SDR (Software Defined Radio) » gr-gsm » OsmocomBB SDR PHY

h1. Usage

First of all, please see [[SDR_PHY#Project-status|known limitations]].

h2. Hardware preparation

You need to have two antennas connected: one for RX, another for TX. Both antennas should be chosen for a proper frequency band, otherwise the distance will be limited. Also, it's strongly recommended to use a band-pass filter for TX in order to *avoid interference*.

_Note: There is a bug of USRP B2X0 hardware, which affects the burst transmission quality. It appears when both transmission and reception are performed of the same side of device. To mitigate this, please use an attenuator or antenna with some resistance between the active pin and ground._

Finally, connect your SDR hardware and make sure it's working.

h2. Transceiver

Check available configuration options:

<pre>

$ grgsm_trx --help

...

  TRX interface specific

   -i --remote-addr  Set remote address (default 127.0.0.1)

   -p --base-port    Set base port number (default 6700)

  Radio interface specific

   -a --device-args  Set device arguments

   -s --sample-rate  Set sample rate

   -g --rx-gain      Set RX gain (default 30)

   -G --tx-gain      Set TX gain (default 10)

      --rx-antenna   Set RX antenna (default RX2)

      --tx-antenna   Set TX antenna (default TX/RX)

      --ppm          Set frequency correction (default 0)

</pre>

If you already have another transceiver runing, e.g. [[OsmoTRX:]], choose a different TRX base port. Keep in mind that a single transceiver process occupies six UDP ports at the same time.

Choose proper RX / TX antennas and corresponding gain values depending on your device. TX gain requires more attention and should be set depending on your environment and antennas used. Feel free to use a spectrum browser, such as GQRX or osmocom_fft, for measuring the proper values.

PPM value is typically measured at runtime, so no need to specify it manually.

<pre>

$ grgsm_trx --rx-gain 30 --tx-gain 80

linux; GNU C++ version 4.8.5; Boost_105500; UHD_003.010.002.000-0-122bfae1

License GPLv2+: GNU GPL version 2 or later <http://gnu.org/licenses/gpl.html>

This is free software: you are free to change and redistribute it.

There is NO WARRANTY, to the extent permitted by law.

[i] Init Radio interface

-- Detected Device: B200

-- Operating over USB 3.

-- Initialize CODEC control...

-- Initialize Radio control...

-- Performing register loopback test... pass

-- Performing CODEC loopback test... pass

-- Setting master clock rate selection to 'automatic'.

-- Asking for clock rate 16.000000 MHz... 

-- Actually got clock rate 16.000000 MHz.

-- Performing timer loopback test... pass

-- Setting master clock rate selection to 'manual'.

-- Asking for clock rate 26.000000 MHz... 

-- Actually got clock rate 26.000000 MHz.

-- Performing timer loopback test... pass

-- Asking for clock rate 26.000000 MHz... OK

[i] Init CTRL interface

[i] Init complete

</pre>

At this step transceiver is ready.

h2. The trxcon application

As we don't use Calypso-based phones, the [[osmocon]] application is useless here. Instead, you need to run another application called trxcon. You should use the same TRX base port as specified to transceiver.

<pre>

$ cd osmocom-bb/src/

$ host/trxcon/trxcon

License GPLv2+: GNU GPL version 2 or later <http://gnu.org/licenses/gpl.html>

This is free software: you are free to change and redistribute it.

There is NO WARRANTY, to the extent permitted by law.

<0001> l1ctl_link.c:235 Init L1CTL link (/tmp/osmocom_l2)

<0003> trx_if.c:646 Init transceiver interface

<0005> sched_trx.c:112 Init scheduler

<0000> trxcon.c:277 Init complete

</pre>

See help details.

h2. L2&3 applications

At this step you should be able to run the higher layer applications.

For example, run [[ccch_scan]]:

<pre>

$ cd osmocom-bb/src/

$ cd host/layer23/src/misc/

$ ./ccch_scan -i 127.0.0.1 -a <ARFCN>

</pre>

It should synchronize with a BTS on specified ARFCN, and start decoding BCCH messages.