INTERNATIONAL TELECOMMUNICATION UNION
RADIOCOMMUNICATION
STUDY GROUPS
Received:
Subject:
WRC-2000 Resolution 137
Document UK-4A/CCC
September 2001
Original: English
UK SG4
CP(01)75
United Kingdom
ON THE USE OF SIMULATION TECHNIQUES TO VERIFY COMPLIANCE OF
NON-GSO FSS SATELLITE SYSTEMS WITH THE ADDITIONAL OPERATIONAL
LIMITS TO epfd
AND PROPOSED MODIFICATION OF PDNR S.[4A/TEMP/100]
Summary
Further simulations have been carried out using the methodology proposed in PDNR
S.[4A/TEMP/100] to demonstrate compliance with the single-entry additional operational
levels of epfd by a non-GSO FSS satellite system into receiving earth stations with 3 m and
10 m diameter antennas operating to GSO FSS satellites. Using a model for non-GSO
systems with tracking antennas, results for 18 hypothetical GSO downlinks are compared
with the single-entry validation limits and single-entry additional operational limits to epfd
in Tables S22-1A and S22-4A1 of the Radio Regulations. Some links exhibited levels of
epfd which exceeded the additional operational limits, and it is shown that, by adjustment of
some system parameters for the non-GSO constellation, the levels of epfd can be constrained
to within the limits.
Additionally, simulations have also been carried out for a non-GSO system with fixed beams,
and a modification to PDNR S.[4A/TEMP/100] is proposed, to provide guidance on
modelling of fixed-beam satellite systems.
1. Simulation of Tracking-Beam Non-GSO System
A previous document, Doc. 4A/151, described simulations of the non-GSO constellation
USAKU-L1 (which uses tracking beams) interfering with downlinks to 3m and 10m diameter
earth station antennas from three hypothetical GSO satellites. Figure 1 illustrates the
disposition of non-GSO earth stations and the three GSO earth stations, each of which
included 3 m and 10 m diameter antennas, operating to three hypothetical GSO satellites.
Details of the parameters used in the simulations are given in Doc. 4A/151.
2
FIGURE 1
Disposition of stations in the simulations
Table 1 lists the elevation angles of the links.
Satellite
GSO-1
TABLE 1
GSO earth station elevation angles (degrees)
ES-1
ES-2
28.5
30.8
ES-3
26.3
GSO-2
41.7
41.9
38.4
GSO-3
13.1
10.4
12.0
Taking account of frequency/polarization re-use schemes proposed for the USAKU-L1
system in Recommendation ITU-R S.1328, and the traffic load model given there, in terms of
variations in satellite transmit power as function of time of day, some of the 18 links modelled
did not fully meet the additional operational limits in Table S22-4A. Figures 2 and 3 show
the resultant cumulative distributions of epfd for the two antenna diameters, together with the
additional operational limits and the verification limits in Table S22.1A.
Further simulations have been carried out with this model, varying the GSO protection
switching angle and the maximum transmit power, to demonstrate that compliance can be
achieved through changes in the system parameters for the non-GSO constellation, and that
this can readily be examined using the simulation methodology proposed in PDNR
S.[4A/TEMP/100].
3
The following parameter values were investigated:




GSO switching angle - 10
GSO switching angle - 15
GSO switching angle - 20
GSO switching angle - 15
maximum e.i.r.p. per carrier 7.98 dBW
maximum e.i.r.p. per carrier 7.98 dBW
maximum e.i.r.p. per carrier 7.98 dBW
maximum e.i.r.p. per carrier 4.98 dBW
The results are shown in Figures 4 to 13 for those links on which the downlink interference
did not meet the additional operational limits in the basic configuration, i.e. with the first set
of parameters given above; more details of the simulations are given in Doc. 4A/151.
In some cases, a change in the GSO protection switching angle is sufficient to ensure that the
additional operational limits are met. For example, the 3m link from GSO-1 would be
protected within the limits if the switching angle is increased to 15 while the 10m link would
require a larger switching angle. In a number of cases, however, changing in switching angle
affects mostly the mid- to longer-term sections of the distribution (time percentages ~ 0.1 –
10%) and the increase in switching angle appears to have little effect at the very short time
percentage end of the distribution. However, a reduction in the maximum non-GSO satellite
e.i.r.p. can clearly achieve compliance with the additional operational limits, either on its
own or coupled with an increase in the GSO protection switching angle.
No attempt has been made in this study to carry out any fine tuning of the parameters to
ensure that the additional operational limits are just met, i.e. without an unnecessary margin.
Such investigations would clearly require some time to carry out, since each of the
simulations in this study required about 7 days of processing time on a 500 MHz machine.
However, this time would be reduced substantially with the latest generation processors.
Furthermore, only two possible parameters have been considered, i.e. the GSO protection
switching angle and the maximum satellite e.i.r.p per carrier. Other parameters which could
be considered include more sophisticated models for traffic loading, for example.
These examples serve to demonstrate, nevertheless, that simulation methodologies, such as
that proposed in PDNR S.[4A/TEMP/100], can readily be exploited to investigate the
variation of non-GSO system parameters to ensure compliance with the additional
operational limits for any particular GSO downlink.
4
Percentage of time epfd exceeded
102
3 m antennas
101
100
10-1
10-2
10-3
10-4
10-5
-210
-200
-190
-180
-170
-160
2
epfd, dBW/m in 40 kHz
FIGURE 2
Cumulative distributions of epfd for 9 GSO downlinks to 3m diameter antennas.
The verification limits are shown by black circles joined by dotted lines, while the additional
operational limits are indicated by black diamonds joined by dotted lines.
102
Percentage of time epfd exceeded
10 m antennas
101
100
10-1
10-2
10-3
10-4
10-5
-220
-210
-200
-190
-180
2
epfd, dBW/m in 40 kHz
FIGURE 3
As Figure 2, for 10 m diameter antennas
-170
-160
5
101
Percentage of time epfd exceeded
GSO-1 3m Link 2
100
10-1
10-2
10-3
10-4
-210
SA 10o
SA 15o
SA 20o
SA 15o -3dB
S.22 Ver
S.22 AOL
-200
-190
-180
-170
-160
2
epfd, dBW/m in 40 kHz
FIGURE 4
Cumulative distributions of epfd for 3 m antenna link for different GSO switching angles:
SA = 10, 15 and 20, and SA = 15 with e.i.r.p. reduced by 3 dB
100
Percentage of time epfd exceeded
GSO-1 10m Link 2
10-1
10-2
o
10-3
10-4
-210
SA 10
SA 15o
SA 20o
SA 15o -3dB
S.22 Ver
S.22 AOL
-200
-190
-180
-170
2
epfd, dBW/m in 40 kHz
FIGURE 5
As in Figure 4, for 10 m diameter antenna
-160
6
101
Percentage of time epfd exceeded
GSO-1 3m Link 3
100
10-1
10-2
10-3
10-4
-210
o
SA 10
SA 15o
SA 20o
SA 15o -3dB
S.22 Ver
S.22 AOL
-200
-190
-180
-170
-160
2
epfd, dBW/m in 40 kHz
FIGURE 6
As in Figure 4
101
Percentage of time epfd exceeded
GSO-1 10m Link 3
100
10-1
10-2
10-3
10-4
-220
SA 10o
o
SA 15
SA 20o
SA 15o -3dB
S.22 Ver
S.22 AOL
-210
-200
-190
-180
2
epfd, dBW/m in 40 kHz
FIGURE 7
As in Figure 4 for 10 m diameter antenna
-170
-160
7
101
Percentage of time epfd exceeded
GSO-2 3m Link 1
100
10-1
10-2
10-3
o
SA 10
SA 15o
SA 20o
SA 15o -3dB
S.22 Ver
S.22 AOL
10-4
10-5
-210
-200
-190
-180
-170
-160
2
epfd, dBW/m in 40 kHz
FIGURE 8
As in Figure 4
101
Percentage of time epfd exceeded
GSO-2 10m Link 1
100
10-1
10-2
10-3
10-4
10-5
-220
SA 10o
o
SA 15
SA 20o
SA 15o -3dB
S.22 Ver
S.22 AOL
-210
-200
-190
-180
2
epfd, dBW/m in 40 kHz
FIGURE 9
As in Figure 4, for 10 m diameter antenna
-170
-160
8
101
Percentage of time epfd exceeded
GSO-2 3m Link 3
100
10-1
10-2
10-3
10-4
10-5
-210
SA 10o
SA 15o
SA 20o
SA 15o -3dB
S.22 Ver
S.22 AOL
-200
-190
-180
-170
-160
2
epfd, dBW/m in 40 kHz
FIGURE 10
As in Figure 4
101
Percentage of time epfd exceeded
GSO-2 10m Link 3
100
10-1
10-2
10-3
10-4
10-5
-220
SA 10o
SA 15o
SA 20o
SA 15o -3dB
S.22 Ver
S.22 AOL
-210
-200
-190
-180
2
epfd, dBW/m in 40 kHz
FIGURE 11
As in Figure 4, for 10 m diameter antenna
-170
-160
9
101
Percentage of time epfd exceeded
GSO-3 3m Link 3
100
10-1
10-2
10-3
10-4
-210
SA 10o
SA 15o
o
SA 20
SA 15o -3dB
S.22 Ver
S.22 AOL
-200
-190
-180
-170
-160
2
epfd, dBW/m in 40 kHz
FIGURE 12
As in Figure 4
101
Percentage of time epfd exceeded
GSO-3 10m Link 3
100
10-1
10-2
10-3
10-4
10-5
-220
SA 10o
SA 15o
SA 20o
o
SA 15 -3dB
S.22 Ver
S.22 AOL
-210
-200
-190
-180
2
epfd, dBW/m in 40 kHz
FIGURE 13
As in Figure 4, for 10 m diameter antenna
-170
-160
10
2. Simulation of Fixed-Beam Non-GSO System
The USAKUM1 constellation was used as an example of a fixed-beam system, with
parameters taken from Recommendation ITU-R S.1328. Table 2 lists relevant parameters for
the constellation.
TABLE 2
Non-GSO orbital parameters
Shape of orbit
Height (km)
Inclination angle (deg)
Orbit period (min)
Number of satellites per plane
Number of orbital planes
Satellite phasing between planes
Circular
20,182
57
718.2
5
4
36
The beam coverage area for USAKUM1 is defined by 37 fixed beams, the azimuth and
elevation of which are given in Table 30 of Recommendation S.1328. A 1-in-3 frequency reuse scheme is employed, shown in Figure 14, where the numbers identify each of the beams,
and the colour coding gives the frequency re-use scheme for the downlinks which was
modelled in the present simulations. Only RHC polarization was modelled, since the
polarization discrimination to the linear polarization modelled for the GSO downlinks will be
the same for both the LH and RH cases.
36
37
38
35
12
33
22
23
24
25
34
12°
32
31
21
11
X
26
39
310
14
27
311
29
12.0 GHz
313
211
210
314
12.2 GHz
30
20
15
28
312
10
00
13
317
316
315
12.4 GHz
FIGURE 14
Schematic of frequency/polarization re-use scheme in satellite beam.
Note that in the simulations, only RHC polarization was employed.
11
The downlink parameters used in the simulations are given in Table 3.
TABLE 3
Non-GSO Downlink Parameters
Satellite transmit antenna beam pattern
Rec.S.1328 Table 31
Satellite transmit peak antenna gain (dBi)
32.2
Maximum satellite e.i.r.p. (dBW)
50.2
GSO arc avoidance (deg)
10
Earth station receive antenna pattern
Rec.S.465
Earth station receive peak antenna gain (dBi)
36.1
Earth station receive noise temperature (K)
232
Allocated bandwidth (MHz)
20
Occupied bandwidth (MHz)
20
Symbol rate (MHz)
20
Access/code
CDMA/QPSK
Number of codes
98
Polarization
RHC
Downlink frequencies (GHz)
12.0, 12.2, 12.4
Figure 15 illustrates the footprints from one of the satellites, together with the disposition of
earth stations used in the simulations.
Recommendation S.1328 specifies that, for USAKUM1, the maximum number of cofrequency earth stations in each beam is 96. It is impracticable to model this number of earth
stations in each beam, and so approximations have to be made, by modelling a reduced
number of earth stations and adjusting the e.i.r.p. in each beam accordingly.
Recommendation S.1328 specifies only that the maximum satellite e.i.r.p. is 50.2 dBW. The
model was therefore set up by distributing varying numbers of earth stations across an area
and observing the number of active beams from each satellites. This varied from one per
satellite up to about 20 per satellite, depending on the locations of the satellites. Taking an
average of about 10 beams per satellite, the e.i.r.p. in each beam was set to 40 dBW.
The downlinks to each earth station were set up to take the frequency from the beam, to
ensure that the earth stations switched frequency when changing to a different beam, as
appropriate.
To determine the interference into GSO earth stations with 3m and 10m antennas, a
hypothetical GSO satellite was located at 73 W transmitting to three earth stations, each with
3m and 10m diameter antennas. The distribution of the GSO earth stations are indicated in
Figure 15, with one station located at a latitude of 76.5N and at the same longitude as the
GSO satellite, which is given as the worst-case location for interference from USAKUM1 in
Recommendation S.1328.
The parameters for the GSO downlink are given in Table 4, and the elevation angles of the
earth station antennas were, from north to south 4, 28 and 35 (ES-1, ES-2 and ES-3).
12
FIGURE 15
Disposition of earth stations used in the simulation, together with footprints from one
USAKUM1 satellite. The three small antenna icons pointing NW represent the locations of
the GSO earth stations.
TABLE 4
GSO Downlink Parameters
Satellite transmit antenna beam pattern
Satellite transmit peak antenna gain (dBi)
3 dB beamwidth (deg)
Transmit e.i.r.p. (dBW)
Earth station receive antenna beam pattern
Earth station peak antenna gain – 3m (dBi)
Earth station –3 dB beamwidth –3m (deg)
Earth station peak antenna gain –10m (dBi)
Earth station –3 dB beamwidth –10m (deg)
Allocated bandwidth (MHz)
Occupied bandwidth (MHz)
Symbol rate (MHz)
Access/code
Polarization
Frequency (GHz)
App 30 Sat Tx
35
3
30
Rec. S.1428
49.3
0.57
59.7
0.17
50
50
50
TDMA/QPSK
Linear H
12.0
The simulations were done with 1 second time steps, for a total of more than 4106 seconds,
representing some 54 days of simulation time. This covered many satellite repeat ground
tracks. Interference was determined on each downlink taking into account both frequency
13
discrimination and polarization discrimination according to the ITU-R tables. The results are
shown in Figures 15 and 16 for the 3m and 10m diameter antennas, respectively.
102
Percentage of time epfd exceeded
3m antennas
101
100
10-1
10-2
ES-1
ES-2
ES-3
S.22 Ver
S.22 AOL
10-3
10-4
-230
-220
-210
-200
-190
-180
-170
-160
2
epfd, dBW/m in 40 kHz
FIGURE 15
Cumulative distributions of interference from USAKUM1 into 3m diameter antennas,
compared with the limits in RR Table S.22
102
10m diameter antennas
Percentage of time epfd exceeded
101
100
10-1
10-2
10-3
10-4
10-5
-240
ES-1
ES-2
ES-3
S.22 Ver
S.22 AOL
-230
-220
-210
-200
-190
-180
-170
-160
2
epfd, dBW/m in 40 kHz
FIGURE 16
Cumulative distributions of interference from USAKUM1 into 10m diameter antennas,
compared with the limits in RR Table S.22
14
The interference distributions were measured using a bin size of 0.25 dB, and despite running
for more than 4 million time steps, some of the distributions do not fall below 0.01% of the
time. USAKUM1 has a orbital period of ~12 hours, so the simulations represent over 100
repeat orbits. Since the beams are fixed, though, the interference into the GSO earth stations
will tend to repeat for each orbit, resulting in large numbers of samples in the highest bins,
and simulation times could be excessively long if the time percentages are to fall below
0.001% or less. For some of the links, though, the time percentage did fall to below the
required level, as specified in the PDNR, and it is unlikely that the distribution would change
significantly if the simulation were to run for longer.
Nevertheless, the results show that a fixed-beam system can be effectively modelled using
simulation methodologies and further suggest that, with the system parameters as modelled
here, the USAKUM1 system should comply with the additional operational limits.
3. Summary and Proposed Modification to PDNR S.[4A/TEMP/100]
This document has shown that simulation methodologies can be used effectively to determine
the likely levels of interference from non-GSO satellite systems into the downlinks of GSO
satellite systems in shared frequency bands. In cases where the results suggest that the likely
levels of interference may exceed the additional operational limits, the simulation
methodology can be used to adjust the parameters of the non-GSO system in such a way as to
ensure that the additional operational limits will be met, for a particular GSO downlink
configuration. Clearly, resolution of any situations in which the additional operational limits
may not be met will involve dialogues between the operators of both the non-GSO and the
GSO systems concerned.
Doc. 4A/TEMP/100 proposes a Preliminary Draft New Recommendation describing a
suitable methodology with which compliance with the additional operational limits may be
verified, and which may be used additionally to investigate adjustments to parameters of the
non-GSO system to ensure that the limits are met, as demonstrated in this document. The
PDNR included a description of methods by which to set up simulations for non-GSO
systems with tracking beams, but did not include any guidance on how to set up simulations
for non-GSO systems which employ fixed beams. This document has suggested a possible
method, particularly for cases where it is impractical to model all possible numbers of earth
stations, which could result in overly excessive run-times for the simulation. By reducing the
number of earth stations to a small number in each beam, sufficient to ensure that each beam
becomes active over the region in which the GSO earth stations are being modelled, and
increasing the effective e.i.r.p. in each beam to compensate, commensurate with the available
values of non-GSO transmit power levels, it is possible to reduce running times of the
simulation to manageable and realistic levels.
The following changes are therefore proposed in PDNR S.[4A/TEMP/100]:
In Annex 1 § 5.1, after Figure 3, replace “[Example of fixed-beam system – TBD]” with
the following text:
“For fixed-beam systems, especially in examples where it is impractical to model the total
number of earth stations which may be specified for the non-GSO system, it should be
15
possible to verify compliance with the additional operational limits using a smaller number
of earth stations, sufficient in density to ensure that each beam of the non-GSO satellite
becomes active over the region in which the GSO earth stations are located, extending that
region outwards by adding concentric rings of non-GSO earth stations until the epfd does not
increase significantly, as measured by successive short runs. To compensate for the reduced
number of non-GSO earth stations, the effective e.i.r.p. in each beam should be increased in a
commensurate way, ensuring that, on the average, the overall beam e.i.r.p. and/or satellite
e.i.r.p. conforms with that specified for the non-GSO satellite system.”
Delete the Table of Parameters at the end of Annex 1.
______________________________