CEPT
ECC
ECC PT1(15)058rev1
Electronic Communications Committee
ECC PT1 #49
Vilnius, Lithuania, 20-21 April 2015
Date issued:
12 May 2015
Source:
Huawei Technologies
Methodology for establishing national frameworks for spectrum sharing
between MFCNs and existing FSS/FS services in the 3.6 – 3.8 GHz band
Subject:
Group membership required to read? (Y/N) N
Summary:
CEPT administrations will need to define national ”spectrum sharing frameworks” in order to
specify the provisions which are necessary to enable and facilitate coexistence between
Mobile/Fixed Communication Networks (MFCNs) and the incumbent Fixed Satellite Service
(FSS) and Fixed Service (FS) in the 3.6-3.8 GHz band.
A spectrum sharing framework can be understood as a set of sharing rules, and its development
will require the involvement of all relevant stakeholders. Such rules can be incorporated in the
relevant national technical licence conditions, as is common practice today, and will also define
procedures to be followed during the roll out of the MFCNs.
This contribution proposes a methodology for establishing a spectrum sharing framework by
means of identifying a toolbox of options which administrations will be able to adopt as best
suited to their national circumstances.
In the proposed methodology the administrations define criteria for the protection of the
incumbent users in the form of maximum permitted interference at the input of the FSS and FS
receivers. These limits are then used to calculate the corresponding exclusion zones or
maximum permitted EIRPs of MFCN base station sectors (within a restriction zone) so as to
avoid harmful interference to the FSS and FS.
No specific values or value ranges are proposed for the various technical parameters involved
in the calculations. These will be the subject of future contributions.
There is always a trade-off between the simplicity of a spectrum sharing framework and
spectrum sharing efficiency. The proposed methodology is intended to provide the flexibility
for administrations to exploit this trade-off.
Proposal:
ECC PT1 is invited to review the proposed methodology for establishing national spectrum
sharing frameworks in the C-Band, and to include the agreed texts in the draft ECC Report
“Operational Guidelines for Spectrum Sharing to Support the Implementation of the Current
ECC Framework in the 3.6-3.8 GHz range”.
Background:
ECC# 38 meeting (25-28 November 2014, Montreux, France) approved the Work Item on
3600-3800 MHz submitted by ECC PT1 to draft an ECC Report providing additional
operational guidelines for sharing and, where appropriate, the implementation of LSA at a
national level. ECC noted that the administration’s support to this Work Item within ECC PT1
and confirmed the time schedule as proposed.
ECC PT1 #48 (19-23 January 2015, Edinburgh, UK) developed a Working Document 1
proposing a preliminary Table of Contents for the draft ECC Report to be developed under the
Work Item. ECC PT1 invited contributions for this meeting on the basis of this working
document.
1 ECC PT1(15)037_A22_3.6-3.8_Table of contents
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ANNEX
A methodology for establishing national frameworks for spectrum
sharing between MFCNs and existing Fixed/Fixed Satellite Services
in the 3.6-3.8 GHz band
Contents
1
Introduction .............................................................................................................................4
2
Spectrum sharing framework...................................................................................................5
3
4
2.1
Planning of MFCNs in the presence of incumbent users ..................................................6
2.2
Exclusion zones: restrictions on the location of MFCN base stations ..............................6
2.3
Restrictions on the EIRP of MFCN base stations ...........................................................10
2.3.1
Accounting for multiple base stations and sectors ..................................................12
2.3.2
Reducing computational complexity through “restriction zones” ...........................12
2.4
Responsibility for specifying the calculations ................................................................14
2.5
Responsibility for performing the calculations ...............................................................15
2.5.1
Access to information on FSS/FS receivers ............................................................17
2.5.2
Access to information on MFCN deployments .......................................................17
Operational guidelines for spectrum sharing .........................................................................18
3.1
Maximum permitted interference level at the FSS/FS receiver ......................................18
3.2
Calculation of maximum permitted EIRP of MFCN base stations.................................19
3.3
Coupling gain ..................................................................................................................21
3.4
Adjacent channel interference ratio ................................................................................24
3.5
Interference from multiple MFCN base stations ............................................................25
3.5.1
Aggregation .............................................................................................................25
3.5.2
Partitioning/distribution of the interference budget .................................................26
Summary and conclusions .....................................................................................................28
3/26
1
Introduction
This contribution proposes suitable options (a toolbox) to assist administrations to implement a
national framework for the sharing of spectrum between Mobile/Fixed Communication
Networks (MFCNs) and the existing Fixed Satellite Service (FSS) and Fixed Services (FS) in the
3.6-3.8 GHz band.
A spectrum sharing framework can be understood as a set of sharing rules. Such rules would be
incorporated in the relevant national technical licence conditions, as is common practice today,
and may include procedures to be followed during the roll out of the MFCNs.
This contribution also outlines the technical parameters and calculations which might be needed
for the implementation of the spectrum sharing framework. No specific values or value ranges
are proposed for the various technical parameters involved in the calculations. These will be the
subject of future contributions.
There is always a trade-off between the simplicity of a spectrum sharing framework and
spectrum sharing efficiency. The proposed methodology is intended to provide the flexibility for
administrations to exploit this trade-off to best suit their national circumstances.
Section 2 outlines the proposed sharing framework. This is based on the specification of the
maximum permitted interference levels at the FSS/FS receiver, and the subsequent calculation of
either geographic exclusion zones or maximum permitted power (EIRP) to be radiated from any
given MFCN base station sector, depending on the preference of the administration.
We explain how the placing of restrictions on the maximum permitted EIRP is equivalent to the
efficient implementation of a very large number of parametric exclusion zone contours, but with
the added flexibility of allowing mechanisms to account for interference from multiple MFCN
operators and base stations.
We also explain how geographic restriction zones can be used as a means of reducing
computational complexity by excluding from the EIRP calculations those MFCN base stations
that are unlikely to cause harmful interference to the FSS/FS.
