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General Informationen

Reception of AIS data with multiplex receivers

AIS standards

The class A AIS service is described in the ITU-R M.1371-1 document. The -R stands for recommendation. This standard is a general document for the AIS service containing recommendations for the class A and B services . The document dated in 2001.

Operation of class A transponders is described in the EN61993-2. This document is obligatory for class A and was published in 2002.

Operation of class B transponders is described in the EN62287. This document is obligatory for class B and was published in 2005.

Class A: EN61993-2-2002:

The class A operation consists of three different types of messages:

• Dynamic information:
• MMSI number
• position of the ship (derived from GPS)
• time, when the position was measured in UTC
• course over ground (COG)
• speed over ground (SOG)
• heading (HOG)
• ship status
• rotational speed/turn rate

• Static information:
• call sign and name of the vessel
• ength and width of the vessel
• IMO-number of the vessel, if existent
• type of vehicel
• position of the GPS sensor onboard

• Journey-related information:
• draught of the vessel
• type of cargo
• port of destination and estimated time of arrival (ETA)
• route plan, optional

The block of dynamic information is the most important block looking for threatening collisions. Therefore this block of information is transmitted in a compulsory way, depending on the vessels movement.

The following table shows the mandatory repetition rate of class A transmissions linked to the ships movement:

Anchored vessels:

3 minutes

Vessels at 0 - 14 kn:

10 seconds

Vessels at 0 - 14 kn, fast manoeuvre:

3.3 seconds

Vessels at 14 - 23 kn:

6 seconds

Vessels at 14 - 23 kn, fast manoeuvre:

2 seconds

Vessels at > 23 kn:

2 seconds

Vessels at > 23 kn, fast manoeuvre:

2 seconds

Static information as well as information belonging to the journey is dispersed every 6 minutes. The reporting intervals correspond to both radio channels (161.975 MHz, 162.025 MHz) together.

Class B: EN62287, 2005: class B operation is described in the standard EN62287, published in 2005. This document is obligatory for class B. Pages 15 and 38 describe the operation:

Reporting intervals are:

Dynamic ship data:

Boats at < 2kn: 3 minutes

Boats at > 2kn: 30 seconds

Static ship data (similar to class A): 6 minutes

These intervals are the standard operation modes.

Competent authorities, like base stations, can have influence on the reporting intervals (as they do with class A as well). Interval timing can be reduced down to 5 seconds in exceptional cases. There is no automatism to change the 30sec/3min dynamic intervals by the ship itself.

Differences between 2-channel full duplex and 2-channel multiplex operation:

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