Re: [wsjt-devel] choosing the best CRC for short data blocks

> On Jan 25, 2018, at 10:26 PM, Paul Black via wsjt-devel > wrote: > > And when I can hear it, see it on the waterfall display and it doesn't decode Frequently caused by computer clock error, but I assume you probably already have that under control. Gary

Re: [wsjt-devel] choosing the best CRC for short data blocks

On 26/01/2018 05:26, Paul Black via wsjt-devel wrote: And when I can hear it, see it on the waterfall display and it doesn't decode, It would be good to have the option of knowing why. I would like a display showing the data received from the packet and an indication of how far it got through

Re: [wsjt-devel] choosing the best CRC for short data blocks

Thanks Mike, And when I can hear it, see it on the waterfall display and it doesn't decode, It would be good to have the option of knowing why. I would like a display showing the data received from the packet and an indication of how far it got through the error correction, decompression and

Re: [wsjt-devel] choosing the best CRC for short data blocks

If you can hear it can't you also see it on the waterfall?  The waterfall is the raw display. de Mike W9MDB On Thursday, January 25, 2018, 5:52:24 PM CST, Paul Black via wsjt-devel wrote: I am a long term WSPR user and more recently FT8. I am also

Re: [wsjt-devel] choosing the best CRC for short data blocks

I am a long term WSPR user and more recently FT8. I am also a bit of a detail obsessive (I'm doing a PhD in malware analysis). While it is great to see that I have a new WSPR detection or FT8 connection, I find myself being deeply curious about cases why I hear the signal on my radio but do

Re: [wsjt-devel] choosing the best CRC for short data blocks

> > the chance that the error pattern passes the CRC test, that's to say the > probability that an error goes undetected, is just inversely propoprtional > to 2^L where L is the CRC polynomial degree. That's why when a system uses an ECC what really matters to counterfeat > undetected errors is

Re: [wsjt-devel] choosing the best CRC for short data blocks

> They all reduce the number of incorrect decodes by about a factor of > 2^12=2048. Obviously, I have a problem with basic arithmetic. I should have said > 2^12=4096. > It looks almost the 1.6 factor Joe was speaking about :-) 73 Nico / IV3NWV

Re: [wsjt-devel] choosing the best CRC for short data blocks

Hi Steve, As it turns out, the most likely number of incorrect bits in the 87-bit > message+CRC block contained within incorrect codewords is 20. After reading Don message I was just figuring out this number for the LDPC code used by FT8 :-) What Don probably misinterpreted is that Koopman's

Re: [wsjt-devel] choosing the best CRC for short data blocks

> They all reduce the number of incorrect decodes by about a factor of > 2^12=2048. > Obviously, I have a problem with basic arithmetic. I should have said 2^12=4096. Steve k9an -- Check out the vibrant tech

Re: [wsjt-devel] choosing the best CRC for short data blocks

Thanks, all, for the information. I had not run into a situation where the "wrong code-word" distance was so high, but it absolutely makes sense, as does the 1/2048 ratio. I appreciate y'all taking the time to educate me. I'm old, but not too old to learn - yet! 73, Don AE0AG On Thu, Jan 25,

Re: [wsjt-devel] choosing the best CRC for short data blocks

Hi Don, To add to what Joe and Bill have already said, I’d like to point out that Koopman’s tables are not particularly relevant for our application. The FT8 decoder always produces a valid 174-bit codeword that satisfies all parity checks. In other words, the decoder always return a codeword

Re: [wsjt-devel] choosing the best CRC for short data blocks

Don -- One other matter... Is there a more detailed description of the various modes available to members of this list?  I am a new ham, but did waveform design and optimal detection for many years until I retired last May.   I may be able to help in some manner. For detailed descriptions

Re: [wsjt-devel] choosing the best CRC for short data blocks

Hi Don, Thanks for your message and your interest in FT8, etc. We're well aware of the tables of "good CRC polynomials" published by Koopman, though admittedly we have not always used them to best advantage. Steve Franke, K9AN, did an extensive series of tests with different CRC generators

Re: [wsjt-devel] choosing the best CRC for short data blocks

On 25/01/2018 19:23, Don Goldston wrote: Sirs, I have not delved into your software, and being old and retired I may not do so.  From the superficial descriptions of FT8 I have found, your group seems to know very well what they are doing.

[wsjt-devel] choosing the best CRC for short data blocks

Sirs, I have not delved into your software, and being old and retired I may not do so. From the superficial descriptions of FT8 I have found, your group seems to know very well what they are doing. https://users.ece.cmu.edu/~koopman/roses/dsn04/koopman04_crc_poly_embedded.pdf Here is a link