Re: OFDM receiver on USRP2

Sorry for bringing up an old thread. I was having the same problem of
not
receiving packets using benchmark_ofdm_* and changing the receiver
frequency
to tune to the transmitter frequency indeed solved the problem.

However, if I have to manually do it every time, I don’t see how I can
get
ofdm tunnel to work. In tunnel, each USRP is both transmitter and
receiver.
The frequency offset of one USRP (A) transmitting to the other (B) will
be
different than B transmitting to A. Since the frequency offset can’t be
set
at run time, I don’t see how to manually tune after running tunnel on
both
USRPs.

Can anyone show me how to make tunnel work?

Thank you very much,

Tuan

On 2/20/2010 7:43 PM, Srinivas wrote:

Hi Tom,

I tried increasing the bandwidth of the filter and also tried changing
the
window type to KAISER, but it didn’t improve on the offset error. I am
getting a constant frequency offset value “-10”. Currently, I am just
compensating for the offset at the receiver or specifying a minimum BW
to be
used for that pair of USRP2s.

Thanks a lot for your time.

Srinivas

Changing the window type isn’t going to help much with this problem.
What I
was suggesting was that the filter is too small, not the wrong type.
Also,
the only way to change the offset value is to actually move the
frequency. I
was just suggesting that you see what that value is to see how many bins
you
are off by (i.e., calculate the bandwidth of a subcarrier and multiply
that
by 10; that’s you’re coarse offset). You can use that to see how much
bigger
to make the channel filter’s bandwidth.

Tom

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