Hi all,
If am using OFDM modulation to transmit QAM-ed data. I want to control
the transmit power.
Increasing the transmit side gain does not seem to be that good an
option as it appears to be causing a significant amount of LO leakage at
the DC subcarrier, greater IQ imbalance at the image frequency and more
secondary harmonics. Also it somewhat seems to make the shape of the
received signal spectrum slightly parabolic (don’t know what that
indicates).
The other way would be by controlling the sample amplitudes. I
understand that magnitudes of the complex samples passed to the UHD
device should be in the range [-1,1]. Since OFDM has large PAPR values,
this is not that effective either. FFT of the transmit signal in GNU
radio shows the flat portion of the spectrum to be around -11 dB
(despite changing the FFT size - No scaling happening on the Tx side!?).
The 2 USRPs are placed only a couple of meters apart … The uhd_fft
utility shows the received signal level to be below -80dB despite
the gains set to 20 db at both ends. Is there any better way to increase
transmit power? Thanks in advance.