Ask Eric Blossom about Software-Defined Radio 181
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.
Bar none? (Score:2, Funny)
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?
Re:Bar none? (Score:1)
Re:Bar none? (Score:3, Interesting)
Hook your computer up to your digital cable system, and have it do the QAM demodulation. Then, pump the results to an MPEG transport demux and MPEG decoder. Boom. Instant digital cable box.
Same thing, in reverse. Output IF, and hook it up to an upconverter and amplifier. Now you're your own cable company. The equipment typically used to do this is insanely expansive, and hard to get. This can make community cable television, for example, much easier and cheaper to implement.
Interestingly, the decoding/encoding is all done on a commodity, general purpose computer, so all copy protection schemes become hackable, the way they were with software DVD players.
More importantly, software is easier to fix and upgrade than hardware. This could result in significant cost savings for people who want to use this kind of technology commercially.
Don't steal cable (Score:1, Troll)
Hook your computer up to your digital cable system, and have it do the QAM demodulation. Then, pump the results to an MPEG transport demux and MPEG decoder. Boom. Instant digital cable box.
Boom. Instant jail time. Digital cable systems are scrambled with 3DES or Rijndael or RC4 or some other cipher. This is what the DMCA was actually intended for: to prevent piracy of cable and satellite television service.
so all copy protection schemes become hackable
By people who don't mind being sexually assaulted in the anus [goatse.cx]. Homosexual rape is one of the biggest problem in American prisons (and I'd imagine, prisons worldwide).
and, having said that, this is not a new concept - winmodems have been doing this for a while now
That was my first thought: "What the heck? A winmodem for 802.11? And it's actually endorsed by the FSF?"
Re:Don't steal cable (Score:1)
Actually I was thinking that this can be a good way for MSOs to offer service to people who don't want a digital cable box.
Of course, knowing how these guys work, it will never happen.
By people who don't mind being sexually assaulted in the anus.
Or people whose country doesn't have DMCA like laws yet, or people who have the sense to distribute their work anonymously, and the means to do so.
I was just stating that software systems can be hacked. I don't think hacking a copy protection scheme is ethically wrong - using this knowledge to violate the social contract that stipulates that people are entitled to compensation for their work, is.
wow, right on time. (Score:2)
FCC vs. Software Radio (Score:3, Interesting)
Re:FCC vs. Software Radio (Score:5, Interesting)
I'm thought something along the same lines... used to be that any RF that came into a person's airspace was fair game... now that's not true. It can be illegal just to 'listen in' (esp. if it involves decrypting the signal).
It seems to me we're moving the complexity away from expense to duplicate hardware into 'free' to duplicate software. With the increase in power and decrease in cost of general purpose (programable) electronics (i.e. CPU, radio recievers, ADCs, etc), one person can write complex software that can then be used to utilize the (relativiely) inexpensive hardware.
Once you have the hardware setup, you can change the software and:
Re:FCC vs. Software Radio (Score:2)
To quote the parent AC -
I guess I don't know if this is true, but it's exactly what I'm talking about. And, saying they are illegal, where does this software stand? If all the work is done by software, it will be easy to distribute the code that allows the illegal actions to take place. And I'm not quite sure if there would be ANY legal use for someone to claim 'fair-use' under.
We're on the edge of all sorts of software becoming illegal... and after that, I fear things like 'right-to-read' and what not.
Information density. (Score:2)
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.
Re:Information density. (Score:1)
That said, we could probably start stuffing multi-channel digital signals into the spaces between the existing analog channels, or do some frequency hopping spread spectrum into those gaps, and get some decent performance in existing bandwidth.
Re:Information density. (Score:2)
While in principle we could do that, in practice the problems are twofold.
Firstly, we'd need to be using extremely good equipment to get the required dropoff in intensity outside our desired bands. Software radio isn't a magic bullet, here. Nonlinearities in your output stages and jittering and drifting in your modulation clock are just a few of the many things that conspire to screw you up here.
And building a bandpass filter that sharp the old-fashioned way is just painful.
So, we wouldn't be able to do this easily or cheaply.
Secondly, getting permission to use an already-claimed section of bandwidth makes pulling teeth look easy, so I doubt such a system would ever realistically be implemented. If you're not worried about legality, just use a lower-quality software radio rig to transmit spread-spectrum signals below the noise floor and pray that nobody near you notices fading.
But, again, it's a nifty toy, and potentially quite useful as a simultaneous multi-channel _receiver_, which is what most of the first-glance stuff on the software radio page was about. Also useful as a tool if you're doing R&D with radio devices (and so have permission to clutter the spectrum in your area).
Hardware requirements (Score:5, Interesting)
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....
Re:Hardware requirements (Score:2, Informative)
You can just use a soundcard if that's all you have. It will get you 44 kHz of bandwidth. Then you'd need a rf tuner in front of that.
On the high end, we use a $1k+ 20Ms/s card with a cable tuner.
It is widely believed, but not yet proven, that you can coax raw samples from a BT8x8 video capture card, which would be a great boon, as those are cheap.
Re:Hardware requirements (Score:3, Insightful)
You can just use a soundcard if that's all you have. It will get you 44 kHz of bandwidth. Then you'd need a rf tuner in front of that.
On the high end, we use a $1k+ 20Ms/s card with a cable tuner.
It is widely believed, but not yet proven, that you can coax raw samples from a BT8x8 video capture card, which would be a great boon, as those are cheap.
No. I think you missed the point of the question, one I would like answered also. What equipment is really needed to receive radio signals? For example, the website shows looking at the FM band, but talks about the same high end $1k+ card that you mentioned that goes up to 20Ms/s samples. Clearly more equipment than this is needed to deal with the 107mhz FM band. You are apparently assuming we have something lying around that will comvert the FM band to a lower frequency. Many of use don't, unless you want to count an FM radio (which makes the need for a software radio less pressing). If we're talking about software modulation/demodulation let's just say so, if we're really talking about "Imagine computing devices that communicate seamlessly across the entire electromagnetic spectrum." then lets spell out all of the equipment that is needed to pick out signals that might be in the Ghz range.
Re:Hardware requirements (Score:4, Insightful)
Re:Hardware requirements (Score:2)
...
Clearly more equipment than this is needed to deal with the 107mhz FM band
I think you are confusing bandwidth with center frequency. FM radio stations are spaced at center frequencies 200 kHz apart e.g. 107.1, 107.3
So the maximum bandwidth they could possibly use is 200 kHz minus the transition bandwidth. I don't know what this is off the top of my head, but I'd guess it's around 50kHz.
You might be able to use 44 kHz of bandwidth to receive an FM radio station, but it wouldn't sound very good, since the dynamic range would be severely clipped.
AM radio stations are spaced 10kHz apart, which would fit quite handily into 44 kHz.
Re:Hardware requirements (Score:2)
You seem confused in that you are missing the main question, which is What equipment is really needed to actually receive radio signals with this software. Sure, you can demux some signals with a sound card (I have some ham software that does a great job of this, was actually able to tune a remote receiver over the Internet, send myself the audio packets, play it back and point a mic at my speaker, recapture and digitize the audio, and pick low level signals out of the resulting information). But the original posting claimed that you could make a radio receiver with this software. Clearly you can't - you need some sort of tuner that operates at much higher frequencies than this will process, even with the fancy $1000 card mentioned, as well as with a common sound card. I want to know just what other hardware I have to have to use this fancy demux software to actually pick signals out of the air, and a sound card ain't gonna cut it.
Sounds familiar (Score:4, Interesting)
Are there parallels to this technology? and if so, how will GNU Radio avoid those pitfalls?
Don't forget proprietary protocols (Score:2)
Relation (Score:2)
Re:Relation (Score:1)
Re:Relation (Score:2)
That depends on how many pringles cans you have lying around.
What external hardware? (Score:4, Interesting)
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.
Re:What external hardware? (Score:1)
Re:What external hardware? (Score:3, Insightful)
At a minimum, this would consist of a mixer and 1st local-oscillator synthesizer, preferably with an RF preamp in front of it all depending on what frequencies you want to cover and what kind of antenna and feedline you're running.
The mixer and RF preamp can be off-the-shelf parts from Mini-Circuits [minicircuits.com] or eBay.
The synthesizer is less convenient. I'm finishing an article on a "turnkey" octave-range VHF/UHF/microwave synthesizer design (http://www.qsl.net/ke5fx/synth.html [qsl.net] that anyone with a decent soldering iron should be able to put together, but it's still not a trivial project.
A lot of software-defined radio efforts are targeted at relatively narrow bands like the 2.4 GHz ISM band, where a bandpass filter can theoretically be used to take advantage of ADC aliasing via undersampling. With a scheme like this, you can dispense with the mixer and synthesizer. I'm not optimistic about these kinds of ideas, though... to achieve competitive performance, every dollar you save on the mixer and 1st LO synthesizer will have to be spent on a super-high-quality ADC configuration. It seems like the sensitivity would be pretty crappy, not to mention the fact that plenty of interfering sources near other aliased frequencies would be likely to survive the trip through the front-end filter. (I will admit that I don't have any direct experience with this topology, though.... there are probably quite a few advantages that I'm glossing over.)
At any rate, though, by keeping the traditional front-end mixer and oscillator while letting software handle the IF processing, you can use an ordinary sound card in a direct-conversion scheme (see this month's QEX [arrl.org] to demodulate just about anything in the entire spectrum -- FM, NBFM, AM, SSB, FSK, QAM, you name it. To me, that seems a lot more interesting than the "Antenna at the ADC" schemes that a lot of people are hyping.
NoiseFigure, Gain, Dynamic Range - No Hope (Score:2, Insightful)
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.
Re:NoiseFigure, Gain, Dynamic Range - No Hope (Score:1)
Of course, concepts like this usually fall within the bounds of the IEEE, or worse, the ITU. Still, this could be a good tool to drive such technologies.
Interference (Score:2, Offtopic)
Keep this away from radio telescopes!
Re:Interference (Score:1)
Re:Interference (Score:2)
It's loan, not lone, but yes. You can use my sig [bs2.org].
S
Re:Interference (Score:2)
It seems like a good idea to put at least one barrier between users and transmitting on police frequencies. But what kind of barrier? Should any restrictions prevent listening as well? What about military transmissions? Or air traffic control frequencies? Or the band the Secret Service uses?
Where should the line be drawn? What does the law say?
Re:Interference (Score:2, Insightful)
First, the old saw about "Don't say anything on the air that you wouldn't want the whole world to hear" has basically been discarded by the Cell Phone industry. They got Congress to put up legislation ensuring that the police need a warrent even to monitor your cordless phone. This is universally regarded as a dumb idea by most people who know what a radio is.
Second, they got certain modulation techniques declared off limits. It is illegal to demodulate an FM subcarrier without permission from the originator of the signal. Again, if I were monitoring SCA broadcasts from an FM station, how would they ever know?
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.
My question for Eric Blossom is whether challenging the ECPA was one of the motivating factors behind this project. If not, are they the least bit interested in adhering to the ECPA's various prohibitions, or is that also irrelevant?
Re:Interference (Score:2)
The parent post really sounds like the common knee-jerk reaction these days whenever a new and potentially industry, culture, or world changing technology comes along.
Repeat after me: technology is neither good nor evil, only its uses are.
Should any restrictions prevent listening as well? What about military transmissions? Or air traffic control frequencies? Or the band the Secret Service uses?
1) Any mission-essential military transmissions have been encrypted pretty much since radio encryption has been possible. I'd even wager that the military were the ones who developed it in the first place. I work on an Air Force flightline and even us maintenance folks use handheld radios with strong encryption.
