azimuth angles from latitude 52.4
degrees (Belarus) and pointing angles to an aircraft from two telemetry
ground stations 30 kilometres apart
0 degrees inclination
Aircraft as seen from telemetry station 30 kilometres to the south
90
Satellite elevation angle in degrees
80
Satellite inclination angles in steps of 1 degree
Satellite longitudes in steps of 10 degrees
70
< Locus of same aircraft from a second aeronautical
telemetry ground station site 17 kilometres to the south
60
50
40
30
< Locus of aircraft from the first aeronautical
telemetry ground station corresponds exactly to
the pointing angles of the geostationary arc
20
10
0
-10
-100
-80
-60
-40
-20
0
20
40
60
80
100
Azimuth angle wrt due north (southern hemisphere) or due south (northern hemisphere) in degrees
FIGURE 3.4B
Belarus
3.5
Average radiation pattern of aeronautical telemetry antennas
The aeronautical telemetry receiving ground station has an antenna gain of from 20 dBi to 41.2 dBi
and has a two dimensional tracking system.
The formulae for the composite average radiation pattern of the two receiving antennas of 29 and
41.2 dBi gain of the aeronautical telemetry ground station are given in Recommendation ITU-R
M.1459 and the resulting pattern is reproduced below in Figure 3.5.
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Radiation pattern of ground based aeronautical telemetry antennas (The pattern is a composite of
two patterns one for an antenna of gain 29 dBi and the other for an antenna of gain 41.2 dBi and is
taken from Rec. ITU-R M.1459 )
50
40
Antenna gain (dBi)
30
20
10
0
-10
0.1
1
10
100
Off-axis angle (degrees)
FIGURE 3.5
Composite average antenna radiation pattern based on measured results
The off-axis angle of two degrees is shown in bold because at angles greater than two degrees the
radiation pattern of the antenna of 2.44 metre diameter is dominant.
3.6
Typical values of antenna diversity at a ground station site
It can be seen from Figures 3.4A and 3.4B above that there is an appreciable angle between the
geostationary satellite causing interference and the aircraft when viewed from the second ground
telemetry site. The antenna gain discrimination, assuming the 2.44 metre and 10 metre antennas
referred to in Recommendation ITU-R M.1459 are placed at the second telemetry ground station
site, has been calculated and the results are given in Figures 3.6A and 3.6B below.
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Angle between aircraft and geostationary satellite as seen from the second ground telemetry station
(18 km south) as a function of azimuth angle at latitude 39 degrees (Andrews Air Force Base, USA)
Off-axis angle (degrees)
Discrimination in dB with 41.2 dBi gain telemetry antenna
Discrimination in dB with 29 dBi gain telemetry antenna
55
45
Antenna discrimination in the case of
the 10 metre antenna in the direction
of the geostationary arc
40
Off axis angle
Antenna discrimination in the direction of the
geostationary satellite at the second telemetry
station (dB)
Angle between aircraft and satellite as seen
from the second ground telemetry station
(degrees)
50
50
45
35
40
30
25
35
Antenna discrimination in the case of the 2.44
metre antenna in the direction of the
geostationary arc
20
30
15
25
10
20
5
0
15
-90
-70
-50
-30
-10
10
30
50
70
90
Azimuth angle
FIGURE 3.6A
Andrews Air Force Base, United States
Angle between aircraft and geostationary satellite as seen from the second ground telemetry station
(30 km south) as a function of azimuth angle at latitude 52.4 degrees (Belarus)
Off-axis angle (degrees)
Discrimination in dB with 41.2 dBi gain telemetry antenna
Discrimination in dB with 29 dBi gain telemetry antenna
50
55
Off axis angle
50
Antenna discrimination in the direction of the
geostationary satellite st the second telemetry
station (dB)
Angle between aircraft and satellite as seen
from the second ground telemetry station
(degrees)
45
Antenna discrimination in the case of
the 10 metre antenna in the direction
of the geostationary arc
40
45
35
40
30
Antenna discrimination in the case of the 2.44
metre antenna in the direction of the
geostationary arc
25
35
20
30
15
25
10
20
5
0
15
-90
-70
-50
-30
-10
10
30
50
70
90
Azimuth angle
FIGURE 3.6B
Belarus
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3.7
Telemetry antenna discrimination as a function of elevation angle
The antenna discrimination in the direction of the geostationary arc at the second telemetry site can
be plotted as a function of elevation angle and the result is shown in Figure 3.7.
Antenna discrimination in the direction of a geostationary satellite for the antenna of 2.44 metres
diameter at the second telemetry station site as a function of elevation angle
Antenna discrimination in the direction of a geostationary
datellite at the second telemetry station site (dB)
40.0
Azimuth bearing 84 degrees
Azimuth bearing 80 degree
35.0
Belarus
30.0
Andrews Air Force Base, USA
25.0
20.0
15.0
0
10
20
30
40
50
60
70
Antenna elevation angle at the second telemetry site (degrees)
FIGURE 3.7
3.8
Stay out zones
It can be seen from Figures 3.6A and 3.6B that providing certain azimuth bearings are excluded at
least 25 dB antenna discrimination at one of the telemetry sites in the direction of an interfering
geostationary satellite is practicable. Thus, if the southerly (second) telemetry stations are
positioned such that azimuth bearings from 83° to 90° degrees at latitude 52.4° and from 81° to 90°
degrees at latitude 39° are excluded from the flight pattern, there will always be at least 25 dB
antenna discrimination.
3.9
Error free data
The transmission path to the aircraft may be switched or handed over between the aeronautical
telemetry receiving ground stations and error free data recovered by off-line processing of all data
transmitted via each transmission path after the trial. Moreover, such a method of processing will
also recover data lost in fades due to the aircraft attitude and variation in the gain of the airborne
telemetry antenna as shown in Figure 2 of Recommendation ITU-R M.1459.
3.10
Assumptions and interference model of Recommendation ITU-R M.1459
Before adopting the characteristic of power flux-spectral density versus elevation angle taken from
Recommendation ITU-R M.1459 and shown in Figure 2, it is necessary to consider the model and
assumptions on which the figure is based.
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3.10.1 Fundamental assumptions of Recommendation ITU-R M.1459
The assumptions on which the value of PFD of –181 dB(W/(4 kHz/m2)) at zero degrees elevation is
based are:
–
Noise temperature of telemetry receiver: 250 Kelvin
–
Telemetry antenna gain: 29 dBi
–
Maximum increase in telemetry receiver noise floor due to interference: 38.46%
–
Number of entries of interference on average: 2.5
–
Frequency: 1 500 MHz
3.10.2 Interference model of Recommendation ITU-R M.1459
The graph in Figure 2 is based on a model of one telemetry station at the centre of a hemisphere and
N satellites placed at random pointing angles as seen from the telemetry station and an aircraft that
can fly anywhere within a range of 320 kilometres of the telemetry station. During the test phase the
aircraft altitude is 20 kilometres, the flight pattern is contained within a 20 kilometre circle and the
range from telemetry station to aircraft is a maximum of 320 kilometres. The proportion of the
hemisphere that is swept by the beam of the telemetry ground station is then calculated as a function
of elevation angle. The flight patterns of an aircraft neat the limit of range (320 km) result in the
scanning of a 3.6 degree sector of the hemisphere near the radio horizon. Whilst in the case of an
aircraft that is regularly overhead the 20 kilometre diameter flight pattern results in the maximum
variation of pointing angles and the scanning of much of the hemisphere by the telemetry station
beam at high elevation angles. Thus the probability of scanning through the coordinates of one of
the randomly placed satellites is high at high elevation angles but the proportion of the time for
which the antenna dwells on those coordinates is very low. It is the limiting of the flight pattern to a
20 km diameter circle that explains these statistics. It is then assumed that a finite value of
unavailability is acceptable, although it is not quoted, and the permitted increase in pfd with
elevation can then be calculated. Thus, the pfd value of –181 dB(W/(4 kHz/m2)) at zero elevation is
a figure that is not based on statistics as the telemetry antenna scans through only 3.6 degrees.
Whilst pfd figures at higher elevation angles are based on assumptions regarding the flight path, a
20 km circle at an altitude of 20 km that result in substantial and rapid movements of the telemetry
antenna.
3.11
Validity of interference model with "stay in" zones and telemetry antenna
redundancy
Is it reasonable to adopt these statistics from Recommendation ITU-R M.1459:
•
when a new model is introduced where the aircraft is no longer free to fly anywhere;
•
the aircraft is restricted to a stay in zone that does not subtend unacceptable azimuth angles
at the telemetry station; and
•
where the principal method of avoiding interference is to use a second telemetry station?
The introduction of a stay out zone only removes a very small part of the hemisphere from the
calculation of unavailability and of necessity must improve the value. Further, the introduction of a
second telemetry station does not invalidate the link unavailability calculations for the link to the
first telemetry station, but must again only improve the value because of the introduction of a
redundant link to a second telemetry station.
The aeronautical network consisting of two telemetry stations will provide higher link availability
providing that the interference satellite pfd is not increased beyond the pfd where the interference to
the second telemetry station exceeds the interference previously received by the first station.
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3.12
Proposed increase in PFD with diversity telemetry station sites
Now from Figures 3.6A, 3.6B and 3.7 it can be seen that the antenna discrimination between the
directions of the aircraft and satellite at the second telemetry station site exceeds 25 dB and can be
higher than 40 dB. Where the antenna discrimination is less than 33 dB the zone is within the stay
out area, which is from azimuth angles 80 to 90 degrees as viewed from the second telemetry
station site. Thus the PFD may be increased by 25 dB and the link availability will be substantially
higher than with the singleton telemetry station sites. This is shown in Figure 3.12.
Proposed MSS satellite power flux spectral density and required MSS satellite antenna
discrimination as a function of satellite elevation angle within the affected aeronautical service
area
30.0
-20
25.0
-40
20.0
-60
Proposed MSS satellite power flux
spectral density
-80
15.0
-100
10.0
-120
-140
5.0
-160
-180 0
-200
10
20
30
40
50
60
required
MSS satellite
antenna
discrimination
Satellite elevation angle within the affected aeronautical service area (degrees)
70 0.0
required MSS satellite antenna
discrimination (dB)
Proposed MSS satellite power
flux spectral density
(dB(W/(4kHz*square metre))
0
-5.0
FIGURE 3.12
Proposed power flux-spectral density limits for geostationary satellites
Therefore, for an aircraft elevation angle of around 5 degrees or more, the associated telemetry site
diversity is a rather effective method to protect the aeronautical telemetry stations from interference.
3.13
Singleton telemetry antenna site
Alternatively, in the case of a singleton telemetry station site, the telemetry station may be sited
between the area above which test patterns are flown and the equator i.e. at a latitude lower than the
latitude of the flight pattern region.
3.14
Satellite antenna discrimination
It is very unlikely that the MSS operator will wish to use a service area with an elevation angle less
than about 15 degrees. Therefore at least 25 dB MSS satellite antenna discrimination may be
assumed in the case of the 12 metre satellite antenna of nominally 45 dBi gain. This value of
satellite antenna discrimination is achieved for angles exceeding 2 degrees subtended at the satellite
between the boresight of every downlink beam and the periphery of the aeronautical telemetry
service area. The value of interference calculated from this value of antenna discrimination is the
aggregate value and corresponds to interference entries from up to around 35 co-frequency beams.
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3.15
Belarus: MSS satellite antenna discrimination needed
The map below is a view from a geostationary satellite at 44° east and shows a beam from a
12 metre antenna of 45 dBi gain pointing at a boresight at 43.2° north and 34° east. The units of the
map are degrees as viewed from 44 east where the sub-satellite point is the origin. The boresight is
selected so that the 30° satellite elevation contour and the –7 dB antenna contour intersect at 51°
north 31° east which is just south of the southern frontier of Belarus. The inner beam contour is the
service area and the outer elevation contour is at 20° elevation. The map illustrates that the region
around Belarus that cannot be within the service area of the beams of the MSS satellite at 44 east is
quite small. Note that from Figure 3.12 above the required satellite antenna discrimination is 5 dB
rather than 7 dB i.e. there is about 2 dB margin. The 20° and 30° elevation contours of the satellite
at 44° east straddle Belarus and from Figure 3.4B it can be seen that there is no need to adopt a
"stay out area" when selecting zones for the flying patterns of the test aircraft.
3.5
2.5
1.5
-1.5
-0.5
0.5
FIGURE 3.15
Map showing the nearest MSS beam south of Belarus
3.16
USA: MSS satellite antenna discrimination needed
The map below is a view from a geostationary satellite at 98° west and shows a beam from a
12 metre antenna of 45 dBi gain pointing at a boresight at 38° north and 100° west. The units of the
map are degrees as viewed from 98 east where the sub-satellite point is the origin. The boresight is
selected so that the 42° satellite elevation contour and the service area contour intersect. The inner
beam contour is the service area and the outer beam contours are the –10, 15 and –20 dB gain
contours. The map illustrates that beams with service areas south of the 42 degree elevation contour
are unaffected by the constraint on e.i.r.p. spectral density. Note that from Figure 3.12 above the
required satellite antenna discrimination is 0 dB rather than 2 dB i.e. there is about 2 dB margin.
The 20° 30° 42° and 50° elevation contours of the satellite at 98° east are shown. Note that the
requirement to achieve 5 dB satellite antenna discrimination at the 30 degree elevation contour is
readily achieved since the –20 dB gain contour does not intersect with the 30 degree elevation
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contour. The 29° degree elevation contour is the lowest within the territory of the United States and
thus from Figure 3.4A it can be seen that there is no need to adopt a "stay out area" when selecting
zones for the flying patterns of the test aircraft. The protection of the United States national
aeronautical telemetry service is not limited to Andrews Air Base but encompasses the whole of the
United States.
3.5
2.5
1.5
0.5
-1.5
-0.5
0.5
1.5
FIGURE 3.16
Map showing the most northerly MSS beam without an e.i.r.p. reduction
4
Summary
It has been shown above that:
•
for geostationary MSS networks where the satellite antenna discrimination may exceed
25 dB;
•
and for networks of aeronautical receiving ground stations consisting of two or more
ground stations;
•
and placed such that one station is between 18 and 30 kilometres north or south of the
other;
•
and placed such that the telemetry station at the lower latitude is positioned so that azimuth
bearings from 80° to 90° degrees are excluded from the flight pattern (note in the case of
the examples selected this was not necessary),
and thus the frequency band 1 518 MHz-1 525 MHz may be shared by the geostationary MSS
space-to-Earth and the national aeronautical mobile telemetry services.
The conditions, imposed on the power flux-spectral density of geostationary MSS networks needed
to achieve these results, are given in Table 2B above and shown in Figure 3.12.
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