How to get CSI from ray tracing?

[remydemy]

Hello,

I've modelled a scene with one transmitter and one receiver, computed their paths and calculated the ofdm channel with cir_to_ofdm_channel().

My goal now is to get some information at the transmitter and receiver so that I can calculate a symmetric key at both ends. It doesn't really matter if I get the info from CSI or some pilot signal or something else. Do I need to send something between them before I can access such data? If so how can I do this? Or am I on a completely wrong path?

What I also don't understand is that is the h that I calculate with cir_to_ofdm_channel() different for the receiver and the transmitter, because they are at different positions in the scene? If so how can I access these different values, because I'm only using this method once (with the a, tau that I got from Paths2CIR).

Thanks for any help!

Best regards,
Emily

[jhoydis]

Hi Emily,

When you compute the CIR between two radio devices via ray tracing, it should not matter which device is the transmitter and which is the receiver. The CIR should be the same. It is therefore not necessary to compute it twice.

In practice, none of the radio devices has access to the CIR and will only get an estimate of it, based on pilots sent by the other radio device. To simplify this approach, you could compute the channel frequency response h once using cir_to_ofdm_channel() and then create two noisy versions of it by adding two different random noise vectors to h.

Hope that helps.

[remydemy]

Thanks for your fast response!
I assume adding AWGN() to simulate noise would be sufficient for this purpose?

[jhoydis]

Yes, you can use this layer, or alternatively use the convenience function sionna.utils.complex_normal(). The variance parameter will determine the quality of your channel estimates. I believe that you should probably set the normalise=True flag in the cir_to_ofdm_channel() function such that the channel frequency response has unit power on average.

[remydemy]

Ok great. I actually already set normalise=True.

You were really helpful!

Kind regards,
Emily

[qiangdadi]

How to using AWGN() in sionna RT?