A few more editorial tweaks, and more text.

git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@6354 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
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Joe Taylor 2016-01-06 00:10:54 +00:00
parent b22f1c6d2e
commit 8ba09d5175
1 changed files with 197 additions and 81 deletions

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@ -139,15 +139,21 @@ WSJT-X
\emph default \emph default
, widely used for amateur weak-signal communication with JT65 and other , widely used for amateur weak-signal communication with JT65 and other
specialized digital modes. specialized digital modes.
The program is freely available and licensed under the GNU General Public The program is freely available
License. \begin_inset CommandInset citation
LatexCommand cite
key "wsjt"
\end_inset
and licensed under the GNU General Public License.
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
The JT65 protocol specifies transmissions that normally start one second The JT65 protocol specifies transmissions that normally start one second
into a UTC minute and last for 46.8 seconds. into a UTC minute and last for 46.8 seconds.
Receiving software therefore has up to several seconds to decode a message, Receiving software therefore has up to several seconds to decode a message
before the operator sends a reply at the start of the next minute. before the start of the next minute, when the operator sends a reply.
With today's personal computers, this relatively long time available for With today's personal computers, this relatively long time available for
decoding a short message encourages experimentation with decoders of high decoding a short message encourages experimentation with decoders of high
computational complexity. computational complexity.
@ -158,7 +164,7 @@ The JT65 protocol specifies transmissions that normally start one second
properties, not least of which is its conceptual simplicity. properties, not least of which is its conceptual simplicity.
Decoding performance and complexity scale in a convenient way, providing Decoding performance and complexity scale in a convenient way, providing
steadily increasing soft-decision decoding gain as a tunable computational steadily increasing soft-decision decoding gain as a tunable computational
complexity parameter is increased over more than 5 orders of magnitude. complexity parameter is increased over more than five orders of magnitude.
Appreciable gain is available from our decoder even on very simple (and Appreciable gain is available from our decoder even on very simple (and
relatively slow) computers. relatively slow) computers.
On the other hand, because the algorithm benefits from a large number of On the other hand, because the algorithm benefits from a large number of
@ -405,7 +411,7 @@ probabilistic
\begin_inset CommandInset citation \begin_inset CommandInset citation
LatexCommand cite LatexCommand cite
after "Chapter 10" after "Chapter 10"
key "key-1" key "lc2004"
\end_inset \end_inset
@ -1224,17 +1230,21 @@ Calculate the hard-decision Hamming distance
\begin_inset Formula $X$ \begin_inset Formula $X$
\end_inset \end_inset
between the candidate codeword and the received symbols, the corresponding between the candidate codeword and the received symbols, along with the
soft distance corresponding soft distance
\begin_inset Formula $d_{s}$ \begin_inset Formula $d_{s}$
\end_inset \end_inset
, and the quality metric and the quality metric
\begin_inset Formula $u$ \begin_inset Formula $u$
\end_inset \end_inset
. .
If
\end_layout
\begin_layout Enumerate
If
\begin_inset Formula $u$ \begin_inset Formula $u$
\end_inset \end_inset
@ -1242,8 +1252,8 @@ Calculate the hard-decision Hamming distance
\begin_inset Formula $u_{1}$ \begin_inset Formula $u_{1}$
\end_inset \end_inset
as by setting
\begin_inset Formula $u_{2}$ \begin_inset Formula $u_{2}=u_{1}$
\end_inset \end_inset
and then set and then set
@ -1262,11 +1272,11 @@ If
\begin_inset Formula $d_{s}<d_{0}$ \begin_inset Formula $d_{s}<d_{0}$
\end_inset \end_inset
, go to step 10. , go to step 11.
\end_layout \end_layout
\begin_layout Enumerate \begin_layout Enumerate
If the number of trials is less than the timeout limit If the number of trials is less than the timeout limit
\begin_inset Formula $T,$ \begin_inset Formula $T,$
\end_inset \end_inset
@ -1287,7 +1297,7 @@ If
\begin_inset Formula $r<r_{1},$ \begin_inset Formula $r<r_{1},$
\end_inset \end_inset
go to step 10. go to step 11.
\end_layout \end_layout
\begin_layout Enumerate \begin_layout Enumerate
@ -1382,18 +1392,18 @@ The FT algorithm is completely general: with equal sensitivity it recovers
much much
\emph default \emph default
smaller list of messages (say, a few thousand messages or less) that we smaller list of messages (say, a few thousand messages or less) that we
can guess may be among the most likely ones to be received. can guess might be among the most likely ones to be received.
One such situation exists when making short ham-radio contacts that exchange One such situation exists when making short ham-radio contacts that exchange
minimal information including callsigns, signal reports, perhaps Maidenhead minimal information including callsigns, signal reports, perhaps Maidenhead
locators, and acknowledgments. locators, and acknowledgments.
On the EME path or on a VHF or UHF band with limited geographical coverage, On the EME path or a VHF or UHF band with limited geographical coverage,
the most likely received messages often originate from callsigns that have the most likely received messages often originate from callsigns that have
been decoded before. been decoded before.
Saving a list of previously decoded callsigns and associated locators makes Saving a list of previously decoded callsigns and associated locators makes
it easy to generate lists of hypothetical messages and their corresponding it easy to generate lists of hypothetical messages and their corresponding
codewords at very little computational expense. codewords at very little computational expense.
The resulting candidate codewords can be tested in the same way as those The resulting candidate codewords can be tested in the same way as those
generated by the probabilistic method described in Setcion generated by the probabilistic method described in Section
\begin_inset CommandInset ref \begin_inset CommandInset ref
LatexCommand ref LatexCommand ref
reference "sec:The-decoding-algorithm" reference "sec:The-decoding-algorithm"
@ -1456,14 +1466,10 @@ For hinted decoding we again invoke a ratio threshold test, but in this
\begin_inset Formula $r_{2}$ \begin_inset Formula $r_{2}$
\end_inset \end_inset
can be a more relaxed limit than the can be a more relaxed limit than that used in the FT algorithm.
\begin_inset Formula $r_{1}$ For the limited subset of messages suggested by operator experience to
\end_inset
used in the FT algorithm.
For the limited subset of messages that operator experience suggests to
be likely, hinted decodes can be obtained at lower signal levels than required be likely, hinted decodes can be obtained at lower signal levels than required
for those obtained from the full universe of for the full universe of
\begin_inset Formula $2^{72}$ \begin_inset Formula $2^{72}$
\end_inset \end_inset
@ -1511,9 +1517,9 @@ reference "sec:Appendix:SNR"
\end_inset \end_inset
. .
Examples of both presentations are included in the following discussion, Examples of both types of plot are included in the following discussion,
where we describe simulations carried out to compare performance of FT where we describe simulations carried out to compare performance of FT
with other algorithms, and with theoretical expectations. with other algorithms and with theoretical expectations.
We have also used simulations to establish suitable default values for We have also used simulations to establish suitable default values for
the acceptance parameters the acceptance parameters
\begin_inset Formula $X_{0},$ \begin_inset Formula $X_{0},$
@ -1599,7 +1605,7 @@ As expected, the soft-decision algorithms, FT and KV, are about 2 dB better
\begin_inset Formula $T=10^{5}$ \begin_inset Formula $T=10^{5}$
\end_inset \end_inset
is small enough to be practical on most of today's home computers. is small enough to be practical on today's home computers.
\end_layout \end_layout
@ -1631,9 +1637,17 @@ Word error rates as a function of
\end_inset \end_inset
the signal-to-noise ratio per information bit. the signal-to-noise ratio per information bit.
Theory: theoretical prediction for the hard-decision BM decoder. The curve labeled
The remaining curves represent simulation results on an AWGN channel for \begin_inset Quotes eld
the BM, KV, and FT decoders. \end_inset
Theory
\begin_inset Quotes erd
\end_inset
shows a theoretical prediction for the hard-decision BM decoder.
Remaining curves represent simulation results on an AWGN channel for the
BM, KV, and FT decoders.
The KV algorithm was executed with complexity coefficient The KV algorithm was executed with complexity coefficient
\begin_inset Formula $\lambda=15$ \begin_inset Formula $\lambda=15$
\end_inset \end_inset
@ -1643,7 +1657,7 @@ Word error rates as a function of
WSJT WSJT
\emph default \emph default
programs. programs.
The FT alrithm was run with timeout setting The FT algorithm used timeout setting
\begin_inset Formula $T=10^{5}.$ \begin_inset Formula $T=10^{5}.$
\end_inset \end_inset
@ -1743,18 +1757,18 @@ name "fig:WER2"
\end_inset \end_inset
Percent of JT65 messages copied as a function of SNR in 2500 Hz bandwidth. Percent of JT65 messages copied as a function of SNR in 2500 Hz bandwidth.
Solid lines with filled circles are results from the FT decoder; numbers Numbers adjacent to curves specify values of timeout parameter
adjacent to the curves specify values of the timeout parameter \begin_inset Formula $T$
\begin_inset Formula $T.$
\end_inset \end_inset
The dotted line with open squares is the KV decoder with complexity coefficient for the FT decoder.
Open circles and dotted line show results for the KV decoder with complexity
coefficient
\begin_inset Formula $\lambda=15$ \begin_inset Formula $\lambda=15$
\end_inset \end_inset
. .
Results from the BM algorithm are shown with a dashed line and crosses. Results for the BM algorithm are plotted with crosses and dashed line.
\end_layout \end_layout
\end_inset \end_inset
@ -1768,12 +1782,12 @@ Percent of JT65 messages copied as a function of SNR in 2500 Hz bandwidth.
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
Timeout parameter Parameter
\begin_inset Formula $T$ \begin_inset Formula $T$
\end_inset \end_inset
is the maximum number of symbol-erasure trials allowed for a particular in the FT algorithm is the maximum number of symbol-erasure trials allowed
attempt at decoding a received word. for a particular attempt at decoding a received word.
Most successful decodes take only a small fraction of the maximum allowed Most successful decodes take only a small fraction of the maximum allowed
number of trials. number of trials.
Figure Figure
@ -1784,18 +1798,20 @@ reference "fig:N_vs_X"
\end_inset \end_inset
shows the number of stochastic erasure trials required to find the correct shows the number of stochastic erasure trials required to find the correct
codeword vs. codeword as a function of
the number of hard-decision errors in the received word, for a run with \begin_inset Formula $X,$
1000 simulated transmissions at \end_inset
the number of hard-decision errors in the received word.
This run used 1000 simulated transmissions at
\begin_inset Formula $\mathrm{SNR}=-24$ \begin_inset Formula $\mathrm{SNR}=-24$
\end_inset \end_inset
dB, just slightly above the decoding threshold. dB, just slightly above the decoding threshold, and the timeout parameter
The timeout parameter was was
\begin_inset Formula $T=10^{5}$ \begin_inset Formula $T=10^{5}.$
\end_inset \end_inset
for this run.
No points are shown for No points are shown for
\begin_inset Formula $X\le25$ \begin_inset Formula $X\le25$
\end_inset \end_inset
@ -1808,7 +1824,7 @@ reference "fig:N_vs_X"
\end_inset \end_inset
shows that the FT algorithm decoded received words with as many as shows that the FT algorithm decodes received words with as many as
\begin_inset Formula $X=43$ \begin_inset Formula $X=43$
\end_inset \end_inset
@ -1910,8 +1926,18 @@ reference "fig:Psuccess"
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
(*** A little more description is needed here, along with new data for the It is interesting to note that while Rayleigh fading severely degrades the
DS curves.***) success rate of the BM decoder, the penalties are much smaller with both
FT and hinted decoding.
Simulated Doppler spreads of 0.2 Hz actually increased the FT and DS decoding
rates slightly at SNRs close to the decosing threshold, presumably because
with the low-rate JT65 code signal peaks can be enough to produce good
copy.
\end_layout
\begin_layout Standard
(*** New data will be used for the DS curves.
***)
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
@ -1955,8 +1981,16 @@ Deep Search
) algorithm. ) algorithm.
Numbers adjacent to the curves are the simulated Doppler spreads in Hz. Numbers adjacent to the curves are the simulated Doppler spreads in Hz.
The curve labeled Sync illustrates the dependence of proper time and frequency The curve labeled
synchronization in the decoder presently implemented in \begin_inset Quotes eld
\end_inset
Sync
\begin_inset Quotes erd
\end_inset
illustrates the rate of correct time and frequency synchronization in the
decoder presently implemented in program
\emph on \emph on
WSJT-X WSJT-X
\emph default \emph default
@ -1982,6 +2016,55 @@ Summary
Still to come ... Still to come ...
\end_layout \end_layout
\begin_layout Standard
Possible ideas:
\end_layout
\begin_layout Standard
Tie it in to
\emph on
WSJT-X
\emph default
and
\emph on
MAP65
\emph default
.
\end_layout
\begin_layout Standard
Mention two-pass decoding.
\end_layout
\begin_layout Standard
Experience with FT on crowded HF bands.
\end_layout
\begin_layout Standard
Maybe one screen shot, or partial screen shot of the
\begin_inset Quotes eld
\end_inset
Band Activity
\begin_inset Quotes erd
\end_inset
window?
\end_layout
\begin_layout Standard
Some EME results needed!
\end_layout
\begin_layout Standard
Something about the code repository and how to build
\emph on
WSJT-X
\emph default
.
\end_layout
\begin_layout Bibliography \begin_layout Bibliography
\begin_inset CommandInset bibitem \begin_inset CommandInset bibitem
LatexCommand bibitem LatexCommand bibitem
@ -1992,9 +2075,11 @@ key "kv2001"
“Algebraic soft-decision decoding of Reed-Solomon codes,” R. “Algebraic soft-decision decoding of Reed-Solomon codes,” R.
Köetter and A. Köetter and A.
Vardy, IEEE Trans. Vardy,
Inform. \emph on
Theory, Vol. IEEE Transactions on Information Theory
\emph default
, Vol.
49, Nov. 49, Nov.
2003. 2003.
\end_layout \end_layout
@ -2003,13 +2088,32 @@ key "kv2001"
\begin_inset CommandInset bibitem \begin_inset CommandInset bibitem
LatexCommand bibitem LatexCommand bibitem
label "2" label "2"
key "wsjt"
\end_inset
\emph on
WSJT Home Page
\emph default
: http://www.physics.princeton.edu/pulsar/K1JT/.
\end_layout
\begin_layout Bibliography
\begin_inset CommandInset bibitem
LatexCommand bibitem
label "3"
key "lhmg2010" key "lhmg2010"
\end_inset \end_inset
"Stochastic Chase Decoding of Reed-Solomon Codes", Camille Leroux, Saied "Stochastic Chase Decoding of Reed-Solomon Codes", Camille Leroux, Saied
Hemati, Shie Mannor, Warren J. Hemati, Shie Mannor, Warren J.
Gross, IEEE Communications Letters, Vol. Gross,
\emph on
IEEE Communications Letters
\emph default
, Vol.
14, No. 14, No.
9, September 2010. 9, September 2010.
\end_layout \end_layout
@ -2017,7 +2121,7 @@ key "lhmg2010"
\begin_layout Bibliography \begin_layout Bibliography
\begin_inset CommandInset bibitem \begin_inset CommandInset bibitem
LatexCommand bibitem LatexCommand bibitem
label "3" label "4"
key "lk2008" key "lk2008"
\end_inset \end_inset
@ -2026,7 +2130,9 @@ key "lk2008"
Decoding," Soo-Woong Lee and B. Decoding," Soo-Woong Lee and B.
V. V.
K. K.
Vijaya Kumar, IEEE Vijaya Kumar,
\emph on
IEEE
\begin_inset Quotes eld \begin_inset Quotes eld
\end_inset \end_inset
@ -2034,25 +2140,31 @@ GLOBECOM
\begin_inset Quotes erd \begin_inset Quotes erd
\end_inset \end_inset
2008 proceedings. 2008 proceedings
\end_layout \emph default
.
\begin_layout Bibliography
\begin_inset CommandInset bibitem
LatexCommand bibitem
label "4"
key "lc2004"
\end_inset
Error Control Coding, 2nd edition, Shu Lin and Daniel J.
Costello, Pearson-Prentice Hall, 2004.
\end_layout \end_layout
\begin_layout Bibliography \begin_layout Bibliography
\begin_inset CommandInset bibitem \begin_inset CommandInset bibitem
LatexCommand bibitem LatexCommand bibitem
label "5" label "5"
key "lc2004"
\end_inset
\emph on
Error Control Coding, 2nd Edition
\emph default
, Shu Lin and Daniel J.
Costello, Pearson-Prentice Hall, 2004.
\end_layout
\begin_layout Bibliography
\begin_inset CommandInset bibitem
LatexCommand bibitem
label "6"
key "ls2009" key "ls2009"
\end_inset \end_inset
@ -2066,7 +2178,11 @@ Stochastic Erasure-Only List Decoding Algorithms for Reed-Solomon Codes,
\end_inset \end_inset
Chang-Ming Lee and Yu T. Chang-Ming Lee and Yu T.
Su, IEEE Signal Processing Letters, Vol. Su,
\emph on
IEEE Signal Processing Letters,
\emph default
Vol.
16, No. 16, No.
8, August 2009. 8, August 2009.
\end_layout \end_layout
@ -2074,12 +2190,12 @@ Stochastic Erasure-Only List Decoding Algorithms for Reed-Solomon Codes,
\begin_layout Bibliography \begin_layout Bibliography
\begin_inset CommandInset bibitem \begin_inset CommandInset bibitem
LatexCommand bibitem LatexCommand bibitem
label "6" label "7"
key "karn" key "karn"
\end_inset \end_inset
Berlekamp-Massey decoder written by Phil Karn, http://www.ka9q.net/code/fec/ Berlekamp-Massey decoder written by Phil Karn, KA9Q: http://www.ka9q.net/code/fec/
\end_layout \end_layout
\begin_layout Section \begin_layout Section
@ -2202,9 +2318,9 @@ reference "eq:Eb_Es"
: :
\begin_inset Formula \begin_inset Formula
\[ \begin{equation}
\mathrm{SNR}_{2500}=1.23\times10^{-3}\frac{E_{b}}{N_{o}}. \mathrm{SNR}_{2500}=1.23\times10^{-3}\frac{E_{b}}{N_{o}}.\label{eq:SNR2500}
\] \end{equation}
\end_inset \end_inset
@ -2213,9 +2329,9 @@ If all quantities are expressed in dB, then:
\begin_layout Standard \begin_layout Standard
\begin_inset Formula \begin_inset Formula
\[ \begin{equation}
\mathrm{SNR}_{2500}=(E_{b}/N_{o})_{\mathrm{dB}}-29.1\,\mathrm{dB}. \mathrm{SNR}_{2500}=(E_{b}/N_{o})_{\mathrm{dB}}-29.1\,\mathrm{dB}=(E_{s}/N_{0})_{\mathrm{dB}}-29.7\,\mathrm{dB}.\label{eq:SNR_all_types}
\] \end{equation}
\end_inset \end_inset