Question to measure SNR


#1

Hi ALL,

i saw there is a function called <gr_probe_mpsk_snr_c>,
but i doesn’t know how to get this to work.

Is there a example which is using this function ?
Can i use this to measure my SNR ?
I have a test sin signal.

I also found the possibility by measuring the SNR by
examine the bit-error-rate.

Are there any example which do this ?

Regards Markus


#2

On Wed, Mar 25, 2009 at 5:20 AM, feldmaus removed_email_address@domain.invalid
wrote:

i saw there is a function called <gr_probe_mpsk_snr_c>,
but i doesn’t know how to get this to work.

This a sink you can attach to a raw MPSK constellation complex sample
stream, and it will estimate the signal-to-noise ratio using the
“squared signal over noise variance” (SNV) technique for SNR
estimation. It’s simple and fast, but not all that accurate below
about 8 or 9 dB.

Is there a example which is using this function ?

It is used in the bit error rate tester (digital-bert) example
receiver. The block is designed to be queried for its current SNR
estimate by an external thread (created by the user outside the
flowgraph). In the BERT receiver, a background thread once per second
queries the flowgraph for the current SNR, bit error rate, frequency
offset, and timing error, then displays these to the screen.

Can i use this to measure my SNR ?
I have a test sin signal.

No, it is explicitly designed for BPSK or QPSK signals, not carriers.
Importantly, it needs to follow a frequency/phase recovery loop such
that there is no residual carrier in the signal.

I also found the possibility by measuring the SNR by
examine the bit-error-rate.

Are there any example which do this ?

It the digital BERT example, you can see the BER and SNR once per
second, and in live testing, they do correlate. But you can’t assume
a fixed relationship between BER and SNR except in a the ideal (“not
real world”) case of pure additive white gaussian noise.

Johnathan