International Civil Aviation Organization
WORKING PAPER
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COMMUNICATIONS PANEL (CP)
Working Group Surface (WGS), 8th meeting, 9 December 2015
AeroMACS Capacity in terms of number of users to be supported
(Prepared and presented by EUROCONTROL)
SUMMARY
This paper provides the initial results of a qualitative investigation of the
capacity of an AeroMACS access network in terms of the maximum number
of users able to be accommodated in such a network under normal conditions.
The constraints on the number of users are analyzed according to two possible
limitations: a) maximum number of registered users in AeroMACS BS and
ASN-GW, and b) number of users considering the maximum throughput
supported by the access network and compared to the required throughput per
user.
ACTION
CP/WG-S is invited to 1) consider the proposed analysis, 2) provide comments
and feedback to finalize the analysis and 3) discuss the benefit of including in
the AeroMACS Manual material in relation to the number of users supported
by AeroMACS
1
AeroMACS capacity:
Number of potential
users
Version: Draft 01, 09/12/2015
Author: ANTONIO CORREAS USON
Developed under contract to EUROCONTROL (contract
13-110459-C “SESAR Project P15.02.07: AeroMACS
Standardisation Support”)
ALOT TECHNOLOGIES, S. L.
2
Executive summary
This paper provides the initial results of a qualitative investigation of the capacity of an
AeroMACS access network in terms of the maximum number of users able to be
accommodated in such a network under normal conditions. The constraints on the number of
users are analyzed according to two possible limitations: a) maximum number of registered
users in AeroMACS BS and ASN-GW, and b) number of users considering the maximum
throughput supported by the access network and compared to the required throughput per user.
Keywords: AeroMACS, data link, user capacity
References
[1] WiMAX Forum AWG, Network Reference Architecture, January 2015
[2] Honeywell, Contribution to AeroMACS Manual – Architecture description v5, July 2015
[3] EUROCAE, AeroMACS MASPS draft v0.30, July 2015
[4] AT4Wireless, AeroMACS Manual Multicast and Broadcast aspects, June 2015
[5] EUROCONTROL, ICAO ACP-WG-S5/WP-10 DL:UL OFDM symbol ratio in
AeroMACS TDD frame, July 2014
Table of contents
Contents
1.
Introduction
4
1.
User registration constraints
5
2.
Throughput constraints
5
3.
2.1
User and BS characterization
6
2.2
Scenario description
8
2.3
Analysis results (for capacity constraints)
Conclusions
10
13
3
1. Introduction
This Technical Note aims to provide some generic guidance on the overall system capacity and
in particular in relation to the number of users that can be supported by an AeroMACS access
network under an acceptable level of service.
Acceptable level of service is defined here as a situation where the system is not under
congested status. In the context of this paper, congestion occurs when the system cannot offer
enough capacity for an additional user and it will reject any additional user entry. The level of
available capacity reaching congestion differs with the scenarios and the assumptions for the
communication requirements of the serviced users.
In the analysis of this paper, “user” is defined as the application client connected to the
AeroMACS service network through a Mobile Station (MS). Each user runs a number of
services described in the scenarios considered in section 3.2. In this analysis, users can be
aircraft, surface vehicles and various types of fixed stations.
It needs to be noted that this study is a qualitative analysis on the capacity that an AeroMACS
access network can provide under a number of assumptions. The objective is not to quantify the
absolute maximum number of users that can be supported, neither to derive operational or
technical requirements.
AeroMACS is based on WiMAX, a cellular technology that enables the access of Mobile
Stations (MS) to user applications on the airport surface. The reference network architecture for
the access network is shown in Figure 1. AeroMACS access service network is provided by a
number of Base Stations (BS) which operate in dedicated 5 MHz bandwidth channels and
manage the access of the Mobile Stations (MSs) to the common channel accessing configured
channels in radio cells, and an ASN Gateway (ASN-GW), which manages the data path with the
Connectivity Service Network (CSN) and handover within the access network.
Figure 1. WiMAX/AeroMACS access network reference architecture [1]
In general in an AeroMACS network, user access constraints may result from two possible
factors:

