Using LimeSDR equipment (LimeNET-Micro / LimeSDR-mini) and MMDVM + GNU radio as core components, the implementation of a full duplex SDR base station was created in order to support the DMR, System Fusion, D-Star and M17 amateur digital voice standards in a multi-carrier configuration, with up to 7 transmitted carriers within 200 kHz bandwidth, in any combination of operating modes and with a configurable channel separation. The channel / mode matrix is entirely user configurable by using multiple MMDVM instances, each of them dedicated to one operating channel.
The long term goal is to continue software development and combine LimeSDR equipment with the LimeRFE front-end and capable computing hardware to supply a self-contained, easily deployable base station in NITB style. The end-user should only need to supply their own antennas, power amplification and duplexing hardware for a complete SDR base station solution.
The current testing status has confirmed operation of the DMR and System Fusion standards, while D-Star and M17 modes are still theoretic and need to be tested. There is interest in further extended support for the new M17 open digital voice standard and investigating how a multi-carrier approach can provide amateur radio operators new avenues of experimentation with topics like trunking, multiple access, IP network facilities and other such topics. Work is in progress to improve code, refine user documentation and create deployable packages.
A video demonstrating the operation of a four-channel mixed DMR and System Fusion duplex repeater system can be seen here: