The multi-point model is not discussed widely but it only used FEC. Packet repeat is handled at higher levels similar to the operation of the Internet. I am not aware of analysis for any of this. The situation is frustrating. The comments about ARRL can be generarlized to the ham community, or turned around to say that the ARRL is a good representation of the community. -- Rud K5RUD ARES AEC Montgomery County, TX http://over50.k5rud.us/wiki/ "Jerry Avins" <jya@ieee.org> wrote in message news:Gb6dnWQIepxL7H_YnZ2dnUVZ_r_inZ2d@rcn.net...> Rud Merriam wrote: > > ... > >> 5. Going beyond the transfer of the bit stream, if interested, opens up a >> lot of questions. Point- to-point using the VSAT hub model is feasible, >> especially if the hub can drop data onto the Internet. >> Point-to-multipoint would be nice to allow a mesh type network. One >> question needing a good analysis and explanation is the trades offs >> between automatic repeat request (ARQ) operation and the use of FEC in >> combination or separately. Included in that is fall-back modes to provide >> to reliable but lower throughput as HF conditions deteriorate. > > I can't imagine how one might use an ARQ protocol in a point-to-multipoint > mesh. Has tha been thought through? > > ... > > Jerry > -- > Engineering is the art of making what you want from things you can get. > ����������������������������������������������������������������������� >----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =----
RFC on HF Protocol
Started by ●February 23, 2007
Reply by ●February 26, 20072007-02-26
Reply by ●February 26, 20072007-02-26
Vladimir Vassilevsky wrote:> > > Tim Wescott wrote: > >>>>> The first question to answer is what is this protocol intended for. >>>>> I.e. what is the concept of the communication system. > > > The one who can't clearly define what he wants should not be surprised > if he will get something incomprehensible as the result. > >> This means that you need a box that will connect to a transceiver that's > > > Is it a conventional SSB transceiver? >Yes. Study the amateur radio market for detail, but for the most part assume a SSB transceiver that's primarily designed for voice communications.>> connected to an antenna, and have the system work well. > > > Work what? Voice, data, video, ethernet, internet, windows, linux, QPSK, > OFDM, opensource, for free and all at once? This is how their RFP looks > like. Duplex or simplex? Broadcast or point-to-point?Jeez. Start reading QST & get a feel for it! Assume data -- voice will be handled with SSB for a good long while. Exactly how the data is handled is going to be an issue; if the computer-side package could attach seamlessly so that a not-so-hypothetical ham without much technical ability can use it that's all the better.> Can the GPS be > used as the external timing reference?If you can keep it within budget, yes.> Is it intended for DX or it > enough to reach the neighbor's house? >HF implies DX. To reach the neighbor's house we have VHF & UHF. Assume a large-scale disaster such as fire, flood, or earthquake has wiped out the regular comms infrastructure. VHF & UHF comms will be used for tactical communications within line-of sight and over the hill if the repeaters aren't down (but if the cell towers go, so go the repeaters). HF will be used to get over the hill, or out of state. Amateur radio gets to play with big swaths of spectrum because when the sh** really hits the fan there's a bunch of radios scattered around in a bunch of houses with trained operators who are ready to pick up the slack.> > BTW, a long time ago I was thinking about the digital voice radio for > amateur communication. At the marginal conditions, the 1200 bps vocoder > should be better than the analog SSB. I would be surprised if it is not > standardized yet. > > > You can put > >> some requirements on turn-around time, but probably nothing tighter >> than AMTOR. You must have a system that will go into a box that >> costs less than $500, and preferably less than $200 -- remember that >> the average radio amateur will spend a man day to save $1, and be >> proud of it. > > > The inexpensive DSP eval boards is in this price range.Yes, but is the eval board, the box and power supply there? What about when you add your GPS?> >> Something that would just plug into a sound card would be better yet, >> from this perspective. The system has to be plug and play for the >> folks who passed their tests by memorizing all possible answers to the >> questions, yet should also provide enough flexibility that experts can >> get significantly better performance. It also has to comply with all >> applicable FCC regulations, some of which are quite sensible and some >> of which are absurd. > > > To my knowledge, it is not allowed to transmit any non-voice signals via > the voice path of a radio unless specifically permitted. They will have > to push whatever new protocol through the FCC.This is allowed for amateur use. The paradigm is a voice radio attached to a signal processor that's generating and receiving audio, and controlling the transceiver's PTT line.> > If the system were robust to having someone naively > >> (or maliciously) transmit a carrier smack in the middle of the signal >> that would be good, but not essential. >> >> There's more, but you should be getting the idea. I suspect that if >> you really wanted to make a project out of this you'd need to take >> that "data sheet" definition from the ARRL and turn it into a number >> of criteria such as I've outlined, agree on them, the work on turning >> _those_ into numbers, if they're not obvious as they stand. > > Here is the second question: how much time and money do they have? >Do you mean the individual hams, or the folks developing the technology? There seems to be a lot of energy available to be devoted to this (hasn't TAPR picked this up?) -- it just takes someone to attract the right kind of attention to it, and make it happen. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/ "Applied Control Theory for Embedded Systems" came out in April. See details at http://www.wescottdesign.com/actfes/actfes.html
