GB2622388A

GB2622388A - Electromagnetic radiation system and method

Info

Publication number: GB2622388A
Application number: GB2213460.5A
Authority: GB
Inventors: Hillman Richard; Blachford Richard; Kenneth Orgill Michael; Trueba Alejandro
Original assignee: Horiba Mira Ltd
Current assignee: Horiba Mira Ltd
Priority date: 2022-09-14
Filing date: 2022-09-14
Publication date: 2024-03-20
Also published as: GB202213460D0

Abstract

A system and method for identifying ghost targets 15 created by multipath signals including: a first linearly polarised receiver configured to receive electromagnetic radiation and to output at least one signal representative of the strength of the received electromagnetic radiation; a second linearly polarised receiver configured to receive electromagnetic radiation and to output at least one signal representative of the strength of the received electromagnetic radiation, wherein the polarisation of the first receiver is offset from the polarisation of the second receiver; and a controller configured to: receive the signals representative of the strength of the received electromagnetic radiation, and determine a confidence level that the received electromagnetic radiation has arrived at the receivers by an indirect path using the signals representative of the strength of the received electromagnetic radiation. The confidence level preferably being determined by determining a ratio between the power and/or amplitude of the radiation received by the first and second receivers.

Description

I

ELECTROMAGNETIC RADIATION SYSTEM AND METHOD

FIELD

The present disclosure relates to systems and methods using electromagnetic radiation, such as radar. For example, systems and methods are provided for identifying ghost objects resulting from multipath reflections. The technology can be applied in the automotive sector, for example to identify ghost objects resulting from multipath reflections from a surface such as a road surface or wall.

BACKGROUND

It is known to use electromagnetic radiation to detect objects, for example using radar or lidar. These systems generally transmit an electromagnetic wave and receive reflections of the wave from target objects. Characteristics such as the distance to the detected object can then be determined.

A problem with such systems is multipath propagation. In a radar system, for example, a received signal may have been reflected directly from a target object (such as a car), or may have been reflected from other surfaces (such as a road surface) en route to the receiver. Reflections may therefore reach the receiver by two or more paths. The presence of multiple propagation paths may lead to the apparent presence of ghost objects, which are not real objects, but appear so to the receiver. It is conventional to refer to these non-existent objects as ghost objects or ghost targets.

Determining which detected objects are real and which detected objects are ghost objects is a problem associated with such systems.

The present disclosure seeks to provide solutions to the problems associated with the prior art.

BRIEF DESCRIPTION OF THE INVENTION

The present disclosure includes a system including: a first linearly polarised receiver configured to receive electromagnetic radiation and to output at least one signal representative of the strength of the received electromagnetic radiation; a second linearly polarised receiver configured to receive electromagnetic radiation and to output at least one signal representative of the strength of the received electromagnetic radiation, wherein the polarisation of the first receiver is offset from the polarisation of the second receiver; and a controller configured to: receive the signals representative of the strength of the received electromagnetic radiation, and determine a confidence level that the received electromagnetic radiation has arrived at the receivers by an indirect path using the signals representative of the strength of the received electromagnetic radiation.

The offset in polarisation between the first and second receivers may be greater than 60 degrees or about 90 degrees.

The system may further include a transmitter configured to transmit electromagnetic radiation, the first and second linearly polarised receivers may be configured to receive reflections of the transmitted electromagnetic radiation, and determining the confidence level that the received electromagnetic radiation has arrived at the receivers by an indirect path may include determining a confidence level that the reflections correspond to a ghost object using the signals representative of the strength of the received electromagnetic radiation.

The transmitter may be configured to transmit linearly polarised electromagnetic radiation.

The transmitter may be configured to transmit electromagnetic radiation polarised at an angle that bisects the angle between the two receivers.

The transmitter may be configured to transmit electromagnetic radiation polarised at an angle in the range of about 30-60 degrees or about 45 degrees relative to horizontal.

The polarisation of the first receiver may be offset from the polarisation of the transmitted electromagnetic radiation by about 40-50 degrees or about 45 degrees.

The transmitter may be configured to transmit electromagnetic radiation polarised at an angle of about 45 degrees relative to horizontal, the first receiver may be horizontally polarised, and the second receiver may be vertically polarised.

The signals representative of the strength of the received electromagnetic radiation may be representative of the power and/or amplitude of the received electromagnetic radiation, and the controller may be configured to determine the confidence level by determining a ratio between the power and/or amplitude of electromagnetic radiation received by the first receiver and the power and/or amplitude of electromagnetic radiation received by the second receiver.

The system may include a radar system and the electromagnetic radiation may include a radio wave.

The transmitter may be configured to transmit electromagnetic radiation within a predetermined frequency band and an operative frequency band of the first and second receivers may correspond to the predetermined frequency band.

The system may further include a vehicle control module operatively coupled to the controller, the controller may be configured to output object data corresponding to the reflections to the vehicle control module, the object data may include the confidence level that the reflections correspond to a ghost object, and the vehicle control module may be configured to control movement of a vehicle based at least partially on the object data.

The vehicle control module may be configured such that object data associated with a lower confidence level of corresponding to a ghost object has a greater influence on the control of the vehicle movement than object data associated with a higher confidence level of corresponding to a ghost object.

The controller may be configured to output object data associated with a lower confidence level of corresponding to a ghost object relative to a predetermined threshold confidence level to the vehicle control module, and to discard object data associated with a higher confidence level of corresponding to a ghost object compared to the predetermined threshold confidence level.

The controller may be configured to determine a distance travelled by the transmitted electromagnetic radiation to a reflecting object, to group reflecting objects having substantially identical determined distances detected at substantially the same time, and to use the highest determined confidence level in the group to determine the confidence levels for the other reflecting objects in the group.

A method is provided including: receiving, at a first linearly polarised receiver, electromagnetic radiation, and outputting at least one signal representative of the strength of the received electromagnetic radiation from the first receiver; receiving, at a second linearly polarised receiver, electromagnetic radiation, and outputting at least one signal representative of the strength of the received electromagnetic radiation from the second receiver, wherein the polarisation of the first receiver is offset from the polarisation of the second receiver; receiving, at a controller, the signals representative of the strength of the received electromagnetic radiation, and determining, using the controller, a confidence level that the received electromagnetic radiation has arrived at the receivers by an indirect path using the signals representative of the strength of the received electromagnetic radiation.

The method may further include: transmitting, from a transmitter, the electromagnetic radiation; and receiving reflections of the transmitted electromagnetic radiation at the first and second receivers, wherein determining the confidence level that the received electromagnetic radiation has arrived at the receivers by an indirect path includes determining a confidence level that the reflections correspond to a ghost object using the signals representative of the strength of the received electromagnetic radiation.

The transmitted electromagnetic radiation may be linearly polarised electromagnetic radiation.

The transmitted electromagnetic radiation may be polarised at an angle that bisects the angle between the two receivers.

The transmitted electromagnetic radiation may be polarised at an angle in the range of about 30-60 degrees or about 45 degrees relative to horizontal.

The transmitted electromagnetic radiation may be polarised at an angle of about 45 degrees relative to horizontal, the first receiver may be horizontally polarised, and the second receiver may be vertically polarised.

The electromagnetic radiation may include a radio wave.

The electromagnetic radiation may be transmitted from the transmitter within a predetermined frequency band and an operative frequency band of the first and second receivers may correspond to the predetermined frequency band.

The method may further include outputting object data corresponding to the reflections to a vehicle control module, the object data may include the confidence level that the reflections correspond to a ghost object, and the vehicle control module may be configured to control movement of a vehicle based at least partially on the object data.

The method may include outputting object data associated with a lower confidence level of corresponding to a ghost object relative to a predetermined threshold confidence level to the vehicle control module, and discarding object data associated with a higher confidence level of corresponding to a ghost object compared to the predetermined threshold confidence level.

Also provided is a system including: a first linearly polarised transmitter configured to transmit electromagnetic radiation in a first coherent processing interval; a second linearly polarised transmitter configured to transmit electromagnetic radiation in a second coherent processing interval, wherein the polarisation of the first transmitter is offset from the polarisation of the second transmitter; a receiver configured to receive reflections of the transmitted electromagnetic radiation and to output a first signal representative of the strength of the electromagnetic radiation received in the first coherent processing interval and a second signal representative of the strength of the electromagnetic radiation received in the second coherent processing interval; and a controller configured to: receive the signals representative of the strength of the received electromagnetic radiation, and determine a confidence level that the reflections correspond to a ghost object using the signals representative of the strength of the received electromagnetic radiation, Also provided is a method including: transmitting electromagnetic radiation in a first coherent processing interval from a first linearly polarised transmitter; transmitting electromagnetic radiation in a second coherent processing interval from a second linearly polarised transmitter, wherein the polarisation of the first transmitter is offset from the polarisation of the second transmitter; receiving, at a receiver, reflections of the transmitted electromagnetic radiation; outputting, from the receiver, a first signal representative of the strength of the electromagnetic radiation received in the first coherent processing interval and a second signal representative of the strength of the electromagnetic radiation received in the second coherent processing interval; and determining, using a controller, a confidence level that the reflections correspond to a ghost object using the signals representative of the strength of the received electromagnetic radiation.

BRIEF DESCRIPTION OF THE FIGURES

In order that the present disclosure may be more readily understood, preferable embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig 1 is a schematic illustration of a system embodying the present disclosure; Fig 2 is a schematic illustration of a multipath reflection causing the appearance of a ghost object; Fig 3 shows a vehicle equipped with a system embodying the present disclosure; Fig 4 shows the results of a MATLAB simulation of a real-world scenario; Fig 5 is a schematic illustration of a system embodying the present disclosure; Fig 6 is a schematic illustration of a system embodying the present disclosure; and Fig 7 is a schematic illustration of a system embodying the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

A system 1 is provided (see e.g. Fig. 1, 5, and 6). The system 1 may be used for detecting objects (e.g. at least one object). The system 1 may be used to determine the distance (e.g. range), angle (e.g. bearing), and/or velocity (e.g. radial velocity) of objects relative to the system 1. Examples of objects include a road surface, a vehicle, a barrier, a wall, a bridge, street furniture, people, trees, or other objects.

A vehicle 12 may be equipped with the system 1 (see e.g. Fig. 3). The vehicle 12 may be any kind of vehicle including but not limited to land-based vehicles (e.g. cars, trucks, lorries, motorcycles, heavy plant machinery etc.), water-based vehicles (e.g. ships, boats, submarines etc.) or air-based vehicles (e.g. aeroplanes, helicopters, hovercraft etc.). In some versions the vehicle 12 may be a car. The system 1 may therefore be referred to as an automotive system 1 in some versions.

The system 1 may be mounted to any part of the vehicle 12. In some versions the system 1 may be mounted on a roof of the vehicle 12. In some versions the system 1 may be installed inside the vehicle 12. The system 1 may be installed in a body of the vehicle 12. The system 1 may be installed on or under a floor of the vehicle 12.

The system 1 may include a controller 102. The system 1 (e.g. the controller 102 thereof) may be operatively coupled to an on-board computer system 121 of the vehicle 12. The on-board computer system 121 may control one or more aspects of the vehicle 12. The on-board computer system 121 may include a vehicle control module such as an adaptive cruise control module, advanced driver-assistance system module, active safety system module and/or autonomous driving module, for example. The vehicle 12 may, therefore, be an autonomous vehicle 12 or may have some automated features, and the system 1 may be integrated with and/or operatively coupled to the control system of the vehicle 12. The system 1 may, therefore, be used to control the movement of the vehicle 12. In some versions the vehicle 12 and/or on-board computer system 121 may be considered part of the system 1. The vehicle control module may therefore be considered part of the system 1 in some versions, and the controller 102 may be operatively coupled to the vehicle control module.

The system 1 (e.g. the controller 102) may, therefore, be configured to output object data to the onboard computer system 121. The object data may provide information regarding objects detected by the system 1, such as the distance (e.g. range), angle (e.g. bearing), and/or velocity (e.g. radial velocity) of detected objects relative to the system 1, for example. The object data may be used by the on-board computer system 121 to control one or more aspects of the vehicle 12, such as an aspect of the movement of the vehicle 12. For example, the object data may be used (e.g. by the on-board computer system 121) to control the speed, bearing, and/or acceleration of the vehicle 12.

In some versions, the object data may be transmitted (e.g. by a wired or wireless communications link) to one or more remote devices 20. The object data may be transmitted directly to the or each remote device 20 and/or may be transmitted through a network 21 (e.g. a wireless network such as a cellular network). The remote device 20 may be any type of computing device and may include a server, data historian, and/or big data analysis module, for example. In some versions the remote device 20 may include another vehicle (e.g. vehicle 12) which may or may not be equipped with the system 1. The vehicles 12 may, therefore, be connected vehicles and/or connected autonomous vehicles. The system 1 may therefore transmit object data to the on-board computer system 121 of one or more vehicles 12, and/or the on-board computer system 121 may transmit object data to other on-board computer systems 121.

The system 1 may be operably coupled to a power source of the vehicle 12, such as a battery, engine (e.g. via an altemator), or fuel cell. The power source may provide power to the system 1.

In other versions the system 1 may be operably coupled to a mains power supply and/or generator and/or the system 1 may include a power source.

The system 1 may include a transmitter 101 (see e.g. Fig. 1). The transmitter 101 may be configured to transmit electromagnetic radiation, such as radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, or gamma rays. In particular, the transmitter 101 may be a radar and/or lidar transmitter 101.

The system 1 may include a receiver arrangement 110. The receiver arrangement 110 may be configured to receive electromagnetic radiation, such as radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, or gamma rays. In particular, the receiver arrangement 110 may be a radar and/or lidar receiver arrangement 110. The transmitter 101 and receiver arrangement 110 may be configured to operate using the same type of electromagnetic radiation (e.g. electromagnetic radiation from the same band of the electromagnetic spectrum).

The system 1 may include the controller 102. The controller 102 may be configured to control the transmitter 101 and/or receiver arrangement 110. The controller 102 may be configured to control the transmissions of the transmitter 101. The controller 102 may be configured to control reception at the receiver arrangement 110. The controller 102 may be configured to receive data from the receiver arrangement 110.

The system 1 may, therefore, include a radar and/or lidar system 1.

A problem with some object detection systems is the detection of ghost objects due to multipath propagation. An example of a scenario resulting in the detection of a ghost object is shown schematically in Fig. 2.

As shown in Fig. 2, a vehicle 13 (known as the "ego" 13) may be travelling on a road. The ego 13 may be equipped with an object detection system such as a radar or lidar system. The ego 13 may, therefore, transmit electromagnetic radiation and receive reflections of the transmitted radiation.

In a scenario, the ego 13 may be following a lead vehicle 14. The ego 13 may, therefore, receive direct reflections of the transmitted radiation via the path 301 (i.e. via a path which follows the route: i. transmission from ego 13; ii. reflection from lead vehicle 14; iii. reception at ego 13). The transmitted radiation may, therefore, be reflected from the lead vehicle 14 at an approximately normal angle (i.e. such that the radiation is reflected directly back to the ego 13).

However, the ego 13 may also receive indirect reflections of the transmitted radiation. For example, the transmitted radiation may follow the path 302 from the ego 13 to the lead vehicle 14.

The transmitted radiation may then be reflected at a non-normal angle from the lead vehicle 14. The transmitted radiation may therefore be reflected along the path 303, which may then lead to another reflection from an object 3 such as a barrier (for example, a concrete central reservation which separates traffic on a motorway). The transmitted radiation may be reflected along the path 304 from the object 3 back to the ego 13. The ego 13 may, therefore, receive indirect reflections of the transmitted radiation (e.g. via a path which follows the route: i. transmission from ego 13; ii. reflection from lead vehicle 14; iii. reflection from object 3; iv. reception at ego 13). Of course, there are many possible indirect reflection paths.

Reception of the reflected radiation from the object 3 along the path 304 results in the apparent presence of the ghost vehicle 15. In other words, the received radiation appears, to the receiver, to have travelled along the path 305, from behind the object 3.

Some object detection systems are unable to differentiate between real objects and ghost objects, which may cause the ego 13 to behave erratically (e.g. if the ego 13 is an autonomous vehicle or a vehicle having some automated features). For example, the ego 13 may react to the apparent presence of the ghost object by accelerating, decelerating, and/or swerving, which may be dangerous for any occupants of the ego 13 and/or other road users.

The disclosed system 1 provides technology for identifying ghost objects, thereby improving the reliability of the object detection and improving the safety of any vehicles using the system 1. The system 1 may determine a confidence level that a detected object (e.g. a reflecting object) is a ghost object and/or may determine a confidence level that electromagnetic radiation received at the receiver arrangement 110 corresponds to a ghost object. In some versions the system 1 may determine a confidence level that electromagnetic radiation received at the receiver arrangement 110 has arrived at the receiver arrangement 110 by an indirect path (which may, therefore, correspond to a ghost object).

In particular, the system 1 may use polarisation characteristics to differentiate between directly received and indirectly received electromagnetic radiation, and in particular to differentiate between reflections corresponding to real objects and reflections corresponding to ghost objects (e.g. to differentiate between direct and multipath reflections).

The receiver arrangement 110 may include a first receiver 111. The first receiver 111 may be configured to receive electromagnetic radiation. The first receiver 111 may be configured to receive polarised electromagnetic radiation. The first receiver 111 may, therefore, be a first polarised receiver 111. The first receiver 111 may be configured to receive linearly polarised electromagnetic radiation. The first receiver 111 may, therefore, be a first linearly polarised receiver 111. In some versions the first receiver 111 may be a radar and/or lidar receiver 111.

In some versions (e.g. as illustrated schematically in Fig. 1), the first receiver 111 may be horizontally polarised. However, other orientations of linear polarisation are possible (e.g. at any angle relative to the horizontal or vertical or at any angle of rotation of the direction of polarisation about the (perpendicular) axis along which the electromagnetic radiation is transmitted and/or received).

The receiver arrangement 110 may include a second receiver 112. The second receiver 112 may be configured to receive electromagnetic radiation. The second receiver 112 may be configured to receive polarised electromagnetic radiation. The second receiver 112 may, therefore, be a second polarised receiver 112. The second receiver 112 may be configured to receive linearly polarised electromagnetic radiation. The second receiver 112 may, therefore, be a second linearly polarised receiver 112. In some versions the second receiver 112 may be a radar and/or lidar receiver 112.

In some versions (e.g. as illustrated schematically in Fig. 1), the second receiver 112 may be vertically polarised. However, other orientations of linear polarisation are possible (e.g. at any angle relative to the horizontal or vertical or at any angle of rotation of the direction of polarisation about the (perpendicular) axis along which the electromagnetic radiation is transmitted and/or received).

The first and second receivers 111,112 may both be linearly polarised. The polarisation of the first receiver 111 may be offset from the polarisation of the second receiver 112. The offset may be at least 10°, at least 20°, at least 30°, at least 40°, at least 50°, at least 60°, at least 70°, at least 75°, at least 80°, at least 85°, at least 86°, at least 87°, at least 88°, or at least 89°. The offset may be approximately 90°. It will be appreciated that 90° is the maximum possible offset between polarisations (e.g. an offset of 180° is equivalent to an offset of 0°).

The linear polarisation of the first receiver 111 may be orthogonal, or substantially orthogonal, to the linear polarisation of the second receiver 112. In some versions the first receiver 111 may be horizontally polarised and the second receiver 112 may be vertically polarised.

The transmitter 101 may be configured to transmit electromagnetic radiation. The transmitter 101 may be configured to transmit polarised electromagnetic radiation. The transmitter 101 may, therefore, be a polarised transmitter 101. The transmitter 101 may be configured to transmit linearly polarised electromagnetic radiation. The transmitter 101 may, therefore, be a linearly polarised transmitter 101. In some versions the transmitter 101 may be a radar and/or lidar transmitter 101.

The transmitter 101 may be configured to transmit linearly polarised electromagnetic radiation at any angle of rotation of a plane in which lies a vector parallel to the axis of transmission (e.g. with the angle measured as the rotation about the axis of transmission), or at any angle of rotation of the direction of polarisation about the (perpendicular) axis along which the electromagnetic radiation is transmitted and/or received.

The transmitter 101 may be configured to transmit electromagnetic radiation polarised at an angle in the range of about 20-70°, about 25-65°, about 30-60°, about 35-55°, or about 40-50° relative to horizontal or relative to a ground surface that supports the transmitter 101 (whether directly or indirectly, e.g. when the system 1 or transmitter 101 is mounted to the vehicle 12).

