P25 repeaters

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Re: P25 repeaters

Postby MattSR » Fri Oct 31, 2008 9:02 pm

Long time no speak.

Funny you should mention OP25 - I've been playing with it for about a week now - the wireshark extensions look quite useful. Next step is to build a dedicated linux machine and move it out of VMware.

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Re: P25 repeaters

Postby escomm » Fri Oct 31, 2008 9:52 pm

:soap:
I'd hit it so hard you'd have to be to King of England to pull me out

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Re: P25 repeaters

Postby mr.syntrx » Fri Oct 31, 2008 10:22 pm

MattSR wrote:Long time no speak.

Funny you should mention OP25 - I've been playing with it for about a week now - the wireshark extensions look quite useful. Next step is to build a dedicated linux machine and move it out of VMware.


I was planning to buy a USRP a few weeks ago for other projects, right before the AUD took a fucking great nosedive :ve4uo: I plan to add this to the list of things to play with when I do eventually pick one up.

I've got a Pentium 4 3GHz box sitting out the back doing very little other than hosting a DVBS MPE PCI card, so that's where the rig will go.
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Re: P25 repeaters

Postby MattSR » Sat Nov 01, 2008 7:28 pm

USRP isn't needed - GNUradio can run off a discriminator tap (apprently) I'm having a hell of a time trying to get it to compile and run properly.. its a fairly big, complex, fragile thing by the looks of it...

escomm - why the soapbox? we're only throwing ieads around to try and get the creative juices going - its not like we're pretending to be experts or anything here... just keen enthusiasts...

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Re: P25 repeaters

Postby escomm » Sat Nov 01, 2008 7:31 pm

im mad cus you dropped off the face off the earth
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Re: P25 repeaters

Postby MattSR » Sat Nov 01, 2008 9:19 pm

motorola_otaku wrote:
MattSR wrote:These chips from CML micros could be the basis for a simple P25 machine. Couple with with an atmel ATMega16 to run the show and bobs your uncle

goto http://www.cmlmicro.com/products/index. ... index=true and click on the C4FM Modem function.

ATmega16 can do SPI which is the bus used to control the CML chip. then all you need is the RF gear and yer done.

Cheers,
Matt

Back on this a little bit.. I'm reading the C4FM modem specs and it lists 4.8 and 9.6 kbps as available sampling rates. Since P25 uses 19.2, wouldn't that render it useless even if we could get one?

Also, it references C-BUS as the communication protocol to the microcontroller, not SPI.

Did I mention that I don't know the first thing about most of this? :baby:


Just went back and re-read the thread from the start. I can see where you got confused - wowbagger mentioned a 19.2k sample rate on the raw unprocessed baseband audio. This gives a 4x oversample rate on the 4800 baud bitstream which is required for DSP work in order to be able to do clock recovery and error correction. The actual raw bit rate is 9600 bits per second.

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Re: P25 repeaters

Postby motorola_otaku » Sat Nov 01, 2008 11:03 pm

MattSR wrote:I can see where you got confused - wowbagger mentioned a 19.2k sample rate on the raw unprocessed baseband audio. This gives a 4x oversample rate on the 4800 baud bitstream which is required for DSP work in order to be able to do clock recovery and error correction. The actual raw bit rate is 9600 bits per second.

Hahaha, pwn3d by baud/bit. I'll just go sit in the corner with the dunce cap now. :baby:

I am in way over my head on much of this, but here's what I see: the goal here is to to create an inexpensive :ham: -grade P25 repeater controller that would go in between passive receivers and transmitters and clean up/reclock the received P25 signal before passing it on to the transmitter, and maybe perform functions like NAC "squelch." The CML chip deals with the P25 signal itself and the ATMega16 chip runs code that controls the reclocking and NAC decoding functions, correct?
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Re: P25 repeaters

Postby MattSR » Sat Nov 01, 2008 11:29 pm

Correct - clock recovery etc is done by the CML chip where as the P25 stuff (NAC, error correction) would be done by the Atmel.

The pdfs from CML explain it better than I can (just delete the codec and mic/speaker bits of the block diagram - thats only used for voice which wouldn't be required for a repeater)

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Re: P25 repeaters

Postby mr.syntrx » Sun Nov 02, 2008 12:05 am

MattSR wrote:USRP isn't needed - GNUradio can run off a discriminator tap (apprently) I'm having a hell of a time trying to get it to compile and run properly.. its a fairly big, complex, fragile thing by the looks of it...


Yep, but a discriminator tap won't cut it for the projects I have in mind, which involve 200KHz wide GMSK carriers. P25 would be an additional for-curiosity project.
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Re: P25 repeaters

Postby MattSR » Sun Nov 02, 2008 12:09 am

Stop playing with the GSM mobile phone networks matt! Dont u know thats illegal :wacker:

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Re: P25 repeaters

Postby mr.syntrx » Sun Nov 02, 2008 5:39 am

Intercepting calls is illegal, cell mapping isn't.
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Re: P25 repeaters

Postby MattSR » Sun Nov 02, 2008 6:20 am

Thats cool, but why?

and why arent you on MSN anymore?

