SOTDMA

  • Print

SOTDMA is the most complex TDMA access scheme defined for AIS and also provides the backbone for autonomous operation of the network offshore.  The complete technical definition of SOTDMA can be found in ITU-R M.1371-4 Annex 2.

The key elements of SOTDMA operation are as follows:

SOTDMA also provides for dynamic and autonomous management of capacity in busy areas. Should a situation occur where all TDMA slots are occupied ‘slot re-use’ rules are applied. This allows the slots occupied by the stations most distant to a particular mobile station to be re-used for its own transmissions. This effectively reduces the size of an AIS ‘cell’ and ensures that position reports from the nearest vessels (which are most relevant to safety of navigation) are not affected.

The essential hardware requirements to support SOTDMA are:

Designed for Class A devices, SOTDMA transmits data as follows: