Usually, all message candidates are speculatively corrected as if
they were DF11/17/18, even if the DF field has a different value. This
allows correction of messages when there is correctable damage to the
DF field.
However, running every message candidate through a couple of CRC checks
is expensive, CPU-wise, when decoding messages off the air, as there are
a large number of message candidates that are actually just junk data, and
computing CRCs for all of those adds up. The --no-fix-df option allows
disabling this sort of correction. The tradeoff is that messages with
damage to the DF field will not be corrected.
DF18 messages don't have a CA field so we can't set airground from that.
That meant that aircraft tracking wouldn't update airground state at all from a DF18
airborne position message, even if the existing tracked airground state was stale.
It seems reasonable to set at least AG_UNCERTAIN if we're seeing airborne positions
with valid altitude data.
Fixes github issue #113
* Create a network service and connection faup's stdin. Create a Modes.faup_rate_multiplier attribute and set from faup command input
* Use faup_rate_multiplier to adjust the minAge for emitting messages
* Convert upload_rate_multiplier to a double and adjust minAge with it
* Cleanup
* Var name change
* MODES_NOTUSED define for unused modes client object
* Sanity check on faup multiplier field
Major changes:
Try to error-correct all messages that potentially could be DF11/17/18
even if the original DF value is different. This allows messages with
correctable damage in the first 5 bits to be correctable.
Track recently-seen DF18 addresses separately to DF17 addresses.
DF18 does not imply Mode S support, so we don't want to treat it like
a known Mode S emitter, but once we've heard some DF18 for an aircraft
we can be more confident about future DF18 messages for the same
address.
Rework the scoring system so it's just a big enum that lists all the
possible outcomes in the order that we want. This makes the relative
ordering of different messages clearer, and makes it easier to move
messages above/below the accept thresholds as needed.
Don't accept 2-bit-error-corrected messages that are from aircraft we
have not previously seen. This greatly reduces the number of garbage
messages when using 2-bit error correction.
Overall results are:
* more CPU required for decoding (approx 30% increase in my tests)
as we're doing a lot more speculative CRC-checking work
* no significant change to message rates with error correction off
* about 5% more 1-bit-corrected DF17 decodes, with a
disproportionate increase in those messages contributing to
successful position decodes / unique aircraft counts
* _fewer_ decodes with 2-bit correction (versus old code with 2-bit
correction), but the message quality is substantially improved,
the rate of garbage decodes / phantom aircraft is greatly reduced
sample stats:
1-bit correction, old code:
141158 total usable messages
137852 accepted with correct CRC
3306 accepted with 1-bit error repaired
27446 DF17 messages
51 unique aircraft tracks
1-bit correction, new code:
141296 total usable messages
137854 accepted with correct CRC
3442 accepted with 1-bit error repaired
27528 DF17 messages
55 unique aircraft tracks
2-bit correction, old code:
142656 total usable messages
137809 accepted with correct CRC
3283 accepted with 1-bit error repaired
1564 accepted with 2-bit error repaired
28803 DF17 messages
349 unique aircraft tracks (<- note that most of these are garbage)
2-bit correction, new code:
142426 total usable messages
137822 accepted with correct CRC
3420 accepted with 1-bit error repaired
1184 accepted with 2-bit error repaired
28666 DF17 messages
55 unique aircraft tracks
eric1tran
Paul Philippov
Oliver Jowett
VasiliyTurchenko
Jurre Van Wouw
George Joseph