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interrogation modes using TDMA techniques. The system is capable of expansion to
accommodate future expansion in the number of users and diversification of applications,
including vessels which are not subject to IMO AIS carriage requirements, aids to
navigation and search and rescue.
With the capabilities of ship-to-ship, ship-to-shore and shore-to-ship communications, AIS
will greatly enhance the safety, improve the efficiency of the traffic management and
increase the vessel security and emergency response capabilities. Specifically, the
potential benefits of AIS include providing a more efficient vessel traffic management as a
result of knowing accurate location and speed of the vessels, monitoring vessel speeds
especially for hazardous cargo and deeper draft vessels in narrow and shallow waters
and faster response time to vessels in case of security concerns and vessel accidents or
incidents. The potential benefits to users include the reduction of overall transit time as a
result of better scheduling and the timely dispatching of pilots etc.
Figure 6-4: Diagram – Kongsberg Maritime System
As indicated in the above diagram AIS can be used on buoys, lighthouses and lightships.
The system uses a self-organised TDMA (SOTDMA 27 ) system with fixed access
(FATDMA) used at base stations and accommodates all users and meets the likely future
requirements for an efficient use of the spectrum. The ship station and base station uses
either 25 or 12.5 kHz single frequency simplex channels. The GMSK coded data
frequency modulates the transmitter; the bit rate is 9600 bit/s independent of the channel
width.
27 By convention, “SODTMA” is used in the Maritime community for self-organising TDMA
whereas “STDMA” is used by the Aeronautical community
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