I have found extense information regarding the 1090ES message structure. However, I have not found reliable information as for the UAT message structure, which surely differs from the 1090ES one.
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$\begingroup$ I feel like this question is a bit broad, without fully understanding the details of the subject. Perhaps this answers your question (perhaps it's a duplicate): aviation.stackexchange.com/questions/29771/… $\endgroup$– Jamiec ♦Commented Dec 2 at 17:50
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1$\begingroup$ You should post what you think you know, with references, so people don't have to recreate/guess. That also provides clarification as to what you are asking. $\endgroup$– PilotheadCommented Dec 2 at 19:33
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1 Answer
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The UAT frame is officially described in ICAO Doc 9861 Manual on the Universal Access Transceiver. It differs from the DF17 messages used by ADS-B using the 1090ES layer of a mode S transponder. For the later you see see this question.
The UAT frame has an ADS-B segment which can contain an ADS-B Message Data Block (MDB). Note the UAT frame is used both by aircraft and ground stations. Ground stations can upload ADS-B data about aircraft they track (TIS-B service). The following describes first the data block sent by aircraft. The MDB is organized into elements.
The MDB actual content is determined by its header containing:
- A type code. There are several types.
- The address qualifier which tells how the aircraft address is to be understood: A 24-bit ICAO address or an anonymous address when the message comes from an aircraft, or a pseudo-address (trackfile ID) when the message comes from a TIS-B ground station which cannot identify the aircraft by an individual address when the aircraft doesn't broadcast in mode S.
The MDB contains first:
A 24-bit ICAO address on 3 bytes
A state vector on 13 bytes:
A mode status on 12 bytes:
It can also contain other elements:
- An auxiliary state vector on 5 bytes, for some block types (altitude from a second source).
- A target state on 4 bytes, describing where the aircraft is aiming to.
- Two trajectory changes on 12 bytes each.
Regarding the pseudorandom addresses which can be used to relate the block to an aircraft, you can read What's the differences and the risk of duplicates, between ADS-B and TIS-B addresses? (inc. ICAO and self-assigned options).
If you need more information on a specific element I can include more details in this answer, but obviously not all elements can be detailed, the specs are 70 pages long.
