The present invention relates to a navigation system which enables signal spoofing and/or jamming to be detected.

A navigation system provided on land, sea and air vehicles consists of many sub-units such as inertial navigation unit, air data unit, global positioning unit, which enable position, speed, timing information and altitude information of the vehicle to be obtained. In these navigation systems, spoofing or jamming of the signals causes instantaneous or time dependent deviation of the data obtained. Such a negative effect causes the vehicle's position, speed, timing information and altitude information to be obtained incorrectly, and there is a possibility that the autopilot and/or a similar module fed with this data causes the cruise to be at risk.

In the United States patent document no. US8922427, which is included in the known- state of the art, a system for detecting spoofing attacks in GPS data and eliminating the error is described. Said system comprises a GPS receiver equipped with GPS antennas and an INS device measuring acceleration and angular velocity located in a navigation unit. It comprises determining the presence of a GPS spoofing attack in the signal by statistically analyzing via hypothesis testing the GPS and INS readings of the corresponding navigational data until a statistically significant difference is found between the GPS and INS readings .

With a navigation system developed with the present invention, a system with high accuracy and reliability is obtained, which detects the interruption, jamming and spoofing of signals used to obtain data that is critical for road safety in a short time.

The navigation system realized to achieve the object of the invention and defined in the first claim and the claims dependent thereon measures air pressure instantaneously with the pitot tube mounted on a surface of the air vehicle. Pressure measurements taken with the pitot tube, which is an element of the air data unit, are used to calculate an angle of attack, an angle of sideslip and an true airspeed for the air vehicle by using conversion formulas. An orientation, acceleration and angular velocity data of the air vehicle are measured by a gyroscope and an accelerometer located in an inertial measurement unit on the air vehicle. An instantaneous speed of the air vehicle according to body frame of the air vehicle is calculated by applying conversions to the angle of attack, sideslip angle and true airspeed data by the flight computer, wherein said data are obtained by means of the air data unit. Speed data of the air vehicle frame are adjusted by using data of the inertial measurement unit, and an air data system-based speed estimation is performed by inserting the data into a Kalman filter that is run on the flight computer. In addition, there is also provided at least one global positioning unit receiving signals from satellites, whose orbits and time information are known and which send uninterrupted information to the earth, with receivers on the air vehicle, and calculating real-time speed data for the air vehicle.

The navigation system of the invention comprises a flight computer which statistically compares the estimated speed data of the air vehicle output by the Kalman filter with the speed data of the air vehicle obtained by means of the global positioning unit, so that each speed signal obtained by the global positioning unit is evaluated separately for providing error detection and error signal generation.

In an embodiment of the invention, the navigation system comprises a flight computer which compares the speed data estimated by the Kalman filter with the speed data obtained by the global positioning unit by a statistical decision method, so that an erroneous speed signal obtained by the global positioning unit is detected.

In an embodiment of the invention, the navigation system comprises a Kalman filter using a dynamic model of the air vehicle or a kinematic model updated with the data of the inertial measurement unit.

In an embodiment of the invention, the navigation system comprises a Kalman filter which estimates north-south component, east-west component and down-up component (NED- SWU) of wind speed and speed parameters of the air vehicle.

In an embodiment of the invention, the navigation system comprises an extended Kalman filter which estimates speed based on data of the air data unit, comprises random walk wind model, and uses kinematic model of the vehicle updated with inertial measurement unit data.

In an embodiment of the invention, the navigation system comprises a flight computer which converts speed data output by the Kalman filter into a north-east-down (NED) frame, which is a type of components of speed data of the global positioning unit, since data with the same frame can be compared.

In an embodiment of the invention, the navigation system comprises a flight computer which converts global positioning unit measurements into air vehicle frame, and thus performs comparison by a statistical method with the estimated speed data output by the Kalman filter.

In an embodiment of the invention, the navigation system comprises a global positioning unit which is any of the GPS, Galileo, GLONASS, COMPASS and QZSS transmitting information via signals and having satellite network features belonging to different countries.

The navigation system realized to achieve the object of the present invention is illustrated in the attached drawings, in which:

Figure 1 is a block diagram of a navigation system.

Figure 2 is a block diagram of a navigation system comprising an extended Kalman filter.

All the parts illustrated in figures are individually assigned a reference numeral and the corresponding terms of these numbers are listed below:

1. Navigation System

2. Air Data Unit

3. Inertial Measurement Unit

4. Flight Computer

5. Kalman Filter

501. Extended Kalman Filter 6. Global Positioning Unit

The navigation system (1) comprises at least one air data unit (2) which is located on the air vehicle and enables angle of attack, angle of sideslip and true airspeed data of the air vehicle to be obtained by dynamically measuring air pressure from the air flow; at least one inertial measurement unit (3) which enables orientation, acceleration and angular velocity data of the air vehicle to be measured by means of motion sensors and angle measuring sensors on the air vehicle; at least one flight computer (4) which enables speed data of the air vehicle to be obtained by processing the data obtained by the air data unit (2); a Kalman filter (5) which estimates speed of the air vehicle by processing the speed data of the air vehicle and the measurement data obtained by the inertial measurement unit (3), which are uploaded to the flight computer (4); at least one global positioning unit (6) which enables real-time speed data of the air vehicle to be obtained by receiving the signals coming from satellites on the earth orbit by means of receivers on the air vehicle (Figure 1).

The navigation system (1) of the invention comprises a flight computer (4) which enables error detection and error signal generation for the speed data obtained with the global positioning unit (6) by statistically comparing the speed data of the air vehicle estimated by the Kalman filter (5) with the speed data of the global positioning unit (6).

