Regarding SNR values

[Siddhartha]

Hi,

 I noticed that gr-gsm does not give snr values in gsmtap header. How can i calculate SNR values from raw sample data or is it already calculated but not added to gsmtap header in gsm receiver?

Thanks and Regards

Siddhartha

[Vasil Velichkov]

Hi Siddhartha,

On 11.07.2018 17:34, Siddhartha wrote:
> I noticed that gr-gsm does not give snr values in gsmtap header. How
> can i calculate SNR values from raw sample data or is it already
> calculated but not added to gsmtap header in gsm receiver?

A simple search in the source code reveals that the SNR calculation is
not implemented.
https://github.com/ptrkrysik/gr-gsm/blob/ac140210c93deb8918f7ab964c2ba8791aea711e/lib/receiver/receiver_impl.cc#L1044-L1045

An example SNR calculation (currently not used) that comes from the OpenBTS.
https://github.com/ptrkrysik/gr-gsm/blob/ac140210c93deb8918f7ab964c2ba8791aea711e/lib/decoding/openbts/BitVector.cpp#L313-L341

[Piotr Krysik]

Hi Siddhartha,

W dniu 11.07.2018 o 17:06, Vasil Velichkov pisze:

As Vasil noted computing of SNR is not implemented. The linked SNR
calculation is for soft bits - I don't know what exactly they put in
soft bits and hence how close the estimate is to the SNR of the signal.
I would probably do it differently, like:
-take some part of a burst with known content,
-subtract the ideal signal from it to get the noise,
-compute noise power,
-compute signal power,
-divide them.

It might be an overkill though and I don't know what is the required
accuracy.

--
Best Regards,
Piotr Krysik

[Siddhartha]

Hi,

I can calculate SNR by the method you described in matlab but i think it would be hard to implement that method in receiver block in runtime. I can try with soft bits but i am not clear on that concept, i will look into that more. Is There any other way i can compute SNR in receiver block?

Thanks and Regards

Siddhartha