In some versions (e.g. as illustrated schematically in Fig. 1), the transmitter 101 (and therefore the transmitted electromagnetic radiation) may be polarised at an angle of about 45° relative to horizontal or relative to a ground surface that supports the transmitter 101. However, other orientations of linear polarisation are possible (e.g. at any angle relative to the horizontal or vertical or at any angle of rotation of the direction of polarisation about the (perpendicular) axis along which the electromagnetic radiation is transmitted and/or received).

The polarisation of the receiver arrangement 110 may be offset from the polarisation of the transmitter 101. In particular, the polarisation of the first and/or second receiver 111,112 may be offset from the polarisation of the transmitter 101. The polarisation of both the first and second receivers 111,112 may be offset from the polarisation of the transmitter 101. The polarisation offset between the first receiver 111 and the transmitter 101 (e.g. measured in degrees) may be substantially equal to the polarisation offset between the second receiver 112 and the transmitter 101 (e.g. measured in degrees). However, the polarisation offset between the first receiver 111 and the transmitter 101 may be in a direction that is substantially opposite to the direction of the polarisation offset between the second receiver 112 and the transmitter 101.

For example, the angle of polarisation of the first receiver 111 may be defined by rotating the angle of polarisation of the transmitter 101 by a predetermined number of degrees in a clockwise direction, whereas the angle of polarisation of the second receiver 112 may be defined by rotating the angle of polarisation of the transmitter 101 by the predetermined number of degrees in an anticlockwise (i.e. counter-clockwise) direction.

For example, the transmitter 101 may be polarised at an angle of approximately 450 relative to horizontal or relative to a ground surface that supports the transmitter 101. The first receiver 111 may be polarised at an angle between 0° and 44° relative to horizontal or relative to a ground surface that supports the first receiver 111 (whether directly or indirectly, e.g. when the system 1 or first receiver 111 is mounted to the vehicle 12), whereas the second receiver 112 may be polarised at an angle between 46° and 90° relative to horizontal or relative to a ground surface that supports the second receiver 112 (whether directly or indirectly, e.g. when the system 1 or second receiver 112 is mounted to the vehicle 12). As stated herein, the offset between the polarisation of the transmitter 101 and each receiver 111,112 may be substantially equal. Therefore, the polarisation of each receiver 111,112 may be offset from the polarisation of the transmitter 101 by about 50, about 100, about 15°, about 200, about 25°, about 30°, about 35°, about 40°, or about 45°. The polarisation of each receiver 111,112 may be offset from the polarisation of the transmitter 101 by an angle in the range of about 5-45°, about 10-45°, about 15-45°, about 20-45°, about 25-45°, about 30-45°, about 35-450, about 40-45°, about 41-45°, about 42-45°, about 43-45°, or about 44-In an example, therefore, the transmitter 101 may be polarised at angle of about 45° relative to horizontal and the polarisation of each receiver 111,112 may be offset from the polarisation of the transmitter 101 by about 45°. In other words, the transmitter 101 may be polarised at an angle of about 45° relative to horizontal, the first receiver 111 may be horizontally polarised, and the second receiver 112 may be vertically polarised (or the first receiver 111 may be vertically polarised with the second receiver 112 horizontally polarised).

In some versions the transmitter 101 may not be polarised. In such versions the polarisation of the first receiver 111 may be orthogonal to the polarisation of the second receiver 112.

In some versions the source of electromagnetic radiation may be outside the system 1 (e.g. sunlight).

The system 1 may be configured to identify ghost objects. In other words, the system 1 may be configured to identify multipath reflections. The system 1 may be configured to determine a confidence level that a detected object (e.g. a reflecting object) is a ghost object and/or that electromagnetic radiation received by the system 1 (e.g. by the receiver arrangement 110 thereof) corresponds to a ghost object. The system 1 may be configured to determine a confidence level that electromagnetic radiation received by the system 1 (e.g. by the receiver arrangement 110 thereof) has arrived at the system 1 (e.g. at the receiver arrangement 110 thereof) by an indirect path.

The transmitter 101 may transmit electromagnetic radiation. The transmitter 101 may transmit electromagnetic radiation at a predetermined frequency or within a predetermined frequency band. The transmitter 101 may transmit pulses of electromagnetic radiation. The transmitter 101 may transmit chirps (e.g. radar chirps). The transmitter 101 may transmit electromagnetic radiation with a predetermined polarisation (e.g. linear polarisation with a predetermined angle of polarisation). The frequency of the electromagnetic radiation transmitted by the transmitter 101 may be in the radio band of the electromagnetic spectrum, and may in particular be in the range of 76-81 GHz.

The characteristics of the transmitted electromagnetic radiation may be controlled by the controller 102. The controller 102 may therefore control the transmitter 101, as described. The controller 102 may therefore control the frequency of the transmitted electromagnetic radiation. The controller 102 may control a frequency or phase modulation of the transmitted electromagnetic radiation. The controller 102 may implement a frequency modulated continuous wave transmission (e.g. frequency modulated continuous wave radar).

The controller 102 may also control the polarisation of the transmitted radiation. In some versions the transmitted electromagnetic radiation may not be polarised, however in some versions the transmitted electromagnetic radiation may be linearly polarised. The controller 102 may control the angle of linear polarisation of the transmitted electromagnetic radiation. The transmitter 101 (or an antenna thereof) may, therefore, be rotatable, and the angle of rotation may be controlled by the controller 102. Accordingly, the system 1 may include a motor configured to rotate the transmitter 101. The motor may be controlled by the controller 102. The controller 102 may be configured to perform electronic beam steering of the transmitted electromagnetic radiation (e.g. by applying different phase shifts).

In some versions the system 1 may include two transmitters 101a,101b (see e.g. Fig. 6), and each transmitter 101a,101b may be operably coupled to the controller 102. The angle of linear polarisation of the transmitted radiation may, therefore, be controlled by transmitting, using the two transmitters 101a,101b, different polarisafions from the same coherent source. Each transmitter 101a,101b may transmit linearly polarised radiation at an amplitude configured to produce a required polarisation angle. The amplitude of radiation transmitted from each transmitter 101a,101b may, therefore, vary in accordance with any variations in the required polarisation angle. The controller 102 may, therefore, control the angle of linear polarisation of the transmitted radiation by varying the amplitude of radiation transmitted from each transmitter 101a,101b.

Reflections of the transmitted electromagnetic radiation may be received by the receiver arrangement 110. Reflections of the transmitted electromagnetic radiation may be received by the first and/or second receivers 111,112. The controller 102 may control the receiver arrangement 110 and may control the first and/or second receivers 111,112. The controller 102 may control an operative frequency band of the receiver arrangement 110 (e.g. of the first and/or second receivers 111,112). The operative frequency band of the receiver arrangement 110 (e.g. first and/or second receivers 111,112) may correspond to the frequency band of the transmitted electromagnetic radiation. The controller 102 may control a receiving interval of the receiver arrangement 110 (e.g. the time interval in which the receiver is active). The controller 102 may control the transmitter 101 and receiver arrangement 110 such that the receiver arrangement 110 is inactive when the transmitter 101 is transmitting (and such that the transmitter 101 is inactive when the receiver arrangement 110 is receiving). In some versions the transmitter 101 and receiver arrangement 110 may be active at the same time.

The controller 102 may control the angle of polarisation of the receiver arrangement 110. The controller 102 may control the angle of polarisation of the first and/or second receivers 111,112. The first and/or second receivers (or an antenna or antennae thereof) may, therefore, be rotatable, and the angle of rotation may be controlled by the controller 102. The system 1 may include a motor configured to rotate the first and/or second receivers 111,112. The angle of polarisation may be controlled electronically in some versions, such as by using solid state apparatus (e.g. a solid state radar system).

The receiver arrangement 110 may output signals representative of the received electromagnetic radiation, which may be representative of the strength of the received electromagnetic radiation. The first receiver 111 may output at least one signal representative of the received electromagnetic radiation (e.g. representative of the strength of the received electromagnetic radiation). The second receiver 112 may output at least one signal representative of the received electromagnetic radiation (e.g. representative of the strength of the received electromagnetic radiation). The signals may be output to the controller 102.

The receiver arrangement 110 may output signals representative of the power and/or amplitude of the received electromagnetic radiation. The first receiver 111 may output at least one signal representative of the power and/or amplitude of the received electromagnetic radiation. The second receiver 112 may output at least one signal representative of the power and/or amplitude of the received electromagnetic radiation. The signals may be output to the controller 102.

The controller 102 may be configured to receive the signals output by the receiver arrangement 110 (e.g. first and/or second receiver 111,112). The controller 102 may be configured to identify ghost objects using the received signals (e.g. using the signals representative of the received electromagnetic radiation and/or signals representative of the strength and/or power and/or amplitude of the received electromagnetic radiation). The controller 102 may be configured to identify multipath reflections using the received signals (e.g. using the signals representative of the received electromagnetic radiation and/or signals representative of the strength and/or power and/or amplitude of the received electromagnetic radiation). The controller 102 may be configured to determine a confidence level that the received electromagnetic radiation has arrived at the receivers by an indirect path using the signals representative of the received electromagnetic radiation (e.g. using the signals representative of the strength and/or power and/or amplitude of the received electromagnetic radiation). The controller 102 may be configured to determine a confidence level that a detected object (e.g. a reflecting object) is a ghost object using the signals representative of the received electromagnetic radiation (e.g. using the signals representative of the strength and/or power and/or amplitude of the received electromagnetic radiation).

