P25 TDMA Conventional

[otobmark]

I understand why Motorola doesn’t do it—force people towards much more expensive trunk system but I don’t know why NO other company doesn’t develop and sell conventional P25 TDMA. Going the other way some companies are making tier 1 subscriber radios in DMR (EFJ).
In Goldielocks and 3 Bears one bed was too soft, 2nd too hard, and 3rd was “just right”. Modern day marketing eliminates the 3rd choice (just right) to force customers to buy more than they need (movie theater drinks..).

 

[gatekeep]

I understand why Motorola doesn’t do it—force people towards much more expensive trunk system but I don’t know why NO other company doesn’t develop and sell conventional P25 TDMA. Going the other way some companies are making tier 1 subscriber radios in DMR (EFJ).
In Goldielocks and 3 Bears one bed was too soft, 2nd too hard, and 3rd was “just right”. Modern day marketing eliminates the 3rd choice (just right) to force customers to buy more than they need (movie theater drinks..).

Because literally per TIA-102 spec, P25 TDMA is *not* designed to work conventionally without a central trunk controller providing slot timing information.

 

[otobmark]

Because literally per TIA-102 spec, P25 TDMA is *not* designed to work conventionally without a central trunk controller providing slot timing information.

So… arbitrary. My point exactly. Design it to work instead of not work. It’s a marketing decision not a technology one. Once 6.25 narrowband becomes law only trunked version P25 Phase 2 will be legal. So no legal way to do P25 simplex Thus no path forward for P25. NXDN may get the last laugh yet..

 

[clbsquared]

Using two time slots for one frequency on conventional DMR is essentially TDMA.

 

[gatekeep]

So… arbitrary. My point exactly. Design it to work instead of not work. It’s a marketing decision not a technology one. Once 6.25 narrowband becomes law only trunked version P25 Phase 2 will be legal. So no legal way to do P25 simplex Thus no path forward for P25. NXDN may get the last laugh yet..

Eah...you do understand that DMR Tier 2/3 or P25 Phase II TDMA doesn't *actually* utilize real 6.25khz. The way both DMR and P25 implement TDMA, the signal still occupies a 12.5khz channel, but just for a small slice of time several milliseconds in length. They are simply allowing multiple users to use the same physical channel simultaneously separated in time, with timing of when a subscriber radio (i.e. your portable) can transmit based on the slot timing data coming back from the base station equipment.

NXDN doesn't do *TDMA* at all, and is a FDMA protocol...the only benefit it has is that it can operate in 4800 baud mode allowing ultra-narrow 6.25khz bandwidth usage when transmitting.

 

[otobmark]

Eah...you do understand that DMR Tier 2/3 or P25 Phase II TDMA doesn't *actually* utilize real 6.25khz. The way both DMR and P25 implement TDMA, the signal still occupies a 12.5khz channel, but just for a small slice of time several milliseconds in length. They are simply allowing multiple users to use the same physical channel simultaneously separated in time, with timing of when a subscriber radio (i.e. your portable) can transmit based on the slot timing data coming back from the base station equipment.

NXDN doesn't do *TDMA* at all, and is a FDMA protocol...the only benefit it has is that it can operate in 4800 baud mode allowing ultra-narrow 6.25khz bandwidth usage when transmitting.

Know all that and so much more. I understand equivalency for legal purposes. NXDN meets standard without equivalency (TDMA etc). If DMR can do TDMA direct or repeated then P25 doing the same is not a challenge technologically. It’s a decision. I’m questioning the decision.

 

[devicelab]

Because literally per TIA-102 spec, P25 TDMA is *not* designed to work conventionally without a central trunk controller providing slot timing information.

And yet Motorola has a firmware out in the wild that allows Phase 2 TDMA on a conventional repeater.

 

[mmckenna]

The APCO committee that develops the P25 standard still meets, and is still developing the protocol. I don't see anything in their list that suggest this, but I have not dug to far into the standards (mainly because I don't want to buy the TIA standards documents).

I think the challenge isn't that manufacturers don't want to build it (as @devicelab mentioned above) it's that there isn't a standard for it. (yet?)

One of the nice things about the P25 standard is that in almost all cases, you can take a P25 radio from any manufacturer and it'll work with another brand.

Until APCO/TIA have the standard established, it would be a really bad idea to have individual brands rolling out their own version of conventional TDMA P25.

 

[KevinC]

Until APCO/TIA have the standard established, it would be a really bad idea to have individual brands rolling out their own version of conventional TDMA P25.

Otherwise you end up with something like Motorola's X2-TDMA.

 

[mmckenna]

Otherwise you end up with something like Motorola's X2-TDMA.

One of the nice things about P25, as you know, is that it is a well accepted standard, and that's kept things pretty nice.

I think the P25 folks at CISA would probably have an issue with a vendor releasing their own version that didn't meet any standard that could be shared by other manufacturers.

But, I can see the desire. I'm using some simplex DMR in two slot mode, and it saved some money on frequency coordination.

 

[redbeard]

And yet Motorola has a firmware out in the wild that allows Phase 2 TDMA on a conventional repeater.