2) ATC transmissions are not really all that interesting, even for someone planning to do something nasty. They are mostly composed of things like: "Control, this is Boeing November 3771 Whiskey requesting an ILS to runway 28L." An unauthorized person transmitting on ATC freqs would be bad, but that's already illegal. (Software radio is hardly required anyway, the equipment to transmit on aviation freqs isn't extremely expensive.)
3) See #1.
In short, everything that needs to be kept secret already is. Transmitting illegaly is still illegal. These two facts would not be changed by the advent of software radio.
This could be dangerous... but..... (Score:2)
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.
Security through Obscurity? (Score:2)
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.
Re:Security through Obscurity? (Score:2)
First, if you accept that the only way to keep a secret is if two people know and one of them is dead and the other dead as well, then you've captured the root of the problem.
At some level, crypto can be cracked. The plan is that by the time someone can DL and crack the crypto, that the transactions have been processed, the sessions closed, etc. and no session hijack is possible.
And you talk about citizen transparency: Do your really want everyone with a radio knowing that the cops are responding to a domestic dispute at your place? Or that they book you for impaired. Or that they didn't actually find a disturbance, just found you naked doing the chicken dance with your boyfriend? That's the kind of "situational reporting" and data that goes into police transfers. Also things like them fetching your police records (criminal history). You'd really like everyone to have free access? What a terrible idea that would be.
You probably shoulnd't be concerned about the FSB finding out you were dancing naked on your lawn, but you might not want your neighbour LoudMouth Bill, the area gossip, finding out and telling everyone.
Also, it is quite difficult to detect penetrations of networks. This is a tough feat in wired networks and none too easy in wireless. Most intrusions by true professional crackers probably go undetected.
We could spend millions of dollars (tens of millions, hundreds of millions) on crypto and infosec and intrusion detection. And we'd be out those many millions and still someone with the will and backing could crack it. And the villains would apply their money to cracking other aspects of the system we can't afford to defend (we underpay our cops, for example).
Security is about balance - You try to arrange every part of your organization's infrastructure and personel base to be difficult to crack in proportion to the risk of a penetration and the likelihood of a penetration.
The Canadian RCMP spend enough money on security to make it difficult for anyone without serious inside knowledge and some heavy backing to crack the system. That's good enough for most situations, and they have special provisions in place for the few cases where this isn't enough.
I'd be more worried if every police data transaction was publicly transparent. Talk about a recipe for disaster....
Re:This could be dangerous... but..... (Score:2)
Most forces that have moved (not all, there are exceptions even yet) to laptops, palmtops, etc., and even some with MDTs, have implemented either application layer security or are using a digital encrypted radio system.
If you are more worried about the conduct of your police than you are about anyone's NCIC queries, etc. being publically accessible, then you've got a far larger problem than anything that crypto can solve.
Crypto makes police dispatch not trackable by bad guys (thus cutting the odds of a B&E team with a scanner booking out whenever cops get nearby) and it helps protect officers. It also protects YOUR data and that of other innocent people that get queried. And it even protects the guilty by not exposing the transactions relating to charges, file information, etc. from becoming public. If you don't think that's important, I think you're worrying too much about the wrong damn thing.
I think this is also maybe a national phobia in the US (I'm guessing you're a USAian). At least her in Canada, though I know the cops are human and do sometimes do some less than admirable things, I think by en large I don't fear my police force. I DO fear anytime someone happens to query my license plate having that information (registered owner, vehicle info) becoming freely available, or if I did happen to get charged with something.
Just to reassure you: Computers in the cars which allow cops to do text messaging but where the messaging is logged centrally - that scares the cops! So does the thought of people monitoring their on-time/off-time, etc. They're worried about witch hunts. So the fear of the technology goes both ways
What does it DO? (Score:2)
Anyone want to clarify?
Re:What does it DO? (Score:4, Informative)
For example, they have demonstrated it decoding two FM radio broadcasts at the same time using their ADC and a cable modem tuner.
It replaces the hardware components involved in decoding signals... you could built a cell phone that only needs a tuner and and ADC, the rest in software. Depending on the tuning range of the tuner you use, your computer could become MANY different kinds of radios.
