Open Source DMR Modem Implementation in SDR with GNU Radio and Codec2

https://qradiolink.org/open-source-DMR-transceiver-implementation.html

by threeme3 • 1 year ago

103 17 1 year ago

lpribis• 1 year ago

I see this is only tier 2 for now (conventional channels) and not tier 3/trunked yet.

Are trunked networks ever used in amateur radio or outside of big commercial/government systems? Is there a standardized way to feed back channel info to the SDR frontend for trunked operation in GNU Radio? Eg. The control channel will tell the terminal to tune to traffic channel at X Mhz to receive or send a call, which requires reconfiguring the frontend.

birdiesanders• 1 year ago

Trunked is essentially useless to HAMs, and we never really use it much. We have essentially everything that trunking was meant to solve for a company; large pre-authorized spectrum space, self-coordination in that space without having to get fcc involved. Use of 25khz FM where part 90 is now only 12.5 also is enabled by being a ham.

mschuster91• 1 year ago

Use of 25khz FM where part 90 is now only 12.5 also is enabled by being a ham.

Y'all can use 25 kHz for repeaters? Here in Germany repeaters are 12.5 kHz only, allegedly due to a lack of free frequencies...

wolrah• 1 year ago

Trunked is essentially useless to HAMs, and we never really use it much.

I wouldn't say it's useless, but the utility is reduced because we typically don't have the density of users where two timeslots on a single channel becomes a real limiting factor. A repeater that's set up for local talkgroups on one timeslot and then open access on the second is generally more than enough unless you have a lot of people trying to use it at once, especially in a world where anyone who wants to can have their own personal hotspot for less than the cost of a HT.

Also the usual "ham not HAM" thing.

ac29• 1 year ago

part 90 is now only 12.5

This is wrong. 25kHz part 90 licenses are still available so long as the system meets the minimum efficiency standard (19.2kbps or better for 25kHz).

wkat42422• 1 year ago

I don't think it's useless at all. It would be amazing, roaming the country and never having to worry about frequency settings. And in that case you do need more time slots. Tetra would be nice with 4 slots. I know in Holland and Germany they're experimenting with it.

kotaKat• 1 year ago

Not really.

Leveraging dvmproject, dvmhost, and the FNE bits, hams can operate their own APCO Project 25 trunking systems with commodity MMDVM hardware and link them across the Internet. You can use various MMDVM boards, use a v.24 serial link to a Quantar repeater, etc...

https://github.com/DVMProject/dvmhost

Ain't nothing wrong in running a single voice-on-control channel simplex hotspot to experiment with P25, or link to bigger systems ;)

Calwestjobs2• 1 year ago

many SDRs can RX/TX spectrum many times wider than you think is required in here.

Try to look at this small enthusiast SDR receiver - http://g4wim.proxy.kiwisdr.com:8073/ / http://kiwisdr.com/public/ you can see that simple 350$ radio can have 100s of "channels" visible/receivable at once. (digital modes are available in bottom right "toolbar", in top right corner, drop menu called "extensions" )

so with (different) SDRs you no longer need to choose one channel and listen to it, you can receive 200 channels at once, storing that data and choose what channel you want to decode later

or decode multiple radio stations realtime at once, even each with different mode (AM/FM/Olivia/USB...) and you can even (UNIX) pipe data from it, to programs not designed for ham / sdr use. data is just data as soon as you have it you can do anything with it. you can even write program/script to send email/notification/sound when specified callsign makes call/connects to trunk. for billing purposes...

or BTS/repeater can listen to 50Mhz wide part of spectrum 400Mhz-450Mhz AT ONCE realtime so no "tuning" necessary. for example 2000$ USRP can do that (but you need amps, filters etc to make full BTS )

fsiefken2• 1 year ago

I wonder if Codec2 could be replaced by one of the low bitrate neural audio codecs, HILcodec and SementiCodec sound better at 2-3 kbps.

https://arxiv.org/pdf/2405.04752

https://arxiv.org/pdf/2409.14085

Calwestjobs2• 1 year ago

i rather transfer few bits of text with text-to-speech and speech-to-text on end device, providing much better experience. and technically with 2kbps it is not very different than what these codecs do.

depends on device, on one hand there are handheld radios which have small ARM for UI and control of dedicated radio chip, and then there are mobile phones/laptops/tablets with so much neural processing on board that it can have model sounding like person/celebrity of your choosing.

fsiefken2• 1 year ago

Yes, i have thought of that once, thanks for reminding me. I am so focused on transparent speech compression that I forgot about a more lossy speech encoding method. So with zstd compression you could reach 30 bps of bandwidth, cloning your voice and your communication partners voice with a voice font and perhaps also clone a personal conversation style with Dia https://github.com/nari-labs/dia - you might get close to the 'natural' conversation.

glzone1• 1 year ago

I really wish we could find some "HD" voice codec / mode - all the SIP protocols have gone pretty HD / zoom etc are HD at this point, a lot of cell has gone HD.

Are the bands really so crowded (think on 70cm?) that we can't afford the bandwidth for something a bit more HD?

tarxvf• 1 year ago

https://www.openresearch.institute/opv/

wkat42422• 1 year ago

Not sure about everywhere but here in Europe (Spain, Ireland) the bands are dead quiet. I became a ham in the 90s and every morning we had a call in on the way to work. Tens of people on the repeater. The repeaters are quiet now. The digital ones sound a bit more active but that's because they're relaying the whole country now.

Hf is still pretty busy I think but I don't do that. No space for antennas in the middle of the city.

But anyway there's definitely space on 70cm. The band plan would have to be redesigned though for wider channels. There's even more space on 13cm. Literally nobody uses that. There used to be some amateur TV but that's gone too.

And yes it's annoying that in this day and age digital radio still sounds way worse than ordinary FM at the same bandwidth.

bigfatkitten• 1 year ago

DMR was designed for commercial land mobile radio.

It is designed to occupy similar bandwidth and have similar performance so that existing LMR spectrum planning assumptions continue to apply.

If you want HD audio, or better weak signal performance at the cost of audio quality etc, you need to design something different.

teleforce• 1 year ago

There's an excellent guide to DMR technology by Andrew Barron (ZL3DW) and brief overview by Motorola Solutions, one of the major suppliers of commercial DMR [1],[2].

[1] Work the world with DMR: Digital Mobile Radio (2022):

https://www.hamradio.com/detail.cfm?pid=H0-019172

[2] WHAT IS DMR?

https://www.motorolasolutions.com/en_xp/solutions/what-is-dm...

Open Source DMR Modem Implementation in SDR with GNU Radio and Codec2

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