The VDL Modes

1
Seminar on the Implementation of Data Link and
Satcom Communications Bangkok, Thailand, 17-19
November 2003
Introduction to Aeronautical Data Links
Prepared by - Loftur Jónasson Jennie
Jónasson Iceland Telecom
2
Introduction

• This presentation is intended to be a basic
  introduction to Air/Ground datalinks, based on
  the work done in ACP (formerly AMCP) WG-M, as
  well as our operations experience with Iceland
  Radio in the North Atlantic, where FANS-1/A is
  currently being utilised.
• This introduction highlights aspects on the
  following topics
• FANS 1A ACARS and ATN messages
• The use of ATN compatible data links
• SATCOM (also called AMSS)
• HF data link (HFDL)
• VHF Digital Links VDL Mode 2
• VDL Mode 3
• VDL Mode 4
• The authors of this presentation have borrowed
  the work of many others in the aviation industry
  for this presentation. The authors would like to
  take this time to thank ARINC, SITA, the FAA, the
  Swedish CAA, Nav Canada, UK NATS and many others.
  The authors would like to thank them all for
  their contributions.

3
Free Flight - the end goal

• From the US FAAs Architecture - Version 4.0,
  Section 6 Free Flight Phase 1, Safe Flight 21,
  and Capstone -
• Free Flight will allow pilots to change routes,
  speeds, or altitudes as needed, while in en route
  and oceanic air space. Air Traffic Controllers
  will not impose restrictions on pilot-initiated
  changes, except when there is a potential
  conflict with other aircraft or special use
  airspace. This capability will allow pilots to
  fly optimized profiles , the most efficient
  cruise speeds, wind-aided routes, and arrival
  descent profiles. Any activity that removes
  operational restrictions is a move towards Free
  Flight.

4
ATN and FANS 1/A
5
ARINCs Explanation of Difference Between a
FANS-1/A ACARS Message and an ATN Message
2
2

P
r
o
t
o
c
o
l
(
B
i
t
-
t
o
-
h
e
x
,

C
R
C
)
A
T

O
8
4
1
4
C
9
6
4
0
E
4
B
0

C
R
C
0
0
1
0
0
0

0
1
0
0

0
0
0
1

0
1
0
0

1
1
0
0

1
1

0
1
1
0

O
8
4
1
4
C
9
6
4
0
E
4
B
0

A
T
C
R
C

0
1
0
0

0
0
0
0

1
1
1
0

0
1
0
0

1
0
1
1

0
0
0
0
A
C
A
R
S

P
r
o
t
o
c
o
l
A
T
N


P
r
o
t
o
c
o
l
6
Character- vs. Bit-Oriented Messages Protocol
Data Units (PDU)

• Character-oriented protocol
• Bit-oriented protocol

PDU n
8-bit ASCII character
PDU m
Arbitrary sized bit fields
7
Transition of FANS 1/A (ACARS) to ATN
8
Transition from FANS 1/A to ATN using VDL Mode 2

Step 1 ACARS
Step 2a Character Applications
over VDL
Step 2b VDL
Step 3 VDL/ATN
9
ICAO data link systems that can be used during
flight
D
e
p
a
r
t
u
r
e
E
n

R
o
u
t
e
A
p
p
r
o
a
c
h
L
a
n
d
T
a
x
i

T
a
x
i
T
a
k
e
-
O
f
f
Within l.o.s. VDL 2, 3, 4 Outside
l.o.s. SATCOM HFDL
VDL 2, 3, 4
VDL 2, 3, 4
VDL 2, 3, 4
VDL 2, 3, 4
VDL 2, 3, 4
VDL 2, 3, 4

l.o.s. line of sight
10
Different types of data link messages as a flight
progresses
D
e
p
a
r
t
u
r
e
E
n

R
o
u
t
e
A
p
p
r
o
a
c
h
L
a
n
d
T
a
x
i

T
a
x
i
T
a
k
e
-
O
f
f
From Aircraft Link Test/Clock Update Fuel/Crew
Information Delay Reports Out To
Aircraft PDC ATIS Weight and Balance Airport
Analysis V-Speeds Flight Plan-Hard Copy Load FMC
From Aircraft Position Reports Weather
Reports Delay Info/ETA Voice Request Engine
Information Maintenance Reports To Aircraft ATC
Oceanic Clearances Weather Reports Reclearance Gro
und Voice Request (SELCAL)
From Aircraft Off
From Aircraft Provisioning Gate Requests Estimate
Time-of-Arrival Special Requests Engine
Information Maintenance Reports To Aircraft Gate
Assignment Connecting Gates Passengers and
Crew ATIS