The controller 102 may be configured to determine a ratio between the signal received from the first receiver 111 and the signal received from the second receiver 112. The controller 102 may be configured to determine a ratio between the strength and/or power and/or amplitude of the electromagnetic radiation received by the first receiver 111 and the strength and/or power and/or amplitude of the electromagnetic radiation received by the second receiver 112. The signals received from the receiver arrangement 110 may, therefore, each have an associated magnitude, and the magnitudes associated with the signals may be compared to determine the ratio between the signals. The determined ratio may, therefore, reflect the relative strength and/or power and/or amplitude of the electromagnetic radiation received by each receiver 111,112. In some versions the strength and/or power and/or amplitude of the electromagnetic radiation detected by each receiver 111,112 may be determined as an absolute value (e.g. measured in dB, dBm, dBW, and/or watts). In some versions the strength and/or power and/or amplitude of the electromagnetic radiation detected by each receiver 111,112 may be determined as a relative value which may not be calibrated to an absolute value. The ratio may be determined by dividing the strength and/or power and/or amplitude of the electromagnetic radiation received by the first receiver 111 by the strength and/or power and/or amplitude of the electromagnetic radiation received by the second receiver 112 (or vice versa). The ratio may therefore be determined in the form x:y where x and y are numbers representing the strength and/or power and/or amplitude of the electromagnetic radiation received by each receiver 111,112 or in the form z where z is a number determined by dividing the strength and/or power and/or amplitude of electromagnetic radiation received by one receiver 111,112 by the strength and/or power and/or amplitude of electromagnetic radiation receiver by the other receiver 111,112, for example.

The controller 102 may be configured to determine a confidence level that the received electromagnetic radiation has arrived at the receivers by an indirect path and/or that a detected object (e.g. a reflecting object) is a ghost object using the determined ratio. For example, the controller 102 may be configured to determine the confidence level by determining a ratio between the power and/or amplitude of electromagnetic radiation received by the first receiver and the power and/or amplitude of electromagnetic radiation received by the second receiver. For example, the confidence level may increase as the difference in strength and/or power and/or amplitude of the electromagnetic radiation received by the receivers 111,112 increases (e.g. as the determined ratio increases). The confidence level may, therefore, be proportional to the determined ratio and/or may be proportional to the difference in strength and/or power and/or amplitude of the electromagnetic radiation received by the receivers 111,112.

The controller 102 may be configured to compare the determined ratio to a threshold value. The threshold value may be a predetermined threshold value. The predetermined threshold value may be a value indicating that the strength and/or power and/or amplitude of the electromagnetic radiation received by one receiver 111,112 (e.g. the first receiver 111) is about 1.1 times, about 1.2 times, about 1.3 times, about 1.4 times, about 1.5 times, about 1.6 times, about 1.7 times, about 1.8 times, about 1.9 times, about 2 times, about 2.5 times, about 3 times, about 3.5 times, about 4 times, about 4.5 times, about 5 times, about 6 times, about 7 times, about 8 times, about 9 times, or about 10 times greater than the strength and/or power and/or amplitude of the electromagnetic radiation received by the other receiver 111,112 (e.g. the second receiver 112).

Likewise, the predetermined threshold value may be a value indicating that the strength and/or power and/or amplitude of the electromagnetic radiation received by one receiver 111,112 (e.g. the first receiver 111) is about 1.1 times, about 1.2 times, about 1.3 times, about 1.4 times, about 1.5 times, about 1.6 times, about 1.7 times, about 1.8 times, about 1.9 times, about 2 times, about 2.5 times, about 3 times, about 3.5 times, about 4 times, about 4.5 times, about 5 times, about 6 times, about 7 times, about 8 times, about 9 times, or about 10 times smaller than the strength and/or power and/or amplitude of the electromagnetic radiation received by the other receiver 111,112 (e.g. the second receiver 112).

In some versions the threshold value may be determined dynamically and may be continuously updated by the controller 102. For example, the threshold value may depend on the angle of polarisation of the transmitter 101 and/or receivers 111,112.

In general, therefore, the threshold value may be a value indicating that the power and/or strength and/or amplitude of the electromagnetic radiation received by one receiver 111,112 (e.g. the first receiver 111) is greater than the power and/or strength and/or amplitude of the electromagnetic radiation received by the other receiver 111,112 (e.g. the second receiver 112).

The controller 102 may be configured to identify an object as a ghost object if the determined ratio exceeds the threshold value. This may occur where one of the receivers 111,112 receives a stronger reflection than the other receiver 111,112. Mere the strength of reflections is similar between the two receivers 111,112, the object may be identified as a real object. Object data determined to correspond to a real object may be referred to as real object data. Object data determined to correspond to a ghost object may be referred to as ghost object data.

In some versions the controller 102 may compare the strength and/or power and/or amplitude of electromagnetic radiation received at each receiver 111,112 using a lookup table. The lookup table may be used to determine the confidence level and/or to identify an object as a real or ghost object.

Without wishing to be bound by theory or conjecture, it is expected that multipath reflections may be at least partially polarised towards the angle of the reflecting surface. For example, multipath reflections reflected from a horizontal surface (e.g. a road surface) may be at least partially horizontally polarised, whereas multipath reflections reflected from a vertical surface (e.g. brick wall or glass window) may be at least partially vertically polarised. Conversely, direct reflections (which may for example be reflected at an approximately normal angle from an object) are expected substantially to maintain the polarisation of the transmitted electromagnetic radiation. The system 1 may therefore distinguish between real and ghost objects, or determine the confidence level that a detected object (e.g. reflecting object) is a ghost object, using the polarisation characteristics of the reflected electromagnetic radiation.

In an example, the transmitter 101 may transmit unpolarised electromagnetic radiation (e.g. radio waves). Direct reflections may, therefore, be received at both receivers 111,112 with similar strength and/or power and/or amplitude (e.g. because the reflected electromagnetic radiation is not polarised). However, multipath reflections may show at least partial linear polarisation, and so may show a stronger reception at the one of the transmitters 111,112 that is most closely aligned with the polarisation of the reflected electromagnetic radiation. The disparity in strength (e.g. power and/or amplitude) of the received reflections may therefore indicate that the reflection is a multipath reflection corresponding to a ghost object.

In another example, the transmitter 101 may transmit electromagnetic radiation with linear polarisation at an angle of about 45° relative to horizontal. The polarisation of the receivers 111,112 may, as described, be equally offset from the angle of polarisation of the transmitted electromagnetic radiation (e.g. both offset by 30° or 45°). One of the receivers 111,112 may therefore be polarised towards the horizontal compared to the transmitted radiation and the other receiver 111,112 may be polarised towards the vertical compared to the transmitted radiation. Accordingly, indirect/multipath reflections reflected from generally horizontal surfaces may be received more strongly at the receiver 111,112 polarised towards the horizontal, and indirect/multipath reflections reflected from generally vertical surfaces may be received more strongly at the receiver 111,112 polarised towards the vertical. Direct reflections may be received with a similar strength at both receivers 111,112.

Transmission of linearly polarised electromagnetic radiation may provide more reliable results than transmission of unpolarised radiation. In addition, due to the abundance of horizontal and vertical man-made surfaces, more reliable results may be obtained using a horizontally polarised receiver 111 and a vertically polarised receiver 112.

In some scenarios a reflecting object may depolarise incident electromagnetic radiation (e.g. due to the material it is made of). Such an object may be referred to as a depolarising object. A problem with depolarising objects may be that the effect of any prior reflection is hidden by the depolarisation (e.g. a first reflection from a polarising surface may be hidden by the depolarisation caused by the depolarising object, thereby hiding the first reflection). The depolarisation may therefore cause an indirect/multipath reflection to appear to be a direct reflection.

The disclosed system 1 may be used to overcome this problem. In particular, the transmitter 101 and the receiver arrangement 110 may be co-located. In other words, the transmitter 101 and receiver arrangement 110 may be located in substantially the same location. The transmitter 101 and receiver arrangement 110 may be located within 50 cm, within 40 cm, within 30 cm, within 20 cm, within 10 cm, within 5 cm, within 1 cm, or within 5 mm of each other.

With a co-located transmitter 101 and receiver arrangement 110, the receiver arrangement 110 (e.g. the first receiver 111 and second receiver 112 thereof) may receive two reflections at substantially the same time. These reflections may correspond to the same reflection path, but traversed in opposite directions by the electromagnetic radiation. For example, the reflection path may be i. transmission; H. reflection from surface one; iii. reflection from surface two; iv. reception. Traversed in reverse, this path may be i. transmission; ii. reflection from surface two; iii. reflection from surface one; iv. reception. If surface one, for example, is a depolarising surface, then reflection from surface one immediately prior to reception may hide the previous reflection, whereas reflection from surface two immediately prior to reception would show polarisation and thereby be identifiable as an indirecUmultipath reflection.

For clarity, ghost objects identified by the methods disclosed above will be referred to as primary ghost objects. An object may be identified as a ghost object if the determined confidence level as described previously exceeds a predetermined threshold. The system 1 (e.g. controller 102) may also be configured to identify secondary ghost objects. Secondary ghost objects may be ghost objects that do not result in a characteristic polarisation of the reflected electromagnetic radiation.

Accordingly, the system 1 (e.g. the controller 102) may be configured to identify reflections received within a predetermined time interval of a primary ghost object as corresponding to secondary ghost objects. The time interval may be ±10% of the reflection time of the primary ghost object (e.g. if the time between transmission of the electromagnetic radiation and reception of the reflection corresponding to the primary ghost object was 1 ms, then the time interval may be 0.9-1.1 ms from transmission). The time interval may be ±20%, ±9%, ±8%, ±7%, ±6%, ±5%, ±4%, ±3%, ±2%, ±1%, ±0.9%, ±0.8±, ±0.7±, ±0.6%, ±0.5%, ±0.4%, ±0.3%, ±0.2%, ±0.1%, ±0.05%, or ±0.01% of the reflection time of the primary ghost object.

The system 1 (e.g. the controller 102) may be configured to identify reflections received from an object, whose apparent distance falls within a predetermined distance interval of a primary ghost object, as corresponding to a secondary ghost object. The distance interval may be ±10 cm, for example, or may be ±20 cm, ±9 cm, ±8 cm, ±7 cm, ±6 cm, ±5 cm, ±4 cm, ±3 cm, ±2 cm, ±1 cm, ±0.9 cm, ±0.8 cm, ±0.7 cm, ±0.6 cm, ±0.5 cm, ±0.4 cm, ±0.3 cm, ±0.2 cm, ±0.1 cm, ±0.05 cm, or ±0.01 cm. Therefore, objects detected at a substantially identical distance to a primary ghost object may be identified as secondary ghost objects.

The system 1 (e.g. controller 102) may be configured to determine a distance travelled by the transmitted electromagnetic radiation to the reflecting object, to group reflecting objects having substantially identical determined distances detected at substantially the same time, and to use the highest determined confidence level in the group to determine the confidence levels for the other reflecting objects in the group. Therefore, the confidence level associated with a primary ghost object may affect the confidence level associated with a secondary ghost object. In this way the system 1 may not apply a binary categorisation of objects as real or ghost, but may instead modify the confidence level associated with reflecting objects based on the confidence level associated with other reflecting objects in a group of reflecting objects.