User registration constraints: The BS and ASN-GW are the two types of devices that
enable the AeroMACS access network. These two devices are limited by design to a
4

number of supported users that are given access service. This limitation depends on the
manufacturer design.
Throughput constraints: Radio access provided by a BS to the MSs covered in the
corresponding cell uses the limited throughput resources of the 5 MHz-wide radio
channel configured in the cell. Assumptions are taken about the types of MS devices
that consume different levels of throughput and modulation scheme in order to calculate
a number of users that allows all the MSs in the cell to be given an acceptable level of
service.
This paper addresses the two constraints mentioned above. For the throughput constraint
analysis, a user characterization and scenario definition is worked out before the analytic results
are presented.
2. User registration constraints
The maximum number of users that can be supported per ASN-GW and BS is limited due to the
size of the database used to register the number of MS (MAC addresses or other parameters).
From ASN-GW perspective, some products are scalable meaning in number of boards and
distributed architecture, hence proposing configurations for thousands of users. Thus, the
limitation in number of registered users will probably not be an issue airport-wide.
BS may impose stricter limits in the number of subscribers registered to operate in the BS radio
channel. Data from one manufacturer indicate 64 units supported per BS1.
To be further discussed and completed with data from other manufacturers.
3. Throughput constraints
The throughput limitation of the AeroMACS access network occurs at the cell level on its
specific radio channel, i.e. it is driven by each BS in the network independently. The analysis of
this limitation is performed here qualitatively and provides a general guidance of the order of
magnitude of this figure given certain assumptions. If a detailed figure needs to be achieved,
simulation or field test should be performed for a specific deployment.
In order to calculate the maximum number of users in a cell limited by throughput, a threeprocess step is followed:



1
First, the throughput needs are defined depending on the type of user, and the
throughput supported by BS is defined depending on the type of BS.
Second, scenarios are defined which specify the ratio of each type of user is foreseen
per BS.
Third, results are calculated analytically indicating the maximum number of users
supported in each scenario.
If the subscriber unit is connected to other end point like users over Wi-Fi this number can be
substantially extended. E.g. each AeroMACS subscriber unit can be connected to a Wi-Fi
Access Point which servers 20 users in average. This could give a total of 1280 end points.
5
3.1
User and BS characterization
This section defines the average and maximum application level bitrate generated in DL and UL
directions per type of user that can be found at the airport, and the maximum bitrate supported
by a BS giving access to such users to the AeroMACS access network.
ASSUMPTION: The user typology is defined in line with the AeroMACS Manual [2] where a
list of devices classes is defined. This document defines the following device configurations of
MS to work out a classification of the types of services to be provisioned, number of
connections and data rates, however it is acknowledged that these would differ on a case by case
basis.






