Negative dB signal to noise ratio Is it common to find systems having signal to noise ratio (SNR) less than 1 i.e. noise is more than signal? I am currently working with SNR of -5db to -20db. And how useful is it to work with sensor readings having negative SNR? I am asking it because the algorithm I am using to solve a problem works well with negative SNR but at positive and higher SNR, it is numerically unstable. This instability arises because of computation of hypergeometric function $_pF_q\left(;;\frac{z}{σ^2}\right)$. At high SNR, i.e. low $σ^2$, the argument $\frac{z}{σ^2}$ becomes very high, making the convergence of hypergeometric function very slow and the algorithm becomes numerically unstable.
Yes, GPS signals are below the noise floor. Link