diff --git a/lib/sfrsd2/sfrsd_paper/sfrsd.lyx b/lib/sfrsd2/sfrsd_paper/sfrsd.lyx index 3aae759c2..60a68f5e5 100644 --- a/lib/sfrsd2/sfrsd_paper/sfrsd.lyx +++ b/lib/sfrsd2/sfrsd_paper/sfrsd.lyx @@ -2,7 +2,7 @@ \lyxformat 474 \begin_document \begin_header -\textclass IEEEtran +\textclass paper \use_default_options true \maintain_unincluded_children false \language english @@ -28,7 +28,7 @@ \spacing single \use_hyperref false \papersize default -\use_geometry false +\use_geometry true \use_package amsmath 1 \use_package amssymb 1 \use_package cancel 1 @@ -52,6 +52,10 @@ \shortcut idx \color #008000 \end_index +\leftmargin 1in +\topmargin 1in +\rightmargin 1in +\bottommargin 1in \secnumdepth 3 \tocdepth 3 \paragraph_separation indent @@ -109,6 +113,10 @@ Koetter-Vardy \end_layout +\begin_layout Section +Introduction +\end_layout + \begin_layout Standard JT65 message frames consist of a short, compressed, message that is encoded for transmission using a Reed-Solomon code. @@ -216,11 +224,11 @@ A decoder, such as BM, must carry out two tasks: \end_layout \begin_layout Enumerate -figure out which symbols were received incorrectly +determine which symbols were received incorrectly \end_layout \begin_layout Enumerate -figure out the correct value of the incorrect symbols +determine the correct value of the incorrect symbols \end_layout \begin_layout Standard @@ -270,24 +278,24 @@ errors When the erasure information is imperfect, then some of the erased symbols will actually be correct, and some of the unerased symbols will be in error. If a total of -\begin_inset Formula $n_{era}$ +\begin_inset Formula $n_{e}$ \end_inset symbols are erased and the remaining unerased symbols contain -\begin_inset Formula $n_{err}$ +\begin_inset Formula $x$ \end_inset errors, then the BM algorithm can find the correct codeword as long as \begin_inset Formula \begin{equation} -n_{era}+2n_{err}\le d-1\label{eq:erasures_and_errors} +n_{e}+2x\le d-1\label{eq:erasures_and_errors} \end{equation} \end_inset If -\begin_inset Formula $n_{era}=0$ +\begin_inset Formula $n_{e}=0$ \end_inset , then the decoder is said to be an @@ -308,7 +316,7 @@ errors-only =25 for JT65). If -\begin_inset Formula $0X$ +\end_inset + +. + Correspondingly, the SFRSD algorithm works best when the probability of + erasing a symbol is somewhat larger than the probability that the symbol + is incorrect. + Empirically, it was determined that good performance of the SFRSD algorithm + is obtained when the symbol erasure probability is somewhat larger than + the prior estimate of symbol error probability. + It has been empirically determined that choosing the erasure probabilities + to be a factor of +\begin_inset Formula $1.3$ +\end_inset + + larger than the symbol error probabilities gives the best results. \end_layout \begin_layout Standard -For each received word: +The SFRSD algorithm successively tries to decode the received word. + In each iteration, an independent stochastic erasure vector is generated + based on a-priori symbol erasure probabilities. + Technically, the algorithm is a list-decoder, potentially generating a + list of candidate codewords. + Each codeword on the list is assigned a quality metric, defined to be the + soft distance between the received word and the codeword. + Among the list of candidate codewords found by this stochastic search algorithm +, only the one with the smallest soft-distance from the received word is + kept. + As with all such algorithms, a stopping criterion is necessary. + SFRSD accepts a codeword unconditionally if its soft distance is smaller + than an acceptance threshold, +\begin_inset Formula $d_{a}$ +\end_inset + +. + A timeout is employed to limit the execution time of the algorithm. + \end_layout -\begin_layout Standard -1. - Determine symbol metrics for each symbol in the received word. - The metrics are the rank {1,2,...,63} of the symbol's power percentage and - the ratio of the power percentages of the second most likely symbol and - the most likely symbol. - Denote these metrics by P1-rank and P2/P1. +\begin_layout Paragraph +Algorithm \end_layout -\begin_layout Standard -2. - Use the erasure probability for each symbol, make independent decisions - about whether or not to erase each symbol in the word. +\begin_layout Enumerate +For each symbol in the received word, find the erasure probability from + the erasure-probability matrix and the +\begin_inset Formula $\{p_{1}\textrm{-rank},p_{2}/p_{1}\}$ +\end_inset + + soft-symbol information. +\end_layout + +\begin_layout Enumerate +Make independent decisions about whether or not to erase each symbol in + the word using the symbol's erasure probability. Allow a total of up to 51 symbols to be erased. \end_layout -\begin_layout Standard -3. - Attempt errors-and-erasures decoding with the erasure vector that was determine -d in step 3. - If the decoder is successful, it returns a candidate codeword. - Go to step 5. +\begin_layout Enumerate +Attempt BM errors-and-erasures decoding with the set of erased symbols that + was determined in step 2. + If the BM decoder is successful go to step 5. \end_layout -\begin_layout Standard -4. - If decoding is not successful, go to step 2. +\begin_layout Enumerate +If decoding is not successful, go to step 2. \end_layout -\begin_layout Standard -5. - If a candidate codeword is returned by the decoder, calculate its soft - distance from the received word and save the codeword if the soft distance - is the smallest one encountered so far. - If the soft distance is smaller than threshold dthresh, delare a successful - decode and return the codeword. +\begin_layout Enumerate +Calculate the soft distance, +\begin_inset Formula $d_{s}$ +\end_inset + +, between the candidate codeword and the received word. + Set +\begin_inset Formula $d_{s,min}=d_{s}$ +\end_inset + + if the soft distance is the smallest one encountered so far. \end_layout -\begin_layout Standard -6. - If the number of trials is equal to the maximum allowed number, exit and - return the current best codeword. - Otherwise, go to 2 +\begin_layout Enumerate +If +\begin_inset Formula $d_{s,min}\le d_{a}$ +\end_inset + +, go to 8. + +\end_layout + +\begin_layout Enumerate +If the number of trials is less than the maximum allowed number, go to 2. + Otherwise, declare decoding failure and exit. +\end_layout + +\begin_layout Enumerate +A codeword with +\begin_inset Formula $d_{s}\le d_{a}$ +\end_inset + + has been found. + Declare that is successful. + Return the best codeword found so far. +\end_layout + +\begin_layout Section +Results +\end_layout + +\begin_layout Section +Summary \end_layout \begin_layout Bibliography