FIELD OF THE INVENTION

Embodiments of the present invention generally relate to radio communications and, in particular, to a method and system for providing legitimacy information about signal sources.

BACKGROUND

[0001] Radio transmissions are used in various communications and positioning system. WiFi, Bluetooth and cellular communications transceiver are ubiquitous. Global navigation satellite system (GNSS) receivers are used in nearly every mobile device and require reliable satellite radio transmissions to accurately determine a GNSS receiver’s position. Systems using these technologies have become critical to functional infrastructure, communications and to the future of transportation. For example, these systems are instrumental in providing functionality to autonomous vehicles. Accurate position and communications to/from autonomous vehicles is a necessity for the vehicle’s operation.

[0002] Unfortunately, there are people that aim to thwart the reliable function of systems that rely on radio transmissions by using spoofing transmitters. Such spoofing creates a substantial cybersecurity threat. Illegitimate transmitters such as spoofing transmitters (aka spoofers) can transmit signals that mimic legitimate signals such that the receiver may receive and process the spoofing signal as if it were legitimate. In, for example, a GNSS receiver, a spoofer may generate signals that cause the receiver to provide inaccurate position information. Such spoofing of GNSS receivers can be an annoyance to someone using the signal for guidance or lead to catastrophe for an autonomous vehicle using the signal for vehicle guidance. [0003] Therefore, there is a need for a method and apparatus for acquiring information on the legitimacy of radio transmissions and providing signal intelligence and security.

SUMMARY OF INVENTION

[0004] In accordance with a first aspect of the invention there is provided a method of obtaining legitimacy information for a remote source, the method comprising: receiving, at a receiver, a signal from the remote source in a first direction; providing a local signal; determining a movement of the receiver; providing a correlation signal by correlating the local signal with the received signal; providing motion compensation of at least one of the local signal, the received signal, and the correlation signal, based on the determined movement in the first direction to provide preferential gain for a signal received along the first direction; identifying, based on the said correlation, a remote source vector corresponding to a portion of a propagation path of the received signal, the portion being coincident with the remote source; and generating the legitimacy information for the remote source in accordance with the remote source vector of the received signal.

[0005] It has been found that the problem of obtaining legitimacy information for remote sources can be addressed by way of a motion-compensated correlation process applied to signals received by a moving receiver. The inventors have realised that the results of motion-compensated correlation, which can provide angle of arrival information for signals received from remote sources, can advantageously be used to obtain accurate determinations as to the legitimacy of these sources.

[0006] The legitimacy information may alternatively be referred to as validity information, security information, or signal intelligence, in the sense that it may comprise information that may concern a spoofer, cybersecurity threat, or other illegitimate signal source. The legitimacy information typically comprises information indicating whether the signal source is a legitimate source or emitter, or whether it is illegitimate. Accordingly, the method may alternatively be thought of as a method of validating or assessing legitimacy of a remote source.

[0007] Once legitimacy information has been acquired, and optionally refined by way of further verification as will be described later in this disclosure, appropriate action may be taken regarding sources that are indicated by that information to be illegitimate, or potentially illegitimate. In some cases, such action may be taken by authorities, and may include investigating, blocking, or disabling illegitimate transmitters. Action may, in some cases, be taken by a receiver, which may be the aforementioned receiver or may be a further receiver having access to the legitimacy information, for example via a data set to which one or multiple receivers or devices coupled to them may contribute. Accordingly, the action may comprise suppressing or discarding signals received from illegitimate sources, or from sources with a legitimacy score parameter value that is below a predetermined threshold value. In this way, a receiver or a device comprising or physically and/or communicatively coupled to the receiver may be configured such that any signals from a source indicated by the legitimacy information to be illegitimate are excluded from any processing that the device is configured to perform otherwise, on legitimate signals. For example, any further signals received from a GNSS signal source that has been identified in the legitimacy information as a probable spoofer may be excluded from positioning calculations based on received GNSS signals.

[0008] Optionally the data may be used by the receiver, or a further receiver, to perform additional assessment or verification of a purportedly illegitimate source, and may do so by performing the motion-compensated correlation-based steps described above, or using any of the secondary verification techniques described later in this disclosure. Thus the method may additionally comprise, prior to any one or more of the above-described steps, obtaining preliminary legitimacy information for a remote source and performing the steps for obtaining legitimacy information if the preliminary information indicates the source to be illegitimate. [0009] The preliminary legitimacy information may be obtained, in some embodiments, from a legitimacy data set, such as a remotely hosted database, and the data therein may have been acquired by way of any one or more of: a method of obtaining legitimacy information as described above, and any alternative method. In some embodiments, the preliminary legitimacy information may be generated in accordance with a type, characteristic, or identifier of a received signal, and may be generated in accordance with a known location of the receiver. For instance, a mismatch between a type of a received signal and data indicating one or more types of signal expected to be present or receivable at a location, estimated or otherwise, of the receiver, or an area in which the receiver is location, may be used to generate a preliminary indication of illegitimacy. Similarly, a signal or transmitter thereof may be preliminarily indicated to be illegitimate if the receiver has not previously received a signal of that type and/or from that purported transmitter. In this way, unnecessary verification of established signals and transmitters may be avoided, while continuing to assess the validity of newly received transmissions.

[0010] The generating of legitimacy information in accordance with the remote source vector may be understood as determining, assessing, estimating, or inferring the legitimacy of the remote source and/or the received signal, based on the remote source vector. This generating may, in other words, be considered as performing legitimacy verification, or a legitimacy check, that is verifying or checking the legitimacy of the source or signal.

[0011] The identifying of a vector or direction, as described in this disclosure, may generally be thought of as calculating or generating a vector. The said correlation may be understood as a correlation of the respective local signal with the received signal. The preferential gain provided may be understood as gain in comparison with a signal received in a respective, second direction, in some embodiments. In some cases, the first direction is a line-of-sight direction between the receiver and the remote source, while the second direction is not. However, in some embodiments the motion compensation is performed in such a way as to provide preferential gain for a signal received along a first direction that is not a line-of-sight direction, in particular where additional information is available to enable remote source vectors to be identified from such non- line-of-sight signals.

[0012] A remote source vector corresponding to a portion of a propagation path may be understood as the remote source vector preferably being collinear with that portion. However, because of the probabilistic nature of ascertained signal directions, the correspondence typically means that the remote source vector is representative or indicative of, or is an estimate of, the portion of the propagation path. For line-of-sight directions between the receiver and the remote source, the remote source vector typically lies along a direction of arrival (DoA) vector, that is the direction from which the receiver received the signal. However, when a given first direction corresponds to a reflected signal, which has had its propagation direction changed by reflection off some object subsequent to being transmitted by the remote source, suitable techniques may be used to calculate, based on the DoA from which the reflected signal is received, the portion of the propagation path between the remote source and a reflective structure. This may be used, for example, when modelling of reflective structures and raytracing can be used to enable the use of a reflected signal in the calculation of a remote source vector. The said propagation path of the received signal may be understood as the propagation path between the remote source and the receiver specifically.

[0013] The motion compensation can be applied to the received signal, the local signal, or a combination thereof before the signals are correlated. Motion compensation may also be applied to the correlation signal, following correlation. By providing motion compensation in the first direction, which extends between the receiver and the remote source, it is possible to achieve preferential gain for signals received along this direction. Thus, a line-of-sight signal between the receiver and the remote source will receive gain preferentially over a reflected signal that is received in a different direction. In a GNSS receiver this can lead to a remarkable increase in the accuracy of calculations based on received signals because non-line-of-sight signals (e.g. reflected signals) are significantly suppressed. The highest correlation may be achieved for the line-of-sight signal, even if the absolute power of this signal is less than that of a non-line-of-sight signal. [0014] A received signal may include any known or unknown pattern of transmitted information, either digital or analogue, that can be found within a broadcast signal by a cross-correlation process using a local copy of the same pattern. The received signal may be encoded with a chipping code that can be used for ranging. Examples of such received signals include GPS signals, which include Gold Codes encoded within the radio transmission. Another example is the Extended Training Sequences used in GSM cellular transmissions.

[0015] Conventionally phase changes in the received signal caused by changes in the line-of-sight path between the receiver and the remote source were viewed as a nuisance that reduced positioning accuracy. The counter-intuitive approach of the invention can actually take advantage of these phase changes to improve identification of the line-of-sight signal from a remote source.

[0016] The motion compensation unit can provide motion compensation to the local signal so that it more closely matches the received signal. In another arrangement motion compensation may be applied to the received signal to reduce the effect on the received signal of the motion of the receiver. Similar results may be achieved by providing partial motion compensation to both the local signal and the received signal. These techniques allow relative motion compensation to be applied between the local signal and the received signal. In some embodiments motion compensation may be performed in parallel with correlation. Motion compensation can also be applied to the correlation signal directly.

[0017] In practice the received signal may be processed as a complex signal, including in-phase and quadrature components. The local signal may be similarly complex. The correlation unit may be arranged to provide a correlation signal which may also be complex and which can be used as a measure of the correlation between these complex signals.

[0018] It may be possible to achieve high accuracy by providing motion compensation of at least one of the local signal and the received signal based on the measured or assumed movement in the first direction. In practice, when applied to GNSS signals, the local and received signals may be encoded with a code which repeats periodically. For the GPS L1 C/A codes for example the local and received signals can include 1023 pseudorandom number code chips. The local and received signals may be analogue waveforms which may be digitised to provide values at the radio sampling rate, which means there may be millions of values over a 1 ms time period. The correlation between the local signal digital values and the received signal digital values may be calculated, having first corrected either set of values using a motion compensation vector for the relevant time period. These data points may then be summed over the time period. In practice this can produce an accurate result because it works at the radio sampling frequency, although it may be computationally intensive.

