Two-Slot TDMA
DMR Tier II/Tier III occupies a 12.5 kHz bandwidth with two channels sharing using Time-Division Multiple Access (TDMA), this results in spectrum efficiency of 6.25 kHz per channel. Comparing the spectrum efficiency of DMR to a wideband analog FM, DMR only uses 25% of the bandwidth per talk channel. Each channel can carry either voice and/or data depending on system design. The two time slots are called Time Slot 1 (TS1) and Time Slot 2 (TS2).
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fc -12.5 fc fc+12.5
Wideband Analog FM 25 kHz Channel Bandwidth (25 kHz per Channel)
fc –6.25 fc fc +6.25
DMR 12.5 kHz Channel Bandwidth (6.25 kHz per Channel)
TS2 TS1
TS2 TS1
TS2 TS1
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Two-Slot TDMA
For the amateur, this means one repeater allows two separate channels at the same time. Currently most amateur DMR repeater system implementations utilize both channels for voice and some limited text messaging. Typically one channel (time slot) is used for wide-area and the second is local and regional talk groups.