Reply by ●February 26, 20072007-02-26
Tim Wescott wrote:> Assume a large-scale disaster such as fire, flood, or earthquake has > wiped out the regular comms infrastructure. VHF & UHF comms will be > used for tactical communications within line-of sight and over the hill > if the repeaters aren't down (but if the cell towers go, so go the > repeaters). HF will be used to get over the hill, or out of state. > > Amateur radio gets to play with big swaths of spectrum because when the > sh** really hits the fan there's a bunch of radios scattered around in a > bunch of houses with trained operators who are ready to pick up the slack.The speculations of the people who don't have any idea of what is a real disaster are very entertaining. This makes them think that their hobby is more worthy then collecting postage stamps. So, leaving alone the childish dreams of heroism in the field of disaster, I can see the good application of the advanced modulation methods for the DX experimenting. A lot of work had been done in that area. Summarizing, the bandwidth of at least several dozen kHz is required to decorrelate the fading in the short waves. Also, a system may do many attempts to transmit the data, so the delay may be up to the several minutes. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Reply by ●February 26, 20072007-02-26
Vladimir, There are hams who have a great deal of experience with diaster communications. I was involved in east Texas during the shuttle Columbia recovery efforts. The only reliable communication in those piney woods was ham radio on 2m using existing or temporary repeaters. The pine needles just absorbed all the other radios they tried to use for local communications. During Katrina hams were active on HF and VHF/UHF. But one group that also helped were the wireless networking Part 15 group. They were able to provide local wireless networking. Hams can do that but were not prepared. The problem is the local wireless needs longer distance support. Hams on HF or with higher power directional VHF/UFH can provide this but the existing techniques are slow. Also portable satcomm is coming along as a possibility using commerical vendors. But hams also are working on a satellite so that is a possibility in the future. Yes, hams have the experience in satellites, some 40 of them, to do this. Are you aware that ham radios are on the space station and many of the astronauts are hams? Getting back to the question, a bandwidth of "several dozen khz" is going to raise a lot of issues. The biggest being the interference with other hams trying to use that bandwidth for voice. The hue and cry will be that multiple voice conversations can be taking place in that same bandwidth. Would the digital signal be noise under the voice communications? -- Rud K5RUD ARES AEC Montgomery County, TX http://over50.k5rud.us/wiki/ "Vladimir Vassilevsky" <antispam_bogus@hotmail.com> wrote in message news:C_GEh.18$iw4.17@newssvr23.news.prodigy.net...> > > Tim Wescott wrote: > > >> Assume a large-scale disaster such as fire, flood, or earthquake has >> wiped out the regular comms infrastructure. VHF & UHF comms will be used >> for tactical communications within line-of sight and over the hill if the >> repeaters aren't down (but if the cell towers go, so go the repeaters). >> HF will be used to get over the hill, or out of state. >> >> Amateur radio gets to play with big swaths of spectrum because when the >> sh** really hits the fan there's a bunch of radios scattered around in a >> bunch of houses with trained operators who are ready to pick up the >> slack. > > The speculations of the people who don't have any idea of what is a real > disaster are very entertaining. This makes them think that their hobby is > more worthy then collecting postage stamps. So, leaving alone the childish > dreams of heroism in the field of disaster, I can see the good application > of the advanced modulation methods for the DX experimenting. > A lot of work had been done in that area. Summarizing, the bandwidth of at > least several dozen kHz is required to decorrelate the fading in the short > waves. Also, a system may do many attempts to transmit the data, so the > delay may be up to the several minutes. > > Vladimir Vassilevsky > > DSP and Mixed Signal Design Consultant > > http://www.abvolt.com > >----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =----
Reply by ●February 26, 20072007-02-26