A number of options are also described relating to the entity responsible for performing the
calculations to derive exclusion zones or maximum permitted EIRPs. It is noted that MFCN
operators are well placed to perform these calculations, subject to regulatory oversight. However,
restricted access to information on the incumbent FSS/FS receivers in certain jurisdictions may
imply that the calculations would need to be performed by the administration, or a third party
acting on behalf of the MFCN operators. Where there is a requirement for the interference from
the base stations of multiple operators to be treated jointly (e.g. for purposes of improved sharing
efficiency), the calculations would again need to be performed by the administration, or a third
party acting on behalf of all the MFCN operators. The ultimate decision as to the most suitable
option rests with national administrations.
Section 3 provides details of the type of calculations needed for deriving the maximum permitted
EIRP from a MFCN base station’s sector in order to avoid harmful interference to the FSS/FS.
Key technical parameters, such as the maximum permitted interference at the FSS/FS receiver,
coupling gain, and adjacent channel interference ratio are also discussed.
A number of options to account for the interference from multiple base station sectors are then
described and assessed. These range from the explicit aggregation of the various interfering
signals, to the possibility of treating each contributing signal on a standalone basis subject to the
inclusion of a safety margin. We also explain how a MFCN operator can flexibly distribute its
allocated interference budget among its base station sectors in order to best meet its coverage and
capacity targets.
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2
Spectrum sharing framework
The CEPT administrations will need to define national spectrum sharing frameworks which
specify the provisions necessary to enable and facilitate coexistence between MFCNs and the
existing services (FSS/FS) in the 3.6-3.8 GHz band.
In doing so, national administrations should account for the latest sharing technologies and
ensure:




the continued operation of FSS/FS,
introduction of most advanced IMT networks,
most efficient use of the available spectrum resource,
least restrictive sharing regulations.
There is always a trade-off between the simplicity of a spectrum sharing framework and
spectrum sharing efficiency. In this respect, we propose a methodology that allows
administrations to strike the most appropriate trade-off according to their available resources and
national circumstances.
To this end, we propose a spectrum sharing framework based on the following principles:
Administrations would define the criteria for the protection of the FSS/FS users by specifying
the maximum permitted interference at the input to the FSS and FS receivers. These limits
would then be used to calculate (as specified by the administration)
a) exclusion zones corresponding to MFCN base stations with a
pre-defined and common set of parameters, or
b) the maximum permitted power (EIRP) to be radiated from any given
MFCN base station sector that is located within a restriction zone.
Note that the maximum permitted interference level at the input to FSS receivers would not
necessarily be the same as the maximum permitted interference level at the input to FS receivers.
Furthermore, different maximum permitted interference levels may be specified for different
receivers of the same service category on a case-by-case basis. This might be appropriate, for
example, where a certain FS receiver operates at a large margin above its minimum sensitivity,
and can therefore tolerate greater levels of interference compared to another FS receiver.
It should also be pointed out that exclusion zones and restrictions on the maximum permitted
EIRP (within a restriction zone) are very much related. Both ensure that the interference at the
input of FSS and FS receivers does not exceed the levels specified by the administration, and
both can be derived with the same type of calculations. However, they represent different tradeoffs between simplicity and efficient spectrum sharing, although an administration may choose
to use a combination of the two approaches (see Section 2.3.2).
In the following sections, we describe the implications of the above framework in the context of
how MFCNs are planned and deployed. We then explore a “toolbox” of options for the
implementation of national spectrum sharing frameworks.
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2.1
Planning of MFCNs in the presence of incumbent users
Cellular terrestrial networks today operate in bands where they have exclusive access to the radio
spectrum. Operators of such networks plan the deployment of their base stations in such a way so
as to achieve certain capacity and coverage targets.
In such cases, a MFCN operator inputs the geographic coordinates and heights of its base
stations into a network planning tool, which then outputs base station parameters such as sector
orientations, down-tilts and EIRPs to meet the coverage and capacity targets.
Here, the only regulatory technical restrictions are for the protection of other MFCN operators
using adjacent frequency blocks, as well as existing services operating in adjacent bands. Such
regulatory technical restrictions are specified through national licence conditions, in line with the
provisions of European regulations (e.g., ECC Decisions and EC Decisions).
The situation is somewhat different in the C-Band, where MFCNs will need to share the
spectrum with the FSS and the FS. Avoiding harmful interference to these two existing services
will require additional (more stringent) restrictions on the MFCN base station EIRPs in
geographic areas that are in the vicinity of the FSS/FS receivers and where there is a risk of
harmful interference. The operators of MFCNs will need to account for these additional
restrictions in the planning of their networks.
According to the proposed framework, these restrictions can take the form of either exclusion
zones or reduced MFCN base station EIRPs within restriction zones. These are each discussed
next.
2.2
Exclusion zones: restrictions on the location of MFCN base stations
The avoidance of harmful interference to the FSS/FS can be achieved through the specification
and imposition of exclusion zones in the geographic vicinity of FSS and FS receivers.
An exclusion zone describes a geographic area in which the deployment of MFCN base stations
is not permitted. This is because the deployment would result in a risk of the interference at the
input of the relevant FSS/FS receivers to exceed the maximum permitted levels specified by the
administration.
The principle of exclusion zones is related to the sharing approach based on the calculation of
“protection distances” (also referred to as “separation distances”). A protection distance refers
to the minimum geographical separation between a MFCN base station and a FSS/FS receiver at
which the interference at the input of the FSS/FS receiver does not exceed the maximum
permitted levels specified by the administration.
If an exclusion zone is defined as a circle, then the protection distance is simply the radius of that
circle. If an exclusion zone is not defined as a circle, then the protection distance varies with the
angle of the radial from the FSS/FS receiver.
Protection distances can be calculated in different ways. Examples of these can be found in ECC
Report 100, ITU-R Report M.2109 and the most recent Draft New Report ITU-R [FSS-IMT CBAND DOWNLINK] developed within the framework of JTG 4-5-6-7. These are described in
<Section 5>. [Editor’s note: Section of the draft ECC Report containing a summary of existing
methodologies and sharing studies].
Figure 2.1 shows an illustrative example of a circular exclusion zone surrounding a FSS/FS
receiver. The exclusion zone identifies the geographic area in which the deployment of MFCN
base stations of EIRP, P = 68 dBm, is not permitted.
