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(a)gnumonks.org>
http://laforge.gnumonks.org/
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