Questions on OFDM transmission on USRP2

GNU Radio
1

Hi

I have some questions and observation on OFDM based transceiver.

I adopted the modified code provided by Veljko P. (link:
www.cs.ucsb.edu/~veljko/downloads/ofdm_example.tar.gz). After trying
different combinations of parameters, I managed to get benchmark to work
with most package received correctly. However, it turned out the CPU
usage
was very high, almost 90% for receiver. Here is the specs: USRP2, WBX,
Ubuntu 10.04, GNU radio 3.3, Intel core 2 duo 2.66GHz, ram 2G. Can
anyone
share the insight why the OFDM receiver is so computationally intensive?
(-f
434M fft-length=128, occupied-tones=80, -d/-i 32, cp-length=32.)

In addition, I also tried to build a new tunnel.py based on the revised
OFDM
codes. I got continuous Timeout (received preamble but not the entire
data
frame) and SSS… (missing packets), evenif only one USRP was turned on.
However, supposedly it should not receive any signals. Does anyone
successfully build an OFDM based tunnel?

An

2

Hi,

Yes, it is quite intensive. You can try increasing the
decimation/interpolation, if you see that the CPU is not keeping up
with the load. However, you have to be careful about the frequency
offset between the transmitter and the receiver as you might get too
large of the misalignment when you use narrow channels. 434MHz for one
device is not necessarily 434MHz for the other device. I use a
spectrum analyzer to figure that difference out.

Cheers,

Veljko

2010/6/16 rick rick [email protected]: