ACP-WGF15/WP21
INTERNATIONAL CIVIL AVIATION ORGANIZATION
MIDDLE EAST OFFICE
FIFTEENTH MEETING OF THE AERONAUTICAL COMMUNICATION
PANEL WORKING GROUP F
(ACP WG-F/15)
(Cairo, 7 – 13 June 2006)
Agenda Item 5: AM(R)S spectrum requirement
SPECTRUM RESOUCE MODEL
JUSTIFICATION OF ASSUMPTIONS AND CALCULATIONS
(Presented by the Eurocontrol Agency)
Summary
This paper supports the ‘Spectrum Resource Model and projected spectrum
requirements’ paper and provides background as to how the various parameters are
attained and the details of the assumptions.
Recommendation
The meeting reviews the assumptions and the parameters being used for the
calculation of the spectrum resource and either revises them or endorses them.
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1.
INTRODUCTION
A separate paper presents a spectrum resource model based on input parameters
determined for the horizon time frame up to 2030.
The precision of the input parameters are variable and this analysis captures
reasonable best and worst case values for each of the important parameters together
with pragmatic averages and standard deviations/deltas.
Constraints
- Net System Capability Nsc, ∆ Nsc
- Adjustment Factor F, ∆F
STATISTICAL
SPECTRUM
RESOURCE
MODEL
Operational requirements
- throughput : T, ∆T
Bw, ∆Bw per band
Figure: Statistical Resource Model
For each band considered
Bw 
TxF
Nsc
Bw, ∆Bw : Total necessar y Bandwidt h and var iat ion ( MHz) f or the
considered band
T, ∆T : throughput and variat ion per sect or (Mb/s)
F, ∆F: Adjustment f actor and var iation f or th e considered band
Nsc, ∆ Nsc: Net system Capabilit y and var iat ion of the total
bit / s
communication system (
)
Hz
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The parameters and process of the model are explained in details in the separate
paper. The aim of this paper is to provide additional details on some parameters and
to justify the possible variations on the input parameters.
2.
ASSUMPTIONS FOR DETERMINING INPUT PARAMETERS
2.1
Determination of factor T: Throughput capacity per Service Volume
2.1.1.Air-Ground throughput capacity (extracted from section 6.4 COCR version 0.9),
Airport (SV)
PHASE 2
Kb/s
Separate
ATS
Separate
AOC
Combined
ATS+AOC
TMA SV
Oceanic/
Remote SV
En route SV
HDEU
HD
LD
HD
LD
16.9
7.0
35.1
31.5
43.6
129.6
13.7
0.7
0.7
140.7
19.0
36.3
32.6
HDUS
Auto
SV
LD
HD
LD
45.6
43.5
38.8
38.1
7.3
68.0
89.9
67.2
24.9
15.9
75.2
192.2
224.9
190.9
124.9
75.8
107.3
Table 2.1.1 - Phase 2 Air/Ground Capacity Requirements (kbps)
-
The capacity table does not include ADS-B related or air-to-air related
services such as PAIRAPP or AIRSEP.
-
The service volumes correlate operational control volumes, i.e. a
volume controlled by a single controller position.
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2.1.2.Air-Air throughput capacity (from section 6.5 COCR version 0.9) in bits per
second
PHASE 2
ADS-B PIAC
ADS-B Range (nm)
ADS-B MsgSize
ADS-B Update Rate
(mps/ac)
ADS-B Latency E2E
ADS-B Latency FRS
ADS-B Bits/Second
PAIRAPP PIAC
PAIRAPP MsgSize
PAIRAPP Update Rate
(mps/ac)
PAIRAPP Latency E2E
PAIRAPP Latency FRS
PAIRAPP Bits/Second
AIRSEP PIAC
AIRSEP
Bytes/Transaction
AIRSEP Update Rate
(mps/ac)
AIRSEP Latency E2E
AIRSEP Latency FRS
AIRSEP Bits/Second
TOTAL Bps
Airport
TMA
ER
OR
AZ
340
5
372
975
60
372
1625
200
372
14
200
372
42
200
372
1
0.167
0.167
0.167
1
1
0.8
1,264,80
0
13
372
6
4.8
6
4.8
1
0.8
604,500
6
4.8
1,007,50
0
8,959
156,240
3.3
3.3
0.3
0.24
161,200
0.3
0.24
768,800
62
372
11
6000
0.2
10
8
66,000
1,426,000
1,373,300
1,007,500
8,959
222,240
Table 2.1.2. Phase 2 Air/Air Capacity Requirements
- The air/air data loading analysis looks at ADS-B/TIS-B and addressed air/air
communication services such as PAIRAPP and AIRSEP.
