Re: Channel State Information of OFDM in gnuradio

[Marcus Müller]

Hi Hamed,

so, estimating anything from noise will be noisy if the estimation has 
something to do with the estimated entity. (Compare, especially, the 
Cramér-Rao Lower Bound: you can't bias-free estimate with zero error in 
a noisy reception.) So, is it right if I assume that you measured or 
calculated the SNR at your receiver (don't know from the top of my head 
what SNR a noise stddev of 0.1 translates to, and the estimator variance 
is unreasonably high in that scenario?

Best regards,
Marcus

On 5/3/23 16:01, Hamed Al-Zubi wrote:
> Dears,
>
> I am doing some analysis on channel state information of OFDM signals.
> I used GNURadion rx_ofdm.grc (gnuradio/gr-digital/examples/ofdm at 
> main · gnuradio/gnuradio 
> <https://github.com/gnuradio/gnuradio/tree/main/gr-digital/examples/ofdm>) 
> for signal transmission and reception through a channel model block. 
> Then, the CSI has been extracted using Tag debug block.
> After that, I used matlab to plot the phase of pilot signals from csi. 
> When I set the noise voltage on the channel block to zero, the phase 
> of each pilot signal is constant. However, when I set the noise 
> voltage to 100m, the phases of the pilot signals vary over time as 
> shown in Fig. (phase_pilot). I used a moving average filter to 
> mitigate the noise impact on the pilot phase. The results were better, 
> but still there is a phase drop as shown in Fig. (phase_pilot_filter).
> As I read, the phase should be constant as long as the environment is 
> static. So, why there is a phase drop? how that can be fixed?
>
> Thanks,
> HZ
>
>
>
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>     gnuradio/gr-digital/examples/ofdm at main · gnuradio/gnuradio
>
> GNU Radio – the Free and Open Software Radio Ecosystem - 
> gnuradio/gr-digital/examples/ofdm at main · gnuradio/gn...
>
> <https://github.com/gnuradio/gnuradio/tree/main/gr-digital/examples/ofdm>