[Discuss-gnuradio] GSM Channel Hopping

[steve]

Hi,

We are trying to understand how to implement GSM channel hopping using
the USRP1.

Reading the docs and specs I think there might be a way of doing it without
any fpga modification. Comments are welcome if there is a mistake in my
thinking.

Inband-Signaling gives us very precise timestamps on received packets:

www.gnuradio.org/trac/browser/gnuradio/trunk/usrp/doc/inband-signaling-usb

We can also use it to have certain commands executed on the fpga at a
certain time:

"Control channel packets shall be processed at the head of the queue,
and shall observe the timestamp semantics described above."

In theory this enables us to send a control channel packet that tunes()
the USRP to a different frequency and have it executed at the precise
time we want the frequency hop to happen.

The latency between USRP and host is between 1-30 gsm bursts. We could
send several control channel packets in advance to the USRP so that
the frequency change happens exactly when we need it to.

How large is the queue on the USRP to store 'delayed control channel packets'?
64?

What control channel packet do I have to send to tune() the USRP to
a different frequency?

regards,

steve