Hi all,
I am trying to estimate SNR in OFDM system using USRP 2. I am using two URSP's (XVCR 2450). To do
that I am using Gnu radio 3.7.2 with slightly modify
OFDM_benchmark_receiver (see img Rx_snr) and transmitter (img Tx_snr).
1. I want to estimate SNR using IQ samples. But when I receive IQ samples on the receiver (img iq_samples_eq) they are all "perfect". So my first question is, is there some kind of "hard decision" in OFDM Frame Equalizer? Without OFDM Frame Equalizer (img iq_samples_no_s)
2. The second problem is, that I need to have a white noise not coloured noise.
And to to that i need to get rid of the equalizer part of the OFDM Frame Equalizer. The part of correction frequency shift on the symbols need to stay.
Do You have some hints how to do that? (Just commented "//" this part ?
// Do the equalizing
d_eq->reset();
d_eq->equalize(out, frame_len, d_channel_state);
d_eq->get_channel_state(d_channel_state);
3. The 3 question is about Constellation Plot in Gnuradio. My system is based on BPSK so on Constellation Plot I am expecting only the +1, -1 values. The IQ samples are showing me that this is correct +1,-1 so why on the plot i have the values (-0.7,-0.7),(0.7,0.7) (img Tx_snr_run) ? Why Constellation Plot is shifting my values?
4. Last question is about the MPSK SNR Estimator. I am wondering is there a possibility to apply this block to OFDM?
Rx_snr.png
Tx_snr.png
iq_samples_eq.png
iq_samples_no_s.png
Tx_snr_run.png