Calypso vs. SDR PHY

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Vadim Yanitskiy axilirator at
Thu Nov 16 05:30:54 UTC 2017

Hello Mychaela,

First of all, my congratulations! I have been watching the project
you lead for some long time, and it's great to see your achievements.

> As I understand it, there are two reasons for why the original
> incarnation of OsmocomBB (prior to the recent addition of SDR PHY
> support) used Calypso phones as its physical transceiver instead of
> USRP-style SDR devices: (1) the work done by the Calypso DSP is
> already done, hence there was less work for OsmocomBB developers to
> do, and (2) Calypso phones used to be dirt-cheap, whereas SDR devices
> cost some non-trivial money.

Yeah, moreover I think when OsmocomBB was initiated, the prices of
available SDR hardware were higher, than today...

> 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?

Personally, for research and development purposes I would preffer SDR.
The main reason is that my research scope isn't limited by GSM only,
there are other pretty interesting technologies like Iridium, TETRA,
GMR, and of course UMTS followed by LTE.

> 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?

SDR PHY isn't finished yet. We only managed to get actual burst
transmission working only a couple of weeks ago. At the moment,
both AGC and Timing Advance loops are missing, and TX power is
not high enough to 'deal' with real base stations...

So, I think, Motorola C1XX phones remain the primary hardware
back-end for now, thus would be better to tell people about them.

> One argument I have heard against the use of SDR for GSM MS role is
> that SDR devices supposedly have a difficult time retuning every
> 4.615 ms, and thus would have a difficult time connecting in the MS
> role to a GSM network that employs frequency hopping.  Is there any
> truth to that argument, or has that problem already been solved?  Are
> there any other areas in which a chipset like the Calypso that is
> specifically designed for the GSM MS role would perform better than an
> SDR device of the kind that are viable cost competitors against newly
> made Calypso hardware?

Yeah, both frequency popping and neighbour power measurement are the
hard topics for SDR PHY. There are some ideas how to implement that,
but right now we are keeping this problem aside until all the rest
is done ;)

With best regards,
Vadim Yanitskiy.
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