On Sun, Sep 6, 2015 at 8:48 PM, < freetel-codec2-requ...@lists.sourceforge.net> wrote:
> Send Freetel-codec2 mailing list submissions to > freetel-codec2@lists.sourceforge.net > > To subscribe or unsubscribe via the World Wide Web, visit > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > or, via email, send a message with subject or body 'help' to > freetel-codec2-requ...@lists.sourceforge.net > > You can reach the person managing the list at > freetel-codec2-ow...@lists.sourceforge.net > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Freetel-codec2 digest..." > > > Today's Topics: > > 1. Re: Smoothing the digital cliff (4+4 QAM bitrate peeling > idea) (Bruce Perens) > 2. Re: Smoothing the digital cliff (4+4 QAM bitrate peeling > idea) (glen english) > 3. Re: Smoothing the digital cliff (4+4 QAM bitrate peeling > idea) (David Rowe) > 4. Re: Smoothing the digital cliff (4+4 QAM bitrate peeling > idea) (Gregory Maxwell) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Sun, 6 Sep 2015 14:04:55 -0700 > From: Bruce Perens <br...@perens.com> > Subject: Re: [Freetel-codec2] Smoothing the digital cliff (4+4 QAM > bitrate peeling idea) > To: freetel-codec2@lists.sourceforge.net > Message-ID: > <CAK2MWOsUJLAe-8vqE20VKzHHw0z3dZzWvza+8= > qszzqu+fj...@mail.gmail.com> > Content-Type: text/plain; charset="utf-8" > > Hi Helmut, > > ANAN-100D provides two phase-coherent receivers in one USD$3500 box, along > with a 100W transmitter. The cost is why I didn't bother mentioning it. But > obviously we can make a dual SDR receiver for a lot less. Are there any > other off-the-shelf hardware solutions today? I have a Hermes and three > USRP's on hand, and might also like to experiment with up-conversion for > Katena (formerly Whitebox) when we have dealt with higher-priority issues. > > Thanks > > Bruce > > On Sun, Sep 6, 2015 at 1:57 PM, Helmut <dc...@gmx.de> wrote: > > > Polarization diversity is another approach to minimize selective fading > we > > have on the to do list. Our HPSDR environment provides excellent > diversity > > performance. > > > > > > > > 73, Helmut, DC6NY > > > > > > > > *Von:* Bruce Perens [mailto:br...@perens.com] > > *Gesendet:* Sonntag, 6. September 2015 21:44 > > *An:* freetel-codec2@lists.sourceforge.net > > *Betreff:* Re: [Freetel-codec2] Smoothing the digital cliff (4+4 QAM > > bitrate peeling idea) > > > > > > > > Any graceful degradation scheme should take into account that the main > > problem we face is frequency-selective attenuation due to fading. The > > mechanism, I am told, is multiple depths of reflection from the > ionosphere > > leading to multiple phases combined at the antenna. There is a lot of > > literature saying that one can actually reduce the fading with circular > > receive antenna polarization. I've not gotten to test it. > > > > > > > > If you plan to make this work with conventional antennas, you can > > experiment with carrier spacing on the theory that some number of > carriers > > would not be in a fade at one time. > > > > > > > > Thanks > > > > > > > > Bruce > > > > > > > > On Sun, Sep 6, 2015 at 9:01 AM, Tomas H?rdin <tjop...@acc.umu.se> wrote: > > > > Hi > > > > (I tried sending this a few days ago but forgot to confirm my > > subscription to this list - oops! So resending) > > > > My name is Tomas and I've been following the development of codec2 on > > and off for a few years now, and since getting my ham license earlier > > this year I find myself thinking about it more. A few days ago I had > > what I thought was a clever idea for fixing the "digital cliff" problem > > Mike mentioned in a talk that's up on YouTube (I forget which). Today I > > see on the roadmap post[1] that this is currently being worked on using > > two GMSK streams, but I thought "hey, maybe someone will find it > > interesting". So here goes: > > > > The idea assumes that codec2 can make use of bitrate peeling. That is, > > that we can split the stream up into two or more streams where the first > > one provides a rough but usable quality, and subsequent streams improve > > upon this. H.264's SVC would be an example from the video world > > > > So the idea is take these streams and modulate