cathalgarvey
Posts: 7
Joined: Tue Aug 30, 2011 3:08 pm
Contact: Website

Re: "Soundmodem" relays for amateur internet backbone

Thu Sep 01, 2011 1:40 pm

Hey all,
Absolutely loving the concept of Raspberry Pi, hoping to get a few for my birthday this November, although sooner would of course be preferable!

My dream application at present (among loads of others including NAT storage etc.) is to embed Raspberry Pis in solar/battery casings with handheld walkie talkies, and to use them as data relays between Nexus Cork in Cork, Tog in Dublin, MilkLabs in Limerick and 091Labs in Galway. An inter-Hackerspace, amateur-owned/operated internet backbone. Slow, but resilient. :)

My understanding is that the "soundmodem" software allows sound cards to encode digital information over anything that'll carry sound. A set of walkie talkies permitting two-way simultaneous communication, or at least VOX control, and some RPis on mountain-tops should do the job, right?

Setup for a relay, I imagine, would involve two walkie talkies (one for either "end" of the link), a Raspberry Pi, an extra sound card for communicating with both walkie talkies, and the Soundmodem Software.

If you were using radios that could handle real-time two way communication without using a "speak" button and without interrupting reception during transmission, you might be able to do away with having so many dedicated RPis and only use them as uplinks and downlinks, with wire-coupled walkie-talkies as the "dumb relays" on the mountaintops.

Legality: You'd have to ensure that the walkie talkies were European "PMR446" compliant, NOT American ones, and you'd be best off putting them in cantennas so that they're roughly directional at one another to avoid being a nuisance (and to avoid snooping). I'm not sure whether you'd be permitted to use encryption under PMR446, though I think that ridiculous restriction only applies to licensed HAM users.

If it were illegal or for some other reason impractical to use walkie-talkies for legal data transfer over long range, what are the odds of doing the above with precisely coupled lasers/photoresistors and RPi/Soundmodem? It'd be harder to set up but possibly lower power, lower signal noise?

Applications:
> Hosting mirrors of critical information resources in case of censorship or emergency failure.
> Offering free internet access to those who can't afford or access it otherwise.
> Proof-of-principal for countries with more urgent need of cheap communication infrastructure.
> Proof-of-principal DIY-provision of "last mile" internet access.
> Having a nice old natter between Hackerspaces in Ireland.

cathalgarvey
Posts: 7
Joined: Tue Aug 30, 2011 3:08 pm
Contact: Website

Re: "Soundmodem" relays for amateur internet backbone

Thu Sep 01, 2011 1:42 pm

Obviously by the way this isn't intended for "broadcast only" applications, we'd probably allow people to bridge the connection to their normal internet connection to allow others to get fully online, or to host their own local websites through the relay, or add their own NAS to an uplink.

Ideally people would be able to join and interact without anything more complicated than a computer and a compatible walkie talkie, possibly with a cantenna to keep things somewhat sane and somewhat more private between user and mountaintop-relay.

obarthelemy
Posts: 1399
Joined: Tue Aug 09, 2011 10:53 pm

Re: "Soundmodem" relays for amateur internet backbone

Thu Sep 01, 2011 3:01 pm

Is there any reason to use SoundModem instead of regular data connections like wifi or wimax ?

cathalgarvey
Posts: 7
Joined: Tue Aug 30, 2011 3:08 pm
Contact: Website

Re: "Soundmodem" relays for amateur internet backbone

Thu Sep 01, 2011 3:13 pm

Wifi has limited range, and WiMax isn't assigned legal spectrum in much or all of Europe. Where it is, it's for carriers to deploy, not individuals. At least, that's my understanding.

Besides which, the infrastructure for effective long-range Wi-fi/Max is simply not available to most people who need it, when they need it. However, a nice packaged and tested method of doing data transfer over walkie-talkies with PCs and software would be trivial to implement anywhere. The advantage of RPi over using old PCs is that the RPi is low-cost and low-power, so operating a relay when it's *not needed* is feasible. In an emergency thereafter, you'd be able to convince people to set up relays countrywide based on the success of an RPi "testnet".

Picture this in use in future Egypt/Syria scenarios, which are bound to become more common over time; next time the "internet" is switched off at the ISP level, people city/countrywide can apply cheap walkie-talkies and PCs to operate relays to an uplink.

Two factors in my mind will have a particularly big impact on the final shape of a project like this:
- Can you run an "ethernet" style connection where many WT systems operate on the same frequency and packets are broadcast everywhere, but decoded only by intended recipient? This would simplify setup and would create something resembling more of a "mesh" than a series of "paths"
- Can you transmit data using audio frequencies above or below the human hearing range over Walkie Talkies? That way, it'll avoid nuisance-factor when others want to communicate on the same spectrum, and would make it less obvious that the frequency is being used for data on cursory inspection.

obarthelemy
Posts: 1399
Joined: Tue Aug 09, 2011 10:53 pm

Re: "Soundmodem" relays for amateur internet backbone

Thu Sep 01, 2011 3:31 pm

I'm really doubtful about many aspects of your plan, so instead of raining on your parade, I'll just shut up.

Svartalf
Posts: 596
Joined: Fri Jul 29, 2011 6:50 pm

Re: "Soundmodem" relays for amateur internet backbone

Thu Sep 01, 2011 3:42 pm

Skip soundmodem. If you're going to use something non-standard, but proven, use a BayCom USB modem. http://www.baycom.org/ This will allow you to link up via standard AX25 packet radio modes on anything you can hook it to and be compliant with regs with rates from 1200 baud to 307kbps in wideband modes. It's standard. It's what the HAM crowd uses worldwide. There's drivers available for the USB version now.

Past that, I'm going to be doing some experimentation on alternate modulation schemes that might be allowable that make it even easier to rig up something like what we're talking about.

cathalgarvey
Posts: 7
Joined: Tue Aug 30, 2011 3:08 pm
Contact: Website

Re: "Soundmodem" relays for amateur internet backbone

Thu Sep 01, 2011 3:44 pm

Er, I posted for feedback. I'd be a pretty lame hacker if I only wanted encouragement.

I'll be the first to admit that I don't know all there is to know about HAM or other forms of radio transmission; I've never actually done it. I've read up on Wikipedia, and I've looked through the Amateur Radio software on Ubuntu to see what's already out there, and I'm wondering how feasible this is. There are also some projects discussed out there and people saying "Yea, I've done it!" but no documentation.

If you have relevant input, I'd like to hear it! :)

Svartalf
Posts: 596
Joined: Fri Jul 29, 2011 6:50 pm

Re: "Soundmodem" relays for amateur internet backbone

Thu Sep 01, 2011 3:48 pm

Quote from obarthelemy on September 1, 2011, 16:31
I'm really doubtful about many aspects of your plan, so instead of raining on your parade, I'll just shut up.

He is right about the limitations of the two prospects you mentioned. As for WiMax being barred, so's some of the modalities that he's thinking of using- so it being "illegal" is a bit of a moot point, really. Expense (either is going to be "cheap" to "almost free" compared to a WiMax type lashup...) and leveraging things that'd be difficult to track down the sum total of the possible devices is the only reasons you'd want to use soundmodem or BayCom in the mode he's envisioning.

cathalgarvey
Posts: 7
Joined: Tue Aug 30, 2011 3:08 pm
Contact: Website

Re: "Soundmodem" relays for amateur internet backbone

Thu Sep 01, 2011 3:50 pm

Quote from Svartalf on September 1, 2011, 16:42
Skip soundmodem. If you're going to use something non-standard, but proven, use a BayCom USB modem. http://www.baycom.org/ This will allow you to link up via standard AX25 packet radio modes on anything you can hook it to and be compliant with regs with rates from 1200 baud to 307kbps in wideband modes. It's standard. It's what the HAM crowd uses worldwide. There's drivers available for the USB version now.
If it were only for my own personal use, I'd definitely go for a commercial solution or for a full HAM license. However, the motivation is the possibility of being able to achieve this using unlicensed spectrum and equipment that is likely to be "lying around" for people.

