We propose two blind techniques to detect
the presence of interference (or jamming signal) in Global
Navigation Satellite System (GNSS) receivers, which do not
require knowledge of the interfering signal or channel noise
characteristics. Both techniques resort to the computation of
the sample covariance matrix: the former is eigenvalue based
and the latter relies on the discrete Fourier transform of the
covariance matrix columns. With these techniques we analyze
two types of interference: narrowband (sinusoidal waveforms)
and wideband (chirp signals).