An apparatus for emulating signal propagation between multiple communication devices and a method thereof

Abstract

An apparatus for emulating signal propagation between multiple communication devices, in particular but not exclusively, radar and communication systems. The invention also extends to a method of emulating signal propagation between multiple communication devices.

Description

[0001] AN APPARATUS FOR EMULATING SIGNAL PROPAGATION BETWEEN MULTIPLE COMMUNICATION DEVICES AND A METHOD THEREOF

[0002] Technical Field of the Invention

[0003] The invention relates to the field of apparatus for emulating signal propagation between multiple communication devices, in particular but not exclusively, radar and communication systems. The invention also extends to a method of emulating signal propagation between multiple communication devices.

[0004] Background to the Invention

[0005] Electromagnetic or acoustic signals are extensively utilised for communication devices such as sensors and communication systems. These systems often require testing either during the technology development cycle, repair, and maintenance or to evaluate the effect of one system on another; in particular interference issues, cooperability, electronic countermeasure effects or electronic protection measures. The parts of the systems being tested may be hardware (for example the receiver and / or transmitter), firmware or software functionality. Known approaches for testing the systems include outdoor field testing or indoor testing in an anechoic chamber facility. An example of such a test may involve a transmitter operated to emit a signal that propagates through the air and is received by the System Under Test (SUT). Typically the SUT will need to be positioned in the far field of the transmitter to provide an accurate test. The far field may be a significant distant therefore this type of testing generally requires large facilities that are expensive and have limited capacity to expand to multiple systems.

[0006] More recently, Direct Signal Injection (DSI) test facilities have been developed that involve mathematical emulation of the signal propagation in a given scenario on a computer or digital signal processor. This may include modelling transmit and / or receive antenna patterns, system noise figure and front-end components with high fidelity in real-time (i.e. typically greater than 250 MHz). Such an approach removes the need to transmit a signal into the air and position the SUT in the far field. Consequently, these DSI facilities can be significantly smaller, cheaper and more expandable.

[0007] One such facility is the Testing Theater Operations Using Real-time Networks Achieving Multiple Interconnected Nodal Tactics (T2OURNAMINT) developed by Lincoln Laboratory, Massachusetts Institute of Technology (MIT). As discussed in the Technical Note titled “Multisystem Simulation with T2OURNAMINT”, dated June 2017 and shown in Fig. 1 , the hardware architecture of a four-channel T2OURNAMINT can be implemented to evaluate a single SUT against multiple hardware radar and threat emulators. The systems interface through RF / microwave connections to converters and through software-managed digital control connections. T2OURNAMINT uses Field Programmable Gate Arrays (FPGAs) to emulate signal propagation paths between connected systems, a high-end commercial server for scenario simulation, and a Graphics Processing Unit (GPU) to simulate software targets and terrain clutter. T2OURNAMINT is scalable in several ways. First, the number of sensor connections can be increased through FPGA processor expansion and additional high-speed data interconnects. T2OURNAMINT also scales in connection quantity through multichannel digital sampling and generation hardware, generally with reduced sample rates and reduced instantaneous bandwidth. T2OURNAMINT scales in frequency by using microwave converters that support other bands. Finally, performance scaling is possible through modular technology that replaces existing modules with more capable equivalents or extends the architecture to new system functionality. This modularity is instrumental to periodic refresh of T2OURNAMINT technology. However, the expansion of this type of approach to multiple systems is limited by the amount of configuration data that can be sent from the processor to the FPGA.

[0008] Therefore, it is the aim of the present invention to provide a solution that mitigates one or more of these issues.

[0009] Summary of the Invention According to a first aspect, the invention provides an apparatus for emulating signal propagation between N communication devices, wherein N > 1 , the apparatus comprising: N nodes, wherein each of the N nodes comprises at least one digital signal processor configured to (i) receive a digital input signal from one of N communication devices or from another node; (ii) calculate a modulation to be applied to the respective digital input signal to emulate a propagation path or antenna associated with one of the N communication devices; and (iii) apply the respective modulation to the digital input signal and output a digital modulated signal for use by another node or one of the N communication devices. Once configured each N node can operate independently without centralised control or further configuration.

