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Software-Defined Radio Could Unify Wireless World
mjdroner writes "Technicians in Ireland are testing a device capable of skipping between incompatible wireless standards by tweaking its underlying code. The article states: 'The device can impersonate a multitude of different wireless devices since it uses reconfigurable software to carry out the tasks normally performed by static hardware. The technology promises to let future gadgets jump between frequencies and standards that currently conflict. A cellphone could, for example, automatically detect and jump to a much faster Wi-Fi network when in a local hotspot.'"
I've been researching similar technologies over the past few years because I believe we can see an amazing communications "utopia" by deregulating (or at least minimizing regulations) all the frequencies we're blocking for specific uses.
Software radios are not new technology, but the implementation has been fairly worthless as frequencies are set up for specific purposes. At any given moment in any given area, there is a ton of bandwidth going unused. Frequency hopping is already pretty well documented in how to maximize its use, and power allocation specifications have been out since pre-cell phone days. Combine that with a much wider bandwidth and we can see higher data rates, lower battery usage and maximum bandwidth allocation everywhere you go.
I know the FCC will never give up the bandwidth to the open market -- it is too lucrative for the few who are in cahoots with the licensing body. But I see so much happening just in the WiFi "unreglated" spectrum that I would really love to live in a world where all that analog TV, digital TV, analog radio, digital radio, CB, HAM and every other heavily regulated piece of spectrum could be allocated to being used for just information transmission. Software radios would set themselves to the best frequency possible to maximize transmission distance (as needed) and minimize power consumption (as needed).
What we have now is more kludge than efficiency. Can you imagine how incredible the Internet would be if we had nearly infinite spectrum to use (compared to the limited spectrum we have now)?
Sure, some people will say "What prevents Megacorp YYY from blasting 100,000 watts over every frequency?" That's pretty simple -- energy costs make it prohibitive to transmit anything but profitable data. The FCC has existed long past its useful life, maybe it is time to open up little bits of unregulated spectrum piece-by-piece and let's see what happens. These software radios are a huge step in the right direction.
Since we're talking about Software Defined Radio, I urge everyone with an interest in the subject to look at the GNU Radio project. They have designed a front end board using generic cable TV tuners feeding an FPGA to perform some initial processing, such as decimation and filtering. The data is then transferred over USB to the host, whose software performs the demodulation and decoding. It's a fascinating project and a great stepping stone into the field.
To really get started on SDR, check out the Ten-Tec RX320D shortwave receiver. It outputs a 12 kHz-wide IF signal from the front end to an audio jack, which can then be fed to a PC soundcard. There are a number of packages that can take this data and demodulate it, including DREAM, an open source DRM (Digital Radio Mondiale) decoder which allows you to listen to the new digital shortwave transmission standard that many of the world's broadcasters are beginning to experiment with.
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It is because it is basically a software defined radio. You have a DPS and a set of AD/DA converters and a baseband (low freqency) to RF (high freqency) converter.
Only difference here is that they are hacking the firmware for their Atheros wifi cards a bit more than the rest of us.
I think you need to remember that the RF spectrum is a finite resource and as such needs to be managed to prevent noise. Deregulate and you would have people lusing HF to go across town and I didn't pass the ham exams to have some bitch in kentucky's email to her boyfriend blocking DX when he lives down the street.
First, how are you going to get the dynamic range you need for RF intense areas if the radio front end has to remain wide open for octaves?
Second, energy costs for radiating Kilowatts are relatively cheap.
Third, what about the near-far problems with spread spectrum?
Fourth, how do you regulate narrowband emergency frequencies in a spread spectrum world?
Fifth, if you're going to push everyone to unlicensed spread spectrum, how do we resolve interference disputes?
I could go on, but I think you can figure out where I'm coming from. The problem is that if we didn't have radio and we were starting from scratch, you might be able to make a case for this technology. But since you clearly don't know how the standards got to where they are today you have no technical basis for trashing them.
Keep dreaming until you get a clue...
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Antennas only affect the shape of the RF output, and the frequency range at which you can efficiently radiate.
Take some examples:
Omni-directional wifi antennas on most APs: a single stick with a fraction of the wavelength of 2.4ghz. Very simple, can do anything from SSB, AM, FM, or OFDM modulation.
Most of what software defined radios is talking about modulation changes, not frequncy changes.
The only difference between 802.11b and 802.11g is the modulation (CCK vs OFDM)
I find it sad that the first post rated "Informative" is almost all political.
Can't we look at this technology without the technology government bashing and utopian (and ignorant) libertarian rants?
SDR is not a new technology, but it is rapidly becoming a good way to do things, as the hardware (digital and analog) to enable it is being designed and built.
Cell phone companies are (or will soon be) using SDR to much more efficiently handle their multichannel cell sites. Instead of having a radio per conversation, or a radio per channel, they can have one or a few radios containing very high speed DSP SDR code. This saves cost and has the obvious flexibility of field upgradeability.
GNU ( http://www.gnu.org/software/gnuradio/doc/exploring -gnuradio.html#software ) has had an SDR project going for quite a while (I do wish they would do APCO P-25 reception, since I don't have the time). Hams have been doing various forms of SDR also - for example, the very narrowband systems that use a PC to do the DSP for HF data communications.
Contrary to what some might think, SDR doesn't give magical powers to radios - the ability to operate on all frequencies at once. Radios have hardware filters in them for reasons that cannot be solved in software: to compensate for the non-linearities in the analog (or digital) software - which especially causes problems in high dynamic range situations. Radios may have to separate signals that differ in power by factors of 10^12 or more, which are relatively close in frequencies. Transmitters have to avoid emitting spurious signals at similar ratios to their output power.
More specifically, if you put two signals (assume sine waves for now) into a non-linear device, it is the equivalent of putting those time-domain functions into a polynomial of degree 2 or more. This means that those sine waves will be multiplied by each other and themselves (and a coefficient which you try to make as small as possible). The result is output at the sum and difference frequencies and the harmonics of the original signals. Non-linearity can crop up in surprising ways. The most common one seen in radio is receive and transmit amplifiers, which are *always* non-linear. In addition, parasitic devices (such as two wires touching each other somewhere nearby) can act as non-linear mixers, generating spurious signals. Anyone who has worked on systems at crowded radio sites knows the fun of tracking down "intermod" signals (which are the result of this process). SDR's do nothing to improve this situation. On the contrary, they may require wider bandwidth amplifiers, which increases the odds of spurious signals. Furthermore, the very process of sampling with non-infinite bit-width A/D's and D/A's is itself a non-linear process that generates mixing.
So SDR still has to deal with the issues at the antenna that analog radios deal with.
Where it gets cool is at the baseband - in other words, at the modulation=baseband level (or in the case of multi-channel receivers/transmitters, at an intermediate level). This is where you take the information you want to send/receive, and convert it into/from the RF representation of that information. A simple example is FM modulation (used in most older land mobile radios - police, fire, cell phones, ham repeaters, etc, and in TV and FM radio broadcast). Here the SDR will take the modulation (voice or music or whatever), and use it to generate the signal equivalent to having it quickly alter the frequency of a carrier wave. Depending on the system, it may literally output a sine wave modulated this way. In other systems, it may generate some intermediate representation that then goes to the radio.
But a far more interesting system might be a trunked narrow-band digital public service radio system (which US public safety organizations are converting to at FCC insistence). These systems are designed for improved flexibility (
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