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The exclusion zone is derived by calculating the corresponding protection distance assuming a
specific base station EIRP, a nominal base station antenna height, an omni-directional base
station antenna pattern, a specific frequency separation from the channel used by the FSS/FS
receiver, an omni-directional FSS/FS receiver antenna pattern, and a generic radio propagation
model (one which does not account for local terrain and clutter). The derivation of the exclusion
zone may also include a safety margin to account for aggregation of interference from multiple
base stations.
Figure 2.1: Illustrative example of a circular exclusion zone surrounding a FSS/FS receiver.
Omni-directional antennas are assumed 2 either as a cautious measure, or simply because the
angular discrimination of the relevant antennas may not be known. The derivation of the
protection distance is then effectively based on the worst case assumption that the main lobes of
the MFCN transmitter and FSS/FS receiver always point towards each other.
Alternatively, non-circular exclusion zones may be defined by using propagation models which
account for the local terrain and clutter, and also accounting for the angular discrimination of the
FSS/FS receiver. This is illustrated in Figure 2.2. Note that the boundary of the exclusion zone is
no longer smooth, and the exclusion zone may not even be contiguous due to the specific
structure of the local terrain.
To derive such exclusion zones, a hypothetical base station with a given EIRP, an omnidirectional antenna installed at a given height, and a specific frequency separation from the
FSS/FS channels is repeatedly placed on a grid of geographic locations. Those locations where
the base station causes harmful interference to the FSS/FS receiver are considered to be inside
the exclusion zone. Otherwise, they are considered to be outside the exclusion zone. The
exclusion zone can be displayed as a map for illustrative purposes. Note that a margin to account
for interference from multiple base stations may be included in the derivation of the exclusion
zone.
2
It is certainly the case that simple circular exclusion zones are usually derived based on the assumption of omnidirectional transmit and receive antennas. However, it is possible to account for the angular discrimination of the
MFCN base station transmitter and the FSS/FS receiver in deriving circular exclusion zones. This is the case, for
example, in the “aggregated” approach defined in ECC Report 100, where multiple hypothetical MFCN base station
transmitters are placed along the boundary of a circle centred on a FSS/FS receiver, assuming specific angular
discrimination patterns of the transmitters’ and the receiver’s antennas.
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It is worth noting that the assumed frequency separation between the MFCN base station
transmitter and FSS/FS receiver plays a major role in the size of the exclusion zone. Co-channel
exclusion zones can be significantly larger than those for adjacent channel scenarios. For this
reason, administrations may choose to specify exclusion zones for more than one frequency
adjacency.
Figure 2.2: Illustrative example of an exclusion zone contour surrounding a FSS/FS receiver,
accounting for the antenna angular discrimination of the FSS/FS receiver
and the impact of terrain and clutter on radio propagation.
In summary, an exclusion zone is derived by assuming that the MFCN base station transmits at a
specific maximum EIRP, with an antenna that is at a specific height and has a specific angular
discrimination pattern, and at a specific frequency separation from the spectrum used by the
FSS/FS receiver. The antenna pattern is typically assumed to be omni-directional.
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The size and shape of an exclusion contour then depends on the assumed





maximum permitted interference at the FSS/FS receiver,
clutter environment at the MFCN transmitter and FSS/FS receiver,
terrain profile between MFCN transmitter and FSS/FS receiver,
antenna gain of FSS/FS receiver, and
antenna angular discriminations of FSS/FS receiver.
As can be seen from the above list, access to information on the FSS and FS receivers is essential
for the calculation of exclusion zones. Each of the above parameters is described in detail in
Section 3.
Where multiple FSS and FS receivers exist in a geographic area, the composite exclusion zone is
the combination (super set) of the exclusion zones required for the protection of the FSS and FS
receivers. This is illustrated in Figure 2.3.
Figure 2.3: Illustrative example of exclusion zone for the protection of
a FSS receiver and a FS receiver. The composite exclusion zone is the superset
of the individual exclusion zones.
The key benefit of exclusion zones is their implementation simplicity. They have proven to be a
robust approach for avoiding harmful interference to fixed receivers at known geographic
locations. However, this simplicity is also accompanied by certain limitations.
One such limitation is that exclusion zones do not easily scale to account for the potentially large
number of combinations of MFCN base station antenna heights, MFCN antenna angular
discrimination patterns, and frequency separations from the spectrum used by the FSS/FS
receivers. As such, exclusion zones must be calculated according to a limited number (typically
only one) of such combinations, and this can impact the efficiency of spectrum sharing.
Another limitation is that exclusion zones cannot account for interference from multiple MFCN
base stations (or base station sectors) other than through the inclusion of a gross safety margin in
the calculation of the exclusion contours. Again, this can impact the efficiency of spectrum
sharing.
The above limitations can be mitigated by adopting an approach which imposes restrictions on
the EIRP of MFCN base station sectors rather than on their geographic location. This is
discussed next.
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2.3
Restrictions on the EIRP of MFCN base stations
Figure 2.4 shows an illustrative example of a MFCN deployment where the operator has
exclusive access to the spectrum. For simplicity, and without loss of generality, all MFCN base
stations are assumed to radiate at the same power, and with the same tri-sector orientations.
Figure 2.4: Illustrative example of a MFCN base station deployment where
the network operator as exclusive access to the radio spectrum.
Figure 2.5 shows the case where a FSS receiver and a FS receiver exist in the deployment area.
Here the EIRPs of individual base station sectors are adjusted according to the requirements
specified by the national administration in order to avoid harmful interference while sharing the
spectrum with the FSS and/or FS. In other words, the EIRPs are reduced such that the
interference at the input to the relevant FSS/FS receivers does not exceed the maximum
permitted levels specified by the administration.
Where multiple FSS and FS receivers are present, only the most susceptible FSS receiver and the
most susceptible FS receiver need to be considered.
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Figure 2.5: An illustrative example of a MFCN base station deployment
subject to the avoidance of harmful interference to the FSS/FS.
This proposed spectrum sharing framework is somewhat more flexible than the use of exclusion
zones, whereby the regulatory decision is binary: a base station with a given EIRP is either
permitted or not permitted at a given location.
The proposed spectrum sharing framework can also be thought of as an efficient description of a
very large family of parametric exclusion contours, where each contour corresponds to a specific
combination of base station parameters, including EIRP, height, sectorisation pattern/orientation,
and transmission frequency.
Finally, the proposed sharing framework allows a range of mechanisms to account for the
aggregation of interference from multiple MFCN base stations which is not readily feasible with
exclusion zones.
Note that for any particular base station sector, the maximum permitted EIRP might be
constrained by a FSS receiver or a FS receiver. Furthermore, the maximum permitted EIRP will
depend on the:







maximum permitted interference at the FSS/FS receiver,
geographic separation between MFCN transmitter and FSS/FS receiver,
frequency separation between MFCN transmitter and FSS/FS receiver,
clutter environment at the MFCN transmitter and FSS/FS receiver,
terrain profile between MFCN transmitter and FSS/FS receiver,
antenna gain of FSS/FS receiver, and
antenna angular discriminations of MFCN transmitter and FSS/FS receiver.
As can be seen from the above list, access to information on the FSS and FS receivers is essential
for the calculation of the maximum permitted EIRPs. Each of the above parameters is described
in detail in Section 3. The next sub-section describes options to account for interference from
multiple MFCN base station sectors.
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2.3.1
Accounting for multiple base stations and sectors
Three possible approaches can be identified to account for interference from multiple MFCN
base station sectors (i.e., for the aggregation effect):
Approach 1. Single-sector calculations with inclusion of a specific safety margin to account for
the actual existence of multiple sectors.
Approach 2. Single-operator (multi-sector) calculations with inclusion of a specific safety
margin to account for the actual existence of multiple sectors from other
operators.
Approach 3. Multi-operator (multi-sector) calculations with no specific safety margin.
In Approach 1, the maximum permitted EIRPs of base station sectors are calculated by explicitly
accounting for only a single base station sector at a time; i.e., by assuming no other sectors exist.
However, the calculations must include a safety margin to account for the fact that in practice
there will be multiple sectors present. The safety margin will need to be “future-proof” in the
sense that it should be sufficient to account for the possibility of increasing base station
deployment densities over time.
In Approach 2, the maximum permitted EIRPs of base station sectors are calculated by explicitly
accounting for all base station sectors of a single MFCN operator at a time. The calculations
must include a safety margin to account for the fact that in practice there will be multiple
networks present. The safety margin will be expected to be smaller than that used in Approach 1.
For example, in the presence of 3 network operators, the safety margin might be of the order of 5
dB (a factor of 3).
In Approach 3, the maximum permitted EIRPs of base station sectors are calculated by explicitly
and jointly accounting for all base station sectors of all operators. No safety margin is required
here.
The three approaches above represent different trade-offs between simplicity of implementation
and efficient spectrum sharing.
Section 3 describes guidelines for the calculations required for the proposed sharing framework.
Specifically, Section 3.5 describes the calculation of interference from multiple MFCN base
stations and sectors as applicable to Approaches 2 and 3 above.
We next describe how restriction zones can be used to reduce the computational complexity
involved in the calculation of maximum permitted EIRPs.
2.3.2
Reducing computational complexity through “restriction zones”
In the above sections we described how the maximum permitted EIRP of a MFCN base station’s
sector can be calculated for the avoidance of harmful interference to the FSS/FS receivers.
It is evident that base stations that are at sufficiently large geographic separations from a FSS or
FS receiver need not be subject to any reduction in EIRP as they are unlikely to add significantly
to the total interference at the input of FSS/FS receivers. Accordingly, it would be wasteful to
perform the EIRP calculations for such distant base stations.
Such calculations can be avoided through the use of restriction zones. These are defined as
geographic areas which surround a FSS/FS receiver, within which MFCN base stations are
permitted to operate but are likely to be subject to certain restrictions for the avoidance of
harmful interference to the FSS/FS receiver, but outside of which MFCN base stations would not
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be subject to any such restrictions. This means that for base stations that are located outside
restriction zones, calculations for reduced EIRP are not required.
In principle, restriction zones might be calculated in an elaborate manner, using sophisticated
propagation models, and accounting with fine granularity for parameters such as base station
EIRP, base station antenna height, base station antenna sectorisation, and interferer-victim
frequency separation.
However the complexity of such sophisticated derivations of restriction zones would soon
approach that of the calculations of maximum permitted MFCN base station EIRPs. This would
defeat the objective of the restriction zones; i.e., reduced complexity.
One possible approach would be to use coarse (cautious) assumptions to derive simple and large
restriction zones, with the understanding that more sophisticated modelling would then be
performed for the calculation of MFCN base station EIRPs inside the restricted zones.
Figure 2.6 shows an illustrative example where the restricted zones are in the form of a small
number of concentric circles centred on the FSS/FS receiver, and whose radii are derived by
assuming a cautious MFCN base station antenna height, omni-directional antennas (both at the
base station transmitter and FSS/FS receiver), and for co-channel and immediate channel
adjacencies. These restriction zones may be readily enhanced by including the directionality of
the FSS/FS receiver antenna, or more sophisticated propagation models. This is illustrated in
Figure 2.7.
Figure 2.6: Simple and cautious restriction zones can be used to reduce computational
complexity. Base stations outside the exclusion zones would not be subject to any restrictions
for the avoidance of harmful interference to the FSS/FS (EIRP calculations are not necessary).
Figure 2.7: More precise restriction zones accounting for the directionality of the FSS/FS
receiver antenna and sophisticated propagation models.
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The methodology for deriving restriction zones shall be specified by the administration, and
calculated by the same entity which performs the detailed calculations of the maximum
permitted EIRPs.
Note that it is possible for an administration to use a combination of exclusion and restriction
zones. An example of this is shown in Figure 2.8 with the understanding that the maximum
permitted EIRP of a MFCN base station is 68 dBm. Here MFCN base stations are not permitted
to be deployed within a distance rX of the FSS/FS receiver (inside the exclusion zone)
irrespective of their EIRP. This might be used as an extra safety measure by the administration
against the risk of harmful interference. MFCN base stations outside the exclusion zone, but
within a radius rR of the FSS/FS receiver (inside the restriction zone), can be deployed subject to
the results of appropriate calculations which may or may not restrict their EIRP. The restrictions
themselves are a function of the base station antenna location and height, antenna angular
discrimination, and frequency separation from the used FSS/FS channels (shown as multiple
curves). MFCN base stations outside the restriction zone can be deployed with no restrictions in
the context of avoiding harmful interference to the FSS/FS receiver, and so EIRP calculations are
not necessary.
Figure 2.8: Illustrative example of combined use of exclusion and restriction zones.
In the remainder of this section, we will focus on some of the options for the implementation of
the proposed sharing framework.
2.4
Responsibility for specifying the calculations
The specification of the maximum permitted interference at the FSS/FS receivers needed to
derive the corresponding MFCN exclusion zones or maximum permitted MFCN base station
sector EIRPs (within a restriction zone) is clearly the responsibility of national administrations.
A national administration may also specify detailed calculations and technical parameter values
that are necessary for performing such calculations. These specifications will help to ensure a
maximum degree of transparency, as well as consistency among the calculations where these are
carried out by entities other than the administration.
These technical specifications would be incorporated in the relevant national MFCN licence
conditions and would implicitly define the rights of the MFCN to use the spectrum.
It is important to note that different national administrations might adopt different approaches in
defining the MFCN licence conditions depending on their available resources and national
circumstances.
14/26
For example, certain administrations might adopt a light touch approach, whereby they would
only specify the maximum permitted interference at the FSS/FS receivers, and require that
MFCN operators ensure that these levels are not exceeded in practice. This might be
complemented by ex post monitoring of MFCN deployments and appropriate regulatory action
in response to reported cases of harmful interference.
Other administrations might adopt a more prescriptive approach where in addition to specifying
the maximum permitted interference at the FSS/FS receivers, they would also specify detailed
calculations required for deriving MFCN exclusion zones or maximum permitted MFCN base
station sector EIRPs. Since technical modelling is never perfect, this would most likely also be
complemented by ex post monitoring of MFCN deployments and appropriate regulatory action
in response to reported cases of harmful interference.
Note that the specification of the calculations required for deriving MFCN exclusion zones or
maximum permitted EIRPs (within a restriction zone) is quite distinct from actually performing
the calculations themselves. This is discussed next.
2.5
Responsibility for performing the calculations
Three broad options can be foreseen regarding the responsibility for performing the calculation
of exclusion zones or maximum permitted MFCN base station EIRPs:
Option A: Calculations are performed by the MFCN operators with ex ante qualification
and/or ex post regulatory oversight.
Option B: Calculations are performed by a third party on behalf of all MFCN operators with
ex ante qualification and/or ex post regulatory oversight.
Option C: Calculations are performed by the national administration.
Figure 2.9, Figure 2.10, and Figure 2.11 illustrate the above options. The purpose of the third
party will become apparent in the following discussions. Note that in the case of Options A and
B, the administration may need to verify that the MFCN operators or the third party perform the
necessary calculations correctly. This could be achieved through a pre-licensing qualification
process and/or a post-licensing pre-deployment qualification process as described in the licence
conditions. The administration may carry out its own calculations as a baseline reference for
regulatory oversight.
MFCN operators are well placed to perform detailed calculations with regards to their network
deployments. However, the most appropriate option may vary from one country to another. This
will depend on the following factors:

The extent to which information on the FSS/FS receivers can be shared with MFCN
operators and/or a third party;

The preferred approach for the evaluation of aggregate interference from multiple
MFCN base stations, and therefore the extent to which information on the MFCN base
station deployments may be shared between MFCN operators.
We elaborate further on these issues in the following sub-sections.
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Figure 2.9: Option A - Calculations are performed independently
by the MFCN operators, with regulatory oversight.
Figure 2.10: Option B - Calculations are performed by a third party
on behalf of all MFCN operators, with regulatory oversight.
Figure 2.11: Option C - Calculations are performed by the national administration.
16/26
2.5.1
Access to information on FSS/FS receivers
As discussed earlier, the calculation of exclusion zones or maximum permitted EIRPs (within a
restriction zone) require information on the technical characteristics of the FSS and FS receivers.
In certain jurisdictions, however, there may be restrictions on MFCN operators regarding access
to information on the FSS and FS receivers. This might be for commercial, legal, or security
reasons. In such cases, the MFCN operators themselves cannot perform the calculations. The
calculation of the exclusion zones or maximum permitted EIRPs will need to be performed either
by the administration, or a trusted third party (subject to regulatory oversight), and
communicated to the MFCN operators. This means that Option A is not viable, and only Options
B and C apply.
If there are no restrictions on access to information on the FSS and FS receivers, then the
calculations can be performed by the MFCN operators themselves. In other words, Option A is
also possible.
2.5.2
Access to information on MFCN deployments
By definition, the calculation of exclusion zones explicitly accounts for radiation from a single
hypothetical MFCN base station. This means that access to information on the technical
characteristics of deployed MFCN base stations is not required. For this reason, exclusion zones
can be calculated by the administration, the MFCN operators, or a third party acting on behalf of
the MFCN operators (with regulatory oversight in the case of the two latter options).
On the other hand, the way in which the calculations of maximum permitted EIRPs (within a
restriction zone) account for the presence of multiple base stations and sectors does have
implications with regards to the nature of the entity which can perform the calculations.
For example, consider the case where these calculations explicitly and jointly account for
interference from all base station sectors of all MFCN operators (Approach 3). The entity which
performs the calculations will need information on the deployments of all MFCN operators. For
reasons of competition, this entity is unlikely to be one of the MFCN operators, but is more
likely to be the administration, or a third party acting on behalf of all the MFCN operators
(subject to regulatory oversight). Here only Options B and C are viable.
In the cases where these calculations explicitly account for interference from the base station
sectors of one MFCN operator at a time (Approach 2), or from a single sector at a time
(Approach 1), no competition issues exist in the context of the sharing of information on MFCN
deployments. Here Options A, B, and C are all viable.
17/26
3
Operational guidelines for spectrum sharing
According to the proposed sharing framework, the national administrations will specify the
maximum permitted interference levels at the FSS/FS receivers. These interference levels will
then be used in the calculation of exclusion zones or the maximum permitted power (EIRP) to be
radiated from any given MFCN base station sector.
This section proposes operational guidelines that may assist administrations in establishing the
sharing framework. Such guidelines will identify and assess the options for the definition of the
maximum permitted interference levels at the FSS/FS receivers, as well as the options available
for the calculation of the corresponding maximum permitted MFCN base station sector EIRPs.
