Abstract: Systems and methods for vehicle attitude determination are provided.

Abstract: A system to detect spoofing attacks is provided. The system includes a satellite-motion-and-receiver-clock-correction module, a compute-predicted-range-and-delta-range module, a subtractor, and delta-range-difference-detection logic. The satellite-motion-and-receiver-clock-correction module periodically inputs, from a global navigation satellite system (GNSS) receiver, a carrier phase range for a plurality of satellites. The satellite-motion-and-receiver-clock-correction module outputs a corrected-delta-carrier-phase range for a current epoch to a first input of a subtractor. The compute-predicted-range-and-delta-range module outputs a predicted delta range to a second input of the subtractor. The predicted delta range is based on inertial measurements observed for the current epoch. The subtractor outputs a difference between the corrected-delta-carrier-phase range and the predicted delta range for the current epoch to delta-range-difference-detection logic.

Abstract: Systems and methods for vehicle attitude determination are provided.

Abstract: A system to detect spoofing attacks is provided. The system includes a satellite-motion-and-receiver-clock-correction module, a compute-predicted-range-and-delta-range module, a subtractor, and delta-range-difference-detection logic. The satellite-motion-and-receiver-clock-correction module periodically inputs, from a global navigation satellite system (GNSS) receiver, a carrier phase range for a plurality of satellites. The satellite-motion-and-receiver-clock-correction module outputs a corrected-delta-carrier-phase range for a current epoch to a first input of a subtractor. The compute-predicted-range-and-delta-range module outputs a predicted delta range to a second input of the subtractor. The predicted delta range is based on inertial measurements observed for the current epoch. The subtractor outputs a difference between the corrected-delta-carrier-phase range and the predicted delta range for the current epoch to delta-range-difference-detection logic.

Abstract: A method comprises generating a respective code-carrier difference for each of a plurality of satellite vehicle and signal frequency combinations, wherein the code-carrier difference is based on a code range and a carrier range. The method also comprises filtering the respective code-carrier difference for an unknown bias and random noise; determining whether multipath is present for each of the plurality of satellite vehicle and signal frequency combinations based on the respective filtered code-carrier difference; and computing a position solution based on trust placed in respective measurements from each of the plurality of satellite vehicle and signal frequency combinations, the trust based on whether multipath is present for the respective satellite vehicle and signal frequency combination.

Abstract: A method comprises generating a respective code-carrier difference for each of a plurality of satellite vehicle and signal frequency combinations, wherein the code-carrier difference is based on a code range and a carrier range. The method also comprises filtering the respective code-carrier difference for an unknown bias and random noise; determining whether multipath is present for each of the plurality of satellite vehicle and signal frequency combinations based on the respective filtered code-carrier difference; and computing a position solution based on trust placed in respective measurements from each of the plurality of satellite vehicle and signal frequency combinations, the trust based on whether multipath is present for the respective satellite vehicle and signal frequency combination.

Abstract: A state is added to a Kalman filter to model GPS multipath errors. The multipath states may be modeled as either a random walk model or a Gauss-Markov process. The choice of the model depends on the characteristics of the multi-path error and the GPS receiver. Adding this state to the Kalman filter to model multipath improves the navigation system's robustness when operating as a deeply integrated system when multipath is present.

Abstract: A method and systems for processing Global Positioning System (GPS) signals is provided. The method includes determining if two signals or more signals with the same pseudorandom number bit sequence (PRN) are detected by a GPS receiver.

Abstract: A state is added to a Kalman filter to model GPS multipath errors. The multipath states may be modeled as either a random walk model or a Gauss-Markov process. The choice of the model depends on the characteristics of the multi-path error and the GPS receiver. Adding this state to the Kalman filter to model multipath improves the navigation system's robustness when operating as a deeply integrated system when multipath is present.

Abstract: A method and systems for processing Global Positioning System (GPS) signals is provided.

