WO2020240571A1

WO2020240571A1 - Method and system of gnss spoofing detection

Info

Publication number: WO2020240571A1
Application number: PCT/IL2020/050604
Authority: WO
Inventors: Erez Sharon
Original assignee: Israel Aerospace Industries Ltd.
Priority date: 2019-05-27
Filing date: 2020-05-26
Publication date: 2020-12-03
Also published as: IL266933B1; IL266933B2; IL266933A

Abstract

A method of GNSS-spoof detection comprises: receiving data indicative of candidate GNSS signal(s), broadcast by a respective GNSS satellite, the data constituting a reading; determining a view direction of antenna array(s) that received the candidate GNSS signal; determining a viewed angular sector of space associated with the antenna array, based at least on the view direction and on antenna array parameters; determining an expected angular position of the GNSS satellite(s); determining a deviation of the expected angular position from the viewed angular sector of space; comparing the deviation to a defined deviation threshold; and in response to the deviation exceeding the defined deviation threshold, determining that the reading is a suspicious reading, thereby enabling determination of at least one of time and object location without use of the suspicious reading.

Description

METHOD AND SYSTEM OF GNSS SPOOFING DETECTION

TECHNICAL FIELD

The presently disclosed subject matter relates to clock synchronization.

BACKGROUND

The term Global Navigation Satellite Systems (GNSS) refers in general to satellite navigation systems such as, for examples. Global Positioning System (GPS), Global Navigation Satellite System (GLONASS) and Galileo. GNSS systems comprise a plurality of satellites and of GNSS receivers. The GNSS receivers are typically configured for receiving incoming satellite signals broadcast by the satellites, and for calculating the position and velocity of a respective GNSS receiver, based on the received signals.

Satellites broadcast a signal that contains, inter alia, orbital data (ephemeris and almanac), which include information with regard to the precise time the signal was transmitted and from which the position and velocity of the satellites can be calculated. Each satellites uses an atomic clock to maintain synchroni zation of all the satellites in the constellation. The GNSS receiver calculates a pseudo-range to the satellites , ultimately enabling generation of a continual fix of its position and velocity, in real time.

In general a GNSS receiver is associated with a moving body (e.g. aircraft, ground vehicles, vessel, missile etc.) and is configured for determining navigation data (such as for example position and velocity) in respect of the moving body. Satellite navigation systems have become a major factor of transportation system worldwide, provide navigation for aviation, ground and marine operations, among other uses.

Notwithstanding their many advantages and uses, GNSS receivers are vulnerable to spoofing. Spoofing is a process which is aimed to feed a GNSS receiver false information, so that the receiver computes an erroneous time and/or location. As a result, the moving body or object which is associated with the GNSS receiver may deviate away from its intended course or destination. GENERAL DESCRIPTION

According to one aspect of the presently disclosed subject matter there is presented a method of GNSS-spoof detection, the method being performed by a processing circuitry^; and comprising:

a) receiving data indicative of at least one candidate GNSS signal, broadcast by a respective GNSS satellite, the data constituting a reading;

b) determining a view direction (e.g. line of sight) of at least one antenna array that received the at least one candidate GNSS signal;

c) determining a viewed angular sector of space associated with the at least one antenna array, based at least on the view direction and on antenna array parameters;

d) determining an expected angular position of the at least one GNSS satellite;

e) determining a deviation of the expected angular position from the viewed angular sector of space;

f) comparing the deviation to a defined deviation threshold; and g) in response to the deviation exceeding the defined deviation threshold, determining that the reading is a suspicious reading,

thereby enabling determination of at least one of time and object location without use of the suspicious reading.

In addition to the above features, the method according to this aspect of the presently disclosed subject matter can include one or more of features (i) to (xxxvii) listed below, in any desired combination or permutation which is technically possible:

(i) the at least one antenna array attached to an object

(ii) the step (b) further comprising obtaining an attitude of the object and an antenna array attitude with respect to the object, wherein the determining the view direction of each antenna array is based on at least the attitude of the object and the antenna array atitude with respect to the object. (iii) the object is a vehicle, wherein the attitude of the object comprises at least one at least one of vehicle pitch, vehicle yaw, and vehicle roll

(iv) the step (c) further comprises obtaining a position of the object, wherein the determining of the viewed angular sector of space is based on the position of the object.

(v) step (d) further comprises obtaining an almanac, wherein the determining of the expected angular position of the each GNSS satellite is based on the almanac.

(vi) step (g) further comprising sending to at least one GNSS receiver an instruction to ignore the suspicious reading.

(vii) the expected angular position and the viewed angular sector of space are expressed in a common reference frame.

(viii) each antenna array of the at least one antenna array comprises at least one antenna.

(ix) the at least one antenna array being directional,

wherein said step (f) further comprising obtaining a reception intensity of the at least one signal,

wherein the de viation threshold is based at least on a relationship between an expected reception intensity' of the at least one signal and on the reception intensity of the at least one signal .

(x) the expected reception intensity being based on an antenna radiation pattern associated with the at least one antenna array.

(xi) the method further comprising:

h) in response to the deviation not exceeding the defined deviation threshold, determ ining that the reading is a likely-valid reading.

(xii) the at least one antenna array comprises a plurality of antenna arrays, wherein each antenna array of the plurality of antenna arrays operatively coupled to a unique GNSS receiver of a plurality of GNSS receivers, wherein viewed angular sectors of space associated with each antenna array of the plurality of antenna arrays are not identical, wherein the data constituting a plurality of readings, each reading of the plurality of readings associated with a respective GNSS receiver of the plurality of GNSS receivers, the method further comprising:

i) classifying the at least one GNSS satellite, the classifying comprising: 1 . in response to a first part of the readings associated with the at least one GNSS satellite are likely-valid readings, associated with a first part of the plurality of antenna arrays, and a second part of the readings associated with the at least one GNSS satellite are suspect readings, associated with a second part of the plurality of antenna arrays, performing the following:

A. obtaining a reception intensity of at least one suspect reading of the some suspect readings, constituting a first reception intensity;

B. obtaining a reception intensity of at least one likely-valid reading of the some likely-valid readings, constituting a second reception intensity;

C. calculating a difference between the first reception intensity and the second reception intensity;

D. comparing the difference to a defined intensity difference threshold; and

E. in response to the difference being greater than the defined intensity difference threshold, the difference indicative of the first reception intensity being larger than the second reception intensity, classify the at least one GNSS satellite as a spoof- victim GNSS satellite,

thereby enabling calculation of at least one of time and object location without use of the spoof-victim GNSS satellite

(xiii) the defined intensity difference threshold being at least 10 dB.

