Hi Daniel, Re FEC currently I am currently trying a Golay (23,11) code which is about half rate, and can correct 3 errors out of 12 data bits. Lots of other possibilities for FEC, for those who are interested in experimenting it would be easy to adapt fec_enc.c & fec_dec.c to other codes.
One key limitation is the nature of 2.5kHz wide HF channels. Sometimes, all the data just gets wiped out for several seconds ...... not much you can do about that but fortunately speech is quite redundant. Now if you could send the data one one channel, and the FEC parity bits on another ... then we might have something. Narrower carrier spacing won't affect the tx power output. Less carriers (like reducing Nc from 14 to 4) might reduce the PAPR and hence allow greater tx power, but its hard to squeeze the data we need into 4 carriers. Thanks for the diversity links. Good to see you working on this. Cheers, David On Wed, 2013-03-06 at 08:14 -0800, Daniel Mundall wrote: > Hi Bruce/David/Barry, > > > I totally like the idea of diversity, and what really needs to happen > is actually testing some links to see how much it helps. I am going > to see about getting some antennas setup here for experimenting. > > > The receive seems like the easiest to work on, using something like > MRC (using the data from the antenna with the best SNR on a frame by > frame basis.) Doing that would insure that you had the best possible > RX between the two antennas. 2RX = ~3db, 4RX = ~6db > > > Maybe .8 wavelengths would be a good spacing? > http://www.jpier.org/PIER/pier64/02.06062401.Khaleghi.pdf > > > > > > > It also looks like something like STD (sending every other frame > through a different antenna can gain a little bit more) Might be > possible with a STDP RF switch and only one radio? Gain: ~2db > > > Bruce, thanks for the links! Very interesting. Now I just want to try > it! :) > > > David, maybe it's just me, but FEC (Reed Solomon) seems kind of > pathetic for the amount of code word vs correction ability. > I think it was something like 35% data added for 7% correction. And > going up from there data wise. But then again it might be possible to > optimize it. > > > One other thing I was thinking about, and I am sure you guys and > already talked about this in times gone by, but would it be possible > to narrow the carriers to something less than 75Hz and keep the symbol > rate the same? It would allow for more power output, right? > > > Anyways, thanks for your thoughts guys, maybe I can try a link with > one of you some time using receive diversity. :) > > > 73s > Daniel VA7DRM > > > Sent from Daniel's iPhone > image.png > > image.png > On Mar 6, 2013, at 4:33 AM, Barry White <[email protected]> > wrote: > > > > An effective fade reduction antenna is to have one vertical and one > > horizontal antenna. Due to changes in the ionosphere the signals > > can > > arrive with constantly changing polarisation. > > > > Barry VK2AAB > > > > > > David Rowe wrote: > > > Hi Daniel, > > > > > > Yes I have wondered if a separate rx with separate antenna might > > > help > > > get around fades. I imagine there needs to be a certain > > > separation > > > (certain number of wavelengths) between the antennas. > > > > > > Some other ways to get that 6dB are coding gain (if FEC can be > > > made to > > > work better) and lower Codec bit rates (if that doesn't make the > > > robustness worse). At the tx end higher average power (reducing > > > PAPR > > > issues) would also help the link budget. > > > > > > Thanks, > > > > > > David > > > > > > On Tue, 2013-03-05 at 20:30 -0800, Daniel Mundall wrote: > > > > David, > > > > Amazing to see all the work that has gone into getting it where > > > > it is. > > > > Thinking about that 6db you are looking for, wouldn't it be > > > > possible > > > > to get that at some point with something like SoftRock with dual > > > > tx-rx > > > > chains (MIMO)? It may not be practical for the lower > > > > bands(antenna > > > > size), but when possible it may be one of the easiest ways to > > > > get that > > > > link budget and possibly even lower the tx power. > > > > I found some of the ideas here interesting > > > > http://www.sequans.com/pdf/SequansUplinkMIMOWP0608_v2.pdf > > > > It may not something for right now, but it looks like something > > > > with > > > > potential for the future. > > > > 73s > > > > Daniel > > > > > > > > > > > > Sent from Daniel's iPhone > > > > > > > > On Mar 5, 2013, at 12:09 PM, David Rowe <[email protected]> > > > > wrote: > > > > > > > > > > > > > Hello, > > > > > > > > > > I have just published a new blog post on making FreeDV robust > > > > > over > > > > > HF > > > > > multipath channels: > > > > > > > > > > http://www.rowetel.com/blog/?p=2905 > > > > > > > > > > Thanks, > > > > > > > > > > David > > > > > > > > > > > > > > > > > > > > ------------------------------------------------------------------------------ > > > > > Everyone hates slow websites. So do we. > > > > > Make your web apps faster with AppDynamics > > > > > Download AppDynamics Lite for free today: > > > > > http://p.sf.net/sfu/appdyn_d2d_feb > > > > > _______________________________________________ > > > > > Freetel-codec2 mailing list > > > > > [email protected] > > > > > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > > > > > > > > > ------------------------------------------------------------------------------ > > > > Symantec Endpoint Protection 12 positioned as A LEADER in The > > > > Forrester > > > > Wave(TM): Endpoint Security, Q1 2013 and "remains a good choice" > > > > in the > > > > endpoint security space. For insight on selecting the right > > > > partner to > > > > tackle endpoint security challenges, access the full report. > > > > http://p.sf.net/sfu/symantec-dev2dev > > > > _______________________________________________ Freetel-codec2 > > > > mailing list [email protected] > > > > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > > > > > > > > > > > > ------------------------------------------------------------------------------ > > > Symantec Endpoint Protection 12 positioned as A LEADER in The > > > Forrester > > > Wave(TM): Endpoint Security, Q1 2013 and "remains a good choice" > > > in the > > > endpoint security space. For insight on selecting the right > > > partner to > > > tackle endpoint security challenges, access the full report. > > > http://p.sf.net/sfu/symantec-dev2dev > > > _______________________________________________ > > > Freetel-codec2 mailing list > > > [email protected] > > > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > > > > > > > ------------------------------------------------------------------------------ > > Symantec Endpoint Protection 12 positioned as A LEADER in The > > Forrester > > Wave(TM): Endpoint Security, Q1 2013 and "remains a good choice" in > > the > > endpoint security space. For insight on selecting the right partner > > to > > tackle endpoint security challenges, access the full report. > > http://p.sf.net/sfu/symantec-dev2dev > > _______________________________________________ > > Freetel-codec2 mailing list > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > > > ------------------------------------------------------------------------------ > Symantec Endpoint Protection 12 positioned as A LEADER in The Forrester > Wave(TM): Endpoint Security, Q1 2013 and "remains a good choice" in the > endpoint security space. For insight on selecting the right partner to > tackle endpoint security challenges, access the full report. > http://p.sf.net/sfu/symantec-dev2dev > _______________________________________________ Freetel-codec2 mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 ------------------------------------------------------------------------------ Symantec Endpoint Protection 12 positioned as A LEADER in The Forrester Wave(TM): Endpoint Security, Q1 2013 and "remains a good choice" in the endpoint security space. For insight on selecting the right partner to tackle endpoint security challenges, access the full report. http://p.sf.net/sfu/symantec-dev2dev _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
