Calypso vs. SDR PHY

Alexander Chemeris alexander.chemeris at gmail.com
Sun Nov 19 15:32:11 UTC 2017


Hi Mychaela,

On Sat, Nov 11, 2017 at 4:17 AM, Mychaela Falconia
<mychaela.falconia at gmail.com> wrote:
> But the dirt-cheap Calypso phone situation is now firmly in the past,
> and newly made Calypso devices like my FCDEV3B are nowhere close to
> cheap.  The qty-1 retail price for one of my FCDEV3B boards is
> $500 USD; if someone were to order a large batch (say, 100 boards),
> I am reasonably confident that the per-unit price can be brought down
> to $300 USD or maybe even lower, but getting any kind of firm numbers
> beyond a guesstimate would require actual work, and that work will
> only be done if I receive some expression of serious and genuine
> interest.  But even if we manage to bring the price down to, say, $200
> per board with a really large order quantity, it *still* won't be
> anywhere near as cheap as old Calypso phones used to be, and the price
> is still essentially in the same ballpark as a midrange SDR device.
>
> Thus with the cost of an SDR device and that of a newly made Calypso
> device being comparable (or as things stand presently, the Calypso
> option is more expensive), is there any remaining reason to use
> Calypso devices as opposed to SDR PHY for OsmocomBB?  In other words,
> is there any solid technical reason (not involving cost) to prefer a
> Calypso device over SDR PHY for OsmocomBB purposes, or is there not?
> Which translates into: is there any reason to support running OsmocomBB
> on FreeCalypso hardware and to market such hw to the OsmocomBB
> community, or would it be better to tell people that if they want
> OsmocomBB, they should use an SDR PHY, and leave FC hardware for
> people like me who are interested in end use applications (as opposed
> to hacking) using TI-based FC firmware?

I'm not an active OsmocomBB user or developer, but being involved with
SDR development since 2008 I want to add my 2cc.

I personally think that the SDR way makes much more sense at this
moment. Combine an SDR like our XTRX with any of the widely available
ARM boards and you get a very portable device which can do GSM and
more. If you create a custom board you can even add PA, filters
(bandpass and/or channel), SIM card slot and get a real phone. Such a
carrier board will be very easy to route and cheap to manufacture so
I'm quite sure it'll be at least no more expensive. And given a much
wider functionality, it will be probably much higher volume, again
helping drive the cost down.

Another benefit of the SDR approach is that it will allow you to have
a real FOSS phone - see Harald's comment which I 100% support.

In a "naive" approach receive sensitivity will be degraded compared to
a real phone, but you can put an extra PLL with channel filter to
resolve this at a slight increase in the cost. Most researchers don't
probably need champion sensitivity though, so you can make this an
option. It's easy to route it so that you can populating or not those
components depending on your customer requirements.

Obvious "cons" of the SDR approach is a higher power consumption. In
our XTRX (not sure about other SDRs) we can turn off RFIC or even the
FPGA but I think it will be more power hungry anyway.

Frequency hoping should be doable as well. We haven't done real
measurements yet, but our back-of-the-envelope calculations showed
that we can hop much faster than what you need for GSM. We'll do
measurements once we're done with more basic stuff.

That said, SDR path while more forward-looking and liberating will
require a different skillset than hacking an existing hardware
platform. So at the end, it's your choice which path you find more
compelling.

-- 
Regards,
Alexander Chemeris.
CTO/Founder, Fairwaves, Inc.
https://fairwaves.co


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