diff --git a/lib/sfrsd2/sfrsd_paper/sfrsd.lyx b/lib/sfrsd2/sfrsd_paper/sfrsd.lyx index f38f390a4..f75b22dc2 100644 --- a/lib/sfrsd2/sfrsd_paper/sfrsd.lyx +++ b/lib/sfrsd2/sfrsd_paper/sfrsd.lyx @@ -89,16 +89,16 @@ The JT65 mode has revolutionized amateur-radio weak-signal communication by enabling amateur radio operators with small antennas and relatively low-power transmitters to communicate over propagation paths not usable with traditional technologies. - A major reason for the success and popularity of JT65 is its use of strong - error-correction coding: a short block-length, low-rate, Reed-Solomon code + A major reason for the success and popularity of JT65 is its use of a strong + error-correction code: a short block-length, low-rate Reed-Solomon code based on a 64-symbol alphabet. Since 2004, most JT65 decoders have used the patented Koetter-Vardy (KV) - algebraic soft-decision decoder. - The KV decoder is implemented in a closed-source program licensed to K1JT - for use in amateur radio applications. + algebraic soft-decision decoder, licensed to K1JT and implemented in a + closed-source program for use in amateur radio applications. We describe here a new open-source alternative called the FT algotithm. - It is conceptually simple, is built around the well-known Berlekamp-Massey - errors-and-erasures algorithm, and perform at least as well as the KV decoder. + It is conceptually simple, built around the well-known Berlekamp-Massey + errors-and-erasures algorithm, and performs at least as well as the KV + decoder. \end_layout \begin_layout Section @@ -106,32 +106,32 @@ Introduction \end_layout \begin_layout Standard -JT65 message frames consist of a short, compressed message encoded for transmiss -ion with a Reed-Solomon code. - Reed-Solomon codes are block codes; as such they are characterized by the - length of their codewords, +JT65 message frames consist of a short compressed message encoded for transmissi +on with a Reed-Solomon code. + Reed-Solomon codes are block codes characterized by \begin_inset Formula $n$ \end_inset -, the number of message symbols conveyed by the codeword, +, the length of their codewords, \begin_inset Formula $k$ \end_inset -, and the number of possible values for each symbol in the codewords. - The codeword length and the number of message symbols are specified as - a tuple in the form +, the number of message symbols conveyed by the codeword, and the number + of possible values for each symbol in the codewords. + The codeword length and the number of message symbols are specified using + the notation \begin_inset Formula $(n,k)$ \end_inset . JT65 uses a (63,12) Reed-Solomon code with 64 possible values for each symbol. - Each symbol represents + Each of the 12 message symbols represents \begin_inset Formula $\log_{2}64=6$ \end_inset message bits. - The source-encoded messages conveyed by a 63-symbol JT65 frame consist + The source-encoded messages conveyed by a 63-symbol JT65 frame thus consist of 72 bits. The JT65 code is systematic, which means that the 12 message symbols are embedded in the codeword without modification and another 51 parity symbols @@ -191,30 +191,31 @@ For the JT65 code, \begin_inset Formula $t=25$ \end_inset -: it is always possible to efficiently decode a received word having no - more than 25 symbol errors. +, so it is always possible to efficiently decode a received word having + no more than 25 symbol errors. Any one of several well-known algebraic algorithms, such as the widely used Berlekamp-Massey (BM) algorithm, can carry out the decoding. Two steps are ncessarily involved in this process, namely \end_layout \begin_layout Enumerate -determine which symbols were received incorrectly +Determine which symbols were received incorrectly. + \end_layout \begin_layout Enumerate -determine the correct value of the incorrect symbols +Find the correct value of the incorrect symbols. \end_layout \begin_layout Standard If we somehow know that certain symbols are incorrect, this information - can be used to reduce the work in step 1 and allow step 2 to correct more - than + can be used to reduce the work involved in step 1 and allow step 2 to correct + more than \begin_inset Formula $t$ \end_inset errors. - In the unlikely event that the location of every error is known, and if + In the unlikely event that the location of every error is known and if no correct symbols are accidentally labeled as errors, the BM algorithm can correct up to \begin_inset Formula $d$ @@ -275,15 +276,7 @@ errors-only \begin_inset Quotes erd \end_inset - decoder and can correct up to -\begin_inset Formula $t$ -\end_inset - - errors ( -\begin_inset Formula $t$ -\end_inset - -=25 for JT65). + decoder. If \begin_inset Formula $0