Automatic Dependent Surveillance-Broadcast
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Automatic Dependent Surveillance-Broadcast (ADS-B) is a function on an aircraft or a surface vehicle that periodically broadcasts its state vector (horizontal and vertical position, horizontal and vertical velocity) and other information. ADS-B supports improved use of airspace, reduced ceiling/visibility restrictions, improved surface surveillance, and enhanced safety such as conflict management. ADS-B should not be confused with the applications it supports.
Under ADS-B, a vehicle periodically broadcasts its own state vector and other information without knowing, a priori, what other vehicles or entities might be receiving it, and without expectation of an acknowledgement or reply. ADS-B is automatic in the sense that no pilot or controller action is required for the information to be issued. It is dependent surveillance in the sense that the surveillance-type information so obtained depends on the suitable navigation and broadcast capability in the source vehicle.
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[edit] Benefits of ADS-B
ADS-B is an enabling technology with benefits in safety and efficiency, when fully implemented and when supporting applications are available. Safety benefits include:
- Improved visual acquisition especially for general aviation under visual fight rules (VFR).
- Reduced runway incursions of the airport surface.
- Provision of graphical weather to general aviation cockpit.
ADS-B enables increased capacity and efficiency by supporting:
- Enhanced visual approaches
- Closely spaced parallel approaches
- Reduced spacing on final approach
- Reduced aircraft separations
- Enhanced operations in high altitude airspace for the incremental evolution of the "free flight" concept
- Surface operations in lower visibility conditions
- Near visual meteorological conditions (VMC) capacities throughout the airspace in most/all weather conditions
- Improved ATC services in non-radar airspace
[edit] Theory of Operation
ADS-B consists of three components:
- A transmitting subsystem that includes message generation and transmission functions at the source.
- The propagation medium.
- A receiving subsystem that includes message reception and report assembly functions at the receiving vehicle or ground system.
The source of the state vector and other transmitted information as well as user applications are not considered to be part of the ADS-B system.[1]
[edit] Relationship to Surveillance Radar
| Radar measures the range and bearing of an aircraft. Bearing is measured by the position of the rotating radar antenna when it receives a response to its interrogation from the aircraft, and range is measured by the time it takes for the radar to receive the interrogation response.
The antenna beam becomes wider as the aircraft gets further away, making the position information less accurate. Additionally, detecting changes in aircraft velocity requires several radar sweeps that are spaced several seconds apart. In contrast, a system using ADS-B creates and listens for periodic position and intent reports from aircraft. These reports are generated and distributed using precise instruments, such as the global positioning system (GPS) and Mode S transponders, meaning integrity of the data is no longer susceptible to the range of the aircraft or the length of time between radar sweeps. PSR is robust in the sense that surveillance outage failure modes are limited to those associated with the ground radar system. SSR failure modes include the transponder aboard the aircraft. Typical ADS-B aircraft installations use the output of the navigation unit for navigation and cooperative surveillance, introducing a common failure mode that must be accommodated in air traffic surveillance systems.[1] |
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[edit] Relationship to Addressed ADS
There are two commonly recognized types of ADS for aircraft applications:
- ADS-Addressed (ADS-A), also known as ADS-Contract (ADS-C), and
- ADS-Broadcast (ADS-B).
ADS-B is inherently different from ADS-A, in that ADS-A is based on a negotiated one-to-one peer relationship between an aircraft providing ADS information and a ground facility requiring receipt of ADS messages. For example, ADS-A reports are employed in the Future Air Navigation System (FANS) using the Aircraft Communication Addressing and Reporting System (ACARS) as the communication protocol. During flight over areas without radar coverage (e.g., oceanic, polar), reports are periodically sent by an aircraft to the controlling air traffic region.[1]
[edit] Relationship to Other Broadcast Services
The ADS-B link can be used to provide other broadcast services, such as FIS-B and TIS-B. Another potential aircraft-based broadcast capability is to transmit aircraft measurements of meteorological data.
[edit] Traffic Information Services-Broadcast (TIS-B)
TIS-B supplements ADS-B air-to-air services to provide complete situational awareness in the cockpit of all traffic known to the ATC system. TIS-B is an important service for an ADS-B link in airspace where not all aircraft are transmitting ADS-B information. The ground ADS-B station transmits surveillance target information on the ADS-B data link for unequipped aircraft or aircraft transmitting only on another ADS-B link.
TIS-B uplinks are derived from the best available ground surveillance source:
- ground radars for primary and secondary targets
- multi-lateration systems for targets on the airport surface
- ADS-B systems for targets equipped with a different ADS-B link[2]
[edit] Multilink Gateway Service
The multilink gateway service is a companion to TIS-B for achieving interoperability in low altitude terminal airspace. Because aircraft that primarily operate in high altitude airspace are equipped with 1090ES, and aircraft operating primarily in low altitude airspace are equipped with UAT, these aircraft cannot share air-to-air ADS-B data. In terminal areas, where both types of ADS-B link are in use, ADS-B ground stations use ground-to-air broadcasts to relay ADS-B reports received on one link to aircraft using the other link.[2]
[edit] Flight Information Services-Broadcast (FIS-B)
FIS-B provides weather text, weather graphics, NOTAMs, ATIS, and similar information. FIS-B is inherently different from ADS-B in that it requires sources of data external to the aircraft or broadcasting unit, and has different performance requirements such as periodicity of broadcast.[1]
In the US, FIS-B services will be provided over the UAT link in areas that have a ground surveillance infrastructure.[2]
[edit] ADS-B Physical Layer
Three link solutions are being proposed as the physical layer for relaying the ADS-B position reports:
- 1090 MHz Mode S Extended Squitter (ES),
- Universal Access Transceiver (UAT) and
- VHF Digital Link (VDL) Mode 4.
[edit] 1090ES
The FAA has announced (FAA 2002) its selection of the 1090 MHz ES and UAT as the mediums for the ADS-B system in the United States. 1090 MHz ES will be the primary medium for air carrier and high-performance commercial aircraft operating at high altitudes, while UAT will be the primary medium for general aviation aircraft operating at lower altitudes.[2]
Europe has also chosen 1090ES as the primary physical layer for ADS-B. However, the second medium has not yet been selected between UAT and VDL Mode 4. (Reference?)
With 1090ES, the existing Mode S transponder (or a stand alone 1090 MHz transmitter) supports a message type known as the ES message. It is a periodic message that provides position, velocity, heading, time, and, in the future, intent. The basic ES does not offer intent since current flight management systems do not provide such data – called trajectory change points. To enable an aircraft to send an extended squitter message, the transponder is modified and aircraft position and other status information is routed to the transponder. ATC ground stations and TCAS-equipped aircraft already have the necessary 1090 MHz receivers to receive these signals, and would only require enhancements to accept and process the additional information. 1090ES will not support FIS-B, due to regulatory requirements. (Reference?)
[edit] Universal Access Transceiver
The UAT system is specifically designed for ADS-B operation. UAT has lower cost and greater uplink capacity than 1090ES. 978 MHz (in the US) is dedicated for transmission of airborne ADS-B reports and for broadcast of ground-based aeronautical information. UAT users would have access to ground-based aeronautical data and would receive reports from proximate traffic (FIS-B and TIS-B). TIS-B will provide reports for non-ADS-B equipped aircraft and a multilink gateway service will provide ADS-B reports for 1090ES equipped aircraft.[2]
[edit] VDL Mode 4
The VDL Mode 4 system could utilize one or more of the existing aeronautical VHF frequencies as the radio frequency physical layer for ADS-B transmissions. VDL Mode 4 uses a protocol (STDMA) that allows it to be self-organizing, meaning no master ground station is required. This medium is best used for short message transmissions from a large number of users. VDL Mode 4 systems are capable of increased range in comparison to 1090ES or UAT systems. (Reference?)
[edit] ADS-B Supported Applications
The ADS-B data link supports a number of airborne and ground applications. Each application has its own operational concepts, algorithms, procedures, standards, and user training.
[edit] Cockpit Display of Traffic Information
A Cockpit Display of Traffic Information (CDTI) is a generic display that provides the flight crew with surveillance information about other aircraft, including their position. Traffic information for a CDTI may be obtained from one or multiple sources, including ADS-B, TCAS, and TIS-B. Direct air-to-air transmission of ADS-B messages supports display of proximate aircraft on a CDTI.
In addition to traffic based on ADS-B reports, a CDTI function might also display current weather conditions, terrain, airspace structure, obstructions, detailed airport maps, and other information relevant to the particular phase of flight.[1]
[edit] Airborne Collision Avoidance
ADS-B is seen as a valuable technology to enhance ACAS operation. Incorporation of ADS-B can provide benefits such as:
- Decreasing the number of active iterrogations required by ACAS, thus increasing effective range in high density airspace.
- Reducing unnecessary alarm rate by incorporating the ADS-B state vector, aircraft intent, and other information.
- Use of the ACAS display as a CDTI, providing positive identification of traffic.
- Extending collision avoidance below 1000 feet above ground level, and detecting runway incursions.
Eventually, the ACAS function may be provided based solely on ADS-B, without requiring active interrogations of other aircraft transponders.[1]
[edit] Conflict Management
[edit] ATS Conformance Monitoring
[edit] Other Applications
Other applications that may benefit from ADS-B include:
- Improved search and rescue
- Enhanced flight following
- Lighting control and operation
- Airport ground vehicle and aircraft rescue and firefighting vehicle operational needs
- Altitude height keeping performance measurements
- General aviation operations control[1]
[edit] Implementation Timetable
The US FAA ADS-B implementation is broken into three segments each with a corresponding timeline. Ground segment implementation and deployment is expected to begin in 2009 and be completed by 2013 throughout the National Airspace System. Airborne equipage is user driven and is expected to be completed both voluntarily based on perceived benefits and through regulatory actions (Notice of Proposed Rulemaking)by the FAA. The cost to equip with ADS-B Out capability is relatively small and would benefit the airspace with surveillance in areas not currently served by radar. The FAA intends to provide similar service within the NAS to what radar is currently providing (5NM en route and 3NM terminal radar standards) as a first step to implementation. However, ADS-B In capability is viwed as the most likely way to improve NAS throughput and enhance capacity.
[edit] FAA Segment 1 (2006-2009)
ADS-B deployment and voluntary equipage, along with rulemaking activities. Pockets of development will exploit equipment deployment in the areas that will provide proof of concept for integration to ATC automation systems deployed in the NAS.
[edit] FAA Segment 2 (2010-2014)
ADS-B ground stations will be deployed throughout the NAS, with an In-Service Decision due in the 2012-13 timeframe. Completed deployment will occur in the 2013-2014 timeframe. Rulemaking action will become effective and equipage is expected to begin after 2010.
- Airport Situational Awareness – A combination of detailed airport maps, airport multilateration systems, ADS-B systems and enhanced aircraft displays have the potential to significantly improve Final Approach and Runway Occupancy Awareness (FAROA).
- Oceanic In-trail – ADS-B may provide enhanced situational awareness and safety for Oceanic In-trail maneuvers as additional aircraft become equipped.
[edit] FAA Segment 3 (2015-2020)
ADS-B In equipage will be based on perceived benefit, but is expected to be providing increased situational awareness and efficiency benefits within this segment. Those aircraft who chose to equip in advance of the rulemaking mandate (2020) will see benefits associated with preferential routes and specific applications. Limited radar decommissioning will begin in the timeframe with an ultimate goal of a 50% reduction in the Secondary Surveillance Radar infrastructure.
- Use of ADS-B and CDTI may allow decreased approach spacing and closely spaced parallel approaches at congested airports to improve capacity during low-visibility operations.
- Sweden. LFV Group in Sweden is implementing a nationwide ADS-B network with 12 ground stations. Installation will commence during spring 2006, and the network will become fully operational in 2007. Based on the VDL Mode 4 standards, the network of ground stations can support services for ADS-B, TIS-B, FIS-B, GNS-B (DGNSS augmentation) and Point-to-Point communication, allowing aircraft equipped with VDL 4-compliant transceivers to lower fuel consumption and reduce flight times.
- Gulf of Mexico – In the Gulf of Mexico, where ATC radar coverage is incomplete, the FAA is locating ADS-B (1090 MHz) receivers on oil rigs and buoys to relay information received from aircraft equipped with ADS-B extended squitters back to the ATC centers to expand and improve surveillance coverage.
- Australia. Australia expects ADS-B to be a much more cost-effective method of providing ATC surveillance coverage for remote areas which currently have limited or no surveillance coverage. Australia currently has several ground stations operational across Western Australia, South Australia, New South Wales and Queensland, and plan to implement full coverage of the continent via ADS-B. Australia will continue implementation throughout its own airspace and expanded coverage into northern areas where aircraft approach Australian airspace boundaries.
