I’ve been working with the OFDM examples that come with GNURADIO
(benchmark_tx.py and benchmark_rx.py). I’ve noticed that my bit error
(BER) increases as the length of my cyclic prefix (CP) increases. This
opposite of what theory predicts, since larger CP decreases inter-symbol
I googled the issue and found this paper document the same issue (page
The paper explains this by saying longer CP adds additional overhead by
making the frames longer, thus leading to worse performance. I’m having
hard time understanding how this explains a performance increase. I see
little change in system performance between CP=1 and 128 when monitoring
system resources, and the number of packets received and number of
packets doesn’t change much from run to run. Just the number of errors
packets that do fail.
I played around with a lot of different input parameters (FFT size,
gain, occupied tones, bandwidth, etc) but the issue persists. There’s
no direct correlation between these parameters and BER, and all these
parameters can increase the complexity of the system.
I’m using a USRP2 with a xcvr2450 daughterboard and the latest version
GNURADIO as of august (I think 3.6?) on ubuntu.
Has anyone else had this issue? Any solutions or insight into the
of the problem?