Patent ID: 6195042
Filing Date: 2001-02-27
Classification: G01S

Abstract:
A method of locating a fixed terminal of a satellite telecommunication system comprising a constellation of satellites, a plurality of gateway stations each associated with a separate geographical cell and connected to a terrestrial telecommunication network, and a plurality of fixed terminals, one or more satellites being active relative to a given gateway station only if they are visible therefrom, each active satellite which receives information from the gateway station relative to which it is active transmits it to the fixed terminal or terminals in its coverage area, each active satellite that receives information from a fixed terminal in its coverage area transmitting the information to the gateway station relative to which it is active, which method comprises an ""intermediate"" location phase comprising the following steps:-i- at a first time t1', said terminal receives from a first active satellite first information relating to the time t1 of transmission of said first information by said first active satellite and the position p1 of said first active satellite at said time t1;-ii- at a second time t2' the same as or close to said first time t1', said terminal receives from a second active satellite second information relating to the time t2 of transmission of said second information by said second active satellite and the position p2 of said second active satellite at said time t2;-iii- said terminal calculates a first hyperboloid H.sub.1,2 on which said terminal is located and such that:H.sub.1,2 :d2-d1=(t2'-t2).c-(t1'-t1).cwhere:d1 is the distance between the terminal and said position p1 of the first active satellite at time t1,d2 is the distance between the terminal and said position p2 of the second active satellite at time t2,t1 and t2 are the first and second times of transmission by said first and second satellites, respectively,t1' and t2' are said first and second times of reception by the terminal, andc is the speed of light;-iv- said terminal reiterates steps -i- through -iii- at least twice to calculate at least second and third hyperboloids on which said terminal is located; and-v- said terminal determines an ""intermediate"" estimated position by calculating the intersection of said first and at least second and third hyperboloids assuming a ""coarse"" estimated position of said terminal to be known.