- Cargo Airline Association. Cargo carriers, notably United Parcel Service(UPS), operating at their hub airports operate largely at night. Much of the benefit to these carriers is envisioned through merging and spacing the arriving and departing traffic to a more manageable flow. More environmentally friendly and efficient decent profiles combined with CDTI equipment, may allow crews to eventually aid controllers with assisted visual acquisition of traffic and limited cockpit based separation of aircraft. The benefits to the carrier are fuel and time efficiencies associated with idle descent and shorter traffic patterns than typical radar vectoring allows.
- Embry Riddle Aeronautical University. Embry Riddle Aeronautical University is equipping the training aircraft at its two main campuses in Florida and Arizona with ADS-B capability as a situational safety enhancement.
- Canada. Canada is planning to use ADS-B to provide coverage of its northern airspace around Hudson Bay, most of which has no radar coverage. ADS-B will be initially deployed in the Hudson Bay Basin in 2007–2008 and the service is expected to be later extended to cover the rest of the Canadian Arctic and eventually to the rest of Canada[4] [5].
[edit] System Design Considerations of ADS-B
A concern for any ADS-B protocol is the capacity for carrying ADS-B messages from aircraft, as well as allowing the radio channel to continue to support any legacy services. For 1090ES, each ADS-B message is composed of a pair of data packets. The greater the number of packets transmitted from one aircraft, the lesser the number of aircraft that can participate in the system, due to the fixed and limited channel data bandwidth.
System capacity is defined by establishing a criterion for what the worst environment is likely to be, then making that a minimum requirement for system capacity. For 1090ES, both TCAS and ATCRBS are existing users of the channel. 1090ES ADS-B must not reduce capacity of these existing systems.
The FAA national program office and other International aviation regulators are addressing concerns about ADS-B non-secure nature of ADS-B transmissions. ADS-B messages can be used to know the location of an aircraft, and there is no means to guarantee that this information is not used inappropriately. Additionally, there are some concerns about the integrity of ADS-B transmissions. ADS-B messages can be produced, with simple low cost measures that could demonstrated, spoof the locations of multiple phantom aircraft to disrupt safe air travel. There is no foolproof means to guarantee integrity, but there are means to monitor for this type of activity.
There are some concerns about ADS-B dependence. The system does not function independently, to the extent that the "D" in "ADS-B" stands for "Dependent". An independent means of verifying surveillance is considered by some to have more value than a dependent means.
There are some General Aviation concerns that ADS-B removes anonymity of the VFR aircraft operations. The ICAO 24-bit code specifically assigned to each aircraft will allow monitoring of that aircraft when within the service volumes of the ADS-B system. Unlike the current Mode A/C transponders, there is no code "1200", which offers casual anonymity. ADS-B identifies the aircraft uniquely among all in the world.
[edit] References
- ^ a b c d e f g h (June 25, 2002) Minimum Aviation System Performance Standards for Automatic Dependent Surveillance-Broadcast (ADS-B). RTCA, Inc. DO-242A.
- ^ a b c d e Scardina, John (June 7, 2002). "Overview of the FAA ADS-B Link Decision". Federal Aviation Administration.
- ^ FAA Office of Public Affairs (July 1, 2002). FAA Announces Automatic Dependent Surveillance-Broadcast Architecture. Press release.
- ^ ADS-B Home Page. Federal Aviation Administration (April 21, 2005). Retrieved on December 26, 2005.
- ^ Orlando, Dr. Vincent A (December 3-8, 2001). "Automatic Dependent Surveillance Broadcast (ADS-B) Mode S Extended Squitter". FAA Working Group 3: 1090 MHz ES Meeting 8.
- AIS-P
[edit] See also
- DO-212 Minimal Operational Performance Standards for Airborne Automatic Dependent Surveillance (ADS) Equipment
- RTCA DO-282A Minimum Operational Performance Standards for Universal Access Transceiver (UAT) ADS-B
- RTCA DO-260A Minimum Operational Performance Standards for 1090 MHz Extended Squitter ADS-B and Traffic Information Services - Broadcast (TIS-B)
- ADS-B ... Terrorist's Dream, Security's Nightmare
[edit] External links
- Airservices Australia ADS-B info
- Official FAA ADS-B Website
- NUP II Project
- NUP II Plus
- Enhanced General Aviation by ADS-B
- ADS-MEDUP Project
- Eurocontrol CASCADE Programme
- European Organisation for Civil Aviation Equipment
- Public database of ICAO24 address codes and aircraft registrations
- Overview of collision avoidance systems
- www.jpdo.aero
- Safe Flight 21 ADS-B Projects
- Capstone ADS-B Project
