op25-dev January 2024

op25-dev@lists.osmocom.org

3 participants
2 discussions

Seeking help/clarification on DMR Reverse Channel signalling
by Adrian Musceac 21 Jan '24

21 Jan '24

Hello OP25 devs, I'm an amateur radio operator working on implementing an open source DMR tier 3 trunked radio base station based on a multi-carrier SDR structure. I have reached a point where I no longer know how to interpret the ETSI standard and I thought to ask for help here due to your expertise with trunked radio systems. The outbound Reverse Channel PDU is used in DMR tier 3 for MS power control and MS de-key (transmit interrupt). Based on my interpretation of the standard, a couple of things are clear: 1. Reverse channel is only available if aligned timing is used 2. It is supposed to be embedded in voice burst F of a voice transmission on the alternate timeslot 3. The MS is supposed to monitor the alternate timeslot during transmit and derive RC information from it There are a few scenarios where it seems to me these tier 3 services (power control, priority interrupt) cannot be available at all... 1. Alternate timeslot is a control channel 2. Alternate timeslot is idle 3. Alternate timeslot carries something other than voice payloads The standard doesn't clarify these cases and I have doubt that these 2 services can even be reliably implemented. Are you able to help me understand how the Reverse Channel is used in the real world by existing industry implementations of DMR tier 3? Thanks, Adrian YO8RZZ

2 2

H-CPM demodulator for SDR?
by nanocask＠gmail.com 04 Jan '24

04 Jan '24

Happy New Year! Has anyone worked on demodulating H-CPM? This is the modulation used by the SU when transmitting in an APCO P25 Phase II system. Thanks Osmocom for all the pioneering SDR work you have done!

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op25-dev January 2024