Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Patent
1992-09-29
1994-07-19
Issing, Gregory C.
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
375 1, G01S 502, H04B 1500
Patent
active
053313291
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to radio navigation systems for position fixing, in particular to radio navigation positioning methods with the aid of satellites and radio navigation systems thereof, based on measuring the phase difference between the radio navigation signals received. More specifically, it relates to systems, wherein the satellites generate pseudorandom radio navigation signals, uniquely related to the satellite's preceision time and frequency primary standard.
PRIOR ART
Currently known in the art is a satellite radio navigation system, named the "Global Positioning System (GPS)" or "Navstar" (Navigation (USA), 1978, v. 25, No. 2), using a plurality of satellites to position any object-user, each object equipped with a receiver sensitive to radio navigation signals of said Navstar system satellites. The Navstar system comprises a total of 18 sattelites, three per each of the six circular 12-hour orbits. The orbit planes are uniformly inclined to their adjacent orbits by 60.degree. and the position of any satellite is precisely known for any moment of time.
The position fix of an object-user in any point of the Earth or near it can be taken by measuring the pseudodistance to four satellites that are in the radio visibility zone of this object.
Furthermore, pseudodistance measurements allow determining the object's time scale shift relative to the universal coordinated time, whereas additional measurements of the radial pseudospeed (the rate of pseudodistance variation) allow defining the speed of the object's movement.
All satellites of the said Navstar system transmit a radio navigation pseudonoise signal with one and the same carrier frequency f.sub.c =1572.42 MHz, Identification of each satellite in the system is by the individual ranging pseudorandom sequence assigned to the satellite and modulating the carrier. In one mode, termed the easily detected (C/A) signal mode, the pseudorandom sequence is the Gold code with a code element transmission rate of 1.023 MHz and each code sequence comprising 1023 elements, so that the repetition rate of the sequence is 1 millisecond.
Along with the Gold code sequence each satellite of the said Navstar system transmits binary symbols at a 50 baud rate, these symbols carrying information on the satellite's ephemerides and clock (navigation data) necessary to calculate the receiver's position fix, and a synchronization code (preamble) marking the reference points of the navigation data. This preamble is repeated every six seconds in the form of a 8-symbol Barker code, the serially transmitted preamble and navigation data constituting the navigation message, thus composed of lines of six second length.
The radio navigation signal generation and transmitting subsystem on board the Navstar system satellites comprises a high-precision time and frequency standard, a carrier frequency generator, a Gold-coded pseudorandom sequence (individual for each sattelite), a navigation data generator, a synchronization code generator, a modulating signal generator to provide two-positional (0.degree.-180.degree.) phase modulation of the carrier frequency, this modulating signal being a modulus 2 sum of the navigation message symbols and pseudorandom sequence elements, and a transmitter.
In the user's receiver the arriving radio navigation signal is correlated to a reference signal. The heterodyne frequency of the reference signal is fixed relative to signals received from all satellites of said Navstar system, and the generated copy of the Gold-coded sequence varies in accordance with the satellite number, whose signal is being received. The correlations between the Gold-coded sequence and its copy is analyzed until the autocorrelation function attains its maximum (autocorrelation peak), this evidencing synchronism between the Gold-coded sequence and its copy. On attaining this synchronism, as well as the synchronization of the carrier frequency phase, the pseudodistance and the pseudospeed are measured and the navigation message is received.
The radio navi
REFERENCES:
patent: 3789409 (1974-01-01), Easton
patent: 4048563 (1977-09-01), Osborne
patent: 4291409 (1981-09-01), Weinberg et al.
Alyabina, deceased German M.
Glazov Stanislav S.
Ivanov Nikolai E.
Kovalenko, administrator Nadezhda V.
Kovalenko, administrator Nikita V.
Issing Gregory C.
Nauchno-Issledovatelsky Institut Kosmicheskogo Priborostoenia
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