tetra

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162 discussions

Where to store the stack "state"
by Sylvain Munaut 25 Apr '11

25 Apr '11

Hi, To add support for traffic extraction, it's necessary to introduce some nothing of "state" in the MAC layer (since the DL_USAGE must be 'remembered' to know how to interpret further data) ... Any suggestion how to achieve that as cleanly as possible ? Having a global doesn't sound that nice, but passing a struct around either. Maybe introduce a pointer to a 'tetra_state' in the primitive struct ? Cheers, Sylvain

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neighboring cells information
by Зайцев Андрей 07 Apr '11

07 Apr '11

Hello and sorry for my english. Please help me. I need to decode the message D-NWRK-BROADCAST (chapter 18.4.1.4.1 from ETSI EN 300 392-2 V2.3.2). The fact is that I want to receive information of neighboring cells, but do not know how to do it. Standard called following about this message: “Upon receipt from the SwMI, the message shall inform the MS-MLE about parameters for the serving cell…” How to modify the source code in order to decode this message. Thank you. With best regards Zaytcev Andrey.

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PI/4 DQPSK
by ikjtel 23 Mar '11

23 Mar '11

Thanks for including my "cqpsk.py" decoder module in your distribution. That looks to be a very old version and there have been some further discoveries since that time which I wanted to pass along, FWIW... First, the Costas frequency lock loop in GR seems to work much better for PI/4 DQPSK signals if it's patched in phase_error_tracking() : #if ENABLE_COSTAS_CQPSK_HACK if (d_interp_counter & 1) // every other symbol sample = sample * PT_45; // rotate by +45 deg d_interp_counter++; #endif /* ENABLE_COSTAS_CQPSK_HACK */ The effect of adding this hack to the code can be seen in Fig. 10 at my page http://www.lightlink.com/mhp/lsm/ With the patch included, the time to achieve lock is much improved... Second, I've found that a Gardner symbol timing loop works much better in our application than the M&M loop used in GR gr_mpsk_receiver(). Both of these improvements are included in a new GR block which has been optimized for the particular flavor of "PI/4 CQPSK" (LSM). It's in our svn repo - see http://sedition.org.au/op25/wiki/BuildInstructionsPage Look for the block in the repeater/src/lib tree - see repeater_gardner_costas_cc.cc YMMV ;-) [update: Tues. morning] two more things... 1. There is also a new Polyphase Filter Bank receiver which has been added in the latest versions of GNU Radio. It would be interesting to test and compare the performance of that receiver with the current one... 2. Would it be possible to post complex sample files (preferably not encrypted) to permit evaluation of this signal type? Best Regards 73 de KA1RBI Max

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Which hardware for playing out with tetra?
by Fabio Pietrosanti 07 Mar '11

07 Mar '11

Hi all, i have an USRP1 with DRX and RFX900 daughterboard and wanted to play a bit with the basic tetra decoder. Which kind of daughterboard has been successfully tested with the current osmocom tetra? Fabio

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calibration option
by Sim IJskes 02 Mar '11

02 Mar '11

Is there a reason for the calibration option to be an int? A eng_float looks much more logical to me, as it is used the spec a freq. Gr. Sim

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filter width
by Sim IJskes 02 Mar '11

02 Mar '11

When i interpret para 4 of ETSI TS 100 392-15 it looks like the channels are spaced at 25Khz. The default low_pass used in all of the demods is 25Khz. But when i look in the FFT of the complex signal, the 25Khz specified in the cutoff_freq of firdes.low_pass causes a passband of twice the width. Isn't this way to much? Shouldnt the cutoff_freq be 12.5Khz, giving a passband of 25Khz? (Or is there an intentional spectral overlap between adjacent channels?) If this is the cause, should we just change the parameter to filterwidth or channelspacing and use a /2 in the cutoff parm? Gr. Sim

1 0

identifying tetra
by Sim IJskes 01 Mar '11

01 Mar '11

I've identified 4 carriers in the 400Mhz band, with a clear 4 state constellation. Is there an easy way to verify it is indeed tetra? I'm using grc. Gr. Sim

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Public Safety and Security Network in Germany
by Markus Zielonka 25 Feb '11

25 Feb '11

Hello. A summary of the University of Hannover: http://www.iwi.uni-hannover.de/lv/seminar_ss04/www/Martin_Bretschneider/xht… Bye Markus

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Renumbering tetra channels in gsmtap.h
by Holger Hans Peter Freyther 28 Jan '11

28 Jan '11

Hi laf0rge, wireshark has more strict compile settings and found this: #define GSMTAP_TETRA_AACH 0x02 #define GSMTAP_TETRA_AACH 0x03 I would remove the second occurrence and renumber the other members? Or should I remove the first one and go with the value of 0x03? z.

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Re: TETRA and GRC?
by Sylvain Munaut 28 Jan '11

28 Jan '11

> [snip] ... but wondered if > anyone had worked on the GR porting of the code. I assume, that is not the > case. No that I know of. What would be the interest exactly ? I mean GR is great for signal processing but once you got the bits, the rest is IMHO way better handled outside gnuradio itself. All the phy/mac levels are no trivial and will need state processing and such ... not something I really see in GR. Using fifo on the filesystem you can pipe directly/live the flow of info from GR outpout to the tetra-rx input. Cheers, Sylvain BTW, you forgot to CC the list in your reply. (I assume it was your intent because of the "with everyone here" comment at the end of your mail).

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