Speed is, of course, going to be rubbish. The point is proof of principal, rather than attempting to even remotely compete with fiber-optic cables.
Other promising solutions included IR or Visible-light relaying, which can achieve impressive speeds but the range is far poorer; 1.4km line-of-sight with a custom-built system: http://ronja.twibright.com

Quote from Svartalf on September 1, 2011, 16:42
Past that, I'm going to be doing some experimentation on alternate modulation schemes that might be allowable that make it even easier to rig up something like what we're talking about.
As in, you're interested in doing what I'm discussing here, or something else?

cathalgarvey
Posts: 7
Joined: Tue Aug 30, 2011 3:08 pm
Contact: Website

Re: "Soundmodem" relays for amateur internet backbone

Thu Sep 01, 2011 3:52 pm

Quote from Svartalf on September 1, 2011, 16:48
He is right about the limitations of the two prospects you mentioned. As for WiMax being barred, so's some of the modalities that he's thinking of using- so it being "illegal" is a bit of a moot point, really. Expense (either is going to be "cheap" to "almost free" compared to a WiMax type lashup...) and leveraging things that'd be difficult to track down the sum total of the possible devices is the only reasons you'd want to use soundmodem or BayCom in the mode he's envisioning.

I'm interested in the legal situation actually, would love to learn more. Provided the transmitting hardware isn't modified, transmission using handsets should be OK, which means legal considerations focus instead on *what's* being transmitted, right? That is, data rather than voice, or encrypted data rather than free text?

I gather that encryption is illegal over HAM in many/most countries, but does that apply also to unlicensed spectrum also?

Svartalf
Posts: 596
Joined: Fri Jul 29, 2011 6:50 pm

Re: "Soundmodem" relays for amateur internet backbone

Thu Sep 01, 2011 3:56 pm

Quote from cathalgarvey on September 1, 2011, 16:44
If you have relevant input, I'd like to hear it! :)

Well, with either a BayCom or using soundmodem, you're going to have to re-rig the push-to-talk switch on the talkies you're using to allow yourself the ability to send when you emit a packet. Most consumer radio gear is simplex, meaning one transmitter, multiple listeners at a time.

The HAM crowd have handie-talkies and other gear where this has already been modified for packet mode (which is what you're doing with soundmodem, really...). This means that you're going to have to rig something up with soundmodem to understand that you're doing this and to operate in bursts (packets...) where you check to see if you can send and then send a burp of data out- and then verify that you got it out without collision with another sender. The BayCom takes care of a substantive portion of this effort via the USB drivers and the AX25 TCP/IP overlay driver that comes with Linux. However, it doesn't QUITE work like WiFi or Ethernet even, so you'd have to learn a bit about it and then maybe figure out how to automate it's care and feeding a bit more than it is automated right now. The other upshot of this is that there ARE people doing packet mode communications in the UK over Citizen's Band.

Svartalf
Posts: 596
Joined: Fri Jul 29, 2011 6:50 pm

Re: "Soundmodem" relays for amateur internet backbone

Thu Sep 01, 2011 10:33 pm

Quote from cathalgarvey on September 1, 2011, 16:50
However, the motivation is the possibility of being able to achieve this using unlicensed spectrum and equipment that is likely to be "lying around" for people.


In those situations, most of the gear you're talking about won't be "lying around", in all honesty. You're going to have to duplicate the control aspects of a BayCom to accomplish what you need out of a soundmodem solution- those presume a duplex operation situation to really work. Most of the radio gear you're going to find "in use" for something like this will be simplex gear. Handie-talkies. Base station units. That sort of thing. The software you're using to act as a modem will have to understand push-to-talk for sending and understand that it might need to re-send because of collisions. BayCom's device mostly does this for you. It's why I suggested it. If you're game, though, go for it. :D


Other promising solutions included IR or Visible-light relaying, which can achieve impressive speeds but the range is far poorer; 1.4km line-of-sight with a custom-built system: http://ronja.twibright.com


Ronja's range exceeds most "gear that's lying about"- most handie-talkies, unless you're talking FRS radios, will be 100-200 yards at best. Base stations might exceed the range in the Citizen's Band frequencies which is what you'll find mostly available for unlicensed operation for. You can get better range out of Ronja if you're using better optics than they used. The big problem with Ronja is that it's a fixed, LOS system. If you're aiming at a mesh-like system (which you should be...) Ronja's not an answer except maybe to bridge back into the Internet proper.