Abstract: A system and method for enhancing the performance of satellite navigation receivers are disclosed, which incorporate a precise frequency reference in a satellite navigation receiver that reduces the system's dependence on maintaining continuous satellite reception for RAIM availability. As one example, a system for enhancing the performance of a satellite navigation receiver is disclosed, which includes a GPS receiver and a high precision (e.g., atomic) clock incorporated into the GPS receiver. The use of the high precision clock reduces clock error and the number of satellite measurements needed to meet existing RAIM availability requirements. For example, incorporating a precision clock into a GPS receiver provides an enhanced system that meets existing RAIM availability requirements with at least one less satellite measurement than the number needed for prior systems using RAIM.

Abstract: A navigation system includes an inertial measurement unit, a navigation computer, a GPS receiver, and a clock controller. The inertial measurement unit has a first clock and a first switch, the navigation computer has a second clock and a second switch, and the GPS receiver has a third clock. The clock controller controls the first and second switches. Accordingly, the inertial measurement unit, the navigation computer, and the GPS receiver may use their own clocks, or the inertial measurement unit and the navigation computer may use the second clock, or the inertial measurement unit, the navigation computer, and the GPS receiver may use the third clock.

Abstract: A GPS receiver acquires GPS data from at least one GPS satellite. A code offset and a frequency offset are determined based on the acquired GPS data. A change in GPS position of the GPS receiver during the determination of the code offset is determined, and a change in rate of the GPS receiver during the determination of the frequency offset is also determined. The code offset is updated based on the change in GPS position, and the frequency offset is updated based on the change in rate. The updated code offset and the updated frequency offset are handed over to a tracking function.

Abstract: A method for detecting lock slip using inertial information is provided. The method involves an epoch comparison of a predicted delta phase range with a measured delta phase range. The predicted delta phase range is calculated by subtracting a previous inertial solution from a current inertial solution. The measured delta phase range is calculated by subtracting a previous carrier phase measurement from a current carrier phase measurement. If a difference between the predicted delta phase range and the measured delta phase range is greater than a threshold amount, a lock slip is declared. The method allows for lock slip detection in Global Positioning System (GPS) attitude determinations without relying on a lock slip notification from the GPS.

Abstract: Multiple pulses of narrow band signals of varying frequency are detected by multiple spaced apart receivers such that average time difference of arrivals of the signals from an item to be located are determined. The average time differences are used to calculate a position of the item to be located with a desired accuracy, such as within one meter in one embodiment. One of multiple receivers or rangers initiates a location process by transmitting a sync pulse. The sync pulse is received by a scout and other rangers. The scout is a small robot which acts as a transponder, sending out its own narrow band return pulse in response to the sync pulse. Each ranger then determines a difference in time between the sync pulse it receives and the return pulse generated by the scout. The location process is then repeated again at different selected narrow band frequencies, and an average of the difference in time at each ranger is determined.

Abstract: A GPS receiver fault detection method for use in a GPS attitude determination system having Q Receivers, wherein Q>3, includes providing R attitude solutions using subsets of P Receivers and signals from two or more space vehicles, wherein 3.ltoreq.P.ltoreq.Q-1. Post-update measurement residual sets equal to the number R of attitude solutions are determined. Each of the post-update measurement residual sets corresponds to one of the attitude solutions. "S" Receiver faults are detected by comparing the R post-update measurement residual sets, wherein 1.ltoreq.S.ltoreq.Q-3. A faulty Receiver detection system for carrying out the method is also described.

Abstract: A method for use in vehicle attitude determination includes generating GPS attitude solutions for a vehicle using three or more antennas receiving GPS signals from two or more space vehicles. An inertial navigation system is initialized by setting the attitude of the inertial navigation system to a GPS attitude solution generated for the vehicle and/or the attitude of the inertial navigation system is updated using the GPS attitude solutions generated for the vehicle or GPS estimated attitude error generated for the vehicle. A system for use in vehicle navigation is also provided.

Abstract: A multipath detection method for use in a GPS position determination system includes providing a code pseudorange measurement representative of a range of an antenna to a space vehicle and a carrier phase pseudorange measurement representative of the range of the antenna to the space vehicle. A code-carrier measurement difference is then generated between the code pseudorange measurement and the carrier phase pseudorange measurement. This code-carrier measurement difference is examined to determine if a multipath component is present. If, the difference indicates that multipath is likely to be present, use of such measurements in computing position solutions, such as attitude solutions, is avoided. A multipath detection system for carrying out the method is also described.