RF signal generating device

Abstract

Apparatus for generating an RF signal for use in RF signal detection is described. The apparatus comprises at least one processor configured to generate a set of IQ data based on at least one set of weighted IQ data, each set of weighted IQ data having a respective weight and a circuit configured to generate an RF signal using the set of IQ data. The at least one processor is configured to calculate each respective weight in dependence upon location of a signal detector or an antenna associated with the RF signal detector.

Claims

1. Apparatus comprising: a positioning device for providing a location of a radio frequency (RF) signal detector or a location of an antenna associated with the RF signal detector; an orientation determining device for providing an orientation of the antenna associated with the RF signal detector; an interface for receiving an instruction modifying the location; at least one processor configured to generate a set of in-phase and quadrature (IQ) data based on at least one set of weighted IQ data, each set of weighted IQ data having a respective weight; and a circuit configured to generate an RF signal using the set of IQ data; wherein the at least one processor is configured to calculate each respective weight in dependence upon the location and the orientation.

2. Apparatus according to claim 1, wherein the at least one processor is configured to calculate each respective weight in dependence upon location of a respective wireless RF transmitter being simulated.

3. Apparatus according to claim 1, wherein the at least one processor is configured to calculate each respective weight in dependence upon orientation of the antenna.

4. Apparatus according to claim 1, wherein the antenna is a handheld antenna.

5. Apparatus according to claim 1, wherein the antenna comprises an orientation determining device.

6. Apparatus according to claim 1, wherein the antenna is a dummy antenna.

7. Apparatus according to claim 1, wherein the at least one processor is configured to generate a set of IQ data based on at least two sets of weighted IQ data by linearly combining the at least two sets of weighted IQ data.

8. A system comprising: at least two apparatuses according to claim 7; and at least two signal detectors; wherein each signal detector is in wired connection with a respective apparatus, wherein each apparatus is configured to simulate the same environment.

9. Apparatus according to claim 1, further comprising: a first database storing data relating to propagation models and terrain; wherein the at least one processor is configured to calculate each respective weight in dependence upon a propagation model and terrain.

10. Apparatus according to claim 1, further comprising: a second database storing data relating to antenna characteristics of a given signal detector; wherein the at least one processor is configured to calculate each respective weight in dependence upon said antenna characteristics.

11. Apparatus according to claim 1, further comprising: a third database storing data relating to characteristics of a plurality of RF transmitters; wherein the at least one processor is configured to calculate each respective weight in dependence upon characteristics of the respective RF transmitter.

12. Apparatus according to claim 11, wherein the characteristics include a transmit power.

13. Apparatus according to claim 12, wherein the location depends on time.

14. Apparatus according to claim 1, further comprising: a synthesiser configured to generate a set of IQ data; wherein the at least one processor is configured to receive the set of IQ data from the synthesiser and to apply a corresponding weight.

15. Apparatus according to claim 1, further comprising: a fourth database storing at least one set of IQ data; wherein the at least one processor is configured to retrieve the set of IQ data from the fourth database and to apply a corresponding weight.

16. Apparatus according to claim 1, wherein the circuit comprises: a pair of digital-to-analog converters (DACs); wherein the DACs are configured to receive the IQ data and to output analog I and Q signals.

17. Apparatus according to claim 1, wherein the circuit comprises: a modulator; wherein the modulator is configured to receive the analog IQ signals from DACs and to modulate the RF carrier signal to provide an intermediate signal.

18. Apparatus according to claim 1, wherein the circuit comprises: a set of at least one up-converter and/or down-converter, one of which is selectable so as to allow up-conversion or down-conversion of the intermediate signal.

19. Apparatus according to claim 1: wherein the set of IQ data is a first set of IQ data, the circuit is a first circuit which is configured to receive the first set of IQ data, a first gain and a first frequency band and to generate a first RF signal in the first frequency band, and wherein the at least one processor configured to generate second set of IQ data based on at least one set of weighted IQ data: a second circuit configured to receive the second set of IQ data, a second gain and a second frequency band which is different to the first frequency band and to generate a second RF signal in the second frequency band.

20. Apparatus according to claim 19, further comprising: an RF signal combiner; wherein the combiner is configured to receive first and second RF signals and to combine the signals to provide a multi-band RF signal.

21. Apparatus according to claim 20, further comprising: a port for supplying the multi-band RF signal to a wired connection.

22. Apparatus according to claim 1, further comprising: a port for supplying the RF signal to a wired connection.

23. Apparatus according to claim 1, further comprising: an interface configured to receive instructions from a remote location for controlling operation of the apparatus.

24. Apparatus according to claim 1, further comprising: an interface configured to provide information on performance.

25. Apparatus according to claim 1, further comprising: an interface configured to provide a reference sequence for supplying to a signal detector; and the signal processor is configured to generate the set of IQ data so as to simulate a signal that would have been received from a virtual test transmitter including a time delay corresponding to a distance between the virtual test transmitter and the signal detector.

26. A system comprising: apparatus according to claim 1; and a signal detector; wherein the signal detector is in wired connection with the apparatus.

27. A system according to claim 26, wherein the signal detector comprises a spectrum analyser.

28. A system according to claim 26, wherein the signal detector and apparatus are comprised in a single unit.

29. A system according to claim 26, wherein the signal detector includes an interface for receiving instruction from a remote location for controlling operation of the apparatus and/or signal detector, and/or for transmitting information on performance.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Certain embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

(2) FIG. 1 schematically illustrates training an operator of an RF signal detector using remote RF sources which transmit wireless RF signals;

(3) FIG. 2 schematically illustrates training an operator of a signal detector using an RF signal generator which provides an RF signal to an RF signal detector via a wired connection;

(4) FIG. 3 schematically illustrates virtual test transmitters simulated using the RF signal generator shown in FIG. 2;

(5) FIG. 4 is a schematic block diagram of an RF signal generator;

(6) FIG. 5 is a schematic block diagram of a transmitter section of the RF signal generator shown in FIG. 4;

(7) FIG. 6 a schematically illustrates training an operator of an RF signal detector by an instructor using a remote station;

(8) FIG. 7 is a process flow diagram of a process carried out by a processing section in the RF signal generator shown in FIG. 7;

(9) FIG. 8 is a process flow diagram of a process of computing IQ data;

(10) FIG. 9 schematically illustrates a RF signal generator receiving antenna orientation data;

(11) FIG. 10 schematically illustrates a RF signal generator being used in time difference of arrival arrangement; and

(12) FIG. 11 schematically illustrates exchanged of signals between detector stations for a time difference of arrival measurement.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

(13) Referring to FIG. 1, a radio frequency (RF) signal detector 1 is shown. The RF signal detector 1 can take the form of spectrum analyser. The RF signal detector 1 is coupled to an antenna 2 thereby allowing the RF signal detector 1 to detect wireless RF signals.

(14) As shown in FIG. 1, a user 3 (herein referred to as an “operator” or “trainee”) can be trained by an instructor (not shown) to use the signal detector 1 by employing one or more test transmitters 4 which transmit respective wireless RF signals 5 located in a surrounding area 6.

(15) The area 6 may be an enclosed space, such as building, installation, vehicle or vessel, or part of a building, installation, vehicle or vessel. The area 6 may be semi-enclosed or bounded, such as a stadium or street. The area 6 may be open, such as open ground. The area 6 may be mixture of different types of spaces. The area 6 may include land and/or sea.

(16) Referring to FIG. 2, a training system 7 is shown. The training system 7 includes the signal detector 1 and an RF signal generator 8. An RF output 9 of the signal generator 8 is coupled to an RF input 10 of the signal detector 1 via a wired connection 11 (such as a co-axial cable) to supply an RF signal 12 directly to the signal detector 1.

(17) The signal generator 8 does not need to transmit a wireless RF signal. Thus, the signal generator 8 may be one which is only capable of transmitting low-power RF signals, for example, in a range of −150 dBm to +10 dBm. However, the signal generator 8 may be one which is capable of transmitting RF signals at a higher power, e.g. greater than +10 dBm.

(18) As shown in FIG. 2, no wireless test transmitters 4 (FIG. 1) need be used.

(19) Referring also to FIG. 3, the training system 7 can be used to provide an apparent signal environment (or “simulated environment”) 13 which includes one or more simulated RF test transmitters 14 (herein referred to as “virtual test transmitters”) transmitting simulated wireless RF signals 15.