As in, you're interested in doing what I'm discussing here, or something else?


Both. ;) Sorry for being a bit inscrutable. Need to validate something before I can go blathering too much about the idea I have here.

Svartalf
Posts: 596
Joined: Fri Jul 29, 2011 6:50 pm

Re: "Soundmodem" relays for amateur internet backbone

Thu Sep 01, 2011 10:42 pm

Quote from cathalgarvey on September 1, 2011, 16:52
I'm interested in the legal situation actually, would love to learn more. Provided the transmitting hardware isn't modified, transmission using handsets should be OK, which means legal considerations focus instead on *what's* being transmitted, right? That is, data rather than voice, or encrypted data rather than free text?


Nope. You must be using a band approved for digital communications modes by the authority for the area for it to be legal.

Just because you're using voice gear un-modified, doesn't mean you're using it in a manner approved. For example, if you took a Part 15 approved kiddie-talkie and attached it in a manner that would work the way you're envisioning and operate it within the States, you could face a $10,000 fine and confiscation of the gear in question at the minimum- along with the prospects of being put up in Club Fed for about a year. Why this is that way is that the gear was approved for voice operation, which has specific sideband and RFI characteristics that were approved at the time the device was submitted to the FCC for approval. Even on an unlicensed band. If you operate it outside of that mode, putting FSK/PSK/etc. from something like soundmodem, the RF output from the device is no longer the signal that was approved and can present varying RFI problems for users in the same band and other bands harmonics up and down from you.


I gather that encryption is illegal over HAM in many/most countries, but does that apply also to unlicensed spectrum also?

Unless the mode is approved for use in the unlicensed spectrum, yes. Some modes, like WiFi with WEP/WPA are allowed. If you're using CB and attach a BayCom, you're in violation, whether you are encrypted or not. If it was approved, like within the UK- you'd have to not encrypt it or be in violation.

__Miguel_
Posts: 59
Joined: Tue Sep 06, 2011 2:49 pm

Re: "Soundmodem" relays for amateur internet backbone

Tue Sep 06, 2011 5:27 pm

Hmm, interesting stuff I've just read.

The walkie-talkie approach, while possibly "cheap-ish", might be a bit impractical, and kind of convoluted. You'd need at least a pair of them to a single link, and speed would be simply atrocious.

The best legal ways of unlicensed long-distance communications (while maintaining a decent throughput) are WiFi and optical point-to-point data links (a.k.a. Ronja). WiFi has actually managed to maintain 50KM+ links with speeds over 1Mbps, I believe, though that is only achievable with heavily modded routers (to compensate for packet lag) and some bad-ass (and I mean HUGE) satellite dishes, and OoS signal strenght.

As for Ronja (which is open-source, too), well, cathalgarvey has already mentioned it: up to 10Mbps full-duplex over red or infrared LoS links (I believe there was a 100Mbps laser version being developed, but I can't find that info anymore). Plus, termination is a standard Ethernet plug, so a RasPi won't really be needed for that, I believe.

Cheers.

Miguel

Svartalf
Posts: 596
Joined: Fri Jul 29, 2011 6:50 pm

Re: "Soundmodem" relays for amateur internet backbone

Tue Sep 06, 2011 8:12 pm

Quote from __Miguel_ on September 6, 2011, 18:27
Hmm, interesting stuff I've just read.


There's a reason I still, from time to time, go through these mental exercises by myself and with others. Much like right now.


The walkie-talkie approach, while possibly "cheap-ish", might be a bit impractical, and kind of convoluted. You'd need at least a pair of them to a single link, and speed would be simply atrocious.


Depends on your modulation technique. You should be able to get up to dialup and maybe even ISDN speeds out of the gear at the least- but you're going to have to wade off a bit into the modifying the gear space to accomplish high speeds with the gear. The big reasoning for this is that the stuff you mention isn't mobile and something you could easily deploy in a mesh or spoke and hub fashion in an emergency or similar circumstance. Think tornado hammering a major city, or an earthquake trashing San Francisco. Infrastructure's toast. You may/may not be able to set up a Ronja or one of those WiFi DX setups. You're more likely to be able to manage a cluster of little bricks about the size of a brick, spread all over the place, or maybe a COW (Cell on Wheels) being rolled in (Since it was designed to make a cell-site totally mobile for this reasoning...)- IF that.


The best legal ways of unlicensed long-distance communications (while maintaining a decent throughput) are WiFi and optical point-to-point data links (a.k.a. Ronja). WiFi has actually managed to maintain 50KM+ links with speeds over 1Mbps, I believe, though that is only achievable with heavily modded routers (to compensate for packet lag) and some bad-ass (and I mean HUGE) satellite dishes, and OoS signal strenght.


The biggest problem with this setup is you've got to modify the routers or the network stack in the R-Pi's to even have a chance of it working- combined with those HUGE dishes.


As for Ronja (which is open-source, too), well, cathalgarvey has already mentioned it: up to 10Mbps full-duplex over red or infrared LoS links (I believe there was a 100Mbps laser version being developed, but I can't find that info anymore). Plus, termination is a standard Ethernet plug, so a RasPi won't really be needed for that, I believe.

Ronja's would be nice for some configurations. Won't argue it. I think, however, they never got the 100Mbit model done. Not wholly sure why unless it just didn't prove out to work as well as planned and they had to re-think things- and then never got back to it for personal life reasons.

__Miguel_
Posts: 59
Joined: Tue Sep 06, 2011 2:49 pm

Re: "Soundmodem" relays for amateur internet backbone

Tue Sep 06, 2011 8:42 pm

Quote from Svartalf on September 6, 2011, 21:12
Depends on your modulation technique. You should be able to get up to dialup and maybe even ISDN speeds out of the gear at the least [snip][/QUOTE]
Well, that's just out of my league. I'm a NAS and network fan, but my background is law, not electronics, so I'm going to take your word on it... hehe

Still, it does seem an awful lot of work to setup on the hardware level. WiFi, though "heavy-duty", seems easier, since it basically involves modifying router firmware, which is only really needed for extra-long links, anything under 10Km should be fine (but again, that's from a non-tech perspective).

I think it boils down to the application. Disasters need portability, community links not so much.


The biggest problem with this setup is you've got to modify the routers or the network stack in the R-Pi's to even have a chance of it working- combined with those HUGE dishes.[/QUOTE]
As I said above, only extra-long links require firmware hacks. Other than that, you only really need AP-to-AP bridging support, which is not that uncommon.

Ronja does need a manual Full Duplex link, though, which might be hard to achieve with standard networking switches...


Ronja's would be nice for some configurations. Won't argue it. I think, however, they never got the 100Mbit model done. Not wholly sure why unless it just didn't prove out to work as well as planned and they had to re-think things- and then never got back to it for personal life reasons.
A few years back, before the site redesign, the Ronja creator clearly stated his goal was to get a dirt-cheap design and final product, using the least expensive materials available (the lenses used are from standard magnifying glasses, just to name one example).

While there is always the chance the "personal life reasons" is true, I think there might be a chance the laser design was just too expensive to achieve, either because of PCB, components, or something else, and so it was scrapped.

I do think there is still a small reference on the Donors page to the laser component, only thing is the whole site seems to have been abandoned...

Anyway, idea exchange is very interesting. It has been a while since I've done this... :)

Cheers.

Miguel

MoonShadow
Posts: 7
Joined: Fri Sep 09, 2011 6:30 pm

Re: "Soundmodem" relays for amateur internet backbone

Fri Sep 09, 2011 7:42 pm

You want to look into Dash7 networking...

http://en.wikipedia.org/wiki/DASH7

Svartalf
Posts: 596
Joined: Fri Jul 29, 2011 6:50 pm

Re: "Soundmodem" relays for amateur internet backbone

Fri Sep 09, 2011 8:07 pm

Quote from MoonShadow on September 9, 2011, 20:42
You want to look into Dash7 networking...

http://en.wikipedia.org/wiki/DASH7

It's a bit of a prospect- but unless it can do mesh networking, it's got a 1km limitation.

__Miguel_
Posts: 59
Joined: Tue Sep 06, 2011 2:49 pm

Re: "Soundmodem" relays for amateur internet backbone

Fri Sep 09, 2011 8:41 pm

Hmm, DASH7 seems interesting... I wonder why hasn't it cropped up as a wireless alternative to X10 and the likes, it seems the main purposes are compatible...