Aircraft at the gate - represents modems installed in aircraft. Considering both safety
and non-safety applications all identified types of connections are recommended for
aircraft except video. The aircraft is at the gate and executing the pre-departure and
post-arrival applications necessary for the turnaround process.
Aircraft at hangar, taxiway or runway – same as above but the aircraft is executing
turnaround processes at the ground movement area or maintenance operations.
Surface vehicle – represents devices hosted on all ground support vehicles including
passenger vans/buses, dollies carrying cargo, refuel trucks, catering vehicles and Push
back tugs/ tractors etc., Generally, most of these vehicles are equipped with PTT
phones. In addition, A-SMGCS (Advanced Surface Movement Guidance & Control
System) may require a safety link for exchanging vehicle’s position information on a
periodic basis to a centralized control system.
Video Sensor – shall be used for sending videos during emergency situations.
Ground critical – represents devices used to monitor/control ground equipment that are
deployed for critical ATS services. Example: Landing Systems, Runway Lighting
controls etc.
Ground Default – All other ground equipment fall under this default category.
ASSUMPTION: Table 1 provides the average and peak throughput requirements at the
application level for each of these types of user. The bitrate for aircraft is based on the
AeroMACS MASPS [3], the rest are assumed based on expected application load and
video/audio codec configuration.
Aircraft at gate4
Average 2 application bitrate
Peak 3 application bitrate
FL
RL
FL
RL
(GS->MS)
(MS->GS)
(GS->MS)
(MS->GS)
150 kbps
150 kbps
600 kbps
300 kbps
2
Using median (50th percentile) is recommended for capacity estimations. Average can lead to wrong
conclusion is the traffic demand is not distributed uniformly over time.
3
“Peak” refers to 95th percentile.
6
Average 2 application bitrate
Peak 3 application bitrate
FL
RL
FL
RL
(GS->MS)
(MS->GS)
(GS->MS)
(MS->GS)
Aircraft
at
hangar, 20 kbps
taxiway or runway3
40 kbps
40 kbps
100 kbps
Surface vehicle
8 kbps
10 kbps
16 kbps
20 kbps
Video sensor5
1 kbps
64 kbps
4 kbps
512 kbps
Ground critical
1 kbps
1 kbps
4 kbps
8 kbps
Ground default
1 kbps
1 kbps
4 kbps
4 kbps
Table 1. Device classes
In order to calculate the throughput limitations in a BS, the modulation/coding rate and the
DL/UL OFDM symbol ratio needs to be derived. Table 2a depicts the [3] calculation of the
application data rate (TCP/IP PDU throughput) in a BS depending on the modulation/coding
scheme used. Note that these results were obtained by applying (31,16) DL/UL OFDM symbol
rate. The rate (26,21) is also considered in this study as the most symmetrical DL/UL
configuration mandated in the profile [5]. The throughput resulting from this configuration is
approximated in Table 2b.
Table 2a. AeroMACS expected TCP/IP throughputs vs modulation schemes for DL/UL
OFDM symbol rate (31,16)
4
ASSUMPTION: Aircraft data requirements in line with [1]
5
ASSUMPTION: Video Works at 360p at 24 FPS and supports compression in low image refresh
periods.
7
MC scheme
Downlink [kbps]
Uplink [kbps]
QPSK ½
824.7
698.77
16QAM ½
1806.18
1621.62
64QAM ½
3015.19
2308
Table 2b. AeroMACS expected TCP/IP throughputs vs modulation schemes for DL/UL
OFDM symbol rate (26,21)
Two types of BS are identified depending on their position and expected coverage:


Micro-cell BS is placed at the gate and gives mainly high-capacity to aircraft and other
devices at the ramp area with a limited service range (covering about 3-5 gates).
ASSUMPTION: 75% of the users are within range to be serviced by 64QAM ½ and
the rest by 16QAM ½.
Macro-cell BS is placed around the airport surface and gives high-range coverage to
most of the airport surface areas. Table 3 shows the result of the total supported
throughput in both directions with the proportion of modulation/coding rates used.
ASSUMPTION: 20% of the users are within range to be serviced by 64QAM ½, 40%
by 16QAM ½ and 40% by QPSK ½.
Micro-cell BS
Modulation/code
scheme
Supported throughput Supported throughput
FL/RL (Mbps) at (31, FL/RL (Mbps) at (26,
16) DL/UL rate
21) DL/UL rate
64QAM ½ (75% users)
3.3/1.7
2.7/2.1
2/1
1.7/1.4
16QAM ½ (25% users)
Macro-cell BS
64QAM ½ (20% users)
16QAM ½ (40% users)
QPSK ½ (40% users)
Table 3. BS types and maximum throughput
3.2
Scenario description
This section describes foreseeable scenarios of the AeroMACS access network. Scenarios are
defined by the placement of the BS in the airport surface, and the proportion of users of each
8
type present on the airport surface. Both factors define the ratio of each user that is present in
each BS on the surface.




Scenario 1. Video surveillance - Represents a scenario in which AeroMACS is used
solely to support fixed video surveillance cameras for security control and operation
safety monitoring and record.
Scenario 2A. Integrated surface management system - Represents a scenario in which
video, sensor networks and surface vehicles are functioning on the airport surface
executing local applications enabling A-SMGCS and surface operation support.
Scenario 2B. Same as Scenario 2A but without including video surveillance sensors.
Scenario 3. Surface management and aircraft turnaround - Represents a scenario with
local services as above, and enables CPDLC and AOC applications with onboard
subscribers on the aircraft to support the turnaround process and maintenance. For
simplicity, it is assumed that aircraft at the gates occupy all the resources of the
dedicated micro-cells at the gates.
ASSUMPTION: Table 4 below indicates the proportion of cell bandwidth dedicated to each
type of users serviced by a BS in each of the scenarios considered.
AeroMACS
% A/C
gate
Scenarios
at % A/C at % Surface % Video % Ground % Ground
hangar,
vehicles
sensors
critical
default
taxiway or
runway
Scenario 1
-
-
-
100
-
-
Scenario 2A
-
-
30
50
10
10
Scenario 2B
-
-
80
-
10
10
Scenario 36
100
(only 50
micro-cells)
15
30
2.5
2.5
Table 4. AeroMACS network scenarios considered, and % of throughput dedicated to
each user type
The results on capacity are given per BS in this study. In order to derive aggregate capacity in
an entire AeroMACS access network, airport categories are based on number of movements and
may be used to define the amount of BSs deployed on the airport surface. The following airport
size types are proposed in line with reference [4].


6
Small (20 operations/hour) – 3 BS
Medium (50 operations/hour) – 9 BS
ASSUMPTION: Micro-cells are used exclusively to service aircraft at the gate [1]
9

Large (100 operations/hour) – 15 BS
When calculating the aggregate capacity in the entire AeroMACS network dependent on the
number of BS deployed in the airport surface, the limitation of 11 channels available for
transmission needs to be taken into account. Such constraint requires frequency reuse and may
result in a lower capacity offered per BS.
3.3
Analysis results (for capacity constraints)
Each scenario is defined by a data rate required per user type and a proportion of user types.
The results of the analysis are given in the form of number of users than can be reasonably
supported by a BS. Given all the assumptions in the previous sections, the maximum number of
users is derived for each scenario based on the user throughput requirements (Table 1) to be able
to serve given the user type ratio in the corresponding scenario (Table 4) within the throughput
constraints (Table 3). Note that a margin is left in the form of unused throughput in order to
account for a certain amount of peak traffic that may be caused by a user in the cell. The level of
margin assumed per cell is based on the peak throughput requirements in Table 1.
Tables 5, 6, 7 and 8 below identify the resulting maximum number of users for the different
scenarios and different DL/UL ratios considered.
Type of BS
#Video sensors
Remaining throughput (margin)
FL
RL
Micro
18
3.28 Mbps (99.5%)
548 kbps (32.2%)
Macro
7
1.99 Mbps (99.6%)
552 kbps (55.2%)
Table 5a. Maximum number of users (per channel) - Scenario 1, DL/UL OFDM symbol
rate (31,16)
Type of BS
#Video sensors
Remaining throughput (margin)
FL
RL
Micro
24
2.67 Mbps (99.1%)
564 kbps (26.8%)
Macro
13
1.69 Mbps (99.2%)
568 kbps (40%)
Table 5b. Maximum number of users (per channel) - Scenario 1, DL/UL OFDM symbol
rate (26,21)
10
Type of BS
#Surface
vehicles
#Video
sensors
#Ground
critical
#Ground
default
Remaining throughput
(margin)
FL
RL
Micro
35
9
115
115
2.75 Mbps 544 kbps
(83.3%)
(32%)
Macro
13
3
45
45
1.8 Mbps 588 kbps
(90%)
(58.8%)
Table 6a. Maximum number of users (per channel)- Scenario 2A, DL/UL OFDM symbol
rate (31,16)
Type of BS
#Surface
vehicles
#Video
sensors
#Ground
critical
#Ground
default
Remaining throughput
(margin)
FL
RL
Micro
50
12
150
150
1.98 Mbps 532 kbps
(73.6%)
(24.6%)
Macro
20
8
65
65
1.4 Mbps 558 kbps
(82.4%)
(39.8%)
Table 6b. Maximum number of users (per channel)- Scenario 2A, DL/UL OFDM symbol
rate (26, 21)
11
Type of BS
#Surface
vehicles
#Ground
critical
#Ground Remaining
default
(margin)
FL
throughput
RL
Micro
143
115
115
1.93 Mbps 40 kbps
(58.4%)
(2.4%)
Macro
87
45
45
1.21 Mbps 40 kbps
(60.5%)
(4%)
Table 7a. Maximum number of users (per channel)- Scenario 2B, DL/UL OFDM symbol
rate (31,16)
Type of BS
#Surface
vehicles
#Ground
critical
#Ground Remaining
default
(margin)
FL
throughput
RL
Micro
176
150
150
0.9 Mbps 40 kbps
(36.7%)
(2%)
Macro
123
65
65
586 kbps 40 kbps
(34.5%)
(3%)
Table 7b. Maximum number of users (per channel)- Scenario 2B, DL/UL OFDM symbol
rate (26, 21)
12
Type
BS
of #A/C
gate
at #A/C at #Surface
hangar,
vehicles
taxiway,
runway
#Video
sensors
#Ground
critical
#Ground
default
Remaining throughput
(margin)
FL
RL
Micro
9
-
-
-
-
-
1.9 Mbps 350 kbps
(59%)
(25%)
Macro
-
5
5
2
35
35
1.83 Mbps 552 kbps
(91.5%)
(55.2%)
Table 8a. Maximum number of users (per channel)- Scenario 3, DL/UL OFDM symbol
rate (31,16)
Type
BS
of #A/C
gate
at #A/C at #Surface
hangar,
vehicles
taxiway,
runway
#Video
sensors
#Ground
critical
#Ground
default
Remaining throughput
(margin)
FL
RL
Micro
12
-
-
-
-
-
900 kbps 300 kbps
(33.3%)
(14.3%)
Macro
-
11
10
4
35
35
1.3 Mbps 534 kbps
(78%)
(38.1%)
Table 8b. Maximum number of users (per channel)- Scenario 3, DL/UL OFDM symbol
rate (26,21)
4. Conclusions
This analysis gives a qualitative guidance on the number of users that can be serviced by an
AeroMACS access network. The study is based on a number of assumptions on the bitrate
requirements by the different users considered, and on the cell deployment at the airport surface.
Four scenarios are considered based on different assumptions.
The analysis does not intend to derive requirements on user service or cell siting. Such aspects
of the AeroMACS implementation are left to the discretion of the network owner. This study
does provide guidelines on the possible limitations that an access network may have. The main
capacity constraints occur in the RL direction in macro-cells. The number of users being
13
serviced in this direction can be significantly dropped especially when servicing video sensors
in the cell.
The number of users that can be supported is mainly limited by channel throughput constraints.
According to the results of this analysis, the maximum number of supported users for the
different type of cells can be considered within the following ranges:

Micro cells: up to 24 video sensors, or up to 170 surface vehicles, or up to 12 aircraft
stationed at the gate and about 300 sensors.

Macro cells: up to 13 video sensors, or up to 120 surface vehicles, or up to 11 aircraft
and about 130 sensors.
Note that throughput margins should be left available in a BS, as was done in the scenarios
considered in this paper, in order to cope with peak traffic. Video peak traffic can be particularly
high and requires a large margin of available throughput (512 kbps assumed).
The analysis shows that micro cell BSs are best suited to cover an area with many users and
within a small range (such as the gate area), while macro cell BSs cover larger areas and with
less number of users (such as airport movement or maintenance areas).
If users transmitting a heavy bitrate are present, such as a video sensors or aircraft stationed at
the gates, micro cells can be used to increase capacity to 2-3 times compared to the capacity
provided using macro cells. However, this is subject to restrictions on:
-
A) number of BSs intended to be deployed (including frequency reuse limitations),
-
B) availability of BS sites in the required areas (note that the micro BS has a limited
range), and
-
C) availability of network connections in the required sites.
Another technique to increase the BS throughput is to reduce the BS range (applying cell siting)
in order to increase the likely modulation code and thus increase the overall capacity of the BS.
This can be done via cell coverage overlap and load balance. In such a case, attention must be
paid to the limitation in the number of available channels which may lead to frequency reuse
and increased interference between cells.
When a large number of users transmitting a low bitrate is present (such as sensors), the
limitation is not the BS throughput but the maximum number of users allowed to be registered
in the BS equipment. A manner to overcome this limitation is to create Wi-Fi access points
behind a subscriber to support multiple users in the same MS. <to discuss>
Another relevant conclusion of this analysis is the impact of the asymmetry of the AeroMACS
link. Note that, using the most symmetric DL/UL ratio (26, 21) in the AeroMACS profile the
number of users supported increases significantly. This is due to the fact that the UL direction
has at least as much traffic load as the DL direction in the scenarios of this analysis. This
situation may occur in operational deployments, especially if video sensors or aircraft are
present. It is thus recommended to:
A) Use appropriate DL/UL ratios in AeroMACS deployments that are expected to use
extensively UL capacity
B) Consider the need to identify additional DL/UL ratio links (possibly in a future revision
of AeroMACS standards) that would support a higher share of the UL capacity
14