In-service SNR estimation without symbol timing recovery for QPSK data transmission systems

In this paper we consider the problem of estimating the signal-to-noise ratio (SNR) of the received signal in a QPSK data transmission system. This estimation must be done in-service (non-data aided), without carrier phase knowledge and without symbol timing phase knowledge. New algorithms with these features are derived from the ratio of two moments. The performance of these algorithms is studied by means of simulations, and it is shown that they are robust against carrier and symbol timing frequency offsets as well. This makes them suitable for a wide range of applications.