1. Aeronautical Communications Technologies Simulator
Bertrand Desperier - EEC
Patrick Delhaise - Eurocontrol DAS/CSM

2. OVERVIEW (i.e physical and data-link layers in OSI model)
Simulating the air/ground sub-network
(i.e physical and data-link layers in OSI model)
A modular architecture for re-using parts
First development for VDL mode 2
Multi platform supported (currently PC under windows)
Adaptation and validation of key air/ground sub-network
Prediction of system performance and capacity limits.
Optimisation of parameters, standards function, and implementation aspects respecting operational requirements

3. Capacity/ Reliability Analyser
Principle
MSG INPUT
-Random
-Deterministic
Area to be studied
AIR TRAFFIC
INPUT
GS3
Communication
Channels
GS1
Frequency
Station 1
Station 2
GS2
Capacity/ Reliability Analyser
Station 3
Time
Station N
SYSTEM PARAMETERS

4. Each station perceives differently the common channel at a given time
Relative channels
Each station perceives differently the common channel at a given time
AC 3
t 1/3 3
AC 2
t 1/2 2
AC 1 1
t(AC 3)
Absolute time
t(AC 2)
t(AC 1)
Level
t 1/2
t 1/3
t 2/3
t 2/3

5. Relative channel information
Generic Architecture
Upper layers
Messages
Channel
STATION (AC or GS)
Relative channel information
CHANNEL FILTER
SYSTEM
Air traffic
System parameters

6. Relative position calculator
Generic Architecture
Analyse
Capacity
reliability
Average delay ...
Upper layers
Messages
Channel
STATION (AC or GS)
CHANNEL FILTER
Propagation
model
Power
Receiver
Data Link Rx
Relative position calculator
Delay
Channel Monitor
Data
Transmitter
SYSTEM
Air traffic
System parameters

7. Propagation model (several accuracy levels)
Inputs
Air traffic
For each station (airborne and ground) 3-D positions in a given area
 Can be extracted from any air traffic simulator (RAMS, TAAM, SAAM…) or radar plots record
Messages profiles
Messages transmission rate distribution
Message length distribution
Messages exchange based on events
System parameters
Propagation model (several accuracy levels)
Physical layer
Medium access control layer
Data-link layer

8. Other ACTS application areas
Validation achieved
Application of Certification tests for single station
Theoretical models-comparison for the whole sub-network (Mathematical checks for simple cases)
Field trials
Cross check with other simulators
Initial operation feedback
Other ACTS application areas
Other VDL modes (3,4)
1090 E.S.
UAT
3G systems
Satellites systems
……………………..

9. VDL Mode 2-ACTS

10. ACARS network ATN ACARS, VDL 2, AOA, ATN, ... Unchanged ACARS
ACARS applications in a Management Unit, CMU or ATSU
Analogic VHF radio or VDR running in ACARS mode
Current ACARS configuration
ACARS
Ground-Stations
ACARS
applications
ACARS network
AOA data path
Unchanged
New CNS/ATM applications
ATN Router
8208
ATN phase
Unchanged
ACARS
applications
AVLC
VDR running VDL mode2
CMU/ ATSU
D8PSK Tx/Rx
CSMA
AOA phase
VDL 2
VDL 2
Ground-Stations
ATN
New CNS/ATM applications

11. VDL2 Simulation Objectives
Accurate evaluation of capacity and performance of any VDL2 channel:
Net Throughput Vs Channel load
Collisions rate, retransmission rate
Transmission delays
Identifying the critical aspects:
The impact of the “hidden and the exposed stations”
The ground-station density as providers currently plan
Critical capacity environment (airport or en-route domains...? )
Best frequency scenarios for current and future ( ) air traffic demands both supporting ATS and AOC needs

12. VDL2 Simulation Objectives
Optimising the VDL Mode 2 MAC sub-layer (CSMA) and data-link layer (AVLC) parameters :
CSMA persistence (p)
Different timers values (e.g M1, TM1, T1)
Evaluating the possible benefit of improvements to VDL Mode 2 standard: among others evaluating the impact of
Different p-values given to avionics (static or dynamic value), ground- stations (en-route) and ground-stations (at airport).
Hand-off mechanism (SQP scale, HO criteria)
Giving input for future real time ATC simulations including data-link :
To evaluate impact on operations of
Transmission delays
Lost messages

13. ACTS VDL2 Capabilities Standards:
Accurate Propagation delay (1m- precision)
VHF propagation model including large scale fading
D8PSK behaviour => BER calculation
Reed Solomon FEC-function, and related Frame error rate
VDL2 specific p-persistent CSMA Mac layer mechanism
Hidden/Exposed terminal effects
AVLC Data link layer aspects including hand-off
Dynamic Air traffic and tuneable Ground stations location
AOC and ATS Traffic Messages distribution in time
AOC and ATS message sizes distribution
Standards:
SARPS - VDL2 Technical Manual
MOPS
ARINC 618-5, 631-3
MASPS RTCA/DO-224 A

14. Main Milestones Sept 02 High Level Simulation Requirements
Oct/Nov 02 Architecture
Jan 03 First Software release including VDL2 physical and MAC layer
Feb 03 AVLC implementation
March 03 First Simulation Inputs Scenarios definition
March-December 03 Theoretical and cross check validation
June 03 Discussion of initial results with AEEC, SITA and ARINC
Nov 03 Definition of second set of simulations
Jan- June 04 Presentation of results and contributions (in AEEC, ICAO WGM, with manufacturers, airlines, standard bodies…)

15. ACTS VDL Mode 2
Technical aspects

16. The simulator is not real time => Time has to be sampled.
Time sampling
The simulator is not real time => Time has to be sampled.
However, the simulator is triggered on events
Time sampling frequency is critical for the simulation accuracy:
eg : with Fs = 300 MHz (period of 33 ns) => Position accuracy = 1m

