mirror of
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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
This commit is contained in:
Joe Taylor
parent
0e1c1a9d75
commit
51bad2584e
@ -139,15 +139,21 @@ WSJT-X
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\emph default
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, widely used for amateur weak-signal communication with JT65 and other
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specialized digital modes.
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The program is freely available and licensed under the GNU General Public
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License.
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The program is freely available
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\begin_inset CommandInset citation
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LatexCommand cite
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key "wsjt"
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\end_inset
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and licensed under the GNU General Public License.
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\end_layout
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\begin_layout Standard
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The JT65 protocol specifies transmissions that normally start one second
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into a UTC minute and last for 46.8 seconds.
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Receiving software therefore has up to several seconds to decode a message,
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before the operator sends a reply at the start of the next minute.
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Receiving software therefore has up to several seconds to decode a message
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before the start of the next minute, when the operator sends a reply.
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With today's personal computers, this relatively long time available for
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decoding a short message encourages experimentation with decoders of high
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computational complexity.
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@ -158,7 +164,7 @@ The JT65 protocol specifies transmissions that normally start one second
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properties, not least of which is its conceptual simplicity.
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Decoding performance and complexity scale in a convenient way, providing
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steadily increasing soft-decision decoding gain as a tunable computational
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complexity parameter is increased over more than 5 orders of magnitude.
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complexity parameter is increased over more than five orders of magnitude.
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Appreciable gain is available from our decoder even on very simple (and
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relatively slow) computers.
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On the other hand, because the algorithm benefits from a large number of
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@ -405,7 +411,7 @@ probabilistic
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\begin_inset CommandInset citation
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LatexCommand cite
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after "Chapter 10"
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key "key-1"
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key "lc2004"
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\end_inset
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@ -1224,16 +1230,20 @@ Calculate the hard-decision Hamming distance
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\begin_inset Formula $X$
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\end_inset
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between the candidate codeword and the received symbols, the corresponding
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soft distance
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between the candidate codeword and the received symbols, along with the
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corresponding soft distance
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\begin_inset Formula $d_{s}$
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\end_inset
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, and the quality metric
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and the quality metric
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\begin_inset Formula $u$
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\end_inset
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.
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\end_layout
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\begin_layout Enumerate
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If
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\begin_inset Formula $u$
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\end_inset
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@ -1242,8 +1252,8 @@ Calculate the hard-decision Hamming distance
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\begin_inset Formula $u_{1}$
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\end_inset
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as
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\begin_inset Formula $u_{2}$
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by setting
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\begin_inset Formula $u_{2}=u_{1}$
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\end_inset
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and then set
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@ -1262,7 +1272,7 @@ If
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\begin_inset Formula $d_{s}<d_{0}$
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\end_inset
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, go to step 10.
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, go to step 11.
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\end_layout
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\begin_layout Enumerate
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@ -1287,7 +1297,7 @@ If
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\begin_inset Formula $r<r_{1},$
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\end_inset
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go to step 10.
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go to step 11.
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\end_layout
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\begin_layout Enumerate
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@ -1382,18 +1392,18 @@ The FT algorithm is completely general: with equal sensitivity it recovers
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much
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\emph default
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smaller list of messages (say, a few thousand messages or less) that we
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can guess may be among the most likely ones to be received.
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can guess might be among the most likely ones to be received.
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One such situation exists when making short ham-radio contacts that exchange
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minimal information including callsigns, signal reports, perhaps Maidenhead
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locators, and acknowledgments.
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On the EME path or on a VHF or UHF band with limited geographical coverage,
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On the EME path or a VHF or UHF band with limited geographical coverage,
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the most likely received messages often originate from callsigns that have
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been decoded before.
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Saving a list of previously decoded callsigns and associated locators makes
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it easy to generate lists of hypothetical messages and their corresponding
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codewords at very little computational expense.
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The resulting candidate codewords can be tested in the same way as those
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generated by the probabilistic method described in Setcion
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generated by the probabilistic method described in Section
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\begin_inset CommandInset ref
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LatexCommand ref
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reference "sec:The-decoding-algorithm"
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@ -1456,14 +1466,10 @@ For hinted decoding we again invoke a ratio threshold test, but in this
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\begin_inset Formula $r_{2}$
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\end_inset
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can be a more relaxed limit than the
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\begin_inset Formula $r_{1}$
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\end_inset
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used in the FT algorithm.
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For the limited subset of messages that operator experience suggests to
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can be a more relaxed limit than that used in the FT algorithm.
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For the limited subset of messages suggested by operator experience to
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be likely, hinted decodes can be obtained at lower signal levels than required
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for those obtained from the full universe of
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for the full universe of
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\begin_inset Formula $2^{72}$
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\end_inset
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@ -1511,9 +1517,9 @@ reference "sec:Appendix:SNR"
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\end_inset
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.
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Examples of both presentations are included in the following discussion,
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Examples of both types of plot are included in the following discussion,
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where we describe simulations carried out to compare performance of FT
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with other algorithms, and with theoretical expectations.
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with other algorithms and with theoretical expectations.
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We have also used simulations to establish suitable default values for
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the acceptance parameters
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\begin_inset Formula $X_{0},$
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@ -1599,7 +1605,7 @@ As expected, the soft-decision algorithms, FT and KV, are about 2 dB better
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\begin_inset Formula $T=10^{5}$
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\end_inset
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is small enough to be practical on most of today's home computers.
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is small enough to be practical on today's home computers.
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\end_layout
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@ -1631,9 +1637,17 @@ Word error rates as a function of
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\end_inset
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the signal-to-noise ratio per information bit.
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Theory: theoretical prediction for the hard-decision BM decoder.
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The remaining curves represent simulation results on an AWGN channel for
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the BM, KV, and FT decoders.
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The curve labeled
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\begin_inset Quotes eld
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\end_inset
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Theory
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\begin_inset Quotes erd
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\end_inset
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shows a theoretical prediction for the hard-decision BM decoder.
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Remaining curves represent simulation results on an AWGN channel for the
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BM, KV, and FT decoders.
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The KV algorithm was executed with complexity coefficient
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\begin_inset Formula $\lambda=15$
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\end_inset
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@ -1643,7 +1657,7 @@ Word error rates as a function of
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WSJT
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\emph default
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programs.
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The FT alrithm was run with timeout setting
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The FT algorithm used timeout setting
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\begin_inset Formula $T=10^{5}.$
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\end_inset
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@ -1743,18 +1757,18 @@ name "fig:WER2"
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\end_inset
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Percent of JT65 messages copied as a function of SNR in 2500 Hz bandwidth.
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Solid lines with filled circles are results from the FT decoder; numbers
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adjacent to the curves specify values of the timeout parameter
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\begin_inset Formula $T.$
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Numbers adjacent to curves specify values of timeout parameter
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\begin_inset Formula $T$
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\end_inset
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The dotted line with open squares is the KV decoder with complexity coefficient
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for the FT decoder.
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Open circles and dotted line show results for the KV decoder with complexity
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coefficient
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\begin_inset Formula $\lambda=15$
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\end_inset
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.
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Results from the BM algorithm are shown with a dashed line and crosses.
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Results for the BM algorithm are plotted with crosses and dashed line.
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\end_layout
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\end_inset
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@ -1768,12 +1782,12 @@ Percent of JT65 messages copied as a function of SNR in 2500 Hz bandwidth.
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\end_layout
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\begin_layout Standard
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Timeout parameter
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Parameter
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\begin_inset Formula $T$
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\end_inset
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is the maximum number of symbol-erasure trials allowed for a particular
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attempt at decoding a received word.
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in the FT algorithm is the maximum number of symbol-erasure trials allowed
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for a particular attempt at decoding a received word.
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Most successful decodes take only a small fraction of the maximum allowed
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number of trials.
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Figure
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@ -1784,18 +1798,20 @@ reference "fig:N_vs_X"
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\end_inset
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shows the number of stochastic erasure trials required to find the correct
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codeword vs.
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the number of hard-decision errors in the received word, for a run with
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1000 simulated transmissions at
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codeword as a function of
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\begin_inset Formula $X,$
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\end_inset
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the number of hard-decision errors in the received word.
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This run used 1000 simulated transmissions at
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\begin_inset Formula $\mathrm{SNR}=-24$
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\end_inset
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dB, just slightly above the decoding threshold.
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The timeout parameter was
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\begin_inset Formula $T=10^{5}$
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dB, just slightly above the decoding threshold, and the timeout parameter
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was
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\begin_inset Formula $T=10^{5}.$
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\end_inset
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for this run.
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No points are shown for
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\begin_inset Formula $X\le25$
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\end_inset
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@ -1808,7 +1824,7 @@ reference "fig:N_vs_X"
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\end_inset
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shows that the FT algorithm decoded received words with as many as
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shows that the FT algorithm decodes received words with as many as
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\begin_inset Formula $X=43$
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\end_inset
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@ -1910,8 +1926,18 @@ reference "fig:Psuccess"
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\end_layout
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\begin_layout Standard
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(*** A little more description is needed here, along with new data for the
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DS curves.***)
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It is interesting to note that while Rayleigh fading severely degrades the
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success rate of the BM decoder, the penalties are much smaller with both
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FT and hinted decoding.
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Simulated Doppler spreads of 0.2 Hz actually increased the FT and DS decoding
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rates slightly at SNRs close to the decosing threshold, presumably because
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with the low-rate JT65 code signal peaks can be enough to produce good
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copy.
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\end_layout
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\begin_layout Standard
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(*** New data will be used for the DS curves.
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***)
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\end_layout
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\begin_layout Standard
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@ -1955,8 +1981,16 @@ Deep Search
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) algorithm.
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Numbers adjacent to the curves are the simulated Doppler spreads in Hz.
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The curve labeled Sync illustrates the dependence of proper time and frequency
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synchronization in the decoder presently implemented in
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The curve labeled
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\begin_inset Quotes eld
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\end_inset
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Sync
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\begin_inset Quotes erd
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\end_inset
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illustrates the rate of correct time and frequency synchronization in the
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decoder presently implemented in program
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\emph on
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WSJT-X
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\emph default
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@ -1982,6 +2016,55 @@ Summary
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Still to come ...
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\end_layout
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\begin_layout Standard
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Possible ideas:
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\end_layout
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\begin_layout Standard
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Tie it in to
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\emph on
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WSJT-X
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\emph default
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and
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\emph on
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MAP65
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\emph default
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.
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\end_layout
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\begin_layout Standard
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Mention two-pass decoding.
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\end_layout
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\begin_layout Standard
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Experience with FT on crowded HF bands.
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\end_layout
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\begin_layout Standard
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Maybe one screen shot, or partial screen shot of the
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\begin_inset Quotes eld
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\end_inset
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Band Activity
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\begin_inset Quotes erd
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\end_inset
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window?
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\end_layout
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\begin_layout Standard
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Some EME results needed!
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\end_layout
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\begin_layout Standard
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Something about the code repository and how to build
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\emph on
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WSJT-X
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\emph default
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.
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\end_layout
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\begin_layout Bibliography
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\begin_inset CommandInset bibitem
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LatexCommand bibitem
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@ -1992,9 +2075,11 @@ key "kv2001"
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“Algebraic soft-decision decoding of Reed-Solomon codes,” R.
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Köetter and A.
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Vardy, IEEE Trans.
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Inform.
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Theory, Vol.
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Vardy,
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\emph on
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IEEE Transactions on Information Theory
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\emph default
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, Vol.
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49, Nov.
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2003.
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\end_layout
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@ -2003,13 +2088,32 @@ key "kv2001"
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\begin_inset CommandInset bibitem
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LatexCommand bibitem
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label "2"
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key "wsjt"
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\end_inset
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\emph on
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WSJT Home Page
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\emph default
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: http://www.physics.princeton.edu/pulsar/K1JT/.
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\end_layout
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\begin_layout Bibliography
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\begin_inset CommandInset bibitem
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LatexCommand bibitem
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label "3"
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key "lhmg2010"
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\end_inset
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"Stochastic Chase Decoding of Reed-Solomon Codes", Camille Leroux, Saied
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Hemati, Shie Mannor, Warren J.
