APRS
(with acknowledgements to Wickipedia)
The Automatic Packet Reporting System (APRS) is an amateur radio based system for real time tactical digital communications of information of immediate value in the local area. In addition, all such data is ingested into the APRS Internet system (APRS-IS) and distributed globally for instant access. In addition to messages, alerts, announcements and bulletins, the most visible aspect of APRS is its map display. Anyone may place any object or information on their map and it is distributed to all maps of all users in the local RF network or monitoring the area via the internet. Any station, radio or object that has an attached GPS is automatically tracked. Other prominent map features are weather stations, alerts and objects and other map related amateur radio volunteer activities.
APRS was developed since the late 80's by Bob Bruninga, currently a senior research engineer at the United States Naval Academy.. The acronym "APRS" was derived from his callsign. In the 1990s as GPS excitement dominated many new applications, the "P" was often referred to as "Position" instead of the original "Packet". This skewed the perception of APRS as only a vehicle tracking system. Recently, the emphasis is that APRS stands for "Automatic Packet Reporting System" because it can do a lot more than just report positions.
APRS is a real-time tactical digital communications protocol for exchanging information between a large number of stations covering a large (local) area. As a multi-user data network, it is quite different from conventional packet radio. Rather than using connected data streams where stations connect to each other and packets are acknowledged and retransmitted if lost, APRS operates entirely in an unconnected broadcast fashion, using unnumbered AX.25 frames. APRS packets are transmitted for all other stations to hear and use. Packet repeaters, called digipeaters, form the backbone of the APRS system, and use store and forward technology to retransmit packets. All stations operate on the same radio channel, and packets move through the network from digipeater to digipeater, propagating outward from their point of origin. All stations within radio range of each digipeater receive the packet. Digipeaters keep track of the packets they forward for a period of time, thus preventing duplicate packets from being retransmitted
APRS contains only four packet types, Position/objects, Status, Messages and Queries. The Position/object packets contain the latitude and longitude, and a symbol to be displayed on the map, and have many optional fields for altitude, course, speed, radiated power, antenna height above average terrain, antenna gain, and voice operating frequency. The map display uses these fields to plot communication range of all participants and facilitate the ability to contact users during both routine and emergency situations.
The Status packet is free-field format that lets each station announce his current mission or application or contact information or any other information or data of immediate use to surrounding activities. The message packet can be used for point-to-point messages, bulletins, announcements or even email. Bulletins and Announcements are treated specially and displayed on a single "community Bulletin board". This community bulletin board is fixed size and all bulletins from all posters are sorted onto this display. The intent of this display is to be consistent and identical for all viewers so that all participants are seeing the same information at the same time. Since lines are sorted onto the display, then individual posters can edit, update, or delete individual lines of their bulletins at any time to keep the bulletin board up-to-date to all viewers.
In its simplest implementation, APRS is used to transmit real-time data, information and reports of the exact location of a person or object via a data signal sent over amateur radio frequencies. In addition to real-time position reporting capabilities using attached GPS receivers. APRS is also capable of transmitting a wide variety of data, including weather reports, short text messages, radio direction finding bearings, telemetry data, short e-mail messages (send only) and storm forecasts. Once transmitted, these reports can be combined with a computer and mapping software to show the transmitted data superimposed with great precision upon a map display.
Posted 14 June, 2010 11:08:29 GMT