That would be interesting if true.

 

[NavyBOFH]

And yet Motorola has a firmware out in the wild that allows Phase 2 TDMA on a conventional repeater.

Where? Feel free to DM me if you don’t want to comment it. While you’re at it, you can explain how infrastructure firmware would exist in the wild with zero trace of subscriber firmware that would support such a “feature”.

Know all that and so much more. I understand equivalency for legal purposes. NXDN meets standard without equivalency (TDMA etc). If DMR can do TDMA direct or repeated then P25 doing the same is not a challenge technologically. It’s a decision. I’m questioning the decision.

Sorry, but there’s a lot more to TDMA between DMR and P25 to be able to draw a direct parallel and then question why vendors “choose not to make it happen”. Passing over the P25 Working Group, there’s more than just “politics” involved.

 

[redbeard]

Passing over the working group...like they did for X2-TDMA you mean? If the '2 mobiles in a box' XPR repeater can do TDMA on DMR, I'm sure a GTR could if they wanted it to. Same with DCDM and mobiles. It's not like Moto is any stranger to taking liberties with the standards...

Where? Feel free to DM me if you don’t want to comment it. While you’re at it, you can explain how infrastructure firmware would exist in the wild with zero trace of subscriber firmware that would support such a “feature”.


Sorry, but there’s a lot more to TDMA between DMR and P25 to be able to draw a direct parallel and then question why vendors “choose not to make it happen”. Passing over the P25 Working Group, there’s more than just “politics” involved.

 

[devicelab]

Where? Feel free to DM me if you don’t want to comment it.

I don't know anything about it. I don't have access to it personally. Something Motorola is testing I presume. AFAIK, it's a repeater firmware update. From what I was told, the SUs don't need it.

 

[NavyBOFH]

Passing over the working group...like they did for X2-TDMA you mean? If the '2 mobiles in a box' XPR repeater can do TDMA on DMR, I'm sure a GTR could if they wanted it to. Same with DCDM and mobiles. It's not like Moto is any stranger to taking liberties with the standards...

X2 TDMA never became P25 Phase 2 because in the P25 Working Group CQPSK modulation was chosen over C4FM which dictated a different transceiver design that would preclude “two mobiles in a box” and makes a timing reference for a disciplined oscillator a necessity. X2 TDMA didn’t require either until you went to simulcast which inherited different challenges.

DMR uses 4FSK or C4FM which is more akin to how X2 TDMA was designed. So in the end - there won’t be a conventional TDMA without the P25 spec being expanded to call for different modulation while operating conventional - especially since I do not see single-channel CQPSK happening without a bunch of expensive hardware which would turn the discussion to “now you have everything for a trunking site anyway”.

I don't know anything about it. I don't have access to it personally. Something Motorola is testing I presume. AFAIK, it's a repeater firmware update. From what I was told, the SUs don't need it.

SU’s would 100% need firmware to support it. Where in any vendor’s current firmware can you even configure slot reference for conventional?

 

[KevinC]

I'm sure MSI has been testing a form of conventional P25 TDMA for quite a while.

 

[KevinC]

X2 TDMA never became P25 Phase 2 because in the P25 Working Group CQPSK modulation was chosen over C4FM which dictated a different transceiver design that would preclude “two mobiles in a box” and makes a timing reference for a disciplined oscillator a necessity. X2 TDMA didn’t require either until you went to simulcast which inherited different challenges.

DMR uses 4FSK or C4FM which is more akin to how X2 TDMA was designed. So in the end - there won’t be a conventional TDMA without the P25 spec being expanded to call for different modulation while operating conventional - especially since I do not see single-channel CQPSK happening without a bunch of expensive hardware which would turn the discussion to “now you have everything for a trunking site anyway”.

SU’s would 100% need firmware to support it. Where in any vendor’s current firmware can you even configure slot reference for conventional?

I've implemented plenty of conventional P25 using CQPSK. Or did I misinterpret what you posted?

 

[gatekeep]

I've implemented plenty of conventional P25 using CQPSK. Or did I misinterpret what you posted?

The problem is -- Phase 2 doesn't *use* CQPSK. Phase 2 uses H-CPM on the uplink/input and PI/4-DQPSK on the downlink/output. These modulation formats are different enough from CQPSK to matter.

 

[KevinC]

The problem is -- Phase 2 doesn't *use* CQPSK. Phase 2 uses H-CPM on the uplink/input and PI/4-DQPSK on the downlink/output. These modulation formats are different enough from CQPSK to matter.

Correct. I was referring to this...

DMR uses 4FSK or C4FM which is more akin to how X2 TDMA was designed. So in the end - there won’t be a conventional TDMA without the P25 spec being expanded to call for different modulation while operating conventional - especially since I do not see single-channel CQPSK happening without a bunch of expensive hardware which would turn the discussion to “now you have everything for a trunking site anyway”.

 

[NavyBOFH]

Yup that was more of a typo/brain fart but gatekeep corrected the modulation. CQPSK is conventional but simulcast so still not fitting for a standalone TDMA conventional repeater to say apples-to-apples with DMR.