It never ceases to amaze me just how much one can learn just by listening to other people's experiences and knowledge. Wow

Cheers.

Miguel

Svartalf
Posts: 596
Joined: Fri Jul 29, 2011 6:50 pm

Re: "Soundmodem" relays for amateur internet backbone

Fri Sep 09, 2011 8:52 pm

Quote from __Miguel_ on September 9, 2011, 21:41
Hmm, DASH7 seems interesting... I wonder why hasn't it cropped up as a wireless alternative to X10 and the likes, it seems the main purposes are compatible...

It was mainly developed for RFID and similar purposes, but it can serve a larger purpose. It was really still kind of under development for the last handful of years; which is why you're just now beginning to see stuff made with the tech. Everyone reaches for ZigBee because it's what they're familiar with- which is "okay", but it's got some obnoxious limitations.

MoonShadow
Posts: 7
Joined: Fri Sep 09, 2011 6:30 pm

Re: "Soundmodem" relays for amateur internet backbone

Fri Sep 09, 2011 11:26 pm

Quote from Svartalf on September 9, 2011, 21:07
Quote from MoonShadow on September 9, 2011, 20:42
You want to look into Dash7 networking...

http://en.wikipedia.org/wiki/DASH7

It's a bit of a prospect- but unless it can do mesh networking, it's got a 1km limitation.

It's got a 1KM limitation in the United States, up to 10Km in parts of Europe due to higher power limitations. That said, a pair of FM talkies using soundmodem is going to suck by comparison. Dash7 uses 443 Mhz as it's base freq, which happens to sit right in the middle of the 70 cm ham radio band. It's a great band for digital modes. And that 1km estimate is based upon a low power transceiver with a coil antenna inside of a small tracking device, which is what Dash7 was originally developed to do. It's not ideal for high bandwidth, but because it's not session based, it has almost zero connection overhead. It can be used in a mesh scenario, but wireless meshes are actually very poor at moving data blocks anyway. There are very good reasons that mesh networks cant compete. Dash7 is ideal for an time sliced, opprotunistic network, however. For example, imagine that every smartphone that had a wifi radio also had a Dash7 radio. Wifi is relatively short range, high bandwidth, high battery demand and session based. Dash7 is inherently low power in receive idle, with very short transmit "hey I'm here" bursts. If two smartphones came within half a click of each other, they would be able to identify each other and turn on their wifi radios to trade data (such as with Forban, (http://www.foo.be/forban/) then turn off the wifi radios as the wifi left range. Dash7 also has built in relative location methods, i.e. the radios can determine if the other radio is getting closer or farther away, how fast and roughly how far away it is based upon signal strength analysis. So when the two Dash7 radios can see each other, they will know when and if their wifi radios can connect. In this way, smartphones can use Dash7 the same way that cell phones use the 'control channel' to track cell towers and know when they need to ring even though the main radio isn't transmitting or connected. The smartphones can then toggle the wifi in an automated fashion beyond what can be acheived by gps based systems such as Locale, permitting a router with dash7 to be discovered. P2p networks such as Bitcoin or Jabber could also make incredible use of Dash7. Jabber over Dash7 could literally create a wireless texting network across a modern city that doesn't require supporting infrastructure at all. Which would be an ideal backup in a natural disaster or a government Internet shutdown scenario. Dash7 also has inherent encryption methods, making snooping of messages a futile endeavor.

MoonShadow
Posts: 7
Joined: Fri Sep 09, 2011 6:30 pm

Re: "Soundmodem" relays for amateur internet backbone

Fri Sep 09, 2011 11:31 pm

Quote from __Miguel_ on September 9, 2011, 21:41

It never ceases to amaze me just how much one can learn just by listening to other people's experiences and knowledge. Wow



Ain't the network effect grand? It's why I start to feel stupid if I can't access the Internet for more than a day. The ability to answer a question in near real time is downright addictive.

__Miguel_
Posts: 59
Joined: Tue Sep 06, 2011 2:49 pm

Re: "Soundmodem" relays for amateur internet backbone

Sat Sep 10, 2011 7:00 am

You're sooo right, MoonShadow...

