mirror of
https://github.com/saitohirga/WSJT-X.git
synced 2025-11-03 21:40:52 -05:00
42b9c5edb1
git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@8118 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
107 lines
4.2 KiB
Plaintext
107 lines
4.2 KiB
Plaintext
=== AP Decoding
|
|
|
|
With the QRA64 decoder Nico Palermo, IV3NWV, introduced a technique
|
|
for decoding with the aid of information that naturally accumulates
|
|
during a minimal QSO. This _a priori_ (AP) information can be
|
|
used to increase the sensitivity of the decoder.
|
|
|
|
When an operator decides to answer a CQ, he already knows his own
|
|
callsign and that of his potential QSO partner. He therefore knows
|
|
what to expect for at least 56 of the 72 message bits in a
|
|
standard-format response to his call. The _WSJT-X_ decoders for QRA64
|
|
and FT8 can use these and similar AP bits to decode messages
|
|
containing them with higher sensitivity than otherwise possible.
|
|
|
|
We have implemented AP decoding in slightly different ways in QRA64
|
|
and FT8. To provide some explicit examples for users, we provide here
|
|
a brief description of the FT8 behavior.
|
|
|
|
AP decoding attempts effectively set the AP bits to the hypothesized
|
|
values, as if they had been received correctly. The decoder then
|
|
proceeds to determine whether the remaining message and parity bits
|
|
are consistent with the hypothesized AP bits. If a codeword is found
|
|
that the decoder judges to have high (but not overwhelmingly high)
|
|
probability of being correct, a ? character is appended when the
|
|
decoded message is displayed. To avoid misleading spots of occasional
|
|
false decodes, messages so marked are not forwarded to {pskreporter}.
|
|
|
|
Successful AP decodes are always labeled with an end-of-line indicator
|
|
of the form aP, where P is one of the single-digit AP decoding types
|
|
listed in Table 1. For example, an `a2` designator says that the
|
|
successful decode used MyCall as hypothetically known information.
|
|
|
|
[[AP_INFO_TABLE]]
|
|
.AP information types
|
|
[width="35%",cols="h10,<m20",frame=topbot,options="header"]
|
|
|===============================================
|
|
|P | Message components
|
|
|1 | CQ     ?     ?
|
|
|2 | MyCall     ?     ?
|
|
|3 | MyCall DxCall     ?
|
|
|4 | MyCall DxCall RRR
|
|
|5 | MyCall DxCall 73
|
|
|6 | MyCall DxCall RR73
|
|
|===============================================
|
|
|
|
Table 2 lists the six possible QSO states that are tracked by the
|
|
WSJT-X auto-sequencer, along with the type of AP decoding that would
|
|
be attempted in each state.
|
|
|
|
[[AP_DECODING_TYPES_TABLE]]
|
|
.AP decoding types for each QSO state
|
|
[width="35%",cols="h10,<m20",frame=topbot,options="header"]
|
|
|===========================================
|
|
|State |AP type
|
|
|CALLING | 1, 2
|
|
|REPLYING | 2, 3
|
|
|REPORT | 2, 3
|
|
|ROGER_REPORT | 3, 4, 5, 6
|
|
|ROGERS | 3, 4, 5, 6
|
|
|SIGNOFF | 3, 1, 2
|
|
|===========================================
|
|
|
|
|
|
=== Decoded Lines
|
|
|
|
Displayed information accompanying decoded messages generally includes UTC,
|
|
signal-to-noise ratio in dB, time offset DT in seconds, and
|
|
audio frequency in Hz. Some modes include additional information such
|
|
as frequency offset from nominal (DF), frequency drift (Drift or F1),
|
|
or distance (km or mi).
|
|
|
|
There may also be some cryptic characters with special meanings
|
|
summarized in the following Table:
|
|
|
|
[[DECODED_LINES_TABLE]]
|
|
.Notations used on decoded text lines
|
|
[width="50%",cols="h,3*^",frame=topbot,options="header"]
|
|
|===========================================
|
|
|Mode |Mode character|Sync character|End of line information
|
|
|FT8 | ~ | | ?   aP
|
|
|JT4 | $ | *, # | f, fN, dNC
|
|
|JT9 | @ | |
|
|
|JT65 | # | |
|
|
|JT65 VHF| # | *, # | f, fN, dNC
|
|
|QRA64 | : | * | R
|
|
|ISCAT | | * | M N C T
|
|
|MSK144 | & | | N H E
|
|
|===========================================
|
|
Sync character::
|
|
`*` - Normal sync +
|
|
`#` - Alternate sync
|
|
|
|
End of line information::
|
|
`?` - Decoded with lower confidence +
|
|
`a` - Decoded with aid of some a priori (AP) information +
|
|
`C` - Confidence indicator [ISCAT and Deep Search; (0-9,*)] +
|
|
`d` - Deep Search algorithm +
|
|
`E` - Size of MSK eye diagram opening - if negative, the eye is closed +
|
|
`f` - Franke-Taylor or Fano algorithm +
|
|
`H` - Number of bit errors corrected +
|
|
`M` - Message length (characters) +
|
|
`N` - Number of Rx intervals or frames averaged +
|
|
`P` - Number indicating type of AP information (Table 1, above) +
|
|
`R` - Return code from QRA64 decoder +
|
|
`T` - Length of analyzed region (s)
|
|
|