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By

Sharad Saurabh3rd year, Dept. of Instrumentation & Control

SRM University

&

Sayan Chakrabarty3rd year, Dept. of Instrumentation & Control

SRM University

Ad-hoc literally means Something ‘created or done for a specific purpose only’.

Ad-hoc network is a dynamic network which can be created anywhere with just two basic nodes and does not require any centralized infrastructure.

Each node has a certain range of communication in which it can transmit or receive data.

If it needs to communicate to a node which is outside its range, it may do so by sending the data to a node which is within its range. That node will transmit to the next and so on till it reaches its designated destination.

Data is transmitted in the form of small packets.2

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Devices such as laptops, PDAs, mobile phones, MP3 players etc, can be made to interact using Ad-hoc networking

In fact this is being used in technologies such as Bluetooth and Wi-Fi to connect various devices. Now-a-days, most of the above mentioned devices come with in built facilities to support ad hoc networking.

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Contemporary communication means in aircrafts include :

Radio Communication from ground (TIS-B) RADAR (Radio Detection and Ranging):

Air Traffic Control (ATC) Radars Secondary Surveillance Radar (SSR) (Airport Surveillance Radar) Ground Control Approach (GCA) Radars PAR Systems

Distance Measuring Equipment (DME) Radio Beacons Identification Friend or Foe (IFF) Systems

IFF Interrogator IFF Transponder

•Altimeter (AL) Radar Systems •Terrain-Following Radar (TFR) Systems

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Automatic Dependent Surveillance-Broadcast (ADS-B)

Data is broadcast in the form of discrete packets.

Since the mid-1990s, FAA has focused on two different ADS-B frequencies-

1. 978 MHz Universal Access Transceiver – used by the General Aviation (GA).

2. 1090 MHz Extended Squitter (ES) – used by airliners and other large aircraft.

The 1090ES is selected for its international interoperability, whereas the UAT link is for its weather graphics up-link capacity and low cost.

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• Accuracy does not seriously degrade with range, atmospheric conditions, or target altitude.

• Update intervals do not depend on the rotational speed or reliability of mechanical antennas.

• Accuracy is unaffected by the range to the aircraft.• Also operable in lower altitudes and mountainous regions.• Relatively inexpensive technology, with costs for equivalent

radar coverage running in the 0.1 to 0.05 range. • A single Mode S 1090ES ADS-B ground station can cost

anywhere from $150,000 - $300,000 USD, including installation.

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Sample Mode S Multilateration and 1090ES ADS-B GroundStation Installation for FAA ASDE-X Program.

Mode S 1090ES ADSBand Multilateration GroundStations Deployed On OilPlatforms In Gulf of Mexico ForHelicopter and En Route Tracking

Airbus has stated its intent to begin equipping all new transport class aircraft it produces with Mode S 1090ES as a standard feature.

UPS, a US freight carrier, is in the process of installing Mode S 1090ES ADS-B avionics on all 107 Boeing 757s and 767s it operates.

Australia, Japan, China and some parts of Europe & Africa have also opted for ADS-B and plan to implement it soon.

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# Map showing European airports with ADS-B compatibility

Essentially a single-node operation scheme.

Range is limited to the direct transmission range of the airborne Antenna.

The 1090ES is likely to support ADS-B applications that do not require air-to-air ranges exceeding 80km when used in the highest density airspace and will provide ranges of 180 km in lower traffic density airspace. This is too short for longer range applications and flight-path-conflict resolutions.

Research is on to implement an airborne ADS-B architecture that will readily accommodate a second ADS-B link in addition to the 1090ES.

However, these additions can be too expensive and problematic, especially when in India, we are yet to realise the full potential benefits of even one digital link of the single-node system.

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Fig illustrates the main drawback of ADS-B

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Multiple-hop means an ad hoc network where the data exchange is not limited to just a single pair but it includes a number of nodes.

The nodes not only transmit their own data but also those received from neighbouring nodes.

One aircraft can be made to broadcast not only its own state information periodically, but also the state information it receives about neighbouring aircrafts.

Clusters can be disjoint from, or overlapped with each other.14

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Fig. shows a cluster of planes forming a multiple hop network

Possible to select more useful information over a larger area for cockpit display and onboard automation systems.

Pilot can virtually see other aircrafts beyond its transmission range.

Live data can be sent in a reliable and timely manner.

Can provide a collision-free and extended traffic coverage.

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The transmitted Protocol specifiesThe maximum number of hops the state information

will be relayedHow often the state information is broadcastWhat state information to broadcastThe mix of own aircraft information vs. information

of other aircraft, etc. The protocol should also specify a transmission rate

such that it is ample to handle the data that it receives and transmits, i.e. the processing rate of the information should be synchronised with frequency with which data is received.

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Fig shows an example of five node network with link delivery probabilities.

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Future Achievability

Extensive research on the following issues is required for future usage :

Security needs to be dealt with, as the data is open to all receivers.

A proper protocol needs to be devised which will address the points mentioned before.

Testing needs to be done using real-time simulations to test the effectiveness.

Issues such as information reachability and effect of signal interference need testing.

Priority should also be specified, so that information about the nearest aircraft is processed first before moving to data from farther aircrafts.

• www.ads-b.com• www.faa.gov• www.wikipedia.com• www.howstuffworks.com• www.springerlink.com• www.sciencedirect.com

• M. S. Nolan, “Fundamentals of Air Traffic Control”, 2nd Edition, Wadsworth Publishing Company.

• J. D. Anderson, “Introduction to Flight”, 4th Edition, McGraw-Hill.

• Charles E. Perkins, “Ad-Hoc Networking”, 1st Edition, Addison and Wesley Publishing Company.

• “Aviation Today” Magazines.

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