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.

Comments

Hardware requirements

[wowbagger]

The GNU radio page is a little thin on the hardware requirements to run the code - could you spell them out?

I realize this might be complex, and that the answer might be of the form

to demodulate a 16QAM signal at 115.2kBaud, you would need an XYZ digitizer card reading the 455 kHz IF and a AAA GHz Athlon CPU. To recover standard multplex FM, you would need a 123 digitizer reading the 455 kHz IF and a BBB GHz Athlon. To decode GSM you need a FFF digitizer reading the 10.7 MHz IF and a quad Athlon.

But as both a ham and one who designs SDRs, I'd like to know where this resides on the Home Hacking Scale....

Sounds familiar

[FreshMeat-BWG]

As in WinModems doing the modulation/demodulation. These devices were a nightmare. After trying several I went back to a good old hardware-based-modulation modem.

Are there parallels to this technology? and if so, how will GNU Radio avoid those pitfalls?

What external hardware?

[Consul]

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?)

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. :o)

Re:FCC vs. Software Radio

[killthiskid]

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:

• Listen to police band.
• Listen to cell phone.
• Listen to XM radio
• Listen to satelite transmissions
• Listen to military communications?

Describe your dream hardware for a software radio

[geirt]

I want a feature list containing all the geeky details

• Frequency range.
• Bandwidth (do you want to sample the whole FM band (or GSM/GPS/CB/ham bands), or just a single channel/station).
• Sample frequency and depth (ie, fast and few bits, and do decimation in software or slow and many bits with less CPU overhead)
• Necessary spurious free dynamic range, or some other dynamic range specification.
• Interface to the PC (PCI, firewire, USB ...).
• Antenna connector (OK, I know that one: BNC)

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.

Some explanation of what can be done with this

[eyefish]

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...