(xiv) the step (1) further comprising:

F. in response to the difference not being greater than the defined intensity difference threshold, classify the at least one GNSS satellite as a suspect-spoof-victim GNSS satellite.

(xv) the step (i) further comprising:

2. in response to all of the readings associated with the each GNSS satellite are suspect readings, classify the at least one GNSS satellite as a spoof-victim GNSS satellite.

(xvi) the step (i) further comprising: 3. in response to all readings associated with the at least one GNSS satellite are likely-valid readings, classify the at least one GNSS satellite as a verified-valid GNSS satellite.

(xvii) the receiving of the data being from the at least one GNSS receiver.

(xviii) further comprising taking an action associated with the spoof detection.

(xix) the action comprises sending to the at least one GNSS receiver the instruction to ignore the suspicious readings.

(xx) the action comprises sending to the at least one GNSS receiver an instruction to ignore readings associated with the each spoof- victim GNSS satellite.

(xxi) the action comprises sending to the at least one GNSS receiver an instruction to utilize readings associated with the each verified- valid GNSS satellite.

(xxii) the action further comprising determining, based at least on the verified- valid GNSS satellite, at least one of: the position of the object and an indication of time.

( xxiii ) the action comprising reporting to at least one other system reported information indicative of at least one of: the at least one suspect reading, the each spoof-victim GNSS satellite, the each suspect-spoof-victim GNSS satellite.

(xxiv) the action further comprising reporting to the at least one other system viewed angular sectors of space associated with the each spoof-victim GNSS satellite.

(xxv) the action further comprising reporting, to the at least one other system, at least one set of object false position coordinates associated with the each spoof-victim GNSS satellite.

(xxvi)the action further comprising reporting, to the at least one other system, at least one object false time measurement associated with the each spoof-victim GNSS satellite.

(xxvii) the first reception intensity and the second reception intensity being provided by the at least one GNSS receiver.

(xxviii) the first reception intensity and the second reception intensity comprise a Signal to Noise Ratio (SNR).

(xxix)the Signal to Noise Ratio (SNR) range from 0 to 99.

(xxx) the defined intensity difference threshold being at least 15 dB.

(xxxi)the defined intensity difference threshold being at least 30 dB. (xxxii) at least a part of the viewed angular sectors of space overlap

(xxxiii) at least a part of the viewed angular sectors of space do not overlap.

(xxxiv) the viewed angular sectors of space differ by at least 20 degrees

(xxxv) the viewed angular sectors of space differ by at least 30 degrees

(xxxvi) the viewed angular sectors of space differ by at least 45 degrees

(xxxvii) the at least one antenna array comprises a plurality of antenna arrays, wherein the plurality of antenna arrays operatively coupled to at least one GNSS receiver, wherein the at least one GNSS receiver receives antenna signals from each antenna array of the plurality of antenna arrays based on a duty cycle, wherein viewed angular sectors of space associated with each antenna array of the plurality of antenna arrays are not identical, wherein the data constituting a plurality of readings, each reading of tire plurality of readings associated with a respective GNSS receiver of the plurality of GNSS receivers, the method further comprising:

j) classifying the at least one GNSS satellite, the classifying comprising:

1. in response to a first part of the readings associated with the at least one GNSS satellite are likely-valid readings, associated with a first part of the plurality of antenna arrays, and a second part of the readings associated with the at least one GNSS satellite are suspect readings, associated with a second part of the plurality of antenna arrays, performing the following:

G. obtaining a reception intensity of at least one suspect reading of the some suspect readings, constituting a first reception intensity;

H. obtaining a reception intensity of at least one likely-valid reading of the some likely-valid readings, constituting a second reception intensity;

I. calculating a difference between the first reception intensity and the second reception intensity;

J. comparing the difference to a defined intensity difference threshold; and

K. in response to the difference being greater than the defined intensity difference threshold, the difference indicative of the first reception intensity being larger than the second reception intensity, classify the at least one GNSS satellite as a spoof- victim GNSS satellite,

thereby enabling calculation of at least one of time and object location wi thout use of the spoof-victim GNSS satellite.

According to another aspect of the presently disclosed subject mater there is presented a method of GNSS-spoof detection, the method being performed by a processing circuitry' and comprising:

i. receiving data indicative of at least one candidate GNSS signal, broadcast by a respective GNSS satellite, the data constituting a plurality of readings;

ii. determining a view' direction of at least one antenna array that received the at least one candidate GNSS signal,

wherein the at least one antenna array comprises a plurality of antenna arrays, wherein each antenna array of the plurality of antenna arrays operatively coupled to a unique GNSS receiver of a plurality of GNSS receivers, wherein viewed angular sectors of space associated with each antenna array of the plurality of antenna arrays are not identical, wherein each reading of the plurality of readings associated with a respective GNSS receiver of the plurality of GNSS receivers;

iii. determining a viewed angular sector of space associated with the at least one antenna array, based at least on the view direction and on antenna array parameters;

i v. determining an expected angular position of the at least one GNSS satellite;

v. determining a deviation of the expected angular position from the viewed angular sector of space;

vi. comparing the deviation to a defined deviation threshold; and vii. in response to the deviation exceeding the defined deviation threshold, determining that the reading is a suspicious reading;

viii. in response to the deviation not exceeding the defined deviation threshold, determining that the reading is a likely-valid reading;

ix. classifying the at least one GNSS satellite, the classifying comprising: 1 . in response to a first part of the readings associated with the at least one GNSS satellite are likely-valid readings, associated with a first part of the plurality of antenna arrays, and a second part of the readings associated with the at least one GNSS satellite are suspect readings, associated with a second part of the plurality of antenna arrays, performing the following:

D. comparing the difference to a defined intensity difference threshold; and

thereby enabling calculation of at least one of time and object location without use of the spoof-victim GNSS satellite.

This aspect of the disclosed subject matter can optionally include one or more of features (i) to (xxxvii) listed above, mutatis mutandis, in any desired combination or permutation which is technically possible.

In addition to the above features, the method according to the above aspects of the presently disclosed subject matter can include one or more of features (xxxviii) to (xlix) listed below, in any desired combination or permutation which is technically possible:

(xxxviii) the object is stationary.

(xxxix) the obj ect is a vehicle. (xi) the vehicle is least one of an airborne vehicle, a balloon, a ground vehicle, and a water-borne vehicle.

(xli) the at least one antenna comprises one antenna.

(xlii) the at least one antenna comprises a plurality of antennas.

(xliii) further comprising repeating the method at least once.

(xliv) wherein an interval between the repetitions is less than or equal to 1/10 second.

(xlv) wherein an interval between the repetitions is less than or equal to 1 second.

(xlvi) the at least one antenna array being in a fixed spatial attitude with respect to the object.

(xlvii) the at least one antenna array being capable of changing a spatial antenna array orientation with respect to the

(xlviii) the determining of the expected angular position of the each GNSS satellite is based at least on satellite identification information associated with the at least one signal.

(xlix) the satellite identification information comprises a satellite Pseudo Random Number (PRN) code.

According to another aspect of the presently disclosed subject matter there is provided a non-transrtory program storage device readable by machine, tangibly embodying a program of instructions executable by the machine to perform any of the above methods of GNSS spoof detection.

According to another aspect of the presently disclosed subject matter there is provided a non GNSS-spoof detection system, a processing circuitry of the GNSS-spoof detection system configured to perform any of the above methods of GNSS spoof detection.

The systems, and the non-transitory computer readable storage media disclosed herein according to various aspects, can optionally further comprise one or more of features (i) to (xlix) listed above, mutatis mutandis, in any technically possible combination or permutation. BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it can be earned out in practice, embodiments will be described, by way of non-limiting examples, with reference to the accompanying drawings, in which:

Figs. 1A and 1B schematically illustrate an example generalized view of an object with antenna arrays, in accordance to some embodiments of the presently disclosed subject matter;

Fig. 1C schematically illustrates an example generalized view of a viewed angular sector of space, in accordance to some embodiments of the presently disclosed subject matter:

Fig. 1D schematically illustrates an example generalized view of an antemra array, in accordance to some embodiments of the presently disclosed subject matter.

Fig. 1E schematically illustrates an example generalized view of antenna arrays, in accordance to some embodiments of the presently disclosed subject matter;

Fig. 2 schematically illustrates an example of certain features of the presently disclosed subject mater

Fig. 3A schematically illustrates an example generalized view of spoofing, in accordance to some embodiments of the presently disclosed subject matter;

Fig. 3B schematically illustrates an example generalized view of spoofing, in accordance to some embodiments of the presently disclosed subject matter;

Fig, 3C and 3D schematically illustrate an example generalized view of antenna array directionality, in accordance to some embodiments of the presently disclosed subject mater; Fig. 4 schematically illustrates an example generalized view of a schematic diagram of a spoof detection system, in accordance to some embodiments of the presently disclosed subject matter;

Fig. 5 schematically illustrates an example generalized view of a schematic diagram of a processor, in accordance to some embodiments of the presently disclosed subject matter;

Fig, 6A and 6B schematically illustrate an example generalized view of a flow for spoof detection, in accordance to some embodiments of the presently disclosed subject mater;

Fig. 7 schematically illustrates a method for classifying readings, in accordance to some embodiments of the presently disclosed subject matter;

Fig. 8 schematically illustrates a method for classifying satellites, in accordance to some embodiments of the presently disclosed subject matter.

DETAILED DESCRIPTION

In the drawings and descriptions set forth, identical reference numerals indicate those components that are common to different embodiments or configurations.

In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the presently disclosed subject matter may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the presently disclosed subject mater.

It is to be understood that tire invention is not limited in its application to the details set forth in the description contained herein or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and earned out in various ways. Hence, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for designing other structures, methods, and systems for carrying out the several purposes of the presently disclosed subject matter.

It will also be understood that the system according to the invention may be, at least partly, implemented on a suitably programmed computer. Likewise, the invention contemplates a computer program being readable by a computer for executing the method of the invention. The invention further contemplates a non-transitory computer-readable memory tangibly embodying a program of instructions executable by the computer for executing the method of the invention.

Those skilled in the art will readily appreciate that various modifications and changes can be applied to the embodiments of the invention as hereinbefore described without departing from its scope, defined in and by the appended claims.

Unless specifically stated otherwise, as apparent from the following discussions, it is appreciated that throughout the specification discussions utilizing terms such as "receiving", "identifying", "generating",“associating” or the like, refer to the action(s) and/or process(es) of a computer that manipulate and/or transform data into other data, said data represented as physical, e.g. such as electronic or mechanical quantities, and/or said data representing the physical objects.. The term“computer” should be expansively construed to cover any kind of hardware-based electronic device with data processing capabilities including a personal computer, a server, a computing system, a communication device, a processor or processing unit (e.g. digital signal processor (DSP), a microcontroller, a microprocessor, a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), etc.), and any other electronic computing device, including, by way of non-limiting example, clock synchronization system 600 and processing circuitry 430 disclosed in the present application.

The operations in accordance with the teachings herein may be performed by a computer specially constructed for the desired purposes, or by a general-purpose computer specially configured for the desired purpose by a computer program stored in a non-transitory computer-readable storage medium.

Embodiments of the presently disclosed subject matter are not described with reference to any particular programming language. It will be appreciated that a variety of programming languages may be used to implement the teachings of the presently- disclosed subject matter as described herein.

The terms "non-transitory memory" and“non-transitory storage medium” used herein should be expansively construed to cover any volatile or non-volatile computer memory suitable to the presently disclosed subject matter.

The operations in accordance with the teachings herein may be performed by a computer specially constructed for the desired purposes or by a general-purpose computer specially configured for the desired purpose by a computer program stored in a non- transitory computer-readable storage medium.

As used herein, the phrase "for example," "such as", "for instance" and variants thereof describe non-limiting embodiments of the presently disclosed subject mater. Reference in the specification to "one case", "some cases", "other cases", "one example", "some examples", "oilier examples" or variants thereof means that a particular described method, procedure, component, structure, feature or characteristic described in connection with the embodiment(s) is included in at least one embodiment of the presently disclosed subject matter, but not necessarily in all embodiments. The appearance of the same term does not necessarily refer to the same embodiment(s) or example(s).

