From dbe082b6725cac64552029f1976fc5ed2b300897 Mon Sep 17 00:00:00 2001 From: Joe Taylor Date: Tue, 24 Oct 2017 17:47:05 +0000 Subject: [PATCH] Improve User Guide text on AP decoding. git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@8183 ab8295b8-cf94-4d9e-aec4-7959e3be5d79 --- .../en/controls-functions-messages.adoc | 2 +- doc/user_guide/en/decoder_notes.adoc | 50 +++++++++---------- 2 files changed, 26 insertions(+), 26 deletions(-) diff --git a/doc/user_guide/en/controls-functions-messages.adoc b/doc/user_guide/en/controls-functions-messages.adoc index cb4f0f8b4..c712feada 100644 --- a/doc/user_guide/en/controls-functions-messages.adoc +++ b/doc/user_guide/en/controls-functions-messages.adoc @@ -16,7 +16,7 @@ Tx sequence) by clicking on the circle under *Next*. * To change to a specified Tx message immediately during a transmission, click on a rectangular button under the *Now* label. Changing a Tx message in mid-stream will slightly reduce the chance of -a correct decode, but it is usually OK if done in the first 10-15 s of +a correct decode, but it is usually OK if done in the first 10-20% of a transmission. * All six Tx message fields are editable. You can modify an diff --git a/doc/user_guide/en/decoder_notes.adoc b/doc/user_guide/en/decoder_notes.adoc index 4d56e45b3..33f4df6ed 100644 --- a/doc/user_guide/en/decoder_notes.adoc +++ b/doc/user_guide/en/decoder_notes.adoc @@ -1,32 +1,26 @@ === AP Decoding -Our decoders for QRA64 and FT8 include optional procedures to use -information that naturally accumulates during a minimal QSO. This _a -priori_ (AP) information can increase the sensitivity of the decoder. +The _WSJT-X_ decoders for QRA64 and FT8 include optional procedures +that use naturally accumulating information during a minimal QSO. +This _a priori_ (AP) information increases sensitivity of the decoder +by up to 4 dB, at the cost of a slightly higher rate of false decodes. -For example, 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 57 of the 72 message bits in a -standard-format response to his call. The task of the decoder can -therefore be reduced to determining the remaining 15 bits of the -message and ensuring that the resulting decode is reliable. 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. +For example: when you decide to answer a CQ, you already know your own +callsign and that of your potential QSO partner. The software +therefore "`knows`" what to expect for 57 of the 72 message bits (28 +bits for each of two callsigns, 1 bit for message type) in the next +received message. The decoder's task can thus be reduced to +determining the remaining 15 bits of the message and ensuring that the +resulting solution is reliable. -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 decoding starts by setting AP bits to the hypothesized values, as +if they had been received correctly. We then determine whether the +remaining message and parity bits are consistent with the hypothesized +AP bits, with a specified level of confidence. Successful AP decodes +are 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, `a2` indicates that the successful decode used MyCall as +hypothetically known information. [[AP_INFO_TABLE]] .AP information types @@ -41,6 +35,12 @@ successful decode used MyCall as hypothetically known information. |6 | MyCall DxCall RR73 |=============================================== +If a codeword is found that is judged 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}. + 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.