[0010] In one embodiment, each of the N nodes may comprise two digital signal processors, a first and second digital signal processor. A first digital signal processor may be configured to undertake steps (i) and (iii), with a second digital signal processor being configured to undertake step (ii). By providing each of the N nodes with a second digital signal processor, the propagation effects associated with each of the N communication devices can be calculated independently. This allows for arbitrary expansion of the apparatus to multiple systems; in principle without any limitations on N. The processing is also more efficient than that of the prior art. Because each node is only concerned with one of the N communication devices, all calculations and data transfer associated with the respective communication device can be performed independently of the other nodes. Thus, the time taken to calculate the respective modulation and the time taken to communicate the configuration data, such as, for example, to a respective first digital signal processor, is reduced.

[0011] One or more of the N communication devices could be any wireless device or a simulator or emulator of a wireless device. For example, an active, semi-active or passive electromagnetic sensing device such as monostatic or multistatic radar, passive radar, missile seeker, LIDAR (Light Detection and Ranging) device, optical sensor or may be an acoustic sensing device such as a sonar. Other examples include a data communication device such as Bluetooth®, modem, network card, smartphone, Wi-Fi® device etc. The receiver and / or transmitters of the device could comprise analogue and / or digital electronics or these could be digitally simulated. Where the communication device is a simulator or emulator, typically the device is modelled in firmware and / or software and coded onto a digital signal processing chip such as an FPGA.

[0012] The digital input signal may be generated by one of the N communication devices of the digital modulated signal generated by another node. The communication device may generate a digital signal directly; particularly if the communication device is a simulator or emulator of a wireless device. Alternatively, the signal generated by the communication device could be an analogue electromagnetic signal such as microwave, Radio Frequency (RF), optical signal or an acoustic signal. The signal may be an Intermediate Frequency (IF) analogue signal, baseband analogue signal or digital signal. In the case of a digital signal, the apparatus may further comprise a Digital Input / Output module and / or the apparatus may further comprise an Analogue- to-Digital Converter (ADC) to convert an analogue signal to a digital signal for a first or second digital signal processor.

[0013] Each node comprises at least one digital signal processor, which could be a digital signal processing chip such as a FPGA or any other type of processor that is capable of processing, calculating and / or modulating the signal in real-time; which is typically 250 MHz or more.

[0014] In one embodiment of the first aspect comprising two digital signal processors, the first digital signal processor is configured to receive a digital input signal. Details of the digital input signal (for example, the digitised waveform) may then be sent to the second digital signal processor via a datalink. Either the first digital signal processor or the second digital signal processor may be configured to calculate a modulation to be applied to the digital input signal. The modulation typically represents the propagation of an analogue signal through the antenna and / or receiver of the respective communication device. Generally, the modulation is calculated using a mathematical model or simulation of a signal propagating through the antenna and / or receiver associated with the communication device. The mathematical model may include details of the signal transmitted by the communication device, signal processing algorithms, front-end circuitry, system noise, antenna patterns or any other feature relating to the communication device. The model / simulation may also include the propagation effects of the signal through a medium such as air, vacuum, conductor, fibre optic, dielectric or any other material over a predetermined distance. The propagation effects may include any modulations that can occur when an electromagnetic signal is propagated through a medium such as air, free space, a conductor, dielectric etc. The effects may include range law, antenna pattern, multipath, clutter, radar cross section reflection, diffraction, refraction, Doppler or any other signal propagation effect or modulation known in the art. The result of the calculation determines the modulation to be applied to the digital input signal. The model / simulation is implemented on the first digital signal processor as software and / or firmware. The model / simulation may be implemented using mathematical modelling techniques of such systems that are well known in the art.

[0015] In one embodiment of the first aspect, comprising two digital signal processors, the result of the model is communicated between the digital signal processors over a datalink in the form of configuration data. One of the digital signal processors receives the configuration data and applies the modulation to the digital input signal (being modulated) based on the configuration data to output a digital modulated signal. The digital modulated signal may be transferred to one or more of the other nodes; the other node(s) being configured to receive the digital modulated signal as its digital input signal and calculate a modulation to simulate a propagation path or antenna associated with another one or more of the N communication devices. Alternatively, the digital modulated signal may be transferred to one or more of the N communication devices. The apparatus may further comprise a Digital-to-Analogue Converter (DAC) to convert the digital modulated signal into an analogue signal for the respective communication device.

[0016] Preferably, the apparatus further comprises a scenario controller configured to store entity state data. The scenario controller is typically a general purpose computer, computer network or other programmable apparatus with a data storage medium. The scenario controller is configured to receive and store entity state data relating to each of the N communication devices. Entity state date may include Cartesian and / or polar coordinates or similar relating to N communication devices in a simulated scenario in one or more dimensions. This may include x, y, z, roll, pitch and / or yaw for each device or a platform comprising the device. The entity state data may also include mechanical and / or electronic antenna pointing angles. The entity state data may be updated automatically at a predetermined update rate using a feedback loop from one or more of the nodes or N communication devices. The update rate of the scenario controller may be of the order of 1 ms.

[0017] Preferably, the digital signal processor is further configured to receive a digital response signal from one of the N communication devices. A digital response signal may be generated by the communication device upon receipt of and in response to the digital modulated signal. The digital response signal may be representative of a skin return (from a simulated target), a radar signal, a jamming signal, or interference signal. These types of signal could be fed back through the apparatus and into one or more of the other nodes to provide closed loop testing. Alternatively, the digital response signal could be a guidance signal used to guide a platform hosting the communication device such as a missile, aircraft etc. The guidance signal being intended to control mechanical components on the platform to control its motion such as rotor blades, fins, etc. The guidance signal could be communicated to the scenario controller, processed and used to automatically update the entity state data. The response signal may be analogue, in which case an ADC may be used to convert it to digital for the digital signal processor.

[0018] Preferably, the digital signals are transferred over fibre optic cables. Any or all of the digital signals such as the digital input signal, digital modulated signal or digital response signal are transferred over fibre optic cables directly. This reduces signal loss that is particularly beneficial where the signals are communicated over significant distances. Fibre optics can also support higher bandwidths than analogue signal distribution. In addition, fibre optic cables can be directed through a router and a single signal can be routed through multiple outputs or vice versa. Furthermore, the data transferred over the fibre optic cables is difficult to intercept thereby providing higher security than other forms of data transfer. Preferably, the digital signals are routed through a data distribution network. This decouples the N nodes from each other and is easily upgraded and expanded. Furthermore, data distribution networks can provide fast data transfer of greater than 100 GHz.

[0019] Preferably, the apparatus comprises standard interfaces.

[0020] Preferably, the apparatus further comprises a precision time distribution network. A precision time distribution network comprises a precision timing module that provides time and frequency reference signals with a high accuracy and stability. These signals are provided to each device, e.g. the scenario controller, central processors, signal processors, sensors, etc. in order to synchronise these devices in time and to ensure phase coherency. The accuracy and stability of the precision timing module is such that RF Phase coherency is maintained across all devices.

[0021] More generally, in preferred embodiments, the apparatus comprises: a plurality of digital signal processors configured to receive digital input signals from N communication devices and to calculate a modulation to be applied to the respective digital input signal to simulate a propagation path or antenna associated with one of the N communication devices and to apply the respective modulation to the digital input signal and output a digital modulated signal for use by another digital signal processor or one of the N communication devices; characterised in that: the plurality of digital signal processors are arranged into N nodes, wherein each of the N nodes comprise at least one digital signal processor, which may be two digital signal processors: for example, a first digital signal processor configured to receive a digital input signal from one of the N communication devices or from another node and to calculate a modulation to be applied to the respective digital input signal to simulate a propagation path or antenna associated with one of the N communication devices; and a second digital signal processor configured to apply the respective modulation to the digital input signal and output a digital modulated signal for use by another node or one of the N communication devices.

[0022] According to a second aspect, the invention provides a method of emulating signal propagation between N communication devices, wherein N > 1 , the method comprising the steps of: providing the apparatus according to the first aspect; and using the apparatus to emulate signal propagation between N communication devices. The apparatus may be used to emulate signal propagation from any one or more of the N communication devices to any one or more of the N communication devices. For example, in some embodiments, the apparatus could be used to emulate the propagation of an RF signal transmitted by an RF transmitter, through a transmit antenna coupled to the RF transmitter, across some distance in free space with reception by a receive antenna coupled to an RF receiver. Whilst the RF transmitter and RF receiver are generally physical pieces of hardware, the transmit and receive antennas and the propagation of the signal across free space are emulated. This is sometimes referred to as Direct Signal Injection testing of the devices. In these embodiments, a first and second node are coupled to the RF transmitter and RF receiver, respectively. Typically the transmit and receive antennas are removed or disconnected from the RF transmitter and RF receiver. The RF signal from the RF transmitter may be extracted via a cable, down-converted and converted to a digital input signal via an ADC for the first node. The first node is configured to emulate the transmit antenna and free space propagation and output a first digital modulated signal for the second node. The second node is configured to receive the first digital modulated signal and emulate the receive antenna and output a second digital modulated signal. The second digital modulated signal can then be converted to analogue via a DAC, up-converted and injected into the RF receiver.

[0023] Any feature in one aspect of the invention may be applied to any other aspects of the invention, in any appropriate combination. In particular device aspects may be applied to method or use aspects and vice versa. The invention extends to a device, method or use substantially as herein described, with reference to the accompanying drawings and examples.

[0024] In all aspects, the invention may comprise, consist essentially of, or consist of any feature or combination of features.

[0025] Brief Description of the Drawings Embodiments of the invention will now be described, purely by way of example, with reference to the accompanying drawings, in which;

[0026] Figure 1 is a schematic of a four-channel T2OURNAMINT system as illustrated in the prior art;

[0027] Figure 2 illustrates a schematic of an apparatus and flow of data representing an embodiment of the invention; and

[0028] Figure 3 illustrates an emulated / simulated scenario according to the embodiment of Fig. 2.

[0029] The drawings are for illustrative purposes only and are not to scale.

[0030] Detailed Description

[0031] Having regard to Figure 2, with reference to the scenario in Figure 3, an apparatus (embodiment of the first aspect of the invention) is illustrated which is configured to emulate the propagation of a radio frequency (RF) signal between a transmitter 101 (which is a feature of a radar 191 , which is associated with a transmit antenna 130) and a receiver processor 105 (which is a feature of an Electronic Support (ES) receiver 195, which is associated with a receive antenna 132). For the avoidance of doubt, the transmitter 101 and receiver processor 105 are not features of the apparatus, however the apparatus emulates the propagation of a radio frequency (RF) signal through directly connecting the actual transmitter 101 and receiver processor 105 to the apparatus. The apparatus then emulates / simulates transmit antenna, free space propagation and receive antenna.

[0032] The apparatus comprises a first node 121 which is arranged to connect to a transmitter 101 , via cable 151 , and a second node 122, which is arranged to connect to a receiver processor 105, via cable 152. The first node 121 comprises a first FPGA 104 configured to receive the digital input signal and provide the details to a second FPGA 103 via cable 163. The second FPGA 103 is configured to simulate the propagation of the RF signal through the transmit antenna 130 across a simulated distance 180 in free space. A scenario controller 102 comprises entity state date stored thereon. The entity state data contains details of the positions of the simulated radar 191 and ES receiver 195 and antenna pointing angles of the simulated transmit antenna 130 and receive antenna 132. The entity state data is transferred from the scenario controller 102 to the second FPGA 103 via a cable 161 and is utilised by the simulation to calculate a transmitter modulation to be applied to the digital input signal. The transmitter modulation is supplied to the first FPGA 104 via cable 162. The first FPGA 104 applies the transmitter modulation to the digital input signal and outputs a digital intermediate signal. The digital intermediate signal being representative of the RF signal following propagation from the transmitter 101 , out of the transmit antenna 130 and across the distance in free space 180 to the front of the receive antenna 132.

[0033] The digital intermediate signal is fed directly into the second node 122 via cable 152. The second node 122 comprises a first FPGA 114 configured to receive the digital intermediate signal and provide the details to a second FPGA 113 via cable 173. The second FPGA 113 is configured to simulate the propagation of the RF signal through the receive antenna 132 to the receiver processor 105. The entity state data is transferred from the scenario controller 102 to the second FPGA 113 via a cable 171 and is utilised by the simulation to calculate a modulation to be applied to the digital intermediate signal. The modulation is supplied to the first FPGA 114 via cable 172. The first FPGA 114 applies the modulation to the digital intermediate signal and outputs a digital output signal. The digital output signal being representative of the RF signal following propagation from the transmitter 101 , out of the transmit antenna 130, across the fixed distance in free space 180 and through the receive antenna 132. The digital output signal is directly injected into the receiver processor 105 via cable 153.

[0034] Having regard to Figure 3, in the simulated scenario, the radar 191 is separated from the ES receiver 195 by a distance 180, which may be a fixed distance, or may be a variable distance depending on the requirements of the scenario. In the simulation, the radar 191 transmits an RF signal towards the ES receiver 195 which subsequently receives it for processing. The transmitter 101 generates a digital signal (which in reality would be converted to analogue and up-converted to the RF signal for transmission out of the transmit antenna 130 into free space 131. Similarly, in reality, the receive antenna 132 would receive the RF signal, down-convert and convert to a digital signal for the receiver processor 105 to process.

[0035] The radar 191 comprises a transmitter 101 , a transmitter front end 181 and a transmit antenna 130. The transmitter 101 is connected to the transmitter front end 181 via cable 151. The transmitter front end 181 is connected to the transmit antenna 130 via cable 112. The ES receiver 195 comprises a receive antenna 132, a front end receiver 185 and a receiver processor 105. The receive antenna 132 is connected to the front end receiver 185 via cable 121. The front end receiver 185 is connected to the receiver processor 105 via cable 153. The mainbeam / antenna beam pattern 131 of the transmit antenna 130 is pointed directly at the receive antenna 132. The mainbeam of the receive antenna 132 (not shown) is pointed directly at the transmit antenna 130. In the simulation, there is no interference, clutter or any other modulations or signals. The simulated distance 180 between the transmit antenna 130 and receive antenna 132 is fixed in this scenario at 300 m; which is the far field for the transmit antenna 130 and the receive antenna 132. The digital input signal is generated by the transmitter 101 , converted to analogue and up-converted to radio frequency by the transmitter front end 181 and transmitted out of the transmit antenna 130. The signal is received by the receive antenna 132, transferred to the receiver front end 185, down-converted to baseband and converted to the digital output signal. The digital output signal is directed into the receiver processor 105 via cable 153.

[0036] The simulation comprises a real time, high fidelity, mathematical model of the transmit antenna 130 including the antenna beam pattern 131 operating on the second FPGA 103, and of the receive antenna 132 including antenna beam pattern operating on the second FPGA 113.

[0037] It will be understood that the present invention has been described above purely by way of example, and modification of detail can be made within the scope of the invention. Moreover, the invention has been described with specific reference to a radar and an ES receiver. It will be understood that this is not intended to be limiting and the invention may be used more generally. For example, the invention may be used more generally for any type of communication device utilising any other electromagnetic and acoustic signal such as different sensors, countermeasure systems and so on.

[0038] Examples may be radar, LIDAR, sonar, optical sensors, jamming systems, missile seekers. Furthermore, the invention may be expanded to any number of communication systems, each connected to a dedicated node configured to emulate a propagation path and / or antenna associated with the respective communication system. The invention may be used to transfer digital signals from one or more communication systems to one or more communication systems.

Claims

CLAIMS1. An apparatus for emulating signal propagation between N communication devices, wherein N > 1 , the apparatus comprising:- N nodes, wherein each of the N nodes comprises at least one digital signal processor configured to:- (i) receive a digital input signal from one of N communication devices or from another node;- (ii) calculate a modulation to be applied to the respective digital input signal to simulate a propagation path or antenna associated with one of the N communication devices; and- (iii) apply the respective modulation to the digital input signal and output a digital modulated signal for use by another node or one of the N communication devices.

2. An apparatus according to Claim 1 , wherein each of the N nodes comprises a first digital signal processor and a second digital signal processor.

3. An apparatus according to Claim 2, wherein the first digital signal processor is configured to undertake steps (i) and (iii) and the second digital signal processor is configured to undertake step (ii).

4. An apparatus according to claims 1 to 3, wherein the apparatus further comprises a scenario controller configured to store entity state data.

5. An apparatus according to claim 2, wherein the first and / or second digital signal processor is configured to receive a digital response signal from one of the N communication devices.

6. An apparatus according to any one of claims 1 , to 5, wherein the digital signals are transferred over fibre optic cables.

7. An apparatus according to any of claims 1 to 6, wherein the digital signals are routed through a data distribution network.

8. An apparatus according to any preceding claim, the apparatus further comprising a precision time distribution network.

9. A method of emulating signal propagation between N communication devices, wherein N > 1 , the method comprising the steps of: a. providing the apparatus according to any preceding claim; and b. using the apparatus to emulate signal propagation between N communication devices.

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