Vladimir Vassilevsky wrote:> > > Tim Wescott wrote: > > >> Assume a large-scale disaster such as fire, flood, or earthquake has >> wiped out the regular comms infrastructure. VHF & UHF comms will be >> used for tactical communications within line-of sight and over the >> hill if the repeaters aren't down (but if the cell towers go, so go >> the repeaters). HF will be used to get over the hill, or out of state. >> >> Amateur radio gets to play with big swaths of spectrum because when >> the sh** really hits the fan there's a bunch of radios scattered >> around in a bunch of houses with trained operators who are ready to >> pick up the slack. > > > The speculations of the people who don't have any idea of what is a real > disaster are very entertaining. This makes them think that their hobby > is more worthy then collecting postage stamps. So, leaving alone the > childish dreams of heroism in the field of disaster, I can see the good > application of the advanced modulation methods for the DX experimenting. > A lot of work had been done in that area. Summarizing, the bandwidth of > at least several dozen kHz is required to decorrelate the fading in the > short waves. Also, a system may do many attempts to transmit the data, > so the delay may be up to the several minutes. > > Vladimir Vassilevsky > > DSP and Mixed Signal Design Consultant > > http://www.abvolt.com >Vladimir: Lower your nose by a couple of notches and start paying attention to your fellow mortals. Amateur radio _is_ used effectively for disaster communications here in the US. It gets kudos after nearly every major disaster and many smaller ones for the competence and work ethic of it's practitioners. It is a vital part of the disaster planning for many governmental emergency services organizations across the US who realize that they simply don't have the bucks to cover all the bases, and can make effective use of the amateur radio community for those exceptional emergencies that overload, damage or destroy their routine communications abilities. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/ "Applied Control Theory for Embedded Systems" came out in April. See details at http://www.wescottdesign.com/actfes/actfes.html
Reply by ●February 26, 20072007-02-26
"Vladimir Vassilevsky" <antispam_bogus@hotmail.com> wrote in message news:EOoEh.887$P47.826@newssvr22.news.prodigy.net...> > > Philip Martel wrote: > >>>To my knowledge, it is not allowed to transmit any non-voice signals via >>>the voice path of a radio unless specifically permitted. They will have >>>to >>>push whatever new protocol through the FCC. >> I'm not sure what you mean by this. Most packet radio boxes connect to >> the radio's mic and headphone. > > It does not imply one can connect anything to the mic input.The FCC is interested in what is going out the antenna, not what you hook to to your microphone.> Those are the FCC allowed boxes which operate in the permitted packet > mode. And the operation is allowed only in the dedicated parts of ham > radio bands, and many other restrictions of FCC apply.I disagree with the phrase "FCC allowed boxes". A PC sound card is just fine, if it puts out the agreed on sounds that match the packet protocol. Or 150 WPM Morse code if you prefer... Actually, the rules are fairly flexible as far as what is permitted as a voice signal... From FCC rules 97.5 (5) Phone. Speech and other sound emissions having designators with A, C, D, F, G, H, J or R as the first symbol; 1, 2 or 3 as the second symbol; E as the third symbol. Also speech emissions having B as the first symbol; 7, 8 or 9 as the second symbol; E as the third symbol. MCW for the purpose of performing the station identification procedure, or for providing telegraphy practice interspersed with speech. Incidental tones for the purpose of selective calling or alerting or to control the level of a demodulated signal may also be considered phone. Best wishes, --Phil Martel, KA1GK> Vladimir Vassilevsky > > DSP and Mixed Signal Design Consultant > > http://www.abvolt.com
Reply by ●February 26, 20072007-02-26
Tim Wescott wrote:>>> Assume a large-scale disaster such as fire, flood, or earthquake has >>> wiped out the regular comms infrastructure.>> The speculations of the people who don't have any idea of what is a >> real disaster are very entertaining.> Lower your nose by a couple of notches and start paying attention to > your fellow mortals. Amateur radio _is_ used effectively for disaster > communications here in the US.Here in US there were no large scale disasters since the civil war. The relatively minor flood in N.O. clearly showed what happens if a disaster comes in. Your notion of disaster is something like a picnic, whereas a real calamity is when the ammunition is the most valid asset.> It gets kudos after nearly every major > disaster and many smaller ones for the competence and work ethic of it's > practitioners. It is a vital part of the disaster planning for many > governmental emergency services organizations across the US who realize > that they simply don't have the bucks to cover all the bases, and can > make effective use of the amateur radio community for those exceptional > emergencies that overload, damage or destroy their routine > communications abilities.Yea, picnickers and boyscouts are saving the world. I have no doubts. VLV
Reply by ●March 1, 20072007-03-01
