Desktop Testing of OpenBTS
Here's the hardware you will need for a desktop testing kit:
- A USRP.
- A computer running Linux or Mac OS X with a USB-2.0 port and libusrp
installed. We recommend against Dell laptops because their hardware tends to
couple a lot of noise into the USRP via the USB cables, at least in some models.
We have had our best results with Apple PowerBooks and MacBooks. We
have not tested a lot of desktop machines, but generally have had better success
with them than with desktops. Virtual machines are not likely to work, nor is
Cygwin. We would be interested in reports of what systems tend to work
- Two RFX900
daughter cards (for GSM 850/900 operation) or two RFX1800 daughter cards (for PCS or DCS
operation). The ISM band filter on the RFX900 will need to be removed, as
described in the wiki link. You need two to minimize crosstalk between the
receive and transmit sections.
- Antennas with SMA connectors to fit the USRP and matched to whatever
cellular band you intend to use. The VERT900 antenna, also available from Ettus
works fine. Or just do a Google search for "cellular antenna SMA" and see what
- At least two GSM phones. Our preferred testing phone is a DCT-3 series
Nokia. (The DTC-3 models are 2100, 3210, 3310, 3315, 3330, 3350, 3390, 3395,
3410, 3610, 3810, 5110, 5130, 5190, 5210, 5510, 6110, 6130, 6138, 6150, 6190,
6210, 6250, 7110, 7190, 8210, 8250, 8290, 8810, 8850, 8855, 8890, 9110.) These
models all support Nokia's field test mode, although
in some cases you need a special Nokia serial cable to enable it. We say at
least two phones, but for full-load testing of a single-ARFCN system you need
- SIMs. Every phone needs a SIM. The requirements for the SIMs depend on the
band in which you chose to operate and are discussed below.
- A SIP phone. We've used a PAP2 adapter and we've used
the Zoiper softphone
The recommended testing configuration is to operate in a cellular band
not used in your area and use test phones that do not support
your local cellular bands. This arrangement forces your test phone to camp to
your basestation. It also prevents you from inadvertently attracting phones from
the local licensed carriers. For example, to test in North America, you might
use the EGSM900 band or the DCS1800 band and use a phone that does not support
GSM850 or PCS1900.
If you do operate in a band that is also used by cellular
carriers in your area, you will need to use SIMs from a carrier that does not
offer service in you area and has no roaming agreements with carriers in your
area. You can then use network parameters matched to the SIM and, hopefully,
your test phones will ignore the local network and phones from your local
network will ignore you.
If you do not operate in a band that is used by cellular
carriers in your area, you can use any SIM you want.
If you want any flexibility at all in your choice of SIMs, you will need to
use unlocked phones.
Be aware of power levels and local regulations. Here are some technical
- Operate in a cellular band not used by your local carriers.
This will reduce your likelihood of interfering with their service and will make
your own test more controllable.
- Do not use a transmit antenna. Plenty of power leaks out of
the USRP for close-range testing.
- Do use a receive antenna. Remember that GSM uses active
uplink power control. The more sensitive your receiver is, the less power the
BTS will need to request from the phone.
- Keep the phones close to the USRP. Again, keeping the distance short (less
than 2m) will allow the BTS to control the phone down to minimum power.
- Be aware of local radio applications and avoid their spectrum. This is
especially important for air navigation and air traffic control radar systems.
- Perform a spectrum survey to know what frequencies are in use in your
- Check you regulator's licensing database to know who holds licenses in your
- Test indoors to limit propagation.
- Use a test phone with an RSSI display. You should not need received power
levels above -80 dBm for desktop protocol testing.
However, these are only technical pointers to help you
comply with your local regulations. They are not legal advice on the regulations
themselves. That is entirely your responsibility.