# Channel impulse response vs sampling frequency

As part of my uni assignment I have to figure out what is the impact of sampling frequency on actual channel impulse response. One obvious thing is that the higher sampling frequency is, the more taps the response has.

But there must have been something more here. When I increase the sampling frequency from 20MHz to 100MHz (and adjust my CP accordingly), I get much better performance. The actual CIR is generated using the following MATLAB code

function cir = getchannel(Trms, sampfreq)
if Trms == 0
Kmax = 0;
vark = 1;
else
% Calculate the exponential decay envelope
Kmax = ceil( 10 * Trms * sampfreq * 1e-9);
var0 = (1 - exp( - 1/(sampfreq*(Trms*(1e-9)))));
k = (0:Kmax);
env = var0 * exp( - k/(sampfreq*(Trms*(1e-9))));
end
stdDevReOrIm = sqrt(env/2);
cir = stdDevReOrIm .* (randn(1, Kmax+1) + j*randn(1, Kmax+1));


I see that in case of 100MHz has a slightly different shape and var0 is much smaller. I wonder why. The following code was implemented based on "IEEE 802.11 Handbook: A Designer's Companion", but I have no access to this book. Also, I was not able to google anything useful, so I decided to ask here.

• the channel impulse response doesn't care how you sample. It's a physical thing you're observing, not something you're effecting. Your estimate of the CIR is of course affected. I know that sounds nitpicky (it is!), but it helps get a few concepts straight when you don't confuse the thing you're observing and the observation. You say "you get much better performance", but you need to say "for what, doing what, measuring what as performance metric". Commented Mar 10, 2022 at 12:56
• Can you explain then why the MATLAB code looks uses sampling frequency to generate CIR? Commented Mar 10, 2022 at 13:00
• you generate a discrete model of a CIR. Commented Mar 10, 2022 at 13:01
• Perfect, and why sampling frequency is used when I generate a discrete model of CIR? Commented Mar 10, 2022 at 13:10
• @Pawel because the matlab code tries to model the same physical thing observed at different sampling rates. That's like asking why a computer-generated image of a bee looks different when you tell the computer program that you want 10000 pixels per mm vs 10 pixels per millimeter. Commented Mar 10, 2022 at 15:14