Positioning problems of disaster communications-low Earth orbit satellite-based least squares method

We have studied on the current Emergency Position Indicating Radio Beacon (EPIRB) of COSPAS-SARSAT. An orbiting satellite receives a signal (406 MHz) sent from earth, and the ground position is calculated from data on at least three Doppler shifts, using the least squares method. However, we can point out some problems that are investigated as follows; 1) The multipath and blocking caused by sea waves and tides adversely affect data communications. 2) Fluctuations in crystal oscillations caused by induced acceleration resulting from waves/tides and temperature change adversely affect the frequency stability of transmission signals, eventually leading to positioning errors. 3) Others. So we feel that a new system should be developed to replace it.