The controller 102 may discard object data determined to correspond to a ghost object (i.e. ghost object data). For example, the controller 102 may not output ghost object data to the on-board computer system 121, or to any other devices. Real object data may be output by the controller 102 to the on-board computer system 121 or to another device (e.g. remote device 20). For example, real object data may be output to the vehicle control module, whereas ghost object data may not be output to the vehicle control module. Accordingly, the controller 102 may be configured to output object data having a confidence level that falls within a predetermined threshold to the vehicle control module and to discard object data having a confidence level that exceeds the predetermined threshold. The controller may be configured to output object data associated with a lower confidence level of corresponding to a ghost object relative to a predetermined threshold confidence level to the vehicle control module, and to discard object data associated with a higher confidence level of corresponding to a ghost object compared to the predetermined threshold confidence level.

In some versions all object data may be output by the controller 102 (e.g. to the remote device 20 and/or on-board computer system 121, for example to the vehicle control module). However, the controller 102 may identify ghost object data and real object data in the output data. The receiving device (e.g. remote device 20 and/or on-board computer system 121) may then discard the ghost object data or exclude the ghost object data from further operations.

The controller 102 may be configured to output object data corresponding to the reflecting object to the vehicle control module, wherein the object data includes the confidence level that the reflecting object is a ghost object, and the vehicle control module may be configured to control movement of the vehicle 12 based at least partially on the object data. The vehicle control module may be configured such that object data associated with a lower confidence level of corresponding to a ghost object has a greater influence on the control of the vehicle movement than object data associated with a higher confidence level of corresponding to a ghost object.

The vehicle control module may, therefore, be configured to control the vehicle 12 using the real object data, but not the ghost object data. In some versions the confidence level associated with the object data may influence the control of the vehicle 12 by the vehicle control module (e.g. such that the object data associated with a lower confidence level of corresponding to a ghost object has a greater influence on the control of the vehicle movement than object data associated with a higher confidence level of corresponding to a ghost object). The safety of the vehicle 12 may therefore be improved. Furthermore, the system 1 provides more reliable object detection in all use cases (e.g. whether applied to the vehicle 12 or not).

In alternative versions, the vehicle control module may be configured such that object data associated with a lower confidence level of corresponding to a ghost object has a lower influence on the control of the vehicle movement than object data associated with a higher confidence level of corresponding to a ghost object.

The system 1 may be provided as a secondary object detection system 1 designed to complement a primary object detection system (which may be a vehicular primary object detection system, e.g. a primary object detection system that is installed in or on the vehicle 12). The primary object detection system may be operably coupled to the vehicle control module and the vehicle control module may control the vehicle 12 based at least partially on data received from the primary object detection system. The primary object detection system may be a radar system, for example. The primary object detection system may include MIMO (multiple input multiple output) sensors (e.g. multiple antennae at the receiver and/or transmitter). The primary object detection system may include a frequency modulated continuous wave radar system. The primary object detection system may detect and/or track objects.

The secondary object detection system 1 may identify objects detected by the primary object detection system as real or ghost objects, or may determine a confidence level for the detected objects (e.g. reflecting objects) as described herein. The secondary object detection system 1 may, therefore, provide a check on the objects detected by the primary object detection system. As such, the secondary object detection system 1 may operate with a slower coherent processing interval compared to the primary object detection system and/or may have a worse resolution than the primary object detection system. The secondary object detection system 1 may operate using a different frequency band to that used by the primary object detection system. The secondary object detection system 1 may operate using a frequency band that is at a lower frequency than the frequency band used by the primary object detection system. The secondary object detection system 1 may operate using a frequency band that is at a higher frequency than the frequency band used by the primary object detection system.

The present disclosure has been described with reference to real and ghost objects for ease of understanding. It will be appreciated that identification of an object as a real object or a ghost object, or determination of a confidence level of an object being a ghost object, may include characterising data points generated by the receiver arrangement 110 as real or ghost data points (or associating a corresponding confidence level with the data points), e.g. as corresponding to direct or indirect/multipath reflections. The identification of objects as real or ghost objects, or the determination of the confidence level, may therefore equivalently be described as the identification of direct or indirecUmultipath reflections (or the determination of a confidence level that received electromagnetic radiation has arrived at the receivers by an indirect path), and an "object" may correspond to received electromagnetic radiation (which can be identified as real, i.e. directly reflected, or ghost, i.e a multipath reflection -or which has an associated confidence level as described).

Fig. 4 shows the output from a MATLAB simulation of the polarisation states of reflected electromagnetic radiation in a scenario. The scenario is a vehicle-mounted system 1 (i.e. ego) following a lead vehicle at a distance of 50 m. A vertical concrete wall is modelled as being positioned 3.5 m to the side of the ego and running parallel with the road along which the ego travels. The system 1 mounted on the ego is modelled as being 0.9 m above the road surface. The road surface and concrete wall are modelled as having identical relative permittivities of Cr = 4.5. The transmitted (outgoing) radar beam is modelled as a linear superposition of unit "vertical" (V) and "horizontal" (H) polarisation states, in-phase, to mimic a transmitted radar pulse with linear polarisation at an angle of 45° relative to horizontal.

The path 601 shows the polarisation state of the transmitted radar pulse, which is 45°. The path 602 shows the polarisation state of a direct reflection from the lead vehicle, which is also 45°. The path 603 shows the polarisation state of a multipath reflection that has been reflected from the lead vehicle and subsequently from the concrete wall, which is closer to the vertical than the transmitted radar pulse. The path 604 shows the polarisation state of a multipath reflection that has been reflected from the lead vehicle and subsequently from the road surface, which is closer to the horizontal than the transmitted radar pulse. Accordingly, multipath reflections from the concrete wall would be received more strongly by a vertically polarised receiver (compared to a horizontally polarised receiver), multipath reflections from the road surface would be received more strongly by a horizontally polarised receiver (compared to a vertically polarised receiver), and the strength of direct reflections would be about equal at a horizontally and a vertically polarised receiver.

In some versions the receiver arrangement 110 may include more than two receivers 111,112, 113,114 (see e.g. Fig. 5). The receiver arrangement 110 may further include a third receiver 113 and may include a fourth receiver 114.

The receiver arrangement 110 may include a third receiver 113. The third receiver 113 may be configured to receive electromagnetic radiation. The third receiver 113 may be configured to receive polarised electromagnetic radiation. The third receiver 113 may, therefore, be a third polarised receiver 113. The third receiver 113 may be configured to receive linearly polarised electromagnetic radiation. The third receiver 113 may, therefore, be a third linearly polarised receiver 113. In some versions the third receiver 113 may be a radar and/or lidar receiver 113.

In some versions (e.g. as illustrated schematically in Fig. 5), the third receiver 113 may be polarised at an angle of about 45° relative to horizontal or relative to a ground surface that supports the third receiver 113. However, other orientations of linear polarisation are possible (e.g. at any angle relative to the horizontal or vertical or at any angle of rotation of the direction of polarisation about the (perpendicular) axis along which the electromagnetic radiation is transmitted and/or received).

The receiver arrangement 110 may include a fourth receiver 114. The fourth receiver 114 may be configured to receive electromagnetic radiation. The fourth receiver 114 may be configured to receive polarised electromagnetic radiation. The fourth receiver 114 may, therefore, be a fourth polarised receiver 114. The fourth receiver 114 may be configured to receive linearly polarised electromagnetic radiation. The fourth receiver 114 may, therefore, be a fourth linearly polarised receiver 114. In some versions the fourth receiver 114 may be a radar and/or lidar receiver 114.

In some versions (e.g. as illustrated schematically in Fig. 5), the fourth receiver 114 may be polarised at an angle of about 45° relative to horizontal or relative to a ground surface that supports the fourth receiver 114. However, other orientations of linear polarisation are possible (e.g. at any angle relative to the horizontal or vertical or at any angle of rotation of the direction of polarisation about the (perpendicular) axis along which the electromagnetic radiation is transmitted and/or received).

The third and fourth receivers 113,114 may both be linearly polarised. The orientation of polarisation of the third receiver 113 may be offset from the orientation of polarisation of the fourth receiver 114. The offset may be at least 10°, at least 200, at least 30°, at least 40°, at least 50°, at least 60°, at least 70°, at least 75°, at least 80°, at least 85°, at least 86°, at least 87°, at least 88°, or at least 89°. The offset may be approximately 90°. It will be appreciated that 90° is the maximum possible offset between polarisations (e.g. an offset of 180° is equivalent to an offset of 0°).

The linear polarisation of the third receiver 113 may be orthogonal, or substantially orthogonal, to the polarisation of the fourth receiver 114. In some versions the third receiver 113 may be polarised at an angle of about 45° relative to horizontal and the fourth receiver 114 may be polarised at an angle of about 45° relative to horizontal, wherein the polarisation of the third receiver 113 is orthogonal to the polarisation of the fourth receiver 114 (see e.g. Fig. 5). The third receiver 113 may, therefore, be polarised at an angle corresponding to a clockwise rotation of about 45° relative to horizontal and the fourth receiver 114 may be polarised at an angle corresponding to an anti-clockwise (or counter-clockwise) rotation of about 45° relative to horizontal.

Each transmitter 101 and receiver 111,112,113,114 described herein may include an associated antenna, which may be polarised as described for each transmitter 101 and/or receiver 111,112,113,114.

In some versions, therefore, the receiver arrangement 110 may include four receivers 111,112,113,114, which may each be linearly polarised. The receiver arrangement 110 may include two pairs of orthogonally polarised receivers 111,112 and 113,114. The angles of polarisation of the first orthogonal pair may be offset from the angles of polarisation of the second orthogonal pair by about 45°. In such versions, the transmitter 101 may be configured to transmit unpolarised electromagnetic radiation. Such arrangements may allow indirect/multipath reflections reflected from a reflecting surface at any angle to be detected by the system 1 (e.g. by the controller 102).

In some versions the system 1 may include more than one transmitter 101. The system 1 may include a plurality of transmitters 101. The system 1 may for example include the first transmitter 101a and the second transmitter 101b. Each transmitter 101a,101b may be polarised and may be linearly polarised. The polarisation of the first transmitter 101a may be offset from the polarisation of the second transmitter 101b. The offset may be at least 100, at least 20°, at least 30°, at least 40°, at least 50°, at least 60°, at least 70°, at least 75°, at least 80°, at least 85°, at least 86°, at least 87°, at least 88°, or at least 89°. The offset may be approximately 90°. It will be appreciated that 90° is the maximum possible offset between polarisations (e.g. an offset of 180° is equivalent to an offset of 0°).

The linear polarisation of the first transmitter 101a may be orthogonal, or substantially orthogonal, to the linear polarisation of the second transmitter 101b. In some versions the first transmitter 101a may be horizontally polarised and the second transmitter 101b may be vertically polarised.

In such versions the system 1 may include the first receiver 111 and the second receiver 112 as described herein (and may optionally include the third and fourth receivers 113,114).

Systems 1 including the first and second transmitters 101a,101b and the first and second receivers 111,112 may therefore include polarimetric systems 1 (e.g. quadrature polarised or fully polarimetric systems 1). The system 1 may therefore include HH, VV, HV, and VH (where H means horizontal and V means vertical) transmit and receive arrangements.

In some versions the system 1 may include the first, second, third and fourth receivers 111,112,113,114 as described herein (e.g. with a 45° polarisation offset between receivers, for example such that the system 1 includes two pairs of orthogonally polarised receivers 111,112 and 113,114. The angles of polarisation of the first orthogonal pair may be offset from the angles of polarisation of the second orthogonal pair by about 45°). The system 1 may also include a pair of transmitters 101a,101b, which may each be linearly polarised. The angle of polarisation of the first transmitter 101a may be offset from the angle of polarisation of the second transmitter 101b by about 45°. One of the transmitters 101a,101b may be polarised at about 45° relative to horizontal and the other of the transmitters 101a,101b may therefore be either horizontally or vertically polarised. In such versions, the first transmitter 101a may use a different frequency band to that used by the second transmitter 101b. The first and second transmitters 101a,101b may transmit at separate time intervals such that the transmissions of the first and second transmitters 101a,101b do not overlap.

In some versions the position and function of the transmitter(s) and receiver(s) described herein may be reversed -i.e. such that the references to transmitter(s) are replaced with references to receiver(s) and vice versa.

The system 1 may, therefore, include a pair of transmitters 101a,101b and a single receiver 111 in some versions (see e.g. Fig. 7). In such versions, only one of the transmitters 101a,101b may be active in a given coherent processing interval. The active transmitter may alternate between the first transmitter 101a and the second transmitter 101b between coherent processing intervals. In a first coherent processing interval the first transmitter 101a may be active, and in a second coherent processing interval the second transmitter 101b may be active. The first and second coherent processing intervals may be sequential coherent processing intervals. The active transmitter may, therefore, alternate between the first transmitter 101a and the second transmitter 101b. The receiver 111 may be active in all coherent processing intervals. Accordingly, only one of the transmitters 101a,101b may be active at any given time.

Accordingly, the arrangement of the transmitters 101a,101b and the receiver 111 may be as described above, with the positions of the transmitters and receivers reversed. The transmitters 101a,101b may each be configured to transmit linearly polarised radiation, and the receiver may also be linearly polarised.

The first transmitter 101a may be configured to transmit electromagnetic radiation. The first transmitter 101a may be configured to transmit polarised electromagnetic radiation. The first transmitter 101a may, therefore, be a first polarised transmitter 101a. The first transmitter 101a may be configured to transmit linearly polarised electromagnetic radiation. The first transmitter 101a may, therefore, be a first linearly polarised transmitter 101a. In some versions the first transmitter 101a may be a radar and/or lidar transmitter 101a.

In some versions (e.g. as illustrated schematically in Fig. 7), the first transmitter 101a may be horizontally polarised. However, other orientations of linear polarisation are possible (e.g. at any angle relative to the horizontal or vertical or at any angle of rotation of the direction of polarisation about the (perpendicular) axis along which the electromagnetic radiation is transmitted and/or received).

The second transmitter 101b may be configured to transmit electromagnetic radiation. The second transmitter 101b may be configured to transmit polarised electromagnetic radiation. The second transmitter 101b may, therefore, be a second polarised transmitter 101b. The second transmitter 101b may be configured to transmit linearly polarised electromagnetic radiation. The second transmitter 101b may, therefore, be a second linearly polarised transmitter 101b. In some versions the second transmitter 101b may be a radar and/or lidar transmitter 101b.

In some versions (e.g. as illustrated schematically in Fig. 1), the second transmitter 101b may be vertically polarised. However, other orientations of linear polarisation are possible (e.g. at any angle relative to the horizontal or vertical or at any angle of rotation of the direction of polarisation about the (perpendicular) axis along which the electromagnetic radiation is transmitted and/or received).

The first and second transmitters 101a,101b may both be linearly polarised. The polarisation of the first transmitter 101a may be offset from the polarisation of the second transmitter 101b. The offset may be at least 100, at least 20°, at least 30°, at least 40°, at least 50°, at least 60°, at least 70°, at least 75°, at least 80°, at least 85°, at least 86°, at least 87°, at least 88°, or at least 89°. The offset may be approximately 90°. It will be appreciated that 90° is the maximum possible offset between polarisations (e.g. an offset of 180° is equivalent to an offset of 0°).

Each transmitter 101a,101b may be configured to transmit linearly polarised electromagnetic radiation at any angle of rotation of a plane in which lies a vector parallel to the axis of transmission (e.g. with the angle measured as the rotation about the axis of transmission), or at any angle of rotation of the direction of polarisation about the (perpendicular) axis along which the electromagnetic radiation is transmitted and/or received.

The receiver 111 may be configured to receive electromagnetic radiation. The receiver 111 may be configured to receive polarised electromagnetic radiation. The receiver 111 may, therefore, be a polarised receiver 111. The receiver 111 may be configured to receive linearly polarised electromagnetic radiation. The receiver 111 may, therefore, be a linearly polarised receiver 111.

In some versions the receiver 111 may be a radar and/or lidar receiver 111.

The receiver 111 may be polarised at an angle in the range of about 20-70°, about 25-65°, about 30-60°, about 35-55°, or about 40-50° relative to horizontal or relative to a ground surface that supports the receiver 111 (whether directly or indirectly, e.g. when the system 1 or receiver 111 is mounted to the vehicle 12).

In some versions (e.g. as illustrated schematically in Fig. 7), the receiver 111 may be polarised at an angle of about 45° relative to horizontal or relative to a ground surface that supports the receiver 111. However, other orientations of linear polarisation are possible (e.g. at any angle relative to the horizontal or vertical or at any angle of rotation of the direction of polarisation about the (perpendicular) axis along which the electromagnetic radiation is transmitted and/or received).

The polarisation of the first and/or second transmitter 101a,101b may be offset from the polarisation of the receiver 111. The polarisation of both the first and second transmitters 101a,101b may be offset from the polarisation of the receiver 111. The polarisation offset between the first transmitter 101a and the receiver 111 (e.g. measured in degrees) may be substantially equal to the polarisation offset between the second transmitter 101b and the receiver 111 (e.g. measured in degrees). However, the polarisation offset between the first transmitter 101a and the receiver 111 may be in a direction that is substantially opposite to the direction of the polarisation offset between the second transmitter 101b and the receiver 111.

For example, the angle of polarisation of the first transmitter 101a may be defined by rotating the angle of polarisation of the receiver 111 by a predetermined number of degrees in a clockwise direction, whereas the angle of polarisation of the second transmitter 101b may be defined by rotating the angle of polarisation of the receiver 111 by the predetermined number of degrees in an anti-clockwise (i.e. counter-clockwise) direction.

For example, the receiver 111 may be polarised at an angle of approximately 45° relative to horizontal or relative to a ground surface that supports the receiver 111. The first transmitter 101a may be polarised at an angle between 0° and 44° relative to horizontal or relative to a ground surface that supports the first transmitter 101a (whether directly or indirectly, e.g. when the system 1 or first transmitter 101a is mounted to the vehicle 12), whereas the second transmitter 101b may be polarised at an angle between 46° and 90° relative to horizontal or relative to a ground surface that supports the second transmitter 101b (whether directly or indirectly, e.g. when the system 1 or second transmitter 101b is mounted to the vehicle 12). As stated herein, the offset between the polarisation of the receiver 111 and each transmitter 101a,101b may be substantially equal. Therefore, the polarisation of each transmitter 101a,101b may be offset from the polarisation of the receiver 111 by about 5°, about 10°, about 15°, about 20°, about 25°, about 30°, about 35°, about 40°, or about 45°. The polarisation of each transmitter 101a,101b may be offset from the polarisation of the receiver 111 by an angle in the range of about 5-45°, about 10-45°, about 1545°, about 20-45°, about 25-45°, about 30-45°, about 35-45°, about 40-45°, about 41-45°, about 42-45°, about 43-45°, or about 44-45°.

In an example, therefore, the receiver 111 may be polarised at angle of about 45° relative to horizontal and the polarisation of each transmitter 101a,101b may be offset from the polarisation of the receiver 111 by about 45°. In other words, the receiver 111 may be polarised at an angle of about 45° relative to horizontal, the first transmitter 101a may be horizontally polarised, and the second transmitter 101b may be vertically polarised (or the first transmitter 101a may be vertically polarised with the second transmitter 101b horizontally polarised).

Accordingly, the system 1 may operate as described previously to identify ghost objects. In other words, the system 1 may be configured to identify multipath reflections. The system 1 may be configured to determine a confidence level that a detected object (e.g. a reflecting object) is a ghost object and/or that electromagnetic radiation received by the system 1 (e.g. by the receiver arrangement 110 thereof) corresponds to a ghost object. The system 1 may be configured to determine a confidence level that electromagnetic radiation received by the system 1 (e.g. by the receiver 111 thereof) has arrived at the system 1 (e.g. at the receiver 111 thereof) by an indirect path, as described previously.

In particular, the receiver 111 may output signals representative of the received electromagnetic radiation, which may be representative of the strength of the received electromagnetic radiation. The receiver 111 may output at least one first signal representative of the received electromagnetic radiation (e.g. representative of the strength of the received electromagnetic radiation) in a first coherent processing interval, which may be representative of a reflection of electromagnetic radiation transmitted by the first transmitter 101a. The receiver 111 may output at least one second signal representative of the received electromagnetic radiation (e.g. representative of the strength of the received electromagnetic radiation) in a second coherent processing interval, which may be representative of a reflection of the radiation transmitted by the second transmitter 101b. The signals may be output to the controller 102.

