NOTE: This page is outdated, the OpenBTS project is abandoned. Please, use Osmocom software which is actively maintained and has reliable UmTRX support.
First ensure that you have the
hardware set up correctly
.
Software setup
UHD with UmTRX support
UHD must be installed along with the UmTRX UHD module. For details see the
Driver
page.
OpenBTS
Download
git clone https://github.com/fairwaves/openbts-2.8.git
Follow the
standard build instructions
.
Run OpenBTS
Follow the standard instructions at
http://wush.net/trac/rangepublic/wiki/BuildInstallRun
Tune OpenBTS for hardware
To get the best performance you need to ensure your cell has good uplink/downlink (UL/DL) balance. Which is to say, it should not be UL- or DL-limited. OpenBTS has several parameters for this purpose and which should be tuned for specific hardware.
Note that the following procedure requires that you have a working OpenBTS setup with at least one connected handset.
Run the
noise
command in the OpenBTS CLI several times to get the worst value (largest) for the noise RSSI of your setup. It should be a negative value, e.g. -44dB.
OpenBTS> noise
noise RSSI is -44 dB wrt full scale
MS RSSI target is -37 dB wrt full scale
Add 6-8dB to the noise RSSI value to get the RSSI level we need to receive phone signal on the BTS without errors. This is called
target RSSI
in OpenBTS and is set with GSM.Radio.RSSITarget value in the config. If noise RSSI is -44dB, then you could set target RSSI to -37dB:
OpenBTS> config GSM.Radio.RSSITarget -37
Make a call
from your test mobile to another mobile or a soft-switch. During the next steps we will use the active channel between the mobile and the base station to estimate link quality, and to tune Rx gain and Tx attenuation.
Adjust rxgain
to provide good reception at the edge of the base station reception area, while at the same time avoiding saturation — and thus bad reception — close to the base station. The easiest way to estimate reception quality is to use
UPFER
value at the
chans
CLI command output. Zero
UPFER
means good reception, non-zero “`UPFER`” means errors on UL channel:
OpenBTS> chans
CN TN chan transaction UPFER RSSI TXPWR TXTA DNLEV DNBER
CN TN type id pct dB dBm sym dBm pct
0 1 TCH/F 1788614112 0.00 -5 5 0 -101 0.00
Good UL quality!
OpenBTS> chans
CN TN chan transaction UPFER RSSI TXPWR TXTA DNLEV DNBER
CN TN type id pct dB dBm sym dBm pct
0 1 TCH/F 22843555 56.80 -27 5 0 -59 0.00
^^^^^
Bad UL reception.
The
power
CLI command sets attenuation of the Tx power relative to the maximum base station power. It has two values,
max
and
min
, but for a small base station it’s easier to set them to the same value. Place the test mobile phone at the edge of good reception area and increase
power
value until
DNBER
starts to increase. It should happen when
DNLEV
reaches around -105dB.
OpenBTS> power 55 55
current downlink power -50 dB wrt full scale
current attenuation bounds 50 to 50 dB
new attenuation bounds 55 to 55 dB
OpenBTS> chans
CN TN chan transaction UPFER RSSI TXPWR TXTA DNLEV DNBER
CN TN type id pct dB dBm sym dBm pct
0 1 TCH/F 1788614112 0.00 -5 5 0 -107 2.26
^^^^^^^^^^^
DL signal is too weak.
If you need to limit the radius of your base station it’s better to do so by decreasing the base station Tx power, i.e. by increasing attenuation with the
power
command.
