Mode-S Beast:AVR Mode CRC Driver

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Obsolete: This feature is meanwhile implemented in the FPGA itself.

The AVR Mode CRC and Bit Error driver is a tool that is running on the PC and has two serial interfaces:

  • First serial interface reads frames from the Mode-S Beast, but also from all other AVR mode receivers.
  • Second serial interface outputs the frames to the GUI application, also on a serial port. At the moment PP cannot read the data by itself, so COM0COM virtual cable must be installed and provide the interface connection.

If the incoming data does not have CRC pre-checked in the receiver/decoder, the bit error driver trys to correct up to to erroneous bits in DF-11 and DF-17/18 frames so that the CRC is correct. It also pre-checks the other frames against the valid aircraft ID, so that the load towards the GUI is reduced.

Bit errors look like this in the signal:

Bit Error 1 Bit Error 2

Currently only F5ANN has that driver in operation. We both see an improvement of about 20% of DF-11/17/18 frames. This output is for example from my currently running instance:

Date Time Frames in out % immediate 1Bit 2Bit DF17/DF11#
24.03.2011 21:29:01 2606 943(36%) 453(17%) 113(25%) 62(13%) 270
24.03.2011 21:30:01 2637 951(36%) 466(17%) 122(26%) 65(14%) 276
24.03.2011 21:31:01 2611 943(36%) 457(17%) 121(26%) 61(13%) 275
24.03.2011 21:32:01 2617 955(36%) 459(17%) 117(25%) 61(13%) 276
24.03.2011 21:33:01 2608 979(37%) 457(17%) 114(25%) 61(13%) 270
24.03.2011 21:34:01 2610 987(37%) 458(17%) 114(25%) 64(13%) 266
  • Frames in is the number of raw, non-CRC checked frames that I am getting from my Mode-S Beast
  • Out is the total number of frames that later are sent to Planeplotter
  • Immediate means the number of DF-11/17/18 frames that do not have a bit error
    (DF-11 includes those with interrogator ID)
  • 1 Bit is the number of DF-11/17/18 frames that suffer from a 1 bit error
  • 2 Bit is the number of DF-11/17/18 frames that suffer from a 2 bit error
  • DF17/11# is the number of DF11/DF17 squittter frames that are sent to Planeplotter
    (same values as ModeSCompare displays)

I am planning to release the driver as soon as it can interface to planeplotter without the need of COM0COM.