The patent's inventors are Rodriguez, Filippo (
This patent was filed on
From the background information supplied by the inventors, news correspondents obtained the following quote: "FIG. 1 shows schematically a Global Navigation Satellite System (GNSS) 1 comprising a plurality of satellites 4 emitting signals directed to a plurality of receivers 2 and local elements 3 (only one of which is shown in FIG. 1), communicating with each other in a manner known per se and hence not described in detail. Each receiver 2 is generally enclosed in a corresponding user terminal configured to execute high level software applications based on the data provided by the receiver 2. From a technical point of view, each receiver 2 may be regarded as a radio-frequency (RF) front-end of the corresponding user terminal, namely the networking part of the user terminal, as opposed to the application part, comprising a user interface and the aforementioned high level applications.
"Each satellite 4 transmits signals modulated by a pseudorandom sequence (PN sequence) characteristic of the satellite 4. Furthermore, signals emitted by each satellite 4 contain a navigation message, in turn containing, besides data suited to improve the accuracy in the calculation of the receiver position, the ephemeris of the satellite, namely mathematical functions describing the satellite orbit in a highly precise manner. Therefore, based on the information carried by the signals, each receiver 2 computes its distance from the satellite 4. In particular, the receiver 2 computes the propagation time of the signal from the satellite 4 to the receiver 2, namely the time difference between the emission time, that is the time at which the satellite 4 emits the signal, and the reception time, that is the time at which the receiver 2 receives the same signal. Afterwards, an approximate estimate of the satellite-receiver distance is obtained by multiplying the propagation time by the light speed; such an approximate estimate of the satellite-receiver distance is known as pseudorange. Pseudoranges related to different satellites (generally, at least four satellites, as shown in FIG. 2) are then used to compute an estimate of the receiver position, as it will be explained below in more detail.
"In some cases, upon having determined the pseudoranges, instead of computing an estimate of its position, the receiver 2 sends the pseudoranges to a local element 3, which is in charge of computing the estimate of the receiver position, and sending the estimation back to the receiver 2. In particular GNSSs, generally known as Assisted Global Navigation Satellite Systems (A-GNSSs), the satellite ephemeris are provided to the receiver 2 by the local elements 3, so that the receiver 2 does not have to extract them from the navigation messages. Based on the pseudoranges and the received ephemeris, the receiver 2 computes an estimate of its position. In particular A-GNSSs, generally known as A-GNSS 'User Equipment Assisted', the receiver 2 just computes estimates of the pseudoranges and send them to a local element 3, which is in charge of all the remaining operations (solving ambiguities in fractional pseudorange measurements, computing the position, . . . ).
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