> The thing does appear to have sufficient horsepower to do some DSP. > I would like to think we can make several things available to this > project. For example, I think a tunable HF receiver for shortwave AM > broadcast is easiy achievable for very modest cost. Further out, I > would to see the use of this machine and OFDM skywave to provide WAN > capability to large areas of the world without such capability.
If we were given a square inch of circuit board space, twenty cents for components and wires and connectors, four pins, 0.2 watts of power when operating, and half a million gates colocated with the CPU and memory bus, what radio capabilities could we offer to the next generation OLPC project? That's the fun challenge. Here's some background. The reason software radio hardware has always cost so much is that it ships in low volumes. The oscilloscope boards we started with were $1400. The USRP is many hundreds, and the USRP-2 will be more. But if the USRP's RF I/O capability was integrated onto a high volume motherboard, it would cost a lot less -- maybe $50 or $25. If it was integrated into a chipset, even cheaper. Similar but specialized wireless capabilities are in USB wifi dongles that *retail* for $40. Today's children's XO laptop is just the first in a series of high volume, low cost laptops -- from a variety of vendors. We can assume that with each generation they will get faster, lower power, and cheaper -- as we learn more about how to design and build in that problem space. (Until Dec 31, you can buy one for $400 -- and a second one will go free to a kid in a developing country. After that, they won't be sold at retail. See http://laptopgiving.org.) For the next generation effort, if they have the design time, they are likely to build a big custom chip that integrates a whole CPU, and a pile of system and peripheral circuitry. Their stretch goal is a $50/ea laptop for kids, one that's much better than the current $200 one. We know they will want 2-channel sound in and out. They have already jiggered their current hardware so that the audio biases and filters can be switched out of the circuit, so that ordinary low voltage sources and sensors can be plugged into the audio port and used to sample real-world sensors. They have full control of the drivers, since they're basing the whole thing on Linux, and they have real kernel hackers and real GUI hackers and such. Their system already uses wireless WiFi, so it has antennas, and they've done a detailed radio analysis of the package and design. The difference between this design effort and the other things the GNU Radio crew has done is that the result has to cost only incremental pennies, cost zero power when not running, and run on batteries when running. On the other hand, gates and connectors and small antennas come almost free (they're making hard-tooled plastic molds anyway; adding a connector or other wires is simple). Assuming their basic design provided roughly their current sound and analog input capabilities, what could we recommend that they do in order to make the platform much more capable for SDR? My first thought is to just increase the sample rate and effective bits per sample of the audio processing hardware, and increase the number of channels so that ordinary stereo audio can happen simultaneously with analog I/O. I think it's a crime that cheap analog I/O chips top out at 200 kilosamples per second. Even making it able to receive AM-band and below, by plugging in a wire of appropriate length as antenna, would provide years of experimentation in the schools. Should the analog circuitry be wired up to the existing "cat ear" antennas on the laptop (which are currently only used by the WiFi chip)? The analog circuitry would need to be switchable for use in three domains: audio (speaker/mic), DC analog (sensors), and radio analog (SDR). Could we make it usefully transmit? Many of Matt's transceiver daughterboard designs are very similar -- with only a few components changed to set the frequency range. If made in high volumes on an existing board, what would the cost come down to? Could we shrink a single band transceiver into the above constraint? Could we design a cheap multi-band transceiver that lets these components be switched under software control? Can the CPU and the free signal processing gates automatically measure and compensate for cheap (signal-distorting) analog circuitry? What kind of signal processing math hardware should we add to the custom chip, assuming that the CPU itself would be low power/low heat/low performance for its time? Should this be a CPU math accelerator, or should it be wired to the digitization hardware? Should it do one thing well (if so, what?) or be more general like traditional x86/PPC/etc DSP instruction sets? Should we suggest making some of "our" gates of the custom chip into a field programmable gate array, reconfigurable in software? If so, what would we *use* that capability for (as opposed to putting in hard circuitry)? Even a receive-only SDR platform that makes it out to millions of third world kids would be a brilliant achievement. (And if we could get inside their Marvell wireless-mesh chip, we would probably end up with lots more capabilities in the WiFi bands, too.) John _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
