On 26/11/2022 15:19, Al Amiri,
Wesam (waalamiri42) wrote:
Dears,
I am working on the implementation of OFDM TX and RX using
GNURadio 3.10.3 and USRP N210 (with UHD_4.2.0). In the
implementation, I followed the GRC flow graph provided by
GNU Radio Workshop (Slides 259 - 260) with changing the
carrier frequency to 2 GHz, Sampling rate 1MHz at TX, and
10 MHz for Rx.
The Tx USRP is connected to a Log Periodic antenna and
similarly for the Rx USRP. There is no LOS between the TX
and Rx antennas. They directed toward a reflective board
so that the transmitted signal will be reflected by the
board and received by the receiver. The implementation
works fine, and I was able to receive the OFDM signal by
the RX USRP.
What I am trying to do is to extract some carriers
from the FFT bins at the demodulator to do phase
measurements on each one of the extracted carriers.
I tried to create my own block to do that, but that
didn't work and caused the GRC graph to freeze. Then, I
tried to do that offline using Matlab, where I attached
the FFT block to a file sink.
In Matlab, I plotted the absolute of I/Q samples of the
file sink as shown in the attached figure. But still, I am
not able to distinguish between the subcarriers.
Could anyone please give me advice how to extract certain
carriers from the FFT bins of the demodulator?
Regards,
Wesam Al Amiri
Without completely dissecting your flow-graph, if this were MY
problem, I might make an embedded Python block that allows me
to select a single FFT bin and pass that along to an
analysis function. The FFT output is a vector, so it should
be straightforward
to implement a "pick a single carrier" function in Python,
since your sample-rate is only 1Msps, and your FFT size is (I
think) 64,
that means your function has to deal with a new vector at
15kHz, which is achievable for a Python embedded block.
That's a quick thought based on an only superficial analysis
of the problem, and others here might have better ways of
doing it.
