Slashdot Mirror
Ask Eric Blossom about Software-Defined Radio
Eric Blossom is an electrical engineer with a history of working with radio and communications security. He gave a presentation at the recent H2K2 conference about his work with GNU Radio, which is, bar none, the single most exciting software project in existence today. (Imagine computing devices that communicate seamlessly across the entire electromagnetic spectrum.) As usual, we'll forward some of the best questions to Eric and post his responses when we receive them.
which is, bar none, the single most exciting software project in existence today
Some people may disagree with this sentiment.
I, for example, am looking forward to Doom3 more than this project which I've only just heard about.
How can you justify these wild claims?
playboy gets an XM radio channel, and development floureshes. just another example of how pr0n drives all new technology.
MARIJUANA, SHROOMS, X: ONLINE?! - E
I was recently at H2K2 and heard this forum which right away made me ecstatic(sp?). An issue that was brought up was how this can impact the DMCA, FCC, and the big corps. You guys were saying Sony, and the other conglomerates were forming a committee that would do a digital signature to say what was allowed to be copied, and not through a dual channel checking...My question is what is the status of digital radio and its rights in the present world? To my understanding you can have a very high number of digital channels inside a single band which makes licensed analog frequencies just a waste of money to corporations if they use GNURadio as a means to transmit data long distances. Anyways, looking forward to some feedback and goodwork, I'll be joining this revolution soon, just got the dual server built ;)
I realize this might be complex, and that the answer might be of the form
But as both a ham and one who designs SDRs, I'd like to know where this resides on the Home Hacking Scale....
www.eFax.com are spammers
Are there parallels to this technology? and if so, how will GNU Radio avoid those pitfalls?
What is the link between GNUradio and 802.11b?
I read through the GNU Radio website, and even though I found it informative in terms of the basic idea and examples, I couldn't find anything relating to what extra hardware is needed. (Maybe I just didn't look long enough?)
:o)
What extra hardware is needed in addition to a computer? Are we talking DSP chips and boards, or something a little more exotic?
Thank you for a potentially exciting project, though. This makes me want to renew my ham radio license.
-----
"You spilled my egg... I needed that egg."
This is one project where hacking the code can kill people or land you in jail. Don't broadcast on the wrong frequency!
Keep this away from radio telescopes!
Anyone want to clarify?
With the restrictions to broaccasting on the internet that seem to be spring up by the day do you think this tech can become a work around. In otherwords most restrictions ar based on the faact that its the audio being rebroadcast. Perhaps is it were the Stations actual signal being broadcast across the net and recided by a capable piece of software, many of the restrictions would no longer apply. Since its the carrier signal taking the content to my computer rather than an audio codec. This would negate most of the complaints that have caused many internet radio stations to go offline....
Your thoughts?
Power Corrupts,Absolute Power Corrupts Absolutely, leaving one person(group)in charge is absolutely corrupt.
What work has been done with the DoD. Can GNU Radio realistly be expected to compete with the likes of the Motorola DMR in the Defense sector?
I mod down any one who says "I'm sure I will get modded down for this"
Isn't the Slashdot blurb.. how shall I put this.. completely and totally incorrect?
The Slashdot story implies this project will bring: computing devices that communicate seamlessly across the entire electromagnetic spectrum.
Surely this is an exaggeration.
It is possible to imagine real-time processing of kHz, and possibly MHz signals in software.
There are issues with getting and antenna with decent response over a very wide range, but we can sidestep that. The point is, the ADC and actual processing of the waveform with the CPU is not unreasonable with x86 hardware.
But if you're looking at microwave communications... that just isn't plausible to me at all.
The ADC time resolution would surely require dedicated equipment. You could put this on a PCI card, but the PCI bus obviously does not have bandwidth for a GHz signal.
I would think the point of this is not to cover a wide range of the spectrum at all, but instead to process a range such as 1 kHz - 10 kHz in new and unusual ways.
And of course the applications are not limited to wireless devices! This could be just as useful with transmission down coax.
[not a question for Eric Blossom unless highly moderated ;)]
Could actually someone explain what GNU radio does? Even after visiting the site, I stil have _no clue_ what it is and what's the goal.
Same for GNU Bayonne.
Both sound like cool projects but hard to understand what they do.
Would someone care to explain to the world what this project is (eg: with this, you can transmit RF waves using only a speaker), that'd be great.
Thx
I want a feature list containing all the geeky details
Radio design is about trading features against each other, eg. if you want a large frequency range, you will usually end up with noisy oscillators giving you poor large signal handling, and low selectivity (ability to listen to weak stations close (in frequency) to a strong one. If you want good sensitivity, you loose large signal handling. If you want narrow filters, you get lower sensitivity (ok, this is a software radio, so you can do extra filtering in software, so this might not apply). You get the idea. Always compromises.
RFC1925
After reading some posts, some people seem to be a bit confused as to what this is and how it can be used. Well, for the /. crowd, here's a specific example which will put all this into perspective:
Now that generating waves becomes a software problem, it means that theoretically anything that before needed hardware to modulate/demodulate (or encode/decode, depending how you look at it) signals can now be done in software. Practially, this means that you can transform your machine into a WiFi or Bluetooth system by simply installing the right software. It also means that as new future wireless technologies emerge, your hardware can support them by a simple software install.
Similarly, anything that uses radio waves can be "emulated", like a good old FM/AM radio (the website has sample code for this), a Walky-Talkie, a home wireless phone, or even a cell phone!!!
So now you see why there's a lot of exitement around this. If the project could only get more funding (Intel? AMD? IBM? Sun? Motorolla? Sony?) to speed this up...
This technology sounds like the kind of thing which could greatly add to the convergence of devices that clutter the electronic life. You could extend convergence not only as a Smartphone but have in one device (though perhaps not simultaneously):
1. Cell phone
2. Computing power (PDA)
3. FRS radio device
4. 802.11x network device
5. Police scanner
6. Television reciever
7. etc.
Have you been approached by police departments, FedEx, etc. to develop devices to allow their people to do more stuff in fewer packages?
To my understanding you can have a very high number of digital channels inside a single band which makes licensed analog frequencies just a waste of money to corporations if they use GNURadio as a means to transmit data long distances.
Not strictly true.
The amount of data that you can stuff into one frequency band within given power and noise specifications has a hard limit, no matter what the encoding scheme. Every once in a while someone claims that spread-spectrum or scrambled or UWB some other encoding scheme will surmount this, and every time someone else points out that this is not correct.
The encoding in conventional radio broadcasts is wasteful, but they don't need to adopt software-controlled radio to get better information densities. Look at satellite relays or any other data transfer in regimes where bandwidth is expensive to see what can actually be done.
Software-definable radio is still an interesting subject, of course.
Will GNU Radio support Ultra Wide Band? Soon, someday, never?
Great project. Thanks.
--Lawrence Lessig for Congress!
I really miss the old FM car radio pushbuttons. Then, again, I miss actually liking the music.
"My repetition threshold has been exceeded."
Practially, this means that you can transform your machine into a WiFi or Bluetooth system by simply installing the right software. It also means that as new future wireless technologies emerge, your hardware can support them by a simple software install.
And a hardware upgrade, since your WaveMangler 3700 card can only handle signals up to 3.7 GHz, but the new Sub Ether Space Net nodes talk at 5.2 GHz...
Still fun and useful, though.
Also, along the same vein, has anyone looked into simply storing the input stream unaltered onto mass storage and then simply picking apart the bits that the user wants to view? This could make a truly ultimate TiVo-like unit once the speed got high enough (pick some times and record *ALL* channels). For now, I'd settle for a radio-TiVO (record all radio/ham stations at once).
It has always been possible to generate waves in software. What's novel here is that it's being done in real time in the IF range of frequencies. Computers are still not quite fast enough to do this in the frequency range of the carrier signal.
When you tune your FM radio, your receiver accepts a signal centered at around 90-100 MHz and downshifts it to 10.7 MHz. The 90-100 MHz is called "radio frequency", the 10.7 MHz is called "intermediate frequency". No matter what station you listen to, it gets shifted down to the same intermediate frequency, so that once it's there, it can go thru exactly the same frequency.
The conversion from RF to IF is a pretty simple process that ignores the actual audio content of the signal. Once it's in IF, an FM demodulator picks off the audio that was modulated onto the carrier at the transmitter. AM radio also uses an intermediate frequency, but it's 455 kHz instead of 10.7 MHz.
GNU Radio depends upon commodity computers to sample and process the signal in real time. The Nyquist sampling theorem says you must sample at twice the frequency of interest as a theoretical minimum; in practice you'd like to sample more like threee or four times the frequency. So when you run GNU Radio, samples are whipping through your computer at 30 or 40 megasamples per second, at least for the IF processing. The audio processing can be done at a much more leisurely pace.
