Transas T214, Technical Manual

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Settings of Base Station configuration
Chapter 6. Commissioning.Internal configuration
65
6.8.2
CAB – Control AIS Base Station
This menu is used to turn on or off the transmission of channel A and B on an AIS
Base Station.
6.8.3
Base Station transmission schedule setup
TDMA algorithms
The AIS stations exchange data on two TDMA VHF channels. All the AIS stations
share TDMA VHF channel time. As a source of standard time, AIS stations use
internal GPS or Glon
а ss/GPS receivers. Malfunctioning of the internal Glonass/GPS
receiver does not bring about the AIS equipment failure, as for cases like this, the
system provides a backup method of AIS equipment synchronising relative to other
AIS stations (indirect UTC synchronising and semaphore method synchronising).
Algorithms for time division of TDMA VHF channels modulation parameters and data
formats are incompliance with ITU-1371-1.
RATDMA – algorithm based on a random choice of slots not occupied by other AIS
stations. There is certainly a probability of two or more AIS stations colliding if they
simultaneously try to find a vacant slot. It is used for transmitting single messages.
SOTDMA – algorithm based on announcing its future transmission in order to inform
other AIS stations that the slot will be occupied. This reduces the probability of
collisions. It is used by the shipboard AIS equipment for transmitting messages
about own coordinates (since this is required to be done at regular intervals, with a
period of once a second to once in 10 seconds depending on the ship speed).
FATDMA – algorithm based on the fixed preset slots. It is used by the AIS Base
Stations.
The schedule setup is made in the Configuration->Setup->BS setup menu.
Use of Access Schemes
«Dependent» operation
When operating as a dependent Base Station the FATDMA access scheme shall be
used. The Base station must use the slot provided by a VDM/TSA Sentence pair.
Dependent Operation shall not use the RATDMA access scheme.
When operating as a Dependent Base Station, the unit shall comply with the
following general rules: