Question...When you have two users with analog radios on the same frequency, but different PL tones, transmitting at the same time, the signals cover each other. Does the same happen with digital transmissions or do they manage to deconflict because of the digital nature and different color codes, etc.
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If two digital signals such as P25 conventional transmit at the same time they will interfere in the same way that analog signals do. There is some capture ratio, a range by which one or the other signals will be significantly understandable, however with narrowband digital signals, that benefit is minimum. Unlike analog signals where a listener might be aware interference is occurring by the sound, in digital, the listener cannot determine if the difficulty is due to range, interference or that there was any attempt to transmit.
Color Codes, NAC/NID's and Talk Groups do nothing to limit potential co-channel contention.
Some digital techniques such as TDMA and CDMA operate under system rules that permit two or more transmitters to seemingly occupy the same channel. These systems coordinate themselves to avoid interference. DMR (and Tetra) uses TDMA and relies on a master/slave arrangement to assign time slots. In this case a user on slot 1 can operate independently from slot 2. However interference from another station that isn't synchronized to avoid an occupied time slot will cause interference. CDMA is the technique used for WiFi and indeed interference cannot always be avoided as the WiFi bands are over loaded. CDMA works for cellphones because the frequency band is managed by the telephone company who make it their business to avoid interference between their own stations.