- Unlike the other loading analyses (which use service volumes that correlate to
operational control volumes), the air/air data loading analysis uses service volumes
that correlate to air/air ranges. The required transmission range for Airport, TMA,
and En Route domains are 5, 60 and 200 NM, respectively.
2.1.3.Voice requirement (from section 8.5 COCR version 0.9)
Voice was considered necessary in both Phase 1 and Phase 2, with decreasing use
in Phase 2. However, when voice was required it was considered to have similar
requirements to current VHF radio usage.
The estimated seconds per hour of active talk time and the access/transaction
information were derived using current usage and extrapolated to the future
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environment. Based on assumed equipage rates for data link and reduction in voice
usage, the growth in traffic can be handled with current voice usage assumptions.
2.1.4.Operational Concepts : Conclusions from section 8 of COCR vers 0.9
A requirement driven approach was taken based on predicted operational concepts in
the 2020 to 2030 and beyond timeframe. This required the review of future concepts
some of which are immature. In some cases it was necessary to use expert opinion to
define some ATS services and how they would be used. The associated
communications operating concept and requirements (COCR), contained in this
document, have been draw from these concepts. Any change in the concepts will
affect the results.
The scope of the COCR covers all air/ground and air/air communications services to
support the operational ATS services including ASAS as well as future AOC services.
Key points in the ATS concepts considered are 




ASAS Operations are implemented in some airspace beginning in
Phase 1, leading to Autonomous Operations in Phase 2.
Larger sectors were assumed in Phase 2 and become more dynamic
in managed airspace.
Air Traffic Management begins using 4-D trajectory - based
operations in managed airspace.
Automation becomes available to both ground and air users enabling
longer range conflict resolution. "Machine-to-Machine" information
exchanges replace many Human-to-Human exchanges.
The controller's role is transformed from a control to a management
paradigm through various decision support tools.
2.1.5..Safety and Security
Safety and security requirements have an impact on the overall communications
performance. To the maximum extent possible, these have been considered in
compiling this document. Both safety and security were considered on an end-to-end
basis. The relevant requirements were then allocated to the future radio system (FRS)
which is in the scope of the COCR document.
For the safety requirements, the primarily effect is on parameters such as availability,
integrity in the Phase 2 timeframe. In an environment when separation standards are
reduced, ground and airborne systems must have the capability to detect conflicts,
provide resolutions, and in rare cases implement the resolutions e.g. auto execution of
the required manoeuvre by the aircraft, without human intervention. This places
considerable demands on the communications systems. However work is required to
complete detailed safety and performance analysis for each service and to refine the
associated message sizes and/or sequences.
Many of the security requirements are outside the scope of the FRS however one that
is directly relevant is the need for mild anti-jam resistance.
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2.1.6 Air Traffic Growth
An important factor in the analysis of communication requirements was the density of
aircraft. Airspace models for ECAC and the U.S. traffic growth were used to
determine numbers of aircraft over the period under consideration. Two models were
used 1) EUROCONTROL SAAM and 2) the U.S. MLM. In reviewing the outputs
from these models it highlighted the basic assumptions behind them. For example, it
is believed that SAAM traffic growth, based on STATFOR predictions, is constrained
by airport capacity and that traffic is spread over the day to handle the growth. The
result is that traffic density does not grow at the rate of traffic growth.
The MLM originally took a similar approach for en-route airspace however it was
modified to enable unconstrained growth of traffic. New satellite airports were
included to cope with the expected traffic resulting from the NGAT concept which
anticipates the introduction of thousands of Micro jets and UAVs into the airspace.
These two approaches resulted in two sets of complementary results with the U.S.
having higher densities in Phase 2 en route airspace.
2.1.7. Radio Channel Queuing Model
A model was developed to determine the required capacity of a communication
system to handle the traffic generated by the ATS and AOC services. A number of
options for the queuing model were considered and the final option implemented used
a single non-pre-emptive queue supporting ATS and AOC. ATS and AOC
requirements were also determined independently.
2.1.8.Communication Requirements
2.1.8.1.Air/Ground data
The resulting communication capacity to meet the requirements with the volume of
traffic generated for Phase 1 and Phase 2 are shown in the Tables below.
PHASE 1
Kbps
Separate
ATS
Separate
AOC
Combined
ATS+AOC
Airport SV
HD
LD
TMA SV
HD
LD
Enroute SV
HD
LD
Oceanic/
Remote SV
HD
LD
7.1
1.4
21.4
18.9
16.0
16.0
1.1
0.8
18.8
3.2
0.5
0.5
10.2
10.2
3.7
3.2
24.2
3.3
21.7
19.1
24.7
24.7
4.0
3.3
Table 2.1.8.1.1 Air ground data phase 1 incorporating queuing model.
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PHASE 2
Kbps
Airport SV
HD
Separate
ATS
Separate
AOC
Combined
ATS+AOC
LD
TMA SV
HD
LD
Oceanic/
Remote SV
Enroute SV
HDEU
HDUS
LD
HD
LD
Auto
SV
16.9
7.0
35.1
31.5
43.6
45.6
43.5
38.8
38.1
7.3
129.6
13.7
0.7
0.7
68.0
89.9
67.2
24.9
15.9
75.2
140.7
19.0
36.3
32.6
192.2
224.9
190.9
124.9
75.8
107.3
Table 2.1.8.1.2 Air ground data phase 2 incorporating queuing model.
Many emerging ATS data link services were included in Phase 1. This resulted in an
increased requirement for bandwidth to support the new services. The highest ATS
requirements for Phase 1 occur in the TMA.
In Phase 2 for the en route and Oceanic/Remote service volumes, the A-EXEC service
generated the most demanding requirements. If the service was not implemented, the
ATS values would be 14.1 and 8.0 kbps versus 43.6 and 38.8 kbps, respectively. In
other words, the required information transfer rate would be reduced by between 68%
and 79%.
The increase in capacity requirements in Phase 2 for the Airport Domain can be
attributed in part to increased message sizes and reduced latencies.
Little information was available on future AOC requirements and therefore many
services considered were extensions of those used currently. More intense use of
AOC data services will impact the results contained in this document.
Some sensitivity analysis was carried out on the results and it was noted that the
capacity requirements do not increase linearly with aircraft density. In some cases,
the latency had the greatest effect on capacity. Under these conditions not all the
capacity was used therefore doubling the aircraft to be supported did not double the
capacity requirements.
2.1.8.2 Air/Air Data
An analysis of the requirements to support broadcast services such as ADS-B/TIS-B
and addressed air/air communication services such as PAIRAPP and AIRSEP was
carried out. A model was developed to evaluate the single aggregate flow to support
the services in volumes that were related to the air/air range. This was a different
approach to the air/ground data analysis.
The analysis showed that that some of the broadcast rates needed exceed the
capabilities of existing technologies. However the estimated information transfer rate
is directly rated to the assumed message size so if the information transfer rates would
be reduced if smaller message sizes were used.
As the COCR is technology independent, consideration was not given to transmission
collision, media access delays and/or scheduling overhead.
2.1.8.3.Voice
A different approach to reviewing the data requirements was adopted for voice. Voice
was considered necessary in both Phase 1 and Phase 2 but with decreasing use in
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Phase 2. However when voice was required it needed it was considered to have
similar requirements to current VHF radio usage.
The estimated seconds per hour of active talk time and the access/transaction
information were derived using current usage and extrapolated to the future
environment. Based on assumed equipage rates for data link and reduction in voice
usage, the growth in traffic can be handled with current voice usage assumptions.
2.1.8.4.Overall
As an overall summary of the results, it appears that the average communication
capacity for ATS air/ground data is relatively modest. However to achieve the
required latency, a high capacity will be needed for a short time. This capacity must
be available when needed and with high integrity. This is reflected in the safety
requirements where, for example, very high availability figures have been identified
for some Phase 2 services.
