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Re: [Discuss-gnuradio] DBSRX tune delay

From: Matt Ettus
Subject: Re: [Discuss-gnuradio] DBSRX tune delay
Date: Tue, 08 Dec 2009 18:27:27 -0800
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20090922 Fedora/3.0-3.9.b4.fc12 Thunderbird/3.0b4

You will need to measure the tune time of the DBSRX synthesizer for your application to see if it can hop fast enough.

For GSM channel hopping within about 50 MHz, you can do it without retuning the DBSRX, just by changing the DDC frequency. You will need to create your own code to do the tuning, however, since the standard code always moves the DBSRX even if it doesn't need to.


On 12/08/2009 12:24 PM, Sylvain Munaut wrote:
Vadim Uvin wrote:
Thanks for the suggestion, Sylvian. But it is not the case, since the
GSM does not use inband signalling.

? I'm taking about inband signalling for the USRP where the USRP marks
each sample received with a timestamp.

Buying the second DBSRX is not very
convenient since I in the future I want to try to implement channel
hopping. That is why I'm wondering is it feasible at all to change USRP
frequency fast enough to keep up with the GSM. By the way, the delay
should be comparable to about 1 ms.

Also, the downlink and uplink channel separation is at least 45 MHz, so
I cannot cover it with USRP's 8 MHz.

2009/12/8 Sylvain Munaut<address@hidden<mailto:address@hidden>>

     Vadim Uvin wrote:
     >  I have USRP+DBSRX. I'm trying to listen to uplink channel (MS->BTS) of
     >  GSM. To do that, I first need to be synced with the BS (i.e. listen to
     >  synchronization channel of BTS). Then I have to change the center
     >  frequency to uplink channel, but I need to know how long it takes
     >  USRP gets stable or I can lost the synchronization. Unfortunately, I
     >  can't find what the tune delay of DBSRX is. Maybe someone knows?

     You should use inband signalling, this way you have a 'sample' counter
     and you know precisely 'where' you are in time.

     Or you use two dbsrx, following both up&  downlink ....


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