DMR inband position transmit

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UA0LMC
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DMR inband position transmit

Post by UA0LMC » Fri Oct 29, 2021 6:23 am

For as long as I remember, OpenGD77 firmware was capable of receiving inband position info (and displaying a grid locator), as well as receiving and sending Talker Alias. And since the recent betas we also have (a some sort of) our own position info for satellite mode.

Has it been considered to enable inband position sending as well? As far as I can understand, most of the required code is already there.

VK3KYY
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Re: DMR inband position transmit

Post by VK3KYY » Fri Oct 29, 2021 10:01 am

UA0LMC wrote:
Fri Oct 29, 2021 6:23 am
For as long as I remember, OpenGD77 firmware was capable of receiving inband position info (and displaying a grid locator), as well as receiving and sending Talker Alias. And since the recent betas we also have (a some sort of) our own position info for satellite mode.

Has it been considered to enable inband position sending as well? As far as I can understand, most of the required code is already there.
The firmware does not support any form of data transmission or reception, either on DMR or FM.

Several people were working on DMR data transmission however, the last thing I heard, over 6 months ago, was that they abandoned this development, because they were unable to continue for various technical reasons.

UA0LMC
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Re: DMR inband position transmit

Post by UA0LMC » Fri Oct 29, 2021 10:44 am

Well, it's not a stand-alone data transmission - it's one of the voice-associated inband data services, just like a Talker Alias.
It's defined in ETSI TS 102 361-2 V2.4.1 part 5.4 (with more detailed PDU description in part 7), where TA description literally goes after the description of inband positioning. To put it simple, it works exactly like (and usually together with) TA - but with different payload being transmitted. Moreover, TA TX/RX and position RX are already implemented in openGD77 firmware.

So, the goal is to generate a GPS info LC PDU as per part 7.1.1.3, and to transmit it along with TA.

Unfortunately, my programming skills are clearly insufficient to mess around with such a complicated firmware without breaking anything, so I won't try to implement this myself, at least for now.

VK3KYY
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Re: DMR inband position transmit

Post by VK3KYY » Sat Oct 30, 2021 3:15 am

UA0LMC wrote:
Fri Oct 29, 2021 10:44 am
Well, it's not a stand-alone data transmission - it's one of the voice-associated inband data services, just like a Talker Alias.
It's defined in ETSI TS 102 361-2 V2.4.1 part 5.4 (with more detailed PDU description in part 7), where TA description literally goes after the description of inband positioning. To put it simple, it works exactly like (and usually together with) TA - but with different payload being transmitted. Moreover, TA TX/RX and position RX are already implemented in openGD77 firmware.

So, the goal is to generate a GPS info LC PDU as per part 7.1.1.3, and to transmit it along with TA.

Unfortunately, my programming skills are clearly insufficient to mess around with such a complicated firmware without breaking anything, so I won't try to implement this myself, at least for now.
OK.

I see what you mean

Possibly the position entered by the operator could be sent as part of the Tx TA.

UA0LMC
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Re: DMR inband position transmit

Post by UA0LMC » Sat Oct 30, 2021 3:48 am

VK3KYY wrote:
Sat Oct 30, 2021 3:15 am
I see what you mean

Possibly the position entered by the operator could be sent as part of the Tx TA.
Yes, that's exactly what I mean.
AFAIK, Hytera radios can do this for a long time, and Motorola has also added inband GPS, as well as TA, since M2020.02 firmware.

UA0LMC
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Re: DMR inband position transmit

Post by UA0LMC » Sat Nov 13, 2021 2:04 am

ve7mdt wrote:
Fri Nov 12, 2021 2:29 pm
The Motorola MotoTRBO location packets are still not supported yet by PNW DMR network at this point, even though this has been looked at for quite a while.

Another side note is that the TYT DMR radios (some versions) can have GPSr built in; but seems no such feature has been written in the custom firmware (for the monoband version) so far that I know of (I haven't really followed that development though).
There are many (too many!) vendor-specific standards to send GPS data over DMR with no specifications available to the public.
As for Motorola - it can't send LRRP packets with GPS data without explicit request to do so from the network.

On the contrary, inband GPS discussed here is well-documented in ETSI standard, and it is supported by at least Hytera, and recently by Motorola.
However, this method has a limitation: the location is being sent only along with at least a few seconds of voice (which is fine for most of the use-case scenarios).
ve7mdt wrote:
Fri Nov 12, 2021 2:29 pm
It'd be nice if there is a variant of GD-77 that can have GPSr inside, if this is going to be feasible.
The idea of modding Baofeng DM-1801 to add a GPS receiver was discussed here in another thread.
Long story short, the answer was "You can do what you want - but you have to add firmware support for the mods yourself, with almost no chance for this support to be added to the main repository." Hope this will change someday.

VK3KYY
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Re: DMR inband position transmit

Post by VK3KYY » Sat Nov 13, 2021 2:18 am

There is virtually no space remaining for new functionality in the program ROM memory.

So we can't afford to implement functionality for which there is no hardware in the radio

We could, and may eventually send the lat / long location set manually by the operator, as this would only require a few hundred bytes of extra space in the program ROM.

But there are myriads of other higher priority things on my to do list.

UA0LMC
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Re: DMR inband position transmit

Post by UA0LMC » Wed Dec 01, 2021 7:18 am

ve7mdt wrote:
Tue Nov 30, 2021 6:33 am
I am not advocating anything. I was trying to further explaining things as much as I understand it. Long story short, I don't really care.
Well, something was probably lost in translation as I'm not native English speaker - but I'm not opposing you as you might think.
Moreover, I thought about the way to do a hardware mods for GPS support, and just mentioned the answer I've got.

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