DBSRX tune delay

GNU Radio
1

Hi everyone,

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 before USRP gets
stable or I can lost the synchronization. Unfortunately, I can’t find
what
the tune delay of DBSRX is. Maybe someone knows?

Thanks.

2

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 before
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 …

Sylvain

3

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.

Matt

4

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.