Radiocommunication Study Groups
CPG(17)011 ANNEX VI-01
Received: DATE 2017
Subject:
WRC-19 AI 1.5
Document 4A/XXX-E
XX YYYY 2017
English only
United Kingdom of Great Britain and Northern Ireland1
PROTECTION OF THE FIXED SERVICE FROM AERONAUTICAL-ESIM
1. Introduction
The CEPT established a framework for ESIM operation in the frequency range 27.5-30.0 GHz and
17.3-20.2 GHz with ECC Decision (13)01. Leading up to the ECC Decision, extensive studies were
performed on the coexistence between Aeronautical-ESIM (A-ESIM) and Fixed Service (FS)
stations. The results of these studies have been recorded in ECC Report 184 and can be utilised in
the context of WRC-19 AI 1.5 on ESIM operating in the 27.5-29.5 GHz.
The CEPT studies established that in order to protect FS links from A-ESIM interference, PFD
levels on the ground need to be established. ITU WP 4A can take advantage of the CEPT analysis
and confirm whether similar or the same PFD levels are sufficient for the protection of FS links in
the ITU.
This contribution introduces the PFD levels defined in ECC Decision (13)01 and the assumptions
based on which these levels were developed. Consequently, it is then verified that the CEPT PFD
levels are sufficient to protect the FS stations that have been included in Annex 17 of the
Chairman’s Report of ITU-R Working Party 4A (4A/196) on “Preliminary study material for the
case of airborne ESIM and fixed service in the 27.5-29.5 GHz frequency band” (4A/196) that was
developed during the WP 4A meeting on 28 September-6 October, 2016. The contribution
consequently suggest to produce a liaison statement to WP 5C to ask for their comments on the
study and confirm whether the correct assumptions about FS networks have been taken into
consideration.
2. Studies of A-ESIM interference into FS in the CEPT
In order to establish the PFD levels to protect the FS, the parameters of stations shown in Table 1
were considered. The parameters were established using Recommendation ITU-R 758-5 (FS 5 and
FS 6) and inputs from CEPT administrations regarding actual FS deployments (FS 1, FS 2, FS 3
and FS 4). It can be seen that both point-to-point (PP) and point-to-multipoint (P-MP) stations were
taken into consideration with various elevation angles, maximum receive antenna gains, noise
figures and patterns.
____________________
1
This contribution has been developed and agreed within the framework of CEPT ECC CPG.
-24A/XXX-E
TABLE 1 FS CHARACTERISTICS USED FOR ESTABLISHING PFD LEVELS
Parameter
FS1 (PP)
FS2 (PP)
FS3 (PP)
FS4(PMP)
FS5
FS6
(PP based on Rec.
ITU-R 758-5)
(P-MP based on Rec.
ITU-R 758-5)
RX antenna
height
20 m
20m
20m
20m
Not specified, 20m
is suggested
Not specified, 20m is
suggested
RX antenna
pattern
ITU-R
Rec.
F.1245
ITU-R
Rec.
F.1245
ITU-R
Rec.
F.1245
ITU-R
Rec.
F.1336
ITU-R Rec. F.
1245
ITU-R Rec. F.1336
Receiver
noise figure
6 dB
6 dB
6 dB
6 dB
8 dB
8 dB
RX
frequency
28 GHz
28 GHz
28 GHz
28 GHz
24.25–29.50 GHz
24.25– 29.50 GHz
RX
elevation
angle
0°
5°
10°
0°
Not specified, 10°
is suggested
Not specified, 0° is
suggested
RX
peak gain
45 dBi
43 dBi
35 dBi
18 dBi
31.5 dBi
6.5 dBi
PFD levels were developed to protect the FS deployments in Table 1 from A-ESIM interference
during aircraft overflight for all azimuth angles. It was concluded during the studies that the FS
stations submitted by CEPT administrations (i.e. FS 1- FS 4 in Table 1) are more sensitive to
interference than the ones derived from Recommendation ITU-R F.758 5 (i.e. FS 5 and FS 6). This
is also obvious when looking at the station parameters in Table 1, as the stations derived based on
ITU-R F.758-5 have lower antenna gains and higher noise figures for the same deployment type
(elevation angle, P-MP/PP). In particular, the key drivers for the development of the PFD levels
were FS 1-FS 3 due to the high antenna gain values.
