GB2576865A

GB2576865A - Jamming remote object

Info

Publication number: GB2576865A
Application number: GB1811250.8A
Authority: GB
Inventors: James Wilkinson Alexander; David Down Christopher
Original assignee: Openworks Eng Ltd
Current assignee: Openworks Eng Ltd
Priority date: 2018-07-09
Filing date: 2018-07-09
Publication date: 2020-03-11
Anticipated expiration: 2038-07-09
Also published as: GB2576865B; GB201811250D0

Abstract

A system for jamming a remote target comprises one or more jamming signal transmitters 101a-c, which generate and transmit at least a first sub-jamming signal and a second sub-jamming signal such that (i) at the location of the target 105, the interfering effects of the first and second sub-jamming signals combine so as to interfere with one or more target signals of the target to cause jamming of the target , and (ii) outside a region of space centred on the target object, the interfering effects of at least one of the first and second sub-jamming signals are insufficient to cause jamming. One or more of the sub-jamming signals may be transmitted in the form of relatively narrow beams directed at the target, one or more of the sub-jamming signals may be transmitted in the form of an omni-directional or wide field transmission. The sub-jamming signals may be transmitted from different locations and/or the same location. An overall jamming signal resulting from the combination of sub-jamming signals may be divided into sub-jamming signals based on time, power, frequency and/or code. The target may be a unmanned aerial vehicle. The jamming signals may be GNSS signals corresponding to different satellites.

Description

(71) Applicant(s):

Openworks Engineering Ltd (Incorporated in the United Kingdom)

4B Stocksfield Hall, Stocksfield, Northumberland, NE43 7TN, United Kingdom (72) Inventor(s):

Alexander James Wilkinson

Christopher David Down (56) Documents Cited:

GB 2546438 A

EP 2387170 A

US 20170163372 A

US 20110102261 A

US 20060105701 A

EP 2496961 A

WO 2007/086790 A

US 20140329485 A

US 20090170422 A (58) Field of Search:

INT CL H04K

Other: WPI, EPODOC, Patent Fulltext (74) Agent and/or Address for Service:

Openworks Engineering Ltd

4B Stocksfield Hall, Stocksfield, Northumberland, NE43 7TN, United Kingdom (54) Title of the Invention: Jamming remote object Abstract Title: Jamming system (57) A system for jamming a remote target comprises one or more jamming signal transmitters 101a-c, which generate and transmit at least a first sub-jamming signal and a second sub-jamming signal such that (i) at the location of the target 105, the interfering effects of the first and second sub-jamming signals combine so as to interfere with one or more target signals of the target to cause jamming of the target, and (ii) outside a region of space centred on the target object, the interfering effects of at least one of the first and second sub-jamming signals are insufficient to cause jamming. One or more of the sub-jamming signals may be transmitted in the form of relatively narrow beams directed at the target, one or more of the sub-jamming signals may be transmitted in the form of an omni-directional or wide field transmission. The sub-jamming signals may be transmitted from different locations and/or the same location. An overall jamming signal resulting from the combination of sub-jamming signals may be divided into subjamming signals based on time, power, frequency and/or code. The target may be a unmanned aerial vehicle. The jamming signals may be GNSS signals corresponding to different satellites.

At least one drawing originally filed was informal and the print reproduced here is taken from a later filed formal copy.

1/7

10 19

Figure 1

2/7

10 19

Figure 2

3/7

10 19 power power power power power

power power power power power

4/7

time time time time time

5/7

10 19

Figure 4

6/7

501

503

505

507

Figure 5

7/7

601

603

605

607

609

Figure 6

JAMMING REMOTE OBJECT

FIELD

The present disclosure relates to a technique for disabling a remote object using jamming signals. For example, certain exemplary examples of the present disclosure provide a system, apparatus and/or method for disabling a remote object using multiple jamming signals. In certain examples, at least some of the jamming signals may be directed towards the remote object and/or may be transmitted from different locations.

BACKGROUND

In the last few years, the commercial availability of cheap, small Unmanned Aerial Vehicles (UAVs), for example drones and quadcopters, has increased greatly, and this has resulted in an increasing number of instances of undesirable, unauthorised or illegal use of UAVs. Examples of such use include the use of UAVs to smuggle contraband into prisons and across borders, use of UAVs near airports which can be a safety concern due to potential collision with aircraft, use of UAVs above sports stadia for the purpose of illegal viewing and/or recording of sports events, and use of UAVs near crowded areas, buildings, structures or other installations where the UAV could cause potentially damage and/or injury. Furthermore, there has been increasing concern in the security industry that a UAV may be used in an attempted terrorist attack, for example to deliver explosives, or disperse chemical or biological agents, to a crowded area, building, structure or installation.

Various techniques have been developed for capturing, immobilising or disabling UAVs. One technique, known as jamming, involves transmitting a jamming signal for interfering with signals (referred to below as UAV signals) received by, or transmitted from a UAV. In particular, a UAV typically receives one or more signals for controlling the operation of the UAV. For example, the UAV may receive control signals transmitted from a remote control operated by an operator and/or Global Positioning System (GPS) signals for assisting navigation of the UAV. The UAV may also transmit one or more signals. For example, the UAV may transmit signals to a receiver on the ground for reporting the position of the UAV and/or signals containing images or other data captured by the UAV.

A jamming signal typically comprises Radio Frequency (RF) signals, which may have characteristics (e.g. frequency) matching the UAV signals, such that the jamming signal acts as an interfering signal with respect to the UAV signals. For this reason, a jamming signal typically has a relatively high power in order to overwhelm the UAV signals. One problem with this approach is that the relatively high-power jamming signal may also interfere with objects other than the target UAV. For example, the jamming signal may interfere with aircraft, which could be dangerous.

In many cases, the precise characteristics of the UAV signals may be unknown. In this situation, a jamming signal having a broad range of characteristics may be used to try and encompass the unknown characteristics of the UAV signals. For example, the jamming signal may comprise a signal have a broad range of frequencies. One problem with this approach is that the jamming signal may interfere with other signals that are not the target of the jamming.

One technique used to reduce the risk of jamming objects other than the target UAV is to provide the jamming signal in the form of a relatively narrow beam directed at the target UAV. However, such signals extend beyond the target UAV as well as in front of the target UAV, and may be reflected from objects such as buildings and trees. Furthermore, the region of influence of such signals is typically a cone shape that increases in cross-section with increasing distance from the transmitter. Therefore, even jamming signals forming a relatively narrow beam still have the potential to interfere with objects other that the target UAV.

Accordingly, what is desired is a technique for disabling a remote object (e.g. a UAV) using jamming signals that minimises interference with other objects.

The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.

SUMMARY

It is an aim of certain examples of the present disclosure to address, solve, mitigate or obviate, at least partly, at least one of the problems and/or disadvantages associated with the related art, for example at least one of the problems and/or disadvantages mentioned herein. Certain examples of the present disclosure aim to provide at least one advantage over the related art, for example at least one of the advantages mentioned herein.

The present invention is defined by the independent claims. A non-exhaustive set of advantageous features that may be used in various exemplary examples of the present disclosure are defined in the dependent claims.

Certain examples of the present disclosure provide a system for jamming a remote target object, the system comprising: one or more jamming signal transmitters, wherein the one or more jamming signal transmitters are configured to generate and transmit at least a first subjamming signal and a second sub-jamming signal such that (i) at the location of the target object, the interfering effects of the first and second sub-jamming signals combine so as to interfere with one or more target signals of a type used by the target object to an extent sufficient to cause jamming of the target object, and (ii) outside a region of space centred on the target object, the interfering effects of at least one of the first and second sub-jamming signals are insufficient to cause jamming (e.g. do not occur).

Certain examples of the present disclosure provide a system for jamming a remote target object, the system comprising: one or more jamming signal transmitters, wherein the one or more jamming signal transmitters are configured to generate and transmit at least a first subjamming signal and a second sub-jamming signal such that (i) the interfering effect of the first sub-jamming signal occurs within a first volume of space, (ii) the interfering effect of the second sub-jamming signal occurs within a second volume of space, and (iii) a volume of intersection of the first and second volumes of space includes the target object.

Certain examples of the present disclosure provide a method for jamming a remote target object, the method comprising: generating and transmitting, by one or more jamming signal transmitters, at least a first sub-jamming signal and a second sub-jamming signal such that (i) at the location of the target object, the interfering effects of the first and second sub-jamming signals combine so as to interfere with one or more target signals of a type used by the target object to an extent sufficient to cause jamming of the target object, and (ii) outside a region of space centred on the target object, the interfering effects of at least one of the first and second sub-jamming signals are insufficient to cause jamming (e.g. do not occur).

Certain examples of the present disclosure provide a method for jamming a remote target object, the method comprising: generating and transmitting, by one or more jamming signal transmitters, at least a first sub-jamming signal and a second sub-jamming signal such that (i) the interfering effect of the first sub-jamming signal occurs within a first volume of space, (ii) the interfering effect of the second sub-jamming signal occurs within a second volume of space, and (iii) a volume of intersection of the first and second volumes of space includes the target object.

Certain examples of the present disclosure provide a jamming signal transmitter for operation in a system for jamming a remote target object, the jamming signal transmitter being configured to generate and transmit at least a first sub-jamming signal that (i) interferes with one or more target signals of a type used by the target object to an extent insufficient to cause jamming of the target object, and (ii) combines with one or more other sub-jamming signals at the location of the target object so as to interfere with the one or more target signals to an extent sufficient to cause jamming of the target object.

Certain examples of the present disclosure provide a method for jamming a remote target object, the method comprising: generating and transmitting, by a jamming signal transmitter, at least a first sub-jamming signal that (i) interferes with one or more target signals of a type used by the target object to an extent insufficient to cause jamming of the target object, and (ii) combines with one or more other sub-jamming signals at the location of the target object so as to interfere with the one or more target signals to an extent sufficient to cause jamming of the target object.

In accordance with an aspect of the present disclosure, there is provided a computer program comprising instructions arranged, when executed, to implement a method, device, apparatus and/or system in accordance with any aspect, embodiment, example or claim disclosed herein. In accordance with another aspect of the present disclosure, there is provided a machine-readable storage storing such a program.

Other aspects, advantages, and salient features of the present disclosure will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the accompanying drawings, disclose examples of the present disclosure.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 illustrates an exemplary jamming system comprising several jamming signal transmitters provided at different respective locations;

Figure 2 is a block diagram of a jamming signal transmitter for use in the system illustrated in Figure 1;

Figure 3a illustrates an example of dividing an overall jamming signal into sub-jamming signals based on transmission power division;

Figure 3b illustrates an example of dividing an overall jamming signal into sub-jamming signals based on time division;

Figures 3c(i) and (ii) illustrates an example of dividing an overall jamming signal into subjamming signals based on frequency division;

Figure 4 illustrates an example of a system for protecting a certain area, in which the characteristics of different sub-jamming signals are different;

Figure 5 illustrates an exemplary method for jamming a target object; and

Figure 6 illustrates another exemplary method for jamming a target object.

DETAILED DESCRIPTION

The following description of examples of the present disclosure, with reference to the accompanying drawings, is provided to assist in a comprehensive understanding of the present invention, as defined by the claims. The description includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the examples described herein can be made without departing from the scope of the present invention, as defined by the claims.

The terms and words used in this specification are not limited to the bibliographical meanings, but, are merely used to enable a clear and consistent understanding of the present disclosure.

The same or similar components may be designated by the same or similar reference numerals, although they may be illustrated in different drawings.

Detailed descriptions of elements, features, components, structures, constructions, functions, operations, processes, characteristics, properties, integers and steps known in the art may be omitted for clarity and conciseness, and to avoid obscuring the subject matter of the present disclosure.

Throughout this specification, the words “comprises”, “includes”, “contains” and “has”, and variations of these words, for example “comprise” and “comprising”, means “including but not limited to”, and is not intended to (and does not) exclude other elements, features, components, structures, constructions, functions, operations, processes, characteristics, properties, integers, steps and/or groups thereof.

Throughout this specification, the singular forms “a”, “an” and “the” include plural referents unless the context dictates otherwise. For example, reference to “an object” includes reference to one or more of such objects.

By the term “substantially” it is meant that the recited characteristic, parameter or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement errors, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic, parameter or value was intended to provide.

Throughout this specification, language in the general form of “X for Y” (where Y is some action, process, function, activity, operation or step and X is some means for carrying out that action, process, function, activity, operation or step) encompasses means X adapted, configured or arranged specifically, but not exclusively, to do Y.

Elements, features, components, structures, constructions, functions, operations, processes, characteristics, properties, integers, steps and/or groups thereof described herein in conjunction with a particular aspect, embodiment, example or claim are to be understood to be applicable to any other aspect, embodiment, example or claim disclosed herein unless incompatible therewith.

It will be appreciated that examples of the present disclosure can be realized in the form of hardware, software or any combination of hardware and software. Any such software may be stored in any suitable form of volatile or non-volatile storage device or medium, for example a ROM, RAM, memory chip, integrated circuit, or an optically or magnetically readable medium (e.g. CD, DVD, magnetic disk or magnetic tape). It will also be appreciated that storage devices and media are examples of machine-readable storage that are suitable for storing a program or programs comprising instructions that, when executed, implement examples of the present disclosure.

Certain examples of the present disclosure provide a system, apparatus and/or method for disabling a remote object using multiple jamming signals. Examples of the present disclosure may be implemented in the form of any suitably arranged apparatus and/or system according to the present disclosure. Examples of the present disclosure may operate according to any suitable method according to the present disclosure. The skilled person will appreciate that the following examples are merely illustrative and that the present invention is not limited to these examples.

Figure 1 illustrates an exemplary jamming system 100 for jamming a target object 105, the system 100 comprising two or more jamming signal transmitters 101a-c provided at different respective locations. Each jamming signal transmitter 101a-c is configured for transmitting a respective jamming signal 103a-c according to one or more schemes as described in greater detail below.

The target object 105 may comprise any appropriate type of object, for example a manned vehicle (e.g. an aerial, space, ground, subterranean, sea or subsea type manned vehicle) or unmanned vehicle (e.g. an aerial, space, ground, subterranean, sea or subsea type unmanned vehicle).

Three jamming signal transmitters 101a-c are illustrated in Figure 1. However, the skilled person will appreciate that any suitable number of jamming signal transmitters may be provided.

In some examples, the jamming signal transmitters 101a-c may have fixed positions. However, in other examples, one or more of the jamming signal transmitters 101a-c may be configured to be moveable or mobile, for example by being mounted on a moveable mount or on a vehicle. In certain examples, the position of a moveable jamming signal transmitter 101a-c may be adjustable by remote control, for example automatically or by a human operator. In other examples, a jamming signal transmitter 101a-c may be provided in the form of a portable or handheld device that may be carried by a human operator. The jamming signal transmitters 101a-c may be positioned or moved, for example, so as to be close to the target object 105 and/or to reduce the risk of jamming objects other than the target object 105.

In the example shown in Figure 1, the jamming signal transmitters 101a-c are arranged circularly with relatively regular spacing. However, the skilled person will appreciate that the jamming signal transmitters 101a-c may be arranged in any suitable configuration or pattern, for example any suitable regular or irregular configuration with any suitable close or wide spacing. If one or more of the jamming signal transmitters 101a-c are moveable then the arrangement of the jamming signal transmitters 101a-c may be adjusted (e.g. dynamically).

In certain examples, to achieve greater localisation of jamming, one or more of the jamming signal transmitters 101a-c are configured for transmitting the jamming signals 103a-c in the form of a relatively narrow beam directed in a specific direction (i.e. towards the target object 105, for example a UAV). A narrow beam may be a beam having a relatively small field of transmission, for example less than or equal to a certain value or threshold, e.g. 1°, 2°, ..., 30°, or any other suitable value. In this case, a jamming signal transmitter 101a-c may be configured so as to allow the direction of the jamming signal 103a-c to be adjusted, for example by being mounted on a rotatable mount. In certain examples, the direction of a jamming signal 103a-c may be adjustable by remote control, for example automatically or by a human operator. In the case that a jamming signal transmitter 101a-c is provided in the form of a portable or handheld device, a human operator may point the jamming signal transmitter 101a-c in a specific direction to direct the corresponding jamming signal 103a-c. The direction of a jamming signal 103a-c may be set so that the jamming signal 103a-c is aimed at the target object 105, and the direction of the jamming signal 103a-c may be adjusted (e.g. dynamically), for example in response to changes in the position of the target object 105 and/or the jamming signal transmitter 101a-c.

On the other hand, as described further below, in certain examples, one or more of the jamming signal transmitters 101a-c may be configured for transmitting the jamming signals 103a-c in the form of an omni-directional transmission, or a transmission having a relatively wide field of transmission, for example greater than or equal to a certain value or threshold, e.g. 30°, 35°, 40°, ..., 360° or any other suitable value. In this case, certain characteristics (e.g. phase characteristics) of the jamming signals 103a-c may be defined so as to achieve greater localisation of jamming. Also, in this case it may not be necessary for the jamming signal transmitters 101a-c to be located at different positions. For example, a single jamming signal transmitter 101a-c may be configured for transmitting multiple distinct jamming signals 103a-c from the same location.

The system 100 may comprise one or more target position detectors 107a-c for determined the position of the target object 105. The determined position of the target object 105 may be used to determine certain characteristics (e.g. direction, signal strength and/or phase) of the jamming signals 103a-c. For example, the jamming signal transmitters 101a-c may be configured to adjust the directions of the transmitted beams 103a-c to be directed towards the target object 105 based on position information obtained from the target position detectors 107a-c. The determined position of the target object 105 may be used to determine other additional or alternative characteristics (e.g. phase characteristics and/or signal strength) of the various jamming signals 103a-c.