The concepts assumed for air/air communications appear to have requirements that
cannot be meet by current technology
2.2
AIRSPACE MODELLING
2.2.1.Radio Cell modelling (from section 7.4 COCR version 0.9)
A typical line-of-sight (LOS) communication system will have a designated
operational coverage volume much larger than a sector. Typically at 5000 ft the
theoretical radio horizon would be 87 NM and 194 NM at FL200
Assuming a radio cell is limited by line of sight coverage, a conservative figure of
60% of the theoretical horizon distance was chosen to account for multipath, effects.
(Of course the actual figure would be dependent on the particular technology e.g. link
budget used, modulation schemes, etc.)
2.2.2 Operational sector modelling (from section 6.2.1 COCR version 0.9)
The sizes of service volumes for Phase 1 are equivalent to control positions/sectors in
existence today. Use of the new operational services in Phase 1 will allow higher
numbers of aircraft to be serviced in the same volume.
In Phase 2, it is expected that the typical TMA sector service volume will have a
twofold increase in size and the En Route sector and Oceanic/Remote sector service
volumes will see a threefold increase in size.
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2.2.3.Airspace modelling (from section 7.4 COCR version 0.9)
Figure below illustrates a test sector as part of the TMA at 5000 ft. The figure also
shows a notional radio horizon based on 60% of the ideal 4/3R radio horizon centred
on the test sector which may not be the case.
At 5000 ft the figure shows the DOC (Designated Operational Coverage) of around
50 NMs. As can be seen the DOC easily covers the test sector and several others.
5000ft
Figure.2.2.3.1 London TMA – 5000ft
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Figure below illustrates the sector as part of the TMA at FL200. The figure also
shows a notional radio horizon based on 60% of the theoretical radio horizon.
It can be seen that the sector is much larger, however the DOC is very large and
covers many other sectors. Around 14 sectors are within the coverage area of the
LOS system.
The results obtained for the test sector need to be applied to a different airspace
volume dependant on the technology considered.
20000ft
Figure.2.2.3.2 London TMA – FL200
Assuming around 6 sectors were supported within the DOC of a communication
system then the worst case capacity needed would be 6 times that identified in the
TMA results. It should be noted however the loading analysis is not linear and some
technologies can be sensitive to this.
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ASSUMPTION ON RADIO CELL MODELLING USED IN THE MODEL
A high density radio cell by the time horizon 2030 is assumed to incorporate
- 1 airport area,
- 7 TMA sectors
- 1 en-route sectors.
These service volumes are mapped into the airspace organisation as defined in
figure 2.3.3.3 to calculate the capacity throughput of the radio cell
Unmanaged
Autonomous Operations
Communications
Buffer Zone
En Route Managed
4D Trajectory, User Pref.
Routes, A - A Sep.
TMA Managed
4D Trajectory, Route Based,
A - A Sep., & Legacy Ops
Unmanaged
Communications
Buffer Zone
Airport
Managed
Figure 2-1. Airspace Organisation in Phase 2
Communications
Buffer Zone
Unmanaged
Figure 2.3.3.3. Airspace Organisation in Phase 2
3.
DETERMINATION OF THE VALUES AND VARIATIONS ON THE
INPUT PARAMETERS
3.1
Baseband communication throughput
Using the input parameters from the COCOM v0.9 study the total communication
throughput per radio cell is 4,37 Mb/s.
There is a high degree of confidence in this figure and consequently the accuracy
can be considered to be with 95% certainty limits within a tolerance of +/- 10%
It should be noted that presently the provision for Unmanned Aerial Vehicles is not
fully included in this figure.
3.2
The NSC
The Net System Capability as defined in ITU M 1390 can be considered to be a
measure of the spectral efficiency of a technology in terms of datarate throughput in
Bits per Hz of RF spectrum per radio cell.
.
It has theoretically been shown that adapting various 2 dimensional mobile
technologies to three dimensional environment reduces the Net System Capability
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(as defined in ITU M 1390). This seems logical as the system C/I value will decrease
as wanted natural obstructions to Line of Sight are removed as altitude is gained in a
3-D mobile environment.
Detailed studies of NSC for various technologies adapted to the Aviation 3D case
have been carried out by Eurocontrol and yield a number of typical NSC values.
Class name
Low
Medium
High
Low data rates
0.04
0.07
0.1
High Data rates
0.1
0.2
0.3
Table 3.2. Three dimensional Mobile system Net System Capability (NSC)
The distribution about these average values is unknown. The general viewpoint is for
the Aviation case (particularly upper airspace) the case will converge towards the
‘low class’ example. Thus an approximation to this distribution can be made to this by
using an average (mean) value μ= 0.1, and a variation of +/- 0.06 (This will give a
95% confidence level)
3.3
The adjustment factor
In the ITU M1390 model, provision is made for an adjustment factor β, this is
described in section D6 of the recommendation but is essentially to allow for:1. Multiple operators of systems if applicable
2. Intra system sharing if applicable;
3. Sharing with non similar services
4. Guard bands;
5. Technology modularity. For example, if a technology uses 10 MHz frequency
division duplex (FDD) channels, then the requirements will necessarily be an
integer factor of 20 MHz;
6. Other adjustments to be justified.
All these points will be applicable to the Aviation case, however probably the most
significant will be points 2 and 3, sharing with similar and other systems.
This is particularly true of the VHF and L candidate bands where the bands are
already highly utilised by the same systems (intrasystem sharing) and different
systems (intersystem sharing).
3.3.1.Band Sharing aspects. Compatibility analysis and deriving sharing
factors.
3.3.1.1.Methodology
A two phase approach is proposed when analysing the sharing capabilities in a band.
Phase 1. Over Simplification of criteria.
This is an initial quick and high level assessment as to what portion of the band is
empty or where there is some natural low spectral power density for whatever
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reason. It can be a straight ratio of empty spectrum slots compared with the total
spectrum in the band.
The same excersize can be carried out in the time domain (particularly when the
incumbent signals show a low duty cycle) and also in the spatial domain using the
natural geometric and geographical factors of protecting wanted signals from
unwanted in the classical frequency management coordination processes.
This high level analysis used conservatively can give a reasonable estimation as to
what spectrum resource is available in the band under study.
It should also be noticed that this method assumes comparing like systems (ie where
the systems have equal transmitted power, the same receiver characteristics and the
same threshold values etc), if characteristics are markedly dissimilar, the analysis will
not hold true and hence the need for more detailed compatibility assessment.
Simply put, the applicable adjustment factor is in direct inverse proportion of empty
resource.
In frequency domain
1 – (portion of frequency allotted or normally utilised MHz)
(portion of frequency allocated MHz)
In time domain
1 - (duty cycle of incumbent systems)
1
In spatial domain
1 – (area where new system can be operated without interference km2)
(total area of a region km2)
Where a number of these ‘mitigation’ techniques are used, the aggregate sharing
factor can be arrived at by straight division
In contrast to this conservative approach, if two or more services are said to
efficiently co operate in a band the sharing factor will tend towards 1 (ie the case
when a system has empty spectrum to operate in)
This gives a useful spread of probabilities.
In the first instance this methodology has been used to derive the extremes of best
and worst case and from this a pragmatic mean and likely standard deviation from
this can be assessed.
Phase 2. Detailed compatibility study.
Obviously if this first phase of analysis shows favourable conditions could exist the
compatibility needs to be investigated at a more detailed and rigorous level. At this
stage this has not been done.
3.3.1.2 Rationale of values chosen for each of the bands.
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Using the methodology described and the phase 1 approach the candidate bands
have been analysed as follows:VHF Band 108-118MHz
 If the band was empty a sharing factor of 1 would be applicable.
 In the medium term the occupancy of this band is expected to continue to be
highly utilised. On one hand the VOR deployment in the European Navigation
Strategy is planned to be reduced, on the other hand the take-up of GBAS is
likely to take this capacity (or in a simple model this could be assumed to be
the case).
 To enable a new system some radical spectrum clearing will be required or
the use of a ‘compatible’ technology such as B-VHF which exploits the
spectrally low power density between VOR or GBAS allocations. In either
case even with substantial clearing it is unlikely that a sharing factor of less
than 2 can be achieved.
 Conversely without any clearing the sharing factor would tend to infinity.
 A pragmatic value is to take a sharing factor of 2 with a variation of +/-1 giving
a 95% confidence factor.
L Band (960 – 1164 MHz)
 If the band was empty a sharing factor of 1 would be applicable.
 This band is used heavily by DME’s, radar and the non disclosed
JTID’s/MID’s system which already takes up some of the frequency domain
natural redundancy
 Considering now the frequency domain utilisation between 960 and 1164
MHz and assuming the JTID’s MID’s element can be spatially coordinated
with a new system, there are some natural null slots between 960 and 977
MHz and again 1146-1156 MHz. This is a total of 27 MHz. This gives a band
sharing factor of (1164-960)/27 = 7.56.
 In addition to this there is a time sharing element to be considered for this
band which generally uses pulsed systems with various duty cycles, under
saturated conditions the duty cycle in a volume could arguably approach 50%
, for equal systems ideally integrated to share this would slice sharing factor
in two (ie 3.75)
 Also the spatial sharing elements could be further exploited, with reasonable
multilateral agreements between military and state, separation between
military excersize areas and civil airspace can be maintained, this would free
up more spectrum for sharing.
 There may be some other methods for reducing this sharing factor that will
become apparent in the more detailed compatibility analysis.
 On balance a mean Sharing factor of 2.5 is considered achievable, with a
broad delta of +/- 1 giving a confidence factor of 95%
C Band
 If the band was empty a sharing factor of 1 would be applicable.
 If each of the systems planned (there are 5 systems, MLS, FSS feeder links,
AMT, Aeronautical Security, Airport Communications FCI element), for in this
5 GHz band were equally apportioned the spectrum and used all the
spectrum in the frequency, time and spatial domains, a sharing factor of 5
would apply. However this is not the case
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Frequency domain analysis
 The MLS is expected to take up upto120/150 MHz [and maybe only 60
MHz]
 FSS feeder links takes up less than 10% of this total spectrum. [15/150
MHz, to be confirmed by Globalstar]
 The Aeronautical Security is only planning to take 15 MHz. (or 15/150 of
the spectrum),
 AMT is planning to take 60/150 MHz of the spectrum.
 Airport Communications FCI element is expected to take up N x 10 MHz
of spectrum (estimate 100 MHz or 100/150)
 GNSS is allocated 20 MHz (between 5010-5030) so takes up 20/150
This totals 330 MHz of spectrum in a band that is 150 MHz wide, or a sharing
factor of 2.2 in the frequency domain
Time domain analysis
Some further reduction of the sharing factor is achievable:






MLS is continuous
FSS is continuous
Aeronautical security shows a duty cycle of less than 50% Air to ground
and similarly ground to air (TDD)
AMT will have a duty cycle of less than 100%
Airport communications FCI will have a duty cycle considerably less than
100% as it is demand assigned in the 802.xx protocol
GNSS should be considered as continuous.
Spatial domain analysis
-some work has been done regarding statistical and special sharing between
AMT, MLS, security system and FSS (See ITU 8B draft new recommendation)
-further it is expected that Airport FCI /AMT and Security (all being Aeronautical
stakeholders) can be coordinated.
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Conclusion:
The sharing factor in the C band should be taken as 2 with a delta of +/- 1 to give
95% confidence
3.3.1.3 Summary of Results
The following table provides some initial sharing factors as defined in phase 1 above,
further verification will be needed as the technology parameters are more clearly
known.
Best case
VHF
(108-118 MHz)
VHF (118-137
MHz)
L band
(960-1164
MHz)
C Band (50005250 MHz)
1
Worst case
3
Pragmatic
mean
2
Delta limits for
95%
confidence
+/- 1
Not feasible in the short term
1
3.75
1
5
2.5
+/- 1
2
+/- 1
Table 3.3 Summary of Adjustment factor parameters for each of the bands
Limitations and assumptions:
See above the limitations of this analysis in the methodology and results.
It should be noted that at this stage, no consideration of multiple operators,
technology modularity/granularity or guard bands have been factored into this
adjustment factor as these are likely to be less significant than the sharing aspect,
however the sensitivity particularly to the modularity/granularity aspect should not be
overlooked [ This can add 100% increase for the larger systems eg W-CDMA]
4.
CONCLUSIONS
The meeting reviews the assumptions and the parameters being used for the
calculation of the spectrum resource
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