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reference

Unmanned Aircraft Remote Control Message syntax

In this section, we detail a binary Unmanned Aircraft Remote Control Message Syntax that is only 600 bytes in size. This 4,800 bit message can be BYTE multiplexed at a rate of 1 message per second with 4,800 bps CELP encoded digitised GCS staff voice. The GCS staff voice together with one remote control message per second can be transmitted using the modem capability of an inexpensive satellite phone.

• Message length
• Remote Control Message keywords
• FCU section
• Settings
• Communication systems
• Reserved_1 for future use
• S+A System
• PAYLOAD system
• Reserved_2 for future use

We calculate a Remote Control Message length for a well equipped Unmanned Aircraft with:

• three engines
• three VHF communication systems
• a Sense and Avoid system
• two payload cameras

• BLOCK 0 consists of a preamble section only
• BLOCK 1 is FEC encoded to 255 Bytes, as is BLOCK 2, using Reed Solomon RS(255,223) coding.
• If the data in BLOCK 1 or in BLOCK 2 is less than 233 Bytes, then the data is padded with NULL_0101 to 233 Bytes. NULL_0101 = 0101 0101, i.e. an alternating sequence of ONEs and ZEROs.
• BLOCK 1 and 2 data may be encrypted using an algorithm that does not increase the message size. Any encryption is performed prior to FEC encoding.
• BLOCK 0 + FEC encoded BLOCK 1 + FEC encoded BLOCK 2 = 600 Bytes = 4,800 bits.
• This Remote Control Message is BYTE multiplexed with the 4,800 bps digitised voice channel to end up with a 9,600 bps digital data signal that can be transmitted via a satellite phone modem.

Compatibility with STANAG 4586

"The length shall be a 32-bit unsigned integer of the number of bytes in the “Message Data”.  The length shall be any number between 1 and 538.

Note the UDP protocol under IPv4 has a guaranteed minimum datagram size of 576 bytes that must be supported by all implementations.  Subtracting the IPv4 header size of 20 bytes and the UDP header size of 8 bytes, leaves 548 bytes as the maximum amount data that can be sent in a datagram that will guarantee interoperability.  Therefore, no message or multi-message datagram shall exceed this data limit.  Subtracting the message wrapper size of 24 bytes, gives 524 bytes as the maximum message length of a single message with no room for another message in the datagram.  Extra care should be taken when packing multiple messages in the same datagram." - STANAG 4586

One can comply with the message size recommended in STANAG 4586 by only sending the BLOCK 1 + BLOCK 2 data (510 Bytes) in a single datagram.

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Status Message keywords

Example

Note that the BEGIN HEADER and the END Item_IDs are not included to save message length.

• HEADER binary message section length = 20 Bytes

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FCU section

FCU section: engines

FCU engine binary message section length = 1 + 3 Bytes per engine

FCU section: flaps

FCU flaps binary message section length = 7 Bytes

FCU section: general

FCU general binary message section length = 1 Byte

Example

• FCU binary message section length = 10 + 7 + 1 = 18 Bytes for a 3 engined Unmanned Aircraft

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Settings