Time-frequency estimation in the COSPAS/SARSAT system using antenna arrays: Variance bounds and algorithms

This paper deals with the signal processing techniques to be applied in the reception of the Search And Rescue (SAR) system COSPAS/SARSAT distress beacons. The receiver unit has to estimate time delays and Doppler shifts of a set of satellite-relayed replicas of the original beacon in order to compute the position where the device has been activated. The Cramér-Rao Bound (CRB), which determines the minimum variance achievable for any unbiased estimator, is computed for the problem at hand considering a receiver provided with an antenna array. Finally, we propose a new sort of beamforming which exploits temporal and spatial references achieving a performance close to the CRB with a moderate implementation effort.