Olpc

GNU Radio
1

This is sent with my OLPC. What a great idea this project is. It
goes to show what can be acccomplished ny dedicated individuals,
something familiar to a lot of people in these two groups.

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.

At least one Negroponte clearly has heart and vision.

Happy holidays and I hope everyone is looking forward to 2008 with as
much anticipation as I am.

Bob

2

Robert McGwier wrote:

At least one Negroponte clearly has heart and vision.

Happy holidays and I hope everyone is looking forward to 2008 with as
much anticipation as I am.

Bob

Bob:

I’ve been thinking along those same lines as well.

I actually am spending about 50% of my time doing security development
for the OLPC (Nortel
is a sponsor of OLPC, and through some internal deals, I got to spend
50% of my time on
OLPC for the last several months).

I did do some paper-tiger designs for a simple front-end to the audio
subsystem for HF reception.
But I was told my time was better spent on other things…

–

Marcus L. Mail: Dept 1A12, M/S: 04352P16
Security Standards Advisor Phone: (ESN) 393-9145 +1 613 763 9145
Strategic Standards
Nortel Networks [email protected]

3

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

4

John G. 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.

5

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

6

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

7

John G. wrote:

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

8

On Mon, Dec 24, 2007 at 02:11:34PM -0800, John G. wrote:

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).

You may be disappointed what you can accomplish with the ARM
microcontroller. It is not responsible for mod/demod. Those functions
are in silicon.

If Marvell would publish the 88W8388 and 88W8015 documentation, it
would jumpstart some open-source development. Source code is a poor
replacement for proper chipset documentation.

Dave

–
David Young OJC Technologies
[email protected] Urbana, IL * (217) 278-3933 ext 24

9

On Dec 24, 2007 5:11 PM, John G. [email protected] wrote:

The Odyssey board operates at 10MHz IF; so wouldn’t it need an external

tuner?

Yes, but many different tuners (band sets) can be serviced by the same
IF
processor.

What kind of antenna would this require? Something external to the
laptop? Or something that could be built into the plastic case?

Depending on the band it could be either or both. A multiloop MW/HF
could be
embedded in the plastic case. A gender-bent SMA could accommodate a wide
variety of V/U/SHF antennas.

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 can argue that a “radio coprocessor” would greatly enhance the range
of
possibilities – DRM (Digital Radio Mondiale) for example, and see
below.

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?

Two problems. One is that the off-the-shelf chips use proprietary IP.
The
other is that the off-the-shelf chips are locked up and it’s next to
impossible to do anything interesting with them that you can’t already
do
with a cheap external radio. I’m not aware of commercial devices that
could
be used to capture and detect all of the signals within a 50 kHz
bandwidth, which could probably be done with ease with the assistance of
a
radio coprocessor. This is an essential step towards “cognitive”
functions
– make the radio functions mutable and dynamic.

I’m glad you-all are pointing out low volume prototypes…
I’d think in part we’d be providing not just sealed up applications but
also
programmable devices and an API, capable of being used in innovative
ways in
software without requiring the chronic intervention of large-scale
chip
producers. Part of the SDR mission, isn’t it?

Regards
Frank
AB2KT

10

John G. wrote:

What kind of antenna would this require? Something external to the
laptop? Or something that could be built into the plastic case?
Gotta go with an external antenna, hopefully something like an RCA
plug. If we’re trying to encourage kids in developing nations to get
into technology, this would be it. That’s how I got started twenty
years ago, with a long-wire connected to an RCA plug, which isn’t too
much real-estate on the case.

DRM is pretty cool and has the /potential/ to provide the kids with a
multimedia experience, even if it takes two laptops “chained” together
to decode the signals…

Dave

11

On Dec 25, 2007 6:05 PM, David H. [email protected] wrote:

DRM is pretty cool and has the /potential/ to provide the kids with a
multimedia experience, even if it takes two laptops “chained” together
to decode the signals…

If the linking were in fact required, it would at least introduce the
concept of distributed computing at a young age and, possibly, with a
new and different perspective of how to accomplish some of the harder
tasks.

Since there is a pretty serious size, weight and power (SWAP)
restriction when dealing with something like the OLPC, complete
integration is key. I’ve been eyeing a Maxim Analog Front End (AFE)
that is dual channel, 10-bits and is extremely low power and cost.

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/5163

Although $9.85@1k is a little steep, it’s also the cheapest and most
fully featured low-power AFE I’ve really seen and at 7mm x 7mm, it’s
almost trivial for real estate.

Given this core technology, and Matt’s experience in IC design coupled
with the quantities an OLPC will be shipping in, it might be possible
to negotiate with Maxim to throw the current CIC filters +
programmable decimating FIR filter along with this core on some
silicon for not much or any more money - basically a hardened
low-power USRP that can hang off the ARM in a memory mapped area.

