In the last post we covered the config required to provision a new BTS in our BSC.

We’re going to do roughly the same thing this time around, as we connect our SDR based BTS to our BSC.

Before we fire up the BTS side of things make sure you’ve stopped the virtual BTS and disabled it.

systemctl stop osmo-bts-virtual
systemctl disable osmo-bts-virtual

Configure Osmo-BTS-TRX

Next up we’ll edit the config of osmo-bts-trx.

vi /etc/osmocom/osmo-bts-trx.cfg

We’ll edit the oml remote-ip to the IP of the server running your BSC, if you’re running on on the same machine you can leave it as localhost (127.0.0.1).

Next up we’ll set the Unit-ID of the BTS, this identifies the BTS inside the BSC,

I’ll set it to unit-id 1234 by changing ipa unit-id 1234 0

Finally we’ll change the logging config to show everything by changing it to:

log stderr
 logging filter all 1
!

Next up we’ll configure the BTS on the BSC

BSC Provisioning

This is essentially a copy of the provisioning process we followed in the last post, the only difference is we’ll use BTS 2 (as BTS 1 is setup for our Virtual BTS) in the config, and set the few different identifier such as the ipa unit id for the SDR based BTS.

telnet localhost 4242
OsmoBSC> enable
OsmoBSC# configure terminal
OsmoBSC(config)# network
OsmoBSC(config-net)# bts 2
OsmoBSC(config-net-bts)# type sysmobts
OsmoBSC(config-net-bts)# description "LimeSDR Based BTS"
OsmoBSC(config-net-bts)# ipa unit-id 1234 0
OsmoBSC(config-net-bts)# band DCS1800
OsmoBSC(config-net-bts)# codec-support fr hr efr amr
OsmoBSC(config-net-bts)# cell_identity 1234
OsmoBSC(config-net-bts)# location_area_code 1234
OsmoBSC(config-net-bts)# base_station_id_code 1234
OsmoBSC(config-net-bts)# base_station_id_code 12
OsmoBSC(config-net-bts)# ms max power 40
OsmoBSC(config-net-bts)# trx 0
OsmoBSC(config-net-bts-trx)# max_power_red 20
OsmoBSC(config-net-bts-trx)# arfcn 876
OsmoBSC(config-net-bts-trx)# timeslot 0
OsmoBSC(config-net-bts-trx-ts)# phys_chan_config CCCH+SDCCH4
OsmoBSC(config-net-bts-trx-ts)# exit
OsmoBSC(config-net-bts-trx)# timeslot 1
OsmoBSC(config-net-bts-trx-ts)# phys_chan_config TCH/F
OsmoBSC(config-net-bts-trx-ts)# exit
OsmoBSC(config-net-bts-trx)# timeslot 2
OsmoBSC(config-net-bts-trx-ts)# phys_chan_config TCH/F
OsmoBSC(config-net-bts-trx-ts)# exit
OsmoBSC(config-net-bts-trx)# timeslot 3
OsmoBSC(config-net-bts-trx-ts)# phys_chan_config TCH/F
OsmoBSC(config-net-bts-trx-ts)# exit
OsmoBSC(config-net-bts-trx)# timeslot 4
OsmoBSC(config-net-bts-trx-ts)# phys_chan_config TCH/F
OsmoBSC(config-net-bts-trx-ts)# exit
OsmoBSC(config-net-bts-trx)# timeslot 5
OsmoBSC(config-net-bts-trx-ts)# phys_chan_config TCH/F
OsmoBSC(config-net-bts-trx-ts)# exit
OsmoBSC(config-net-bts-trx)# timeslot 6
OsmoBSC(config-net-bts-trx-ts)# phys_chan_config TCH/F
OsmoBSC(config-net-bts-trx-ts)# exit
OsmoBSC(config-net-bts-trx)# timeslot 7
OsmoBSC(config-net-bts-trx-ts)# phys_chan_config TCH/F
OsmoBSC(config-net-bts-trx-ts)# exit 
OsmoBSC(config-net-bts-trx)# exit
OsmoBSC(config-net-bts)# exit
OsmoBSC(config-net)# exit
OsmoBSC(config)# exit 
OsmoBSC# copy running-config startup-config 

Starting the SDR based BTS

Before we start the SDR based BTS it’s probably best to have 3 terminals open,

One logged into Osmo-BSC with logging enabled (see the last post for info on how to do that).

We’ll start another terminal for running the TRX modem / Layer 1 interface:

osmo-trx-lms -C /etc/osmocom/osmo-trx-lms.cfg

And in another new terminal we’ll start the BTS side;

osmo-bts-trx -c /etc/osmocom/osmo-bts-trx.cfg

All going well our terminal with Osmo-BSC should report the connection:

OsmoBSC#
<0016> input/ipa.c:287 0.0.0.0:3003 accept()ed new link from 10.0.1.252:39595
<0003> osmo_bsc_main.c:291 bootstrapping RSL for BTS/TRX (2/0) on ARFCN 875 using MCC-MNC 001-01 LAC=1234 CID=1234 BSIC=12

And the osmo-trx-lms and osmo-bts-trx windows should have data flying by at a rate of knots.

Verifying Cell Operation

If all is going to plan, our SDR is connected to our machine via osmo-trx-lms which is acting as a modem for osmo-bts-trx which is now connected to the BSC. Lot to go through, but it gets easier from here.

Let’s run a scan of the networks on our phone. I found putting mine on GSM only before scanning for networks meant it popped up a heck of a lot faster.

And lo, there it is.

Our cell is online and broadcasting it’s info. You won’t be able to connect to it at this stage as we’ve still got a few more steps to go.

In the next post we’ll introduce the Home Location Register and then the MSC.