The Journey of Radios From Hardware to Software 114
An anonymous reader writes "The New York Times is carrying a story all about the process of replacing radios with software. The article tells the tale of Vanu Bose, son of the man who started the Bose company, and his quest to bring software to what was previously a hardware-only enterprise. He met a lot of resistance in the 90s to his ideas, because processor technology was not up to the task. Now that technology has caught up with Vanu, his software (and other products like it) are increasingly replacing now-outdated hardware components. 'Well-established companies like Motorola and Ericsson now use elements of software-defined radio for their base stations. But Mr. Bose was the first to come to market with software that could handle multiple networks with the same equipment. Software radio appears to offer an elegant solution to what has been a vexing problem: how to have a single handset, like a cellphone, communicate across multiple networks. For instance, the G.S.M. standard, for global system for mobile communications, is used broadly in Europe, and most notably in the United States by AT&T.'"
It's the multiplexing (Score:5, Informative)
It's not that a single software-defined radio is all that important. It's that you can do the transforms on the incoming waveform and then extract N different channels with one signal processing system. That's what's been making cellular base stations go for almost two decades. (All the hard work is on the receive side; transmission is easy.)
First generation cellular base stations (i.e. AMPS) had one big analog card per channel, each heavily shielded from its neighbors. The amount of hardware required was huge, and cell sites tended not to be fully populated with channel cards, so they were easy to overload.
Then things started to go digital, with combinations of analog and DSP components processing the signal. Both GSM and CDMA inherently assume digital processing, and in early systems, hard-wired special purpose components were used. As CPUs get faster, there's a steady trend toward using general purpose CPUs.
It's still rare to actually process RF directly in software. Usually, there's a local oscillator and mixer to down-convert the desired band to a working IF frequency, which is then digitized and processed. So it's only necessary to digitize at maybe 10-100MHz, not up in the gigahertz range.
For lower bands, though, a true software RF receivers [rfspace.com] are available. These just suck up everything from 0 to 30MHz and digitize it. An attached PC does all the hard work.
Two Words (Score:5, Informative)
Bose blows (Score:1, Informative)
Mod parent up (Score:2, Informative)
Re:Two Words (Score:3, Informative)
Even if you're not an amateur radio operator, it's worth checking out if you're interested in SDR. And the banquet speaker this year is Bruce Perens of Debian and OSI fame.
http://www.tapr.org/dcc [tapr.org]
Re:An interesting idea (Score:5, Informative)
Well, yeah. Square wave outputs do tend to generate alllll sorts of harmonics. But it does technically work. If I were serious about it, I'd at least add a capacitor across the output, to make some attempt at filtration.
The "schematic" involved an 8-pin microprocessor, with two outputs each connected to a 1k resistor. The other ends of both resistors were connected to the antenna. Not very efficient, but as a proof of concept, it was a cool toy. Tuning was completely via software (tweak the timing loop to provide the correct waveform.)
You want pictures? Happy to oblige. (The idea was to see just how simple a transmitter I could make...)
http://www.intellectualism.org/electronics/schematic.jpg [intellectualism.org]
http://www.intellectualism.org/electronics/Closeup.jpg [intellectualism.org]
Re:Two Words (Score:4, Informative)
You can use a capture card with a BT878 chip as a cheap entry into SDR and GNU Radio. See Here [domenech.org]
The card I have didn't require any kind of modifications, and I've successfully captured signals all the way up to about 400kHz directly from the air simply using a long wire, including digital radio (the unfortunately named DRM [wikipedia.org]) signals.
Re:didn't someone ... (Score:3, Informative)
Nyquist apply to the signal you want to process. If you want to do your filtering in the digital domain you will first have to capture both your wanted signal and the signals you seek to suppress. Otherwise you have your selectivity in your hard-ware and not in your software.
The function of "ADC with lots of front-end bandwidth" is what the hardware in the RF front-end is doing in a traditional radio system.
In GSM you must be able to detect your own signal at say -108dBm while you have a blocker at 0dBm. Every 3dB is a doubling in power, 0dBm is 1mW so -108dBm is 1/(2^36)=1.45e-11 mW. If you need 3 bit s/n in your wanted signal to decode it you will need at least 3+36 bits to represent the samples.
As mentioned in the parent post you can do sub-sampling (If the carrier is at 1000MHz you can sample at a fraction like 100MHz) as long as your signal have a bandwidth smaller than half the sampling frequency. The fly in the ointment is that your blocker in GSM can be from DC to 12.7GHz and a blocker at any multiplum of the sampling frequency will interfere with the desired signal. If you are allowed 5 exceptions to the blocker requirement you will need to sample with at least 12.7GHz/5 meaning >2GHz sampling frequency.
While this is possible it is not the simplest or the lowest power consuming way of doing it.
This is why in any practical radio receiver you will have band filtering before your A/D converter and this filter is NOT implemented in SW.
Re:Vanu Bose's bitter battle with MIT (Score:2, Informative)
To paraphrase the argument, MIT its entitled to royalties, which are tied to the value of the patent, but not equity, since the company's value is more than just the patent (unless that company exists only to hold the patent).
Re:An interesting idea (Score:4, Informative)
Bottom line - the harmonics can be taken care of by wave-shaping, i.e. you take the output load configuration into equation as you design the radio.
Re:Bose blows (Score:3, Informative)
Ok, I'll bite.
I worked years ago in the Audio department at a best buy. I don't know the current state of home electronics, but I know what the mid-range state of electronics was about, oh, 8 years ago.
If Bose is not a quality audio solution, then who is? Are we back to Sony, Pioneer?
I'd rather have EITHER of those brands of speakers over bose. Any day. We also sold Cerwin Vega and JBL and yamaha, and I'd rather have any of those. The only brand that I'd buy bose over was "KLH", which was our generic house brand, and to be honest, I might still buy the KLH and save 75%, and just live with the cardboard speaker cones.
Commercial bose speakers suck. Period. Maybe their high end stuff is good, but if you walk into an electronics store, and you pick up bose bookshelfs (301's or 501's), you will be vastly dissapointed. Even more so, if you pick up the little cubes-and-subwoofer. Here's the clue, those cubes are like 2.5" drivers with very little dynamic range - they peak somewhere around 10kh and they don't go above or below it by more than a bit. Unless you buy the horribly expensive one (it was $1200 when I worked there, god knows how much it is now) the subwoofer will NOT BE POWERED. I mean, come on, wtf. Those speaker systems at the low end can't do 5.1 sound, because you're expected to run the speakers all to the bose sub first, then off to the cubes. The sub has a crossover where it takes out the mids and lows and sends the highs to the cubes. And on top of that, even if you get the powered sub, it's still only one or two 6.5" speakers. Good luck getting any quality bass out of that where anything below 140hz doesn't sound like a wet fart.*
And then there's the wave radio. Yes, what I wanted on my music was EXTRA post processing that adds reverb and stereo separation, and then I want the music to travel through long windy tubes in order to cancel out all the crisp highs. Oh, and if you could charge me $500 for a CD-clock radio, that'd be great.
Seriously, buy anything but bose. I like JBL speakers, and even though I wouldn't buy a Sony receiver, I own sony speakers.
*I'm looking at best buy's site now, and they're selling the Bose 6.1 system for
Whatever. Seriously, I'm no audiophile, but I know what sounds good and what doesn't, and after working in the audio department for months, and listening to the same songs on 6 different brands of speakers, I can tell you... bose is not good.
~Wx