What if you could pinpoint a ship’s location down to the minute with one tool?
Different AIS products use the slot map in different ways, some can reserve their slot, some send without having a slot, whilst others scan for a free slot to transmit data into. Self Organised Time Division Multiple Access (SOTDMA) is used by Class A transceivers. The AIS format uses TDMA radio access that allows for just 4,500 time slots per minute. One time slot equates to a single vessel transmission. Any more than that and the individual signals start to interfere with each other, corrupting the data held within. How AIS Works. AIS uses a technique called TDMA. that allows multiple transmitters to grab available time slots during which they can transmit their information. There are 4500 time slots every minute and if overloaded, Class A systems can share time slots and only vessels further away will be subject to drop-out.
The industry's first online software for tracking real-time marine traffic, AISLive delivers updated movements for 130,000+ ships and vessels every 60 seconds, including activity at 16,000+ ports and terminals worldwide. Available through three different subscription levels, AISLive Premium includes access to terrestrial and satellite ship movements (view the latest edition to our terrestrial networks) and to the Sea-web Ports module for greater visibility into your fleet’s deep sea and offshore movements. All AISLive subscriptions offer a user-friendly mapping tool and 197 search filters. Find out how you can connect your port or area to the AISLive network.
You can learn more about AISLive in the following languages: Chinese and Korean.
Marine equipment companies, port authorities and service providers, ship owners, managers, agents, charterers and brokers as well as government and civil authorities use AISLive to:
- Boost operational efficiencies: Follow your fleet’s global movements – routes, speeds, arrival times – including deep sea activity
- Enhance domain awareness: Track all ships sailing in your waters
- Uncover ship movement and commodity trade trends: Reveal competitor positions, create trading positions and identify business opportunities
- Mitigate risk: Identify, watch and set alerts for ships that could be a security risk in your waters
Ais Time Slots Games
Watch this brief demo to see AISLive and Sea-web in action
It’s not entirely clear who it was that came up with the first AIS vessel tracking and identification system, but like so much other technology that we take for granted these days, it came out of the introduction of GPS for civilian purposes, which achieved global coverage in the early 1990s. It was then the integration of GPS time and position data with long-standing VHF radio technology that enabled the development of AIS. We’ll delve into a bit more into the history of AIS in this article.
Ais Time Slots Poker
The early years
In its early years its primary use was as a ship-to-ship anti-collision system for use in poor visibility and at night, in support of radar and conventional watch keeping. Over time the amount of information that could be transmitted in the VHF signal grew and its usefulness increased. In 2002 it finally went global when the IMO in its landmark SOLAS convention mandated that all passenger ships and other commercial vessels over 300 GT should carry Class-A AIS transceivers. At the time this affected around 100,000 ships, but since then use has expanded as the unit cost of transceivers has fallen and both compulsory and voluntary adoption has increased.
The final frontier
Originally developed as a short range identification and vessel tracking system, at the start of the 21st century it was discovered that AIS transmissions could be received at ranges of up to 400km above the surface of the earth, whereas on the surface the maximum effective distance is around one tenth of that. This revolutionised AIS, taking it from a coastal and ship-to-ship tracking application to a vessel management system with global coverage. However, the challenge for satellite operators looking to develop this opportunity now is managing the enormous volumes of data that this creates for individual satellites each monitoring thousands of square kilometres of ocean.
Future-proofing
The AIS format uses TDMA radio access that allows for just 4,500 time slots per minute. One time slot equates to a single vessel transmission. Any more than that and the individual signals start to interfere with each other, corrupting the data held within. The terrestrial AIS infrastructure with its short range and higher density does not have the same capacity problems.
The satellite developers are, however, working on ways of receiving and processing incoming data at faster rates and rapid advances are being made.
An important tool in the box
There is no perfect vessel tracking system, but AIS is becoming increasingly effective as accuracy and refresh rates get ever better. Its ability to interface with other detection sources makes it an important component of integrated navigation and warning systems, and the addition of supplementary environmental and situational data makes it yet more versatile. Without a doubt AIS is now one of the most valuable information sources available for anyone involved in the maritime sector.
Ais Time Slots Online
About BigOceanData
BigOceanData is a leader in maritime tracking and telemetry, delivering global vessel tracking and monitoring services along with fleet management tools via its sophisticated browser-based interface. Key features of the BigOceanData product include its ability to fuse data from AIS signals and a range of onboard satellite reporting systems so as to both improve position accuracy and reduce data costs. The system also integrates a series of data feeds and management tools that show users not only vessel locations and movements, but situational data such as marine charting, terrestrial mapping, weather and sea-state (current and forecast), and piracy and other security alerts.
Ais Time Slots Game
For more information contact sales@bigoceandata.com or call +44 (0) 207 998 3048.