L-band Digital Aeronautical Communications System (LDACS)
draft-maeurer-raw-ldacs-00
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| Authors | Nils Mäurer , Thomas Gräupl , Corinna Schmitt | ||
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draft-maeurer-raw-ldacs-00
RAW N. Maeurer, Ed.
Internet-Draft T. Graeupl, Ed.
Intended status: Informational German Aerospace Center (DLR)
Expires: 8 May 2020 C. Schmitt, Ed.
Research Institute CODE, UniBwM
5 November 2019
L-band Digital Aeronautical Communications System (LDACS)
draft-maeurer-raw-ldacs-00
Abstract
This document provides an overview of the architecture of the L-band
Digital Aeronautical Communications System (LDACS), which provides a
secure, scalable and spectrum efficient terrestrial data link for
civil aviation. LDACS is a scheduled, reliable multi-application
cellular broadband system with support for IPv6.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 8 May 2020.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Please review these documents carefully, as they describe your rights
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provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Terms used in this document . . . . . . . . . . . . . . . 3
3. Motivation and Use Cases . . . . . . . . . . . . . . . . . . 4
3.1. Voice Communications Today . . . . . . . . . . . . . . . 5
3.2. Data Communications Today . . . . . . . . . . . . . . . . 5
4. Provenance and Documents . . . . . . . . . . . . . . . . . . 6
5. Characteristics . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. LDACS Physical Layer . . . . . . . . . . . . . . . . . . 7
5.2. LDACS Data Link Layer . . . . . . . . . . . . . . . . . . 8
5.3. LDACS Data Rates . . . . . . . . . . . . . . . . . . . . 8
5.4. Reliability and Availability . . . . . . . . . . . . . . 8
5.4.1. LDACS Medium Access . . . . . . . . . . . . . . . . . 8
5.4.2. LDACS Resource Allocation . . . . . . . . . . . . . . 9
5.4.3. LDACS Handovers . . . . . . . . . . . . . . . . . . . 9
6. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 10
6.1. Protocol Stack . . . . . . . . . . . . . . . . . . . . . 10
6.1.1. Medium Access Control (MAC) Entity Services . . . . . 12
6.1.2. Data Link Service (DLS) Entity Services . . . . . . . 13
6.1.3. Voice Interface (VI) Services . . . . . . . . . . . . 13
6.1.4. Link Management Entity (LME) Services . . . . . . . . 13
6.1.5. Sub-Network Protocol (SNP) Services . . . . . . . . . 13
6.2. LDACS Logical Communication Channels . . . . . . . . . . 14
6.3. LDASC Framing Structure . . . . . . . . . . . . . . . . . 15
6.3.1. Forward Link . . . . . . . . . . . . . . . . . . . . 15
6.3.2. Reverse Link . . . . . . . . . . . . . . . . . . . . 15
7. Security Considerations . . . . . . . . . . . . . . . . . . . 16
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 17
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17
11. Normative References . . . . . . . . . . . . . . . . . . . . 17
12. Informative References . . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
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1. Introduction
One of the main pillars of the modern Air Traffic Management (ATM)
system is the existence of a communication infrastructure that
enables efficient aircraft guidance and safe separation in all phases
of flight. Current systems are technically mature but suffering from
the VHF band's increasing saturation in high-density areas and the
limitations posed by analogue radio. Therefore, aviation globally
and the European Union (EU) in particular, strives for a sustainable
modernization of the aeronautical communication infrastructure.
In the long-term, ATM communication shall transition from analogue
VHF voice and VDL2 communication to more spectrum efficient digital
data communication. The European ATM Master Plan foresees this
transition to be realized for terrestrial communications by the
development and implementation of the L-band Digital Aeronautical
Communications System (LDACS). LDACS shall enable IPv6 based air-
ground communication related to the safety and regularity of the
flight. The particular challenge is that no new frequencies can be
made available for terrestrial aeronautical communication. It was
thus necessary to develop procedures to enable the operation of LDACS
in parallel with other services in the same frequency band.
2. Terminology
2.1. Terms used in this document
The following terms are used in the context of DetNet in this
document:
A/A Air-To-Air
AeroMACS Aeronautical Mobile Airport Communication System
A/G Air-To-Ground
AM(R)S Aeronautical Mobile (Route) Service
ANSP Air traffic Network Service Provider
AOC Aeronautical Operational Control
AS Aircraft Station
ATC Air-Traffic Control
ATM Air-Traffic Management
ATN Aeronautical Telecommunication Network
ATS Air Traffic Service
CCCH Common Control Channel
DCCH Dedicated Control Channel
DCH Data Channel
DLL Data Link Layer
DLS Data Link Service
DME Distance Measuring Equipment
DSB-AM Double Side-Band Amplitude Modulation
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FAA Federal Aviation Administration
FCI Future Communication Infrastructure
FDD Frequency Division Duplex
FL Forward Link
GANP Global Air Navigation Plan
GNSS Global Navigation Satellite System
GS Ground Station
GSC Ground-Station Controller
HF High Frequency
ICAO International Civil Aviation Organization
IWF Interworking Function
kbit/s kilobit per secong
LDACS L-band Digital Aeronautical Communications System
LLC Logical Link Layer
LME LDACS Management Entity
MAC Medium Access Layer
MF Multi Frame
MIMO Multiple Input Multiple Output
OFDM Orthogonal Frequency-Division Multiplexing
OFDMA Orthogonal Frequency-Division Multiplexing Access
PDU Protocol Data Units
PHY Physical Layer
QoS Quality of Service
RL Reverse Link
SARPs Standards And Recommended Practices
SESAR Single European Sky ATM Research
SF Super-Frame
SNP Sub-Network Protocol
SSB-AM Single Side-Band Amplitude Modulation
SNDCF Sub-Network Dependent Convergence Function
TBO Trajectory-Based Operations
TDM Time Division Multiplexing
TDMA Time-Division Multiplexing-Access
VDL2 VHF Data Link mode 2
VHF Very High Frequency
VI Voice Interface
3. Motivation and Use Cases
Aircraft are currently connected to Air-Traffic Control (ATC) and
Airline Operational Control (AOC) via voice and data communications
systems through all phases of a flight. Within the airport terminal,
connectivity is focused on high bandwidth communications, while
during en-route high reliability, robustness, and range is the main
focus. Voice communications may use the same or different equipment
as data communications systems. In the following the main
differences between voice and data communications capabilities are
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summarized. The assumed use cases for LDACS completes the list of
use cases stated in [RAW-USE-CASES] and the list of reliable and
available wireless technologies presented in [RAW-TECHNOS].
3.1. Voice Communications Today
Voice links are used for Air-To-Ground (A/G) and Air-To-Air (A/A)
communications. The communication equipment is either ground-based
working in the High Frequency (HF) or Very High Frequency (VHF)
frequency band or satellite-based. All voice communications is
operated via open broadcast channels without any authentication,
encryption or other protective measures. The use of well-proven
communication procedures via broadcast channels helps to enhance the
safety of communications by taking into account that other users may
encounter communication problems and may be supported, if required.
The main voice communications media is still the analogue VHF Double
Side-Band Amplitude Modulation (DSB-AM) communications technique,
supplemented by HF Single Side-Band Amplitude Modulation (SSB-AM) and
satellite communications for remote and oceanic areas. DSB-AM has
been in use since 1948, works reliably and safely, and uses low-cost
communication equipment. These are the main reasons why VHF DSB-AM
communications is still in use, and it is likely that this technology
will remain in service for many more years. This however results in
current operational limitations and becomes impediments in deploying
new Air-Traffic Management (ATM) applications, such as flight-centric
operation with point-to-point communications.
