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Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
"Mike Gathergood (G4KFK)" wrote in message oups.com... Radium wrote: What is FEC? Forward Error Correction. Google it :-) Just to add to Mike's comment, FEC works by send the same message several times- in simple terms, in the hope that one with get through correctly. It is simple to implement, your recieving system just needs to be able to identify a correct message and use it, not spot a bad message and initiate either a request for resend or applly some sort of correction method (assuming there is error correcting code in the message). -- 73 Brian www.g8osn.org.uk |
#2
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Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
Brian Reay wrote: "Mike Gathergood (G4KFK)" wrote in message oups.com... Radium wrote: What is FEC? Forward Error Correction. Google it :-) Just to add to Mike's comment, FEC works by send the same message several times- in simple terms, in the hope that one with get through correctly. It is simple to implement, your recieving system just needs to be able to identify a correct message and use it, not spot a bad message and initiate either a request for resend or applly some sort of correction method (assuming there is error correcting code in the message). -- 73 Brian www.g8osn.org.uk These comms are in one direction, so you don't resend a packet as there is no way to make such a request. In practice, the codes have both error detection and correction capabilities, so to the degree the coding allows, the signal can be corrected with the bits that were received. Note nobody mentioned a modulation scheme for sending this data. As a bit of trivia, Reed Solomon encoding was invented without a way to decode it. That's what you get when you let mathematicians run wild. For absolutely nothing of any value other than bragging rights, name the guy who invented the decoding scheme for Reed Solomon. [Hopefully this isn't wikied someplace. I did one class in grad school on error detection and correction, and it was a pain in the ass if you get into the theory. Implementation is quite simple.] |
#4
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Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
Geoffrey S. Mendelson wrote: wrote: As a bit of trivia, Reed Solomon encoding was invented without a way to decode it. That's what you get when you let mathematicians run wild. For absolutely nothing of any value other than bragging rights, name the guy who invented the decoding scheme for Reed Solomon. [Hopefully this isn't wikied someplace. I did one class in grad school on error detection and correction, and it was a pain in the ass if you get into the theory. Implementation is quite simple.] It makes sense. The encoding software had to be ready to put into a probe before the launch date. Once it was up it could not be changed. Decoding software was another matter. Since they had years, maybe even decades to decode the data, and it did not have to be real time, they could continue to work on it. All they had to do is not loose the tapes. :-( Geoff. -- Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM IL Voice: (07)-7424-1667 Fax ONLY: 972-2-648-1443 U.S. Voice: 1-215-821-1838 Visit my 'blog at http://geoffstechno.livejournal.com/ I'm not sure what you mean by the "probe". The deal with Reed Solomon is it is a non-binary code, which was a big deal at the time. The buzzword is Galois mathematics. There wasn't any hardware that could handle the code when it was invented. |
#5
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Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
Brian Reay wrote: Just to add to Mike's comment, FEC works by send the same message several times- in simple terms, in the hope that one with get through correctly. It is simple to implement, your recieving system just needs to be able to identify a correct message and use it, not spot a bad message and initiate either a request for resend or applly some sort of correction method (assuming there is error correcting code in the message). FEC is generally used in applications where you don't have time to request a retransmission of an errored packet, and/or where the transmission path is simplex, and/or where there are multiplex receivers for a single transmitter. If you have the luxuries of time and a full-duplex point-to-point environment, ARQ is better. Cheers Mike |
#6
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Receiving Pulse-Code Modulation on AM radio at 3 Mhz?
Brian Reay wrote:
"Mike Gathergood (G4KFK)" wrote in message oups.com... Radium wrote: What is FEC? Forward Error Correction. Google it :-) Just to add to Mike's comment, FEC works by send the same message several times- in simple terms, in the hope that one with get through correctly. You may want to read up on Viterbi, Sequential, Turbo Product Codes (TPC) and Low Density Parity Check (LDPC) forms of FEC to see how they work and see if that statement still holds true! It's truly amazing how many errors Turbo codes and LDPC codes can actually correct even with only an additional 5% of error correction coding on top of the data stream in some cases! |
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