17. Hidden and exposed terminal
GS1 and GS2 can not see each other, Aircraft sees both GS
Hidden terminal can create collisions on the uplink
Exposed terminal can delay the downlink messages
GS 1
GS 2
RH AC1
Interfering Area
RH GS1
Area to be studied
RH AC1
Cases to be considered

18. VHF Propagation Models
Free space propagation model commonly used by other simulators
Large scale fading (2 rays model vertical polarisation) which have been validated by STNA
Free Space
Large scale

19. Receiving process
Relative
Tx/Rx positions
Out of LOS ?
SNR
process
Receiver N0
Collided
Frames power
Rx filter width
Modulation
Scheme
BER
Tx and Rx filter loss
Correcting
Code
Frame length
FER
Propagation
model P
Received power No
Success/Failure
Random
Reception success rate can be derived from the transmitter/ receiver relative position

20. Message collision process
For collision, worst cases are always considered:
Frames involved in collision are considered as additional WGN
=> BER and FER are then computed as previously with the specific noise level

21. List of system parameters
Propagation model
Model in use
ground type
Physical parameters
Transmission power
Antenna gain
Cable loss
VSWR Possibility to define range for these values
Noise figure
Filter width
Channel frequency
Mac sub-layer (CSMA)
Station’s persistence
TM1 : timer between two attempts M1
TM2
AVLC
AVLC (VME, DLS) timers
Number of retransmission
Hands off algorithm

22. INPUTS Collection Process High- Level
ARINC
SITA
ECTL Analysis and Statistics
LINK 2000+
ACTS
Traffic
Simulator
Replay
ECTL CFMU Flight DB

23. Air Traffic input
The first step shall consist in using an Air traffic simulator log file.
Time ID Lat Long Alt Status
04:40:18 TYR413D ON TAXI TO GATE
04:40:18 TYR531L ON APPROACH
04:40:18 TYR541G ON TAXI TO GATE
04:40:21 TYR413D ON TAXI TO GATE
04:40:21 TYR531L ON APPROACH
04:40:21 TYR541G ON TAXI TO GATE
04:40:24 TYR413D ON TAXI TO
The second step shall be to run an external library using CFMU flight plan as an input and able to give at any time any flight information. RAMS will provide such tool.
For more accurate simulations other information about aircraft behaviour, such as pitch, roll… could be integrated to achieve a more realistic link budget.

24. AOC Message profiles
Formal co-operation with ARINC and SITA is setup to provide under NDA typical AOC traffic message profiles for airlines flying in Europe.
4 classes of airlines in terms of data-link usage:
Class 0 No data-link
Class S Small
Class M Medium
Class L Large
Both deterministic and stochastic message distribution : The number of exchanged messages depends on :
The airline
The flight phase (random distribution into the Flight Phase)

25. AOC Messages profile 4 classes of data-link users :
Class 0 No data-link
Class S Small
Class M Medium
Class L Large
A message size distribution is also implemented for uplink and downlink, it depends on the airline class.

26. ATS- Link 2000+ Applications
CM Application Service
DLIC (Datalink initiation Capability)
CPDLC Application Service
ACM (ATC communication management)
ACL (ATC clearance)
AMC (ATC Microphone check)
DCL (Departure clearance)
DSC (Downstream clearance)
DFIS Application Service
D-ATIS
ADS Application Service
FLIPCY (Flight plan consistency)
Transactions per flight
1 DLIC / FIR (ATSU)
1 FLIPCY / FIR (ATSU)
1 D-ATIS / Departure airport
1 D-ATIS / Departure TMA
1 D-ATIS / Arrival TMA
1 D-ATIS / Arrival airport
1 DCL / Departure airport
1 ACM / ATSU sector
5 ACL (3U,2D) / Departure TMA
16 ACL (1-2 per ATSU) in En-Route
10 ACL (6U,4D) / Arrival TMA
1DSC / En-Route
1 AMC / Sector

27. Simulator Output (per station)
Transmitter
Number of INF transmission request
Number of INF transmitted
% Re-transmission 0, 1, 2 …N2
Average and maximum CSMA delay
% of TM2 occurrence
Receiver
Number of received INF
Transmission delay (Average, maximum) (CSMA, propagation) in s
Round trip delay in s
% of msg out of delay (depending on the application)
% of successfully acknowledged transmitted messages
Application related statistics:
%CPDLC within allowed round trip delay
% CAP within allowed one way delay
Others statistics:
% of lost frames : % collision + % low SNR
Hands off successes and failure
Log on delay

28. Simulator Output (common to all stations)
Average and maximum uplink and downlink transmission delay
Average and maximum uplink, downlink round trip delay
Real channel load (for each GS point of view) (in % of time)
Net Throughput :with regards to INF0 frames (in kbits/s)
User data rate (without layers overhead) (in kbit/s)
Uplink and downlink success rate
Hands off success rate

29. Scenarios
2 main scenarios based on a critical sector : CDG-airport, Paris
The air traffic will be the peak hour of the peak day of 2002 (30 August)
2005
Single VDL 2 channel across Europe
GS deployment as shown on map
All AOC traffic assumed migrated to VDL2
2010
Stepwise, from 2 possibly up to 4 frequencies
GS configuration as shown on map
Increased AOC traffic, all ATS/Link2000 applications considered
Aircraft equipment rate according to EUROCONTROL STATFOR inputs

30. Sita VDL2 Ground stations in 2005
Area to be studied
Interfering area

31. For further information please contact :
Patrick DELHAISE
EUROCONTROL DAS/CSM
Tel
Fax
Bertrand DESPERIER
EEC / Brétigny CNS
Tel
Fax