3.2. Data Communications Today
Like for voice, data communications into the cockpit is currently
provided by ground-based equipment operating either on HF or VHF
radio bands or by legacy satellite systems. All these communication
systems are using narrowband radio channels with a data throughput
capacity of some kilobits per second. While the aircraft is on
ground some additional communications systems are available, like
Aeronautical Mobile Airport Communication System (AeroMACS),
operating in the Airport (APT) domain and able to deliver broadband
communication capability.
The data communication networks used for the transmission of data
relating to the safety and regularity of the flight must be strictly
isolated from those providing entertainment services to passengers.
This leads to a situation that the flight crews are supported by
narrowband services during flight while passengers have access to
inflight broadband services. The current HF and VHF data links
cannot provide broadband services now or in the future, due to the
lack of available spectrum. This technical shortcoming is becoming a
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limitation to enhanced ATM operations, such as Trajectory-Based
Operations (TBO) and 4D trajectory negotiations.
Satellite-based communications are currently under investigation and
enhanced capabilities are under development which will be able to
provide inflight broadband services and communications supporting the
safety and regularity of the flight. In parallel, the ground-based
broadband data link technology LDACS is being standardized by ICAO
and has recently shown its maturity during flight tests [SCH191].
The LDACS technology is scalable, secure and spectrum efficient and
provides significant advantages to the users and service providers.
It is expected that both - satellite systems and LDACS - will be
deployed to support the future aeronautical communication needs as
envisaged by the ICAO Global Air Navigation Plan (GANP).
4. Provenance and Documents
The development of LDACS has already made substantial progress in the
Single European Sky ATM Research (SESAR) framework, and is currently
being continued in the follow-up program, SESAR2020 [RIH18]. A key
objective of the SESAR activities is to develop, implement and
validate a modern aeronautical data link able to evolve with aviation
needs over long-term. To this end, an LDACS specification has been
produced [GRA19] and is continuously updated; transmitter
demonstrators were developed to test the spectrum compatibility of
LDACS with legacy systems operating in the L-band [SAJ14]; and the
overall system performance was analyzed by computer simulations,
indicating that LDACS can fulfil the identified requirements [GRA11].
LDACS standardization within the framework of the ICAO started in
December 2016. The ICAO standardization group has produced an
initial Standards and Recommended Practices (SARPs) document
[ICAO18]. The SARPs document defines the general characteristics of
LDACS. The ICAO standardization group plans to produce an ICAO
technical manual - the ICAO equivalent to a technical standard -
within the next years. Generally, the group is open to input from
all sources and develops LDACS in the open.
Up to now the LDACS standardization has been focused on the
development of the physical layer and the data link layer, only
recently have higher layers come into the focus of the LDACS
development activities. There is currently no "IPv6 over LDACS"
specification; however, SESAR2020 has started the testing of
IPv6-based LDACS testbeds. The IPv6 architecture for the
aeronautical telecommunication network is called the Future
Communications Infrastructure (FCI). FCI shall support quality of
service, diversity, and mobility under the umbrella of the "multi-
link concept". This work is conducted by ICAO working group WG-I.
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In addition to standardization activities several industrial LDACS
prototypes have been built. One set of LDACS prototypes has been
evaluated in flight trials confirming the theoretical results
predicting the system performance [GRA18] [SCH191].
5. Characteristics
LDACS will become one of several wireless access networks connecting
aircraft to the Aeronautical Telecommunications Network (ATN).
Access to the ATN is handled by the Ground-Station Controller (GSC),
while several Ground-Stations (GS) are connected to one GSC. Thus
the LDACS access network contains several GS, each of them providing
one LDACS radio cell. LDACS can be therefore considered a cellular
data link with a star-topology connecting Aircraft-Stations (AS) to
GS with a full duplex radio link. Each GS is the centralized
instance controlling all A/G communications within its radio cell. A
GS supports up to 512 aircraft. All of this is depicted in Figure 1.
AS11--------------+
|
AS12-------------GS1------GSC------>ATN
. | |
. | |
AS1n--------------+ |
|
AS21--------------+ |
| |
AS21-------------GS2-------+
. |
. |
AS2n--------------+
Figure 1: LDACS wireless topology
The LDACS air interface protocol stack defines two layers, the
physical layer and the data link layer.
5.1. LDACS Physical Layer
The physical layer provides the means to transfer data over the radio
channel. The LDACS GS supports bi-directional links to multiple
aircraft under its control. The forward link direction (FL; ground-
to-air) and the reverse link direction (RL; air-to-ground) are
separated by frequency division duplex. Forward link and reverse
link use a 500 kHz channel each. The ground-station transmits a
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continuous stream of Orthogonal Frequency-Division Multiplexing
(OFDM) symbols on the forward link. In the reverse link different
aircraft are separated in time and frequency using a combination of
Orthogonal Frequency-Division Multiple-Access (OFDMA) and Time-
Division Multiple-Access (TDMA). Aircraft thus transmit
discontinuously on the reverse link with radio bursts sent in
precisely defined transmission opportunities allocated by the ground-
station. LDACS does not support beam-forming or Multiple Input
Multiple Output (MIMO) [SCH192].
5.2. LDACS Data Link Layer
The data-link layer provides the necessary protocols to facilitate
concurrent and reliable data transfer for multiple users. The LDACS
data link layer is organized in two sub-layers: The medium access
sub-layer and the logical link control sub-layer. The medium access
sub-layer manages the organization of transmission opportunities in
slots of time and frequency. The logical link control sub-layer
provides acknowledged point-to-point logical channels between the
aircraft and the ground-station using an automatic repeat request
protocol. LDACS supports also unacknowledged point-to-point channels
and ground-to-air broadcast.
5.3. LDACS Data Rates
The user data rate of LDACS is 315 kbit/s to 1428 kbit/s on the
forward link, and 294 kbit/s to 1390 kbit/s on the reverse link,
depending on coding and modulation. Due to strong interference from
legacy systems in the L-band, the most robust coding and modulation
should be expected for initial deployment i.e. 315/294 kbit/s on
theforward/reverse link, respectively.
5.4. Reliability and Availability
LDACS has been designed with applications related to the safety and
regularity of the flight in mind. It has therefore been designed as
a deterministic wireless data link (as far as possible).
5.4.1. LDACS Medium Access
LDACS medium access is always under the control of the ground-station
of a radio cell. Any medium access for the transmission of user data
has to be requested with a resource request message stating the
requested amount of resources and class of service. The ground-
station performs resource scheduling on the basis of these requests
and grants resources with resource allocation messages. Resource
request and allocation messages are exchanged over dedicated
contention-free control channels.
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5.4.2. LDACS Resource Allocation
LDACS has two mechanisms to request resources from the scheduler in
the ground-station. Resources can either be requested "on demand"
with a given class of service. On the forward link, this is done
locally in the ground-station, on the reverse link a dedicated
contention-free control channel is used called Dedicated Control
Channel (DCCH); roughly 83 bit every 60 ms). A resource allocation
is always announced in the control channel of the forward link
(Common Control Channel (CCCH); variable sized). Due to the spacing
of the reverse link control channels of every 60 ms, a medium access
delay in the same order of magnitude is to be expected.
Resources can also be requested "permanently". The permanent
resource request mechanism supports requesting recurring resources in
given time intervals. A permanent resource request has to be
canceled by the user (or by the ground-station, which is always in
control). User data transmissions over LDACS are therefore always
scheduled by the ground-station, while control data uses statically
(i.e. at net entry) allocated recurring resources (DCCH and CCCH).
The current specification documents specify no scheduling algorithm.
However performance evaluations so far have used strict priority
scheduling and round robin for equal priorities for simplicity. In
the current prototype implementations LDACS classes of service are
thus realized as priorities of medium access and not as flows. Note
that this can starve out low priority flows. However, this is not
seen as a big problem since safety related message always go first in
any case. Scheduling of reverse link resources is done in physical
Protocol Data Units (PDU) of 112 bit (or larger if more aggressive
coding and modulation is used). Scheduling on the forward link is
done Byte-wise since the forward link is transmitted continuously
bythe ground-station.
5.4.3. LDACS Handovers
In order to support diversity, LDACS supports handovers to other
ground-stations on different channels. Handovers may be initiated by
the aircraft (break-before-make) or by the ground-station (make-
before-break) if it is connected to an alternative ground-station via
the same ground-station controller. Beyond this, FCI diversity shall
be implemented by the multi-link concept.
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6. Architecture
Aircraft-Station (AS), Ground-Station (GS) and Ground-Station
Controller (GSC) form the basic LDACS network. 512 aircraft can be
served by one GS where the GS sends a continuous data stream in the
Forward Link (FL) to the AS. The Reverse Link (RL) consists of
individual bursts of data from each AS to GS. This means, for every
RL communication the AS first needs to request the respective
resource allocation within its cell from the GS before being able to
send. Both FL and RL communication, including user and control data,
is done via the air gap over the radio link between AS and GS. On
the ground a GSC is responsible for serving several GSs on the
control plane, forming an LDACS sub-network with its LDACS internal
control plane infrastructure. The GSs are linked to an access router
in the user plane, which in turn is linked to an Air/Ground router,
being now the direct connection to the ground network. The ATN is
used for example by Air traffic Network Services Providers (ANSP) and
airlines to exchange Air Traffic Service (ATS) or Airline Operational
Control (AOC) data between the ground infrastructure and the
aircraft. Figure 2 provides a more detailed overview.
wireless user
link plane
A--------------G-------------Access---A/G-----ATN
S..............S Router Router
. control . |
. plane . |
. . |
GSC.............. |
. |
. |
GS----------------+
Figure 2: LDACS sub-network with two GSs
6.1. Protocol Stack
The protocol stack of LDACS is implemented in the AS and GS as
follows: It consists of the Physical Layer (PHY) with five major
functional blocks above it. Four are placed in the Data Link Layer
(DLL) of the AS and GS: (1) Medium Access Layer (MAC), (2) Voice
Interface (VI), (3) Data Link Service (DLS), (4) LDACS Management
Entity (LME). The last entity resides within the sub-network layer:
Sub-Network Protocol (SNP).
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The LDACS network is externally connected to voice units, radio
control units, and the ATN network layer through a Sub-Network
Dependent Convergence Function (SNDCF; OSI network layers),
Convergence Sub-layer, or Interworking Function (IWF; legacy
networks) not discussed here.
The SNP connects the AS and GS DLL providing end-to-end user plane
connectivity between the LDACS AS and GS.
The DLL provides Quality of Service (QoS) assurance. Multiplexing of
different service classes is possible. Except for the initial
aircraft cell-entry and a Type 1 handover, which is not discussed
here, medium access is deterministic, with predictable performance.
Optional support for adaptive coding and modulation is provided as
well. The four functional blocks of the LDACS DLL are organised into
two sub-layers, the MAC sub-layer and the Logical Link Control (LLC)
sub-layer discussed in the next sections. [GRA19].
Figure 3 shows the protocol stack of LDACS as implemented in the AS
and GS.
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IPv6 network layer
|
|
+------------------+ +----+
| SNP |--| | sub-network
| | | | layer
+------------------+ | |
| | LME|
+------------------+ | |
| DLS | | | logical link
| | | | control layer
+------------------+ +----+
| |
DCH DCCH/CCCH
| RACH/BCCH
| |
+--------------------------+
| MAC | medium access
| | layer
+--------------------------+
|
+--------------------------+
| PHY | physical layer
+--------------------------+
|
|
((*))
FL/RL radio channels
separated by FDD
Figure 3: LDACS protocol stack
6.1.1. Medium Access Control (MAC) Entity Services
Time Framing Service: The MAC time framing service provides the frame
structure necessary to realise slot-based Time Division Multiplex
(TDM) access on the physical link. It provides the functions for the
synchronisation of the MAC framing structure and the PHY layer
framing. The MAC time framing provides a dedicated time slot for
each logical channel. [GRA19]
Medium Access Service: The MAC sub-layer offers access to the
physical channel to its service users. Channel access is provided
through transparent logical channels. The MAC sub-layer maps logical
channels onto the appropriate slots and manages the access to these
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channels. Logical channels are used as interface between the MAC and
LLC sub-layers. [GRA19]
6.1.2. Data Link Service (DLS) Entity Services
The DLS provides acknowledged and unacknowledged (including broadcast
and packet mode voice) bi-directional exchange of user data. If user
data is transmitted using the acknowledged data link service, the
sending DLS entity will wait for an acknowledgement from the
receiver. If no acknowledgement is received within a specified time
frame, the sender may automatically try to retransmit its data.
However, after a certain number of failed retries, the sender will
suspend further retransmission attempts and inform its client of the
failure. [GRA19]
6.1.3. Voice Interface (VI) Services
The VI provides support for virtual voice circuits. Voice circuits
may either be set-up permanently by the GS (e.g. to emulate voice
party line) or may be created on demand. The creation and selection
of voice circuits is performed in the LME. The VI provides only the
transmission services. [GRA19]
6.1.4. Link Management Entity (LME) Services
Mobility Management Service: The mobility management service provides
support for registration and de-registration (cell entry and cell
exit), scanning RF channels of neighbouring cells and handover
between cells. In addition, it manages the addressing of aircraft/
ASs within cells. It is controlled by the network management service
in the GSC. [GRA19]
Resource Management Service: The resource management service provides
link maintenance (power, frequency and time adjustments), support for
adaptive coding and modulation (ACM), and resource allocation.
[GRA19]
6.1.5. Sub-Network Protocol (SNP) Services
Data Link Service: The data link service provides functions required
for the transfer of user plane data and control plane data over the
LDACS sub-network. [GRA19]
Security Service: The security service shall provide functions for
secure communication over the LDACS sub-network. Note that the SNP
security service applies cryptographic measures as configured by the
ground station controller. [GRA19]
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6.2. LDACS Logical Communication Channels
Data Link Service: The data link service provides functions required
for the transfer of user plane data and control plane data over the
LDACS sub-network. [GRA19]
In order to communicate, LDACS uses several logical channels in the
MAC layer [GRA19]:
1. The GS announces its existence and several necessary physical
parameters in the Broadcast Channel (BCCH) to incoming AS.
2. The Random Access Channel (RACH) enables the AS to request access
to an LDACS cell.
3. In the Forward Link (FL) the Common Control Channel (CCCH) is
used by the GS to distribute and grant access to system resources.
4. The reverse direction is covered by the Reverse Link (RL), where
aircraft need to request resources (in so called resource
allocation) in order to be allowed to send. This happens via the
Dedicated Common Control Channel (DCCH).
5. User data itself is communicated in the Data Channel (DCH) on the
FL and RL.
Figure 4 shows in detail the distribution of each slot. The LDACS
super-frame is repeated every 240 ms and carries all control plane
and user plane logical channels in separate slots of variable length.
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^
| +-------------+------+-------------+
| FL | DCH | CCCH | DCH |
| +-------------+------+-------------+
| <---- Multi-Frame (MF) - 58.32ms -->
F
R +------+---------------------------+
e RL | DCCH | DCH |
q +------+---------------------------+
u <---- Multi-Frame (MF) - 58.32ms -->
e
n +------+------------+------------+------------+------------+
c FL | BCCH | MF | MF | MF | MF |
y +------+------------+------------+------------+------------+
| <---------------- Super-Frame (SF) - 240ms ---------------->
|
| +------+------------+------------+------------+------------+
| RL | RACH | MF | MF | MF | MF |
| +------+------------+------------+------------+------------+
| <---------------- Super-Frame (SF) - 240ms ---------------->
|
----------------------------- Time ------------------------------>
|
Figure 4: LDACS frame structure
6.3. LDASC Framing Structure
The LDACS framing structure for FL and RL is based on Super-Frames
(SF) of 240 ms duration. Each SF corresponds to 2000 OFDM symbols.
