Apparatus for verifying GPS satellite data

An apparatus for verifying GPS satellite data comprising:

• receiver means for receiving information from a plurality of GPS satellites each of which delivers information relating to its own orbit and timing thereof;
• positioning calculation means for calculating the position of a point of reception based on information received by the receiver means from the plurality of GPS satellites;
• verified position determining means for determining a verified position of the point of reception based on information received from at least three GPS satellites registered as available;
• first distance calculating means for calculating a distance between an unverified GPS satellite and the point of reception based on positional information of the unverified GPS satellite determined from the received orbital information and information relating to the verified position of the point of reception determined by said verified position determining means;
• second distance calculating means for determining a time delay required for propagation of information delivered from the unverified GPS satellite received at the point of reception based on received timing information and the point in time when such timing information is received, and calculating a distance between the unverified GPS satellite and the point of reception from the determined time delay;
• verifying means for determining a difference between the distance determined by the first distance calculating means and the distance determined by the second distance calculating means, and registering the unverified GPS satellite as one which is available for use in the calculation by the positioning calculation means whenever the difference is less than a predetermined threshold and registering the unverified GPS satellite as unavailable for use in the calculation by the positioning calculation means whenever the difference is greater than the predetermined threshold, wherein said verifying means operates when a verification flag is set;
• and
• auxiliary verifying means for obtaining a plurality of positions of the point of reception based on combinations of three entities chosen from among four entities of information received from four GPS satellites, comparing a difference between any two of the plurality of positions with the threshold value, for determining whether the four GPS satellites are available for use in the calculation of the positioning calculation means, registering the four GPS satellites as available, and setting the verification flag, wherein said verifying means verifies remaining GPS satellites which are not registered as available after the four GPS satellites are registered as available by the auxiliary verifying means.

A method for verifying data from a satellite among a first plurality of satellites each of which transmits a signal, the method comprising the steps of:

• a) receiving at a point of reception the signals transmitted from the first plurality of satellites and based on the received signals determining a position of the point of reception;
• b) verifying data transmitted by each satellite of a second plurality of satellites, wherein each of said second plurality of satellites is included in the first plurality of satellites, wherein step b) comprises the steps of:
• b1) performing satellite positioning calculations based on said second plurality of satellites thereby determining a plurality of positions;
• b2) computing differences between said plurality of positions and comparing the differences with a first predetermined threshold value;
• and
• b3) registering as verified each of said second plurality of satellites if the differences computed in step b2) do not exceed the first predetermined threshold value;
• c) selecting one of the first plurality of satellites which is not one of said second plurality of satellites, and verifying the data transmitted by the selected satellite, wherein step c) comprises the steps of:
• c1) measuring a distance between the point of reception and the selected satellite, based on a time delay of the selected satellite signal;
• c2) calculating a line-of-sight distance between the selected satellite and the position of the point of reception;
• and
• c3) comparing the range measured in step c1) with the line-of-sight distance calculated in step c2) and registering the selected satellite as verified if the comparison is less than a second predetermined threshold value;
• and
• d) repeating step c) when another one of the first plurality of satellites is selected which is not registered as verified.