What is the typical range of the AIS?

Typically, an AIS-Receiving station utilizing an outer reception apparatus put 15 meters above sea level, will get AIS data from AIS-prepared vessels that cruise inside a scope of 15-20 nautical miles around it. Base stations situated at a higher height may stretch out the range up to 40-60 NM relying upon variables, for example, rise, radio wire type, snags around the reception apparatus and climate conditions.

The most significant factor for a productive gathering is the rise of the base station recieving wire. The higher, the better. For instance, the MarineTraffic Network Team figured out how to follow vessels 200 NM away, with a little versatile recieving wire put on an island mountain on 700 meters elevation! Most of our base stations completely spread a scope of 40 miles and, intermittently, may get data about some progressively removed vessels!

The Ship Tracker earthbound based AIS arrange gives broad, continuous inclusion of vessels' situations at a few a large number of ports and beach front transportation courses around the world. Satellite AIS information comes as a perfect enhancement, as it empowers the checking of vessels' tracks well past seaside areas, including the seas!

Each AIS system consists of one VHF transmitter, two VHF TDMA receivers, one VHF DSC receiver, and standard marine electronic communications links (IEC 61162/NMEA 0183) to shipboard display and sensor systems (AIS Schematic). Position and timing information is normally derived from an integral or external global navigation satellite system (e.g. GPS) receiver, including a medium frequency differential GNSS receiver for precise position in coastal and inland waters. Other information broadcast by the AIS, if available, is electronically obtained from shipboard equipment through standard marine data connections. Heading information and course and speed over ground would normally be provided by all AIS-equipped ships. Other information, such as rate of turn, angle of heel, pitch and roll, and destination and ETA could also be provided.

AIS normally works in an autonomous and continuous mode, regardless of whether it is operating in the open seas or coastal or inland areas. Transmissions use 9.6 kb GMSK FM modulation over 25 or 12.5 kHz channels using HDLC packet protocols. Although only one radio channel is necessary, each station transmits and receives over two radio channels to avoid interference problems, and to allow channels to be shifted without communications loss from other ships. The system provides for automatic contention resolution between itself and other stations, and communications integrity is maintained even in overload situations.

Each station determines its own transmission schedule (slot), based upon data link traffic history and knowledge of future actions by other stations. A position report from one AIS station fits into one of 2250 time slots established every 60 seconds. AIS stations continuously synchronize themselves to each other, to avoid overlap of slot transmissions. Slot selection by an AIS station is randomized within a defined interval, and tagged with a random timeout of between 0 and 8 frames. When a station changes its slot assignment, it pre-announces both the new location and the timeout for that location. In this way new stations, including those stations which suddenly come within radio range close to other vessels, will always be received by those vessels.