Calypso vs. SDR PHY

Harald Welte laforge at gnumonks.org
Sat Nov 18 19:26:06 UTC 2017


Hi Mychaela,

On Fri, Nov 10, 2017 at 05:17:21PM -0800, Mychaela Falconia wrote:
> 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.

Actually, it's also
(3) the (particularly) receiver performance of the TIS DSP is pretty
    damn good and it is quite some effort to achieve comparable performance
    with a general-purpose SDR.  You can e.g. add external band filters
    for downlink, but then you're still missing the analog matches 270kHz
    baseband filter in front of the ADC to avoid loosing any ADC resolution
    to nearby in-band carriers.  The analog filters in integrated RFICs
    today typically don't go smaller than 1MHz (if at all) which is quite
    far from the 270kHz that GSM uses.
(4) you can actually run the entire application (e.g.
    http://osmocom.org/projects/baseband/wiki/Rssibin) inside a small,
    hand-held, battery-powered device. Try that with PC + SDR and look
    at your size + power budget.
(5) somewhat ties into (4): One goal was always to run also 'mobile'
    inside a phone and have a FOSS-based telephone.  Nobody has had
    the time + endurance to get there, and I doubt it will still happen
    at this point.

> 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.  

It is also something to keep in mind that a lot of the people who had
an interest in OsmocomBB have those phones for years.  And the number
of new people who haven't been around for many years with an interest
in playing with "old" cellular systems such as GSM is quite low.

> 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, 

Having done a fair amount of electronics manufacturing in this kind of
quantity, I would seriously be surprised if you'd still be at that kind
of pricing in a MOQ-100 situation.  But sure, it will not be at the
level of a used old phone.

> 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?

See above.

-- 
- Harald Welte <laforge at gnumonks.org>           http://laforge.gnumonks.org/
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