The calculation of exclusion zones is also described in the context of the above framework.
3.1
Maximum permitted interference level at the FSS/FS receiver
The national administration shall specify the criteria for the protection of the incumbent users in
terms of the maximum permitted (target) interference levels IFSS,T and IFS,T at the input of FSS
and FS receivers, respectively.
Criterion for specification
The maximum permitted interference level, IT, may be specified according to one of two criteria:

“I/N” criterion. Here, the value of the maximum permitted interference is defined in
relation to the thermal noise floor, N. For example, for a target rise of 1 dB in the noise
floor, the value of IT would need to be 6 dB below the thermal noise floor. This criterion
might be appropriate where the receiver operates at or close to its minimum sensitivity.

“C/(N+I)” criterion. Here, the value of the maximum permitted interference is defined in
relation to a target reduction in the receiver’s signal-to-interference-plus-noise ratio. This
criterion might be appropriate where the receiver operates at some margin above its
minimum sensitivity. For example, if a receiver requires a minimum C/(N+I) of 20 dB,
and it currently operates with a C/N of 40 dB (in the absence of interference from the
MFCN), then the value of IT can be approximately 20 dB greater than the thermal noise
floor, N.
Note that the value of the maximum permitted interference is a function of the bandwidth of the
FSS/FS channel. Furthermore, the C/(I+N) criterion is applicable only in cases where
information on the link budgets of the FSS or FS receivers is available.
Percentage time
Long-range propagation is often subject to atmospheric phenomena (also called “ducting”)
which can occasionally enhance radio propagation and hence interference. This is commonly
accounted for in propagation models, whereby the propagation gain is greater at lower
percentage times. For example, the propagation gain might be -180 dB at 50% time, but -170 dB
at 1% time3.
3
That is to say, for 1% of time over a long time interval of say a month or a year, the propagation gain would
exceed -170 dB.
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For this reason, and irrespective of the criterion used for specifying the maximum permitted
interference, the administration may wish to associate the value of IT with a time percentage.
It should be noted that this approach can result in complexities when interference from multiple
sources is aggregated. This is because the percentage time requirement is accounted for via the
propagation gain of individual links. The way in which the percentage time of individual links
translates to the percentage time of the composite interference is not trivial and depends on the
number of signals aggregated, their relative strengths, and their statistical distributions.
For the above reason, if the inclusion of a time percentage is considered to be essential, a more
viable approach would be to specify a single percentage time value, TL, which would apply to all
individual links, with the understanding that the percentage time, T, for the composite
interference will be different but appropriate. The value for the percentage time, TL, can be
derived by off-line simulations of a range of deployment scenarios and geometries.
3.2
Calculation of maximum permitted EIRP of MFCN base stations
The example in Figure 3.1 illustrates a tri-sector MFCN base station deployed in the proximity
of a FSS earth station receiver and a FS link. Multiple FSS and FS receivers may exist in the
same geographic area, however, the receivers depicted in the figure are those that are most
susceptible and define the restrictions on the operation of the MFCN base station transmitter.
Figure 3.1: Illustrative example of a coexistence geometry.
The following text describes the calculations required to derive the maximum permitted EIRP, P,
of a single MFCN base station sector based on MFCN and FSS/FS parameters and the maximum
permitted interference levels at the FSS/FS receivers. Calculations would need to be repeated for
each sector.
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The approaches to account for the aggregation of interference from multiple sectors were
presented in Section 2.3.1 and are further addressed in Section 3.5.
Let the maximum permitted (target) interference at the FSS and FS receivers be specified as
IFSS,T and IFS,T , respectively. Also let the actual interference at the FSS and FS receivers be
denoted as IFSS and IFS. In order to avoid harmful interference, the following conditions need to
be met:
I FSS  I FSS, T
I FS  I FS,T
(3.1)
Then, following the conventional approach for the calculation of interference we can write (in
the linear domain):
I FSS 
GFSS P
1

I FSS, T
ACIR FSS (Δf FSS )
M
(3.2)
I FS 
GFS P
1

I FS, T
ACIR FS (Δf FS )
M
where GFSS/GFS are the coupling gains from the base station sector to the FSS/FS receivers,
ACIRFSS/ACIRFS are the relevant adjacent channel interference ratios, fFSS/fFS are the relevant
carrier-to-carrier frequency separations, and M  1 is a ‘safety’ margin.
The value of the safety margin, M, will depend on the approach used to account for interference
from multiple MFCN base station sectors (see the three approaches in Section 2.3.1) 4 . In
Approach 3, where we explicitly account for all base station sectors of all operators, M = 1. In
Approach 2, where for example two MFCN operators might exist, M = 2 (i.e., a safety margin of
3 dB).
To derive the maximum permitted base station sector EIRP, Equations (3.2) can be rearranged as
P
ACIR FSS (Δf FSS )
I FSS, T  Pmax, FSS
M GFSS
(3.3)
P
ACIR FS (Δf FS )
I FS, T  Pmax, FS
M GFS
where Pmax,FSS and Pmax,FS are the maximum permitted EIRPs for the avoidance of harmful
interference to the FSS and FS receivers, respectively. Then, for the joint avoidance of harmful
interference to both the FSS and FS receivers, we have


P  min  Pmax, FSS , Pmax, FS 


(3.4)
Harmful interference can therefore be avoided so long as the sector’s EIRP does not exceed the
lower of the two limits required for the protection of FSS and FS receivers individually.
4
The value of the safety margin specified by national administrations may also depend on other factors, such as the
degree of averseness to the risk of harmful interference.
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Note that the calculation of exclusion zones can be performed by interpreting the above result in
a different way. In this case we must assume that a base station has an EIRP of P BS, an omnidirectional antenna installed at a given height, and specific frequency separations from the
FSS/FS channels. Then, if PBS is greater than the value P calculated in Equation (3.4), then the
base station cannot be deployed; i.e., it effectively falls within an exclusion zone and its
deployment is prohibited. If required, the above analysis can be repeated over a grid of
geographic locations, and the result displayed as a map of an exclusion zone contour for EIRP P.