The target position detectors 107a-c may be implemented using any suitable technology, for example based on radar, lidar, sonar, laser range-finding, optics (e.g. imaging and image processing), etc. In certain examples, a target position detector 107a-c may be provided in the form of a manually operated device which the operator points at the target object 105, whereby a measure line-of sight distance from the device to the target object 105 in combination with a measure orientation of the device allows the position of the target object 105 (relative to the device) to be determined.

In the example illustrated in Figure 1, three target position detectors 107a-c are provided. However, the skilled person will appreciate that any suitable number of target position detectors 107a-c (e.g. one or more target position detectors) may be provided. When several position detectors 107a-c are provided, position information obtained from two or more target position detectors 107a-c may be combined or selected to obtain a more reliable target 105 position. For example, one or more most reliable pieces of position information may be selected and/or two or more pieces of position information may be combined (e.g. by averaging) to generate a composite position measurement. Such combining or selecting may be performed by any suitable entity, for example one or more of the target position detectors 107a-c, a central processing unit, or any other suitable device.

In the example illustrated in Figure 1, each target position detector 107a-c is incorporated into a respective jamming signal transmitter 101a-c. However, the skilled person will appreciate that a target position detector 107a-c may be provided as a self-contained device, or may be incorporated into any other suitable device.

The position of the target object 105 may be expressed in any suitable form, for example in terms of an absolute position (e.g. GPS coordinates, or coordinates in a local coordinate system defined within the system), or in terms of a relative position representing the relative position of the target object 105 with respect to the target position detector 107a-c (or an entity in which the target position detector 107a-c is incorporated).

In certain examples, the system 100 may be provided with means for measuring the positions of one or more of the jamming signal transmitters 101a-c. For example, a jamming signal transmitter 101a-c may be provided with a self-position detector for measuring its own position. It may be required to know the positions of the jamming signal transmitters 101a-c to enable the relative positions between the target object 105 and the jamming signal transmitters 101a-c to be determined. However, means for measuring the position of a jamming signal transmitter 101a-c may not be required, for example if the jamming signal transmitter 101a-c is in a known fixed position, or if a target position detector 107a-c directly measures the relative position of the target object 105 with respect to the jamming signal transmitter 101a-c.

In certain examples, the system 100 may comprise a central controller for performing various processing for controlling the overall system. However, in other examples, a central controller may not be required, and the required processing may be distributed among the various entities in the system in any suitable way, or may be delegated to a certain entity.

One or more of the various entities (e.g. jamming signal transmitters 101a-c, target position detectors 107a-c, central controller, means for measuring the positions of the jamming signal transmitters 101a-c, etc.) within the overall system 100 may be provided with transmitters and/or receivers to enable relevant entities to pass any relevant pieces of information (e.g.

position information and control signals, etc.) necessary for overall operation of the system between each other.

Figure 2 is a block diagram of a jamming signal transmitter for use in the system 100 illustrated in Figure 1. The skilled person will appreciate that the configuration of Figure 2 is merely exemplary and that, in other examples, one or more of the illustrated components may be omitted, one or more components may be added, and one or more of the illustrated components may be replaced with alternative equivalent components (e.g. components for performing an equivalent function).

As shown in Figure 2, the jamming signal transmitter 200 comprises a processor (or controller) 201 for performing necessary processing operations, a jamming signal generator 203 for generating a jamming signal 103a-c under the control of the processor 201, and a transmitter 205 for transmitting the jamming signal 103a-c. In this example, the transmitter 205 is configured for transmitting the jamming signal 103a-c in the form of a relatively narrow beam directed in a specific direction. However, in other examples, the transmitter 205 may be configured for transmitting the jamming signals 103a-c in the form of an omni-directional transmission (or a transmission having a relatively wide field of transmission). The jamming signal transmitter 200 also comprises a moveable and rotatable mount 207 for adjusting, under control of the processor 201, the physical position of the jamming signal transmitter 200, and for adjusting, under the control of the processor 201, the orientation of the jamming signal transmitter 200 to adjust the direction (e.g. azimuthal and/or elevation angles) of the transmitted jamming signal 103a-c. The jamming signal transmitter 200 also comprises a target position detector 209 for measuring the position of a target object 105, and a selfposition detector 211 for measuring the position of the jamming signal transmitter 200. The target position detector 209 and the self-position detector 211 are configured for outputting the measured positions to the processor 201. The jamming signal transmitter 201 also comprises a transceiver 213 for transmitting and receiving information and control signals to and from other entities within the overall system 100.

Various exemplary schemes for performing jamming of a target 105 object will now be described. The skilled person will appreciate that the present invention is not limited to any of these specific examples.

In the following examples, jamming of a target object 105 is achieved by jamming a signal received by the target object 105 and/or a signal transmitted from the target object 105, where the signal received and/or transmitted by the target object is a signal for operation of the target object 105 and/or for conveying information to and/or from the target object 105, whether for operation of the target object 105 or otherwise. Such a signal is referred to below as a “target signal” (or “target object signal”).

The target signal may be defined in terms of one or more characteristics, for example frequency characteristics, power characteristics, time characteristics, phase characteristics and/or code characteristics. The skilled person will appreciate that a signal may be defined in terms of any suitable combination of characteristics. In some cases, the characteristics of the target signal may be unknown. The target signal is jammed using a “jamming signal” having characteristics matching or encompassing characteristics (which may be known, guessed, predicted or expected characteristics) of the target signal, such that the jamming signal acts as an interfering signal with respect to the target signal.

According to various examples of the present disclosure, the jamming signal is produced by a combination or superposition of two or more “sub-jamming signals” (or “partial jamming signals”) 103a-c, which may be transmitted separately. For example, each sub-jamming signal 103a-c may be transmitted by a respective jamming signal transmitter 101a-c. In particular, the system 100 is configured to transmit two or more sub-jamming signals 103a-c such that, in a relatively small region containing (e.g. substantially centred on) the target object 105, the sub-jamming signals 103a-c combine or superimpose to generate the overall jamming signal sufficient to jam the target signal. On the other hand, outside of that region, the sub-jamming signals 103a-c do not combine or superimpose to generate a signal with the necessary characteristics to achieve jamming (or sufficient jamming to disable an object).

In some examples, there may be multiple target signals, and it may be necessary to jam two or more of the target signals (e.g. simultaneously) to achieve effective jamming of the target object 105. In some examples, different target signals may originate from different locations (e.g. signals received by the target object 105 transmitted by different satellites or by different base stations). In cases where there are multiple target signals to be jammed, a set of sub-jamming signals sufficient to jam all relevant target signals may be generated and transmitted. For example, a set of sub-jamming signals may be generated and transmitted for each target signal.

In various examples described below, each jamming signal transmitter 101a-c is located at a different geographic position, and each jamming signal transmitter 101a-c is configured to transmit a respective sub-jamming signal 103a-c in the form of a relatively narrow beam (e.g. a beam having an angular spread or solid angular spread below a certain threshold) towards the target object 105, such that the influence of a sub-jamming signal 103a-c outside of its transmission beam is very low or zero.

Thus, it can be seen that the region in which the various sub-jamming signal 103a-c beams intersect will be a relatively small region containing the target object 105. Within this relatively small “region of intersection”, all of the sub-jamming signals 103a-c combine or superimpose to achieve an overall jamming signal with the necessary characteristics to jam the target signal. However, outside of the relatively small region of intersection, in most regions of space, none of the sub-jamming signals 103a-c will have any significant influence, and even in regions of space (outside the region of intersection) falling within a certain subjamming signal 103a-c beam, at most only one sub-jamming signal 103a-c will have any significant influence. Accordingly, if a sub-jamming signal 103a-c is defined such that, by itself, it does not have the necessary characteristics to cause jamming, it can be seen that objects located outside of the region of intersection will not be jammed. Even if a subjamming signal 103a-c, by itself, has characteristics that cause some jamming, it can be seen that objects located outside of the region of intersection are jammed less severely than the target object 105 located within the region of intersection.

According to the above scheme, each sub-jamming signal 103a-c may be regarded as a subset or component of, or a contribution to, the overall jamming signal. The characteristics of each sub-jamming signal 103a-c may be regarded as comprising a certain subset or component of, or a certain contribution to, the characteristics of the overall jamming signal.

The characteristics of the overall jamming signal are chosen to match the characteristics of the target signal, and the characteristics of the individual sub-jamming signals 103a-c are chosen accordingly. For example, if the target signal is known to occupy a certain frequency band, the sub-jamming signals 103a-c may occupy respective sub-bands which combine to form the known frequency band. If the characteristics of the target signal are unknown, or are not known exactly, the characteristics of the overall jamming signal may be chosen to encompass the likely characteristics of the target signal, and the characteristics of the individual sub-jamming signals 103a-c are chosen accordingly. For example, if the frequency band of the target signal is unknown, the sub-jamming signals 103a-c may occupy respective sub-bands which combine to form a relatively wide frequency band that is likely to contain the frequency or frequency band of the target signal.

Various examples of sub-jamming signals 103 will now be described. In these examples, an overall jamming signal is divided into sub-jamming signals 103 based on time, power, frequency and/or code. However, the skilled person will appreciate that the present invention is not limited to these examples. In the following, it is assumed that there are n jamming signal transmitters 101, 200 labelled Τι, T2, ..., T_n.