On Tue, 27 Feb 2007 01:22:42 GMT, Vladimir Vassilevsky <antispam_bogus@hotmail.com> wrote:> > >Tim Wescott wrote: > > >>>> Assume a large-scale disaster such as fire, flood, or earthquake has >>>> wiped out the regular comms infrastructure. > > >>> The speculations of the people who don't have any idea of what is a >>> real disaster are very entertaining. > >> Lower your nose by a couple of notches and start paying attention to >> your fellow mortals. Amateur radio _is_ used effectively for disaster >> communications here in the US. > >Here in US there were no large scale disasters since the civil war. The >relatively minor flood in N.O. clearly showed what happens if a disaster >comes in. Your notion of disaster is something like a picnic, whereas a >real calamity is when the ammunition is the most valid asset. > > >> It gets kudos after nearly every major >> disaster and many smaller ones for the competence and work ethic of it's >> practitioners. It is a vital part of the disaster planning for many >> governmental emergency services organizations across the US who realize >> that they simply don't have the bucks to cover all the bases, and can >> make effective use of the amateur radio community for those exceptional >> emergencies that overload, damage or destroy their routine >> communications abilities. > >Yea, picnickers and boyscouts are saving the world. I have no doubts. >Vladimir, While your technical comments here have been often appreciated, I think you need to reconsider posting your value judgements. It's not helping you. Eric Jacobsen Minister of Algorithms Abineau Communications http://www.ericjacobsen.org
Reply by ●March 1, 20072007-03-01
On Fri, 23 Feb 2007 16:09:49 -0600, "Rud Merriam" <k5rud@arrl.net.net> wrote:>The Amateur Radio Relay League (ARRL) is requesting comments on HF radio >digital protocol. See http://www.arrl.org/news/stories/2007/02/22/102/?nc=1. > >A major component is going to be DSP so this DSP group is a good place for >discussion. I know just enough about RF communications and DSP to be very >dangerous so I personally see this as a learning opportunity. > >I have a paper from Agilent (referenced at >http://www.k5rud.us/over50/wiki/index.php/Modulation%20Techniques) that >discusses the basics of modulation, although it does not go into OFDM. A >table on page 17 leaves me bewildered. As I (mis?)understand it the >theoretical limits on bit rate FSK/BPSK start at 1 bps/Hz and increase for >more complex modulation techniques, e.g. 8PSK, nQAM. Practical results, page >18, are somewhat less (pi/4 DQPSK at 1.6 bps) but still respectable. > >The only commercially available HF modem I am familiar with, I am sure there >are others, uses a protocol called Pactor III. It uses the 3k Hz bandwidth >to achieve some 3k bps with a lot of "black magic" under good conditions. >Once the SNR gets bad the rate slows. [Personally I do not think they are >taking advantage of good FEC.] Why are better results not obtained? > >Given a blank white board, where would you start?I am, unfortunately, coming late to the conversation due to the usual bizarre newsreader buffering behavior that many of us see from time to time. I have some basic comments and questions: 1. If the bandwidth is really limited to 3kHz I don't see how OFDM is a practical candidate, but that should ultimately be determined by the channel response. 2. Has anyone characterized the HF channels in order to provide the basis of a channel model? I'd think that this could be done by some cooperative HAM operators, i.e., capture some impulse or linear-FM responses and make a statistical model of the channel. Of course when doing this the radio equipment response needs to be considered as well. 3. I don't know that one can decide many details about the "best" approach, or even come up with a good menu of "good" approaches, until (2) has been addressed. I'm not familiar with ham HF radio technology or even the details of its use, but the basic channel impulse response characteristics under various conditions, the fading behavior, and the channel delay spread behavior will dictate a LOT of the characteristics of whatever modulation is selected. 4. Since anything that fits within a 3kHz bandwidth will have a pretty low symbol rate, this is definitely something that can be done in software on a PC via a sound card or some other low-cost data capture device. How well it works, ultimately, will be partly determined by the net response of all the filters, etc., in the transceiver and the data capture/transmit device. 5. One nice thing about such an automated system, though, is that two devices in a link may be able to handshake and negotiate the "best" technique after sounding the channel between them. This is something that can be done periodically to track and adapt to fading. It takes up some overhead, but the net result is a more reliable link. I think this is a really interesting problem and am happy to help where I can. I've personally seen the benefits of ham networks in emergency situations where infrastructure was damaged, and even beyond that just the hobby value for long-distance comm is great. Here's the highlight of my limited hands-on ham exposure so far: http://www.ne7x.com/ww7cpu.htm About halfway down are some pics of me 'helping' to tune a diplexer. I was responsible for one of the only useful wireless labs in Intel in Arizona at the time, so we used our equipment to rehab the diplexer. Eric Jacobsen Minister of Algorithms Abineau Communications http://www.ericjacobsen.org
Reply by ●March 1, 20072007-03-01
Eric Jacobsen wrote:>>>>>Assume a large-scale disaster such as fire, flood, or earthquake has >>>>>wiped out the regular comms infrastructure. >> >> >>Here in US there were no large scale disasters since the civil war. The >>relatively minor flood in N.O. clearly showed what happens if a disaster >>comes in. Your notion of disaster is something like a picnic> While your technical comments here have been often appreciated, I > think you need to reconsider posting your value judgements.Do you have any particular objections to the facts? > It's not helping you. Don't worry. I can afford what most of people can't: having the opinion of their own. VLV