(20) The virtual test transmitters 14 do not physically exist. However, the signal generator 8 imitates the signal environment that the virtual test transmitters 14 would have produced at the RF input of the signal detector 1 if they were real. Thus, the signal generator 8 can help circumvent the need for using real test transmitters 4 (FIG. 1).

(21) Each virtual test transmitter 14 may be fixed or mobile. The signal generator 8 can mimic the signal environment as it would appear to the signal detector 1 at a particular position, p.sub.d. The signal detector position may include latitude and longitude (or other set of two-dimensional coordinates) and, optionally, height.

(22) As will be explained in more detail later, the signal generator 8 can simulate changes in signal strength resulting from changes in orientation of a real, but non-operational directional antenna or substitute device 41 (FIG. 9). The signal generator 8 can play back previously recorded signals. The signal generator 8 can be controlled from a remote station 36 (FIG. 6) by an instructor 38 (FIG. 6) and so vary the signal environment presented to the operators 3.

(23) The training system 7 may be used for training and/or assessing operators 3 in techniques of signal detection, direction finding (or “transmitter geolocation”), signal identification and eavesdropping. The system 7 can be used in-the-field, for example, in an area of the type in which the signal detector 1 would typically be used.

(24) The signal generator 8 may be portable. However, the signal generator 8 may be semi-portable (i.e. capable of being moved by, for example one or two persons, but is not intended for ready transportation) or mounted to a vehicle (such as a truck) or fixed platform. The sensing equipment 1 may be portable, semi-portable, or mounted to a vehicle or fixed platform.

(25) The sensing equipment 1 need not be specially-adapted other than by replacing a connection to the antenna 2 (FIG. 1) by the wired connection 11. Thus, the signal generator 8 can be used with an existing signal detector 1, for example, detection equipment that a customer already has in service.

(26) Referring to FIG. 4, an example of a signal generator 8 is shown.

(27) The signal generator 8 is able to produce signals corresponding to a large number (e.g. hundreds) of virtual test transmitters 14 (FIG. 3), each having a respective position at a given time.

(28) The signal generator 8 includes a signal processor 21, a weight calculator 22, memory 23, one or more RF signal-generating circuits 24 (herein referred to as “tuneable RF modulator sections”) and an RF signal combiner 25. The signal processor 21 and a weight calculator 22 are implemented in software running on one or more processors 26.

(29) In some embodiments, the one or more processors 26 may include one or more programmable central processing units capable of executing code to perform the functions and operations taught herein. In some embodiments, the one or more processors 26 may include one or more circuits or circuitry, for example, field programmable gate arrays configurable or programmable to perform the functions and operations taught herein. In some embodiments, the one or more processors 26 may include a combination of one or more programmable central processing units and one or more configurable circuits or circuitry to perform the functions and operations taught herein.

(30) The signal generator 8 includes first and second sources 27, 28 of digital in-phase (I) and quadrature (Q) data (herein referred to simply as “IQ data”) which are used to generate signals corresponding to the virtual test transmitters 14 (FIG. 3).

(31) The first IQ data source 27 takes the form of a synthesiser which calculates and outputs an IQ time series of I and Q data pairs for a given virtual test transmitter 14 (FIG. 3). The synthesiser 27 may be implemented in software running on the one or more processors 26.

(32) The second IQ data source 28 takes the form of a database 23 (herein referred to an “IQ data source database”) which stores pre-recorded IQ data. The IQ data can be obtained using an RF signal detector by demodulating a received RF signal to produce analog I and Q components, digitising the analog I and Q components to produce digital I and Q data streams and storing the I and Q data streams. Pre-recorded IQ data may correspond to a single virtual test transmitter 14 (FIG. 3). However, pre-recorded IQ data may correspond to more than one virtual test transmitter 14 (FIG. 3). A recording of RF signals from, say, a distant city or other site having multiple RF sources can be used.

(33) Referring still to FIG. 4, the signal generator 8 includes additional databases 29, 30, 31 and a positioning device 32. A propagation model and terrain database 29 stores data relating to propagation models and terrain. An antenna characteristics database 30 stores data relating to characteristics of the signal detector antenna 2 (FIG. 1). A virtual test transmitter database 31 stores data regarding the virtual test transmitters 14 (FIG. 3) including transmit power, antenna gain and (time-dependent) position. The databases 22, 29, 39 31 may be stored on one or more hard disk drives and/or solid-state hard drives (not shown).

(34) The positioning device 32 is used to provide the position of the signal detector 1. The positioning device 32 takes the form of a global positioning system (GPS) receiver. Additionally or alternatively, an inertial navigation system may be used. The position may be entered manually via a user interface (not shown).

(35) Based on data taken from the databases 29, 30, 31 and the signal detector position, the weight calculator 22 calculates a weight w, typically a real number, for each selected virtual test transmitter 14 (FIG. 3) and supplies the weights w to the signal processor 21.

(36) The signal processor 21 applies the weight w (by multiplication) to a set of synthesised or pre-recorded IQ data to generate a set of weighted IQ data.

(37) The signal processor 21 linearly combines one or more sets of weighted IQ data to form a set of IQ data for a tuneable RF modulator section 24. As will be explained in more detail later, different IQ data can be provided to different tuneable RF modulator sections 24.

(38) Referring also to FIG. 5, each tuneable RF modulator section 24 includes a pair of digital-to-analog converters (DAC) 33 and a tuneable RF section 34. The signal processor 21 supplies IQ data to the DACs 33 for conversion into corresponding analog I and Q signals. The signal processor 36 also supplies a gain value and frequency band information to the tuneable RF section 34. Frequency bands having the same or different widths can be used.

(39) The tuneable RF section 34 modulates a carrier frequency to produce an intermediate frequency (IF) signal. The tuneable RF section 34 may include a frequency conversion section which may include one or more up-conversion and/or down-conversion paths. A path can be chosen to select the required frequency band.

(40) Other forms of tuneable RF modulator section 24 may be used. For example, modulation can be performed in the digital domain and the resulting digital data stream is converted by a single DAC into an analogue signal. The analogue signal can then be up-converted or down-converted as necessary.

(41) The signal generator 8 can replicate virtual transmitter characteristics (such as modulation waveform, etc.), although this may be limited by the bandwidth and dynamic range of the tuneable RF modulator sections 24.

(42) A scenario, i.e. positions as a function of time and signal characteristics of virtual transmitters 14 (FIG. 3), may be pre-programmed (stored in the virtual transmitter database 31). However, the scenario may be controlled from a remote station.

(43) Referring to FIG. 6, an instructor-controlled training system is shown. The system includes the signal detector 1 and signal generator 6 provided with a communications network interface 35 and a remote station 36 provided with a communications network interface 37. The communications network may wireless or wired. The remote station 36 may take the form of a personal computer. The remote station 38 might be used, for example, by an instructor 38 to create dynamic, time-varying signal detection problems for a trainee (i.e. operator 3) by transmitting instructions 39 for controlling the signal generator 8 and to receive telemetric information 40 on his or her performance. This can include setting or adjusting the location of the signal detector 1 and/or the location(s) of the virtual transmitter(s).

(44) Referring to FIGS. 4 to 8, operation of the signal generator 8 will be further described in more detail.

(45) When operation starts, a stream of synthesised or pre-recorded IQ data begins to be buffered in memory 23 (step S1).

(46) The signal processor 21 initialises a tuneable RF modulator section counter, j (step S2).

(47) Taking IQ data from memory 23, the signal processor 21 calculates IQ data in a first time window for a first tuneable RF modulator section 24 (step S3) and outputs a stream of IQ data, a gain value and frequency band information to the first tuneable RF modulator section 24 (steps S4 & S5).

(48) In step S3, the signal processor 21 identifies the virtual test transmitters 14 (FIG. 3) which need to be considered for the current (j-th) section 24 and determines their number, N.sub.j (step S3.1). This is to take into account the fact that certain virtual test transmitters 14 (FIG. 3) may not contribute to the current frequency band. For example, one of the two GPS carrier frequencies may fall into the frequency range of the current tuneable RF modulator section 24 and so virtual test transmitters 14 (FIG. 3) which are not a source or a significant source of RF power in this frequency band can be ignored, while other sources (such as a GPS jammers) are included and counted.

(49) The signal processor 21 initialises a virtual test transmitter counter i (step S3.2) and clears a section of memory 23 reserved for storing a windowed stream of accumulated weighted IQ data, i.e. to form a windowed stream of linearly-combined IQ data (step S3.3).

(50) The weight calculator 22 retrieves the characteristics for the current (i.e. i-th) virtual transmitter 24 and other data from databases 29, 30, 31 (step S3.4). Using this data and the current position, the weight calculator 22 calculates the weight w for the current virtual transmitter and passes this to the signal processor 21 (step S3.5).

(51) The signal processor 21 retrieves a windowed stream of synthesised or pre-recorded IQ data from (a different section of) memory 23, applies the calculated weight to each IQ data value (step S3.6) and adds this windowed stream of weighted IQ data to the section of memory 23 reserved for storing accumulated weighted IQ data (step S3.7).

(52) The signal processor 21 increments the virtual test transmitter counter i (step S3.8) and repeats steps S3.4 to S3.7 for the virtual test transmitter counter 24 until all relevant virtual test transmitters have contributed to accumulated weighted IQ data (step S3.9).

(53) The signal processor 21 then reads out the accumulated weighted IQ data (i.e. linearly-combined IQ data) as a stream of IQ data to the current tuneable RF modulator section 24 (step S3.10).

(54) The signal processor 21 increments the tuneable RF modulator section counter j (step S6) and repeats steps S3 to S5 for the next tuneable RF modulator section 24 in the same time window until respective IQ data, gain values and frequency band information have been provided to all the tuneable RF modulator sections 24 (step S7).

(55) Thus, each tuneable RF modulator section 24 generates a (single-band) RF signal in a time window. The combiner 25 add these signals to form the (multi-band) output RF signal 12 which is presented to the RF output port 9.

(56) Using a directional antenna can help identify and locate an RF source. Accordingly, the signal generator 8 can be adapted to take into account orientation of a directional antenna. Thus, training in direction-finding (DF) techniques can be provided using the signal generator 8. For example, the operator must determine a signal direction by finding the direction of strongest signal.

(57) Referring to FIG. 9, an arrangement is shown which includes a directional antenna (or a substitute device) 41 and a sensing device 42 attached to the antenna 41 capable of measuring instantaneous angle(s) of orientation of the antenna 41 and outputting antenna orientation data 43. The sensing device 42 may include MEMS-type accelerometers and/or a magnetic compass. If an antenna is used (i.e. a substitute device is not used), then no RF signal is taken from the antenna.

(58) The antenna orientation data 43 includes an azimuthal angle (or “bearing”). The antenna orientation data 43 may include an angle of elevation. This can be used to train the operator to find an elevated (or lowered) or airborne RF sources. The antenna orientation data 43 may include axial rotation. This can be used to train the operator to identify polarized sources.

(59) As shown in FIG. 9, the signal generator 8 receives the antenna orientation data 43 via input 44. The weight calculator 22 (FIG. 4) takes into account the antenna orientation data when calculating weights. In particular, weight calculator 22 (FIG. 4) uses the antenna orientation data together with antenna gain characteristics stored in the antenna characteristics database 30 (FIG. 4).

(60) Thus, the signal generator 8 can mimic the effect on the strengths of the signals received from virtual transmitters that would have been produced by the actual directional antenna gain at the measured orientation of the device. The operator can respond to the signal indicated by the signal detector 1 by moving the directional antenna 41.

(61) The antenna or substitute device 41 may be handheld. However, the antenna need not be handheld but can be any form of rotatable directional antenna, for example, mounted on a vehicle or fixed platform.

(62) Information relating to movement of the signal detector 1 and/or antenna 41 over time can be recorded and may be stored in the signal generator 8 and/or transmitted via a wireless data interface (not shown) to a remote station, e.g. for use by an instructor.

(63) As shown in FIG. 2, a single signal detector 1 can be used in conjunction with a single signal generator 8. However, the system may include more than one signal detector 1 and a corresponding number of signal generators 8 that are synchronised and so present signals from the same set of virtual transmitters to each signal detector 1.

(64) This can be used for team training, where members of a team co-operate to detect and identify multiple virtual signals.

(65) Techniques used by teams include carrying out angle of arrival (AOA) direction-finding measurements from multiple locations to triangulate a transmitter location.

(66) Signal detectors 1 and signal generators 8 may also be used for training operators at a control centre (not shown). Pairs of signal detector detectors 1 and signal generators 8 may report measurements to a remote control centre and the operators at the control centre (not shown) can interpret the measurements.

(67) Another technique, used by individuals or teams, is proximity detection using power on arrival (POA). This technique is particularly useful when used in confined space, such as a building. In this technique, an RF source is located by approaching it closely enough to maximise power received.

(68) It is also possible for members of a team, who are able to communicate with each other, to be trained in time difference of arrival (TDOA) transmitter location, using signal generators 8.

(69) To make TDOA measurements, a signal detector 1 needs an IQ reference sequence, for example, in the form of sampled time series, as the basis for correlation with the received signal. In existing systems, such reference sequences are sent over wireless broadband communications links. However, in the present system, reference sequences can be sent from the signal generators 8, which already has IQ sequence information for the virtual transmitter, to the signal detector 1.

(70) Referring to FIG. 10, a TDOA arrangement is shown.

(71) Correlation measurement data 51 are exchanged with other team members via a communications antenna 52 and a low-bandwidth (i.e. not broadband) data communications interface 53 in the signal detector 1.

(72) The signal generator 8 includes a data communications interface 54 and a wired connection 55 to provide the reference sequences 56 using, for example, short-range Ethernet.

(73) Referring also to FIG. 3, the signal generator 8 sends an RF signal 12 to the signal detector 1, simulating the signal that would have been received from a virtual test transmitter 14 including the relevant time delay corresponding to the distance between the virtual test transmitter 14 and the signal detector 1.

(74) Referring also to FIG. 11, correlation measurements made at various (at least three) detector stations 61 are shared between team members over low data rate wireless communications links, as are the locations of the detector stations 61. A TDOA location estimation calculation may then be performed at any of the detector stations that has received a full set of correlation results and associated detector locations. The behaviour of the signal generators can be synchronised using GPS.

(75) Thus, using signal generators 8 can help to reduce greatly the wireless bandwidth required for transmission between detector stations.

(76) As explained earlier, the signal generator 8 may be incorporated into a signal detector 1 to form a single unit (not shown). Thus, an operator may switch the signal detector 1 into “simulation mode” in which the unit is programmed to output pre-defined signals.

(77) The signal generator portion of the unit may provide an RF signal to the signal detector portion of the unit in the analog domain.

(78) Alternatively, the signal generator portion of the unit may provide digital signals to the signal detector portion of the unit in the digital domain. In this case, digital signals can be “injected” into a digital path near the detector output (such as a processor input, prior to the data or representation of the data being displayed).

(79) A further use of signal injection in the digital domain is the simulation of TDOA measurements. Signals can be injected into a central calculation point for transmitter location estimation.

(80) All the techniques hereinbefore described may be combined in a single training or assessment exercise, to include multiple in-field individuals and controllers at a central point, all overseen by an instructor who can determine the signal scenarios presented to the trainees, and measure their performance.

(81) The examples hereinbefore described use wired connections to avoid the need for wireless RF test transmitters 4 (FIG. 1).

(82) However, the RF signal 12 (FIG. 2) can be wirelessly transmitted from the signal generator 8 (FIG. 2) using an antenna (not shown).

(83) A signal generator 8 which wirelessly transmits an RF signal (FIG. 2) may also serve as a geo-location beacon for use by receivers when GPS is not available.

(84) For example, wireless transmission of an RF signal (FIG. 2) from a signal generator 8 can be used to synchronise a network of signal detectors 1, such as RFeye® nodes, by providing a timing beacon in the absence of effective GPS signals.

(85) Wireless transmission of an RF signal (FIG. 2) from a signal generator 8 can be used for tracking of assets, such as vehicles, by placing a signal generator 8 on each asset. Surrounding receiver, such as RFeye® nodes, can locate the asset using direction-finding techniques.

(86) It will be appreciated that many modifications may be made to the embodiments hereinbefore described.

(87) For example, the signal detector may be a digital or analog detector. The signal detector may include a display for displaying a signal.

(88) The signal generator can be used be to test signal detecting equipment.