Position-fixing system

Abstract

Several satellites serving as reference stations (S.sub.j) for a user revolve about the earth in different orbits. At least four reference stations must be within sight of a user station (N) at the same time. The user station measures the ranges to at least four reference stations by one-way ranging. From these ranges and the positions of the reference stations, which are transmitted as data words, the user station determines its position. To determine the positions of the reference stations, the ranges from the respective reference station to at least three ground stations (B.sub.i) are measured by two-way ranging. From these ranges and the known positions of the ground stations, the position of the reference station is obtained. The interrogation signals of all reference stations contain the same basic signal (K.sub.s), which represents a pseudorandom code. The reply signals of the ground stations contain differently coded signals (K.sub.Bi), so that the ground stations are identifiable with the aid of the codes assigned to them. If the interrogation and reply signals contain the times of transmission (t.sub.j) and arrival (t.sub.i), respectively, of the interrogation signal, and the signal transit times are measured, the clocks of the reference stations and of the ground stations can be synchronized.