A global navigation satellite system (“GNSS”) positioning method is provided, based upon a GNSS radio signal that comprises a navigation message transmitted as a succession of data packets. Each data packet is present in the GNSS radio signal as a sequence of symbols obtained by application of a code preceded by a synchronization symbol header. The data packets are organized internally into data fields. At least certain data packets of the succession of data packets contain a synchronization bit field translated by application of the code into a synchronization symbol pattern.

Methods and apparatus to monitor GPS/GNSS atomic clocks are disclosed. An example method includes establishing a measured difference between an atomic frequency standard (AFS) and a monitoring device. The method also includes modeling an estimated difference model between the AFS and the monitoring device, and computing a residual signal based on the measured difference and the estimated difference model. In addition, the method includes analyzing, by a first detector, the residual signal at multiple thresholds, each of the thresholds having a corresponding persistency defining the number of times a threshold is exceeded before one or more of a phase jump, a rate jump, or an acceleration error is indicated. Furthermore, the method includes analyzing, by a second detector, a parameter of the estimated difference model at multiple thresholds, each of the thresholds having a corresponding persistency defining the number of times a drift threshold is exceeded before a drift is indicated.

Methods and apparatus to monitor GPS/GNSS atomic clocks are disclosed. An example method includes establishing a measured difference between an atomic frequency standard (AFS) and a monitoring device. The method also includes modeling an estimated difference model between the AFS and the monitoring device, and computing a residual signal based on the measured difference and the estimated difference model. In addition, the method includes analyzing, by a first detector, the residual signal at multiple thresholds, each of the thresholds having a corresponding persistency defining the number of times a threshold is exceeded before one or more of a phase jump, a rate jump, or an acceleration error is indicated. Furthermore, the method includes analyzing, by a second detector, a parameter of the estimated difference model at multiple thresholds, each of the thresholds having a corresponding persistency defining the number of times a drift threshold is exceeded before a drift is indicated.

A method for evaluating the quality of a radio frequency signal for a satellite navigation system, the method comprising: sampling the payload radio frequency signal of a satellite to obtain an intermediate frequency signal, and filtering the signal; downconverting the filtered intermediate signal to obtain the corresponding actual baseband signal; generating the signal components of the ideal baseband signal branches on the basis of the obtained actual baseband signal and the signal system thereof; reproducing the ideal baseband signal, which is used to evaluating the actual baseband signal; establishing a correlation function between the actual baseband signal to be evaluated and the ideal baseband signal, and obtaining through corresponding calculations a series of quality evaluation indexes such as spurious transmission in the band and related loss, thereby enabling the evaluation of the quality of the radio frequency signal. The present invention clarifies the relation between signal quality indexes and the capturing, tracking, and demodulation performance of a signal, and can clearly and regularly evaluate the effect of the signal quality on navigation performance.

System and method to protect the privacy of ADS-B messages transmitted by aircraft. The system includes one or more ground stations with a ground station control unit and a ground ADS-B transponder for receiving an ADS-B message. The ground station control unit includes an aircraft position determination module for retrieving an aircraft position included in the ADS-B message; an operating conditions module for determining the fulfillment of operating conditions including determining if the aircraft position is an actual aircraft position; and a fake aircraft position generator for computing one or more fake aircraft positions. The ground station control unit broadcasts one or more fake ADS-B messages including the fake aircraft positions if the operating conditions are met. With this system only trusted receivers can obtain the real position of the aircraft.

System and method to protect the privacy of ADS-B messages transmitted by aircraft. The system includes one or more ground stations with a ground station control unit and a ground ADS-B transponder for receiving an ADS-B message. The ground station control unit includes an aircraft position determination module for retrieving an aircraft position included in the ADS-B message; an operating conditions module for determining the fulfillment of operating conditions including determining if the aircraft position is an actual aircraft position; and a fake aircraft position generator for computing one or more fake aircraft positions. The ground station control unit broadcasts one or more fake ADS-B messages including the fake aircraft positions if the operating conditions are met. With this system only trusted receivers can obtain the real position of the aircraft.

Systems, methods, and apparatus for power adjustment for code signals are disclosed. In one or more embodiments, a disclosed method for adjusting power for code signals comprises determining, by at least one processor, a code loss for the transmission of the code signals by using a symbol table. The method further comprises determining, by at least one processor, an amount of change in attenuation for at least one adjustable attenuator on at least one vehicle by using the code loss. Further, the method comprises adjusting an attenuation, for at least one adjustable attenuator, by the amount of change in attenuation.

A satellite orbiting in one of a plurality of orbital planes of a satellite constellation system at an altitude range corresponding to low earth orbit includes at least one processor configured to generate satellite state data, and to generate a navigation signal based on the satellite state data. The satellite includes at least one transmitter configured to transmit the navigation signal for receipt by at least one client device on earth. Each of the plurality of orbital planes includes a corresponding one of a plurality of satellite subsets of a plurality of satellites of the satellite constellation system. Each of the plurality of orbital planes is within the altitude range, and the plurality of orbital planes includes a set of inclined orbital planes at a non-polar inclination.

A satellite orbiting in one of a plurality of orbital planes of a satellite constellation system at an altitude range corresponding to low earth orbit includes at least one processor configured to generate satellite state data, and to generate a navigation signal based on the satellite state data. The satellite includes at least one transmitter configured to transmit the navigation signal for receipt by at least one client device on earth. Each of the plurality of orbital planes includes a corresponding one of a plurality of satellite subsets of a plurality of satellites of the satellite constellation system. Each of the plurality of orbital planes is within the altitude range, and the plurality of orbital planes includes a set of inclined orbital planes at a non-polar inclination.

A lunar orbiting satellite system executes orbit planning of assigning a function (positioning, communication, and flashing) to an artificial satellite (AS) depending on a relative position of the AS to the moon at a time when the moon and the AS are observed from an input point on the earth, and correcting the relative position, which changes in accordance with the moon revolution period. The system includes: a satellite orbit planner which assigns a function to each ASs forming an AS group flying around the moon depending on a relative position of each ASs to the moon at a time when the moon and ASs are observed from an input point on the earth, and set a target orbit according to the function; and a satellite controller which causes the each ASs to execute control based on the function to implement switching of the function.