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Re: P25 repeaters

Postby mr.syntrx » Sun Nov 02, 2008 6:56 am

Been busy lately. Work, travel for work (four countries so far), real life etc, so almost all of my projects have taken a back seat as a result.
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Re: P25 repeaters

Postby Wowbagger » Sun Nov 02, 2008 8:39 am

mr.syntrx wrote:Even the engineers working down the hall from me have a fuckload of trouble getting CML samples.

Buy a USRP with the appropriate transmitter and reciever modules, and... http://www.sedition.org.au/op25/

:baby:


Iiiiiiiiinterestink. However, I think they are going to have real problems with the IMBE decoder. I'm not saying they cannot reverse engineer the codec, but there is no way to implement IMBE without infringing upon DVSI's patents, and I'm pretty sure that if you start distributing an implementation of IMBE without DVSI's permissions their will sic their HordeO'Lawyers(TM) on you.

The Wireshark plug-in is interesting as well. I'd said years ago that I'd love to have something like the Ethereal interface for packet logging, which is why I designed the XML logger in the 3900 the way I did. I wonder if I ought to point out the DTD and RelaxNG schema for our XML logger to them - we (Aeroflex) would like to see others using that for logging.
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Re: P25 repeaters

Postby escomm » Sun Nov 02, 2008 12:18 pm

MattSR wrote:and why arent you on MSN anymore?

:anus:
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Re: P25 repeaters

Postby MattSR » Sun Nov 02, 2008 5:28 pm

better than that AIM thinger :(

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Re: P25 repeaters

Postby MattSR » Sun Nov 02, 2008 5:30 pm

Wowbagger wrote:but there is no way to implement IMBE without infringing upon DVSI's patents..


A hardware dongle with an appropriately licensed and purchased codec chip would be OK.

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Re: P25 repeaters

Postby mr.syntrx » Tue Nov 04, 2008 2:16 am

Is IMBE available in one-off units, or is it a quantity only item?
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Re: P25 repeaters

Postby MattSR » Tue Nov 18, 2008 1:12 am

Wowbagger wrote:I wonder if I ought to point out the DTD and RelaxNG schema for our XML logger to them - we (Aeroflex) would like to see others using that for logging.

I will pass this onto the project leader..

One of the things to investigate is a C4FM modulator/RRC filter/Shaping filter/NFM modulator series of blocks in GNUradio. a SDR Repeater would be very cool and could do things like switch between DSTAR/NFM and P25 in real time.

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Re: P25 repeaters

Postby MattSR » Tue Nov 18, 2008 1:13 am

Ahh fuck. can someone fix my quote tag plz?

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Re: P25 repeaters

Postby airwaves882 » Mon Mar 09, 2009 12:23 am

Driven by the Thirst for Knowledge.

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Re: P25 repeaters

Postby MattSR » Thu Jul 02, 2009 7:34 pm

GNUradio 3.2 stable was released a few weeks ago, and OP25 is coming along nicely under the new platform. There have been a number of very interesting additions to the code, and it is expected that over the next month or so some more features will be added.

I requested some additions to the GUI that have been added also, an info panel is now available that displays a monitored P25 signals parameters like KID, ALGID, MI, RID, NAC, NID etc etc all in real time. Its become quite an interesting little project!

Cheers,
Matt

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Re: P25 repeaters

Postby motorola_otaku » Fri Jul 03, 2009 11:31 am

All cool, but I'm still waiting on an economical P25 repeater controller. Raytheon has one, but it's priced comparable to what used Quantars go for.
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Re: P25 repeaters

Postby MattSR » Sun Jul 05, 2009 11:02 pm

OP25 will get there. Once the receive code is complete, then work will start on tx code.

Cheers,
Matt

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Re: P25 repeaters

Postby Wowbagger » Sat Jul 11, 2009 7:14 am

MattSR wrote:OP25 will get there. Once the receive code is complete, then work will start on tx code.

Cheers,
Matt

How are you handling the vocoding? Are you using the DVSI USB dongle, or just spacing that bit off for now?

Also, are you deriving any of the parametrics on the signal, such as Mod Fidelity error or EVM for the PSK signals?
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Re: P25 repeaters

Postby Strike Team » Sat Jul 11, 2009 2:52 pm

Getting back to M3ECM's original issue - the desire to avoid talking to the multipolicity of fucktards on 2M, rather than splashing out on P25, wouldn't it be cheaper and simpler to get some 70 MHz rigs?

A Philips FM1000 or Key KM-80, along with a CB dipole cut down for 70 MHz, would be a very cost-effective way to enjoy asshole-free radio communication.
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Re: P25 repeaters

Postby MattSR » Wed Jul 22, 2009 7:51 am

Wowbagger wrote:
MattSR wrote:OP25 will get there. Once the receive code is complete, then work will start on tx code.