them onto a hierarchical > > QAM system. The simplest would be to take the current FDMDV modem and > > instead of using 14x QPSK (aka 4-QAM) carriers you use 7x 16-QAM > > carriers. You then code the more important bitstream into the most > > significant bits in each 16-QAM symbol, and the improvement stream into > > the lower bits (assuming the two streams have identical bitrate). Since > > you now have half the number of carriers you can put twice the amount of > > power into each carrier > > > > That's about it. Lots of variants are of course possible, but this > > should get the point across. I may experiment with the idea once I get > > some suitable SSB equipment, but for now I'm interested in feedback even > > if it's just shooting it down :) > > > > /Tomas, SA2TMS > > > > [1] http://www.rowetel.com/blog/?p=3931 > > > > > > > > > > > ------------------------------------------------------------------------------ > > > > _______________________________________________ > > Freetel-codec2 mailing list > > Freetel-codec2@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > > > > > > > > > > > ------------------------------------------------------------------------------ > > > > _______________________________________________ > > Freetel-codec2 mailing list > > Freetel-codec2@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > > > > > -------------- next part -------------- > An HTML attachment was scrubbed... > > ------------------------------ > > Message: 2 > Date: Mon, 07 Sep 2015 08:16:30 +1000 > From: glen english <g...@cortexrf.com.au> > Subject: Re: [Freetel-codec2] Smoothing the digital cliff (4+4 QAM > bitrate peeling idea) > To: freetel-codec2@lists.sourceforge.net > Message-ID: <55ecbb3e.3090...@cortexrf.com.au> > Content-Type: text/plain; charset="us-ascii" > > An HTML attachment was scrubbed... > > ------------------------------ > > Message: 3 > Date: Mon, 7 Sep 2015 12:48:11 +0930 > From: David Rowe <da...@rowetel.com> > Subject: Re: [Freetel-codec2] Smoothing the digital cliff (4+4 QAM > bitrate peeling idea) > To: freetel-codec2@lists.sourceforge.net > Message-ID: <55ed01f3.5020...@rowetel.com> > Content-Type: text/plain; charset=windows-1252; format=flowed > > Thomas, > > See "Suggestion to dynamic bandwidth adaption" thread above. It would > be interesting to add QAM constellations to the cohpsk modem. The > pilots symbols could be used as an amplitude as well as phase reference. > > -/- > > Glen, > > Reports of a quite a few NVIS contacts already, in fact we have a websdr > here in Adelaide without a ground wave path from my QTH that I regularly > use for just that purpose. Power as low as 500mW with 0 BER. > > Curiously, I haven't had a _single_ report of a high SNR path that > breaks FreeDV 700(B). For example a path that works well for SSB, but > makes the FreeDV 700 modem fall over, would indicate the modem can't > handle the channel. > > Cheers, > > David > > On 07/09/15 07:46, glen english wrote: > > Hi Thomas > > You are talking about hierarchical coding and transmission, and it has > > been discussed here widely. > > > > We have considered it and I think it is in the informal roadmap, IE > > when conditions are good, we have a low priority stream that enhances > > the user experience. > > > > The frequency selective narrowband HF channel represents rather > > different character compared to the VHF narrowband channel which is > > primarily a flat fading condition. > > > > Frequency diversity is the most efficient system wide method of solving > > the problem on HF > > > > I suspect when the frequency selective performance is deemed OK by the > > users, and that is the frequency selective channel properties generated > > by say, a >600km ionospheric path, then the users will begin to push the > > vertical incidence ability of FreeDV, this is a high random doppler > > profile and will likely spur another round of development to cope with > it. > > > > regards > > > > glen english VK1XX > > > > > > On 7/09/2015 2:01 AM, Tomas H?rdin wrote: > >> Hi > >> > >> (I tried sending this a few days ago but forgot to confirm my > >> subscription to this list - oops! So resending) > >> > >> My name