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Slow fading channel & SNR

Started by Walidmq 3 years ago6 replieslatest reply 3 years ago180 views

Can anyone help with this question please?

Slow-fading will mean that the signal will vary by more than 30dB on a timescale of a few seconds. How will you know what the SNR is at any time?

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Reply by SlartibartfastMarch 13, 2019

Yes, you need a way to measure it, and there are potentially a number of ways to do it depending on your system, the signal modulation, and the receiver architecture.

e.g., if it is a PSK system and the receiver maintains lock, SNR can be estimated by taking statistics on the error vectors after bit slicing.

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Reply by WalidmqMarch 13, 2019

Thanx

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Reply by kazMarch 13, 2019

measure it...

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Reply by shafie7March 13, 2019

"Slow fading" refers to comparison with respect to Symbol Rate, SR.

There are Large and Small Scale Fading, see "Fading Manifestations and Mitigation Techniques"

https://ortenga.com/blog/#Fading

Small Scale fading is a random variable, so you cannot predict SNR at each point in time, but rather know the distribution function, Rayleigh or Rician.

Best regards,

Shahram Shafie

https://ortenga.com/

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Reply by WalidmqMarch 13, 2019

Got it. thnx Shafie

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Reply by adiduaMarch 14, 2019

The SNR is a random variable in a fading environment, so have to think of it in terms of a distribution, from which you can derive summary statistics (e.g. mean SNR). In a practical implementation, one would typically estimate it from a pilot channel (where the transmitted information is known). For typical fading profiles used in simulations (e.g. Rayeligh) you can derive it analytically.