Rune Allnor wrote:> On 9 Nov, 18:13, Rob Gaddi <rga...@technologyhighland.invalid> wrote: > >>On 11/9/2011 9:03 AM, Rune Allnor wrote: >> >>>People have been *talking* and *writing* about such >>>stuff for decades. You would be hard pressed to >>>come up with examples of systems that actually *work*.Well, I did such demo once. It is trivial to accomplish trivial data rate; it is non-trivial to get beyond that.>>The oil well guys do acoustic channel transmission, they call it >>pressure pulses or something of that nature. Data rates in the 5 baud >>(that's not a typo) > > I know. Investigating the reasons why one can't get more, is > really enlightening.The downhole telemetry has different set of problems; slow data rate is not only because of accoustics.> I didn't say this is *impossible*; just that there are > very good reasons that very few such systems exist.Why spending lots of effort with knowingly small outcome when better solutions exist?> I know acoustic comm systems is used in certain marine > between-submersibles comms, so that's two applications > of acoustic comms. > > I would be very surprised if one cane come up with as > many as five. > > RuneVladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Modulation/Signaling scheme for transfering information over an acoustic channel
Started by ●November 9, 2011
Reply by ●November 9, 20112011-11-09
Reply by ●November 9, 20112011-11-09
Tim Wescott wrote:> Hand-held DTMF generators, from back when rotary dial phones were still > commonplace, but voice-response systems were starting to take over the > WORLD!!!The ~200 bit/s is a great accomplishment, especially if you could get the DTMF to work reliably from one side of a room to the other. VLV
Reply by ●November 9, 20112011-11-09
On Wed, 09 Nov 2011 17:08:51 +0000, Eric Jacobsen wrote:> On Wed, 9 Nov 2011 06:49:41 -0800 (PST), John McDermick > <johnthedspguy@gmail.com> wrote: > >>Which modulation scheme is most suitable for transmitting information (a >>bitstream) over an acoustic channel? i.e. a loudspeaker outputs the >>modulated signal and a cell phone microphone picks up the acoustic >>signal and extracts the information from the modulated signal. I'm >>looking for a modulation/signaling scheme which is robust with respect >>to ambient noise in the acoustic channel. >> >> > A friend used BPSK transmitted from a little speaker and picked up by > the mic on a laptop. It actually worked pretty well, considering. > > BPSK is pretty fundamental and robust. That being said, the range will > be expected to be short and there will be susceptibility to interference > from ambient noise.I think that FSK with wide spacing would wind the "fundamental and robust" contest. OFDM may be a good candidate, too. In fact, the free-space audio channel probably has the same sorts of difficulties (only way more marked) as long distance transmission in HF, so that may be a place to mine for ideas. I suspect that the reason this isn't done more often is that it would be really _annoying_ to both user and bystanders. -- www.wescottdesign.com
Reply by ●November 9, 20112011-11-09
On Wed, 09 Nov 2011 10:11:04 -0600, Vladimir Vassilevsky wrote:> John McDermick wrote: >> Which modulation scheme is most suitable for transmitting information >> (a bitstream) over an acoustic channel? i.e. a loudspeaker outputs the >> modulated signal and a cell phone microphone picks up the acoustic >> signal and extracts the information from the modulated signal. > > And there is a vocoder in the path, too ? > >> I'm >> looking for a modulation/signaling scheme which is robust with respect >> to ambient noise in the acoustic channel. > > Aborigenes use tomtoms.I'm pretty sure that one can access the microphone signal directly with an app in an Android phone or iPhone. That would take care of the vocoder issue. Otherwise -- yes, your message had better sound like singing, or it's not getting through. -- www.wescottdesign.com
Reply by ●November 9, 20112011-11-09
Vladimir Vassilevsky wrote:> > > Tim Wescott wrote: > > >> Hand-held DTMF generators, from back when rotary dial phones were >> still commonplace, but voice-response systems were starting to take >> over the WORLD!!! > > > The ~200 bit/s is a great accomplishment, especially if you could get > the DTMF to work reliably from one side of a room to the other.Oops; it is ~50 b/s actually
Reply by ●November 9, 20112011-11-09
