OsmoTRX is a software-defined radio transceiver that implements the Layer 1
physical layer of a BTS comprising the following 3GPP specifications:

TS 05.01 "Physical layer on the radio path"
TS 05.02 "Multiplexing and Multiple Access on the Radio Path"
TS 05.04 "Modulation"
TS 05.10 "Radio subsystem synchronization"

In this context, BTS is "Base transceiver station". It's the stations that
connect mobile phones to the mobile network.

3GPP is the "3rd Generation Partnership Project" which is the collaboration
between different telecommunication associations for developing new
generations of mobile phone networks. (post-2G/GSM)