CEPT studies concluded that the following PFD mask on the ground is sufficient to protect FS
deployments:
PFD(δ) = −124.7
PFD(δ) = −120.9 + 1.9 ∙ log10(δ)
PFD(δ) = −116.2 + 11 ∙ log10(δ)
PFD(δ) = −116.2 + 18 ∙ log10(δ)
PFD(δ) = −117.9 + 23.7 ∙ log10(δ)
PFD(δ) = −96.5
(dBW/m2/14 MHz)
(dBW/m2/14 MHz)
(dBW/m2/14 MHz)
(dBW/m2/14 MHz)
(dBW/m2/14 MHz)
(dBW/m2/14 MHz)
for
for
for
for
for
for
0° ≤ δ ≤ 0.01°
0.01° ≤ δ ≤ 0.3°
0.3° < δ ≤ 1°
1° < δ ≤ 2°
2° < δ ≤ 8°
8° < δ ≤ 90.0°
where δ is the angle of arrival at the Earth’s surface (degrees) and the PFD value us in dBW/m2 in a
reference bandwidth of 14 MHz
CEPT studies also indicated that while scenarios of excessive interference can theoretically be
identified even when the PFD is used, the probability of interference occurring in practise is very
low and is therefore acceptable.
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3. Applicability of CEPT defined PFD mask for WRC-19 AI 1.5
Resolution 158 resolves to invite ITU-R 2 provides that the operations of ESIM in the 17.7-19.7
GHz and 27.5-29.5 GHz should ensure protection of, and not impose undue constraints on, services
allocated in these frequency bands. Further, according to recognising further k) fixed and mobile
services are allocated on a global, primary basis in the 27.5-29.5 GHz.
ITU-R Working Party 4A has already produced a preliminary interference study in Annex 17 of
4A/196 which draws upon the elements of the CEPT studies, as it analyses interference into CEPT
defined FS stations FS 1, FS 2 and FS 3 in Table 1from aircraft operating on altitudes on 1, 5 and
10 km.
In order to verify the applicability of the PFD mask developed in CEPT for the protection of the FS,
a similar analysis to the one in Annex 17 of 4A/196 is produced. Specifically, the study uses the
same FS system parameters, aircraft altitudes and interference criteria, however, a different
interference scenario is established. The aircraft is modelled to create exactly the PFD levels shown
in section 2 on the ground at the location of the FS station during each step of the flight. This means
that parameters such as propagation models, A-ESIM elevation angles and power levels, aircraft
body loss is irrelevant for this type of analysis. Interference at the FS receiver changes due to the
antenna gain pattern of the FS station and aircraft flight direction. The analysis considers a worstcase scenario flight-path, where the aircraft appears on the visible horizon of the FS station in the
azimuth of maximum gain and follows that azimuth until it passes over the FS station and reaches
the horizon facing the back-lobe of the FS antenna. The same interference set up was also
considered in the CEPT studies to develop the PFD levels and has been illustrated on Figure 1
below.
Figure 1 Interference geometry between FS stations and ESIM considered in CEPT studies
The same interference criteria for the protection of the FS as shown in Annex 17 of 4A/196 is used
in the analysis and is summarised in Table 2 below.
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TABLE 2 INTERFERENCE CRITERIA FOR THE PROTECTION OF FS USED IN ANNEX 17 OF 4A/196
Parameter
Value
Source
FS bandwidth
14 MHz
Long-term (LT) interference criterion
-10 dB (20% of time)
ITU-R F.758-6
Short-term (ST) interference criterion
25 dB (0.005% of time)
ITU-R SM.1448
Noise Figure
8 dB
ITU-R F.758-6
Permissible interference power LT
-134.5 dBW/14 MHz
Permissible interference power ST
-99.5 dBW/14 MHz
The results of the analysis are indicated in Table 3 below.
TABLE 3 PFD VERIFICATION RESULTS
Parameter
Aircraft Height
1 km
5 km
10 km
FS Station Type
FS 1
FS 2
FS 3
FS 1
FS 2
FS 3
FS 1
FS 2
FS 3
LT Interference
duration
27.1%
5.8%
2.9%
15.9%
11.3%
6.2%
11.9%
13.9%
8.42%
ST interference
duration
0%
0%
0%
0%
0%
0%
0%
0%
0%
LT criterion
exceeded (by %)
YES
(7.1%)
NO
NO
NO
NO
NO
NO
NO
NO
ST criterion
exceeded
(by %)
NO
NO
NO
NO
NO
NO
NO
NO
NO
The results indicate that the short-term interference criterion is not exceeded for any of the cases.
The long term interference criterion is exceeded by 7.1% in the case of FS 1 using 1 km aircraft
altitude. Based on these results, low altitude flights were examined further and it was found that the
PFD mask on the ground exceeds the protection criterion for flights lower than 2.5 km. Further,
flights in the direction of the FS station, but slightly off the azimuth of maximum gain of FS1 were
also explored and it was established that at an altitude of 2.5 km, if the aircraft route deviates 0.2
degrees away from the azimuth direction of the FS station, then the interference criteria will not be
exceeded. Hence, it can be concluded that interference at FS stations only occurs:





for a specific aircraft flight direction that is within 0.2 degrees from the azimuth
direction of the FS station maximum gain;
The aircraft passes directly overhead the FS station;
for aircraft altitudes lower or equal to 2.5 km;
for a specific FS station deployment type (FS 1 as shown in Table 1);
when the A-ESIM and FS receiver are co-frequency.
The probability of occurrence of such conditions is analysed in more detail in the next section.
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4. Interference probability
The probability of interference into FS 1 station from ESIM terminals on aircraft flying at an
altitude of 2.5 km is studied in detail below. Considering uniform distribution of frequency usage
and airplane locations, two main factors determine the probability of interference:
 The probability that the aircraft will be flying within 0.2 degrees from both sides of the FS1
station maximum gain azimuth- PA;
 The probability that FS 1 and A-ESIM frequency channels overlap – PB.
As indicated in the previous section, interference only occurs if the aircraft flies in a specific
direction – within 0.2 degrees from the azimuth of maximum gain of the FS 1 station. The
probability of an aircraft flying in this direction can be easily determined by dividing the number of
the flight paths where interference occurs with the flight paths where interference does not occur:
𝑷𝐴 =
0.4
= 0.0011
360
This scenario is illustrated on Figure 2 below.
Figure 2 Area of interference for FS1 considering aircraft attitude of 2.5 km
In addition to the location specific probability, the FS station would also need to operate on the
same frequency channel as the A-ESIM. The FS station can operate in a channel anywhere in the
27.5-30 GHz range (2500 MHz). Given that the FS station has a bandwidth of 14 MHz and the AESIM bandwidth is around 10 MHz, then the probability of an A-ESIM station occupying a FS
channel can simply be found as:
14
= 0.0056
2500
Since probability 𝑷𝐴 and 𝑷𝐵 are independent of each other, the total probability for A-ESIM
interference into FS 1 can be determined as:
𝑷𝐵 =
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𝑃𝐴 (0.0011) × 𝑃𝐵 (0.0056) = 0.00000616 × 100 = 𝟎. 𝟎𝟎𝟎𝟔𝟐%
The above is applicable when the possible number of A-ESIM interferers is limited to one. The
potential impact of multiple A-ESIM interferers has been considered in the following section.
5. Number of possible A-ESIM interferers
Ka-band satellites operate using spotbeams, which vary in shape and size, but can be generally
compared to the area where the A-ESIM station is visible to the FS station. For instance, the visible
area of FS 1 assumed to be located in United Kingdom for an aircraft height of 2.5 km has been
shown on Figure 3 below (in black). In comparison, the GSO satellite spotbeam (in red) is indicated
assuming 3dB beamwidth of 0.5 degrees and an orbital location on the same longitude as the FS
station.
FIGURE 3 VISIBLE AREA OF FS 1 (IN BLACK) AND GSO SATELLITE 0.5 DEGREE SPOTBEAM (IN RED)
In order to control intra-system satellite noise levels, the same frequency channel cannot be
operated within the same satellite beam by multiple A-ESIM terminals at the same time. As the
visible area of the FS station is almost fully covered by the satellite beam, we can conclude that the
same operator is not able to cause aggregate interference to the FS station from multiple A-ESIM
stations.
In addition, the same frequency channel is normally not used in the adjacent beams at the same time
either, since this would also produce high levels of intra-system interference. This creates a large
area around a specific FS station, where the same frequency channel cannot be operated by multiple
A-ESIM stations by the same satellite operator.
There is a risk that multiple A-ESIM operators will be using the same frequency at the same time in
the visible area of the FS station. However, the probability that two A-ESIM operators happen to
use the same A-ESIM channel in the same geographic area indicates that such an occurrence is very
unlikely.
In the 27.5-30 GHz band there are roughly 250 channels (2500/10) to choose from. The probability
of an A-ESIM of one operator using the exact same channel as another operator in that case is:
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1
= 0.004
250
In addition, we need to consider the probability that these two channels would need to overlap with
a FS station channel. This can be calculated by multiplying the 𝑷𝑡𝑤𝑜_𝑜𝑝 with the probability that the
FS station also falls on the same channel (𝑷𝐵 as calculated in section Error! Reference source not
found.).
𝑷𝑡𝑤𝑜_𝑜𝑝 =
𝑷𝑡𝑤𝑜 𝑒𝑠𝑖𝑚 = 𝑷𝑡𝑤𝑜𝑜𝑝 × 𝑷𝐵 = 0.004 ∙ 0.0056 ∙ 100 = 𝟎. 𝟎𝟎𝟐𝟐%
In addition, similarly to the interference from one A-ESIM terminal, multiple A-ESIM terminals
can only produce interference to the FS station under certain conditions. First of all, multiple
aircraft would need to operate on low altitudes and within a small geographic area in the direction
of the FS azimuth of maximum gain. Secondly, the actual pfd produced by an A-ESIM will vary
with azimuth due to the variation in the off-axis antenna gain of the A-ESIM and due to variation in
fuselage blocking. Consequently, an aircraft which just meets the pfd on the worst case azimuth
will produce a pfd lower than the limit for other azimuths. Hence the worst case occurs for a rare
case when the azimuth of the A-ESIM station points towards the FS station. The occurrence of all
of the above conditions for two A-ESIM during the same time and in the same geographic area is
unlikely based on the nature of aircraft traffic management alone. To add to this, considering that
two A-ESIM operators are able to coordinate the same frequency usage in the same geographic area
we can assume that they would require satellite orbital separation of about 3°, which for the
example of an A-ESIM in the United Kingdom would already provide 3.8 degrees of antenna
pointing separation.
The above considerations lead to the conclusion that simulating one A-ESIM co-frequency with an
FS receiver in a given area is an appropriate assumption for the interference studies.
6. Conclusion of study and suggested action
The results of the verification of the PFD values are similar to the results obtained during CEPT
studies, where some scenarios of interference can theoretically be identified, but the likelihood of
these events in practise is low. In particular, it was identified that interference could occur only for
one specific FS station deployment type and for aircraft altitudes lower than 2.5 km. However, it
was identified that the probability for such a scenario to occur is 0.00062%, which makes it very
insignificant. This is based on the assumption that only one A-ESIM station can interfere with an
FS station in a specific geographic area at the same time. The probability of multiple A-ESIM
operating at the same time on the same frequency range in the same area was studied and it was
concluded that it is appropriate to assume that only one A-ESIM can produce co-frequency
interference into the FS station.
It is therefore suggested for WP4A:
1) To continue the A-ESIM interference into FS station study using the PFD values developed
by the CEPT;
2) To include this study into Annex 17 of 4A/196 and produce a liaison statement to WP 5C to
ask for their comments on the study and in particular confirm the following:
a. Whether the correct short-term and long-term interference criterion has been used;
b. Whether appropriate FS station parameters have been identified (antenna pattern,
gain, elevation).
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