In the above we have shown how the maximum permitted EIRP of a MFCN base station’s sector
can be calculated as a function of the maximum permitted interference, coupling gain, and
adjacent channel interference ratio. These parameters are described in more detail in the
following sections.
3.3
Coupling gain
Coupling gain is the ratio of the MFCN base station signal power at the input to the FSS/FS
receiver over the power radiated by the MFCN base station. In other words, if P is the EIRP of
the base station, and G is the coupling gain, then the power arriving at the input to the FSS/FS
receiver is GP (in the linear domain). This is illustrated below.
Figure 3.2: illustration of coupling gain as the combined effect of propagation,
antenna installation gain and angular discrimination.
Specifically, we may write the coupling gain, G, as
G(dB)  g Tx ( T x ,  T x ) (dB)  GProp(dB)  GA, Rx (dB)  g Rx ( Rx ,  Rx ) (dB)
(3.5)
where
gTx
GProp
GA,Rx
gRx
, 
is the MFCN base station sector’s antenna angular discrimination,
is the radio propagation (including building penetration) gain,
is the FSS/FS receiver antenna’s gain (incl. cable loss),
is the FSS/FS receiver’s antenna angular discrimination,
are relevant horizontal and vertical angles of the interference link
w.r.t. to the antenna boresights.
Note that the FSS/FS receiver antenna is characterised by the combination of two separate
elements 5. The first element is the antenna gain GA,Rx , which represents the net gain of the
5
Given the relatively large separations (likely hundreds of metres) between the MFCN base stations and the FSS/FS
receivers, it is unlikely that accounting for polarisation discrimination would provide material benefits in efficient
coexistence.
21/26
receiver antenna including cable loss. The second element is the antenna angular discrimination
gRx, which identifies the angle-dependent gain of a directional antenna.
22/26
Propagation gain
The propagation gain can be modelled in a variety of ways. These could range from flat-earth
free-space path loss in one extreme, to empirical models such as extended Hata (e.g., as specified
by SEAMCAT) complemented by clutter databases6, to more elaborate models which account
for both clutter and terrain profiles, and might even utilise high-resolution 3D maps of buildings
and structures. If required, these propagation models can also include an allowance for
percentage time (see Section 3.2).
In all cases, the propagation gain will be a function of the geographic locations and heights of the
MFCN base station and the FSS/FS receiver, as well as the frequency of operation.
It stands to reason that more accurate and elaborate (computationally complex) modelling of the
propagation gain would result in more efficient spectrum sharing between the MFCN and the
FSS/FS. This is particularly the case in urban areas with dense building clutter and where the
antennas of MFCN base stations are located below the height of local clutter.
The propagation gain usually has the most profound effect on the interference link budget, and is
one of the most important parameters in the calculation of coexistence restrictions.
The administration may specify a default model for the calculation of the propagation gain.
MFCN operators (or, where applicable, the third party who manages the interference to
incumbents on behalf of all MFCN operators) may use this default model. Alternatively, they
may use more sophisticated models subject to the approval of the administration.
MFCN base station (sector) antenna angular discrimination
This will be specified by the MFCN operator (or, where applicable, the third party who manages
the interference to incumbents on behalf of all MFCN operators) and will be based on the base
station sector antenna pattern and horizontal/vertical antenna orientation as deployed on the
ground.
FSS/FS receiver antenna gain and angular discrimination
These will be specified by the administration based on information provided by the incumbents,
accounting for the actual antenna pattern and horizontal/vertical antenna orientation of the
FSS/FS receiver. In the absence of such information, the administration may specify a default
pattern, a nominal orientation, and a nominal gain.
Building penetration loss
This applies to cases where the MFCN base station is located indoors, and where its radiated
signals are attenuated by the building’s structure. The building penetration loss can vary
significantly (by tens of dBs) from building to building, depending on the architecture and the
construction materials used.
The administration may specify a nominal default value to be used for the building penetration
loss. In addition, the administration may allow the MFCN operator (or the third party who
manages the interference to incumbents) to use a different building penetration loss for specific
indoor base stations on a case-by-case basis. This would need to be subject to some level of
regulatory oversight.
6
Several clutter databases are commercially available.
23/26
3.4
Adjacent channel interference ratio
The adjacent channel interference ratio relates the received in-block (carrier) power, PU, of an
adjacent channel interferer to the interference power, I, experienced by a receiver. This is
illustrated in Figure 3.3 below. Note that in the absence of any channelisation rasters (as in the
current instance), adjacent channel simply refers to adjacent frequencies.
Figure 3.3: Adjacent channel interferer, ACLR and ACS.
By definition, the interference power experienced by a receiver can be written as
I  POOB 
PU
ACS (Δf )
(3.6)
where ACS is the adjacent channel selectivity of the receiver, POOB is the interferer’s out-ofblock emissions at the receiver, and f is the frequency separation between the wanted and
unwanted signals. Dividing through by PU, we have
P
I
1
1
1
 OOB 


PU
PU
ACS(Δf ) ACLR(Δf ) ACS(Δf )
(3.7)
P
1
ACIR(Δf )  U 
I
ACLR 1 (Δf )  ACS 1 (Δf )
(3.8)
so that
where ACLR is the interferer adjacent-channel leakage ratio. In scenarios where the interferer is
co-channel with the wanted signal, and they are both of the same bandwidth, ACIR = 1. Where
the bandwidths of the wanted and interferer signals are not equal, appropriate bandwidth
corrections should be applied.
The ACLR is defined by the spectrum emission mask of the MFCN base station transmitter. This
is usually subject to regulatory limits defined in the form of block edge masks (BEM).
Note that the ACS describes the susceptibility of a receiver to an adjacent channel interferer. The
ACS can be measured in the laboratory by injecting spectrally clean adjacent channel interferers
into a receiver, and measuring the rise in the interference-plus-noise floor.
In practice, the value of ACS reduces as the receiver begins to overload due to increased input
signal powers and becomes more susceptible to adjacent channel interferers. Such non-linear
behaviour can be captured by modelling the ACS as a function of both the frequency separation
f, and the received wanted signal power PW.
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3.5
Interference from multiple MFCN base stations
In the previous sections we focused on the calculation of the maximum permitted EIRP of an
individual MFCN base station sector, subject to the avoidance of harmful interference to the
FSS/FS. This section addresses the issue of interference from multiple base stations and sectors.
Specifically, we discuss the issues of aggregation and also the partitioning/distribution of the
interference budget among multiple base stations and sectors.
Note that explicit aggregation of interference from multiple base stations and sectors is not
absolutely essential. The proposed framework allows for each base station sector to be examined
independently of others, subject to the inclusion of a safety margin to account for the presence of
other radiating base stations (see Approach 1 in Section 2.3.1)7. However the included safety
margin would need to account for the existence of multiple base stations, and also be “futureproof”, i.e., be sufficient to account for the possibility of increasing base station deployment
densities over time.
3.5.1
Aggregation
Assume that K mobile network base station sectors exist in the vicinity of a FSS or FS receiver.
We later show that we only need to consider those base stations that are within so-called
restriction zones and are likely to cause harmful interference. The total interference I from these
sectors can be explicitly modelled, and the criterion for the avoidance of harmful interference
can be written as
I
K
 Ik
k 1

1
IT
M
(3.9)
where Ik is the interference from the kth sector, IT is the relevant maximum permitted interference
at the FSS or FS receiver and M is a safety margin. The value of M will depend on the approach
used to account for interference from multiple MFCN base station sectors (see the approaches in
Section 2.3.1). In Approach 3, where we explicitly account for all base station sectors of all
operators, M = 1.
Following the previous notation, we have
Ik 
Gk Pk
ACIRk ( f k )
(3.10)
where Gk is the coupling gain between the kth sector and FSS/FS receiver, ACIR is the adjacent
channel interference ratio, and fk is the (carrier-to-carrier) frequency separation between the kth
sector and the FSS/FS receiver.
The aggregation process is illustrated in Figure 3.4 below. Note that it is common practice in
spectrum engineering to add the sources of interference in descending order of power, and
terminate the aggregation once the last added source contributes less than 0.5 dB to the total
level of interference and then add a further 0.5 dB to account for all remaining lower power
sources of interference. In the example of Figure 3.4 the aggregation is terminated after the 5th
interferer (sector).
7
This approach might, for example, be adopted for the case of small cells, where the aggregation of interference
from a large number of base stations can be avoided.
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Figure 3.4: Aggregation of interference from multiple MFCN base station sectors.
3.5.2
Partitioning/distribution of the interference budget
From the point of view of mitigating the risk of harmful interference, it is essential that the total
interference at the FSS/FS receiver does not exceed the maximum permitted limit, IT; i.e., that
the total received interference does not exceed the pre-defined interference budget.
Where different MFCN operators independently manage 8 their interference to the FSS/FS
(Option A in Section 2.5), the partitioning of the total interference budget among the operators
would also be a regulatory issue. The default approach might be that each operator is allocated
an equal fraction (”fair share”) of the total interference budget. This is illustrated in Figure 3.5.
However, note that the way in which a MFCN operator’s allocated interference budget can be
partitioned among individual sectors of the same operator’s base stations need not be prespecified, and can be under the full control of the operator (applicable to Approaches 2 and 3 in
Section 2.3.1).
There might be a number of reasons why an operator might wish to have control over the
partitioning of its allocated interference budget among its base stations (sectors).
One reason might be for the purpose of adjusting (shaping) of the maximum permitted EIRP
profile across the sectors of different base stations (or even sectors of the same base station). The
objective of this might be to provide the required levels of capacity/coverage at key locations.
Another reason might be for the purpose of allocating different amounts of the total interference
budget to different layers of a heterogeneous network. For example, it stands to reason that hightower macro base stations are more likely to cause harmful interference to a FSS/FS receiver
than low-height pico base stations, and that the former category would be subject to greater
restrictions in their maximum permitted EIRP. This can be remedied by allocating a greater
proportion of the total interference budget to high-tower macro base stations.
8
Where a third party manages the interference to the incumbents on behalf of all MFCN operators (Option B in
Section 2), this can be treated as if only a single MFCN operator is involved. The partitioning of the interference
budget among the different MFCN operators is then an issue for the MFCN operators (and not the administration).
26/26
Figure 3.5: An example of how the total interference budget might be equally partitioned and
allocated to three MFCN operators, each of which in turn distributes its allocation among its
base station sectors according to its circumstances.
The key point here is that while the specification of the total interference budget (maximum
permitted interference) and the partitioning of that interference budget among MFCN operators
are regulatory issues9, the way in which a MFCN operator’s allocated interference budget is
distributed among its own base station sectors is a matter for the operator alone.
9
Assuming that the different MFCN operators manage their interference to the FSS/FS independently.
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4
Summary and conclusions
This contribution proposes a methodology for establishing national frameworks for spectrum
sharing between Mobile/Fixed Communication Networks (MFCNs) and the existing Fixed
Satellite Service (FSS) and Fixed Service (FS) in the 3.6-3.8 GHz band.
In the proposed framework the national regulatory authorities define criteria for the protection of
the incumbent users in the form of maximum permitted interference at the input of the FSS and
FS receivers. These limits are then used to calculate the corresponding exclusion zones or
maximum permitted EIRPs of MFCN base station sectors (within a restriction zone) so as to
avoid harmful interference to the FSS and FS.
The framework gives the administration the flexibility to choose the most appropriate approach
for defining the technical conditions which the MFCN operators would need to comply with.
This flexibility includes three approaches to account for interference from multiple MFCN base
station sectors. These range from the explicit aggregation of the multiple interfering signals, to
the possibility of treating each contributing signal on a standalone basis, subject to the inclusion
of an appropriate safety margin.
In the cases where the MFCN operators are allocated specific interference budgets to exploit,
they can have the flexibility to distribute their interference budgets among their base station
sectors according to the specific coverage and capacity targets.
This contribution also presents a number of options with respect to the entity responsible for the
calculation of the maximum permitted MFCN base station EIRPs. The MFCN operators might
be well placed to perform these calculations. However, in circumstances where MFCN operators
might have restricted access to information on the FSS/FS receivers, or where greater
efficiencies can be achieved by jointly accounting for the base stations of all the MFCN
operators, the calculations would need to be performed by the administration or a third party
acting on behalf of the MFCN operators. The ultimate decision as to the most suitable option
rests with national administrations.
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