Hi,
With reading more about FEC systems and coding for the header of c2-gmsk modem; I have also been thinking about other (better) FEC systems for the voice-part of the stream. One of the things I like to implement is lower baudrate modems; starting with 3600 baud and later 2400 baud. For 3600 baud, we still have a FEC of 1/2 (1400 bps codec2 * 2 = 2800 bps) but already limit the RF spectrum to around 6 Khz. I would then also implement this for the 4800 baud modem (instead of the current 1/3 "best-out-of-three" system now) so to get some free space for sending data alongside voice. Somebody already send me code for 1/2 FEC gollay. For 2400 baud, I need a FEC of 2/3 (1400 * 1.5 = 2100 bps) which means I need to do some more reading on how to implement punctuated coding. So, is there here somebody who has more expertise in FEC who can answer this: - if we stick to block encoding, what is the best coding system now out there. Conditions are: -> open source code available -> free of patents. - standard golay is based on a 12 bits (which are concerted to 23 or 24 bits). The standard codec2 voiceframe at 1400 bps is 56 bits (for 40 ms of voice). This does not fit very well. Does there exist versions of golay using (say) 14 bits instead of 12 bits packets? Are there other block encoding systems that can be used at 14 bits. If not, I need to code my way around this but it would probably result in additional latency. - there was still the idea to protect only parts of the voice-frame as certain information is more inportant then other. Is this idea still valid? What bit would be concidered "important" and which are not. perhaps this can be used to tune the FEC block-size for that. Cheerio! Kr. Bonne. ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