is Tomas and I've been following the development of codec2 on > >> and off for a few years now, and since getting my ham license earlier > >> this year I find myself thinking about it more. A few days ago I had > >> what I thought was a clever idea for fixing the "digital cliff" problem > >> Mike mentioned in a talk that's up on YouTube (I forget which). Today I > >> see on the roadmap post[1] that this is currently being worked on using > >> two GMSK streams, but I thought "hey, maybe someone will find it > >> interesting". So here goes: > >> > >> The idea assumes that codec2 can make use of bitrate peeling. That is, > >> that we can split the stream up into two or more streams where the first > >> one provides a rough but usable quality, and subsequent streams improve > >> upon this. H.264's SVC would be an example from the video world > >> > >> So the idea is take these streams and modulate them onto a hierarchical > >> QAM system. The simplest would be to take the current FDMDV modem and > >> instead of using 14x QPSK (aka 4-QAM) carriers you use 7x 16-QAM > >> carriers. You then code the more important bitstream into the most > >> significant bits in each 16-QAM symbol, and the improvement stream into > >> the lower bits (assuming the two streams have identical bitrate). Since > >> you now have half the number of carriers you can put twice the amount of > >> power into each carrier > >> > >> That's about it. Lots of variants are of course possible, but this > >> should get the point across. I may experiment with the idea once I get > >> some suitable SSB equipment, but for now I'm interested in feedback even > >> if it's just shooting it down :) > >> > >> /Tomas, SA2TMS > >> > >> [1]http://www.rowetel.com/blog/?p=3931 > >> > >> > >> > >> > >> > ------------------------------------------------------------------------------ > >> > >> > >> _______________________________________________ > >> Freetel-codec2 mailing list > >> Freetel-codec2@lists.sourceforge.net > >> https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > > > > -- > > - > > Glen English > > RF Communications and Electronics Engineer > > > > CORTEX RF > > & > > Pacific Media Technologies Pty Ltd > > > > ABN 40 075 532 008 > > > > PO Box 5231 Lyneham ACT 2602, Australia. > > au mobile : +61 (0)418 975077 > > > > > > > > > ------------------------------------------------------------------------------ > > > > > > > > _______________________________________________ > > Freetel-codec2 mailing list > > Freetel-codec2@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > > > > > > ------------------------------ > > Message: 4 > Date: Mon, 7 Sep 2015 03:48:04 +0000 > From: Gregory Maxwell <gmaxw...@gmail.com> > Subject: Re: [Freetel-codec2] Smoothing the digital cliff (4+4 QAM > bitrate peeling idea) > To: freetel-codec2@lists.sourceforge.net > Message-ID: > < > caas2fgtb9wabp7wfkybzseyxcr2kedt8cjnt_alivnds+v5...@mail.gmail.com> > Content-Type: text/plain; charset=UTF-8 > > On Mon, Sep 7, 2015 at 3:18 AM, David Rowe <da...@rowetel.com> wrote: > > Curiously, I haven't had a _single_ report of a high SNR path that > > breaks FreeDV 700(B). For example a path that works well for SSB, but > > makes the FreeDV 700 modem fall over, would indicate the modem can't > > handle the channel. > > Or thar you're already far enough ahead of SSB in low SNR that SSB is > more or less busted already in cases where the model is giving up > where a better one would keep going. :) > > Maybe further improvement needs better competition. :) > > > > ------------------------------ > > > ------------------------------------------------------------------------------ > > > ------------------------------ > > _______________________________________________ > Freetel-codec2 mailing list > Freetel-codec2@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > > > End of Freetel-codec2 Digest, Vol 65, Issue 8 > ********************************************* > -- ------------------------------ John D. Hays K7VE PO Box 1223, Edmonds, WA 98020-1223 <http://k7ve.org/blog> <http://twitter.com/#!/john_hays> <http://www.facebook.com/john.d.hays>
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