Usage of conditional language, such as“may”,“might”, or variants thereof should be construed as conveying that one or more examples of the subject mater may include, while one or more other examples of the subject matter may not necessarily include, certain methods, procedures, components and features. Thus such conditional language is not generally intended to imply that a particular described method, procedure, component or circuit is necessarily included in all examples of the subject mater. Moreover, the usage of non-conditional language does not necessarily imply that a particular described method, procedure, component or circuit is necessarily included in all examples of the subject matter.

It is appreciated that certain embodiments, methods, procedures, components or features of the presently disclosed subject matter, which are, for clarity, described in the context of separate embodiments or examples, may also be provided in combination in a single embodiment or examples. Conversely, various embodiments, methods, procedures, components or features of the presently disclosed subject matter, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

It should also be noted that each of the figures herein, and the text discussion of each figure, describe one aspect of the presently disclosed subject matter in an informative manner only, by way of non-limiting example, for clarity of explanation only. It will be understood that that the teachings of the presently disclosed subject matter are not bound by what is described with reference to any of the figures or described in other documents referenced in this application.

Bearing this in mind, attention is drawn to Figs. 1A and 1B, schematically illustrating an example generalized view of an object with antenna array s, in accordance to some embodiments of the presently disclosed subject mater in the figure, the object 110 is the non-limiting example of a vehicle, specifically an aircraft 110. In the example, the object has mounted on it, or otherwise attached to it, four arrays of GNSS antennas -- 120 on the top, 130 on the bottom, 125 on the left side and 135 on the right side. These antenna arrays serve as the examples in the following figures. In general, one or more antenna arrays may be attached to the object. Note that in the example, they do not all pointin the same view direction.

In some examples, the object is stationary, e.g. a building. In such a case, GNSS might be used for time determination only, since the building position does not change. Examples of a vehicle include an airborne vehicle, a balloon, a ground vehicle, and a water-borne vehicle. Attention is drawn to Fig. 1C, schematically illustrating an example generalized view of a viewed angular sector of space, in accordance to some embodiments of the presently disclosed subject mater. Object (aircraft) 110 has antenna array 120 with a view direction 170 In some examples, view direction 170 is a line of sight 170 The GNSS satellites sit in space, surrounding the earth, and they sit in a portion of space having roughly a globe shape, denoted schematically by 160. The array receives GNSS signals not only from direction 170, but also from satellites located at certain angles off of 170. This is denoted in the example by an ellipsoid 180, referred to herein also as a viewed angular sector of space.

Attention is drawn to Fig. 1D, schematically illustrating an example generalized view of an antenna array, in accordance to some embodiments of the presently disclosed subject matter. An antenna can comprise one or more antennas. In the example are shown three antennas, each pointed in a different direction. All the antennas of the array are connected to one GNSS receiver, not shown. In the example, each antenna has a viewed angular sector of space 30 degrees, and the array as a whole has a viewed angular sector of space of 90 degrees.

Attention is drawn to Fig. 1E, schematically illustrating an example generalized view of antenna arrays, in accordance to some embodiments of the presently disclosed subject matter. In the example, two antenna arrays 120 and 122 have overlapping viewed angular sector of space, where the overlap is the angle E. Satellite 5 is located in the overlapping portion. If E > 0 , there is overlap. If E==0, there is no overlap. If E < 0, there is no overlap, and there is a gap in the view of space, e.g. neither antenna array will see satellite 5. In some examples, the viewed angular sectors of space differ by at least 20 degrees. In some examples, the viewed angular sectors of space differ by at least 30 degrees. In some examples, the viewed angular sectors of space differ by at least 45 degrees.

Attention is drawn to Fig, 2, schematically illustrating an example generalized view' of spoofing, in accordance to some embodiments of the presently disclosed subject matter. The example shows an aerial view 200 of object 110, with a heading phi shown relative to North. This is a yaw angle, in some examples. Real GNSS satellites S 1, S2, S3, S5 are shown. Antenna array 135 has a viewed angular sector of space of Eta. S 1 is located at an expected angular position alpha from North. Since it falls within the viewed angular sector associated with 135, it is expected that 135 will receive GNSS signals from S I, as well as from S2. If 135 receives signals from S3 and S5, not located within its viewed angular sector of space, it might be that the S3 and S5 signals are in fact sent by spoofers, indicated in the figure by Fake S3 and Fake S5.

Attention is drawn to Fig. 3A, schematically illustrating an example generalized view of spoofing, in accordance to some embodiments of the presently disclosed subject matter. The example shows a side view 300 of object 310, a ground vehicle. Real GNSS satellite S5 are shown. Antenna array 320 has a viewed angular sector of space of Rho. S5 is located at an expected angular position beta from the horizontal. Since it falls within the viewed angular sector associated with 320, it is expected that 320 will receive GNSS signals from S5, as well as from S2. Note that in general, the expected angular position can be expressed in terms of Azimuth and Elevation.

Attention is drawn to Fig. 3B, schematically illustrating an example generalized view of spoofing, in accordance to some embodiments of the presently disclosed subject matter. Tire example shows a side view 350 of object 110, an aircraft. Unlike the ground vehicle 310, aircraft 110 is also capable of pitch theta. Real GNSS satellites S1, S2, S3, S4, S5 are shown. Antenna array 120 has a viewed angular sector of space of gamma. SI, S4 and S5 all fall within the viewed angular sector associated with 120, so it is expected that 135 will receive GNSS signals from them. If 135 receives signals from S3 and S2, not located within its viewed angular sector of space, it might be that the S3 and S2 signals are in fact sent by spoofers, indicated in the figure by Fake S3 and Fake S2. Similarly, if antenna array 130 receives signals from SI , it might be that the S1 signals are in fact sent by spoofers, indicated in the figure by Fake S I.

Note that aircraft 110 is capable also of roll, but this angle is not shown for simplicity of exposition. The view direction of the antenna arrays, and thus the viewed angular sector of space, would in such a case take into account the roll as well.

Note that there are advantages to detecting those signals that are likely spoofed, and those satellites which are being spoofed. This knowledge can, for example, he used to ensure that GNSS-based location and/or time calculations make use of only known- valid readings and/or verified-valid satellites. In other examples, this knowledge can be used to ensure that GNSS-based location and/or time calculations do not make use of suspicious readings and/or verified-spoofed satellites. In some examples, a first method of spoof detection is to determine the view direction 170 of the antenna array 120, and based on that and on antenna parameters (e.g. as disclosed with reference to Figs. 3C and 3D), determine a viewed angular sector of space (e.g. start-rho to end-rho, and start-gamma to end-gamma, in the figures) associated with the antenna array 320, 120. An expected angular position (e.g. alpha, beta) of each relevant GNSS satellite is determined, using for example almanac and ephemeris data. This data can be received from external systems, e.g. the Internet, or can be received as part of the candidate GNSS signals.

