Digital Mobile Radio (DMR) is a land-mobile radio network standard developed by the European Telecommunications Standards Institute (ETSI). DMR is used by thousands of professional land-mobile radio networks worldwide.
A wide variety of DMR mobile, base and portable equipment is available from numerous manufacturers.
DMR uses Time Division Multiple Access (TDMA) to provide two 30 ms “slots” per 12.5 kHz radio channel.
Each slot can carry independent voice conversations – this means that each DMR repeater provides two simultaneous voice channels – illustrated in the diagrams below:
Analogue vs. TDMA (courtesy Vertex Standard)
Two channel analogue/FDMA vs. TDMA (courtesy dmruk.net)
Each slot can also have an almost unlimited number of “talk groups”– these function as discrete channels within that slot. Users on one talk group will not hear those on another.
DMR provides better noise rejection and weak signal performance than analogue systems by using advanced Forward Error Correction (FEC) and codecs to remove noise and reconstruct signals that would otherwise be lost – depicted in the following diagram:
DMR vs. analogue weak signal performance (courtesy Tait Communications)