Open Source DMR Modem Implementation in SDR with GNU Radio and Codec2

Summary

Open source DMR (Digital Mobile Radio) modem implementation in software defined radio with GNU Radio and Codec2 Digital Mobile Radio (DMR) is a mobile radio standard created by ETSI, which is very popular within the amateur radio community. DMR radios are easily available on the market and the costs are low compared to D-Star or YSF radios, although the complexity of usage creates a barrier for entry. In addition, there is a very large community of listener-only amateurs who are interested in receiving digital transmissions using this mode. A very basic DMR modem (receiver and transmitter), capable of voice calls, that could emulate a subscriber radio using a SDR transceiver as the radio interface is described in this page. While this modem is just a proof-of-concept interpretation of the DMR standard with no real use-case, there exists at least one open source project which proposes to create an open source DMR transceiver. The OpenRTX project is "a free and open source firmware for digital ham radios designed with a top-down approach with the objectives of modularity, flexibility and high performance", which aims to create a fully open source radio for amateur radio usage in real life applications. Currently OpenRTX supports the M17 digital mode, but DMR capability seems to be on its roadmap as well. This particular modem could be a source of inspiration, but would require a complete rewrite to work on top of OpenRTX and a real DMR radio, due to various technical limitations (computing power and memory constraints for example). In previous articles, a SDR device-based implementation of a DMR repeater (BS in ETSI terminology) was discussed (including multi-carrier and Tier III), using GNU Radio for the lower physical layer and MMDVM-SDR / MMDVMHost-SDR ( slightly modified forks of Jonathan Naylor's MMDVM and MMDVMHost) for the actual DMR repeater functionality. This page is instead related to subscriber radio (MS in ETSI terminology) functionality only. The base co...