The detection system will then determine whether the expected angular position is within the viewed angular sector of space. For example, it will determine a deviation of the expected angular position from the viewed angular sector of space, and then compare the deviation to a defined deviation threshold. If the deviation exceeds the defined deviation threshold, the system determines that the reading is a suspicious reading. Else it determines that the reading is a likely-valid reading. More detail is disclosed with reference to Figs. 6A, 6B and 7.

In an second example method, the detection system looks at different readings, from different antenna arrays, associated with the same satellite, and looks at their intensities. More detail is disclosed with reference to Figs. 6 A, 6B and 8.

Attention is drawn to Fig. 3C and 3D, schematically illustrating an example generalized view of antenna array directionality, in accordance to some embodiments of the presently disclosed subject matter. Graph 370 represents gain of signals received by an omni antenna array. The intensity of the received GNSS signals will be the same from all angles. Graph 380 represents gain of signals received by a directional antenna array. The intensity of the received GNSS signals vary based on the angle. In the example of 380, a signal received from angle 270, relative to the view direction of the antenna array 120, will be received with a gain of approximately -4.5 dB, compared to a signal received from angle 0. In some examples, the expected reception intensity of the signal is associated with the directionality of the antenna, and this expected intensity- may he utilized to detect spoofing, as disclosed further herein.

Attention is drawn to Fig. 4, schematically illustrating an example generalized view of a schematic diagram of a spoof detection system, in accordance to some embodiments of the presently disclosed subject matter. The spoof detection system 420 comprises a processing circuitry 430, which may be, in non-limiting examples, general- purpose computers specially configured for the desired purpose by a computer program stored in a non-transitory computer-readable storage medium. They may be configured to execute several functional modules in accordance with computer-readable instructions. In other non-limiting examples, the processing circuitry may be computers specially constructed for the desired purposes. The processing circuitry may comprise a processor 432, also referred to herein as a central processing unit, and a memory 434.

The processor 432 may be operatively coupled 447 to one or more GNSS receivers. Each GNSS receiver is operatively coupled 437 to antenna arrays 120, 125, 130, 135, shown here as each comprising one antenna. The antenna arrays receive 1 18 candidate GNSS signal(s). Each candidate GNSS signal is broadcast 115 by a real GNSS satellite, or broadcast 112 by a fake (spoofed) GNSS satellite. The processor receives 447 from each GNSS receiver data indicative of one or more candidate GNSS signals -- this data is referred to herein also as a reading. Each GNSS receiver has its respective readings, per respective candidate GNSS signal.

The processor 432 also receives information from other systems about the attitude 480 of the object, e.g. yaw, roll and pitch of a vehicle. It also is operatively coupled to external systems 490, which in some examples send it tire GNSS almanac. It can also send alerts and other information to these external systems 490. The almanac may be stored 445 in a storage 440 of the spoof detection system 420.

The Memory_'· 434 may in some examples store data derived during the processing of received data, and used by the various processing stages.

Attention is drawn to Fig, 5, schematically illustrating an example generalized view of a schematic diagram of a processor 432, in accordance to some embodiments of the presently disclosed subject matter. The processor may comprise at least one or more function modules. In some examples it may perform at least functions, such as those disclosed further herein. Example modules are shown in the figure. Note that the modules can be implemented in hardware, software and/or firmware.

Figs. 4 and 5 illustrate only a general schematic of the system architecture, describing, by way of non-limiting example, certain aspect of the presently disclosed subject matter in an informative manner only, for clarity of explanation only. It will be understood that that the teachings of the presently disclosed subject matter are not bound by what is described with reference to Figs. 4 and 5. Only certain components are shown, as needed to exemplify the presently disclosed subject mater. Other components and sub-components, not shown, may exist. Systems such as those described with respect to the non-limiting examples of Figs. 4 and 5, may be capable of performing all, some, or parts of the methods disclosed herein.

Each system component and module in Figs. Figs. 4 and 5 can be made up of any combination of software, hardware and/or firmware, as relevant, executed on a suitable device or devices, which perform the functions as defined and explained herein. The hardware can be digital and/or analog. Equivalent and/or modified functionality, as described with respect to each system component and module, can be consolidated or divided in another manner. Thus, in some embodiments of the presently disclosed subject matter, the system may include fewer, more, modified and/or different components, modules and functions than those shown in Figs. 4 and 5.

One or more of these components and modules can be centralized in one location or dispersed and distributed over more than one location.

Each component in Figs. 4 and 5 may represent a plurality of the particular component, possibly in a distributed architecture, which are adapted to independently and/or cooperatively operate to process various data and electrical inputs, and for enabling operations related to damage detection and verification in some cases multiple instances of a component, may be utilized for reasons of performance, redundancy and/or availability. Similarly, in some cases, multiple instances of a component may be utilized for reasons of functionality or application. For example, different portions of the particular functionality may be placed in different instances of the component. Those skilled in the art will readily appreciate that the components of the system can be consolidated or di vided in a manner other than that disclosed herein.

The communication between the various components of the systems of Figs. 4 and 5, in cases where they are not located entirely in one location or in one physical component, can be realized by any signaling system or communication components, modules, protocols, software languages and drive signals, and can be wired and/or wireless, as appropriate.

