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Advanced Aviation Technology Ltd.
 
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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.

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Advanced Aviation Technology Ltd.
The Old Post Office,
The Street, Compton,
Surrey GU3 1ED. ENGLAND.
Tel. 44 1483 811 311.

Email: kim.oneil@aatl.net

 
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