Re: [Discuss-gnuradio] OLPC - next generation with SDR?
As preface, I'm not a radio engineer. I'm a software guy with pretentions to understanding digital hardware. I have a few signal processing books on a dusty shelf. You lose me as soon as you start talking Q signals. The Odyssey board operates at 10MHz IF; so wouldn't it need an external tuner? I am in agreement with Frank that we can currently do it for a few tens of dollars ~$50 in small quantities and that include parts and boards. We can even put together a prototype which will allow HF shortwave reception from low bands through about 21 Mhz covering these bands: [15m thru 120m] What kind of antenna would this require? Something external to the laptop? Or something that could be built into the plastic case? The dsPIC33 has more than enough horsepower to provide good (synchronous) detected AM and even some modest AGC. We won't need a processor; the laptop will come with a processor much faster than 40 MIPS. (The current XO CPU is a Geode LX 433 MHz x86, with MMX, 3DNow, and some SSE instructions.) We need a DDS and a QSD (we do not need the QSE for the receive only version) if we are going to tune the HF shortwave broadcast bands and get reasonable performance at low cost. I think that single chips are available that do broadcast-band AM and FM decoding for cheap; has nobody done this for the television and shortwave bands? Or is the problem that nobody's done this digitally? If we can provide something that gives real benefit for the target kids, we shouldn't be dogmatic about analog versus digital. Alternatively, if OLPC provided a million-unit order for a digital tuner chip that would target all these bands, others could then buy the cheap chip for a variety of projects. This would provide a clear example of how it could be done. It does not meet the price point, but it shows the capabilities and then we can negotiate. I'm glad you-all are pointing out low volume prototypes. I hope we'll get someone interested who has designed high volume digital radio electronics. High volume ~= million-unit. (Do any people like this exist? Perhaps Matt's bluetooth design has shipped in that quantity; WiFi does too.) There's already an entire high speed digital radio transceiver in the existing XO: it's the Marvell Libertas WiFi 88W8388 controller chip and 88W8015 radio chip. It's reprogrammable, though the ARM code that runs in it isn't open source yet (the high level code can be open sourced, but it runs on a proprietary RTOS). I think the best strategy for a $50 laptop's radio would be to have either an internal antenna or a single connector; a small number of cheap analog components; perhaps *one* analog/digital chip (multi channel DAC/ADC radio chip); and stuff *everything* else into a corner of the digital system-on-chip that implements the rest of the laptop. It's hard to prototype such a thing, though perhaps using an FPGA that come with a fast embedded MIPS or ARM CPU would be the closest. The current XO uses two custom chips (the DCON display controller, and the CAFE camera/flash/SD controller), some very custom mesh firmware for the ARM core inside the WiFi chip, and some very custom firmware for the EC embedded controller battery charger chip. A $50 laptop version would probably mash all these chips together with the CPU, GPU, and its southbridge support chip, leaving only one system-on-chip, plus flash, DRAM, a few external analog chips, and a pile of analog electronics for power supply and such. John ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] OLPC - next generation with SDR?
John Gilmore wrote: 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. I am in agreement with Frank that we can currently do it for a few tens of dollars ~$50 in small quantities and that include parts and boards. We can even put together a prototype which will allow HF shortwave reception from low bands through about 21 Mhz covering these bands: # 15 meters – 18.90–19.02 MHz – Seldom used. # 16 meters – 17.48–17.90 MHz – Day reception good, night reception varies seasonally, with summer being the best. # 19 meters –15.00–15.825 MHz – Day reception good, night reception variable, best during summer. Time stations such as WWV are clustered around 15 MHz. # 22 meters – 13.57–13.87 MHz – Similar to 19 meters; best in summer. # 25 meters – 11.50–12.16 MHz – Generally best during summer; said to be ideal during the period before and after sunset. # 31 meters – 9250–9995 kHz – Good year-round night band; seasonal during the day, with best reception in winter. Time stations are clustered around 10 MHz. # 41 meters – 7100–7600 kHz – Reception varies by region – reasonably good night reception, but few transmitters in this band are targeted to North America. # 49 meters – 5800–6300 kHz – Good year-round night band; daytime reception is lacking. # 60 meters – 4400–5100 kHz – Mostly used locally in tropical regions, though usable at night. Time stations are clustered around 5000 kHz. # 75 meters – 3900–4050 kHz – Mostly used in Eastern Hemisphere, not widely received in the Americas. # 90 meters – 3200–3400 kHz – Mostly used locally in tropical regions, with limited long-distance reception at night. # 120 meters – 2300–2495 kHz – Mostly used locally in tropical regions, with time stations clustered around 2500 kHz. Not technically a shortwave band; resides in the upper reaches of the medium wave band The dsPIC33 has more than enough horsepower to provide good (synchronous) detected AM and even some modest AGC. We need a DDS and a QSD (we do not need the QSE for the receive only version) if we are going to tune the HF shortwave broadcast bands and get reasonable performance at low cost. This would provide a clear example of how it could be done. It does not meet the price point, but it shows the capabilities and then we can negotiate. Bob -- AMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats, NJQRP, QRP ARCI, QCWA, FRC. ARRL SDR WG Chair “An optimist may see a light where there is none, but why must the pessimist always run to blow it out?” Descartes ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] OLPC - next generation with SDR?
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
Re: [Discuss-gnuradio] OLPC - next generation with SDR?
John -- Have you looked at all at the Siren board? It's part of the HPSDR and Suitsat II projects: a low-power, low-cost SDR engine using the dsPIC33F embedded controller from Microchip. The current design uses 10 MHz RF in and out, and the QSD and QSE for complex sampling and excitation. There is also an onboard TI stereo codec for I/O in the audio range. Digital data can be synchronously imported and exported over one or more SPI buses. It's not perfectly general. Many of the algorithms we'd like to run on it need to be tailored to the hardware in a way that's more constrained than we'd like in general. That notwithstanding, it should be capable of handling 48 kHz bandwidth, and muxing and demuxing several channels within that span. So far, as far as I know, only prototypes and first-gen boards are in circulation. The power consumption is already very low; there's a lot of board real estate eligible for shrinking as well. Frank On Dec 21, 2007 11:02 PM, John Gilmore [EMAIL PROTECTED] wrote: The thing does appear to have sufficient horsepower to do some DSP. ... ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] OLPC - next generation with SDR?
John Gilmore wrote: 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. I think that adding a fast, complex, sampler capable of doing many megasamples, with DMA support, etc, would be a worthy goal. A little anti-alias filtering and some digitally-controllable gain (70dB or more) in front of the samplers, and you have yourself a nice little HF receiver. I wonder if you could suck the entire 30Mhz of HF spectrum into the Geode in one gulp if there's adequate DMA support, etc? If not, you'd probably like some hardware-based DDCs and decimators, etc. signature.asc Description: OpenPGP digital signature ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
