OLPC hardware: what if there was an SDR modem / chipset?

Luke Kenneth Casson Leighton lkcl at lkcl.net
Mon Jan 25 10:42:57 EST 2010

dear olpc devel people,

i've been doing some research and found a couple of companies with SDR
R.F. front-end ICs.  one is 40nm and is so tiny that it will only cost
about $2, mass-produced.  also thanks to being in 40nm, the speed of
the (SoC / embedded) ARM9 core is so fast that it's perfectly capable
of handling multiple protocols.  as you're no doubt aware,
Software-Defined Radio has been "full of promise" for quite some time
as "The" low-cost transceiver option, but it's only recently that the
speed of embedded ICs has gone up enough and the geometry small enough
to bring the cost down into the affordable range.

key to making SDR "work" is of course having the software :)  but,
i've found a company who already have GSM through EDGE; there's
http://openbts.org and also of course there's the gnu-radio project
which has produced part of 802.11, amongst other things.  ( but,
remember: the nice thing about the 2.4ghz and 5ghz bands is that you
don't _actually_ need to do 802.11, you can in fact just use the
entire set of bands to do absolutely anything you want.  and, with
SDR, you _could_ do anything you want).

the neat thing about SDR is that the _same_ solution replaces:

* a WIFI chipset ($10)
* a GSM chipset ($12 lowest i've found in 100k+ volumes)
* or a 3G chipset ($30 lowest i've heard about in mass-volume)
* a GPS chipset ($6 and that's again an SDR solution,
   you need a DSP to translate; $12 for dedicated chipset)
* a WIMAX chipset (haven't even looked this up, but estimate $20)
* a DVB TV chipset (approx $5 and again that's an SDR solution)
* an FM Radio chipset (don't know its cost, don't honestly care!)

i repeat.  all those can be replaced with _one_ i repeat _one_ single
solution, costing roughly... $12, if that.

issues which need to be resolved:

* paying for a minimum of 8 40nm 10in wafers (appx 5000 ICs per wafer)
@ $0.50 ea, running the test vectors @ $0.75 ea, packaging @ $0.50 ea
it works out roughly at $2.00 times 40,000.

* creating the PCB with RF MEMS filters
(http://en.wikipedia.org/wiki/RF_MEMS) and other assorted components,
coax connectors for antenna, the remaining components are going to be
somewhere around $10.

* license compliance and Certification in the countries in which the
final modem is deployed (remember that if frequencies other than
2.4ghz or 5ghz @ greater than 100mW are used or 400mW in Hong Kong
then licenses are NOT required)

even with these issues to be costed out and resolved, i wanted to ask:

* is the incredible low-cost and flexibility of SDR worth pursuing?

* is the current Marvell 88688 "proprietary firmware" 802.11 blob
_that_ acceptable / accepted?

* is the possibility of being able to run an XO up a pole (or placed
at the top of any tall building) and have it _be_ the GSM or WIMAX
base station for an entire town or village and the surrounding
countryside for miles around the kind of thing that is attractive to,
and useful to the aims of the OLPC project, or not?

also - one thing that also would help to have an answer to : if
answers above turn out to be resounding "yes", what's next?  who makes
the decision?


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