EFFICIENT DETECTION OF A CONTINUOUS-WAVE SIGNAL WITH A LINEAR FREQUENCY DRIFT

An efficient method is presented for the detection of a continuous-wav e (CW) signal with a frequency drift that is linear in time. Signals o f this type occur if the transmitter and receiver are rapidly accelera ting with respect to one another, for example, as in interplanetary an d space communications. We assume that both the frequency and the drif t are unknown. We also assume that the signal is weak compared with th e Gaussian noise. The signal is partitioned into subsequences whose di screte Fourier transforms provide a sequence of instantaneous spectra at equal time intervals. These spectra are then accumulated with a shi ft that is proportional to time. When the shift is equal to the freque ncy drift, the signal-to-noise ratio increases and detection occurs. I n this paper, we show how to compute these accumulations for many shif ts in an efficient manner using a variant of the fast Fourier transfor m (FFT). Computing time is proportional to LlogL, where L is the lengt h of the time series. Computational results are presented.