The receiver 111 may output signals representative of the power and/or amplitude of the received electromagnetic radiation. The receiver 111 may output at least one first signal representative of the power and/or amplitude of the received electromagnetic radiation from the first coherent processing interval (e.g. corresponding to radiation transmitted by the first transmitter 101a). The receiver 111 may output at least one second signal representative of the power and/or amplitude of the received electromagnetic radiation from the second coherent processing interval (e.g. corresponding to radiation transmitted by the second transmitter 101b). The signals may be output to the controller 102.

The controller 102 may be configured to receive the signals output by the receiver 111. The controller 102 may be configured to identify ghost objects using the received signals (e.g. using the signals representative of the received electromagnetic radiation and/or signals representative of the strength and/or power and/or amplitude of the received electromagnetic radiation). The controller 102 may be configured to identify mulfipath reflections using the received signals (e.g. using the signals representative of the received electromagnetic radiation and/or signals representative of the strength and/or power and/or amplitude of the received electromagnetic radiation). The controller 102 may be configured to determine a confidence level that the received electromagnetic radiation has arrived at the receivers by an indirect path using the signals representative of the received electromagnetic radiation (e.g. using the signals representative of the strength and/or power and/or amplitude of the received electromagnetic radiation). The controller 102 may be configured to determine a confidence level that a detected object (e.g. a reflecting object) is a ghost object using the signals representative of the received electromagnetic radiation (e.g. using the signals representative of the strength and/or power and/or amplitude of the received electromagnetic radiation).

The controller 102 may be configured to determine a ratio between the first signal (corresponding to the first coherent processing interval and/or corresponding to radiation transmitted by the first transmitter 101a) received from the receiver 111 and the second signal (corresponding to the second coherent processing interval and/or corresponding to radiation transmitted by the second transmitter 101b) received from the receiver 111. The controller 102 may be configured to determine a ratio between the strength and/or power and/or amplitude of the electromagnetic radiation received by the receiver 111 in the first coherent processing interval and/or from the first transmitter 101a and the strength and/or power and/or amplitude of the electromagnetic radiation received by the receiver 111 in the second coherent processing interval and/or from the second transmitter 101b. The signals received from the receiver 111 may, therefore, each have an associated magnitude, and the magnitudes associated with the signals may be compared to determine the ratio between the signals.

The determined ratio may, therefore, reflect the relative strength and/or power and/or amplitude of the electromagnetic radiation received by the receiver 111 in each coherent processing interval and/or from each transmitter 101a,101b. In some versions the strength and/or power and/or amplitude of the electromagnetic radiation detected by the receiver 111 may be determined as an absolute value (e.g. measured in dB, dBm, dBW, and/or watts). In some versions the strength and/or power and/or amplitude of the electromagnetic radiation detected by the receiver 111 may be determined as a relative value which may not be calibrated to an absolute value. The ratio may be determined by dividing the strength and/or power and/or amplitude of the electromagnetic radiation received by the receiver 111 in the first coherent processing interval and/or from the first transmitter 101a by the strength and/or power and/or amplitude of the electromagnetic radiation received by the receiver 111 in the second coherent processing interval or from the second transmitter 101b (or vice versa). The ratio may therefore be determined in the form x:y where x and y are numbers representing the strength and/or power and/or amplitude of the electromagnetic radiation received by the receiver 111 or in the form z where z is a number determined by dividing the strength and/or power and/or amplitude of electromagnetic radiation received by the receiver 111 in the first coherent processing interval and/or from the first transmitter 101a by the strength and/or power and/or amplitude of electromagnetic radiation receiver by the receiver 111 in the second coherent processing interval and/or from the second transmitter 101b (or vice versa), for example.

The controller 102 may be configured to determine a confidence level that the received electromagnetic radiation has arrived at the receiver by an indirect path and/or that a detected object (e.g. a reflecting object) is a ghost object using the determined ratio. For example, the controller 102 may be configured to determine the confidence level by determining a ratio between the power and/or amplitude of electromagnetic radiation received by the receiver 111 during the first coherent processing interval and/or from the first transmitter 101a and the power and/or amplitude of electromagnetic radiation received by the receiver 111 in the second coherent processing interval and/or from the second transmitter 101b. For example, the confidence level may increase as the difference in strength and/or power and/or amplitude of the electromagnetic radiation received by the receiver 111 in each coherent processing interval and/or from each transmitter 101a,101b increases (e.g. as the determined ratio increases). The confidence level may, therefore, be proportional to the determined ratio and/or may be proportional to the difference in strength and/or power and/or amplitude of the electromagnetic radiation received by the receiver 111 in each coherent processing interval and/or from each transmitter 101a,101b.

The system 1 may, therefore, use two transmitters 101a,101b and a single receiver 111 to identify ghost objects and/or determine a confidence level that received electromagnetic radiation has arrived at the receiver 111 by an indirect path and/or that a detected object (e.g. a reflecting object) is a ghost object in a similar manner to the system 1 with one transmitter 101 and two receivers 111,112 described previously, with the signals used by the controller corresponding to first and second coherent processing intervals (i.e. radiation transmitted from the first transmitter 101a and second transmitter 101b) rather than corresponding to first and second receivers.

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The invention may also broadly consist in the parts, elements, steps, examples and/or features referred to or indicated in the specification individually or collectively in any and all combinations of two or more said parts, elements, steps, examples and/or features. In particular, one or more features in any of the embodiments described herein may be combined with one or more features from any other embodiment(s) described herein.

Protection may be sought for any features disclosed in any one or more published documents referenced herein in combination with the present disclosure.

Although certain example embodiments of the invention have been described, the scope of the appended claims is not intended to be limited solely to these embodiments. The claims are to be construed literally, purposively, and/or to encompass equivalents.

ASPECTS

1. A system including: a first linearly polarised transmitter configured to transmit electromagnetic radiation in a first coherent processing interval; a second linearly polarised transmitter configured to transmit electromagnetic radiation in a second coherent processing interval, wherein the polarisation of the first transmitter is offset from the polarisation of the second transmitter; a receiver configured to receive reflections of the transmitted electromagnetic radiation and to output a first signal representative of the strength of the electromagnetic radiation received in the first coherent processing interval and a second signal representative of the strength of the electromagnetic radiation received in the second coherent processing interval; and a controller configured to: receive the signals representative of the strength of the received electromagnetic radiation, and determine a confidence level that the reflections correspond to a ghost object using the signals representative of the strength of the received electromagnetic radiation.

2. A system according to aspect 1, wherein the offset in polarisation between the first and second transmitters is greater than 60 degrees or is about 90 degrees.

3. A system according to any preceding aspect, wherein the receiver is a linearly polarised receiver.

4. A system according to aspect 3, wherein the polarisation angle of the receiver bisects the angle between the two transmitters.

5. A system according to aspects or 4, wherein the receiver is polarised at an angle in the range of about 30-60 degrees or about 45 degrees relative to horizontal.

6. A system according to any of aspects 3-5, wherein the polarisation of the first transmitter is offset from the polarisation of the receiver by about 40-50 degrees or about 45 degrees.

7. A system according to aspect 6, wherein the receiver is polarised at an angle of about 45 degrees relative to horizontal, the first transmitter is horizontally polarised, and the second transmitter is vertically polarised.

8. A system according to any preceding aspect, wherein the signals representative of the strength of the received electromagnetic radiation are representative of the power and/or amplitude of the received electromagnetic radiation, and the controller is configured to determine the confidence level by determining a ratio between the power and/or amplitude of electromagnetic radiation received in the first coherent processing interval and the power and/or amplitude of electromagnetic radiation received in the second coherent processing interval.

9. A system according to any preceding aspect, further including a vehicle control module operatively coupled to the controller, wherein the controller is configured to output object data corresponding to the reflections to the vehicle control module, wherein the object data includes the confidence level that the reflections correspond to a ghost object, and wherein the vehicle control module is configured to control movement of a vehicle based at least partially on the object data.

10. A system according to aspect 9, wherein the vehicle control module is configured such that object data associated with a lower confidence level of corresponding to a ghost object has a greater influence on the control of the vehicle movement than object data associated with a higher confidence level of corresponding to a ghost object.

11. A system according to aspect 9 or 10, wherein the controller is configured to output object data associated with a lower confidence level of corresponding to a ghost object relative to a predetermined threshold confidence level to the vehicle control module, and to discard object data associated with a higher confidence level of corresponding to a ghost object compared to the predetermined threshold confidence level.

12. A system according to any preceding aspect, wherein the controller is configured to determine a distance travelled by the transmitted electromagnetic radiation to a reflecting object, to group reflecting objects having substantially identical determined distances detected at substantially the same times, and to use the highest determined confidence level in the group to determine the confidence levels for the other reflecting objects in the group.

13. A method including: transmitting electromagnetic radiation in a first coherent processing interval from a first linearly polarised transmitter; transmitting electromagnetic radiation in a second coherent processing interval from a second linearly polarised transmitter, wherein the polarisation of the first transmitter is offset from the polarisation of the second transmitter; receiving, at a receiver, reflections of the transmitted electromagnetic radiation; outputting, from the receiver, a first signal representative of the strength of the electromagnetic radiation received in the first coherent processing interval and a second signal representative of the strength of the electromagnetic radiation received in the second coherent processing interval; and determining, using a controller, a confidence level that the reflections correspond to a ghost object using the signals representative of the strength of the received electromagnetic radiation.

14. A method according to aspect 13, wherein the offset in polarisation between the first and second transmitters is greater than 60 degrees or is about 90 degrees.

15. A method according to any of aspects 13-14, wherein the receiver is a linearly polarised receiver.

16. A method according to aspect 15, wherein the polarisation angle of the receiver bisects the angle between the two transmitters.

17. A method according to aspect 15 or 16, wherein the receiver is polarised at an angle in the range of about 30-60 degrees or about 45 degrees relative to horizontal.

18. A method according to any of aspects 15-17, wherein the polarisation of the first transmitter is offset from the polarisation of the receiver by about 40-50 degrees or about 45 degrees.

19. A method according to aspect 18, wherein the receiver is polarised at an angle of about 45 degrees relative to horizontal, the first transmitter is horizontally polarised, and the second transmitter is vertically polarised.

20. A method according to any of aspects 13-19, wherein the signals representative of the strength of the received electromagnetic radiation are representative of the power and/or amplitude of the received electromagnetic radiation, and the controller is configured to determine the confidence level by determining a ratio between the power and/or amplitude of electromagnetic radiation received in the first coherent processing interval and the power and/or amplitude of electromagnetic radiation received in the second coherent processing interval.

21. A method according to any of aspects 13-20, further including outputting object data corresponding to the reflections to a vehicle control module, wherein the object data includes the confidence level that the reflections correspond to a ghost object, and wherein the vehicle control module is configured to control movement of a vehicle based at least partially on the object data.

22. A method according to aspect 21, wherein the vehicle control module is configured such that object data associated with a lower confidence level of corresponding to a ghost object has a greater influence on the control of the vehicle movement than object data associated with a higher confidence level of corresponding to a ghost object.

23. A method according to aspect 21 or 22, including outputting object data associated with a lower confidence level of corresponding to a ghost object relative to a predetermined threshold confidence level to the vehicle control module, and discarding object data associated with a higher confidence level of corresponding to a ghost object compared to the predetermined threshold confidence level.

24. A method according to any of aspects 13-23, including determining, using the controller, a distance travelled by the transmitted electromagnetic radiation to a reflecting object, grouping reflecting objects having substantially identical determined distances detected at substantially the same times, and using the highest determined confidence level in the group to determine the confidence levels for the other reflecting objects in the group.

Claims

CLAIMS1. A system including: a first linearly polarised receiver configured to receive electromagnetic radiation and to output at least one signal representative of the strength of the received electromagnetic radiation; a second linearly polarised receiver configured to receive electromagnetic radiation and to output at least one signal representative of the strength of the received electromagnetic radiation, wherein the polarisation of the first receiver is offset from the polarisation of the second receiver; and a controller configured to: receive the signals representative of the strength of the received electromagnetic radiation, and determine a confidence level that the received electromagnetic radiation has arrived at the receivers by an indirect path using the signals representative of the strength of the received electromagnetic radiation.
2. A system according to claim 1, wherein the offset in polarisation between the first and second receivers is greater than 60 degrees or is about 90 degrees.
3. A system according to any preceding claim, further including a transmitter configured to transmit electromagnetic radiation, wherein the first and second linearly polarised receivers are configured to receive reflections of the transmitted electromagnetic radiation, and wherein determining the confidence level that the received electromagnetic radiation has arrived at the receivers by an indirect path includes determining a confidence level that the reflections correspond to a ghost object using the signals representative of the strength of the received electromagnetic radiation.
4. A system according to claim 3, wherein the transmitter is configured to transmit linearly polarised electromagnetic radiation.
5. A system according to claim 4, wherein the transmitter is configured to transmit electromagnetic radiation polarised at an angle that bisects the angle between the two receivers.
6. A system according to claim 4 or 5, wherein the transmitter is configured to transmit electromagnetic radiation polarised at an angle in the range of about 30-60 degrees or about 45 degrees relative to horizontal.
7. A system according to any of claims 3-6, wherein the polarisation of the first receiver is offset from the polarisation of the transmitted electromagnetic radiation by about 40-50 degrees or about 45 degrees.
8. A system according to claim 7, wherein the transmitter is configured to transmit electromagnetic radiation polarised at an angle of about 45 degrees relative to horizontal, the first receiver is horizontally polarised, and the second receiver is vertically polarised.
9. A system according to any preceding claim, wherein the signals representative of the strength of the received electromagnetic radiation are representative of the power and/or amplitude of the received electromagnetic radiation, and the controller is configured to determine the confidence level by determining a ratio between the power and/or amplitude of electromagnetic radiation received by the first receiver and the power and/or amplitude of electromagnetic radiation received by the second receiver.
10. A system according to any preceding claim, wherein the system includes a radar system and the electromagnetic radiation includes a radio wave.
11. A system according to any of claims 3-10, wherein the transmitter is configured to transmit electromagnetic radiation within a predetermined frequency band and an operative frequency band of the first and second receivers corresponds to the predetermined frequency band.
12. A system according to any of claims 3-11, further including a vehicle control module operatively coupled to the controller, wherein the controller is configured to output object data corresponding to the reflections to the vehicle control module, wherein the object data includes the confidence level that the reflections correspond to a ghost object, and wherein the vehicle control module is configured to control movement of a vehicle based at least partially on the object data.
13. A system according to claim 12, wherein the vehicle control module is configured such that object data associated with a lower confidence level of corresponding to a ghost object has a greater influence on the control of the vehicle movement than object data associated with a higher confidence level of corresponding to a ghost object.
14. A system according to claim 12 or 13, wherein the controller is configured to output object data associated with a lower confidence level of corresponding to a ghost object relative to a predetermined threshold confidence level to the vehicle control module, and to discard object data associated with a higher confidence level of corresponding to a ghost object compared to the predetermined threshold confidence level.
15. A system according to any of claims 3-14, wherein the controller is configured to determine a distance travelled by the transmitted electromagnetic radiation to a reflecting object, to group reflecting objects having substantially identical determined distances detected at substantially the same times, and to use the highest determined confidence level in the group to determine the confidence levels for the other reflecting objects in the group.
16. A method including: receiving, at a first linearly polarised receiver, electromagnetic radiation, and outputting at least one signal representative of the strength of the received electromagnetic radiation from the first receiver; receiving, at a second linearly polarised receiver, electromagnetic radiation, and outputting at least one signal representative of the strength of the received electromagnetic radiation from the second receiver, wherein the polarisation of the first receiver is offset from the polarisation of the second receiver; receiving, at a controller, the signals representative of the strength of the received electromagnetic radiation, and determining, using the controller, a confidence level that the received electromagnetic radiation has arrived at the receivers by an indirect path using the signals representative of the strength of the received electromagnetic radiation.
17. A method according to claim 16, wherein the offset in polarisation between the first and second receivers is greater than 60 degrees or is about 90 degrees.
18. A method according to claim 16 or 17, further including: transmitting, from a transmitter, the electromagnetic radiation; and receiving reflections of the transmitted electromagnetic radiation at the first and second receivers, wherein determining the confidence level that the received electromagnetic radiation has arrived at the receivers by an indirect path includes determining a confidence level that the reflections correspond to a ghost object using the signals representative of the strength of the received electromagnetic radiation.
19. A method according to claim 18, wherein the transmitted electromagnetic radiation is linearly polarised electromagnetic radiation.
20. A system according to claim 19, wherein the transmitted electromagnetic radiation is polarised at an angle that bisects the angle between the two receivers.
21. A method according to claim 19 01 20, wherein the transmitted electromagnetic radiation is polarised at an angle in the range of about 30-60 degrees or about 45 degrees relative to horizontal.
22. A method according to any of claims 18-21, wherein the polarisation of the first receiver is offset from the polarisation of the transmitted electromagnetic radiation by about 40-50 degrees or about 45 degrees.
23. A method according to claim 22, wherein the transmitted electromagnetic radiation is polarised at an angle of about 45 degrees relative to horizontal, the first receiver is horizontally polarised, and the second receiver is vertically polarised.
24. A method according to any of claims 16-23, wherein the signals representative of the strength of the received electromagnetic radiation are representative of the power and/or amplitude of the received electromagnetic radiation, and the controller is configured to determine the confidence level by determining a ratio between the power and/or amplitude of electromagnetic radiation received by the first receiver and the power and/or amplitude of electromagnetic radiation received by the second receiver.
25. A method according to any of claims 16-24, wherein the electromagnetic radiation includes a radio wave.
26. A method according to any of claims 18-25, wherein the electromagnetic radiation is transmitted from the transmitter within a predetermined frequency band and an operative frequency band of the first and second receivers corresponds to the predetermined frequency band.
27. A method according to any of claims 18-26, further including outputting object data corresponding to the reflections to a vehicle control module, wherein the object data includes the confidence level that the reflections correspond to a ghost object, and wherein the vehicle control module is configured to control movement of a vehicle based at least partially on the object data.
28. A method according to claim 27, wherein the vehicle control module is configured such that object data associated with a lower confidence level of corresponding to a ghost object has a greater influence on the control of the vehicle movement than object data associated with a higher confidence level of corresponding to a ghost object.
29. A method according to claim 27 or 28, including outputting object data associated with a lower confidence level of corresponding to a ghost object relative to a predetermined threshold confidence level to the vehicle control module, and discarding object data associated with a higher confidence level of corresponding to a ghost object compared to the predetermined threshold confidence level.
30. A method according to any of claims 19-29, wherein the controller is configured to determine a distance travelled by the transmitted electromagnetic radiation to a reflecting object, to group reflecting objects having substantially identical determined distances detected at substantially the same times, and to use the highest determined confidence level in the group to determine the confidence levels for the other reflecting objects in the group.
31. A system including: a first linearly polarised transmitter configured to transmit electromagnetic radiation in a first coherent processing interval; a second linearly polarised transmitter configured to transmit electromagnetic radiation in a second coherent processing interval, wherein the polarisation of the first transmitter is offset from the polarisation of the second transmitter; a receiver configured to receive reflections of the transmitted electromagnetic radiation and to output a first signal representative of the strength of the electromagnetic radiation received in the first coherent processing interval and a second signal representative of the strength of the electromagnetic radiation received in the second coherent processing interval; and a controller configured to: receive the signals representative of the strength of the received electromagnetic radiation, and determine a confidence level that the reflections correspond to a ghost object using the signals representative of the strength of the received electromagnetic radiation.
32. A method including: transmitting electromagnetic radiation in a first coherent processing interval from a first linearly polarised transmitter; transmitting electromagnetic radiation in a second coherent processing interval from a second linearly polarised transmitter, wherein the polarisation of the first transmitter is offset from the polarisation of the second transmitter; receiving, at a receiver, reflections of the transmitted electromagnetic radiation; outputting, from the receiver, a first signal representative of the strength of the electromagnetic radiation received in the first coherent processing interval and a second signal representative of the strength of the electromagnetic radiation received in the second coherent processing interval; and determining, using a controller, a confidence level that the reflections correspond to a ghost object using the signals representative of the strength of the received electromagnetic radiation.