APCO P25, IMBE, CAI, questions on terms and compatibility

[CTfed]

A theory question for the APCO experts>..


IMBE, what exactly is it and how does it relate to APCO-P25 codec?

What is CAI when used in a digital string of a moto "ASTRO CAI IMBE" Q806 Option

Just tryng to educate myself on terms and compatibility. Are all of these compatible APCO P25 formats? I see some Spectras that are ASTRO but not IMBE, does this mean it is not compatible or will communicate with another Moto APCO -25 IMBE radio?

If not, then what is required? New firmware?

I apologize for the novice nature of this thread, but trying to educate myself on the basics before I become more involved with the equipment.

Thanks

[wa8pyr]

Originally Posted by CTfed

A theory question for the APCO experts>..


IMBE, what exactly is it and how does it relate to APCO-P25 codec?

Simple answer: Improved Multi-Band Excitation is the P25 on-air modulation scheme.

What is CAI when used in a digital string of a moto "ASTRO CAI IMBE" Q806 Option

CAI = Common Air Interface. Simply refers to the P25 standard digital audio, which can be used trunked or conventional.

Are all of these compatible APCO P25 formats? I see some Spectras that are ASTRO but not IMBE, does this mean it is not compatible or will communicate with another Moto APCO -25 IMBE radio?

If not, then what is required? New firmware?

The non-IMBE Astro Spectra uses VSELP (Vector Sum Excited Linear Prediction) modulation; it's Motorola's original digital modulation which was replaced by P25. There are very, very few VSELP users left out there; the City of Cleveland, Ohio is one of the last large users (there never were many) and even they are considering the jump to P25.

A non-IMBE radio, for the most part, cannot be made to do IMBE. I *think* some models with sufficient firmware memory capacity *might* be able to accept a firmware upgrade to do IMBE, but I'm not sure and wouldn't count on it. If you want to do IMBE, the best bet is to get a radio that is known to do IMBE, or at least is capable of being upgraded.

[N_Jay]

Originally Posted by wa8pyr

Simple answer: Improved Multi-Band Excitation is the P25 on-air modulation scheme.

Simply wrong.
IMBE is the VOCODER, it is the method the voice is turned into a bit stream, or more correctly digital frame stream.
This is coded onto a channel with additional information, and then modulated onto a RF channel with C4FM/CQPSK to get to the "on-air" scheme.

Originally Posted by wa8pyr

CAI = Common Air Interface. Simply refers to the P25 standard digital audio, which can be used trunked or conventional.

The CAI = Common Air Interface includes all three parts described above, Vocoding, Channel coding, and Modulation.

Originally Posted by wa8pyr

The non-IMBE Astro Spectra uses VSELP (Vector Sum Excited Linear Prediction) modulation; it's Motorola's original digital modulation which was replaced by P25.

VSEP was Motorola's original VOCODER, and not compatible with IMBE (P25).

As for the rest, ask a Motorola hardware expert, as it is a "product/model/variation specific" question, not a "P25" question.

[16b]

EDIT: I just saw N_Jay's post, and some of this is redundant in light of his information, but I'll leave it.

IMBE is the Vocoder / Codec specified in the Project 25 standard (phase one, anyhow).

Common Air Interface is basically the over-the-air protocol. Project 25 specifies many other interfaces (listed in the linked article above) that have to do with things like networks and telephone interfaces. But, since we're mostly concerned with radios here, CAI is about the only interface you'll hear about (a lot of people don't know about the other ones, anyway).

An Astro Spectra (or Astro Saber or XTS3000) is capable of either VSELP or Project 25 operation, as Tom said. All of these radios can be upgraded by Motorola to be capable of Project 25. Pretty much everything you need to know to be dangerous with Motorola Astro radios can be found in this document: http://www.hamradio-dv.org/p25/Guide...italRadios.pdf

[immelmen]

here is a simple bit of info I didn't read in the above posts I thought might help someone completely new to it. "Astro" is just a brand name of Motorola. Motorola "Astro" Spectra is like a Chevy "SS" Camaro....kinda...in a very basic way. looks the same on the outside, but under the hood a whole different beast.

Also, "astro" radios can come from moto capable of nothing but good old FM. all astros can talk to each other on FM, but you could have 3 different astros and none of them be able to talk digital. (As mentioned most of this stuff can be "upgraded" so that it can do IMBE.)

the most basic ground zero beginners explanation(as it applies to a hobbiest anyway):

APCO Project 25 = interoperability of communications program

CAI = just that, the Common Air Interface of Project 25

IMBE = the chosen method of modulation for the CAI of P25

[W8RW]

Originally Posted by immelmen

here is a simple bit of info I didn't read in the above posts I thought might help someone completely new to it. "Astro" is just a brand name of Motorola.

Actually, Astro is a dog:

[N_Jay]

Originally Posted by immelmen

here is a simple bit of info I didn't read in the above posts I thought might help someone completely new to it. "Astro" is just a brand name of Motorola.

Good point.
I have brought that up in similar threads but did not think to here.

Originally Posted by immelmen

IMBE = the chosen method of modulation for the CAI of P25

Close. It is the VOCODER, not the MODULATION.

[N_Jay]

Originally Posted by W8RW

Actually, Astro is a dog:

Yes, we did all get "Astro" (the dog) pins back in the early days.

[CTfed]

Thanks everyone. Great information all the way around, and great job breaking it down. I hope it aids some Project 25 newcomers in the future.

Again, Thanks!

"Rorge"

That's what Astro sounds like ;-)