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Gross, IEEE Communications Letters, Vol.
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Gross,
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\emph on
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IEEE Communications Letters
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\emph default
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, Vol.
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14, No.
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9, September 2010.
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\end_layout
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@ -2017,7 +2121,7 @@ key "lhmg2010"
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\begin_layout Bibliography
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\begin_inset CommandInset bibitem
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LatexCommand bibitem
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label "3"
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label "4"
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key "lk2008"
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\end_inset
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@ -2026,7 +2130,9 @@ key "lk2008"
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Decoding," Soo-Woong Lee and B.
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V.
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K.
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Vijaya Kumar, IEEE
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Vijaya Kumar,
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\emph on
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IEEE
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\begin_inset Quotes eld
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\end_inset
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@ -2034,25 +2140,31 @@ GLOBECOM
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\begin_inset Quotes erd
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\end_inset
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2008 proceedings.
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\end_layout
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|
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\begin_layout Bibliography
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\begin_inset CommandInset bibitem
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LatexCommand bibitem
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label "4"
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key "lc2004"
|
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|
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\end_inset
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|
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Error Control Coding, 2nd edition, Shu Lin and Daniel J.
|
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Costello, Pearson-Prentice Hall, 2004.
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2008 proceedings
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\emph default
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.
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\end_layout
|
||||
|
||||
\begin_layout Bibliography
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\begin_inset CommandInset bibitem
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LatexCommand bibitem
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label "5"
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key "lc2004"
|
||||
|
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\end_inset
|
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|
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|
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\emph on
|
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Error Control Coding, 2nd Edition
|
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\emph default
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||||
, Shu Lin and Daniel J.
|
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Costello, Pearson-Prentice Hall, 2004.
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\end_layout
|
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|
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\begin_layout Bibliography
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\begin_inset CommandInset bibitem
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LatexCommand bibitem
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label "6"
|
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key "ls2009"
|
||||
|
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\end_inset
|
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@ -2066,7 +2178,11 @@ Stochastic Erasure-Only List Decoding Algorithms for Reed-Solomon Codes,
|
||||
\end_inset
|
||||
|
||||
Chang-Ming Lee and Yu T.
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Su, IEEE Signal Processing Letters, Vol.
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||||
Su,
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||||
\emph on
|
||||
IEEE Signal Processing Letters,
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||||
\emph default
|
||||
Vol.
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||||
16, No.
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||||
8, August 2009.
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||||
\end_layout
|
||||
@ -2074,12 +2190,12 @@ Stochastic Erasure-Only List Decoding Algorithms for Reed-Solomon Codes,
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\begin_layout Bibliography
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\begin_inset CommandInset bibitem
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LatexCommand bibitem
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label "6"
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label "7"
|
||||
key "karn"
|
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|
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\end_inset
|
||||
|
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Berlekamp-Massey decoder written by Phil Karn, http://www.ka9q.net/code/fec/
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Berlekamp-Massey decoder written by Phil Karn, KA9Q: http://www.ka9q.net/code/fec/
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\end_layout
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|
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\begin_layout Section
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@ -2202,9 +2318,9 @@ reference "eq:Eb_Es"
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|
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:
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||||
\begin_inset Formula
|
||||
\[
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||||
\mathrm{SNR}_{2500}=1.23\times10^{-3}\frac{E_{b}}{N_{o}}.
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||||
\]
|
||||
\begin{equation}
|
||||
\mathrm{SNR}_{2500}=1.23\times10^{-3}\frac{E_{b}}{N_{o}}.\label{eq:SNR2500}
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||||
\end{equation}
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\end_inset
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@ -2213,9 +2329,9 @@ If all quantities are expressed in dB, then:
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||||
|
||||
\begin_layout Standard
|
||||
\begin_inset Formula
|
||||
\[
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||||
\mathrm{SNR}_{2500}=(E_{b}/N_{o})_{\mathrm{dB}}-29.1\,\mathrm{dB}.
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||||
\]
|
||||
\begin{equation}
|
||||
\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}
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\end{equation}
|
||||
|
||||
\end_inset
|
||||
|
||||
|
||||
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