[0019] A lower accuracy may be achieved by providing motion compensation of the correlation signal. In the above example, when applied to the GPS L1 C/A codes, the correlation may be performed independently on each of the -1000 pseudorandom number code chips to produce -1000 complex correlator signal outputs. The motion compensation vector can then be applied to these -1000 correlation signal components. Finally, the motion compensated correlation signal can be summed to produce a measure of the correlation. Thus, motion compensation of the correlation signal may produce an approximation of the result that can be achieved by motion compensation of the local signal and the received signal. However, for some applications the loss in accuracy may be negligible, and may be accepted because it enables a reduction in computational load.

[0020] A remote source vector can be used to obtain various indicators of legitimacy, as will be described later in this disclosure. Any one or more of these types of information, which can relate to altitude, movement, and geographic locations of sources, for example, can be used individually or in combination, and in some embodiments in cooperation with reference data, to generate the legitimacy information.

[0021] In some embodiments the legitimacy information is generated in accordance with a signal type of the received signal. Knowledge of the type of signal, for example GNSS, cellular, WiFi, or Bluetooth, can facilitate the determination as to whether a signal source is legitimate, not least because angular or positional information gleaned from a remote source vector can be compared to, or assessed against, the expected properties or angular or positional information for legitimate sources of a given type of signal. The method may be beneficial for validating signals that are expected to originate from a particular height or at a given azimuthal angle. For example, the method may be applied to GNSS signals, which ought to be transmitted from sources higher in the sky, and so ought to have more steeply inclined DoA and/or remote source vectors. Ground-based spoofing sources, for example, may be identified by their having less steeply inclined transmission paths than expected. Accordingly, the method may comprise, when an angle formed by the remote source vector and a horizontal direction, or alternatively or additionally an angle between the horizontal and the direction of arrival, is smaller than a predefined threshold angle, generating the legitimacy information to indicate, or such that it indicates, that the remote source is an illegitimate source. That is to say, if the angle that can be calculated based on the identified remote source vector is smaller than expected for a legitimate source, the legitimacy information may be generated so that it is indicative of the source being illegitimate. This may be, for example, in the form of a flag or any suitable form of data to indicate the invalid or potentially suspicious source.

[0022] The said predetermined threshold angle may, in some embodiments be 5 degrees, or in some cases 10, 20, 30, or 40 degrees, in dependence on a chosen level of discrimination to be applied. The said horizontal direction may be understood as a direction that is orthogonal to the vertical direction and lying in the same vertical plane as the remote source or direction of arrival vector with which the angle is formed. A horizontal direction may also be thought of as a direction or vector parallel to the plane of the horizon and lying in the same vertical plane as the said vector. Such horizontal and vertical reference vectors or directions may be defined, in some embodiments, with respect to a position of the receiver, for instance at the time of signal receipt thereby, or by the location at which a vector collinear with the remote source vector is incident upon the surface of the earth. The vertical reference direction may be defined as a direction parallel to the direction of gravity experienced at the said point on the surface of the earth or at the said location of the receiver.

[0023] For some signal types, a determination of legitimacy or illegitimacy may be aided by ascertaining whether the angle at which the signal was transmitted from the source is as steep as expected, as an addition or alternative to the approach described above. Accordingly, in some embodiments, the method may comprise, when an angle formed by the remote source vector and a horizontal direction is greater than a predetermined threshold angle, generating the legitimacy information to indicate that the remote source is a legitimate source. Further, a positive determination as to the legitimacy of a signal source may be made, for signals originating from earth-orbiting satellites, for instance, when the azimuthal angle of transmission is sufficiently great.

[0024] In embodiments where a threshold angle is used to determine that a source is illegitimate, as described above, the threshold angle used for either of these determinations may be the same, but are preferably different. The first threshold angle, below which sources may be deemed to be illegitimate, is preferably smaller than the second threshold angle, above which sources may be deemed to be legitimate. The difference between the two threshold angles may be, for example, 5, 10, or 15 degrees. In this way, three ranges of azimuthal angles may be defined, above, below, and between these two threshold angles, and the obtaining of legitimacy information may be performed by comparing the remote source vector to these ranges. In some embodiments, particularly if a signal ostensibly originates from a satellite, remote source vectors in the shallowest of the three ranges may be an indicator that the source is illegitimate, a remote source vector in the highest of the three angle ranges may cause the source to be deemed legitimate, while the third, intermediate range may correspond to the source being classified or indicated to be potentially legitimate, for instance being flagged as such so that further investigation as to that source can be carried out.

[0025] As alluded to above, positional information based on an identified remote source vector can be used to validate a source, additionally or alternatively to using the angular information as such. Location information for remote sources may be found based on receiving and identifying the remote source vectors for more than one signal from the source. In some embodiments, the method further comprises: for each of a plurality of signals received at the receiver from the remote source, each of the signals being received in a respective first direction: providing a respective local signal; determining a respective movement of the receiver; providing a respective correlation signal by correlating the respective local signal with the received signal; providing motion compensation of at least one of the respective local signal, the received signal, and the respective correlation signal, based on the respective determined movement in the respective first direction to provide preferential gain for a signal received along the respective first direction; and identifying, based on the said correlation, a respective remote source vector corresponding to a portion of a propagation path of the received signal, the portion being coincident with the remote source. The said plurality of received signals will be understood as including the previously described received signal. Thus such embodiments of the method comprise steps of providing a local signal, determining respective movement, and providing a respective correlation signal, for at least a second received signal received from the remote source in a second direction. Preferably, however, in such embodiments, further signals are received at the receiver from the source, and corresponding steps performed for those signals also. In this way, greater numbers of remote source vectors can be obtained, which can be to improvement of accuracy of information about a source. The respective local signal, respective movement, and respective correlation signal corresponding to the first received signal may be understood as being the same as the local signal, movement, and correlation signal described above.

[0026] It may be considered that, in embodiments involving a plurality of signals, the said plurality of signals, or at least a subset of them, are transmitted by the remote source as part of a single transmission. That is to say, the distinction between different ones of the plurality of signals may be arbitrary, as those different signals, despite being treated, for the purposes of the method, as separate or distinct in the identification of their corresponding remote source vectors, are typically portions of a given transmission by the remote source.

[0027] An individual signal might typically be defined by the differences in the time at, or during which, the receiver receives a given transmission or transmission portion, and/or by the position, and/or change in position, of the receiver as it receives, for example. The distinction between the signals will therefore be understood as being generally unrelated to the content of the signals. Any two or more of the plurality of signals may comprise or consist of different, or identical, information. Typically, therefore, each of the plurality of signals is a portion of a transmission from the remote source received by the receiver during a respective one of a plurality of time periods.

[0028] In addition to providing an improvement to the determination of legitimacy by increasing the number of remote source vectors identified, such embodiments can, as noted above, improve this determination further still by providing location information for the source. In the context of this disclosure, location information may be understood as data that is indicative of a position, be it absolute or relative, to a receiver for instance, or, for example, a geolocation. In some embodiments, the location information comprises a geolocation of the remote source, and it will be understood that the location information may pertain to the remote source transmitter antenna. The method may therefore be thought of as including a step of locating the remote source. In some embodiments, the method further comprises generating location information for the remote source by identifying one or more locations at which two or more of the respective remote source vectors of the plurality of received signals intercept. The legitimacy information may then be generated in accordance with that location information. In this way, signal intelligence for the source can be obtained based on the calculated location of the source. Knowledge of the location of a source, whether that comprises an indication of a geographical location such as a geocoordinate, or an indication of an elevation of the source, for example an altitude, or an indication of a location in the sky or an orbital position, can be used to determine the authenticity of a source. [0029] With respect to the position and/or orientation of the receiver, in particular the receiving antenna thereof, two of the plurality of signals received, preferably more than two, and more preferably all of those signals, may be received along different respective first directions. In some embodiments, these directions of signal receipt differ, during the method being performed, owing to movement, with respect to the remote source, or within the vicinity of the remote source, of the receiver during that time. In such cases the movement of the receiver may include one or two components orthogonal to the direction of signal arrival or receipt.

[0030] However, it will be understood that the aforementioned movement of the receiver through the vicinity of the source need only be sufficient for performing the described motion-compensated correlation. That is to say, the movement generally comprises a component directed along a direction parallel to the direction of arrival vector for a signal, and to a spatial and/or temporal extent that allows the compensation calculations to be made. However, no movement of the receiver other than that which enables the motion-compensated correlation to be performed need necessarily be effected in order for the described generating of location information. Therefore, the extent of any receiver movement, or any component thereof, which is transverse to the direction of arrival and/or to a straight line between the receiver and the source, need not be sufficiently great that an angle subtended by that movement or component at the remote source, and/or at a location at which a signal is reflected towards the receiver, is large enough to permit or facilitate the calculation of location information based on two remote source vectors. Rather, movement of the receiver can, in some cases, be insufficient for that purpose as such, with the calculation of any intersection locations instead, or additionally, being based on direction of arrival vector differences that are attributable to differences in signal propagation paths.

[0031] Therefore, a difference in the direction of signal receipt for any two or more signals received during the method being performed may, in some embodiments, result from a propagation path of one or more of those signals including one or more changes in direction, that is from one or more of those signals having been reflected. In this way, two sufficiently different remote source vectors, corresponding to two different transmission angles, can be obtained, and an intersection location of those vectors calculated, regardless of whether the receiver has moved to an extent that enables triangulation of line-of-sight vectors to the source. In other words, by including one or more reflected signals in the basis for the calculations, a location of a remote source may still be identified even if the receiver does not move sufficiently to enable adequately precise triangulation based on two line-of-sight signal vectors.

[0032] The generating of the location information may be performed, for example, such that location information comprises a point corresponding to an average, in particular a mean, location, of multiple locations at each of which two or more of the identified remote source vectors intersect. The generating of the location information may also be understood as being based on the said one or more locations of intersection. Each location of intersection may correspond to a point, or a one-, two-, or three-dimensional region defined by an intersection between two remote source vectors, and typically also by any degrees of uncertainty in the identified vectors. Typically at least two, preferably more than two, identified remote source vectors intersect at each of the one or more locations of intersection.

[0033] The method facilitates the accurate calculation of a location of a remote source relative to the receiver. An absolute location of a remote source, with respect to an established coordinate system for example, such as geolocation data, may be found by way of locating the receiver in that coordinate system. Accordingly, in some embodiments the method further comprises obtaining location information for the receiver. The location information for the remote source may be generated based on the location information for the receiver, for example based on locating one or more points or regions of intersection between remote source vectors with respect to the receiver. The receiver location is typically obtained for at least one of the plurality of received signals, that is to say it may comprise information indicating a location of the receiver at the time of receipt of, or during receipt of, at least one of the plurality of received signals. The receiver location may be obtained using GNSS (Global Navigation Satellite System) and/or IMU (Inertial Measurement Unit) data, and may additionally be obtained based on determined movement of the receiver, such as respective determined movement corresponding to any one or more of the received signals.

[0034] As noted earlier in this disclosure, it is possible in some embodiments to use additional information about a received signal to enable the method to account for signals that may be non-line-of-sight signals. The identifying a remote source vector for the signal may accordingly comprise obtaining respective line- of-sight information about the received signal. In particular this additional, line-of- sight information may indicate whether the received signal is a line-of-sight signal. Advantageously, this indication may be used to determine whether to use, discard, or perform additional processing or calculations on, a direction of arrival vector, for the purposes of identifying an intersection location. The additional information may indicate whether the propagation path from the source to the receiver is direct, that is along a line-of-sight between them. For some signals, the line-of- sight information might, on the contrary, indicate the received signal to be a non- line-of-sight signal such as a reflected signal.

[0035] By using this information it is possible to utilise a greater number of signals that might be received in a given time period or during movement of the receiver along a given path portion, since non-line-of-sight signals may be identified as such. Those signals may therefore be used, in spite of their indirect propagation paths, in locating an intersection between remote source vectors, and thereby the remote source, more quickly and precisely. Accordingly, the identifying a remote source vector for a received signal may further comprise identifying, based on the said correlation, a respective direction of arrival, and identifying the remote source vector in accordance with the respective direction of arrival and the respective line-of-sight information. The direction of arrival may be thought of as the direction or vector corresponding to or representative of the direction from which the signal is received at the receiver, and/or the direction of travel of the signal as it is received at the receiver. It will be understood that, in general, the method typically comprises estimating a direction of arrival (DoA) for a signal using the supercorrelation technique discussed in greater detail later in this disclosure. [0036] For line-of-sight signals, the DoA and remote source vector typically correspond to the same direction, that is they may be thought of as parallel and typically having collinear vectors. Line-of-sight information may be used to enhance the method, such that, for non-line-of-sight signals, the supercorrelation technique is applied to obtain the DoAs. Those DoAs may then be used, in conjunction with knowledge of the reflective structures in the vicinity, such as any one or more of position, orientation, shape, of one or more reflective surfaces or objects, to calculate remote source vectors. Thus additional data, and so improved positional precision, can be obtained by using additional remote source vectors, even if they are calculated based on DoAs that do not directly correspond to the direction in which the signal was received from the source. These additional remote source vectors may also be useful if, for example, line-of-sight signals from a given transmitter are occluded or attenuated to the point that they cannot be used to obtain the location information.

[0037] The identifying of the remote source vector in accordance with the direction of arrival and line-of-sight information typically comprises a modification to the motion-compensated correlation technique that causes preferential gain to be achieved for signals received along these non-line-of-sight directions, in particular on the basis that they may nonetheless be used. Alternatively, one or more signals that are indicated to be reflected signals may, in some embodiments, be excluded from the said plurality of signals based on which the calculations for obtaining the location information are performed.

[0038] In embodiments involving the use of non-line-of-sight signals in spite of their indirect propagation paths, the method may further comprise obtaining reflection model data comprising a geometrical model of a set of structures capable of reflecting signals. Such a model, which can enable the calculation of remote source vectors based on DoAs of reflected signals, may be particularly useful in urban environments. It may be beneficial to avail the method of a predetermined 3D building model, for example, that represents the structures that may obstruct and/or reflect transmissions such as those comprising the received signals. Using techniques such as ray tracing, propagation paths through such environments can be modelled in such a way that useful remote source vector information may be inferred even when the only signal received, for instance for a given position along a movement path of a receiver, is one that has been reflected by one or more structures. It will be understood that the said geometrical model may include a set of one or more structures, which may be natural or artificial, for example buildings, landscape, and terrain features. Those structures being capable of reflecting signals may be understood as their being capable in particular of reflecting, that is of being reflective to, signals of the same or similar type as one or more of the plurality of signals. For example, in the vicinity of the receiver, a model representing structures within a predetermined radius of, or within a region containing, an estimated or obtained location of the receiver at a given time, may be obtained and used to model propagation paths. Typically, the model data comprises three-dimensional geometrical data representative of reflective structures and containing sufficient information about their position and/or orientation to allow a propagation path including one or more reflections by them to be calculated.

[0039] The identifying the remote source vector in accordance with the respective direction of arrival and the respective line-of-sight information may comprise, if the respective line-of-sight information indicates that the received signal is not a line-of-sight signal, calculating the respective remote source vector based on the reflection model data and the respective direction of arrival. Typically the aforementioned use of estimated non-line-of-sight directions of arrival requires geometrical information that allows directions of transmission, or remote source vectors, to be calculated or estimated. In embodiments involving reflection model data, compensation can be applied to account for the fact that there has been a reflection, which might otherwise cause a positioning error, or the reflected signal may be used in some other way to enhance positioning accuracy.

[0040] In various embodiments, the reflection model data and the line-of-sight information may be separate, or they may be related, or the same. For example, a set of line-of-sight information may indicate that a direction of arrival is that of a non-line-of-sight signal by virtue of it indicating that the direction of arrival vector intersects or coincides with a reflective structure modelled within the reflection model data.

[0041] The method may further comprise obtaining time of arrival data, or time difference of arrival data, for one or more of the plurality of received signals the line-of-sight information may be obtained in accordance with the time of arrival data. For example, anomalous time of arrival data may be used to make a determination that a received signal is a line-of-sight signal, and vice versa. This may then be used to exclude a non-line-of-sight signal from one or more calculations, in acquiring location information for a remote source. This may also be used to perform additional processing, for example using the reflection model data.

[0042] In some embodiments, the generating of the legitimacy information in accordance with the location information comprises obtaining reference location data, which may also be referred to as reference source location data, indicative of one or more legitimate signal sources, and generating the legitimacy information based on a comparison between the generated location information and the reference location data. For example, the reference location data may comprise one or more areas, or an indication thereof, in which legitimate sources are known to be located. Thus the determining the remote source to be illegitimate may be based on its generated location information indicating the source to be outside of that area or areas.

[0043] Notwithstanding whether the reference location data is available so as to allow comparisons of the determined source locations with known transmitter locations or regions containing them, the generated location information may also be used to judge legitimacy based on whether signal sources ought to be in a particular area at all. In some embodiments, therefore, the method further comprises obtaining reference geographic data corresponding to, or containing information about, one or more geographic regions and comprising information indicating an expected presence of one or more legitimate sources therein, and generating the legitimacy information in accordance with the generated location information and the reference geographic data. [0044] The reference geographic data may define any of a boundary of a geographic region and an extent, or area, of a geographic region, or indeed any information sufficient for determining whether a given location lies within that region. A geographic region may be understood as a specific area on and/or above the surface of the earth. The one or more geographic regions may contain or be coincident with a location, particularly a geographic location, that may be indicated by the location information. The expected presence may be understood as a presence level, or a degree of presence of legitimate sources and may be expressed in terms of an absolute or relative quantity, number, or density, or a spatial distribution of legitimate sources. For example, it may indicate an expected level, and so may be thought of as an expected presence or absence of legitimate sources from a region.

[0045] In such embodiments, the location information may be used to identify a geographic region, corresponding to the reference geographic data, in which the source is located. Accordingly, an assessment may be made as to the validity of the source based on the expected presence of legitimate sources there. For example, trivially, if the expected presence in an area from which was transmitted a signal has been determined to have been transmitted is zero, the method may include determining that the source is illegitimate. The method may also involve calculating or otherwise determining a quantity of sources within a region, for example by obtaining location information for a plurality of sources that indicates them as being located therein, and comparing the quantity to an expected presence. For instance, if an excessive quantity of sources, compared to the reference data quantity, are found within a region, then one, or each of the sources identified as being in that region can be determined to be illegitimate, or potentially so. Furthermore, the method may involve carrying out additional checks for those sources, as will be described in greater detail later in this disclosure.

[0046] The reference geographic data may comprise expected source type information. This information may correspond to the one or more geographic regions, and the legitimacy information may be generated in accordance with a comparison between the said source type and an identified type of one or more of the plurality of received signals. An expected source type, as may be indicated by the expected source type information, may refer to an expectation based on some knowledge of what types of source ought to be present in the region, and/or what sources are known or likely to be transmitted from the region. A source type may include or be indicated by or inferred from any one or more of: signal wavelength, signal content, time and/or date of transmission or receipt of the signal. The expected source type information may indicate any one or more of one or more types of source that are expected to be present in the region; one or more types of source that are expected to be absent from the region. For example, the method may include inferring illegitimacy of a source if its content or a different indication of its source type is unexpected within a given type of terrain, body of water, or geopolitically defined area. The method may include identifying or determining a signal type in order to obtain the said identified type of one or more of the plurality of received signals.

[0047] In embodiments that involve the use of a plurality of received signals, the method may further comprise generating, based on the plurality of remote source vectors, that is the respective remote source vectors of the plurality of received signals, which include the first remote source vector as noted above, source movement information indicative of a movement state of the remote source. The legitimacy information may then be generated in accordance with the source movement information.

[0048] Acquiring multiple remote source vectors of signals transmitted at different times can reveal clues to the legitimacy of a source. In particular, obtaining an accurate indication of whether a source is moving or stationary, together with knowledge of whether a legitimate source of that type would be moving, is valuable for the obtaining of legitimacy information. The movement state referred to above may therefore be understood as information about whether and how the source is moving. The generating of the source movement information may comprise calculating the movement, or a component thereof. For example, it may involve calculating a coordinate, position, speed, velocity, acceleration, or components thereof, for the source. In some components that information may simply indicate whether a first and second remote source vector of the plurality of remote source vectors differ, or whether they are the same, or whether they differ by more than a threshold angle, for instance. The remote source vectors remaining the same across a given time period may indicate no movement, for example, while, conversely, a difference between them may indicate movement of the source.

[0049] The method may further comprise obtaining reference source movement data indicative of an expected movement state of the legitimate remote source. That reference source movement data may indicate, for example, whether the source ought to be moving. This may be based on the type of signal, for example for a signal reportedly transmitted by a cellular network base station, the reference data may indicate that the source should not be moving. The indication within the data may comprise an explicit flag, or can be implicit, for example within the type of source and/or signal. The data can include expected movement states for multiple signal and source types. The method may comprise generating the legitimacy information in accordance with the generated source movement information and the reference source movement data. This typically comprises a comparison between the source movement information and the reference source movement data. If the generated movement information differs from, or is inconsistent with the reference data, the legitimacy information may be generated to indicate the source to be illegitimate. For example, for a cellular base station, if the generated source movement information indicates movement of the source, contrary to the implicit or explicit indication by the reference data to the contrary, the source may be marked as illegitimate.

[0050] It will be understood that, in some embodiments, assessing source legitimacy based on a determination of its movement need not require the location of the source, or a change therein, to be calculated. Rather, movement of a source may in some cases be inferred from a change in the identified remote source vector. Preferably, however, a sufficient number of remote source vectors are calculated for a source, and if a sufficient number are obtained, that data may be used to calculate two or more intersection locations of those remote source vectors, each corresponding to signals transmitted at different times, so that two or more locations for the source at those different times may be found. [0051] However, in some embodiments, the remote source vectors may be used to infer source movement independently of any calculated locations. That is, at least an angular change or an angular/transverse component of movement may be inferred from the remote source vectors themselves over a given time period, and this need not necessarily include calculating a radial component of the movement, that is a component of the movement in the direction of the remote source vector or direction of arrival. However, the assessment of legitimacy may be improved by calculating two or more locations based on obtained remote source vectors, as noted above.

[0052] The method may accordingly further comprise: generating first location information for the remote source by identifying one or more locations at which a first set of two or more plurality of remote source vectors intersect, generating second location information for the remote source by identifying one or more locations at which a second set of two or more of the plurality of remote source vectors, different from the first set, intersect, and generating the source movement information based on the first and second location information. The second set of remote source vectors may be different from the first set in that they correspond to signals received or transmitted at a different time. That is, preferably each of the remote source vectors of the second set correspond to signals transmitted after one or all of the signals of the first set. Preferably, the receipt and/or transmission times corresponding to the two sets are separated by a duration that is sufficiently long for the movement of the source to be assessed. For example, this duration may be in the order of seconds, tens of seconds, minutes, or hours.

[0053] The generating of the source movement information may involve comparing the first and second location information, or calculating a difference therebetween. Furthermore, the method may include additionally using third, fourth, and any number of further sets of remote source vectors that correspond to respective different signal transmission times, to calculate respective further locations. It may be possible to define an estimated movement path for the remote source using the plurality of identified locations. The comparison of a movement path with an expected pattern or type of movement for a legitimate source may aid in the obtaining of legitimacy information. Accordingly, in some embodiments, the generated source movement information comprises a generated source movement path based on, that is calculated based on, the first and second location information. Indeed, this may be based on any additional location information. In some preferred embodiments, a detailed path may be produced, tracing the estimated movement of the source with sufficient sets of remote source vectors and correspondingly calculated locations.

[0054] The reference source movement data may comprise an expected legitimate source movement path, and the legitimacy information may be generated in accordance with a comparison between the generated source movement path and the expected source movement path. That is to say, if the comparison operation returns a difference or discrepancy between the paths, for example a displacement or deviation from the path expected for a legitimate source, which is greater than a predetermined threshold, the legitimacy information may be generated to indicate the source as illegitimate. Likewise, if the calculated difference between the paths is less than a predetermined tolerance, or if no difference or substantially no difference is identified, the legitimacy information may indicate the source to be legitimate.

[0055] Preferably, the method comprises storing the legitimacy information for the remote source in a remote source legitimacy data set. In this way a receiver, or preferably a plurality of receivers operating in a region, concurrently or at different times, can build up a store of data that can be used to confirm the legitimacy of transmitting sources therein and/or to flag, notify, or alert any parties to the presence of illegitimate sources in the region so that appropriate action may be taken. Such a dataset is preferably stored in a database, which is typically implemented on one or more servers or other computer devices that are preferably remote from the receiver, and are preferably accessible directly or indirectly by the receiver via one or more wired or wireless communication links or any other mode of transferring data.

[0056] The source legitimacy data set may indicate, for each source for which information is recorded therein, any of: a legitimacy status, a legitimacy flag, a legitimacy score, and any other form of legitimacy indicator. Preferably the data set additionally includes, for one or more sources, location information for the source. More preferably, that stored location information indicates or represents a geographic location of the source, for example in the form of a geocoordinate.

[0057] Source location information to be stored in the data set may be acquired by various means, including as part of the method, for example by receiving and identifying the remote source vectors for more than one signal from the source, and, for instance, identifying an intersection location, as described earlier in this disclosure. In some embodiments, location information for a source is obtained by other techniques or using further data. For example, satellite or aerial imagery representing a geographic area in which a source is situated may be used to infer visually a location of a transmitter, and may in some embodiments be used for a secondary legitimacy check for a source.

[0058] In some embodiments the location information comprises a relative location, indicating a position of the source with respect to the receiver at the time of signal receipt for example. Such relative location information may additionally or alternatively comprise angular or directional information, and may in particular comprise an indication of a direction in which a source is located relative to the receiver. The information may comprise an indication of the remote source vector together with location information derived from location information for the receiver. In this way, for implementations in which a position of a source is not necessarily acquired during the method, a range of locations that lie along the remote source vector and thus include a true or at least approximate location of the source can be obtained. Such information may be used in conjunction with similar information acquired by the method being executed multiple times, using the receiver and preferably one or more further receivers.

[0059] By providing, or updating, a data set with information about illegitimate transmitter locations, any receivers that may be entering or passing through the broadcasting range of those transmitters or may be in receipt of transmissions from those locations can be afforded preliminary indications or warnings as to the potential presence, direction, and/or position of the identified transmitters. This may be the case even where no location, or no precise location, is known for a receiver arriving at or approaching the vicinity. It is possible for the data set to be used by receivers to establish, for instance, a range of directions, with respect to its own known or estimated location, in which illegitimate, or potentially illegitimate, transmitters are indicated by the previously acquired legitimacy information to be, or from which transmissions from such sources are to be expected based on that information. Using that knowledge, a receiver can avail itself of the data set so as to take appropriate action in regard to signals received from a direction or an area from which the legitimacy information indicates illegitimate transmissions may originate. Such action may include selective processing or exclusion of certain signals, as described earlier in this disclosure, and it may include these receivers performing their own primary and/or secondary legitimacy verification upon the signals by way of any of the techniques described herein. Thus the legitimacy information that may be added to the data set may itself constitute preliminary legitimacy information for subsequent use by any receiver.

[0060] It will be understood that, in some cases, the legitimacy or illegitimacy of a source might not be definitively determined by the method, and that the generated legitimacy information may indicate a source to be potentially illegitimate rather than definitively so. In some embodiments, therefore, it may be useful to carry out a further legitimacy assessment, in accordance with a certainty level or parameter associated with the information, or on the condition that the remote source vector-based assessment indicates that a source is not necessarily legitimate. Therefore, some embodiments further comprise, if the legitimacy information indicates that the remote source is an illegitimate source: performing legitimacy verification for the remote source using, or based upon, the received signal. The method may therefore further include updating the legitimacy information in accordance with a result of that legitimacy verification and/or a certainty parameter.

[0061] The said legitimacy verification may be thought of as a secondary legitimacy check, or a second legitimacy verification, in view of the initial generating of the legitimacy information which may be thought of as a first check or first verification step. It may be useful to perform one or more such ancillary checks. However, the efficiency of the process of verifying sources and identifying illegitimate sources is typically improved by carrying out these additional checks conditionally, having first identified potentially illegitimate sources based on remote source vectors that are determined accurately using the motion compensated correlation technique.

[0062] Preferably the extra verification is performed based on one or more signal characteristics other than direction information. That is, the characteristics may exclude direction of arrival, remote source vector, or other information generally relating to or derived from a propagation path of the signal or any portions thereof. The said updating of the legitimacy information may be an optional step in some embodiments, or may itself be performed conditionally. For example, legitimacy information may be left unchanged if it is consistent with or corroborated by the secondary check. For example, if the check returns a result that confirms the illegitimacy of a source, the update may be performed so that the indicated legitimacy in the data is unchanged, although preferably the data may be updated to indicate that a secondary check has been carried out.

[0063] In some embodiments, the updating may comprise modifying or adding to the legitimacy information, such as modifying a source/signal legitimacy or illegitimacy indication comprised by the data. This update may in some cases confirm an initial indication that the source is valid or invalid. For example, in some other cases, if further checks conclude that a potentially illegitimate source is in fact valid, the information may be updated to reflect that modified illegitimacy indication. Likewise, following any number of ancillary checks, the update may comprise flagging a signal or source for further investigation, for example if those further checks are inconclusive as to the legitimacy.

[0064] The information may also be updated to include further detail for the source, for example monitored properties of the source, technical information, results of tests, recorded signal content, and characteristics.

[0065] In general, the result of the illegitimacy verification may comprise any data produced as an outcome of the verification step. Typically, this indicates the legitimacy of the source as assessed by that verification process. [0066] An example of a scenario in which a secondary verification step would be of value involves the receipt of a signal that has been reflected, in particular one whose propagation path involves reflection by a moving object. For instance, a signal, such as a cellular base station transmission, may be reflected over a period of time by a moving vehicle such as a bus or heavy goods vehicle, and received by the receiver. In that situation, the receiver would calculate the remote source vectors without knowledge of the signal having been reflected by the vehicle, typically, since any geometrical data by which indirect propagation paths may be modelled will generally omit transient reflective structures and surfaces such as vehicles. In that case, calculating multiple remote source vectors on the assumption that the signals are line-of-sight signals, and determining a movement state, ora movement path for the source based thereon, would indicate the source to be moving. A comparison with an expected movement state for a transmitter such as a cellular base station may then cause the legitimacy information to be initially generated to indicate the source as illegitimate. Therefore, the secondary verification of the legitimacy of the source may be advantageous in order for the maintained legitimacy information to be accurate.

[0067] The secondary verification may, for example, involve obtaining additional signals from the source, which may include signals for which a remote source vector that truly coincides with the transmitter of the source (whether that be a line-of-sight signal or an indirect signal whose reflected propagation path can be accurately modelled) can be found. In this way the legitimacy of the source may be verified, and additionally the obtained information may be updated in such a way to indicate that moving signals received therefrom may be reflected and ought to be discarded, for example.

[0068] One manner of carrying out a secondary check, which is particularly advantageous when the potentially illegitimate received signal is a positioning broadcast, such as a GNSS signal, may involve assessing an impact of the signal on positioning calculation results. Accordingly, in some embodiments, particularly wherein the signal is a positioning signal, which may be enumerated a first positioning signal, the legitimacy verification may comprise: performing a first positioning calculation based on a plurality of received positioning signals including the first positioning signal, so as to obtain first location information for the receiver, performing a second positioning calculation based on a plurality of received positioning signals excluding the first positioning signal, so as to obtain second location information for the receiver, and obtaining a comparison between the first location information and the second location information. In other words, the additional verification may be at least partly based on comparing two calculated receiver positions, one being based on one or more suspected illegitimate broadcast, the other being based on positioning broadcasts that exclude the one or more suspected illegitimate ones. If a comparison between the two positioning results indicates a discrepancy between the calculated locations, for example a positional difference, preferably defined as a difference in excess of a predetermined distance or difference threshold, then the verification may confirm the source and/or signal as being illegitimate.

[0069] Typically, illegitimate transmitters include lower-quality components than legitimate ones. In particular, illegitimate sources generally use less stable and/or accurate frequency standards. This common shortcoming may be used as an indicator of illegitimacy, and the presence of these components may be inferred from signal characteristics, and so used as a secondary check for those sources which the initial legitimacy information might have indicated to be potentially illegitimate. The legitimacy verification may accordingly comprise obtaining, using the received signal, a source quality parameter for the remote source. That parameter may be indicative of an assessed quality level for a component of the remote source. The obtaining of the parameter may comprise analysing the stability, accuracy, and/or phase noise of the carrier frequency. If the source quality parameter, or a value thereof, is below, or indicates a component quality is below, a predetermined threshold, for example being lower than is expected for a legitimate source corresponding to the ostensibly legitimate source, then the legitimacy information may, and in some embodiments, be updated to confirm or reaffirm the illegitimacy.

[0070] As noted above, the said component of the remote source may be a frequency standard component. The source quality parameter is typically obtained, in such embodiments, by calculating a quality of a frequency standard component of the remote source based on the received signal. The quality is typically defined as a frequency stability, or a measure or indication thereof, for a frequency standard used by the transmitting source. For example, a metric such as an Allan variance may be used.

[0071] A further approach for performing the secondary verification may involve the polarization state of the radiation carrying the signal. In other words, the legitimacy verification may, in some embodiments, be based on a monitored polarization state of the received signal. The signal may, accordingly, be received using an antenna with which the polarization state of the radiation carrying the signal can be monitored. The method may comprise comparing that state to an expected polarization state, for example as expected for a legitimate signal of the same type, and/or from the same type of source, and/or from the same location.

[0072] In some embodiments, a mixed-modality signal assessment may be performed during either or both of a secondary verification step and a step to obtain preliminary legitimacy information as described earlier in this disclosure. Examining different kinds of signal in addition to the signal for which legitimacy is being verified can advantageously improve the efficiency of the method and the quality of the signal intelligence obtained. Such an assessment may accordingly yield a preliminary and/or secondary indication of legitimacy of a signal source. The assessment typically comprises, for one or more further received signals, different from, and preferably of a different signal type or modality to, the first received signal, performing a comparison between one or more signal characteristics and a corresponding set of one or more signal characteristics. Characteristics may include any one or more of direction of arrival at the transmitter, signal type or modality, strength, duration, and content. The expected characteristics may be obtained by way of reference data, which is typically associated with, and acquired in relation to, one or more given geographic areas in which the receiver may operate. For example, where a received GNSS signal is to be verified, that is have legitimacy information obtained in respect of it, by the method, the additional mixed-modality signal assessment may involve monitoring a set of further signals, and typically their direction of receipt and type, and comparing the monitored signals, in those respects at least, to the signals that would be expected to be present in the region. For example, a discrepancy between monitored and expected signals may indicate the presence of invalid sources, and conversely a confirmed similarity between measurement and expectation may be used to confirm or indicate to a receiver an area or location in which is it operating, which may consequently be used to identify an erroneous position calculated using positioning broadcasts such as the GNSS signal, and thereby indicate the illegitimacy of those broadcasts.

[0073] In accordance with a second aspect of the invention there is provided a system comprising a local signal generator, configured to provide a local signal; a receiver configured to receive a signal from a remote source in a first direction; a motion module configured to provide a determined movement of the receiver; a correlation unit configured to provide a correlation signal by correlating the local signal with the received signal; a motion compensation unit configured to provide motion compensation of at least one of the local signal, the received signal, and the correlation signal based on the determined movement in the first direction; a source vector unit configured to identify, based on the said correlation, a remote source vector corresponding to a portion of a propagation path of the received signal that is coincident with the remote source and a legitimacy information unit configured to generate legitimacy information in accordance with a remote source vector of a received signal.

[0074] Typically, any one or more of the local signal generator, motion module, correlation unit, motion compensation unit, source vector unit, and legitimacy information unit are provided as part of a single device. In some embodiments, that device further comprises the receiver. Typically, the device comprising the receiver is a user equipment (UE) in a communications network. Any one or more of the modules and units may be provided separately from the receiver, or the device comprising it, so that the system is distributed. For example, certain calculations, such as those performed by the motion compensation unit and/or the correlation unit, may be undertaken by processors in a network or otherwise in data communication with the device comprising the receiver. In this way a UE may offload calculations to remote or distributed processes, where appropriate, for the purposes of efficiency and user equipment battery usage. In some embodiments, the system, and preferably the device comprising the receiver, includes a GNSS positioning device. The output of the positioning device and/or that of an inertial measurement unit that may also be comprised by the system or user equipment specifically, or device comprising the receiver, may be used in either or both of providing the determined movement of the receiver and providing one or more pieces of location information for the receiver to enable absolute locations and/or movement paths of remote sources to be ascertained based on relative location information therefore, with respect to the receiver.

[0075] In accordance with a third aspect of the invention there is provided a computer program product comprising executable instructions which, when executed by a processor, cause the processor to undertake steps, comprising: receiving, at a receiver, a signal from the remote source in a first direction; providing a local signal; determining a movement of the receiver; providing a correlation signal by correlating the local signal with the received signal; providing motion compensation of at least one of the local signal, the received signal, and the correlation signal, based on the determined movement in the respective first direction to provide preferential gain for a signal received along the respective first direction; identifying, based on the said correlation, a remote source vector corresponding to a portion of a propagation path of the received signal, the portion being coincident with the remote source; and generating the legitimacy information for the remote source in accordance with the remote source vector of the received signal.