In a first example illustrated in Figure 3a, the overall jamming signal is divided into a number of sub-jamming signals 103 based on transmission power division. In this example, the target signal comprises a signal having certain characteristics (in this example a signal transmitted at a particular frequency /_T) and the overall jamming signal comprises a signal having the same characteristics (in this example a signal having the same frequency /_T). The effective transmission power, Pj, of the overall jamming signal is chosen such that the strength of the overall jamming signal at the location of the target object 105 is sufficient to jam the target signal.

In this example, n sub-jamming signals 103 are generated, wherein each sub-jamming signal 103 comprises a signal having substantially the same characteristics as the overall jamming signal (i.e. a signal transmitted at frequency /_T) but transmitted at a lower power. For example, if the transmission power of the Ah jamming signal transmitter is denoted Pj®, then the transmission powers of the sub-jamming signals 103 may be chosen such that Σ Pj® = Pj. In certain examples, the transmission powers of each sub-jamming signal 103 may be the same, such that Pj®= Pj/n.

Each jamming signal transmitter 101, 200 transmits a respective sub-jamming signal 103 in the form of a beam directed towards the target object 105. To achieve this, the target position detector 209 determines the position of the target object 105 (and tracks the position if the target object 105 is moving) and provides the position to the processor 201. The processor 201 then controls the mount 207 to orientate the jamming signal transmitter 200 (and continually adjust the orientation if the target object 105 is moving) such that the transmitted sub-jamming signal 103 is directed towards the target object 105. The processor 200 controls the jamming signal generator 203 to generate the sub-jamming signal 103, and the jamming signal generator 203 passes the generated sub-jamming signal 103 to the transmitter 205, which transmits the sub-jamming signal 103.

Figure 3a illustrates the transmission powers of jamming signal transmitters Ti to T5 101, 200 as a function of time. As illustrated, each jamming signal transmitter 101, 200 continuously transmits a signal at a constant power of Pj/n.

Within the region of intersection of the various sub-jamming signal 103 beams, which contains the target object 105, the various sub-jamming signals 103 transmitted with relatively low power Pj® converge and combine to produce an overall jamming signal with a relatively high power (i.e. an effective transmission power of Pj) sufficient to jam the target signal. On the other hand, any objects located outside the region of intersection will be affected by one sub-jamming signal 103 at most, having a relatively low power insufficient to cause jamming.

In the above example, the sub-jamming signals 103 each have the same transmission power. In other examples, the transmission powers of the various sub-jamming signals 103 may be chosen such that the transmission powers of sub-jamming signals 103 transmitted in certain directions are relatively high, while the transmission powers of sub-jamming signals 103 transmitted in certain other directions are relatively low. For example, if the system 100 is provided to protect an area near an airport, the transmission powers of sub-jamming signals 103 directed towards areas where aircraft pass (e.g. in a direction towards a runway) may be chosen to be relatively low. On the other hand, the transmission powers of sub-jamming signals 103 directed away from areas where aeroplanes pass (e.g. in a direction away from runway) may be chosen to be relatively high. Accordingly, the strength of sub-jamming signals 103 directed towards aircraft is minimised while maintaining a sufficient strength of the overall jamming signal at the location of the target object 105.

Figure 4 illustrates one example of the above technique, in which a system comprising five jamming signal transmitters Ti to T5 101 is provided to protect a first area, A1, adjacent to a runway, R. When aiming at a target object 105, O, within area A1, the jamming signal transmitters Τι, T2 and T3 101 will tend to transmit sub-jamming signals 103 away from the runway (as indicated by arrows 1, 2 and 3), whereas jamming signal transmitters T4 and T5 101 will tend to transmit sub-jamming signals 103 towards from the runway (as indicated by arrows 4 and 5). Accordingly, the transmission powers used by jamming signal transmitters T4 and T5 101 may be chosen to be relatively low in order to avoid interfering with aircraft that are taking off and landing using the runway.

The transmission powers of the jamming signal transmitters 101 may be varied over time. For example, if the presence of another object (e.g. an aircraft) for which jamming is undesirable is detected (e.g. using radar or any other suitable detection scheme), and the position of such an object is known, then the transmission powers of the jamming signal transmitters 101 may be adjusted accordingly to minimise jamming of the other object. In certain examples, if the other object moves, then its position may be tracked and the transmission powers of the jamming signal transmitters 101 may be adjusted dynamically as appropriate to minimise jamming of the moving other object.

In a second example illustrated in Figure 3b, the overall jamming signal is divided into a number of sub-jamming signals 103 based on time division. In this example, the target signal comprises a signal having certain characteristics (e.g. a signal transmitted at a particular frequency /_T) and the overall jamming signal comprises a signal having the same characteristics (e.g. a signal transmitted at the same frequency /_T). The effective transmission power, Pj, of the overall jamming signal is chosen such that the strength of the overall jamming signal at the location of the target object 105 is sufficient to jam the target signal.

In this example, n sub-jamming signals 103 are generated, wherein each sub-jamming signal 103 comprises a signal having substantially the same characteristics as the overall jamming signal (i.e. a signal transmitted at frequency /_T) and is transmitted with power Pj. In this example, time is divided into time slots and the sub-jamming signals 103 are transmitted in respective time slots such that at least one sub-jamming signal 103 is transmitted in each time slot, and such that each jamming signal transmitter 101 does not transmit in at least one time slot. In addition, the transmission powers of the sub-jamming signals 103 are chosen such that the sum of transmission powers of the sub-jamming signals 103 transmitted in any given time slot is greater than or equal to Pj. This may be achieved, for example, by transmitting only one sub-jamming signal 103 with transmission power Pj in a certain time slot, or by simultaneously transmitting two sub-jamming signals with transmission powers that sum to Pj in a certain time slot.

Each jamming signal transmitter 101 transmits a respective sub-jamming signal 103 in the form of a beam directed towards the target object 105. This may be achieved in the manner as described above. In addition, the various jamming signal transmitters 101 synchronise between themselves so as to allow correct timing of transmission of the various sub-jamming signals 103. For example, this may be achieved by means of a synchronisation signal or beacon signal in a manner that will readily occur to a skilled person.

Figure 3b illustrates the transmission powers of jamming signal transmitters Ti to T5 101 as a function of time. Figure 3b illustrates two examples, the first in which sub-jamming signals 103 are transmitted in turn in a staggered or non-overlapping manner, and the second in which there is some overlap between transmissions of different sub-jamming signals 103.

The skilled person will appreciate that the transmission patterns illustrated in Figure 3b are merely exemplary, and that any suitable sequence or order of transmission may be used, where the sequence of transmission may be regular, periodic, non-periodic, random, quasirandom, repeating or non-repeating. The skilled person will also appreciate that one or more of the transmission patterns (used by one or more, or all, jamming signal transmitters) may stay the same over time, or alternatively may change over time (e.g. a pattern through which transmissions repeat may change over time). In general, any transmission pattern may change over time to improve jamming effectiveness or reduce the collateral jamming effect. In addition, in the examples illustrated in Figure 3b, each time slot has the same length At. However, the skilled person will appreciate that the time slots may be different lengths.

Within the region of intersection of the various sub-jamming signal 103 beams, which contains the target object 105, the various sub-jamming signals 103, which individually are intermittent in time, converge and combine to produce an overall jamming signal that is continuous in time. On the other hand, any objects located outside the region of intersection will be affected by one sub-jamming signal 103 at most, and will therefore experience a jamming signal intermittently, which may be insufficient to cause jamming. It certain examples, the sub-jamming signals 103 may be defined such that the overall jamming signal is also intermittent, to a degree less than any individual sub-jamming signal 103 but to a degree sufficient to cause effective jamming of the target object 105.

In certain examples, the transmission duty cycle (e.g. as defined by the proportion of total time spent transmitting, or the time-averaged transmission power) of different jamming signal transmitters 101 may be different. Also, in certain examples, the transmission duty cycle of a specific jamming signal transmitter 101 may vary over time. For example, the duty cycle may be adjusted by adjusting the transmission power (when transmitting is occurring) and/or the length of time transmission occurs in each transmission cycle and/or the length of time between transmissions.

The transmission patterns and/or duty cycles described above may be determined according to any suitable scheme or algorithm, many examples of which will readily occur to the skilled person.

In an analogous manner to the technique described above in relation to Figure 4, the system 100 may be controlled such that the transmission duty cycle of those jamming signal transmitters 101 transmitting sub-jamming signals 103 in certain directions (e.g. directions towards areas where aircraft pass) is relatively high, while the transmission duty cycle of those jamming signal transmitters 101 transmitting sub-jamming signals 103 in certain other directions (e.g. directions away from areas where aircraft pass) is relatively low. Accordingly, the proportion of time during which sub-jamming signals 103 are directed towards aircraft, and/or the time-averaged transmission power of sub-jamming signals 103 directed towards aircraft, may be minimised while maintaining a continuous jamming signal of sufficient power to cause jamming at the location of the target object 105.