That is the cool thing about SDR... when a new fancy modulation technique comes along, you only have to upgrade the software... cell companies love this. I would assume those base stations can get pricey...
Re:What does it DO? (Score:1)
Re:What does it DO? (Score:1)
If you don't mind having a bulky fan-cooled mobile phone with minimal battery life
Actually, I was under the impression that techniques like this were already in widespread use (albeit with DSP chips rather than x86 PCs)
Re:What does it DO? (Score:1)
Good old Moore's Law has come to the rescue again.
The best part of SDR is it lets you design/test NEW modulation techniques changing hardware... maybe someone will cook up a new modulation scheme optimized for P2P MP3 and prOn sharing. (j/k).
It is some pretty neat stuff, and I hope more companies pick up on this. Maybe someone could create a universal cell phone that reconfigures itself to the network is on (FPGA based possibly). The RF hardware could stay fixed in the shell of the phone, the software could do the rrest...
Work Arounds (Score:3, Interesting)
Your thoughts?
GNU Radio vs Motorola (Score:3, Interesting)
You can transmit radio signals without speakers to (Score:1, Interesting)
The "entire EM spectrum?" (Score:4, Informative)
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.
becomes a question of antennae design (Score:2)
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.
but WHAT is it ? (Score:3, Insightful)
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
Re:but WHAT is it ? (Score:2)
- Go over to your clock radio on your bed stand and crack it open.
- Look at all the radio-related things in there. You've got some capacators, resistors, a neato tuning thing.
- GNU Radio replaces all that with software.
What's good/neat? Well, right now, the "decoding" of radio waves to sound is done totally analog. This new system would give the same results, but you could apply filters to never have any static. Also, you woudln't be limited by the range of frequencies the tuner deal could handle. It's just as easy (provided you have the cpu) to decode 97.1 FM as some 900 MHz cordless phone.And, it's all done in software, and it's all digital, and that's always good!
Describe your dream hardware for a software radio (Score:4, Interesting)
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.
The entire spectrum? (Score:1)
Okay, I'm imagining it. But that's not what this is, right (even though it's a cool project)? Radio's just a tiny part of the electromagnetic spectrum [lbl.gov]. This presumably isn't going to be transmitting in visible light, let alone hard X-rays and gamma rays.
Some explanation of what can be done with this (Score:5, Interesting)
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...
Limits of adaptability (Score:2)
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.
Processor speed, and bandwidth (Score:4, Informative)
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.
Re:Processor speed, and bandwidth (Score:2)
Brain spazz, sorry. That should say "circuitry". Once you're in the IF domain, the circuitry is carefully tuned for 10.7 MHz. For instance filters can have fixed-value components, which is cheaper and more reliable than trying to make them adjustable.
Nyquist limit (Score:3, Insightful)
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.
Re:Nyquist limit (Score:2)
You're right, that would work for a receiver. You couldn't use that idea for a transmitter, though.
A cool thing would be to have two carrier-frequency oscillators running at 90 degrees representing the cosine and sine. If you multiply them both by coefficients and add them, and the coefficients are band-limited signals, you've got a very flexible modulator. It's also pretty easy to build a demodulator that works the same way. And you don't need an IF stage.
If FSF is going to build a radio PCI board, I'm hoping they'll do the cosine-sine-modulator version.
IQ modulation (Score:2)
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 [educatorscorner.com] that shows what's going on.
Re:Intersil 50217 (Score:2)
Note to self: Intersil has an office on Route 9 near Shopper's World, and uses Arrow and Newark as distributors.
Re:Intersil 50217 (Score:2)
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.
Re:Some explanation of what can be done with this (Score:2)
That doesn't seem possible. At the very least an antenna and possibly some signal amplification/attenuation circuitry will be needed, no? Soundcards only have a limited amount of bandwidth, S/N, etc. so what other type of hardware will I need before it's -actually- "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.
Again, I'm not an RF expert, but are you saying there will be no need to buy different antenna hardware for different parts of the EM spectrum?
Re:Some explanation of what can be done with this (Score:2)
You are also correct that you need more then a soundcard to get good bandwidth.
The question is: why would you want to do WiFi or Bluetooth in software? It would be the same as a software only winModem. Dedicated hardware for that is cheap. Where the power of software radio really comes from is the ability to prototype new modes, and Hams are going to love this. As another poster wrote, nice all-mode rigs are expensive. Software radio, a soundcard, and transciever, will do the job at an affordable price.
Re:Some explanation of what can be done with this (Score:2)
Convergence Devices (Score:4, Insightful)
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?
Spectrum regulators (Score:1)
Plans for UWB (Score:2)
Great project. Thanks.
Buttons? Will it have Push-Buttons? (Score:2, Funny)
"My repetition threshold has been exceeded."
My question and the *ULTIMATE* TiVo? (Score:2)
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).
How will this pan out on the hardware side? (Score:2)
Hams using SDRs already (Score:2)
Check out the DSP-10 [tapr.org] designed by Bob Larkin, W7PUA and offered as a kit by TAPR [tapr.org]. 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.
A Timely Example of Software Radio (Score:3, Informative)
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
As a college student, how do I get involved? (Score:4, Insightful)
Re:As a college student, how do I get involved? (Score:1)
Particularly, I'm curious as to what areas would be good to do research in. I'd like to try and help out in a part that doesn't already have a lot of support (like decoding FM radio). Any ideas?
Wicked Thought (Score:2)
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'.
Re:Wicked Thought (Score:2)
I don't think Club Spectrum Sampling would be nearly as interesting as Bistromathics.
Plugins... (Score:2)
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.)
Spread Spectrum Napster (Score:2, Funny)
Neat hack, but not new (Score:2)
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.
Prior 'Art' (Score:1)
applications (Score:2, Interesting)
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?
Commercial efforts? Patents? (Score:1)
UWB, remote communications (Score:1, Interesting)
Second, what is the bandwidth limitations of the SDR in the GNU project, if any? Audio?
Finally, I want a duplex link to a remote device (more than 100 miles away) that I can send commands to and get back data such as pictures from a digital camera. Low bandwidth in the link is OK. What would you suggest?
Regards,
Chip
...what it means to business (Score:3, Interesting)
- dedicated semiconductors vs general-purpose processors
- Vendors vs OS designers and software programmers
- short term: certification
- long term: standardication & spectrum management
Simple question (Score:1)
Reference Hardware, Realtime interface, compilers (Score:1)
Also, is the code generated solely for PPC/x86 processors, or can you generate code for Digitial Signal Processors? What is the current limitation on the signal bandwidth that can be processed digitally - processing power, data throughput, or what?
Worries (Score:1)
Hardware patents? (Score:3, Interesting)
I read what GNU Radio about, but what's it about? (Score:1, Interesting)
In a nutshell (Score:3, Insightful)
Is this illegal? (Score:1)
entire spectrum? (Score:1)
Isn't this just an impossible dream... (Score:2, Insightful)
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?
Question for Eric (Score:2, Interesting)
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
What if GNU Radio gets outlawed in the US? (Score:1)
As you are probably aware, the fruits of the Broadcast Protection Discussion Group were brought before congresspeople. Rep. Tauzin and Sen. Hollings both urged the FCC to move forward on the broadcast flag mandate.
Since a broadcast flag is only effective if devices that receive it can act on it, legislation would be passed to outlaw devices that don't act on the flag or that allow their users to modify their behavior.
This would make GNU Radio illegal.
Since GNU Radio is obviously a good thing, what would you if such legislation came to pass?
Programmable Hardware? (Score:2)
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?
The Analog Hole (Score:2)
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
--
How will the DMCA affect this kind of radio? (Score:2)
Roaming through downloads (Score:2)
Re:Grass Growing Channel Outrates This (Score:1)
Marconi had the exciting project because he took it somewhere. Tesla pushed the barriers more than any man of his time but he stunk at follow-through.