Global Airline Operational
Communications
Kim O'Neil,
Advanced
Aviation Technology Ltd.
kim.oneil@aatl.net
Lars Holmstrom Swedish
Space Corporation
Lho@ssc.se
Abstract
Recent advances in technology and the introduction of
new global Telecoms services have significantly increased the options available
to airlines for Airline Operational Communications (AOC). These options can
significantly reduce the cost of AOC services and radically improve capacity,
availability and reliability over existing services. Perhaps, even more
significantly, is the opportunity to fully integrate AOC within an Airline
Intranet leading to comprehensive commercial and operational gains. This paper
will discuss the role of Low Earth Orbit (LEO) communications services such as
Orbcomm in liberalising and liberating AOC services.
1. Introduction
Traditional Airline Operational Communications (AOC)
have suffered from high costs, poor availability and equally poor reliability.
This has been exacerbated by the lack of choice in service providers - in what
are effectively regional monopolies. This is one of the few remaining areas of
Telecommunications still to be liberalised. Some commentators have cited the
relatively small size of the aeronautical market as the reason for the apparent
lack of interest of Telecoms service providers.
However, the main reason for the lack of competition
in this area is the regulated nature of the market and the critical dependence
of services on the allocation of a small number of VHF frequencies providing
the air/ground data-link. Frequency protection criteria and the choice of
unfavourable modulation schemes have prevented frequency sharing, making this
market difficult to penetrate. Add to this the need to maintain regional ground
infrastructures and it is easy to see why services and costs are so arcanely
uncompetitive.
Yet it is surprising that airlines, who operate in a
highly competitive market, seem content with such poor performance and so
accepting of virtual monopolies in service provision. This may, in part, be due
to the ownership of at least one of the AOC service providers by a group of
airlines, but this still does not justify services that drastically
under-perform by almost all the measurable criteria that matter: Costs,
Availability, Reliability, Timeliness and Security. Competition is essential if
these parameters are to be improved and the true operational potential of AOC
is to be realised.
2. Traditional AOC Services
For many years AOC services have been limited by its
main medium: that of VHF radio. The fundamental service relies on a carrier
sense technology that connects a single aircraft with a single ground-station
on a very low bit rate (300 bits per second) data-link. The box in the aircraft
that performs this function is known as ACARS (Airline Communication Airline
Reporting System). The limitations of this particular air/ground connection are
clear:
2.1 Availability
Availability is restricted - as only one aircraft at a
time may communicate with the ground-station and usually only on a single
frequency.
2.2 Reliability
Reliability is poor because low bit rates mean that
breaks in transmissions are highly likely (due to the high probability of 'out
of range' loss of the ground-station connection). The potential for
interference also significantly increases the risk of message loss.
2.3 Timeliness
Billing arrangements lead to all messages being
shipped around the world even when the sender and receiver may only be a few
hundred metres apart. This form of "store and forward" severely affects time
critical messages.
2.4 Costs
Costs are high due to the need to maintain proprietary
networks, the choice of technology, poor capacity and performance and the lack
of competition.
2.5 Security
ACARS Security is equally poor due to inherent
weaknesses in the ACARS system - a system in which ACARS messages can be
routinely recorded and decoded by others.
3. HF Data-link
In addition to VHF and satellite solutions, the
potential for HF radio data-link has also been explored. This again depends on
a carrier sense technology and the vagaries of HF communications. Whilst it may
provide another data-link medium (which has the benefit of long range) it has
severe practical and capacity limitations.
4. Early Satellite Services
The introduction of high cost geo-stationary satellite
communications services during the 1970's and 1980's did little to improve the
situation. These satellite services were launched and operated by a mixture of
State run organisations and monopoly Telecoms operators. The aircraft equipment
and its installation costs were enormous and the operational costs of the
service prohibitive. Originally intended as a communications service for safety
messages, the lack of applications, poor take-up and high cost forced aviation
to try to spread the costs by permitting non-safety message traffic.
This still did little to improve the use of the
geo-stationary service due to its poor cost/benefit performance. Airlines
opting for this solution needed to have a compelling reason to choose this
service. Consequently, few aircraft operators made use of the system.
This particular market has now been transformed by the
introduction of privately funded commercial satellite communications networks
such as Orbcomm which operate in Low Earth Orbits (LEO) and provide realistic
alternatives to existing service providers.
5. Low Earth Orbit Services:
Orbcomm The introduction of LEO satellite services
operating a cellular VHF data-link service will utterly transform the AOC
market in almost every respect. It will improve performance, availability,
reliability and will significantly reduce costs. It opens up the opportunity
for airlines to develop AOC services that are fully integrated within a
company's internal networks i.e. Corporate Intranets. This alone will lead to
novel developments and competitive advantage for those airlines ready to take
up the challenge.
5.1 Orbcomm System Description
Orbcomm consists of a constellation of Low Earth Orbit
(LEO) satellites orbiting the earth at a height of 424 miles (775km) in three
orbital planes each of 8 satellites providing a packet switched two-way data
communications system. The complete system will consist of 36 satellites when
the fourth orbital plane is in place. The Orbcomm system provides complete
operational redundancy in the availability of satellites, such that the loss of
an individual satellite will not be noticed by subscribers.
Orbcomm employs a range of mature VHF communications
technologies making it possible to keep costs down and provide a competitive
satellite based communications service. It is designed to be robust and
resistant to interference, enabling reliable and near real-time communications.
This provides a simple and low cost solution for global tracking and
communication with mobile assets. The final system will consist of four logical
segments:
- Space segment consisting of 36 satellites,
- Ground segment consisting of Orbcomm Gateways,
- Control segment managing information through
Orbcomm and a
- Subscriber segment communicating with LEO
satellites.
5.1.1 Space Segment
The space segment consists of 36 microstar satellite
arranged in six orbital planes at an altitude of 775km (424 nautical miles).
Four of the orbital planes (A, B, C and D) will each consist of 8 satellites
with a further two planes (F and G) each containing 2 satellites. Each
satellite transmits on the down-link channels in the 137-137 MHz band with
extensive frequency re-use. Up-link channels from subscriber terminals are in
the 148-150.5 MHz band. The satellites also transmit a beacon signal at 400.1
MHz to increase the accuracy of the doppler positioning available within the
Orbcomm system.
The satellite normally transmits to subscriber
terminals at 20 Watts although the satellite has an operational power of up to
40 Watts. The data rate is currently 4.8 kbps increasing to 9.6 kbps on the
down-link and 2.4 kbps on the up-link from the subscriber terminals.
The system is also highly resistant to interference
and will automatically switch to other frequencies if interference is detected
- this is done by a process called dynamic channel assignment.
5.1.2 Ground Segment
The Orbcomm gateways provide a connection between the
Orbcomm satellite system and the rest of the world. Users with Orbcomm
terminals (known as subscriber communicators) can send messages e.g. email, via
satellite to other Orbcomm users or to users connected to the conventional
Telecom infrastructure. Similarly, Orbcomm users can be contacted from the
conventional Telecom infrastructure. The ground segment provides connection to:
- Dedicated Access
- Dial-up Access
- Public Switched Network
- Email Services (X.400, Internet…)
Orbcomm was designed to permit all mobile users to
have access to its LEO satellite communications network and onward connection
to conventional terrestrial services.
5.1.3 Control Segment
The control segment is responsible for managing and
monitoring message traffic. This segment provides the necessary real-time
information on the performance and status of all relevant network elements and
provides the tools for problem management. It is largely constructed from 'off
the shelf' and fully proven components. Overall Command and Control of the
world-wide WAN is maintained over the Orbcomm Gateways at all times. The Global
Network Control Centre is staffed 24 hours a day, 365 days a year.
5.1.4 Subscriber Segment
Orbcomm subscriber terminals are designed to provide
low power VHF two-way digital connection to the satellite network. These
terminals can operate on Land, at Sea and in the Air. The up-link data-rate is
2.4 kbps operating in the 148 - 150.5 MHz band at a maximum transmission power
of 5 Watts. Receiver dynamic range is -118 to -80 dBm. Subscriber terminals are
available from several sources as low weight industrial units that will accept
a variety of interfaces, configuration and development options. The market for
subscriber terminals is very wide, encompassing many land mobile, aviation and
maritime applications. This will result in many further enhancements appearing
on the market.
6. AOC Applications
The opportunities that Orbcomm presents, to radically
improve Airline Operational Communications (AOC) can be clearly stated:
- Global Availability
- High Reliability
- Near Real-time Access
- Reduced Cost
- Flexible for many Applications e.g. Airline
Intranets
These properties allow extensive development of AOC
that encompasses many more cockpit and cabin applications. Indeed, cabin crew
access can be provided to significantly improve cabin crew services to
passengers. The same technology could also be used to provide a number of
passenger services from email through to on-line duty free ordering.
Areas of application (limited only by imagination)
include:
- Airline applications (fleet management, operational
control, airline intranet etc.)
- Cockpit and communication applications (weather,
position, status, operational messaging etc.)
- Cabin applications (purser, passenger information,
duty free etc.)
- Passenger Services (email, online, marketing and
information services etc.)
Other services can be envisioned including
applications for which Orbcomm is better suited than that proposed for, say,
existing terrestrial services. More importantly, airlines need not make a big
initial investment to decide if Orbcomm services are right for them. Orbcomm
can be evaluated at low cost. Perhaps even more interestingly, there are no
arbitrary restrictions and no dependence on a third party provider in
developing services.
7. Installation
Installation of Orbcomm in aircraft is unlikely to
pose problems as this VHF technology operates at low power and will not require
significant modifications to the aircraft into which it is installed. Orbcomm
has been designed to co-exist with Aeronautical applications operating in the
136-137 MHz band and the specifications and operating parameters have been
agreed at ITU with the participation of the aeronautical community. The
aircraft transmitter operates at 5W in the 148-150.5 MHz band, posing no risk
to airline communications systems. No complex interfacing is required as
installation can be made as a purely standalone application (or integrated into
the CMU if desired).
8. Costs
Subscriber terminal equipment is low cost and the
development of applications can be done in many cases by the adaptation and
configuration of existing 'off the shelf' applications (in many cases as simple
PC applications). Installation costs are likely also to be low. Operating costs
are likely to be significantly lower than existing AOC costs - with the
advantage of global availability and higher performance.
9. Summary
Orbcomm provides a very flexible, near real-time data
communication capability - ideal for mobile applications such as Airline
Operational Communications (AOC). The global availability of Orbcomm services
coupled with its high reliability, capacity and low cost make it an ideal
competitor to the current monopoly AOC service providers. Orbcomm will allow
airlines to develop novel applications such as Airline Intranets, so permitting
the closer integration of their business activities and providing more
efficient operational control as well as opening the door many new business
opportunities and passenger services. |