In a third example illustrated in Figure 3c, the overall jamming signal is divided into a number of sub-jamming signals 103 based on frequency division. In this example, the target signal comprises a signal having certain frequency characteristics (e.g. a signal having certain frequency components, or a signal having a particular frequency bandwidth) and the overall jamming signal comprises a signal having the same frequency characteristics.

In this example, n sub-jamming signals 103 are generated, wherein each sub-jamming signal 103 comprises a signal having frequency characteristics that are a subset of the frequency characteristics of the target signal. For example, in the case that the target signal comprises n frequency components, then each sub-jamming signal 103 may comprises a signal having one of the n frequency components. As another example, in the case that the target signal comprises an overall frequency band, then each sub-jamming signal may have a certain frequency sub-band that is a subset of the overall frequency band.

Each jamming signal transmitter 101 transmits a respective sub-jamming signal 103 in the form of a beam directed towards the target object 105. This may be achieved in the same manner as described above.

Figure 3c illustrates the transmission frequencies of jamming signal transmitters Ti to T5101.

Within the region of intersection of the various sub-jamming signal 103 beams, which contains the target object 105, the various sub-jamming signals 103 having different frequency characteristics converge and combine to produce an overall jamming signal having a broader range of frequency characteristics sufficient to jam the target signal. On the other hand, any objects located outside the region of intersection will be affected by one subjamming signal 103 at most, having only a subset of the frequency characteristics required for jamming.

In an analogous manner to the technique described above in relation to Figure 4, the system 100 may be controlled such that sub-jamming signals 103 comprising frequency components that may interfere with other objects (e.g. aircraft) may be directed away from areas where such objects may be located (e.g. away from areas where aircraft pass), while sub-jamming signals 103 comprising frequency components that are unlikely to interfere with other objects (e.g. aircraft) may be directed towards areas where such objects may be located.

In a further example, the target signal may apply a frequency hopping technique. In this case, each jamming signal transmitter 101 may transmit a respective sub-jamming signal 103 having a respective frequency that is, or is likely to be, a frequency component used in the hopping pattern. If the hopping pattern is known then a jamming signal transmitter 101 that transmits at a certain frequency may transmit only during a time slot in which that frequency occurs in the hopping pattern. On the other hand, if the hopping pattern is not known then each jamming signal transmitter 101 may transmit continuously, or for relatively extended periods of time.

In yet another example, the overall jamming signal is divided into a number of sub-jamming signals based on code division. In this example, the target signal may comprise a number of components that are combined using a code division multiplexing technique. For example, the target signal may comprise a sum of n modulated signals, where each modulated signal is formed by modulating a respective data signal with a respective orthogonal code. In this case, each sub-jamming signal 103 may comprise a modulated signal generated by modulating a jamming data signal with a respective orthogonal code that is the same as an orthogonal code used to generate the target signal.

Each jamming signal transmitter 101 transmits a respective sub-jamming signal 103 in the form of a beam directed towards the target object 105. This may be achieved in the manner described above.

Within the region of intersection of the various sub-jamming signal 103 beams, which contains the target object 105, the various sub-jamming signals 103, which each contain only one code component, converge and combine to produce an overall jamming signal comprising all of the code components.

Accordingly, when the target object 105 attempts to decode the target signal using the codes to extract the data signals, the decoded signals would comprise a superposition of the jamming data signal and the real data signal, thereby rendering the real data signal unreadable. On the other hand, any objects located outside the region of intersection will be affected by one sub-jamming signal 103 at most, having only one of the code components, which may be insufficient to cause jamming.

In the examples above, the sub-jamming signals 103 may be transmitted in the form of beams directed towards the target object 105. Transmitting sub-jamming signals 103 in this manner reduces the region of effective jamming influence of each individual sub-jamming signal 103, and achieves localisation of the combined or overall jamming signal.

In certain examples, one or more of the sub-jamming signals 103 may be transmitted in the form of beams directed towards the target object 105, and one or more of the sub-jamming signals 103 may be transmitted in the form of an omni-directional transmission (or a transmission having a relatively wide field of transmission). A sub-jamming signal 103 transmitted omni-directionally (or with a relatively wide field of transmission) will have a significantly larger region of effective jamming influence than a sub-jamming signal 103 transmitted as a beam. However, by combining omni-directional transmission (or a transmission having a relatively wide field of transmission) and beam-type transmission, localisation of the overall jamming signal may still be achieved by the beam-type transmissions, while the overall system may be simplified, for example since omni-directional transmitters are typically less complex than beam-type transmitters, and since it is not necessary for the omni-directional transmitter to know the position of the target object 105.

The various sub-jamming signals 103 to be transmitted may be predetermined, for example if the target signal is known. On the other hand, if the target signal is unknown, then the system 100 may comprise one or more target signal detectors (for example incorporated into one or more of the jamming signal transmitters 101, 200 and/or provided as one or more separate units) for detecting and analysing the target signal to allow the appropriate subjamming signals 103 to be determined.

The sub-jamming signals 103 to be transmitted by each jamming signal transmitter 101, 200 may be predetermined. For example, each jamming signal transmitter 101, 200 may be allocated a predetermined sub-jamming signal 103 to transmit. Alternatively, the subjamming signals 103 to be transmitted by each jamming signal transmitter 101, 200 may be determined dynamically, for example according to a changing environment.

Figure 5 illustrates an exemplary method for jamming a target object 105, in which any of the techniques described herein may be applied.

As illustrated in Figure 5, in a first step 501, the system determines the position of a target object 105, for example in a manner described above. In a next step 503, each jamming signal transmitter 101, 200 generates a respective sub-jamming signal 103, for example according to one or more of the techniques described herein. In a next step 505, each jamming signal transmitter 101, 200 transmits its respective sub-jamming signal 103 that was generated in step 503.

One or more (or all) of the sub-jamming signals 103 transmitted in step 505 may be transmitted in the form of a beam in a direction towards the target based on the position of the target object 105 determined in step 501. In certain examples, one or more of the subjamming signals 103 transmitted in step 505 may be transmitted in the form of an omnidirectional transmission (or a transmission having a relatively wide field of transmission).

In certain examples in which the target object 105 moves, in a next step 507, the system tracks the movement of the target object 105 and certain jamming signal transmitters 101, 200 adjust the transmission direction of the sub-jamming signals 103 accordingly, if necessary· In certain examples, the method may comprise a step of dynamically adjusting the sub-jamming signals 103, for example in a manner described above, for example based on a changing environment or the presence of objects other than the target object (e.g. an aircraft).

The skilled person will appreciate that the techniques described herein involving power division, time division, frequency division and code division of the overall jamming signal may be used independently or in any suitable combination.

As mentioned above, it may not be necessary to transmit one or more of the sub-jamming signals 103 in the form of a beam. As described in more detail below, at least in the case that the overall jamming signal is divided into a number of sub-jamming signals 103 based on code division, it may not be necessary to transmit any of the sub-jamming signals 103 in the form of a beam. Furthermore, in the same case, it may not be necessary for the subjamming signals 103 to be transmitted from different locations.

A specific example will now be described in relation to jamming of a Global Positioning System (GPS) receiver of a target object 105. The skilled person will appreciate that the present invention is not limited to this specific example, and may be applied to other types of positioning or navigation system (e.g. a type of Global Navigation Satellite System, GNSS, other than GPS), or any other type of system that uses code division multiple access. The skilled person will also appreciate that the techniques described herein may be applied in systems in which signals may be transmitted by entities other than satellites, for example by ground stations (e.g. in an assisted GPS, A-GPS, system, or a system that does not use satellites).

The techniques described herein may be applied in systems in which a target object relies on properly receiving, detecting and/or decoding multiple signals (possibly originating from different locations) substantially simultaneously. The techniques described herein may be used to jam the combination of such multiple signals.

In a satellite navigation system (e.g. GPS), a receiver receives signals from a number of different satellites, which allow the receiver to compute (or “fix”) its position. Typically, signals from at least four satellites are required to fix a position, although between 6-10 satellites are typically visible at any given position and time in a clear unobscured environment. The satellite signals are transmitted on carriers having a limited number of frequencies (possibly a single frequency), and therefore code division multiple access (CDMA) techniques are used to enable the receiver to distinguish between signals transmitted by different satellites on the same carrier frequency. Each satellite transmits a signal that combines a ranging signal used for determining distances to the satellites, and a navigation message used to carry data.

The ranging signals are used by the receiver to determine pseudo-ranges to each satellite. Pseudo-ranges are essentially ranges (or distances) to the satellites having the same range error resulting from a synchronisation error between a clock in the receiver on the one hand and the clocks in the satellites (which are highly synchronised between themselves) on the other hand.

