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

Luke Kenneth Casson Leighton lkcl at lkcl.net
Mon Jan 25 13:05:11 EST 2010

On Mon, Jan 25, 2010 at 4:24 PM,  <david at lang.hm> wrote:
> On Mon, 25 Jan 2010, Luke Kenneth Casson Leighton wrote:
>> 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,
> are you sure that your $2 SDR chip is going to be able to do a protocol as
> complex as wifi?

 the $ RF front-end chip ends at an "A-D" / "D-A" converter.  after
that, it's well known that DSPs can handle the rest of the work.

> that will take quite a bit of computing power (digital
> signal processing isn't something you do efficiantly on the ARM9 core), so
> it may push you from the $2 chip to a $10 chip (what do you think the
> existing wifi chipsets are?)

 ARM9 or ARM7 cores plus a DSP.

> while the chip can decode all the different protocols you mention below, the
> problem is that these cover many different frequency ranges, and getting the
> RF portion of the device (including antennas) to handle all those different
> bands on one device, let alone at one time, is far more complex than you
> imagine

 and there is expertise in the world to take care of it.  admittedly
it's an area where the expertise is becoming increasingly rare, but
the expertise exists.

> (and would you really want a device that could be wifi, OR GPS
> OR.... but not more than one at a time?)

 a) two $2 transceiver chips - knock yourself out! :)

 b) i believe that the RF transceiver chip is multi-channel (simultaneous)
     so can actually handle two separate protocols at once.

 either way, it's just extra load on the DSP.

> you also ignore licensing and regulatory approval.

 no, i didn't, but it's worth mentioning again so that it's not
forgotten as part of the cost.

 the key questions to be asking are: in light of the massive volumes
involved with OLPC XOs, is SDR worth pursuing, given all the
development costs, but given all the benefits especially where SDR can
be re-programmed to do "whatever" in bands where licensing and
regulatory approval is _not_ required, on a per-country basis?


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