ACP-WGF18/WP-17
International Civil Aviation Organization
12-22 May 2008
WORKING PAPER
AERONAUTICAL COMMUNICATIONS PANEL (ACP)
18th MEETING OF WORKING GROUP F
Montreal, Canada 12 – 22 May 2008
Agenda Item 5
Development of material for ITU-R meetings
Recommendations to consider in L-band AMS(R)S spectrum estimation
(Presented by Waldir Nunes)
SUMMARY
This paper presents two recommendations to be considered in formulation of a
methodology for spectrum estimation for AMS(R)S in L-band, as required by
WRC-11, agenda item 1.7 studies.
ACTION
The meeting is invited to consider this information in developing the
methodology for spectrum estimation for AMS(R)S in L-band, as required by
WRC-11, agenda item 1.7.
1.
INTRODUCTION
1.1
Agenda item 1.7 for WRC-11 is "to consider the results of ITU-R studies in accordance
with Resolution 222 (Rev.WRC-07) in order to ensure long-term spectrum availability and access to
spectrum necessary to meet requirements for the aeronautical mobile-satellite (R) service, and to take
appropriate action on this subject, while retaining unchanged the generic allocation to the mobile-satellite
service in the bands 1 525-1 559 MHz and 1 626.5-1 660.5 MHz;".
1.2
Part of studies is the estimation of spectrum needed. This paper presents two
recommendations to be considered in formulation of a methodology for spectrum estimation for
AMS(R)S in L-band, as required by WRC-11, agenda item 1.7.
ACP-WGF18/WP-17
2.
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DISCUSSION
2.1
In order to adequately estimate the amount of spectrum necessary to AMS(R)S in L-band,
the basic methodology has to consider three main parameters/aspects:
(a) the peak instantaneous aircraft count inside a coverage area;
(b) the total amount of data to flow between each aircraft and the correspondent air traffic control
office and the aircraft operator; and
(c) the technology available to implement the required flows, as dimensioned based on the first
two parameters.
2.2
The third aspect is directly related to several possibilities, such as spot-beams utilization,
efficient frequency reuse capability, efficient spectrum utilization (in terms of bits/Hertz and also by the
use of “good” access methods, in order to minimize control messages and unused time), and others. It will
not be considered in this paper.
2.3
About the peak instantaneous aircraft count, considering that the spectrum estimation, in
this case, will support decisions with long-term consequences; it is recommended that this parameter be
based on minimum separation values, instead of future expectations of airspaces occupancy.
2.4
About the amount of data flowing between each aircraft and the correspondent air traffic
control office and aircraft operator, it is important to consider, if possible, a clear approach, based on
applicable parameters, in such a way that allows other instances (for example, ITU-R) to understand and
accept the spectrum needs.
2.5
Annex I brings a simple theoretical example to illustrate the use of such
recommendations.
3
ACTION BY THE MEETING
That ACP WGF is invited to adopt, in order to estimate spectrum needs for AMS(R)S in L-band:
i)
minimum separation values to estimate peak instantaneous aircraft count;
ii) a clear formulation, if possible, of the amount of data flowing between each aircraft and the
correspondent air traffic control office and aircraft operator.
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ACP-WGF18/WP-08
Annex I – theoretical spectrum estimation for AMS(R)S in L-band
Consider an airspace covered by a satellite spot-bean well formed, with a perfect circular form (ray Rspot),
where exist only parallel airways.
The total amount of aircrafts inside the service volume is:
Nacft = Nfl × Σ i = 0.. k int([Rspot2 – (i × Sl)2] 1/2 ÷ Sa)
where,
Nfl: flight levels allowed in this airspace
Sl: minimum lateral separation
Sa: minimum longitudinal separation
Sa
int(.): biggest integer contained in the argument
k: int(Rspot÷Sl)
Sl
Superior view of a spot beam with ray Rspot and aircrafts inside
Given the peak instantaneous aircraft capability of this specific airspace, it is necessary to identify the
total amount of data each aircraft has to transmit and to receive. It can be estimated considering a
superposition of processes of generation of messages:
νacft = λATC × μATC + λAOC × μAOC + λ CM × μCM
where
λATC: average rate of generation of ATC messages (msg/s/acft)
μATC: average size of ATC messages (bit/msg)
λAOC: average rate of generation of AOC messages (msg/s/acft)
μAOC: average size of AOC messages (bit/msg)
λCM: average rate of generation of CM (msg/s/acft)
μCM: average size of CM messages (bit/msg)
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It has been considered that the messages generation processes have intervals independents and
equally probabilistic distributed, and that the distribution is unknown. The average total amount of
data per second generated or sunk inside the spot bean can be estimated as follow:
νTotal = Nacft × (λATC × μATC + λAOC × μAOC + λ CM × μCM)
Considering, also, additional inter-spot handoof capabilities, a bigger amount of aircrafts has to be
considered. It is possible to be addressed using a N’acft > Nacft, where N’acft is a funtion of
technological means and Nacft. A special case is when channels are allocated to aircrafts near (and
outside) the spot-bean, so it can be used R’spot > Rspot for N’acft calculation.
Considering that it is possible to utilize σ Hertz to transmit one bit (where σ is a function of
technological means),
E[BW] = N’acft × σ × (λATC × μATC + λAOC × μAOC + λ CM × μCM) Hertz
Where E[BW] is the average spectrum needed for the specific spot. Due to unknown probabilistic
characterization of intervals betweeen message generation times, it can be assumed maximum values
to each average parameters (λ and μ) as an extreme measure.
This calculation was based on a approximation of superposition of renewal processes. It can be
verified in: Whitt, W. 1982. "Approximating a Point Process by a Renewal Process, I: Two Basic
Methods", Operations Research, Vol. 30, No. 1, 125-147.