| Automatic Dependent Surveillance-broadcast |
Article Index for Automatic |
Website Links For Automatic |
Information AboutAutomatic Dependent Surveillance-broadcast |
| CATEGORIES ABOUT AUTOMATIC DEPENDENT SURVEILLANCE-BROADCAST | |
| avionics | |
|
The ADS-B system was developed in the 1990s. It relies on data from the Global Positioning System , or any navigation system that provides an equivalent or better service. The maximum range of the system is line-of-sight, typically less than 200 Nautical Mile s (370 km). The ADS-B transmissions are received by Air Traffic Control stations, and all other ADS-B equipped aircraft within reception range. Reception by aircraft of ADS-B data is known as "ADS-B in". USAGE The initial use of ADS-B is expected to be by Air Traffic Control and for surveillance purposes and for enhancing pilot situational awareness. ADS-B is lower cost than conventional radar and permits higher quality surveillance of airborne and surface movements. ADS-B is effective in remote areas or in mountainous terrain where there is no radar coverage, or where radar coverage is limited. The outback of Australia is one such area where ADS-B will provide surveillance where previously none existed. ADS-B also enhances surveillance on the airport surface, so it can also be used to monitor traffic on the taxiways and runways of an airport. ADS-B equipped aircraft may also have a Display unit in the cockpit picturing surrounding air traffic from ADS-B data (ADS-B in) and TIS-B (Traffic Information Service-Broadcast) data derived from air traffic radar. Both Pilots and Air Traffic Controller s will then be able to "see" the positions of air traffic in the vicinity of the aircraft, and this may be used to provide an ASAS (Airborne Separation Assurance System). Airborne Collision Avoidance Systems may in the future also make use of "ADS-B in", supplementing the existing TCAS collision avoidance system by what is called 'hybrid surveillance'. Airbus and Boeing are now expected to include ADS-B out (i.e. the transmitter of information) as standard on new-build aircraft from 2005 onwards. This is in part due to the European requirements for Mode S Elementary Surveillance (which uses 1090MHz Mode S transponder which now is normally capable of ADS-B via Extended Squitter), and some common functionality with ADS-B out. ADDRESSED AND BROADCAST ADS The Radio Technical Commission for Aeronautics’ ( RTCA ) Free Flight Selection Committee defines surveillance as “detection, tracking, characterization and observation of aircraft, other vehicles and weather phenomena for the purpose of conducting flight operations in a safe and efficient manner." Automatic Dependent Surveillance (ADS) is described as the process of creating and sending a message including the sender’s current position and other surveillance information, such as velocity, intent and flight identification. This information supports aircraft separation management by improving surveillance information at increased ranges, situational awareness and decision making. ADS data can be used in cooperation with data from current radar beacon systems, such as Air Traffic Control Radar Beacon Systems (ATCRBS), Mode S, Traffic Collision Avoidance Systems (TCAS) and primary Air Traffic Control (ATC) radar, and may also be used as a sole means of surveillance. There are two commonly recognized types of ADS for aircraft applications:
ADS-A provides a surveillance data report that is sent to a specific addressee. 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 transoceanic flight, reports are periodically sent by an aircraft to the controlling air traffic region. When ADS-B is used, aircraft and other vehicles continuously broadcast a message including position, heading, velocity and intent. Other uses may include obstacles transmitting a position message. Aircraft, ground-based stations, and other users monitoring the channels can receive the information and use it in a wide variety of applications. Because of this potential for broad utilization, a system using ADS-B is most often discussed as a replacement for or an augmentation to current methods of monitoring aeronautical traffic. To understand the full capability of ADS-B, consider how the current Air Traffic Control system creates information. The 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 get farther 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. The enhanced accuracy of the information will be used to improve safety, support a wide variety of applications and increase airport and airspace capacity. Use of ADS-B for ground-based surveillance requires only ADS-B Out (transmit) capability on the aircraft. With the addition of ADS-B In (receive) capability, the potential for ADS-B applications grows significantly. Some of the equipment and services associated with ADS-B In capability include:
ADS-B PHYSICAL LAYER Three link solutions are being proposed as the physical layer for relaying the ADS-B position reports:
Mode S The FAA has announced 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 while UAT will be the primary medium for general aviation aircraft. Europe has also chosen 1090 MHz as the primary physical layer for ADS-B. However, the second medium has not yet been selected between UAT and VDL Mode 4. With 1090 ES, 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. 1090 ES will not support FIS-B, due to regulatory requirements. Universal Access Transceiver The UAT system is specifically designed for ADS-B operation. A 1 MHz channel at 978 MHz is dedicated for transmission of airborne ADS-B reports and for broadcast of ground-based aeronautical information. UAT users would have access to the additional ground-based aeronautical data and would receive reports from proximate traffic (FIS-B and TIS-B). 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 L Band Mode S (1090 MHz) or UAT systems. IMPLEMENTATION TIMETABLE The timetable for airborne ADS-B equipage will be determined by ground and airborne facility implementation, equipment cost, perceived benefits of equipping and regulatory actions by the Civil Aviation Authorities (CAA). The cost to equip with ADS-B Out capability is relatively small and would benefit the airspace by enabling increased situational awareness. ADS-B In capability can provide additional benefits when ground stations and the critical mass of aircraft are also equipped. This data was taken into consideration when building the following estimated implementation timetable. Near-term Implementation (2006-2008) The next three years will see a continuation of ADS-B trials and some implementation in “pockets” where limited aircraft equipage can bring operational benefits. Some of these include:
Mid-term Implementation (2008-2012) Within four to eight years, an increasing number of aircraft with ADS-B Out capability along with the start of ground-based ADS-B infrastructure will begin to make a number of ADS-B applications attractive.
Long-term Implementations (2012 and beyond)
REFERENCES SEE ALSO
EXTERNAL LINKS
|
|
|