[0076] Any of the properties, features, and steps described in relation to the preceding and following embodiments in this disclosure may relate to the method of the first aspect, the system of the second aspect, the computer program product of the third aspect, or the below-described aspect.

[0077] In accordance with a fourth aspect of the invention there is provided a method for locating cellular emitters using a receiver, comprising: performing motion compensated correlation upon at least one received signal to generate at least one motion compensated correlation result; identifying a direction of arrival for the at least one received signal using the at least one motion compensated correlation result; and determining, from the direction of arrival of the at least one received signal, the location of a cellular emitter.

[0078] In any of the aspects of the invention provided in this disclosure, the method may comprise any one or more of: determining a time of arrival of the at least one received signal; and using the time of arrival to remove received signal direction of arrivals that are associated with non-line-of-sight signals; and determining whether the emitter is legitimate or illegitimate; and if the emitter is illegitimate, taking action to mitigate interference generated by the illegitimate emitter.

[0079] In accordance with a further aspect of the invention there is provided an apparatus for performing signal correlation within a signal processing system, comprising at least one processor and at least one non-transient computer readable medium for storing instructions that, when executed by the at least one processor, causes the apparatus to perform operations comprising: performing motion compensated correlation upon at least one received signal to generate at least one motion compensated correlation result; identifying a direction of arrival for the at least one received signal using the at least one motion compensated correlation result; and determining, from the direction of arrival of the at least one received signal, the location of a cellular emitter.

[0080] Embodiments of the present invention generally relate to a method and apparatus for providing signal intelligence and security as shown in and/or described in connection with at least one of the figures.

[0081] These and other features and advantages of the present disclosure may be appreciated from a review of the following detailed description of the present disclosure, along with the accompanying figures in which like reference numerals refer to like parts throughout.

BRIEF DESCRIPTION OF DRAWINGS

[0082] So that the manner in which the above recited features of the present invention can be understood in detail, a particular description of the invention, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

[0083] FIG. 1 depicts a block diagram of a scenario having a receiver for providing signal intelligence in accordance with at least one embodiment of the invention;

[0084] FIG. 2 is a block diagram of the receiver of FIG. 1 in accordance with at least one embodiment of the invention;

[0085] FIG. 3 depicts a scenario of operation of the receiver of Figures 1 and 2 in accordance with at least one embodiment of the invention;

[0086] FIG. 4 is a flow diagram of a method of operation for the signal processing software in accordance with at least one embodiment of the invention; and

[0087] FIG. 5 is a flow diagram of a method of operation of the emitter location software in accordance with at least one embodiment of the invention.

DETAILED DESCRIPTION

[0088] Embodiments of the present invention comprise apparatus and methods for providing signal intelligence and security. Digital communications systems such as cellular, Bluetooth or WiFi utilize encoded digital signals to improve communication throughput and security. Most of these systems utilize some form of deterministic digital code to facilitate signal acquisition, e.g., Gold codes, training sequences, synchronization words, channel characterization sequences, or other forms of acquisition codes. GNSS transmissions also utilize repeatedly transmitted acquisition codes. Such a digital code is deterministic by the receiver and repeatedly broadcast by the transmitter to enable the receivers to acquire and receive the transmitted signals. Using such deterministic codes combined with an accurate motion model of a receiver, embodiments of the invention are useful for identifying a direction of arrival (DoA) for a propagation path between the receiver and transmitter. The technique for performing this DoA determination using receiver motion information is known as SUPERCORRELATION™ and is described in commonly assigned US patent 9,780,829, issued 3 October 2017; US patent 10,321 ,430, issued 11 June 2019; US patent 10,816,672, issued 27 October 2020; US patent publication 2020/0264317, published 20 August 2020; and US patent publication 2020/0319347, published 8 October 2020, which are hereby incorporated herein by reference in their entireties. The receiver may use this DoA data to determine information regarding an emitter or emitters proximate the receiver. For example, the DoA data may be used to identify the location of spoofing emitters as well as the location of legitimate emitters. A map of the legitimate emitters may be created using the locations such that, in the future, emitters that are not on the map may be considered illegitimate emitters requiring further investigation. From the DoA data, user receivers (e.g., mobile devices or GNSS receivers) may be operated to avoid or suppress signals from the spoofing emitters such that these illegitimate emitters are no longer a threat. Using the illegitimate emitter locations, government authorities can identify and disable these emitters.

[0089] In one exemplary embodiment, a receiver may be transported through an area containing various emitters and be able to identify signal propagation paths and location of each nearby emitter. These emitters may be GNSS satellites, cellular signal transceivers, WiFi transceivers, Bluetooth transceivers, and the like. The receiver may be carried by a pedestrian and be made functional via application software to map emitters in the local area. Alternatively, emitter location and mapping may be performed by moving the receiver using a vehicle on a ground path. In other embodiments, the receiver may be carried by an airborne vehicle - manned or unmanned (e.g., drones, helicopters, airplanes, etc.). The functions of embodiments of the invention may be embedded into cellular telephones, Internet of Things (loT) devices, mobile computers, tablets, control systems for autonomous vehicles and the like. Embodiments find use on any moving platform that receives signals that can be correlated with a locally generated signal.

[0090] As the receiver traverses an area, it collects DoA data for the emitters that are nearby (i.e., within range of the emitter). The receiver knows its position through the use of a global navigation satellite system (GNSS) receiver and/or an inertial guidance system. From the receiver position and a plurality of DoA vectors (representing direction from receiver to emitter) to a particular emitter, embodiments of the invention compute the location of the emitter relative to the receiver. The relative location can then be translated to a geocoordinate. As emitter locations are computed, a geocoordinate map is produced showing the locations of the emitters.

[0091] In some embodiments, multiple receivers may be used to receive signals in a coordinated manner. In further embodiments, the receiver(s) may receive signals from multiple types of emitters operating in various frequency bands to facilitate gathering information related to many systems to generate a signal profile for a given area. Some embodiments may perform the signal processing locally on the moving platform. In other embodiments, the emitter information, receiver motion information and receiver location information may be gathered at the moving platform and communicated (wired or wirelessly) to a server for remote processing in real-time or at a later time. In some embodiments, the data is stored and processed when need arises, e.g., when law enforcement requires a traveled path of a particular cell phone or other emitter.

[0092] FIG. 1 depicts a block diagram of a scenario 100 having at least one receiver 102 for receiving signals from emitters 106, 108 and 110 in accordance with at least one embodiment of the invention. In other embodiments, a plurality of receivers 102 may be deployed to gather emitter information. An emitter 106, 108, 110 may be a legitimate emitter (communications or positioning emitter) or an illegitimate emitter (jammer or spoofer). The emitters 106, 108, 110 may be stationary or moving. Each of the at least one receiver 102 comprises an emitter locator 104 configured to receive and process signals transmitted by emitters 106, 108, 110 (three emitters are depicted, but the receiver 102 may process the signals from any number of emitters). The signals from the legitimate emitters 106 and 110 may be intended to communicate with, for example, a mobile device 114, e.g., cellular telephone, laptop computer, tablets, Internet of Things (loT) devices, autonomous vehicle, etc. The mobile device may communicate with the emitters 106, Ho using cellular signals, e.g., CDMA, GSM and the like that support cellular standards such as, but not limited to, 3G, 4G, LTE, and/or 5G standards. Alternatively, or in addition, the legitimate emitters 106, 110 may be WiFi or Bluetooth or other communications devices that communicate amongst themselves or with mobile devices 114. Further, the legitimate emitters 106, 110 may be satellite-based transmitters of GNSS signals.

[0093] The scenario 100 comprises at least one illegitimate emitter 108 such as a jammer or spoofer that may target a mobile device, e.g., device 114. The intent of a jammer is to interfere with reception of transmissions of legitimate emitters 106, 108. A jammer may transmit signals similar to the legitimate emitter signals to overwhelm or confuse the signal processing capabilities of a target receiver. A spoofer, on the other hand, transmits signals that resemble legitimate emitter signals such that the target receiver may acquire the spoofing signal and even process the signal as if it were legitimate.

[0094] The receiver 102 comprises an emitter locator 104 operating to accurately locate emitters 106, 108, 110 in accordance with at least one embodiment of the invention. The emitter locator 104 may locate both legitimate and illegitimate emitters or the locator 104 may only locate illegitimate emitters. As shall be evident from this description, the goal of the emitter locator is to provide signal intelligence for the transmissions occurring in its vicinity. Using the signal intelligence, action may be taken to improve signal security for users of the transmissions, e.g., avoid or suppress reception of illegitimate transmissions, disable illegitimate emitters and the like.

[0095] In one embodiment, the emitter locator 104 in the at least one receiver 102 receives and processes the emitter transmissions locally within the receiver. In other embodiments, the receiver based emitter locator 104 may collect data regarding emitter transmissions and receiver parameters (e.g., receiver motion, position, etc.). The emitter data may be communicated immediately or stored for later communication through a communication network 114 to a server 112. The server 112 comprises an emitter locator 104 for processing the emitter data to determine emitter locations. The emitter data may be processed in real-time or at a later time. In other embodiments, emitter data may be processed partially in a receiver 102 and partially in the server 112.