Cheers,
Matt

How are you handling the vocoding? Are you using the DVSI USB dongle, or just spacing that bit off for now?

Also, are you deriving any of the parametrics on the signal, such as Mod Fidelity error or EVM for the PSK signals?


Its a work in progress. There is support to plug a DVSI VC55 in, and also there's something else in the pipeline too.

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Re: P25 repeaters

Postby MattSR » Thu Aug 20, 2009 9:27 am

Work continues. There is now discriminator tap support, amongst other improvements.

The latest update enabled me to capture the following screenshots - one is an ADP tranmission, another DES-OFB. The Symbol scope shows the output from the C4FM demodulator.


Image
Image
Image

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Re: P25 repeaters

Postby MattSR » Thu Aug 20, 2009 9:29 am

Work continues. There is now discriminator tap support, amongst other improvements.

A DV Dongle AMBE decoder has been ordered and we will try feeding IMBE frames into it. Hopefully it works!

The latest update enabled me to capture the following screenshots - one is an ADP tranmission, another DES-OFB. The Symbol scope shows the output from the C4FM demodulator.

Image
Image
Image

Regards,
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Re: P25 repeaters

Postby Wowbagger » Thu Aug 20, 2009 9:39 am

Very impressive. Are you a contributor to the code, or "just a user" (not that being "just a user" is a bad thing, as good user feedback is VERY important)?

I am interested in this project, but due to my position I get nervous when thinking about looking at or contributing, due to possible conflicts of interest.
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Re: P25 repeaters

Postby MattSR » Thu Aug 20, 2009 11:47 am

Like any software project, (especially one like OP25) this project has people with all sorts of eclectic skills.

Join the mailing list and you'll see exactly how/what I contribute. Surely your employer won't discipline you for reading up on our efforts.

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Re: P25 repeaters

Postby Wowbagger » Thu Aug 20, 2009 1:55 pm

MattSR wrote:Like any software project, (especially one like OP25) this project has people with all sorts of eclectic skills.

Join the mailing list and you'll see exactly how/what I contribute. Surely your employer won't discipline you for reading up on our efforts.


It's not a question of that - it's the questions of:
1) Potential "contamination" of our closed-source code with GPL code. Yes, I am disciplined enough to not do so on purpose, but, having seen a GPL implementation, it is possible I might accidentally come close with our implementation.
2) Potential "contamination" the other way: there's almost no safe way they could ever accept anything put high-level specifications from me, as I've "seen too much" that is under NDA.
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Re: P25 repeaters

Postby MattSR » Thu Aug 20, 2009 8:47 pm

I wouldn't be worried about number 1 - Aeroflex's framework would be vastly different and more mature than OP25/GNUradio since the latter are only part time "enthusiast" type projects. Your analyzers appear to be designed and built/coded to a spec - OP25 is more 'beta' software at this stage, and as you said its a matter of professionalism for yourself also.

Point number 2 is the one that intrigues me - OP25 has been implemented from the TIA/ETSI specs and publicly available information such as the Daniels P25 training manual - nothing more.. Apart from the DVSI stuff, is there anything else that's encumbered by NDA/patents?

As much as we need good contributors, at the end of the day, its a not-for-profit, research project - if its going to threaten your income or career then its simply not worth it. Morally and ethically, you could contribute things are that are public knowledge, but it could be a potential minefield for you if anyone wanted to play hardball.

Cheers,
Matt

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Re: P25 repeaters

Postby Wowbagger » Thu Aug 20, 2009 8:55 pm

MattSR wrote:Point number 2 is the one that intrigues me - OP25 has been implemented from the TIA/ETSI specs and publicly available information such as the Daniels P25 training manual - nothing more.. Apart from the DVSI stuff, is there anything else that's encumbered by NDA/patents?


Oh, things like how Motorola does their ADP encryption, modulation parameters on some of the derivative protocols like Wide-Pulse and LSM - and other things that I really cannot talk about.

Perhaps it is just an over-abundance of caution on my part, but I'd rather not have even "the appearance of impropriety".
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Re: P25 repeaters

Postby MattSR » Thu Aug 20, 2009 10:30 pm

OK cool, that puts my mind at rest. I expected as much re the wide pulse/LSM/other proprietary stuff

Yes - ADP algorithm isn't part of the P25 spec, so I would automatically consider that to be proprietary. Here's where it gets tricky though. the Keyfill interface/protocol *is* part of the publicly available spec, and several manufacturers have developed keyloaders to fill P25 radios. Would it then be considered a breach of Motorola's IP to design a KFD that can load a 40-bit key using the TIA102-AACD specs? Since the spec itself is public, I wouldn't think so - all you're doing is loading an arbitrary 40-bit key into a subscriber unit, all the proprietary stuff is done inside the radio.. Just as long as you didn't use the word "ADP" it should be fine..


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