A ranging signal typically comprises a pseudo-random (PRN) binary code comprising a quasi-random sequence of 1s and Os. Each satellite uses a unique PRN code allocated from a set of PRN codes that are orthogonal to each other (i.e. the cross-correlation between different PRN codes is low). This allows the receiver to distinguish between signals transmitted by different satellites on the same carrier frequency. In addition, the autocorrelation function of each PRN code is characterised by a narrow spike at zero lag (or delay) and a low value at non-zero lag. This allows the receiver to detect the phase of the PRN code in a received signal (and hence the pseudo-range) by correlating the received signal with a local copy of the known PRN code at different lags and detecting the lag that results in a correlation spike. One type of ranging signal used in GPS is the “coarse/acquisition (C/A) code”, which is a “Gold code” having a period of 1023 chips (or bit sequence values). The C/A code in GPS is transmitted at 1.023 Mbit/s giving a period of 1ms.

Navigation messages are carried in 1500 bit long frames transmitted at 50 bps giving a frame period of 30 seconds. The navigation messages carry information including almanac data and ephemeris data. The almanac data includes relatively coarse data on the orbits of the satellites in the satellite constellation, as well as various other information. Each satellite may transmit almanac data for several (possibly all) satellites. Almanac data is split between frames, and the receiver must process 25 frames to receive the complete almanac. Therefore, the almanac data takes a relatively long time (12.5 minutes) to download completely from a single satellite. However, once downloaded the almanac data is considered valid for a relatively long time (e.g. 180 days). On the other hand, ephemeris data includes highly detailed information on a satellite’s orbit (i.e. the current and predicted future locations), and each satellite transmits its own ephemeris data only. Complete ephemeris data is contained in each frame. The receiver cannot use a certain satellite to fix its position until that satellite’s ephemeris data has been completely downloaded.

While the receiver requires the ephemeris data to fix its position, the receiver may use the almanac data to generate a list of visible satellites, thereby assisting the receiver in the acquisition of satellite signals in order to subsequently download the ephemeris data. Updated ephemeris data is broadcast by the satellites every 2 hours and is generally valid for 4 hours, while almanac data is updated less frequently.

The navigation message (e.g. 50 bps in GPS) and the C/A code (e.g. 1.023 Mbps in GPS) are combined by modulo-2 addition, and the resulting combined signal is modulated onto a relatively high-frequency carrier using binary phase shift keying (BPSK) for transmission. GPS utilises a carrier having a frequency of 1575.42 MHz, referred to as L1, for transmitting the combined C/A code and navigation message.

In addition to the above, GPS simultaneously utilises a second ranging code, known as the precision code or P-code. Similar to the C/A code, the P-code is a PRN code. However, the P-code is much longer (6.1871x10¹² bits) than the C/A code and is transmitted at a higher bit-rate (10.23 Mbits/s) than the C/A code, allowing for greater positional fix accuracy and reduced range ambiguity. To resist spoofing, the P-code is encrypted by modulating the Pcode with a secret code, known as the W-code, to generate a Y-code or P(Y)-code, which is what is transmitted. However, the W-code is secret and is generally restricted to military use. The P(Y)-code is also modulated onto the L1 carrier using BPSK but in quadrature (i.e. 90° out of phase) to the C/A code. The P(Y)-code is also transmitted on a second carrier having a frequency of 1227.60 MHz, referred to as L2. Transmitting the P(Y)-code on two different frequencies from the same satellite provides increased resistance to jamming, but also allows an ionospheric delay error to be directly measured and therefore removed.

The receiver demodulates a received satellite signal from the L1 carrier, and then decodes the resulting data signal (including the PRN code and the navigation message) using a local copy of the PRN code with the same phase as the PRN code in the satellite signal to recover the navigation message. The receiver determines the phase of the received PRN code by performing a phase search. That is, the receiver correlates the received signal with a local copy of the PRN code with varying phase shifts and determines the particular phase shift that results in a correlation peak, indicating that the local copy of the PRN code is aligned (i.e. in phase with) with the PRN code included in the received signal. The determined phase shift is used firstly to compute the pseudo-range of the satellite, and secondly to enable the PRN code component of the received signal to be removed to thereby extract the navigation message.

Since the receiver may not know which satellite transmitted the signal, the receiver may be required to repeat the above search process using PRN codes of different satellites. The particular PRN code that results in a correlation peak indicates the satellite that transmitted the signal. If the almanac is available, this may be used by the receiver to determine which satellites are likely to be visible, thereby narrowing down the number of possible PRN to search.

The receiver repeats the above process for signals from different visible satellites to obtain pseudo-ranges of those satellites and navigation messages transmitted by those satellites, including the ephemeris data and almanac data. This information is then used by the receiver to fix its position.

In order to jam a GPS receiver provided in a target object (e.g. an aerial vehicle), one approach is to transmit one or more jamming signals that attempt to interfere with one or more signals (“satellite signals”) transmitted by one or more satellites.

In the following example, a first jamming signal is generated and transmitted by a jamming signal transmitter (JST), wherein the first jamming signal is intended to interfere with signals transmitted by a particular first satellite that utilises a particular known first PRN code. Since the JST is relatively close to the target object in comparison to the first satellite, the first jamming signal may be transmitted with a relatively low power. As discussed further below, the JST may generate and transmit one or more further jamming signals for interfering with one or more respective further satellite signals.

To generate the first jamming signal, the JST combines the first PRN code with arbitrary data (e.g. random data) and uses the combined data signal to modulate an L1 carrier. This process is performed in the same manner in which the first satellite combines the first PRN code with navigation message data and uses the combined data signal to modulate an L1 carrier, as described above. That is, the first jamming signal attempts to mimic or spoof the first satellite signal, except that the first jamming signal contains arbitrary data rather than a navigation message. The first jamming signal is then transmitted towards to the target object.

The phase of the PRN code in the transmitted first jamming signal is controlled such that the PRN code in the first jamming signal and the PRN code in the first satellite signal arrive at the target object in phase. The combined signal received by the receiver is a superposition of the first jamming signal and the first satellite signal. Since the PRN codes of the first jamming signal and the first satellite signal arrive at the target in phase, the receiver will perceive the PRN code component of the combined signal as the same as the code component in the original first satellite signal (other than having a higher power). On the other hand, the receiver will perceive the data component of the combined signal as formed of a superposition of the navigation message and the arbitrary data. Accordingly, when the receiver attempts to demodulate and decode the received signal to recover the navigation message, the extracted data will be a superposition of the navigation message and the arbitrary data, rendering the navigation message unintelligible.

If the PRN code of the first jamming signal and the PRN code of the first satellite signal were to arrive at the target object out of phase then the receiver would be able to distinguish between, and separate, the arbitrary data and the navigation message using CDMA techniques. In particular, any phase difference would result in two correlation peaks when the receiver correlates a local copy of the PRN code with the combined signal, allowing the receiver to distinguish the two signal components. In this case, during decoding, due to the auto-correlation property of the PRN code, when the local copy of the PRN code is properly aligned with the PRN code of the first satellite signal (and therefore misaligned with the PRN code of the first jamming signal), the first jamming signal component would be treated as noise and effectively removed by the correlation operation during decoding.

The JST may determine the correct phase of the PRN code for the first jamming signal in the following manner. The JST may comprise a GPS receiver configured to perform normal GPS receiver operations to fix the position of the JST. This process provides the JST with information including (i) the position of the first satellite (from the ephemeris data), (ii) the PRN code phase of the first satellite signal at the position of the JST (from the PRN code phase search described above), and (iii) the position of the JST (from the GPS position fix). In addition, the JST may measure the position of the target object relative to the JST. For example, the JST may measure the line-of-sight distance to the target object using a distance sensor (e.g. rangefinder), and may measure the direction towards the target object using one or more direction sensors (e.g. one or more accelerometers and/or gyroscopes and/or a magnetometer).

From this information, the JST may deduce the PRN code phase of the first satellite signal at the position of the target object. For example, the JST may compute the distance, d, between the JST and the target object in the direction of the first satellite (i.e. the dot product of (i) a first vector joining the JST and the target object, and (ii) a second vector joining the JST and the first satellite, normalised to have a length of unity). This distance, d, corresponds to a phase difference between the phase of the PRN code in the first satellite signal at the target object and the phase of the PRN code in the first satellite signal at the JST. Specifically, the phase difference (in code chips) may be computed as d-(R/c), where R is the code rate and c is the speed of signal propagation (i.e. approximately the speed of light). This phase difference may then be added to or subtracted from (depending on whether the target object is closer to or further from the satellite than the JST) the detected phase of the PRN code at the JST to obtain the correct PRN code phase for the jamming signal.

In the following, it is shown that, even if the first jamming signal described above is transmitted omni-directionally, the first jamming signal causes jamming (in the sense of preventing recovery of the navigation message) within a relatively small volume of space. Essentially, such jamming only occurs in regions of space where the PRN code of the first jamming signal and the PRN code of the first satellite signal are in phase. In most regions of space, the PRN codes are out of phase and therefore jamming in the above sense does not occur.

In the following, a coordinate system is defined such that the JST is located at the origin, the z-axis lies on a line connecting the JST and the first satellite, and the x-axis and y-axis are perpendicular to the z-axis and to each other.

It is assumed that the first satellite is sufficiently distant from the origin such that, close to the origin (i.e. in the vicinity of the target object and the JST), a given wave front of the first satellite signal may be regarded as having the form of a plane (perpendicular to the z-axis and propagating in the negative z direction). Accordingly, the code phase of the first satellite signal at position s=[x,y,z] and time t (where s is assumed to be sufficiently close to the origin that the above assumption holds) is given by:

Λ A ^R ®satellite\$j t) + ^z + ψ satellite

Where R is the code rate, c is the speed of signal propagation (i.e. approximately the speed of light), and </>_Sateinte is a phase offset.

On the other hand, the JST transmits the first jamming signal such that, close to the origin (i.e. in the vicinity of the target object and the JST), a given wave front of the first jamming signal may be regarded as having the form of the surface of a sphere (centred on the origin and increasing in diameter over time). Accordingly, the code phase of the first jamming signal at position s=[x,y,z] and time t is given by:

&jammer(jL> 0 ^{— —} ~ + + ^) + Ψ jammer

Where jammer is a phase offset.

At an arbitrary position and time, the code phases of the first satellite signal and the first jamming signal are the same when:

^satellite jammer ft R _{7 7} ,

Rt 3 ^z + (Psatellite ~ Rt (.^x O' T Z ) + <Pjammer c c

I _Λ72 I ry2 ^{<Pjammer ~ Vsatellite)

Eq. 1

As described above, the phase offset of the first jamming signal, jammer, is chosen such that the code phases of the first satellite signal and the first jamming signal are the same at all time at the position of the target object, Starget~ [Xiargei, Ytarget, Ztarget] ^x tar get T Ytarget T ^ztarget target p (jP jammer ^satellite) (Pjammer (Psatellite T (^-target T Ytarget T ^ztarget T ^zt_arg_et) Eq. 2

Substituting Equation 2 into Equation 1 gives:

^x O' T ^z +z — Xt_arg_et + Ytarget + ^ztarget + ^ztarget => S + S ‘ Σ₁ — Star get T S_target '

Eq. 3

Where s² is shorthand notation for |s|² and Σι denotes a unit vector in the direction from the JST to the first satellite.

Each term in Equation 3 is invariant under a rotation of the coordinate system about the origin, and therefore Equation 3 is valid for any such rotated coordinate system.

The set of values of s satisfying Equation 3 define a two-dimensional surface in threedimensional space on which the first jamming signal causes jamming (in the sense of preventing recovery of the navigation message).

In practice, since jamming may occur even if there is a small degree of misalignment between the PRN codes, the region of space in which jamming occurs as a result of the first jamming signal will actually be in the form of a relatively thin shell having the shape of the two-dimensional surface corresponding to the solution to Equation 3, and having a thickness that depends on the allowable degree of misalignment. For example, assuming that the PRN codes may be misaligned by up to 5% of a chip, and given a code rate of 1 Mbit/s and a signal propagation speed equal to the speed of light (3x10⁸ m/s), then the shell thickness is 30m. Accordingly, the region of space in which jamming occurs (i.e. the region inside the shell) is relatively small.

The region of space in which jamming occurs as a result of the first jamming signal may be reduced further by transmitting the first jamming signal in the form of a relatively narrow beam directed towards the target object, rather than in the form of an omni-directional transmission (or a transmission having a relatively wide field of transmission).

In a similar manner to the first jamming signal, the JST (located at the same position) may generate and transmit a second jamming signal intended to interfere with signals transmitted by a particular second satellite that utilises a particular known second PRN code. It can be seen that Equation 3 depends on the direction of the first satellite with respect to the JST, and that the corresponding equation for the second jamming signal is the same as Equation 3 except that Σι is replaced with Σ2, denoting a unit vector in the direction from the JST to the second satellite. Accordingly, the region of space in which jamming occurs as a result of the second jamming signal will be in the form of a relatively thin shell having the same shape as the shell corresponding to the first jamming signal, but rotated by an angle corresponding to the difference in the directions of the first and second satellites with respect to the JST.

As with the first jamming signal, the region of space in which jamming occurs as a result of the second jamming signal may be reduced further by transmitting the second jamming signal in the form of a relatively narrow beam directed towards the target object.

The region of space in which jamming occurs as a result of both the first and second jamming signals is the intersection of the two shells described above. Accordingly, even if the first and second jamming signals are transmitted omni-directionally from the same location, this region of space is relatively small.

The region of space in which jamming occurs as a result of both the first and second jamming signals may be reduced further by transmitting the first and second jamming signals in the form of a relatively narrow beams directed towards the target object, and from different locations. Thus, the jamming region is further restricted to the intersection of the transmitted beams.

The JST may generate and transmit any suitable number of jamming signals in a similar manner as described above. In general, the JST may generate and transmit N different jamming signals intended to interfere with N satellite signals transmitted by N satellites that utilises N PRN codes, respectively. The resulting jammed regions of space will comprise N shells of the same shape but oriented differently according to the different positions of the N satellites. Jamming as a result of all N jamming signals will occur only in a relatively small region of intersection of the N shells (i.e. a region surrounding the target object). To restrict the region of jamming further, one or more of the jamming signals may be transmitted in the form of a relatively narrow beam directed towards the target object. The various jamming signals may be transmitted from the same location. Alternatively, one or more of the jamming signals may be transmitted from different locations.

An object other than the target object located outside the jamming region (i.e. the region of intersection of the shells and/or the region of intersection of the beams) will be jammed by one jamming signal at most. Since the number of visible satellites is typically greater than the four satellites required to fix a position, such an object is likely to be able to utilise a sufficient number of non-jammed satellite signals to fix its position, even if one of the satellite signals is jammed. On the other hand, the target object (located in the region of intersection) will be simultaneously jammed by several jamming signals such that the number of nonjammed signals is too small to enable the receiver to fix a position.

In some examples the PRN code may be periodic. In this case, the jamming region corresponding to a certain jamming signal will be periodic in space, such that the jamming region comprises a series of concentric shells. However, for certain values of the code rate, code length, and speed of signal propagation, the distance between the shells may be relatively large. For example, a code rate of 1 Mbps, a code length of 1000 chips, and a speed of signal propagation approximately equal to the speed of light (3x10⁸ m/s) gives a distance of 300km between shells. The transmission strength of the jamming signals may be selected such that the jamming signal strength at second and subsequent shells (e.g. >300km from the JST) is zero or negligible. Accordingly, the first (innermost) shell closest to the JST may be regarded as the only region of space in which jamming occurs.

In the above, jamming has been described with reference to preventing the recovery of a navigation message. However, since the jamming signals described above include PRN codes used by the satellites, then an object other than the target object may mistake a jamming signal for a satellite signal when performing a PRN code phase search as described above to determine a pseudo range based on the signal.

In this case, a receiver may employ one or more criteria for rejecting a jamming signal while accepting genuine satellite signals. For example, a receiver may reject a signal if the data recovered therefrom is not a valid navigation message (e.g. arbitrary data not having the correct format and/or content of a navigation message). This indicates to the receiver that the signal is a jamming signal rather than a genuine satellite signal. Alternatively or additionally, a receiver may reject a signal if the pseudo range determined therefrom is inconsistent with one or more other determined pseudo ranges. For example, pseudo ranges determined from several genuine satellite signals will be compatible with a unique position fix solution. On the other hand, a pseudo range determined from a jamming signal is likely to be inconsistent with such a solution, and therefore may be rejected.

Accordingly, a receiver provided in an object other than the target object may reject any jamming signals, and may utilise a sufficient number of genuine non-jammed satellite signals to obtain pseudo ranges and navigation messages to allow the receive to fix its position. On the other hand, due to the jamming technique described above, a receiver provided in the target object is unable to recover navigation messages from a sufficient number of satellite signals to fix its position, even if it is capable of obtaining the corresponding pseudo ranges.

Figure 6 illustrates an exemplary method for jamming a target object, which may apply, for example, to the jamming of a GPS (or other GNSS) receiver of a target object.

As illustrated in Figure 6, in a first step 601, the system determines the position of a target object, for example in the manner described above. In a next step 603, each jamming signal transmitter determines the code phase of a satellite signal transmitted by a respective satellite (where the determined code phase is the code phase occurring at the position of the jamming signal transmitter), for example in the manner described above. In a next step 605, each jamming signal transmitter determines an appropriate code phase of a respective subjamming signal to be transmitted by each jamming signal transmitter, for example in the manner described above. The determination in step 605 may be made based on the position of the target object determined in step 601, the position of the satellite, and the code phase determined in step 603. The determination in step 605 may include a sub-step of determining the code phase the target object is receiving based on the (relative) position of the target object determined in step 601, the position of the satellite, and the code phase determined in step 603, and a sub-step of determining an appropriate phase offset to apply to the code phase determined in the previous sub-step to take into account the phase delay when transmitting a signal from the jamming signal transmitter to the target object. In a next step 607, each jamming signal transmitter generates a respective sub-jamming signal having a code phase determined in step 607, for example in the manner described above. In a next step 609, each jamming signal transmitter transmits its respective sub-jamming signal that was generated in step 607.

