Estimates of closely spaced signals using adaptive FOS

An adaptive candidate approach for the fast orthogonal search (FOS) algorithm is presented for detecting signals the frequencies of which are much more closely spaced than can be resolved by the fast Fourier transform (FFT). The algorithm is shown to give solutions comparable to a global minimisation of the sum squared error, but with much greater speed. It can also surpass the Cramer-Rao lower bound on frequency resolution.