Aeronautical Communications Technologies Simulator Bertrand Desperier - EEC bertrand.desperier@eurocontrol.int Patrick Delhaise - Eurocontrol DAS/CSM patrick.delhaise@eurocontrol.int

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

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

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

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

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

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

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 ……………………..

VDL Mode 2-ACTS

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

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 (2005-2010) air traffic demands both supporting ATS and AOC needs

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

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

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…)

ACTS VDL Mode 2 Technical aspects

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

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

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

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

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

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

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

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 47.8003 13.0192 1411 ON TAXI TO GATE 04:40:18 TYR531L 47.9715 16.4778 3000 ON APPROACH 04:40:18 TYR541G 48.0987 16.5806 586 ON TAXI TO GATE 04:40:21 TYR413D 47.8005 13.0194 1411 ON TAXI TO GATE 04:40:21 TYR531L 47.9725 16.4809 3000 ON APPROACH 04:40:21 TYR541G 48.0985 16.5803 586 ON TAXI TO GATE 04:40:24 TYR413D 47.8007 13.0196 1411 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.

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)

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.

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

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

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

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

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

For further information please contact : Patrick DELHAISE EUROCONTROL DAS/CSM Tel +32 2 729 34 78 Fax +32 2 729 35 11 patrick.delhaise@eurocontrol.int Bertrand DESPERIER EEC / Brétigny CNS Tel +33 1 69 88 76 09 Fax +33 1 69 88 78 90 bertrand.desperier@eurocontrol.int