Just now, after reading your previous post, my jaw dropped (and made me, once again, wish I had been an IT major, not a Law major... Too late for that, though). The sheer amount of information you can have access to makes your IQ go up by at least 5 times, probably more (which would mean I'm way over 600 right now... lol).

Now, if only wearable PCs were already a viable (and cheap) alternative... OR if we could actually have a direct I/O port to our brains (I'd be so there for the human trials...), that would be sweet...

But I digress. That Jabber over DASH7 seems quite a good solution for a disaster scenario, actually. Even if you don't have the WiFi toggle in place, a quick way to move small amounts of information (people location, medical status, relevant news, etc.) seems to be somewhat sufficient, especially since you can probably build a powered mobile version of it (or semi-static), with reception and transmission amplifiers to cover a larger area (you know, so you can hear nodes that too far away from anyone else, and to get information to them).

Yep, that seems an interesting KISS approach. And, of course, for bigger data needs, P2P WiFi with toggling might do the trick, but in a disaster situation, WiFi should only be used when imperative: it sucks power tremendously, power that might not be readily available.

Ah, my morning learning fix... So cool :)

Cheers.

Miguel

beagle7
Posts: 1
Joined: Sat Sep 10, 2011 1:23 am

Re: "Soundmodem" relays for amateur internet backbone

Tue Sep 13, 2011 8:25 pm

Check out this link (BCWARN)
http://wiki.bcwarn.net/bcwarn-wiki/
They have already used wifi frequencies to do ~ 75 mile hops from Vancouver BC to Victoria.
I believe the power levels are between 1-10 watts.

Svartalf
Posts: 596
Joined: Fri Jul 29, 2011 6:50 pm

Re: "Soundmodem" relays for amateur internet backbone

Tue Sep 13, 2011 10:23 pm

Quote from MoonShadow on September 10, 2011, 00:26
It's got a 1KM limitation in the United States, up to 10Km in parts of Europe due to higher power limitations. That said, a pair of FM talkies using soundmodem is going to suck by comparison. Dash7 uses 443 Mhz as it's base freq, which happens to sit right in the middle of the 70 cm ham radio band. It's a great band for digital modes. And that 1km estimate is based upon a low power transceiver with a coil antenna inside of a small tracking device, which is what Dash7 was originally developed to do. It's not ideal for high bandwidth, but because it's not session based, it has almost zero connection overhead. It can be used in a mesh scenario, but wireless meshes are actually very poor at moving data blocks anyway. There are very good reasons that mesh networks cant compete. Dash7 is ideal for an time sliced, opprotunistic network, however. For example, imagine that every smartphone that had a wifi radio also had a Dash7 radio. Wifi is relatively short range, high bandwidth, high battery demand and session based. Dash7 is inherently low power in receive idle, with very short transmit "hey I'm here" bursts. If two smartphones came within half a click of each other, they would be able to identify each other and turn on their wifi radios to trade data (such as with Forban, (http://www.foo.be/forban/) then turn off the wifi radios as the wifi left range. Dash7 also has built in relative location methods, i.e. the radios can determine if the other radio is getting closer or farther away, how fast and roughly how far away it is based upon signal strength analysis. So when the two Dash7 radios can see each other, they will know when and if their wifi radios can connect. In this way, smartphones can use Dash7 the same way that cell phones use the 'control channel' to track cell towers and know when they need to ring even though the main radio isn't transmitting or connected. The smartphones can then toggle the wifi in an automated fashion beyond what can be acheived by gps based systems such as Locale, permitting a router with dash7 to be discovered. P2p networks such as Bitcoin or Jabber could also make incredible use of Dash7. Jabber over Dash7 could literally create a wireless texting network across a modern city that doesn't require supporting infrastructure at all. Which would be an ideal backup in a natural disaster or a government Internet shutdown scenario. Dash7 also has inherent encryption methods, making snooping of messages a futile endeavor.

Sounds like to me we need to contemplate looking into Dash7 stuff for things. I'd say that while it's bandwidth sucks compared to other things, it's a gem for the sorts of things we're talking about here. Is it truly an unlicensed band for this use?

Return to “Other projects”