The potential is there for sure.

Brian

12

Frank B. wrote:

On Dec 24, 2007 5:11 PM, John G. <[email protected]
mailto:[email protected]> wrote:

The Odyssey board operates at 10MHz IF; so wouldn't it need an external
tuner?

Yes, but many different tuners (band sets) can be serviced by the same
IF processor.

Not to mention that Odyssey can take a few dollar DDS input in place of
the crystal and tune all of the HF shortwave bands. The performance
will go DOWN because of the spurs generated by the inexpensive DDS but
that is probably acceptable as opposed to people not having a shortwave
radio at all or only those they cannot afford. Further, to increase
performance, some kind of band switching apparatus, strictly for front
end filtering changes, needs to be provided.

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.)

The OLPC chip is capable and can run a small dedicated sdr/dsp core to
do many functions. I would like to see us offload stuff on to some kind
of helping processor so we could do more than just 5 kHz wide AM/SSB, or
NBFM, etc.

bandwidth, which could probably be done with ease with the assistance of
> This would provide a clear example of how it could be done. It
of large-scale chip producers. Part of the SDR mission, isn’t it?
Open Standards, open source, free infrastructure? That is a little
radical isn’t it? Should that be our mission?

I certainly hope so. That is my life’s mission, which I am grateful in
the extreme that my employer is allowing me to pursue with a vengeance
and with (probably) more clout than I deserve. I am determined to help
end the repeated purchase of, and closed system support of,
infrastructure that should be available to all (and which we are tired
of paying for over and over and over). With this freeing of resources,
we would be leaving the companies, individuals, governments, students,
WHATEVER, to innovate ON TOP of that already done infrastructure. Think
of how much more productive the existing money pool would be if almost
ALL infrastructure code was free (operating systems, word processors,
spreadsheet, radio basic functions, etc.) and we were not having
companies, governments, etc. repeatedly paying for the same closed
system infrastructure to be done as well as the huge support tail for
maintaining it. Then companies would be free to spend lots more of their
money on innovation, creativity, and more, held back then mostly by the
huge part that must go to lawyers to make sure they have a sufficiently
large patent portfolio to defend the innovation (Can we stop that next?)
I just don’t understand why all of the corporate, government,
educational, etc. world is not HOWLING for free, open standards based,
and preferably open source infrastructure code for almost everything and
the end of this closed system and amassing of patent portfolios spending
completely unproductive money (and more importantly time) on lawyers. I
have two friends, one of them for about 25 years. Both are brilliant
engineers, and are members of these mail groups. One has a name that
will be known, and live long after he is dead and gone. He is now
spending almost ALL of his time helping lawyers make the existing
corporate portfolio fit the “crime”. It is an utterly ridiculous waste
of a great mind.

Sigh, don’t get me really started. I might yield an opinion!

The second generation OLPC, which I hope is on the drawing board, should
have inexpensive radio, done by software in every way possible, to give
the OLPC recipient access to communications with the rest of the world.
I suggest that we contact a few companies, such as Microchip and ask
how much for a dsPIC33 in quantity 1 million? But we have the OLPC
going out the door today. If it fails, I think OLPCv2 is going to have
a hard time going forward. There are already “nay sayers” and
competitors with questionable agendas showing up. If an inexpensive
external device could be done for the OLPC, using its existing
processor, that would be a very nice first step. We could indeed build
a transceiver with that. John’s price point, power and size constraints
seems to limit us almost completely to a receive only device. Maybe
that is as it should be but I just want that argued and accepted clearly
as the correct goal. With the external device, done in quantity to
reduce costs, we could more easily have a transceiver. If that is not
desirable, then so be it.

Ordering from Digikey, we could build an HF receiver interface using
QSD and a DDS plugging into the USB port on the OLPC for ~ $30 at
quantity 1500 with the most expensive part being the DDS and accounting
for nearly 1/2 of the cost. That says to me that if we got the
quantities well up from 1500, we could get the price down significantly
but I just do not see it getting down to under $1. We need to add SMT
based bandpass filtering.

Maybe a device like this one:

http://rfdesign.com/rfic/radioscape_chip_frontend/

Done by this company:

http://www.radioscape.com/

could be made in large quantities at low cost but under $1? I have my
doubts that it and others like can be unless some players in industry
are going to step up and provide these kinds of pieces to us. For us to
succeed in the quest for the lowest cost devices, it is my opinion that
we have to find EXISTING technology, learn how to use it, and then try
to convince the owner/developer of the IP that there is a serious
business case for getting it to us cheaply.

Regards
Frank
AB2KT

Season’s greeting to all and Happy New Year.
Bob McGwier

–
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