The FL and RL SF boundaries are aligned in time (from the view of the
GS).
6.3.1. Forward Link
In the FL, an SF contains a Broadcast Frame of duration TBC = 6.72 ms
(56 OFDM symbols), and four Multi-Frames (MF), each of duration TMF =
58.32 ms (486 OFDM symbols).
6.3.2. Reverse Link
In the RL, each SF starts with a Random Access (RA) message of length
TRA = 6.72 ms with two opportunities for sending reverse link random
access frames, followed by four MFs. These MFs have the same fixed
duration of TMF = 58.32 ms as in the FL, but a different internal
structure.
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7. Security Considerations
Aviation will require secure exchanges of data and voice messages for
managing the air-traffic flow safely through the airspaces all over
the world. The main communication method for ATC today is still an
open analogue voice broadcast within the aeronautical VHF band.
Currently, the information security is purely procedural based by
using well-trained personnel and proven communications procedures.
This communication method has been in service since 1948. Future
digital communications waveforms will need additional embedded
security features to fulfil modern information security requirements
like authentication and integrity. These security features require
sufficient bandwidth which is beyond the capabilities of a VHF
narrowband communications system. For voice and data communications,
sufficient data throughput capability is needed to support the
security functions while not degrading performance. LDACS is a
mature data link technology with sufficient bandwidth to support
security.
Security considerations for LDACS are the official ICAO SARPS
[ICAO18]:
1. LDACS shall provide a capability to protect the availability and
continuity of the system.
2. LDACS shall provide a capability including cryptographic
mechanisms to protect the integrity of messages in transit.
3. LDACS shall provide a capability to ensure the authenticity of
messages in transit.
4. LDACS should provide a capability for nonrepudiation of origin
for messages in transit.
5. LDACS should provide a capability to protect the confidentiality
of messages in transit.
6. LDACS shall provide an authentication capability.
7. LDACS shall provide a capability to authorize the permitted
actions of users of the system and to deny actions that are not
explicitly authorized.
8. If LDACS provides interfaces to multiple domains, LDACS shall
provide capability to prevent the propagation of intrusions within
LDACS domains and towards external domains.
The cybersecurity architecture of LDACS [ICAO18], [MAE18] and its
extensions [MAE191], [MAE192] regard all of the aforementioned
requirements, since LDACS has been mainly designed for air traffic
management communication. Thus it supports mutual entity
authentication, integrity and confidentiality capabilities of user
data messages and some control channel protection capabilities
[MAE192].
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More details can be found here [MAE18], [MAE192] and [ICAO18].
From the very beginning of the development process security for LDACS
has been addressed by design and thus meets the security objectives
as standardized by ICAO [ICAO18].
8. Privacy Considerations
LDACS provides a Quality of Service (QoS), and the generic
considerations for such mechanisms apply.
9. IANA Considerations
This memo includes no request to IANA.
10. Acknowledgements
The authors want to thank all contributors to the development of
LDACS. Further, thanks to SBA Research Vienna for fruitful
discussions on aeronautical communications concerning security
incentives for industry and potential economic spillovers.
11. Normative References
12. Informative References
[MAE191] Maeurer, N., Graeupl, T., and C. Schmitt, "Evaluation of
the LDACS Cybersecurity Implementation", IEEE 38th Digital
Avionics Systems Conference (DACS), pp. 1-10, New York,
NY, USA , November 2019.
[MAE192] Maeurer, N. and C. Schmitt, "Towards Successful
Realization of the LDACS Cybersecurity Architecture: An
Updated Datalink Security Threat- and Risk Analysis", IEEE
Integrated Communications, Navigation and Surveillance
Conference (ICNS), pp. 1-13, New York, NY, USA , November
2019.