With at least one pitot static tube, which is the air data unit (2) element located on the air vehicle, angle of attack, angle of sideslip and true airspeed of the air vehicle are calculated by measuring the air pressure around the air vehicle. Using these measurement parameters, the speed components of the air vehicle according to the body frame thereof are calculated using formulas. Since said speed components are considered as measurements, the measurements are linear. Longitudinal, lateral and vertical acceleration is measured by at least three accelerometers in the inertial measurement unit (3), which can be one of the strapdown or gimballed types which are located in the air vehicle, and orientation angles and angular velocities are measured by at least three gyroscopes. With the Kalman filter (5), the estimation of the next state is made based on the measurement valuesand estimation of the previous state . In the flight computer (4), the speed components according to the frame of the air vehicle obtained by the air data unit (2) are adjusted with the acceleration and angular velocities obtained with the inertial measurement unit (3), and the speed estimation is performed by inputting the adjusted speed data and the measurements of the inertial measurement unit (3) into the Kalman filter (5) loaded on the flight computer (4). Speed information of the air vehicle is obtained in real time by the global positioning unit (6) by receiving, by the receivers on the air vehicle, the coordinate and time information provided in uninterrupted signals which are sent to the earth from satellites located in the orbit of the earth in the form of a network.

The current speed value of the air vehicle is estimated by the Kalman filter (5) by using the previous estimated data of the air vehicle and the instantaneous speed data of the air vehicle measured by the air data unit (2) adjusted by the measurements of the inertial measurement unit (3). The speed data estimated by the Kalman filter (5) and the data of the global positioning unit (6) are statistically compared with the algorithm that performs the fault detection run by the flight computer (4), and it detects a defective situation in the data obtained by the global positioning unit (6). An error signal is generated by the flight computer (4) for the speed data detected to be defective, the reliability of the data coming from the channel through which the global positioning unit (6) making defective data measurement sends data are evaluated, the speed data of the air vehicle is calculated and the autopilot or similar flight critical modules are fed. Thus, in the event of a spoofing or jamming in the signals to the air vehicle, speed measurement data of the global positioning unit (6) for which a defective situation is detected will not be taken into consideration, and a stable and safe flight will be maintained for such cases. In the error detection structure, each speed signal obtained by the global positioning unit (6) is evaluated separately and a separate structure is created for error detection by comparing the individual signals.

In an embodiment of the invention, the navigation system (1) comprises a flight computer (4) which uses hypothesis test method as a statistical comparison method. Statistical calculations are made with the ratio of the difference between the instantaneous velocity data estimated with the Kalman filter (5) and the instantaneous velocity measurements obtained with the global positioning unit (6) to the square root of the total error variances of these measurement values, the limit values of the statistics are determined and the threshold value is selected by the user. With the two hypotheses generated, a defective state and a non-defective state in the speed data measured by the global positioning unit (6) can be detected. According to the statistical result, when the threshold value selected by the user is higher than the statistical calculation value, the speed data measured by that global positioner (6) is considered to be in the non-defective state, and when the threshold value is lower than the statistical value, the speed data is considered to be in the defective state. The threshold value can be updated by collecting flight data containing spoofing and/or jamming occurring in the global positioning unit (6).

In an embodiment of the invention, the navigation system (1) comprises a Kalman filter (5) using a dynamic model or a kinematic model. Kinematic model is used to identify the motion of the air vehicle. As a result of the motion of the air vehicle, the angular velocity measured by the inertial measurement unit (3) on the body frame is formed by the function of the change according to the roll, pitch and yaw. Dynamic model of the air vehicle is created by the connection between forces, energy and the motion of the air vehicle subjected to a force. The adjusted kinematic or dynamic model of the air vehicle can be used in Kalman filter (5).

In an embodiment of the invention, the navigation system (1) comprises a Kalman filter (5) which estimates wind speed components and air vehicle speed parameters according to the north-east-down (NED) frame. With the Kalman filter (5), the next state is estimated according to the previous state estimation and the measurement values.

In an embodiment of the invention, the navigation system (1) comprises an extended Kalman filter (501) which estimates speed based on measurements of the air data unit (2), comprises random walk wind model, and uses a kinematic model updated by using the data measured by inertial measurement unit (3). Extended Kalman filter (501) used as a state estimation method for the nonlinear state space model makes estimations according to the body frame-based data of the velocity data of the air vehicle obtained by the air data unit (2). A model written in stochastic process is required to estimate wind speed. Since the wind speed is random in nature, a random walk wind model is used to estimate the wind speed. The extended Kalman filter (501) uses the kinematic model updated by transferring the angular velocity and directional accelerations obtained by the inertial measurement unit (3) to the navigational plane (Figure-2). In an embodiment of the invention, the navigation system (1) comprises a flight computer (4) which converts the speed components estimated according to the air vehicle frame into a north-east-down (NED) frame in order to compare the estimated speed data with the speed data of the global positioning unit (6). The data measured by the global positioning unit (6) are according to the north-east-down (NED) frame. In order to implement the statistical comparison method performed to detect errors in the data measured by the global positioning unit (6), the velocity data must be fitted to the same frame. Therefore, the velocity data and wind velocity components obtained according to the body frame are converted into the north-east-down (NED) frame.

In an embodiment of the invention, the navigation system (1) comprises a flight computer (4) which converts the data of the global positioning unit (6) into the speed data of the air vehicle frame and statistically compares them with the estimated speed data. In order to compare the speed data, they must be converted into the same frame.

In an embodiment of the invention, the navigation system (1) comprises a global positioning unit (6) which is any of the satellite network types GPS, Galileo, GLONASS, COMPASS and QZSS that transmit information with signals. Data of the global positioning unit (6) belonging to different countries that are desired to be used in the air vehicle can be utilised.