How does the DV4Mini license their DMR implementation? I just feel like we should be able to homebrew this stuff at this point.
I think the only part that is really proprietary is DVSI's AMBE voice codec, which is used in most (maybe all?) digital systems. I'm not familiar with the DV4Mini but I assume it's either using those parts or has reversed engineered patented & copyright IP. Everything else is somewhere between open source and freely licensed from JARL, Yaesu, etc. The DMR protocol is an ETSI standard.
http://www.etsi.org/technologies-clusters/technologies/digital-mobile-radio
Motorola's MOTOTRBO is an extension of DMR, which is what most commercial surplus radios use. For example, I still have VXD radios, which are repackaged Motorola XPR models. Motorola added the IP layer to interconnect repeaters, trunking and some privacy stuff.
From a ham user standpoint the encryption stuff isn't legal anyway. The fundamental part, time slots, framing, packet definitions, that's all ETSI standards.
There's a global Motorola-based (using C-Bridges to interconnect) amateur network called DMR-MARC, which was what started it all and still is the framework for talkgroups and the database of user IDs. And if I understand it correctly, the IP Site Connect has been worked around using Brandmeister. So it's really just the AMBE stuff that's closed.
And why Yaesu decided to use it when that could have been the *one* thing they could have done differently is beyond me. But then I can't say how difficult it is to develop a new codec that works as well while also being different enough not to infringe on DVSI, so it may not be easily done.