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India opens upHow Delhi airport is expanding Indias horizons
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German ATC supplier COMSOFT has
developed its surveillance products to
provide an end-to-end solution. Having
established itself as a competent and reliable supplier
of equipment for processing, tracking, analysing and
displaying airspace information it has turned its
attention to the collection of surveillance information.
The result is Quadrant.
Quadrant was developed from a single automatic
dependent surveillance-broadcast (ADS-B) sensor
into a comprehensive and flexible surveillance
solution. It now incorporates multiple ADS-B sensors
with a central processor to enable multilateration;
provides local transmitters for site monitoring,
reference transponders and ground-based vehicle
transponders; and includes a distributed interrogation
capability to extract information from Mode A, Mode
C and Mode S aircraft.
Quadrant was produced to meet the changing requirements of
established and emerging air navigation service providers (ANSPs). The
flexibility of the system makes it attractive for many users whether they
are looking at a token ADS-B capability, a method of enhancing andaugmenting an existing capability or a complete operational
surveillance system. The development path has adapted to meet the
changing needs and emerging markets.
ADS-B
Quadrant emerged from an existing multilateration system and
began with the creation of a robust and flexible ADS-B sensor.
Initially ADS-B was seen as the key market because it provided an
expandable surveillance solution with the addition of more sensors.
The Quadrant ADS-B sensor is specifically designed for deployment
in remote areas where regular access for maintenance is not
convenient. It is also small enough to be carried as hand-baggage
and consumes less than 10W. It can obtain its
power from an existing supply, via solar panels or
over the Ethernet feed that provides its
connectivity. The sensor is intended to be installed
once and does not require any routine on-site
maintenance as there are no moving parts and no
fans (see Figure 1, left).
Standards change, improvements need to be
made and occasional defects have to be fixed, so
all software and firmware on a Quadrant ADS-B
sensor can be installed, updated, monitored and
controlled remotely via the Ethernet connection.
The Quadrant Control and Monitoring System
(QCMS) provides a comprehensive monitoring
capability and enables loading, coverage and
numerous performance statistics to be reported.
The compiled ADS-B information is provided via
ASTERIX CAT021 messages. All recent versions are supported andindividual clients may select the version they wish to receive, while
new versions are easily incorporated through the remote upgrade
process. Up to 20 clients can connect to each sensor to receive an
independent stream each with a specific version and a bespoke
user application profile (UAP). However, most users prefer to use
the often limited bandwidth between remote sites to transfer data
to a single point from where it can be integrated and distributed in
a highly flexible way using the Quadrant Integrator.
Figure 1: Quadrant ADS-B Sensor
Developed to meet the requirements o air navigation service providers, Quadrants fexibility makes itattractive or users looking at a token ADS-B capability, a method o enhancing and augmenting anexisting capability or a complete operational surveillance system, writesCOMSOFTs Michael Leeson.
Quadrant: from Mode S
to multilateration
Quadrant was produced to meetthe changing requirements oestablished and emerging airnavigation service providers.
Figure 2: Principle of multilateration
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Multilateration
A geographically distributed network of Quadrant ADS-B sensors
provides the basis of a multilateration system, which is an integral part
of the ADS-B sensor and no modification or upgrade is necessary.Quadrant began as a multilateration system and this is where its
strengths still lie. The ADS-B sensor and Quadrant Central Processor
share the processing necessary to perform multilateration and this
minimises the bandwidth demands, while the detection of a
transmitted signal, its decoding into recognisable formats and the
timing of its arrival are all performed within the sensor. There is no
need to transfer huge amounts of sampled data because the
intelligence to recognise the message resides in the sensor. New RF
messages and improved detection algorithms can all be uploaded to
the sensor remotely too.
Detection and timing of signals is only part of the multilateration
solution; the remaining intelligence lies within the Quadrant Central
Processor. Synchronisation of clocks in each sensor is a major issuewith any multilateration system and the Quadrant approach makes
use of the distributed intelligence of the system. The clock within
each sensor is aligned with those in other sensors by processing
timing events from reference transponders and GPS. The Central
Processor uses the available information to maintain an accurate and
consistent time. This provides Quadrant with positional accuracy to
support ground movement, local and wide area surveillance (see
Figure 2, bottom left).
The parallel development of multilateration and an ADS-B
capability has meant that the obvious method for identifying a target
is via its 24-bit ICAO address (more commonly known as the Mode S
address). The availability of this address in both long and short
squitter messages, as well as many other downlink formats, makes it
easy to associate multiple messages and multilateration plots with
the same aircraft. Quadrant is able to create target tracks, based
upon this address, and collect a rich data set used to produce both
ADS-B and multilateration outputs.
Multilateration surveillance data is provided as ASTERIX CAT020
format messages. In common with the ADS-B output, all recent
versions are available and each client may select the preferred
version. New versions are incorporated by updating the software in
the Central Processor.
Other aircraft transmissions can also be used to generate
multilateration plots including Mode A and Mode C replies.
Quadrant can optionally include other plot association algorithms,
based upon timing and geographical proximity, to enable additional
plots to contribute to a target track. Making use of the content of
these messages is harder to achieve; indeed, it is not possible to
differentiate between Mode A or Mode C without knowledge of the
related interrogation. However, there is much useful information
that can be obtained from interrogation and hence Quadrant
provides a complete interrogation capability.
Interrogation
In keeping with the Quadrant philosophy, the interrogation system is
provided by multiple remote transmitters, which contain some of the
required intelligence, and a Quadrant Interrogation Controller. Multiple
transmitters enable a wide airspace to be covered with low-power
transmissions, which are targeted at a small area. This reduces the
impact of Quadrant on other surveillance systems by reducing theamount of False Replies Uncorrelated In Time (FRUIT).
The Quadrant Interrogation Controller was developed to integrate
completely with the Central Processor in order to meet the demand for
multilateration of aircraft without ADS-B capability. It determines the
information required from each aircraft, identifies the most suitable
transmitter and schedules the necessary uplink formats. The
transmitter network operates to the same time frame as the Central
Processor and this enables interrogations and replies to be correlated.
Transmitters have the ability to vary transmission power and
can use omnidirectional and sectorised antennas to restrict the
transmission to the necessary area. The choice of antenna pattern, the
optimal power and indeed the location of transmitters is crucial to
achieving good performance at an acceptable price. The location of
There is no need to transfer hugeamounts of sampled data becausethe intelligence to recognise themessage resides in the sensor.
Figure 3: Quadrant Interrogator
Figure 4: Coverage tool
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multilateration sensors is also crucial to the achievable accuracy of the
system. As the sensors and transmitters are designed to be installed
once and left, and as the installation geography is the most costly
component to change, Quadrant uses numerous modelling and
analysis tools to determine a suitable configuration (see Figure 3,previous page).
Monitoring, analysis and expandability
The Quadrant coverage tool provides a model of system performance
based upon terrain data, antenna patterns and the performance of
sensors and transmitters. The ADS-B sensor is able to detect aircraft
beyond 250NM if there is line-of-site. In general, it is terrain which
determines coverage and multilateration accuracy that drives the
selection of sites. Location of transmitters and sensors, and the
expected performance can be visualised (see Figure 4, previous page).
A model is only as good as its data and no chances are taken with
the Quadrant coverage tool. Real sensors can be deployed on a
temporary basis to any potential site and the actual coveragemeasured using available ADS-B reports. Coverage, loading and
distribution of downlink formats are just some of the numerous sensor
statistics available
ADS-B and multilateration are new concepts for many customers
and are considered a risky alternative to radar. The advantages over
radar are attractive: higher accuracy, lower cost, greater redundancy,
but radar is a well-known technology and potential users must be
convinced and assured that Quadrant is a reliable and viable
alternative. A phased introduction is the
recommended approach and is beneficial
in many ways. For example, a single
sensor provides ADS-B coverage but also
enables a huge amount of data to becollected and analysed; additional sensors
increase the coverage area incrementally
but also enable multilateration to be
demonstrated. ADS-B and multilateration
is completely passive and can work
alongside existing secondary surveillance
radars (SSRs) and will make use of the
responses to their interrogations. When
the amount of parasitic interrogations is
insufficient, or when an SSR is replaced,
the active components of Quadrant can
fill in the gaps.
Every Quadrant installation is different
and brings new challenges. The robust
technology, the intelligent design and
the reassuring analysis provided ensure
that each challenge is met fully, safely
and reliably.
COMSOFT GmbH is a leading software
specialist of the ATC domain, delivering
technical expertise and services to civil
and military aviation authorities and
ANSPs. Operating for more than 30 years
in over 60 countries around the world, it
specialises in ATM solutions, aeronauticalmessage handling and information
management, surveillance
communication, recording and, of course,
in ADS-B and multilateration.
Further informationCOMSOFT GmbH
www.comsoft.aero
is making the link
COMSOFTCOMSOFT GmbH Wachhausstr. 5a 76227 Karlsruhe Germany
T +49 721 9497 0 www.comsoft.aero info@comsoft.aero
aftn/cidin/amhs systems
aeronautical information systems
surveillance communication
surveillance display & processing
integrated radar/voice recording
atm systems & safety netsasterix tools & systems
artas installations & services
ads-b & multilateration sensors
Visit us:
9 - 11 March 2010
Amsterdam RAI
Stand H216
_ _ _ . . .