[0096] As described in detail below, the emitter locator 104 (whether receiverbased or server-based) uses a SUPERCORRELATION™ technique as described in commonly assigned US patent 9,780,829, issued 3 October 2017; US patent 10,321 ,430, issued 11 June 2019; US patent 10,816,672, issued 27 October 2020; US patent publication 2020/0264317, published 20 August 2020; and US patent publication 2020/0319347, published 8 October 2020, which are hereby incorporated herein by reference in their entireties. The technique determines a direction of arrival (DoA) of signals received at a receiver (i.e., received signals) from an emitter 106, 108, 110. As the receiver 102 moves (represented by arrow 118), the emitter locator 104 computes motion information representing motion of the receiver 102. The motion information is used to perform motion compensated correlation of the received signals. From the motion compensated correlation process, the emitter locator 104 estimates the DoA of the received signals. The emitter locator 104 uses the receiver position along the DoA data to determine a location of the emitter 106, 108, 110. The intersection of a plurality of DoA vectors generated as the receiver moves along path 118 identifies the location of the emitters 106, 108, 110 as described in detail below.

[0097] From the signal DoA data, the receiver 102 or server 112 may create a map of the emitter locations. In one embodiment, the location information may be accumulated within the receiver and downloaded to a mapping application at a later time. In an alternative embodiment, the emitter locations may be continuously, periodically, or intermittently transmitted via cellular or WiFi communications to a server 112 where a mapping application creates a map of the emitter locations. [0098] In alternative embodiments, the received signals may be processed to determine time of arrival (TOA) or time difference of arrival (TDOA) information for the signals. As is known in the art, the TOA and TDOA information may be used for position calculations of the emitter. Such calculations may be used to augment the DoA vector processing to improve the speed at which a position solution is attained. Additionally, TOA and/or TDOA information may be used to identify delayed received signals which is indicative of non-line-of-sight (NLOS) signal paths. The DoA vectors associated with NLOS signals may be removed from the emitter location calculation to reduce the amount of computation and/or remove a source of location error.

[0099] FIG. 2 is a block diagram of the receiver 102 in accordance with at least one embodiment of the invention. The receiver 102 comprises a mobile platform 206, an antenna 202, receiver front end 204, signal processor 206, and motion module 228. The receiver 102 may form a portion of a laptop computer, mobile phone, tablet computer, Internet of Things (loT) device, unmanned aerial vehicle, mobile computing system in an autonomous vehicle, human operated vehicle, etc.

[00100] In the receiver 102, the mobile platform 200 and the antenna 202 are an indivisible unit where the antenna 202 moves with the mobile platform 200. The operation of the SUPERCORRELATION™ technique operates based upon determining the motion of the signal receiving antenna. Any mention of motion herein refers to the motion of the antenna 202. In some embodiments, the antenna 202 may be separate from the mobile platform 200. In such a situation, the motion estimate used in the motion compensated correlation process is the motion of the antenna 202. In most scenarios, the motion of the mobile platform 200 is the same as the motion of the antenna 202 and, as such, the following description will assume that the motion of the platform 200 and antenna 202 are the same.

[00101] The mobile platform 200 comprises a receiver front end 204, a signal processor 206 and a motion module 228. The receiver front end 204 downconverts, filters, and samples (digitizes) the received signals in a manner that is well-known to those skilled in the art. The output of the receiver front end 204 is a digital signal containing data. The data of interest is a deterministic training or acquisition code, e.g., Gold code, used by the emitter to synchronize the transmission to a transceiver.

[00102] The signal processor 206 comprises at least one processor 210, support circuits 212 and memory 214. The at least one processor 210 may be any form of processor or combination of processors including, but not limited to, central processing units, microprocessors, microcontrollers, field programmable gate arrays, graphics processing units, digital signal processors, and the like. The support circuits 212 may comprise well-known circuits and devices facilitating functionality of the processor(s). The support circuits 212 may comprise one or more of, or a combination of, power supplies, clock circuits, analog to digital converters, communications circuits, cache, displays, and/or the like.

[00103] The memory 214 comprises one or more forms of non-transitory computer readable media including one or more of, or any combination of, readonly memory or random-access memory. The memory 214 stores software and data including, for example, signal processing software 216, emitter location software 208 and data 218. The data 218 comprises the receiver location 220, direction of arrival (DOA) vectors 222 (collectively, DoA data), emitter locations 224, and various data used to perform the SUPERCORRELATION™ processing. The signal processing software 216, when executed by the one or more processors 210, performs motion compensated correlation upon the received signals to estimate the DoA vectors for the received signals. The motion compensated correlation process is described in detail below. The operation of the signal processing software 216 functions as the emitter locator 104 of FIG. 1 .

[00104] As described below in detail, the DoA vectors 222 and receiver location 220 are used by the emitter location software 208 to determine the location of each emitter. The data 218 stored in memory 214 may also include signal estimates, correlation results, motion compensation information, motion information, motion and other parameter hypotheses, position information and the like. [00105] The motion module 228 generates a motion estimate for the receiver 102. The motion module 228 may comprise an inertial navigation system (INS) 230 as well as a global navigation satellite system (GNSS) receiver 226 such as GPS, GLONASS, GALILEO, BEIDOU, etc. The INS 230 may comprise one or more of, but not limited to, a gyroscope, a magnetometer, an accelerometer, and the like. To facilitate motion compensated correlation, the motion module 222 produces motion information (sometimes referred to as a motion model) comprising at least a velocity of the antenna 202 in the direction of an emitter of interest, i.e. , an estimated direction of a source of a received signal. In some embodiments, the motion information may also comprise estimates of platform orientation or heading including, but not limited to, pitch, roll and yaw of the platform 200/antenna 202. Generally, the receiver 102 may test every direction and iteratively narrow the search to one or more directions of interest.

[00106] FIG. 3 depicts a scenario 300 of operation of the receiver 102 of FIGs.

1 and 2 in accordance with at least one embodiment of the invention. The scenario 300 comprises the receiver 102 moving from position 1 along path 302 to position 2, and then moving along path 304 to position 3. As the receiver 102 traverses the area, the receiver 102 computes a DoA vector 306 at position 1 , 308 at position 2 and 310 at position 3. The three DoA vectors 306, 308 and 310 intersect at the location 312 of the emitter 106. Although three discrete positions are described as where the DoA vectors are computed, in other embodiments, the DoA vectors may be computed periodically, intermittently, or continuously as the receiver moves. Additional vectors may be used to converge the solution onto an accurate emitter location. Further, the emitter 106 may be moving such that the convergence point moves and can be tracked. The receiver 102 may be a single receiver or a plurality of different receivers that coordinate their data gathering efforts. The DoA vectors may be processed at a remotely located server to determine locations of emitters using the vectors from different receivers.

[00107] In an urban environment, some DoA vectors 302, 304, 306 are line-of- sight (LOS) and some DoA vectors 314 are non-line-of-sight (NLOS), i.e., LOS vectors represent signals that are transmitted directly from the emitter 106 to the receiver 102, while NLOS vectors may be reflected from structures 316 in the vicinity of the receiver 102. In one embodiment, the received signals that may lead to NLOS vectors (e.g., undesirable signals) can be ignored in the DoAand location computations. In another embodiment, as more and more DoA vectors are collected and processed, the LOS vectors converge on a particular location, e.g., location 312. In addition, if TOA or TDOA information is available, the information may be used to remove DoA vectors of NLOS paths because the arrival times will be anomalous (delayed) for the NLOS signals versus the LOS signals, i.e. , the time information of NLOS signals will contain a delay compared to the LOS signals.

[00108] In other embodiments, the structures 316 may be modeled in a building model. The building model in conjunction with ray tracing techniques can be used to determine the DoA of reflected signals. Consequently, the path of the reflected emitter signal is estimated and the reflected signals may be used in the emitter localization calculation.

[00109] In other embodiments, one or more receivers 102 may collect all emitter signals, LOS and NLOS, over a period of time while the receivers are traversing an area. These collected signals may be processed using the emitter localization techniques described herein to create a signal profile for a region. The signal formula will contain DoA vector intersection regions that identify emitter locations. In some embodiments, a Bayesian estimator may be used to compare various hypotheses as to emitter location using information provided by available measurements.

[00110] Typically, vector intersection location 312 is not a point, but rather it’s a region or area due to the probabilistic nature of the DoA vectors, i.e., the determined direction of each vector has an uncertainty caused by measurement error and the intersection forms a region rather than a point. The region of intersection will form a maximum that defines the location of the emitter 106.

[oom] Since the receiver 102 knows its position through GNSS and/or INS calculations, the geolocation coordinate of the receiver 102 may be translated into a geolocation coordinate for emitter location 312. As such, a geolocation map of emitter locations may be generated. Although the scenario depicts a receiver 102 computing a location 312 of a single emitter 106, in various other embodiments, the receiver 102 may produce locations for many nearby emitters sequentially and/or simultaneously.

[00112] The forgoing embodiment performs the emitter vector and location determination within the receiver 102. In other embodiments, the data (i.e. , emitter data) for producing DoA vectors, DoA vectors themselves, position information, etc. may be transmitted from the receiver to a server (112 in Fig. 1) for processing to produce the emitter locations.

[00113] FIG. 4 is a flow diagram of a method 400 of operation for the signal processing software 216 in accordance with at least one embodiment of the invention. The method 400 may be implemented in software, hardware or a combination of both (e.g., using the signal processor 206 of FIG. 2).

[00114] The method 400 begins at 402 and proceeds to 404 where signals are received at a receiver from at least one remote source (e.g., transmitters such as the emitters 106, 108, 110 of FIG. 1) in a manner as described with respect to FIG.

1. Each received signal comprises a synchronization or acquisition code, e.g., a Gold code, extracted from the radio frequency (RF) signal received at the antenna. The process of downconverting the RF signal and extracting the digital code is well known in the art. At 406, the method 400 receives motion information from the motion module 228 of FIG. 2. The motion information comprises an estimate of the motion of the receiver 102 of FIG. 1 , e.g., one or more of velocity, heading, orientation, etc.

