Re: [Discuss-gnuradio] Precise freq hopping w/ inband signaling

[Brian Padalino]

On Tue, May 13, 2008 at 6:44 PM, George Nychis <address@hidden> wrote:
> Hi all,
>
> I'm trying to understand if this is possible in the FPGA. Let's assume we
> initially tune a card to 2.4G and then every 650us we want to retune it to
> the prev frequency plus 100MHz, up until 2.5G and then wrap back to 2.4G.
> That is very easy to accomplish using inband command packets with timestamps
> spaced by 650us IF the FPGA can somehow retune the center freq. It would
> probably be best to recompute the dxc freq and such from the host, who has
> access to the tuning code, and then transfers the results. Is the FPGA able
> to directly access what is needed for the retune?

Surprisingly enough, this came up recently on the IRC channel for a
DBS RX daughterboard.  I think they wanted to tune the MAX2118 chip to
do GSM frequency hopping.

Anyways, the issue is that the SPI bus goes over to the FPGA, but not
the I2C bus which connects up to the daughterboard.  From what I could
tell, the I2C bus is only connected up to the FX2 so unless the
frequency hopping commands were implemented within the FX2 with
specific timers, it will definitely involve some sort of USRP hardware
modification.

The last thing you'll have to figure out is exactly how long it takes
for your system to lock.  Hopping every 650us sounds like it's pretty
darn quick.  If locking doesn't happen for 200us, you only really get
450us of usable data before you switch again.  Is there a field in the
in-band stuff that says "this transmission was received on frequency
X"?  That might be useful.

Anyway, sorry for rambling.  I hope this somewhat answered your question.

Brian