Attention is drawn to Figs. 6A and 6B, schematically illustrating an example generalized view of a flow for spoof detection, in accordance to some embodiments of the presently disclosed subject matter. This process may be performed by the processing circuitry of Fig. 4. In some examples, the process includes:

a) receiving data indicative of at least one candidate GNSS signal, broadcast by a respective GNSS satellite, the data constituting a plurality of readings;

b) determining a view direction 170 antenna array(s) that received the at least one candidate GNSS signal,

c) determining a viewed angular sector of space associated with the at least one antenna array, based at least on the view' direction and on antenna array parameters;

d) determining an expected angular posi tion of the at least one GNSS satellite;

e) determining a deviation of the expected angul ar position from the viewed angular sector of space;

f) comparing the deviation to a defined deviation threshold; and g) in response to the deviation exceeding the defined deviation threshold, determining that the reading is a suspicious reading;

h) in response to the deviation not exceeding the defined deviation threshold, determining that the reading is a likely-valid reading;

i) classifying the at least one GNSS satellite, the classifying comprising:

1. in response to a first part of the readings associated with the at least one GNSS satellite are likely-valid readings, associated with a first part of tire plurality of antenna arrays, and a second part of die readings associated with the at least one GNSS satellite are suspect (i.e. suspicious) readings, associated with a second part of the plurality of antenna arrays, performing the following:

F. obtaining a reception intensity of at least one suspect reading of the some suspect readings, constituting a first reception intensity;

G. obtaining a reception intensity of at least one likely -valid reading of the some likely-valid readings, constituting a second reception intensity;

H. calculating a difference between the first reception intensity and the second reception intensity;

I. comparing the difference to a defined intensity_' difference threshold; and

j. in response to the difference being greater than the defined intensity difference threshold, the difference indicative of the first reception intensity being larger than the second reception intensity, classify the at least one GNSS satellite as a spoof- victim GNSS satellite,

Note that the terms "suspicious" and "suspect" readings are used herein interchangeably.

Note, regarding block 715, that one implementation, non-limiting, is to create a list of candidate GNSS signals received by each antenna array. The list may include Satellite ID info, and received power information associated with the signal. Examples of satellite identification information include a satellite Pseudo Random Number (PRN) code .

Note, regarding 724, that in some examples the system is obtaining an attitude of the object (e.g. yaw , pitch and roll angles) and an antenna array attitude with respect to the object, and determining the view direction of each antenna array is based on at least the atitude of the object and the antenna array atitude with respect to the object.

Note also, that the antenna array(s) may be in a fixed spatial attitude with respect to the object, e.g. in a fixed mounting; or alternatively, the antenna array(s) may be capable of changing a spatial antenna array orientation or tilt with respect to the object. This will affect the calculation of the view direction 170 Known trigonometric transformations can be performed, for example.

Note, regarding 726, that in some examples, determining the viewed angular sector 170 of space further comprises obtaining a position of the object, and determining of the viewed angular sector of space is based on the position of the object. For example, an airplane over Australia should see a different sector of space, and thus different GNSS satellites, than an airplane over Canada.

In block 743, in some examples the expected angular position and the viewed angular sector of space are expressed in a common reference frame, for ease of comparison and calculation. Also, in some examples, where an antenna array being directional, the system obtains a reception intensity of the candidate GNSS signal, and the deviation threshold is based at least on a relationship between the expected reception intensity of the signal and on the reception intensity of the signal Thus, looking at graph of antenna radiation pattern 380, if the expected angular position of the satellite is 270 degrees, but the viewed angular sector of space is for example 280 degrees, the satellite may be considered to deviate within the threshold, if the received signal intensity is for example -12 dB, at or lower than the expected reception intensity of -4.5 dB associated with that angle.

Note that in blocks 750 and 755, "processed" refers to performing the blocks 740, 743, 745 and 747.

As indicated above, example criteria for step 760 include: in response to a first part of the readings associated with the at least one GNSS satellite are likely-valid readings, associated with a first part of the plurality of antenna arrays, and a second part of the readings associated with the at least one GNSS satellite are suspect (i.e. suspicious) readings, associated with a second part of the plurality of antenna arrays, performing the following:

K. obtaining a reception intensity of at least one suspect reading of the some suspect readings, constituting a first reception intensity;

L. obtaining a reception intensity of at least one likely-valid reading of the some likely -valid readings, constituting a second reception intensity; M. calculating a difference between the first reception intensity and the second reception intensity;

N. comparing the difference to a defined intensity_' difference threshold; and

O. in response to the difference being greater than the defined intensity difference threshold, the difference indicative of the fi rst reception intensity being larger than the second reception intensity, classify the at least one GNSS satellite as a spoof- victim GNSS satellite,

L. in response to the difference not being greater than the defined intensity difference threshold, classify the at least one GNSS satellite as a suspect-spoof-victim GNSS satellite.

M. in response to tire difference not being greater than the defined intensity difference threshold, classify the at least one GNSS satellite as a suspect-spoof-victim GNSS satellite.

Similarly, in response to all of the readings associated with the each GNSS satellite are suspect readings, the system may classify the at least one GNSS satellite as a spoof-victim GNSS satellite In response to all readings associated with the at least one GNSS satellite are likely-valid readings, , the system may classify the at least one GNSS satellite as a verified-valid GNSS satellite.

The various actions of block 770 are optional. The system can report some of the disclosed information, or not at all. In some cases, the reported information allows the external system, for example a control center, to better understand the nature of the spoof, in terms of: from which direction is it coming, which satellites are being spoofed, what misin formation is the spoofer attempting to provide (e.g. what erroneous position and/or time does the spoofer want the object to think are the actual ones). For example, the detection system can report reported information indicative of at least one of: the at least one suspect reading, the each spoof-victim GNSS satellite, the each suspect-spoof-victim GNSS satellite. For example: reporting viewed angular sectors of space associated with each spoof-victirn GNSS satellite; reporting at set(s) of object false position coordinates associated with each spoof-victim GNSS satellite; reporting object false time measurement(s) associated with each spoof-victim GNSS satellite In some examples, the spoof detection system resides in the GNSS receiver, and thus the system communicates with itself regarding which readings and satellites to consider and ignore, when calculating position and/or time. In some examples, the detection system is separate from the receivers, but the system performs the position and time calculations based on the relevant readings --- for example using vehicle position determination module 550.

Note that this flow is only a non-limiting example. In other examples, all antenna arrays and/or GNSS satellites are considered in parallel.

In the example flow, the processed is performed once. In other examples, spoofing detection is performed more than once, e.g. repeatedly. In some examples, an interval between the repetitions is less than or equal to 1/10 second. In some examples, an interval between the repetitions is less than or equal to 1 second.

The above disclosure is for a case where each antenna array is associated with a unique GNSS receiver. In another example, at least some of the antenna arrays are connected to a single GNSS receiver, but that GNSS receiver receives antenna signals from each of those antenna arrays based on a duty cycle.

Attention is drawn to Fig. 7, schematically illustrating a method for classifying readings, in accordance to some embodiments of the presently disclosed subject matter. Table 700 shows example readings received by the four antenna arrays of Figs. 1 A and IB. For each reading, there is shown the receiving antenna array, the satellite ID and the received power or intensity. The power is expressed her as SNR, on a scale of 0-100. The fourth column show's whether the satellite is expected to be in the relevant viewed angular sector, based for example on the determination of 743. In the case where the satellite is not expected in the sector, result # 1 shows a classification of the reading as a suspect reading. Where the satellite is expected in the sector, result #1 show's a classification of the reading as a likely-valid reading, abbreviated in the table as "valid".

