Slow fading channel & SNR

Started by Walidmq 5 years ago6 replieslatest reply 5 years ago245 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 14, 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 14, 2019


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Reply by kazMarch 14, 2019

measure it...

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Reply by shafie7March 14, 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"


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


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Reply by WalidmqMarch 14, 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.