From Aircraft Engine Start To Aircraft Flight
Plan Update Weather Reports
From Aircraft On
From Aircraft In Fuel Information Crew
Information Fault Data from Central Maintenance
Computer

11
Overview of the VDL Modes
12
The VDL Modes

• The numbers mean what order they entered ICAO for
  standardising they are not in succession

VDL Mode-1 Taken out of Annex 10 before ever
implemented no longer exists
VDL Mode-2 Data Only Successor to ACARS 25
kHz
VDL Mode-3 Voice Data together US FAA
Program 25 kHz
VDL Mode-4 Data Only Primary purpose is
ADS-B Swedish design 25 kHz
13
The VDL Modes and 25 kHz/8.33 kHz voice systems
Simultaneous Voice Data (4 channels voice or
ATN A/G data)
Data Only (ATN A/G and ADS-B)
Data Only (ATN A/G)
Analog Voice
Analog Voice
Analog Voice
Analog Voice
CSMA
CSMA
STDMA
STDMA
TDMA
TDMA
DSB AM
DSB AM
DSB AM
DSB AM
DSB AM
DSB AM
GFSK
GFSK
D8PSK
D8PSK
D8PSK
D8PSK
DSB AM
DSB AM
8.33
8.33
8.33
25kHz
25kHz
25kHz
25kHz
25kHz
Voice Channels
Voice Channels
MODE 4
MODE 4
MODE 2
MODE 3
MODE 2
MODE 3
14
Long range data link systems Propagation Paths of
SATCOM and HFDL
(Satellite)
SCINTILLATION CLOUD
Jónhvolf in Icelandic
IONOSPHERE
HF
SATCOM
Propagation problems affecting HF and SATCOM are
fairly independent
HFDL GS
GES
GSGround station
GESGround Earth Station
15
HFDL(HF Data Link)

• HFDL - High Frequency Data Link
• With ground stations around the world
• Iceland Radio houses one of the Ground Stations
• Can accommodate ACARS or ATN
• Developed to be used in areas where satellite
  cannot be used
• Cheaper alternative to SATCOM

16
SATCOM(AMSS)

• Satellite Communications
• A system available for ACARS and for ATN
• Satellites can be used for Data Link and for
  voice - often referred to as SAT Voice
• Inmarsat is the current provider for aeronautical
  communications 1

17
ADS-CAutomatic Dependent Surveillance-Contract

• The C stands for contract. An ADS-C message is
  only sent after a link contract between the
  aircraft and the ground has been established.
• ADS-C is currently used using SATCOM or HF data
  link.

18
ADS-BAutomatic Dependent Surveillance-Broadcast
ADS-B is a broadcast of the aircrafts position,
mainly derived from the GNSS system. It provides
the pilot of a properly equipped aircraft a
display on his instrument panel of where other
aircraft are in relation to his aircraft.
19
ADS-Broadcast Concept

20
Mode-S Extended Squitter

• Mode-S was standardised by ICAO several years
  ago
• The ICAO 11th Air Navigation Conference has
  decided that all ADS-B implementations should
  support the use of Mode-S squitter

21
ICAO Communications/Navigations Surveillance
(CNS) Environment
22
What is the ATN?

• The ATN concept emerged from a need to
  interchange bit-oriented digital data over
  dissimilar aeronautical data links, using, for
  interoperability purpose, the principles of the
  International Organization for Standardization
  (ISO) open systems interconnection (OSI)
  architecture.

23
Describe the ATN

• The ATN design supports the incorporation of
  different air-ground subnetworks and different
  ground-ground subnetworks, resulting in a common
  data transfer service. Furthermore, the ATN
  design is such that user communication services
  may be introduced in an evolutionary manner

24
OSI 7 Layer Protocol Reference Model

• System A System B

25
First CPDLC Message in Miami area