One or more (or all) of the sub-jamming signals transmitted in step 609 may be transmitted in the form of a beam in a direction towards the target based on the position of the target object determined in step 601. Additionally or alternatively, one or more (or all) of the subjamming signals transmitted in step 609 may be transmitted in the form of an omnidirectional transmission (or a transmission having a relatively wide field of transmission). As mentioned above, in certain examples some or all of the jamming signal transmitters may be at different locations, and in certain examples some or all of the jamming signal transmitters may be provided at the same location (e.g. some or all of the jamming signal transmitters may be combined into a single unit).

In the above example, if the target object already possesses up-to-date almanac data and ephemeris data (e.g. from previously acquired and stored data), then the target object may still be able to fix its position correctly by using the pre-stored data and pseudo-ranges determined using the sub-jamming signals (which have the correct code phases) so long as the pre-stored data remains valid. In this case, the sub-jamming signals may be configured so as to move from in-phase to out-of-phase and then jump back so as to confuse the target object receiver. This may be performed by each of the jamming signal transmitters in an unsynchronised manner so that the target object receiver never receives a completely correct set of signals.

The skilled person will appreciate that certain features in the example described above in relation to GPS (or other GNSS) may be omitted in other examples to obtain a less complex system.

For example, in some cases, it may not be required to match the code phases of the subjamming signals and the satellite signals at the position of the target object. In this case, it may not be required for the jamming signal transmitters to decode the satellite signals to determine the code phases at the positions of the jamming signal transmitters, then determine the appropriate code phases for the sub-jamming signals based on the position of the target object. Rather, each jamming signal transmitter may transmit a sub-jamming signal based on a respective code having an arbitrary code phase. The sub-jamming signals may be transmitted such that the target object receives the sub-jamming signals with a higher power than the satellite signals.

Typically, a GPS receiver receives a given satellite signal via multiple paths, for example including relatively strong initial signal (e.g. via a line-of sight path) and one or more relatively weaker delayed signals (e.g. via reflected paths, for example resulting from reflections of the signal within the surrounding environment). Some GPS receivers may use a strongest received signal for fixing a position (even if the resulting code phase is not close to a previously determined code phase). In this case, when a sub-jamming signal is transmitted with a strength such that the sub-jamming signal is the signal received by the target object with the highest received signal strength, then the target object uses the subjamming signal, rather than the actual satellite signal, to fix its position. However, since the sub-jamming signal is transmitted having an arbitrary code phase, the target object would determine an incorrect pseudo-range from that signal. The same applies to each of the other sub-jamming signals. Accordingly, the target object would be rendered unable to fix its position.

In some cases, it may not be required to modulate any data onto the sub-jamming signal. For example, since the above-described technique renders the target object unable to fix its position (based on incorrect pseudo-ranges) even if the target object possesses correct almanac data and ephemeris data (which the target object may have acquired and stored previously), it may not be necessary to jam receipt of navigation messages by the target object by modulating arbitrary data onto the sub-jamming signals.

In certain examples applying the above simplified technique, unintentional jamming of 10 objects other than the target object may be achieved by transmitting the sub-jamming signals in the form of beams in the manner described above.

In the above examples, the codes used in the sub-jamming signals are the same as the codes used by the satellites. However, in other examples, the sub-jamming signals may use codes that are different to the ones used by the satellites, for example codes that are 15 specially designed to maximise interference with the satellite signals.

Claims

1. A system for jamming a remote target object, the system comprising:

one or more jamming signal transmitters, wherein the one or more jamming signal transmitters are configured to generate and transmit at least a first sub-jamming signal and a second sub-jamming signal such that (i) at the location of the target object, the interfering effects of the first and second sub-jamming signals combine so as to interfere with one or more target signals of a type used by the target object to an extent sufficient to cause jamming of the target object, and (ii) outside a region of space centred on the target object, the interfering effects of at least one of the first and second sub-jamming signals are insufficient to cause jamming (e.g. do not occur).

2. A system according to claim 1, wherein the one or more jamming signal transmitters are configured to generate and transmit the first and second sub-jamming signals such that (i) the interfering effect of the first sub-jamming signal occurs within a first volume of space, (ii) the interfering effect of the second sub-jamming signal occurs within a second volume of space, and (iii) a volume of intersection of the first and second volumes of space includes the target object.

3. A system according to claim 1 or 2, wherein the one or more jamming signal transmitters comprise at least:

a first jamming signal transmitter at a first location and configured to transmit the first sub-jamming signal in the form of a beam directed towards the target object; and a second jamming signal transmitter at a second location different from the first location and configured to transmit the second sub-jamming signal in the form of a beam directed towards the target object.

4. A system according to claim 1 or 2, wherein one of the first and second sub-jamming signals is transmitted in the form of a beam directed towards the target object, and wherein the other of the first and second sub-jamming signals is transmitted in the form of an omni-directional transmission or a transmission having a relatively wide field of transmission.

5. A system according to any of claims 1 to 4, wherein the first sub-jamming signal has signal characteristics that comprise a first subset of the signal characteristics of the one or more target signals, and wherein the second sub-jamming signal has signal characteristics that comprise a second subset of the signal characteristics of the one or more target signals.

6. A system according to any preceding claim, wherein the first sub-jamming signal is configured to interfere with a first signal component of the one or more jamming signals, and wherein the second sub-jamming signal is configured to interfere with a second signal component of the one or more jamming signals.

7. A system according to claim 5 or 6, wherein the signal characteristics or signal components comprise one or more of frequency, power, time, phase, and code characteristics or components.

8. A system according to claim 7, wherein the one or more target signals comprise a certain frequency band and/or a certain set of frequency components, wherein the first sub-jamming signal comprises a first frequency sub-band of the frequency band and/or a first subset of the frequency components, and wherein the second sub-jamming signal comprises a second frequency sub-band of the frequency band and/or a second subset of the frequency components.

9. A system according to claim 7 or 8, wherein the first and second sub-jamming signals each have a power insufficient to cause jamming of the one or more target signals, and wherein the combined power of the sub-jamming signals is sufficient to cause jamming of the one or more target signals.

10. A system according to claim 7, 8 or 9, wherein the first sub-jamming signal is transmitted only during one or more first periods of time, wherein the second sub-jamming signal is transmitted only during one or more second periods of time, and wherein the first and second periods of time do not completely overlap.

11. A system according to any one of claims 7 to 10, wherein the one or more target signals comprise at least a first component including a first code and a second component including a second code, wherein the first sub-jamming signal comprises the first code, and wherein the second sub-jamming signal comprises the second code.

12. A system according to claim 11, wherein the first and second sub-jamming signals are transmitted such that, at the position of the target object, the phases of the codes in the first and second sub-jamming signals match the phases of the codes in the first and second components, respectively, of the one or more target signals.

13. A system according to claim 12, wherein the one or more jamming signal transmitters are configured to determine the phases of the codes in the transmitted first and second subjamming signals based on (i) the phases of the codes in the first and second components of the one or more target signals received by the one or more jamming signal transmitters, and (ii) the position of the target object relative to the one or more jamming signal transmitters.

14. A system according to claim 11, 12 or 13, wherein the one or more jamming signal transmitters are configured to modulate data onto the first and second sub-jamming signals.

15. A system according to any of claims 11 to 14, wherein the first and second subjamming signals are transmitted from substantially the same location.

16. A system according to any of claims 11 to 15, wherein the first and second subjamming signals are each transmitted in the form of an omni-directional transmission or a transmission having a relatively wide field of transmission.

17. A system according to any of claims 11 to 16, wherein the first component of the one or more target signals comprises a global navigation satellite system, GNSS, signal transmitted by a first satellite, and the second component of the one or more target signals comprises a GNSS signal transmitted by a second satellite.

18. A system according to any preceding claim wherein the one or more target signals used by the target object comprise one or more signals received by the target object and/or one or more signals transmitted by the target object.

19. A system according to any preceding claim, wherein the target object is an unmanned aerial vehicle, UAV, an unmanned ground vehicle, or an unmanned subsea vehicle.

20. A method for jamming a remote target object, the method comprising:

generating and transmitting, by one or more jamming signal transmitters, at least a first sub-jamming signal and a second sub-jamming signal such that (i) at the location of the target object, the interfering effects of the first and second sub-jamming signals combine so 5 as to interfere with one or more target signals of a type used by the target object to an extent sufficient to cause jamming of the target object, and (ii) outside a region of space centred on the target object, the interfering effects of at least one of the first and second sub-jamming signals are insufficient to cause jamming (e.g. do not occur).

10

21. A jamming signal transmitter for operation in a system for jamming a remote target object, the jamming signal transmitter being configured to generate and transmit at least a first sub-jamming signal that (i) interferes with one or more target signals of a type used by the target object to an extent insufficient to cause jamming of the target object, and (ii) combines with one or more other sub-jamming signals at the location of the target object so 15 as to interfere with the one or more target signals to an extent sufficient to cause jamming of the target object.

Intellectual

Property

Office

Application No: GB1811250.8

Examiner: Mr Robert Macdonald