2. Simulation of Fixed-Beam Non-GSO System - Ofcom

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Subject: WRC
-
2000 Resolution 137






United Kingdom



ON THE USE OF SIMULATIO
N 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 PDN
R
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
limit
s

to
epfd


in Tables S22
-
1A and S22
-
4A1 of the Radio Regulations. Some lin
ks 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, simulati
ons 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 docume
nt, 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.


INTERNATIONAL TELECOMMUNICATION UNION

RADIOCOMMUNICATION

STUDY

GROUPS


Document UK
-
4A/CCC

September 2001

Original: English

UK SG4

CP(01)75


2





FIGURE 1

D
isposition of stations in the simulations



Table 1 lists the elevation angles of the links.


TABLE 1

GSO earth station elevation angles (degrees)

Satellite

ES
-
1

ES
-
2

ES
-
3

GSO
-
1

GSO
-
2

GSO
-
3

28.5

41.7

13.1

30.8

41.9

10.4

26.3

38.4

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 constellatio
n, 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


maximum e.i.r.p. per carrier 7.98 dBW



GSO switching angle
-

15


maximu
m e.i.r.p. per carrier 7.98 dBW



GSO switching angle
-

20


maximum e.i.r.p. per carrier 7.98 dBW



GSO switching angle
-

15


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 sufficien
t 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 case
s, 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 distri
bution. 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 methodologie
s, 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


3 m antennas
epfd
, dBW/m
2
in 40 kHz
-210
-200
-190
-180
-170
-160
Percentage of time
epfd
exceeded
10
-5
10
-4
10
-3
10
-2
10
-1
10
0
10
1
10
2

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 dotte
d lines.


10 m antennas
epfd
, dBW/m
2
in 40 kHz
-220
-210
-200
-190
-180
-170
-160
Percentage of time
epfd
exceeded
10
-5
10
-4
10
-3
10
-2
10
-1
10
0
10
1
10
2

FIGURE 3

As Figure 2, for 10 m diameter antennas




5



GSO-1 3m Link 2
epfd
, dBW/m
2
in 40 kHz
-210
-200
-190
-180
-170
-160
Percentage of time
epfd
exceeded
10
-4
10
-3
10
-2
10
-1
10
0
10
1
SA 10
o

SA 15
o

SA 20
o

SA 15
o
-3dB
S.22 Ver
S.22 AOL

FIGURE 4

Cumulative distributions of
epfd


for 3 m antenna link for different GSO switching angles:

SA = 10

, 15


and 20

, a
nd SA = 15


with e.i.r.p. reduced by 3 dB

GSO-1 10m Link 2
epfd
, dBW/m
2
in 40 kHz
-210
-200
-190
-180
-170
-160
Percentage of time
epfd
exceeded
10
-4
10
-3
10
-2
10
-1
10
0
SA 10
o

SA 15
o

SA 20
o

SA 15
o
-3dB
S.22 Ver
S.22 AOL


FIGURE 5

As in Figure 4, for 10 m diameter antenna




6

GSO-1 3m Link 3
epfd
, dBW/m
2
in 40 kHz
-210
-200
-190
-180
-170
-160
Percentage of time
epfd
exceeded
10
-4
10
-3
10
-2
10
-1
10
0
10
1
SA 10
o

SA 15
o

SA 20
o

SA 15
o
-3dB
S.22 Ver
S.22 AOL

FIGURE 6

As in Figure 4


GSO-1 10m Link 3
epfd
, dBW/m
2
in 40 kHz
-220
-210
-200
-190
-180
-170
-160
Percentage of time
epfd
exceeded
10
-4
10
-3
10
-2
10
-1
10
0
10
1
SA 10
o

SA 15
o

SA 20
o

SA 15
o
-3dB
S.22 Ver
S.22 AOL

FIGURE 7

As in Figure 4 for 10 m

diameter antenna




7

GSO-2 3m Link 1
epfd
, dBW/m
2
in 40 kHz
-210
-200
-190
-180
-170
-160
Percentage of time
epfd
exceeded
10
-5
10
-4
10
-3
10
-2
10
-1
10
0
10
1
SA 10
o

SA 15
o

SA 20
o

SA 15
o
-3dB
S.22 Ver
S.22 AOL

FIGURE 8

As in Figure 4


GSO-2 10m Link 1
epfd
, dBW/m
2
in 40 kHz
-220
-210
-200
-190
-180
-170
-160
Percentage of time
epfd
exceeded
10
-5
10
-4
10
-3
10
-2
10
-1
10
0
10
1
SA 10
o

SA 15
o

SA 20
o

SA 15
o
-3dB
S.22 Ver
S.22 AOL

FIGURE 9

As in Figure 4, for 10 m diameter antenna




8

GSO-2 3m Link 3
epfd
, dBW/m
2
in 40 kHz
-210
-200
-190
-180
-170
-160
Percentage of time
epfd
exceeded
10
-5
10
-4
10
-3
10
-2
10
-1
10
0
10
1
SA 10
o

SA 15
o

SA 20
o

SA 15
o
-3dB
S.22 Ver
S.22 AOL

FIGURE 10

As in Figure 4


GSO-2 10m Link 3
epfd
, dBW/m
2
in 40 kHz
-220
-210
-200
-190
-180
-170
-160
Percentage of time
epfd
exceeded
10
-5
10
-4
10
-3
10
-2
10
-1
10
0
10
1
SA 10
o

SA 15
o

SA 20
o

SA 15
o
-3dB
S.22 Ver
S.22 AOL


FIGURE 11

As in Figure 4, for 10 m diameter antenna



9

GSO-3 3m Link 3
epfd
, dBW/m
2
in 40 kHz
-210
-200
-190
-180
-170
-160
Percentage of time
epfd
exceeded
10
-4
10
-3
10
-2
10
-1
10
0
10
1
SA 10
o

SA 15
o

SA 20
o

SA 15
o
-3dB
S.22 Ver
S.22 AOL


FIGURE 12

As in Figure 4

GSO-3 10m Link 3
epfd
, dBW/m
2
in 40 kHz
-220
-210
-200
-190
-180
-170
-160
Percentage of time
epfd
exceeded
10
-5
10
-4
10
-3
10
-2
10
-1
10
0
10
1
SA 10
o

SA 15
o

SA 20
o

SA 15
o
-3dB
S.22 Ver
S.22 AOL

FIGURE 13

As in Figure 4, for 10 m diameter antenna






10

2.

Simulation of Fixed
-
Beam Non
-
GSO System


The USA
KUM1 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

Circular

Height (km)

20,
182

Inclination angle (deg)

57

Orbit period (min)

718.2

Number of satellites per plane

5

Number of orbital planes

4

Satellite phasing between planes

36


The beam coverage area for USAKUM1 is defined by 37 fixed beams, the azimuth and
elevation of whi
ch are given in Table 30 of Recommendation S.1328. A 1
-
in
-
3 frequency re
-
use 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.

00
10
13
15
14
12
11
32
22
31
21
33
314
315
313
29
210
311
28
312
310
27
35
34
36
23
24
317
211
316
20
30
38
25
26
39
37
12°
X
12.0 GHz
12.2 GHz
12.4 GHz


FIGURE 14

Schemati
c 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)




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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 pa
ttern

App 30 Sat Tx

Satellite transmit peak antenna gain (dBi)

35

3 dB beamwidth (deg)

3

Transmit e.i.r.p. (dBW)

30

Earth station receive antenna beam pattern

Rec. S.1428

Earth station peak antenna gain


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10
6

seconds,
representing some 54 days of simulation time. This covered many satellite repeat ground
tracks. Interference was determined on each downlink taking into ac
count 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.

3m antennas
epfd
, dBW/m
2
in 40 kHz
-230
-220
-210
-200
-190
-180
-170
-160
Percentage of time
epfd
exceeded
10
-4
10
-3
10
-2
10
-1
10
0
10
1
10
2
ES-1
ES-2
ES-3
S.22 Ver
S.22 AOL

FIGURE 15

Cumulative dist
ributions of interference from USAKUM1 into 3m diameter antennas,

compared with the limits in RR Table S.22

10m diameter antennas
epfd
, dBW/m
2
in 40 kHz
-240
-230
-220
-210
-200
-190
-180
-170
-160
Percentage of time
epfd
exceeded
10
-5
10
-4
10
-3
10
-2
10
-1
10
0
10
1
10
2
ES-1
ES-2
ES-3
S.22 Ver
S.22 AOL

FIGURE 16

Cumulative distributions of interference from USAKUM1 into 10m diameter antennas,

compared with the limi
ts 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 coul
d 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
signif
icantly 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 sat
ellite 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 me
t 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

limi
ts 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 simula
tions 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 mod
el 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 manageab
le 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 wher
e 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 densit
y 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 significan
tly, 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 satel
lite
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.




______________________________