Improving coherent tonal detection with phase interpolation and compensation

Tonal detection is very important in weak signal detection field, and phase coherent averaging tonal detector is superior to incoherent averaging power spectrum detector. For the purpose of resolving the problem of inaccurate phase compensation introduced by the existing coherent averaging tonal detector, the gain loss with inaccurate phase compensation is analyzed, and a modified detector using frequency domain interpolation to estimate the phase difference accurately is proposed. The three point interpolation in frequency domain is applied to obtain the accurate phase difference estimate when the averaging segment length is not exactly the integer times of the signal period, thus to avoid the gain loss introduced by averaging the segmented data not in-phase. Theoretical analysis shows that there will be a gain of 3.9dB at most with the modified detector. The detection performance of incoherent average power (AVGPR) detector, coherent generalized likelihood ratio test (CGLRT) detector, and the modified CGLRT detector is compared by computer simulations, and the results show that the modified detector operates better than the other two detectors especially with low SNR. Both theoretical analysis and simulations verify the effectiveness of the modified detector.