On 9 Nov, 19:24, Tim Wescott <t...@seemywebsite.com> wrote:> On Wed, 09 Nov 2011 09:03:05 -0800, Rune Allnor wrote: > > On 9 Nov, 17:48, John McDermick <johnthedsp...@gmail.com> wrote: > >> These papers talks about transmitting information over an acoustic > >> channel: > > >>http://www.cmlab.csie.ntu.edu.tw/~ipr/mmsec2007/data/homework/hw2/ > Int... > > >>http://www.apl.utoronto.ca/publication/i/nevena_tmm06.pdf > > > People have been *talking* and *writing* about such stuff for decades. > > You would be hard pressed to come up with examples of systems that > > actually *work*. > > Hah! > > Hand-held DTMF generators, from back when rotary dial phones were still > commonplace, but voice-response systems were starting to take over the > WORLD!!!If you count acoustic components in systems (SAWs, quartz crystals) the list might be very long indeed. But do those count as acoustic comm channels?> Hold gizmo up to mouthpiece, punch buttons -- joy ensues (well, as much > joy as can ensue when you're in Voice Mail Hell).Ok, certain antropocentric comm components might well require an acoustic connecting link. But is it an acoustic comm *system*?> Hah!! > > Old-style modems, with the handset holder thingie. �Put handset in > holder, joy ensues (well, as much -- oh, never mind). > > (I'm trying to get up to four examples so I can say 'Hah!V', but I'm not > getting there, unless you count shouting).Acoustic modems for phone lines? Maybe, but again, it is actually a acoustic comm *system*? Or does it just take advantage of the acoustic conector to the regular phone system? Rune
Reply by ●November 9, 20112011-11-09
Tim Wescott <tim@seemywebsite.com> wrote: (snip, and previous snip on acoustic data transmission)> Hand-held DTMF generators, from back when rotary dial phones were still > commonplace, but voice-response systems were starting to take over the > WORLD!!!> Hold gizmo up to mouthpiece, punch buttons -- joy ensues (well, as much > joy as can ensue when you're in Voice Mail Hell).> Old-style modems, with the handset holder thingie. Put handset in > holder, joy ensues (well, as much -- oh, never mind).But in both of those there is very close, maybe even a rubber seal, coupling between the two. The OP wants to go through open air. Maybe the OP should consider closer coupling, with the receiver as close as possible to the transmitter. (Though likely no rubber seal.) Otherwise, to keep noise away it will need to be at a very high level, which will not make the user or his/her neighbors happy. (and might burn out the loudspeakers.) With data rate pretty much proportional to bandwidth, it will be the tweeter side that is most useful, the most prone to burn out at high power levels, and most irritating to users at high (or even medium) power levels. -- glen
Reply by ●November 9, 20112011-11-09
On 11/9/2011 12:03 PM, Rune Allnor wrote:> On 9 Nov, 17:48, John McDermick<johnthedsp...@gmail.com> wrote: >> These papers talks about transmitting information over an acoustic >> channel: >> >> http://www.cmlab.csie.ntu.edu.tw/~ipr/mmsec2007/data/homework/hw2/Int... >> >> http://www.apl.utoronto.ca/publication/i/nevena_tmm06.pdf > > People have been *talking* and *writing* about such > stuff for decades. You would be hard pressed to > come up with examples of systems that actually *work*.How do you classify acoustic modems? Jerry -- Engineering is the art of making what you want from things you can get.
Reply by ●November 9, 20112011-11-09
On 9 Nov, 21:26, Jerry Avins <j...@ieee.org> wrote:> On 11/9/2011 12:03 PM, Rune Allnor wrote: > > > On 9 Nov, 17:48, John McDermick<johnthedsp...@gmail.com> �wrote: > >> These papers talks about transmitting information over an acoustic > >> channel: > > >>http://www.cmlab.csie.ntu.edu.tw/~ipr/mmsec2007/data/homework/hw2/Int... > > >>http://www.apl.utoronto.ca/publication/i/nevena_tmm06.pdf > > > People have been *talking* and *writing* about such > > stuff for decades. You would be hard pressed to > > come up with examples of systems that actually *work*. > > How do you classify acoustic modems?As an acoustic interface to an EM comm channel. Rune
Reply by ●November 9, 20112011-11-09
On 11/9/2011 1:31 PM, Vladimir Vassilevsky wrote:> > > Vladimir Vassilevsky wrote: > >> >> >> Tim Wescott wrote: >> >> >>> Hand-held DTMF generators, from back when rotary dial phones were >>> still commonplace, but voice-response systems were starting to take >>> over the WORLD!!! >> >> >> The ~200 bit/s is a great accomplishment, especially if you could get >> the DTMF to work reliably from one side of a room to the other. > > Oops; it is ~50 b/s actuallyI'm looking at an old 300 Baud acoustic modem built into a TI thermal-printer terminal. Jerry -- Engineering is the art of making what you want from things you can get.