Since the computer can't hope to keep up with the 90-100 MHz raw carrier (yet, anyway) there must still be some external circuitry to perform the RF->IF downshift. But that's the relatively simple circuitry - by specifying everything else in software you get a hugely flexible radio. I've drooled with envy watching people use all-mode radios to talk to satellites in orbit, but those suckers are expensive! You need to be able to do AM modulation on the 2 meter band (144-148 MHz). Now maybe I can try it one of these days.
WWJD for a Klondike Bar?
I gather from some prior posts that a single device won't allow this software to "communicate seamlessly across the entire electromagnetic spectrum". However, this doesn't rule out the possibility of a range of devices that can accomplish this. What do you see when you envision these devices? What are the implications of such devices in terms of possible applications and possible ubuses, intentional or unintentional?
Check out the DSP-10 designed by Bob Larkin, W7PUA and offered as a kit by TAPR. It receives and transmits in the 2 meter amateur band (144-148MHz) using a standalone DSP card (that has power similar to a PC sound card). The code to drive it is all open source, and the DSP can not only handle traditional modes, but can also be programmed to do all sorts of neat stuff. New modulation schemes programmed into the DSP-10 have resulted in successful "moonbounce" (that's right, using the moon as a radio signal reflector) contacts with much lower power/smaller antennas than ever before used.
Perhaps one of the best current applications of software radio is to act as a bridge between multiple radio systems.
Take for example an event, such as a terrorist attack, that warrants the use of many agencies that span a wide spectrum of roles and budgets. In the US, this means from local fire, EMS, law enforcement, response teams, HazMat, right on up to FBI, US Marshalls, Secret Service, FEMA and across to public works and everyone else involved in the response effort.
Communications in these situation has always been a big problem. It was highlighted nearly a year ago in New York and Arlington.
What a software radio unit would allow you to do is set up on site and when in operation the unit allows all the different radio systems of the agencies - who of course have different budgets, and hence equipment - to communicate relatively easily with each other as the software radio does the transformations from one radio signal and channel to another. And this can be done without reprogramming the frequencies on the radios, as you can use agencies predesiginated channels.
Perhaps the coolest thing is that it can be set up to work with current equipment, so apart from the bridge, and associated hardware, agencies preexisting radios will work. This is all good especially when you consider that people at the Pentagon were carrying around combos like 2 radios, 3 cell phones, and 3 pagers just to keep on top of everything.
By moving it to software, you can target everything to nearly one device - to the point where you plug phone lines (could be cable/sattelite/rf) into the bridge, and people on radios can make phone calls.
Another benefit is that it could be used in radio dense environments to bridge radio communications as radio devices increase in popularity by allowing them to use frequencies they weren't originially designed for. I think thats pretty cool.
Cheers
If I'm interested in doing research in this field someday, and I'm currently a computer engineering major, what are some good electives that I might take? Aside from general programming necessities, what sort of signal processing courses are necessary to understand the underlying aspects of software-defined radio?
"I may be quite wrong." - Socrates
Imagine computing devices that communicate seamlessly across the entire electromagnetic spectrum.
Did you say the entire electromagnetic spectrum? Visible and otherwise, I hope?
Someone needs to sneak one of these into a dance club. Preferably one with an impressive multicolored light show, and strobe lights. And clubbers using cell phones and other 'chic' wireless devices. That should cover a wide electromagnetic range.
Just to see what they get out of all that 'input'.
Good judgment comes from experience.
Experience comes from bad judgment.
That's what always galled me, the fact that Linux / BSD / ABM couldn't use them.
Infuriate left and right
So, will there be a way/API for writing our own plugins/working with other plugins? Or, better yet, a way to get the output from this out to other apps (sockets, etc)?
The reason I ask is that I'd love to take the planned GPS code (mentioned in the "future directions" section of the project) and use it to make a GPS-based stratum-1 NTP source. Real stratum-1 time servers are expensive...doing this all w/software would be cool.
(Yes, I know, it wouldn't be easy to get microsecond accuracy, but it'd be a hell of a lot better than nothing.)
Another option would be to have a cable hooked up that is wound on a cable that you can wind or unwind to match the wave length you are monitoring.
science is a religion
Perhaps this could allow Napster to reinvent itself as a encrypted broadband spread spectrum music distribution service.
GNU Radio typically uses a TV tuner card that downconverts 6MHz of spectrum (one TV signal, or about half the FM broadcast band) and digitizes it. Software can then be used to do an FFT and extract a few channels. More CPU power lets you extract more stations.
Again, an neat hack, but not a big deal.
In the future will this project let me do the folloing.
Watch digital TV
Listen to digital radio
and analog of the above
using just my PC and an inexpensive cature card eg bt848?
what about encryped signals will systems like this be able to brute force encrypted digital TV/ cabel/satterlite chanels?
- dedicated semiconductors vs general-purpose processors
- Vendors vs OS designers and software programmers
- short term: certification
- long term: standardication & spectrum management
Actually, you DON'T need to sample a 10.7 IF at double speed.
The Nyquist theorm states you must sample your signal at not less than twice the bandwidth of your signal. You can limit the 10.7 IF to 60 kHz bandwidth and then sample it at 120 kHz just fine - this is called subsampling.
In effect your analog to digital converter becomes an additional mixer in the processing chain. If you think about it, sampling is just multiplying the signal by a stream of Dirac impulses in the time domain, which corrisponds to convolution by a Dirac impulse in the frequency domain - just like an analog mixer.
HOWEVER - you HAVE to bandwidth limit your IF correctly - if you sample at 120kHz and you have stuff leaking through at a bandwidth of 70 kHz you are screwed - your signals will fold over in the frequency domain.
For those who are interested, look up the Intersil 50216 - it is a dedicated chip that does much of the signal processing for you.
What would be COOL would be for the FSF to sell PCI cards with a 50216, 50217, and an FPGA - then you could really do some cool stuff.
www.eFax.com are spammers
Up until now, free software has mostly threatened closed commercial software. GNU Radio, however, might make some hardware manufacturers squirm a bit. If I can use a generic device along with GNU Radio to emulate a range of devices how will this impact the makers of those devices and are you (or users of GNU Radio) possibly violating patents for some of those devices? It seems that GNU Radio will stir up more mud in the IP and DRM debates. What are your thoughts on this?
This project is to the radio what the general purpose computer is to the abacus.
If tits were wings it'd be flying around.
This discussion has an apalling lack of 'peers' who are RF qualified.
Software radio has been a fad for at least a decade, but in a much less ambitious sense. Mostly the focus has been on using embedded DSP in place of dedicated radio circuits - and the cost/power performance has moved in this direction (generally), particularly for smaller manufacturing volumes .
A 'universal' radio is substantially more difficult. Radio sensitivity is limited by the inherent noise of the receiver, the dynamic range of the receiver components, including the demodulator, and gain. These components are in 'conflict', that is, more gain can limit the noise of the receiver, but may limit dynamic range more.
There are also difficult architectural issues. A direct conversion radio (converts in one step to baseband) suffers from LO re-transmission (illegal if over certain limits), DC-offset and drift, noise and dynamic range. Single conversion to an Intermediate Frequeny (IF) simplifies these problems, but the choice of Local Oscillator (Synthesizer), including noise characteristics, switching frequency and bandwidth, combined with the necesary amplifier gain, broadband filters, mixer dynamic range, input power and noise, are complex.
Any attempt to transmit raises complex circuit and regulatory issues.
Radio requires a real investment in time to understand RF circuits, modulation theory, encoding and decoding techniques, protocols and regulations.
Jumping ahead to a Linux application that 'assumes' an always appropriate (wideband or universal) radio seems like an unfortunate waste of time.
The same code might be interesting, however, as a tutorial on modulation and protocols - if it's any good, but there are better sources.
In my experience, it's much harder to develop DSP software compared to developing hardware for the same task. Hardware design these days is a mature engineering discipline. Software development remains a high-risk black art, DSP doubly so. Also, for some signal processing tasks, the demand on processing power far outstrips the current processors. For something like a 3G modem you might need 20 Gigaflops to implement it in software. Even a plain well designed comms receiver from 20 years ago with a couple of crystal filters cannot be fully emulated with today's DSP technology. Complemented and enhanced - yes, but not emulated. How do you show that software-defined radio is up to more than just filling a very limited and specialised niche?
"Argue with idiots, and you become an idiot." -- Paul Graham
How does this project relate to other Open Software defined radio projects such as the ARRL digital radio group and the Tuscan Amateur Packet Radio's Software Defined radio project?
. html for a report from the ARRL committee.
Can you give us more information on the goals of your project in relation to the goals for these other projects? Thanks.
See http://www.tapr.org/tapr/dv/index.html for info on the TAPR digital voice group. Go to http://www.arrl.org/announce/reports-0107/digital
Jay Sissom KA9OKT
It turns out there's a name for this, IQ modulation, where "I" means "in phase" and "Q" means "quadrature". There is a quite elegant Java simulation that shows what's going on.
WWJD for a Klondike Bar?
For a couple of hundred US dollars I can get a PCI card with an FPGA or some such field-programmable logic device. Isn't this the right way to do most of the signal processing for "software" radio? Why or why not?
I love the idea of software defined radio. I may get involved in the project in some fashion.
Would you care to speculate on the probability of success for those who want to pass legislation aimed at "plugging the analog hole?"
I ask because it seems to me that such mis-guided legislation would be poison to many endeavors, yours included.
respectfully,
Mamba-mamba
--
By including this sig, the copyright holders of this work or collection unreservedly place it in the public domain.
...transmitting with unlicensed transmitters in regulated frequency bands is already illegal. In Canada, CRTC uses various methods of ELINT to track down such folks and I'm sure FCC does the same in the States.
Is having every Tom, Dick and Harry transmitting on whatever band they feel like at whatever power they feel like a good idea? Hell no. That's why it is illegal, and if you do so and they catch you, the results are pretty ugly. If it kills someone, I'm not sure you might not get charged with some sort of related Felony.
One other poster said:
Just as Open Source is driving copyright owners and licensing contract lawyers nuts, so too is Software Defined Radio. It basically brings all modulation techniques back within easy reach of the average Joe radio listener. No more of this nonsense of saying that demodulating police MDT transmissions is illegal.
What use will demodulating a data signal do? I guess if everything is sent en-clair in ASCII text without a lot of heavy archaic or proprietary protocol overheads, you could get a lot out of old style MDTs. Most modern police mobile computers (palmtops, laptops, etc.) integrate at least rudimentary encryption (some limitations are placed by the public data network used as a VPN in many cases - low BW channels make long keys and multi-transaction authentications a very bad thing...).
I worked on systems for a Canadian federal police agency and they integrated encryption to prevent some geek with a scanner and a PC from harvesting police transactions. It's true the basic crypto probably wouldn't stand up to rigoous long-term attack, but it would at least deter casual busybodies and peeping Toms. Stopping dedicated hackers with time/capability/intent is a much uglier proposition, as we all know.
The legislation going in place now is stupid because it is relatively unenforceable (re decoding encodings/modulations like FM). But, OTOH, it is just one more play in the Gov't playbooks if someone gives them an opportunity by getting caught doing something dumb.
I really hate unenforceable laws - they're a waste of taxpayers money. Kinda like the rules about your dog defecating in your back yard, where the Bylaw officer is not a Peace officer and has no right to enter your property.... unenforceable. And therefore retarded.
But then, if the gov't (especially as it pertains to computers/comms) wasn't bought by lobbyists and run by the techno-clueless (for the most part), the world would be a very different place methinks.
-- Mal: "Well they tell you: never hit a man with a closed fist. But it is, on occasion, hilarious."
Note to self: Intersil has an office on Route 9 near Shopper's World, and uses Arrow and Newark as distributors.
WWJD for a Klondike Bar?
What I mean by this is since this is digital, is it encrypted by default? If this is so, how will the DMCA affect this type of radio?
Eventually, software-defined radio will come to mobile phones and PDAs, and you'll be able to just download new software to switch from CDMA to GSM and so on. At least, that's the vision - your RF hardware must still be able to handle the right frequencies.
Were I designing such a board, what I would do is use an FPGA that had an available PCI core with scatter/gather support. That way, you could feed the parts with buffer lists in main memory, and get a pretty high bandwidth to and from the parts.
I'd also put a FIFO between the parts and the bus controller, so that brief contention with other devices wouldn't drop samples.
Lastly, I'd suggest using LVDS to talk to the DAC/ADC - that way you can get them OUT of the computer case and away from all the noise.
www.eFax.com are spammers
Sounds like the worst of the official mindset. We lose the transparency of citizens hearing police communications, but the determined and well-funded bad guy can still intercept them. And since there's an appearance of security, the agency will be less alert to such interception. So Scientology, organzied crime, and foreign intelligence get a boost in eluding investigations.