[GRA19] Graeupl, T., Rihacek, C., and B. Haindl, "LDACS A/G
Specification", German Aerospace Center (DLR), Germany,
SESAR2020 PJ14-02-01 D3.3.010 , 2017.
[MAE18] Maeurer, N. and A. Bilzhause, "A Cybersecurity
Architecture for the L-band Digital Aeronautical
Communications System (LDACS)", IEEE 37th Digital Avionics
Systems Conference (DASC), pp. 1-10, New York, NY, USA ,
2017.
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[GRA11] Graeupel, T. and M. Ehammer, "L-DACS1 Data Link Layer
Evolution of ATN/IPS", 30th IEEE/AIAA Digital Avionics
Systems Conference (DASC), pp. 1-28, New York, NY, USA ,
2011.
[GRA18] Graeupel, T., Schneckenburger, N., Jost, T., Schnell, M.,
Filip, A., Bellido-Manganell, M.A., Mielke, D.M., Maeurer,
N., Kumar, R., Osechas, O., and G. Battista, "L-band
Digital Aeronautical Communications System (LDACS) flight
trials in the national German project MICONAV", Integrated
Communications, Navigation, Surveillance Conference
(ICNS), pp. 1-7, New York, NY, USA , 2018.
[SCH191] Schnell, M., "DLR Tests Digital Communications
Technologies Combined with Additional Navigation Functions
for the First Time", November 2019.
[SCH192] Schnell, M., "Update on LDACS - The FCI Terrestrial Data
Link", 19th Integrated Communications, Navigation and
Surveillance Conference (ICNS), pp. 1-10, New York, NY,
USA , November 2019.
[ICAO18] International Civil Aviation Organization (ICAO), "L-Band
Digital Aeronautical Communication System (LDACS)",
International Standards and Recommended Practices Annex 10
- Aeronautical Telecommunications, Vol. III -
Communication Systems , 2018.
[SAJ14] Sajatovic, M., Guenzel, H., and S. Mueller, "WA04 D22 Test
Report for Assessing LDACS1 Transmitter Impact upon DME/
TACAN Receivers", 19th Integrated Communications,
Navigation and Surveillance Conference (ICNS), pp. 1-10,
New York, NY, USA , 2014.
[RIH18] Rihacek, C., Haindl, B., Fantappie, P., Pierattelli, S.,
Graeupl, T., Schnell, M., and N. Fistas, "LDACS A/G
Specification", Integrated Communications Navigation and
Surveillance Conference (ICNS), pp. 1-8, New York, NY,
USA , 2018.
[RAW-TECHNOS]
Thubert, P., Cavalcanti, D., Vilajosana, X., and C.
Schmitt, "Reliable and Available Wireless Technologies",
Work in Progress, Internet-Draft, draft-thubert-raw-
technologies-03, 1 July 2019,
<https://tools.ietf.org/html/draft-thubert-raw-
technologies-03>.
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[RAW-USE-CASES]
Papadopoulos, G., Thubert, P., Theoleyre, F., and C.
Bernardos, "RAW use cases", Work in Progress, Internet-
Draft, draft-bernardos-raw-use-cases-00, 5 July 2019,
<https://tools.ietf.org/html/draft-bernardos-raw-use-
cases-00>.
Authors' Addresses
Nils Maeurer (editor)
German Aerospace Center (DLR)
Muenchner Strasse 20
82234 Wessling
Germany
Email: Nils.Maeurer@dlr.de
Thomas Graeupl (editor)
German Aerospace Center (DLR)
Muenchner Strasse 20
82234 Wessling
Germany
Email: Thomas.Graeupl@dlr.de
Corinna Schmitt (editor)
Research Institute CODE, UniBwM
Werner-Heisenberg-Weg 28
85577 Neubiberg
Germany
Email: corinna.schmitt@unibw.de
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