Progress on the GSM network at FreeCalypso HQ

[Mychaela Falconia]

Hello FC community,

I got a progress update on the setup of our own GSM network at our
FreeCalypso HQ: thanks to Harald's willingness to sell me one at a
steeply discounted price, I just received a sysmoBTS 1002, a picocell
BTS made by Sysmocom, and I got it successfully installed in the place
of the ebay-sourced ip.access nanoBTS I tried to use previously.

Prior to getting this sysmoBTS, when I was playing with nanoBTS hw
driven by Osmocom CNI sw stack, I ran into some unexpected problems:

1) I have two nanoBTS units, one for PCS1900 band and one for GSM850
band, and I played with the PCS1900 unit first.  Everything appeared
to work fine at first: phones would connect (Location Update
successful), SMS and USSD worked, but voice calls failed to connect.
Analysis of Osmocom sw logs showed that the BTS was no longer hearing
the MS once the conversation moved from SDCCH to TCH, and Harald
further noted on the openbsc ML that the timing control loop in the
BTS seemed to be broken.

2) When I tried to fire up the other nanoBTS, the one for GSM850 band,
I got it to work minimally too, but then quickly got a nasty surprise:
Motorola C139 connected fine, but Nokia C3-00 failed to connect.
Analysis of the logs revealed that this GSM850 band nanoBTS unit (or
rather its fw version) does not support A5/3 - whereas Nokia C3-00
supports it, and I have it enabled (along with A5/1) in my OsmoBSC and
OsmoMSC configs.  I didn't get as far as testing voice calls, as I am
not too keen on using a fw-crippled BTS.  And yes, we all know that
our dear Calypso can't do A5/3, but I am leaving the door open for the
possibility that some day we might produce our own chip to be its
successor - hence I run my GSM network with both A5/1 and A5/3
available, and I use Nokia C3-00 to test the latter.

Replacing nanoBTS with sysmoBTS solved all of these problems: the new
BTS supports both A5/1 and A5/3, and voice calls from one phone to
another work like a charm.

In terms of frequency bands, I currently operate my sole sysmoBTS in
the PCS1900 band.  (Unlike nanoBTS, sysmoBTS 1002 hw is quadband.)
GSM850 might provide better distance reach, but for my lab I need a
PCS1900 cell to which I can connect legacy phones that can't do GSM850
- and because I have only one good BTS (as opposed to defective-by-
design proprietary fw), I am sticking with PCS1900 for now.

In terms of distance reach, sysmoBTS 1002 puts out 23 dBm max (same as
nanoBTS), which isn't much.  Operating at max power, and using 20 cm
antennas which _might_ be a little better than the tiny ones from
Sysmocom, I get good coverage on the street and in the parking area
around my apartment building, but when I walk over to the nearest
social meeting place (a Mexican restaurant across the street), the
signal is marginal - not good enough to hold GSM/2G Lovers Club
meetings with demos. :(

It appears that in order to make our pirate GSM signal go far enough
to reach nearby social meeting venues (a little farther than the
Mexican restaurant, there is a larger meeting hall where a group of
really hard-core freedom lovers meet every month - it would be awesome
to market my GSM/2G work to that crowd), I would need to add an
amplifier - here is one model that has been recommended to me:

https://www.shireeninc.com/osc/pico-cell-amplifier-1900-mhz-gsm-edge-lte-cdma-mcs5-9-8psk

and an antenna like this one - officially made for outdoor
installation. but can also be installed surreptitiously inside my
apartment, I reason:

https://excel-wireless.com/product/1850-1990-mhz-omni-directional-antenna-10-dbi/

The antenna is very affordable at $120, but the Shireen amplifier is
pricey at $2600 - ouch!  Because of this cost factor, I am currently
deprioritizing this direction of work (seeking distance reach), and
instead I will put a higher priority on functionality for my own lab
use, for tests conducted either inside my place or from the downstairs
parking area at the farthest.

One avenue which I will need to explore soon is outside PSTN
connectivity.  Right now I can make calls and send SMS from one phone
connected to my one-cell network to another phone connected to the
same, but there is no outside connectivity and no outside phone
numbers.  I need to look into VoIP or SIP trunk services, or whatever
is the correct terminology for a service that provides a small batch
of real 10-digit phone numbers in USA numbering plan and provides
access to these numbers via VoIP/SIP.

Hasta la Victoria, Siempre,
Mychaela aka The Mother