[00115] In some embodiments, the receiver uses a single local oscillator for receiving emitter signals and for receiving GNSS signals. As such, prior to processing emitter signals, the SUPERCORRELATION™ technique is applied to the GNSS signals to facilitate improved position accuracy and to correct local oscillator instability. Consequently, the receiver position is very accurate and the local oscillator is stable over long periods such that very long coherent integration times (e.g., 1 second) may be used for processing both GNSS signals and the emitter signals.

[00116] At 408, the method 400 generates a plurality of phasor sequence hypotheses related to a direction of interest of the received signal. Each phasor sequence hypothesis comprises a time series of phase offset estimates that vary with parameters such as receiver motion, frequency, DoA of the received signals, and the like. The signal processing correlates a local code encoded in a local signal with the same code encoded within the received RF signal. In one embodiment, the phasor sequence hypotheses are used to adjust, at a subwavelength accuracy, the carrier phase of the local signal. In some embodiments, such adjustment or compensation may be performed by adjusting a local oscillator signal, the received signal(s), or the correlation result to produce a phase compensated correlation result. The signals and/or correlation results are complex signals comprising in-phase (I) and quadrature phase (Q) components. The method applies each phase offset in the phasor sequence to a corresponding complex sample in the signals or correlation results. If the phase adjustment includes an adjustment for a component of receiver motion in an estimated direction of the emitter, then the result is a motion compensated correlation result. For each received signal, at 410, the method 400 correlates the received signals with a set (plurality) of direction hypotheses containing estimates of a phase offset sequences necessary to accurately correlate the received signals arriving from a particular direction over a long coherent integration period (e.g., 1 second). There is a set of hypotheses representing a search space for each received signal and each parameter of interest, e.g., receiver motion and/or signal DoA.

[00117] The motion estimates are typically hypotheses of the motion in a direction of interest such as in the direction of the emitter of interest that transmitted the received signal, i.e., if the illegitimate emitter is the emitter of interest, generate a search space of hypotheses containing a component of the receiver’s motion that is in the direction of the illegitimate emitter. At initialization, the direction of interest may be unknown or inaccurately estimated. Consequently, a brute force search technique may be used to identify one or more directions of interest by searching over all directions and correlating signals received in all directions. A comparison of correlation results over all the directions enables the method 400 to narrow the search space. There is very strong correlation between the true values of these hypotheses between code repetition, such that the initial search might be intensive, but subsequent processing only requires tracking of receiver motion and signal DoA in the receiver as those parameters evolve. Consequently, subsequent compensation is performed over a narrow search space.

[00118] In one embodiment, if a signal from a given emitter was received previously, the set of hypotheses for the newly received signal include a group of phasor sequence hypotheses using the expected frequency and frequency rate and/or last frequency and last frequency rate used in receiving the prior signal from that particular emitter. The values may be centered around the last values used or the last values used additionally offset by a prediction of further offset based on the expected receiver motion. At 410, the method 400 correlates each received signal with that signal’s set of hypotheses. The hypotheses are used as parameters to form the phase-compensated phasors to phase compensate the correlation process. As such, the phase compensation may be applied to the received signals, the local frequency source (e.g., an oscillator signal), or the correlation result values. In addition to searching over the DoA space, the method 400 may also apply hypotheses related to other variables (parameters) such as oscillator frequency to correct frequency and/or phase drift, or heading to ensure the correct motion compensation is being applied. The number of hypotheses may not be the same for each variable. For example, the search space may contain ten hypotheses for searching DoA and have two hypotheses for searching a receiver motion parameter such as velocity - i.e. a total of twenty hypotheses (ten multiplied by two). The result of the correlation process is a plurality of phase- compensated correlation results - one phase-compensated correlation result value for each hypothesis for each received signal.

[00119] At 412, the method 400 processes the correlation results to find the “best” or optimal result for each received signal. The correlation output may be a single value that represents the parameter hypotheses (preferred hypotheses) that provide an optimal or best correlation output. In general, a cost function is applied to the correlation values for each received signal to find the optimal correlation output corresponding to a preferred hypothesis or hypotheses, e.g., a maximum correlation value is associated with the preferred hypothesis for the correct signal DoA.

[00120] At 414, the method 400 identifies the DoA vector of each received signal from the optimal correlation result for the signal. The received signals along the DoA vector typically have the strongest signal to noise ratio and represent line of sight (LOS) reception between the emitter and receiver. As such, using motion compensated correlation enables the receiver 102 to identify the DoA vector of the received signal(s). The method 400 ends at 416.

[00121] In other embodiments, rather than using the largest magnitude correlation value, other test criteria may be used. For example, the method 400 may monitor the progression of correlations as hypotheses are tested and apply a cost function that indicates the best hypotheses when the cost function reaches a minimum (e.g., a small hamming distance amongst peaks in the correlation plots). In other embodiments, additional hypotheses may be tested in addition to the DoA hypotheses to, for example, ensure the motion compensation (i.e. , speed and heading) is correct.

[00122] FIG. 5 is a flow diagram of a method 500 of operation of the location software 288 in accordance with at least one embodiment of the invention. The method 500 may be performed locally within the receiver or may be performed remotely on a server. If performed remotely, the DoA vectors or data to generate the DoA vectors are transmitted from the receiver to the remote server for processing in accordance with method 500.

[00123] The method 500 begins at 502 and proceeds to 504 where the method 500 receives the DoA vectors for a particular emitter. At 506, the method 500 determines a location where the DoA vectors intersect. The emitter location is relative to the receiver position. The process may be iterative as additional DoA vectors are generated or may be calculated when a predefined number (e.g., three, five, ten, etc.) of DoA vectors have been determined. In some embodiments, the position computation may be augmented using TOA or TDOA information. For example, the time information related to the time a signal is received at various receiver positions can be used to identify LOS signals versus NLOS signals, e.g., NLOS signals have a delayed reception time as compared to LOS signals. DoA vectors associated with NLOS signals may then be removed from the vector set used to determine emitter location.

[00124] At 508, the method 500 computes a geolocation coordinate for the emitter location by translating the known geolocation coordinate of the receiver to the emitter location determined at 506. At 510 the method updates a map or database with the emitter geolocation such that a comprehensive list of emitter locations is created. At 512, the method queries whether another set of DoA vectors for another emitter are available for processing. If the query is affirmatively answered, the method 500 returns to 504 to process additional DoA vectors. If the query is negatively answered, the method 500 ends at 514.

[00125] Embodiments of the invention may be used to collect emitter data over time without processing the data, i.e. , the emitter and receiver data is stored for subsequent processing on an as needed basis. For example, an autonomous vehicle may collect and store emitter and receiver data that is processed after a traffic accident has occurred. The processing may indicate that a GNSS spoofing emitter may have caused the vehicle’s GNSS receiver to malfunction and follow an incorrect path.

[00126] Embodiments of the invention may be used to process collected cellular telephone data where the cellular telephone is the emitter of interest and police cars with embodiments of receivers described above collect emitter data for subsequent processing. Upon a need arising, emitter data from receivers known to be in the area of a crime may be processed to determine a particular cellular telephone’s movement over a particular period. Such movement evidence may form useful evidence in an investigation.

[00127] The emitter locator 104 may be a feature of a mobile device such that, once an illegitimate emitter is found, the mobile device may use the emitter’s location to take action to suppress signals arriving from the emitter's DoA. Such action may involve altering an antenna pattern of the mobile device or may involve using the SUPERCORRELATION™ technique to suppress reception of signals from the emitter’s location and/or enhance reception of signals from legitimate emitters.

[00128] Here multiple examples have been given to illustrate various features and are not intended to be so limiting. Any one or more of the features may not be limited to the particular examples presented herein, regardless of any order, combination, or connections described. In fact, it should be understood that any combination of the features and/or elements described by way of example above are contemplated, including any variation or modification which is not enumerated, but capable of achieving the same. Unless otherwise stated, any one or more of the features may be combined in any order.

[00129] As above, figures are presented herein for illustrative purposes and are not meant to impose any structural limitations, unless otherwise specified. Various modifications to any of the structures shown in the figures are contemplated to be within the scope of the invention presented herein. The invention is not intended to be limited to any scope of claim language.

[00130] Where “coupling” or “connection” is used, unless otherwise specified, no limitation is implied that the coupling or connection be restricted to a physical coupling or connection and, instead, should be read to include communicative couplings, including wireless transmissions and protocols.

[00131] Any block, step, module, or otherwise described herein may represent one or more instructions which can be stored on a non-transitory computer readable media as software and/or performed by hardware. Any such block, module, step, or otherwise can be performed by various software and/or hardware combinations in a manner which may be automated, including the use of specialized hardware designed to achieve such a purpose. As above, any number of blocks, steps, or modules may be performed in any order or not at all, including substantially simultaneously, i.e., within tolerances of the systems executing the block, step, or module.

[00132] Where conditional language is used, including, but not limited to, “can,” “could,” “may” or “might,” it should be understood that the associated features or elements are not required. As such, where conditional language is used, the elements and/or features should be understood as being optionally present in at least some examples, and not necessarily conditioned upon anything, unless otherwise specified.

[00133] Where lists are enumerated in the alternative or conjunctive (e.g., one or more of A, B, and/or C), unless stated otherwise, it is understood to include one or more of each element, including any one or more combinations of any number of the enumerated elements (e.g. A, AB, AC, ABC, ABB, etc.). When “and/or” is used, it should be understood that the elements may be joined in the alternative or conjunctive. [00134] While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.