Joint algorithm for time of arrival estimation of S-mode baseband signals with low SNR

To improve the wide area multilateration (WAM) accuracy when receiving S-mode baseband signals with low signal-to-noise ratio (SNR), a joint time of arrival (TOA) estimation algorithm based on non-coherent integration was proposed.According to the correlation characteristics of target reply signals during the beam scanning dwell time of the secondary surveillance radar (SSR), a low SNR baseband pulse signal rising edge estimation method with a four-pulse matched filter and amplitude squared operation and accumulation was proposed, which effectively improved the TOA estimation accuracy of S-mode baseband signals with a low SNR ranging from −15 dB to 5 dB. The Monte Carlo simulation results show that the root mean square error (RMSE) of TOA estimation by using the joint algorithm is less than 25 ns for S-mode signals with a low SNR ranging from −15 dB to 5 dB. For non-ideal S-mode baseband signals, when the SNR is as low as −15 dB, the TOA estimation accuracy of the joint algorithm after the non-coherent integration of five pulses can reach 22.245 ns, which is much better than the WAM requirement.