Note also that the GNSS receivers may send a reading for all satellites in view' per the almanac, though some may have 0 power. For simplicity, readings with 0 power are deleted from tables 700 and 800.

Attention is drawn to Fig. 8, schematically illustrating a method for classifying satellites, in accordance to some embodiments of the presently disclosed subject matter. Table 800 shows example the same readings received by the four antenna arrays, as seen in Table 700, but grouped by satellite. Based on a comparison of likely-valid and suspect readings per satellite, and based on a comparison of reception intensities for each such reading, the satellite is classified as a spoof-victim satellite, suspect-spoof-vietim (i.e. suspect, unknown) satellite, and verifled-valid satellite. More disclosure is presented with reference to Figs. 6.

Note that Figs. 7 and 8 visualize the determinations by means of tables, for simplicity of exposition. This is one non-limiting implementation.

In some embodiments, one or more steps of the various flowcharts exemplified herein may be performed automatically. The flow and functions illustrated in the various flowchart figures may for example be implemented in system 420 or processing circuitry 430, and may make use of components described with regard to Figs. 4 and 5.

It is noted that the teachings of the presently disclosed subject matter are not bound by the flowcharts illustrated in the various figures. The operations can occur out of the illustrated order. Similarly, some of the operations or steps can be integrated into a consolidated operation, or can he broken down to several operations, and/or other operations may be added.

It is also noted that whilst the flowchart is described with reference to system elements that realize steps, such as for example system 420 and processing circuitry 430, this is by no means binding, and the operations can be performed by elements other than those described herein.

In embodiments of the presently disclosed subject matter, fewer, more and/or different stages than those shown in the figures can be executed. In embodiments of the presently disclosed subject matter one or more stages illustrated in the figures can be executed in a different order and/or one or more groups of stages may be executed simultaneously.

In the claims that follow , alphanumeric characters and Roman numerals used to designate claim elements are provided for convenience only, and do not imply any particular order of performing the elements.

It should be noted that the word "comprising” as used throughout the appended claims is to be interpreted to mean“including but not limited to”.

While there has been shown and disclosed examples in accordance with the presently disclosed subject matter, it will be appreciated that many changes may be made therein without departing from the spirit of the presently disclosed subject mater. It is to be understood that the presently disclosed subject matter is not limited in its application to the details set forth in the description contained herein or illustrated in the drawings. The presently disclosed subject matter is capable of other embodiments and of being practiced and carried out in various ways. Hence, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for designing other structures, methods, and systems for earning out the several purposes of the present presently disclosed subject matter.

It will also be understood that the system according to the presently disclosed subject matter may be, at least partly, a suitably programmed computer. Likewise, the presently disclosed subject matter contemplates a computer program product being readable by a machine or computer, for executing the method of the presently disclosed subject matter or any part thereof. The presently disclosed subject mater further contemplates a non-transitory machine-readable or computer-readable memory tangibly embodying a program of instructions executable by the machine or computer for executing the method of the presently disclosed subject mater or any part thereof. The presently disclosed subject mater further contemplates a non -transitory computer readable storage medium having a computer readable program code embodied therein, configured to be executed so as to perform the method of the presently disclosed subject mater.

Claims

CLAIMS:

1, A method of GNSS-spoof detection, the method being performed by a processing circuitry and comprising:

a) receiving data indicative of at least one candidate GNSS signal, broadcast by a respective GN SS satellite, the data constituting a reading:

b) determining a view direction of at least one antenna array that received the at least one candidate GNSS signal;

e) determining a viewed angular sector of space associated with the at least one antenna array, based at least on the view direction and on antenna array parameters;

d) determining an expected angular position of the at least one GNSS satellite;

2. The method of the previous claim, wherein the at least one antenna array attached to an object,

wherein the step (b) further comprising obtaining an attitude of the object and an antenna array attitude with respect to the object, wherein the determining the view direction of each antenna array is based on at least the attitude of the object and the antenna array attitude with respect to the object.

3. The method of the previous claim, wherein the object is a vehicle, wherein the attitude of the object comprises at least one at least one of vehicle pitch, vehicle yaw, and vehicle roll.

4. The method of any one of claims 1 to 3, wherein the step (c) further comprises obtaining a position of the object, wherein the determining of the viewed angular sector of space is based on the position of the object.

5. The method of any one of claims 1 to 4, wherein the step (d) further comprises obtaining an almanac, wherein the determining of the expected angular position of the each GNSS satellite is based on the almanac.

6. The method of any one of claims 1 to 5, wherein said step (g) further comprising sending to at least one GNSS receiver an instruction to ignore the suspicious reading.

7. The method of any one of claims 1 to 6, wherein the expected angular position and the viewed angular sector of space are expressed in a common reference frame.

8. The method of any one of claims 1 to 7, wherein each antenna array of the at least one antenna array comprises at least one antenna

9. The method of any one of claims 1 to 8, wherein the at least one antenna array being directional,

wherein the deviation threshold is based at least on a relationship between an expected reception intensity of the at least one signal and on the reception intensity of the at least one signal .

10. The method of the previous claim, wherein the expected reception intensity being based on an antenna radiation pattern associated with the at least one antenna array.

11. The method of any one of claims 1 to 10, further comprising: h) in response to the deviation not exceeding the defined deviation threshold, determ ining that the reading is a likely-valid reading.

12. Tire method of claim 11, wherein the at least one antenna array comprises a plurality of antenna arrays, wherein each antenna array of the plurality of antenna arrays operatively coupled to a unique GNSS receiver of a plurality of GNSS receivers, wherein viewed angular sectors of space associated with each antenna array of the plurality of antenna arrays are not identical, wherein the data constituting a plurality of readings, each reading of the plurality of readings associated with a respective GNSS receiver of the plurality of GNSS receivers, the method further comprising:

i) classifying the at least one GNSS satellite, the classifying comprising:

1 . in response to a first part of the readings associated with the at least one GNSS satellite are likely-valid readings, associated with a first part of the plurality of antenna arrays, and a second part of the readings associated with the at least one GNSS satellite are suspicious readings, associated with a second part of the plurality' of antenna arrays, performing the following:

A. obtaining a reception intensity of at least one suspicious reading of the suspicious readings, constituting a first reception intensity;

D. comparing the difference to a defined intensity difference threshold; and

13, The method of the pre vious claim, wherein the defined intensity difference threshold being at least 10 dB

14, The method of one of claims 12 to 13, wherein the step (1 ) further comprising:

15, The method of any one of claims 12 to 14, wherein the step (i) further comprising:

2. in response to all of the readings associated with the each GNSS satellite are suspicious readings, classify the at least one GNSS satellite as a spoof-victim GNSS satellite.

16, The method of any one of claims 12 to 15, wherein the step (i) further comprising:

3. in response to all readings associated with the at least one GNSS satellite are likely-valid readings, classify the at least one GNSS satellite as a verified-valid GNSS satellite

17, The method of any one of claims 12 to 16, wherein the receiving of the data being from the at least one GNSS receiver.

18, The method of any one of claims 12 to 17, further comprising taking an action associated with the spoof detection.

19, The method of the previous claim, wherein the action comprises sending to the at least one GNSS receiver the instruction to ignore the suspicious readings.

20, The method of any one of claims 18 to 19, wherein the action comprises sending to the at least one GNSS receiver an instruction to ignore readings associated with tire each spoof-victim GNSS satellite.

21, The method of any one of claims 18 to 20, wherein the action comprises sending to the at least one GNSS receiver an instruction to utilize readings associated with the each verified-valid GNSS satellite.

22, The method of any one of claims 18 to 21, the action further comprising determining, based at least on the verified-valid GNSS satellite, at least one of: the position of the object and an indication of time.

23, The method of any one of claims 18 to 22, the action comprising reporting to at least one other system reported information indicative of at least one of: the at least one suspicious reading, the each spoof-victim GNSS satellite, the each suspect-spoof-victim GNSS satellite.

24, The method of claim 23, the action further comprising reporting to the at least one other system viewed angular sectors of space associated with the each spoof-victim GNSS satellite.

25, The method of any one of claims 23 to 24, the action further comprising reporting, to the at least one other system, at least one set of object false position coordinates associated with the each spoof-victim GNSS satellite.

26, The method of any one of claims 23 to 25, the action further comprising reporting, to the at least one other system, at least one object false time measurement associated with the each spoof-victim GNSS satellite.

27, The method of any one of claims 12 to 26, wherein the first reception intensity and the second reception intensity being provided by the at least one GNSS receiver.

28, The method of the previous claim, wherein the first reception intensity and the second reception intensity comprise a Signal to Noise Ratio (SNR).

29, The method of the previous claim, wherein values of the Signal to Noise Ratio (SNR) range from 0 to 99.

30, The method of any one of claims 12 to 29, wherein the defined intensity difference threshold being at least 15 dB.

31, The method of any one of claims 12 to 30, wherein the defined intensity difference threshold being at least 30 dB.

32, The method of any one of claims 12 to 31, wherein at least a part of the viewed angular sectors of space overlap.

33, The method of any one of claims 25 to 32, wherein the viewed angular sectors of space differ by at least 20 degrees.

34, A method of GNSS-spoof detection, the method being performed by a processing circuitry and comprising:

b) determining a view direction of at least one antenna array that received the at least one candidate GNSS signal,

wherein the at least one antenna array comprises a plurality of antenna arrays, wherein each antenna array of the plurality of antenna arrays operatively coupled to a unique GNSS receiver of a plurality of GNSS receivers, wherein viewed angular sectors of space associated with each antenna array of the plurality of antenna arrays are not identical, wherein each reading of the plurality of readings associated with a respective GNSS receiver of the plurality of GNSS receivers; c) determining a viewed angular sector of space associated with the at least one antenna array, based at least on the view direction and on antenna array parameters;

d) determining an expected angular position of the at least one GNSS satellite;

i) classifying the at least one GNSS satellite, the classifying comprising:

1. in response to a first part of the readings associated with the at least one GNSS satellite are likely-valid readings, associated with a first part of the plurality of antenna arrays, and a second part of the readings associated with the at least one GNSS satellite are suspicious readings, associated with a second part of the plurality of antenna arrays, performing the following:

B. obtaining a reception intensity of at least one likely-valid reading of the some likely -valid readings, constituting a second reception intensity;

D. comparing the difference to a defined intensity' difference threshold; and

35. The method of any one of claims 1 to 34, wherein the object is stationary.

36. Tire method of any one of claims 1 to 35, wherein the object is a vehicle.

37. The method of the previous claim, wherein the vehicle is least one of an airborne vehicle, a balloon, a ground vehicle, and a water-borne vehicle.

38. The method of any one of claims 1 to 37, wherein the at least one antenna comprises one antenna.

39. The method of any one of claims 1 to 38, wherein the at least one antenna comprises a plurality of antennas.

40. The method of any one of the preceding claims, further comprising repeating the method at least once.

41. The method of claim 40, wherein an interval between the repetitions is less than or equal to 1/10 second.

42. The method of any one of claims 40 to 41, wherein an interval between the repetitions is less than or equal to 1 second.

43. Tire method of any one of claims 1 to 42, wherein the at least one antenna array being in a fixed spatial attitude with respect to the object.

44. The method of any one of claims 1 to 43, wherein the at least one antenna array being capable of changing a spatial antenna array orientation with respect to the object.

45. The method of any one of claims 1 to 44, wherein the determining of the expected angular position of the each GNSS satellite is based at least on satellite identification information associated with the at least one signal.

46. The method of the previous claim, wherein the satellite identification information comprises a satellite Pseudo Random Number (PRN) code.

47. A GNSS-spoof detection system, a processing circuitry of the GNSS-spoof detection system configured to perfonn a method, the method comprising: a) receiving data indicative of at least one candidate GNSS signal, broadcast by a respective GNSS satellite, the data constituting a reading;

d) determining an expected angular position of the at least one GNSS satellite;

48, The GNSS-spoof detection system of the previous claim, wherein the GNSS-spoof detection system comprised in a GNSS receiver.

49, A non-transitory computer readable storage medium tangibly embodying a program of instructions that, when executed by a computer, causing the computer to perform a method of GNSS-spoof detection, the method being performed by a processing circuitry and comprising:

d) determining an expected angular position of the at least one GNSS satellite; e) determining a deviation of the expected angular position from the viewed angular sector of space: