Description:TECHNICAL FIELD
[0001] The present disclosure relates, in general, to signal processing, and more specifically, relates to a multi-band multi-channel array-based surveillance system using opportunistic radio transmissions.

BACKGROUND
[0002] Conventional surveillance systems consist of a transmitter and receiver which are collocated. The transmitter sends a signal, which gets reflected by the target of interest and is received by the receiver. The time delay between the transmission and reception can be used to estimate the range of the target. If the target is moving with some radial velocity, the transmitted signal gets modified due to the Doppler effect, which can be utilized to estimate the target velocity. In most applications, the dedicated transmitter is designed whose specifications like transmitted frequency, power level, signal shape and the like are tailored for the given application. Conventional surveillance systems use active transmitter architecture. While the aforementioned factors are advantageous in certain cases, they can also make it vulnerable to particular electronic countermeasures from the enemy side. For example, using the knowledge about transmitter location and other parameters like transmitted power level, and frequency, sometimes the enemy can jam the transmitted signal.
[0003] In addition, electromagnetic spectrum congestion has also become an ever-growing problem. More and more portion of the spectrum has been allocated to telecommunications to cater for the need of civilian applications. It has become increasingly difficult to allocate new frequency bands for surveillance applications and this may become a more challenging problem. In the case of a Passive Coherent Locator (PCL), there is no dedicated transmitter. The system utilizes already existing opportunistic emitters like FM, DVB-T/T2, GNSS etc. The time difference of arrival of the direct signal from the above-said emitters and the scattered emissions from the targets are used to estimate the bi-static range of the target. The bi-static Doppler shift can also be measured which can be used in the estimation of target velocity.
[0004] Since there are no dedicated transmitters, the probability of the enemy becoming aware of the presence of the target-locating receiver setups is less. In other words, PCL is more silent and hence less vulnerable to jamming and other countermeasures compared to conventional surveillance systems. An additional advantage of PCL is the better chance of identification of stealth aircraft. Stealth aircraft avoid detection mainly due to the physical design which scatter the incoming radio signals in different direction and also by special coating materials which can absorb the same. But most of stealth aircraft are designed to be invisible at microwave frequencies. In most cases, the PCL may be operating at a Very High Frequency (VHF) or Ultra High Frequency (UHF) range due to the nature of the broadcast transmitters and have a greater chance of detecting the stealth aircraft compared to the conventional surveillance systems. Since the PCL exploits the already existing broadcast emitters, the electromagnetic congestion problem can be tackled to some extent.
[0005] Efforts have been made in related arts to address the above problem using a system. An example of such a system is recited in European Patent EP1972962A2 entitled “Transmitter Independent Techniques to Extend the Performance of Passive Coherent Location” which discloses the methods for tracking the targets using multiple receivers utilizing the radio signals generated by one or more controlled or uncontrolled transmitter sources and applying pattern recognition techniques to the reflected signals along with a system that minimises the reliance on the transmitters that are in the line of sight.
[0006] Another example of a similar system is recited in US Patent US7155240B2 titled “Method of Determining the Position of a Target Using Transmitters of Opportunity” which describes the methods to determine the position of targets using components in wireless communication system in which pre-stored codes are included in transmissions of communications signals as part of a communication protocol, comprising the following steps: a) providing a transmitter which transmits a communication signal, b) providing plurality of receivers which receive the signal from above transmitter, determine the time of arrival information of the said received communications signal which is utilised to determine the target location. The said method focuses mainly on digital communication signals where the receiver identifies the data formats for reference.
[0007] Another example is recited in European Patent EP1992963B1 “Enhanced passive coherent location techniques to track and identify UAVS, UCAVS, MAVS, and other objects” which discloses a system comprising of a Passive Coherent Location (PCL) receiver system where the received signal scattered by the targets of interest and the direct signal from broadcast transmitters of opportunities are used to estimate the target location; coupled along with a Passive Emitter Tracking (PET) system that uses the cooperative signals emitted by the targets to estimate the Time Difference of Arrival. Another example of a similar system is recited in US Patent US7012552 entitled “Civil Aviation Passive Coherent Location System and Method” which describes a Passive Coherent Locator which tracks the airborne target by enhancing the object state awareness. The said system comprises of a receiver subsystem to receive the direct reference signals from an uncontrolled transmitter and scattered transmissions originating from an uncontrolled transmitter and scattered by an airborne target, a front-end processing system to determine the radial velocity of the object based on the received transmissions and a back end processing subsystem to determine object state estimates based on the determined radial velocity.
[0008] The processing for such Passive surveillance requires high computing capability and is surrounded by many issues due to a lack of control over transmitted signals. The target detection in such a system is achieved by correlating signals received directly from the transmitter direction and that of the direction we intend to patrol. To create a dependable practical system, much highly resource-intensive processing to remove clutter, clean the reference and extract and track the target have to be deployed. To extract far-range weak targets, a long integration time implied more memory to store grabbed data and a long computation time for processing is also required. This restricts the update rate and brings down the overall alertness of the system. Also, the presence of strong targets in the surveillance direction leads to the masking of weak targets.
[0009] Since the opportunistic transmitters are operating at UHF/VHF bands, the range resolution that can be provided by the passive surveillance systems is less compared to the existing active transmitter-based surveillance systems. FM radio-based passive surveillance, even though capable of achieving longer detection range due to high transmitted power, the range resolution achieved could be less due to the varying bandwidth. For DVB-T/T2, since it operates at higher bandwidth provides a higher range resolution. However, the high bandwidth makes the total integration timeless due to the huge data rate requirement. None of the previous inventions mentions any method to tackle the above said problems.
[0010] Therefore, it is desired to overcome the drawbacks, shortcomings, and limitations associated with existing solutions, and develop a passive surveillance system to provide users the best possible alertness without losing the far-range detection performance of the system.

OBJECTS OF THE PRESENT DISCLOSURE
[0011] An object of the present disclosure relates, to signal processing, and more specifically, relates to a multi-band multi-channel array-based surveillance system using opportunistic radio transmissions.
[0012] Another object of the present disclosure is to provide a system that is designed to process multiple channels and bands simultaneously, allowing for comprehensive surveillance coverage.
[0013] Another object of the present disclosure is to provide a system that process and merges short-range, long-range, and high-resolution surveillance: The system integrates the processing of different surveillance ranges to provide a complete picture of the surveillance scenario, addressing the shortcomings of individual processing channels.
[0014] Another object of the present disclosure is to provide a system that ensures a high update rate for detecting nearby targets, enabling timely monitoring and response.
[0015] Another object of the present disclosure is to provide a system that enhances the detection of far-range weak targets by mitigating the masking effects caused by nearby strong targets' side lobes.
[0016] Another object of the present disclosure is to provide a system that includes a dedicated channel that performs target detection according to priorities set by a tracker. It utilizes adaptive parameter control based on tracker inputs to enhance the accuracy and effectiveness of target detection.
[0017] Yet another object of the present disclosure is to provide a system that leverages its capability to use high bandwidth transmission, enabling the detection and tracking of short-range targets with high-range resolution.

SUMMARY
[0018] The present disclosure relates to signal processing, and more specifically, relates to a multi-band multi-channel array-based surveillance system using opportunistic radio transmissions. The main objective of the present disclosure is to overcome the drawback, limitations, and shortcomings of the existing system and solution, by providing a surveillance system called passive opportunistic transmission-based surveillance system. The system addresses the limitations of individual processing channels by employing a multichannel, multiband processing approach. It integrates short-range, long-range, and short-range high-resolution surveillance, ensuring faster update rates for nearby targets while maintaining detection performance for long-range targets. Additionally, the system enhances long-range detection by suppressing strong nearby targets to reveal weak targets buried in side lobes. The system also includes a channel that improves target detection based on the priority assigned by a tracker, utilizing adaptive parameter control guided by tracker inputs. Leveraging high bandwidth transmission, the system excels at detecting and tracking short-range targets with high-range resolution.
[0019] The present disclosure focuses on signal processing, specifically targeting the extraction procedure in a passive surveillance system that operates on non-cooperating opportunity transmissions such as FM radio or DVB-T2 transmissions. The process involves digitizing and down-converting the received reference signal and surveillance signal, dividing them into multiple channels, and mitigating clutter to create a range-Doppler map through cross-correlation. To improve the probability of detection, the invention employs a detection process to identify targets and utilizes a data clustering mechanism to generate plots or centroids at the peak values of the plot. The innovation further enhances target detection by processing the received data through separate signal processing channels dedicated to short-range targets, long-range targets, tracker-based targets, and a channel that leverages high-bandwidth opportunistic transmissions for short-range, high-resolution target detection. Each channel is optimized to achieve the best possible performance in terms of target detection capability and update rates. The present disclosure aims to enhance the tracking and localization of multi-static targets in practical passive surveillance systems.
[0020] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The following drawings form part of the present specification and are included to further illustrate aspects of the present disclosure. The disclosure may be better understood by reference to the drawings in combination with the detailed description of the specific embodiments presented herein.
[0022] FIG. 1 illustrates the entire workflow of both hardware blocks and software blocks for a passive opportunistic transmission-based target surveillance system, in accordance with an embodiment of the present disclosure.
[0023] FIG. 2 illustrates the RF front-end block, in accordance with an embodiment of the present disclosure.
[0024] FIG. 3 illustrates the target detection module, in accordance with an embodiment of the present disclosure.
[0025] FIG. 4 illustrates a flow chart of a method for target extraction in surveillance using opportunistic multi-broadcast transmissions, in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION
[0026] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. If the specification states a component or feature “may”, “can”, “could”, or “might” be included or have a characteristic, that particular component or feature is not required to be included or have the characteristic.
[0027] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0028] The present disclosure relates, in general, to signal processing, and more specifically, relates to a multi-band multi-channel array-based surveillance system using opportunistic radio transmissions. The present disclosure relates to a system for target extraction in surveillance using opportunistic multi-broadcast transmissions, the system includes a radio frequency (RF) front end having two different antenna array structures adapted for different broadcast signals, the broadcast signals pertain to FM radio and DVBT, the RF front end can include a low noise amplifier (LNA) that amplifies received signals while minimizing noise. An RF filter filters different broadcast signals, removes unwanted signals and noise outside the desired frequency range and selectively allows signals within a specific frequency range to pass through. A variable amplifier adapted for post amplification of the filtered signals. A digitizer and down conversion module configured to convert the conditioned analog signals into digital form through analog-to-digital converters (ADCs), wherein the digitized signals are down-converted to baseband, undergo digital filtering for removing noise and extracting various FM channels and DVB-T2 signal from the digitized signals, and are decimated to reduce the sampling data rate of the digitized signals and an adaptive gain control module configured to control the gain of the variable amplifier and capturing data directly from the digitizer and down conversion module and calculating an appropriate gain level.
[0029] The system can include a signal processing unit separates reference and surveillance signals using array processing techniques, wherein the reference signal corresponds to the direct path signal and the surveillance signal corresponds to signals from desired surveillance directions. The signal processing unit that receives the digitized signals from opportunistic FM radio transmitters and are processed to extract targets for surveillance, the signal processing unit configured to remove unwanted reflections from the reference signal by leveraging known properties of the signals, wherein the FM radio direct signal is cleaned based on properties such as constant amplitude; and suppress ground clutter in the surveillance signal using information from the reference signa, thereby preventing masking of weak targets of interest by strong clutter side-lobes, wherein the surveillance signal, after ground clutter suppression, is processed using three separate signal processing chains.
[0030] In an aspect, the three separate signal processing chains can include a short-range high update rate channel for detecting short-range targets with a high update rate. A long-range channel for detecting long-range targets while suppressing nearby strong targets and a tracker-based adaptive plot extraction channel for targeted investigation based on input from a tracker. The short-range high update rate channel for target extraction in surveillance is configured to integrate short durations of data to form a range doppler map, perform detection and plot extraction using the integrated short-duration data and obtain high update rate by utilizing short durations of data, which require less processing resources.
[0031] The long-range channel for target extraction in surveillance is configured to extract the plot from the high update rate obtained from short-range high update rate channel, clean the surveillance signal by suppressing short-range strong targets, preventing masking of weak targets of interest in the long range by strong nearby target side-lobes, integrate long durations of data to form a range doppler map and perform detection and plot extraction using the integrated long-duration data.
[0032] The tracker-based adaptive plot extraction channel for target extraction in surveillance configured to receive input from data processing to improve the current detection performance, utilize parameters based on high priority target tracks to determine the direction of gain of the antenna array, adjust the duration of data for processing to obtain refined measurements; and incorporate adaptive techniques to enhance target extraction based on real-time input and track priorities, wherein the tracks based on the health are sent as feedback to channel to improve detection performance.
[0033] The signal processing unit that receives the digitized signals from opportunistic DVB-T2 transmitters and are processed to extract targets for surveillance, the signal processing unit configured to remove unwanted reflections from the reference signal by leveraging known properties of the signals, wherein the DVB-T2 signals are cleaned based on known pilot signal information, suppress ground clutter in the surveillance signal using information from the reference signal, thereby preventing masking of weak targets of interest by strong clutter side-lobes and a predetermined duration of data is integrated to form a range doppler map and perform target detection and extraction of high-resolution short-range target measurements.
[0034] Further, the signal processing unit combines the plots obtained from different channels, each with distinct update rates and range resolutions are fused together to form a consolidated bi-static tracks, wherein the consolidated bi-static tracks are formed based on the fused plots, providing a comprehensive representation of the targets and wherein the consolidated bi-static tracks are then transmitted for multi-static localization facilitating target localization. The present disclosure can be described in enabling detail in the following examples, which may represent more than one embodiment of the present disclosure.
[0035] The advantages achieved by the system of the present disclosure can be clear from the embodiments provided herein. The present disclosure provides advanced surveillance system that combines multiple channels, addresses the limitations of individual processing channels, and offers improved detection performance, range resolution, and target tracking capabilities. The description of terms and features related to the present disclosure shall be clear from the embodiments that are illustrated and described; however, the invention is not limited to these embodiments only. Numerous modifications, changes, variations, substitutions, and equivalents of the embodiments are possible within the scope of the present disclosure. Additionally, the invention can include other embodiments that are within the scope of the claims but are not described in detail with respect to the following description.
[0036] FIG. 1 illustrates the entire workflow of both hardware blocks and software blocks for passive opportunistic transmission-based target surveillance system, in accordance with an embodiment of the present disclosure.
[0037] Referring to FIG. 1, passive bistatic receiver architecture (also referred to as system 100, herein) for various broadcast signals encompasses several hardware and software components that collaborate to carry out their designated functions. The system can include RF front end, digitization and down conversion module, digital beam forming module, signal processing and GPU computing.
[0038] The RF front end (102-1, 102-2) is the initial stage of the passive bistatic receiver architecture 100. The RF front end (102-1, 102-2) is responsible for capturing the broadcast signals from the environment. It includes antennas, amplifiers, filters, and other components that facilitate the reception of signals across a range of frequencies. The first stage of RF front end starts with an antenna, the adopted front end has two different antenna array structures for different broadcasts. It can include two different antenna array structures for different broadcast signals. First circular antenna array structure 104-1 utilizes an FM dipole as a single element, while the second circular antenna array structure 104-2 employs a DVBT antenna as a single element. The circular antenna array structure enables beamforming in all directions, making it suitable for the passive opportunistic transmission-based surveillance system. The RF front end (102-1, 102-2) includes a Low Noise Amplifier (LNA) module 202 shown in FIG. 2, which amplifies received signals while minimizing noise. An RF filter module 204 is used to remove unwanted signals and noise outside the desired frequency range.
[0039] The next stage of the RF front end (102-1, 102-2) is the Low Noise Amplifier module 202. The LNA 202 is used to amplify the signals that are received by the antenna, while also minimizing the noise that is introduced into the system. The next stage is the RF filter module 204, which is used to remove unwanted signals and noise from the signal that is received by the LNA 202. The RF filter 204 is designed to only allow signals within a specific frequency range to pass through while blocking signals that are outside of this range. Two parallel RF front ends (102-1, 102-2) with different bandpass filters are implemented to filter different broadcast signals such as FM radio and DVBT. A feedback mechanism is implemented between a variable gain amplifier/attenuator 206 and analog to digital converter 208 to adjust the signals to ADC dynamic range. This adaptive gain adjustment technique can allow the system to work within permissible limits with a change in the physical location of the passive surveillance receiver.
[0040] In the digitization and down-conversion module (106-1, 106-2), the received signals are digitized and down-converted. The signals from the antenna array are sent to the analog-to-digital converter (ADC) 208 via the variable gain amplifier/attenuator 206. The received analog signals are converted into digital format through analog-to-digital converters (ADCs) 208. The digitization process enables further processing and analysis of the signals. The feedback mechanism allows for adaptive gain adjustment to ensure the signals are within the dynamic range of the ADC 208. The digitized signals are then down-converted to baseband, undergo digital filtering, and are decimated to reduce the sampling rate. Down conversion may also occur to adjust the frequency range of the signals for subsequent processing stages. The digital down conversion of signal is required to reduce the sampling rates of signals this block typically involves converting the signal to base band, digital filtering and decimation of signal. The down converted signal from each antenna from the module (106-1, 106-2) is sent to for reference extraction module (108-1, 108-2) for reference extraction.
[0041] The digital beamforming combines the down-converted signals from each antenna element to form a beam pointing toward the direction of the transmitter. This process involves applying weight vectors to each signal and summing them accordingly. The coefficients for beamforming in each sector are predetermined, and calibration values are used to calculate the coefficients for each beam. Digital beamforming enhances the signal-to-noise ratio by combining data from multiple antennas. The signals from multiple antennas are combined to form a beam pointing towards the direction of the transmitter this process is done in the digitization and down conversion module (106-1, 106-2).
[0042] Let 𝑆𝑎𝑛𝑡(𝑖,𝑛) be the signal of 𝑖𝑡ℎ instant corresponding to the 𝑛𝑡ℎ antenna and 𝑊𝑟𝑒𝑓(𝑛) be the weight vector, then the reference signal 𝑆𝑟𝑒𝑓(𝑖) can be written as

Where 𝑁𝑒 is the number of antenna elements in the array.
[0043] The Reference (𝑆𝑟𝑒𝑓) signal and 𝑆𝑎𝑛(𝑖,𝑛) were then sent to ground clutter suppression block (110-1, 110-2). The ground suppression block (110-1, 110-2) cancels the returns of stationary clutter and the direct path components from the surveillance signal so that the weak targets become detectable. The characteristics of transmitted signals are time-varying and therefore the side-lobes of the ambiguity function of opportunistic transmissions are highly unpredictable and often the power level of these side-lobes is discernible. Thus, the reflections from the ground and the leakage from the reference signal mask the target echoes in the surveillance signal. These returns are removed by adaptively calculating the weight vectors for different delays of reference signals and then suppressing the weighted delayed references/direct path component from the surveillance signal. This is done on each antenna channel 𝑆𝑎𝑛(𝑖,𝑛) separately.
[0044] The clutter-suppressed signal from each ground suppression block (110-1, 110-2) channel is processed in block 112 (also referred to as signal processing unit 112, herein) where the 𝑁𝑒 element array signal is converted into different sector/beam data. The coefficients for beamforming in each sector are predetermined. The beamforming is performed to attain better signal-to-noise ratio by combining data from multiple sensors. The calibration values required are predetermined and coefficients for each beam are calculated with respect to the direction and the antenna element calibration values. Let 𝑊𝑏(𝑛,𝑏) be the coefficient corresponding to 𝑛𝑡ℎ antenna and 𝑏𝑡ℎ beam, then Signal for each beam is computed as

Each beam signal 𝑆𝑏𝑒𝑎𝑚 is processed parallel to extract target detections
[0045] In digital beam forming, the digitized signals are manipulated using digital signal processing techniques to optimize the reception of desired signals and reject unwanted interference. Digital beamforming helps enhance the signal quality and extract relevant information.
[0046] The signal processing unit 112 involves various algorithms and techniques to extract meaningful information from the received signals. It includes tasks such as target detection, parameter estimation, waveform analysis, and other relevant signal processing operations. Graphics Processing Units (GPUs) are utilized for high-performance computing and parallel processing. In the context of a passive bistatic receiver, GPUs can be leveraged to handle the computational demands of processing multiple channels simultaneously, leading to faster and more efficient data processing.
[0047] These modules collectively form a comprehensive architecture for a passive bistatic receiver, enabling the reception, digitization, beamforming, and subsequent signal processing of broadcast signals. The utilization of GPUs for multi-channel processing contributes to improved computational performance and overall system efficiency.
[0048] The reference signal 𝑆𝑟𝑒𝑓 and surveillance signal of reach beam 𝑆𝑏𝑒𝑎𝑚 are correlated to detect the echoes of the target from the cross-correlation and detection block 302. This block extracts range-doppler map of the scenario. Here both the signals are split into several blocks with respect to parameters such as the Maximum range of detection required, the Doppler ambiguity required with respect to the length of the data.
[0049] The Range-doppler map so formed is then passed through a 2-dimensional CFAR detection block 304 to obtain a hit map/ detection map to detect the presence of targets. A further group of detections from the same target are consolidated using a data clustering algorithm and Centroids or measurement as a single point is given out based on amplitude based centroiding. The centroid or measurement contains Range, Doppler, Azimuth and Time stamp as the parameters. More parameters like range spread, Doppler spread, amplitude, SNR can be added to aid data processing
[0050] The data from the ground suppression block (110-1, 110-2) is separated into parallel channels for improving the target detection capability of the system. The system provides faster update rate detection for nearby targets at the same time without compromising detection performance for long-range targets. Further, long-range detection is improved by unmasking far range weak targets buried in side lobes by suppressing nearby strong targets. The system also includes another channel which performs target detections based on the priority assigned by tracker. Due to the capability of the system to use high bandwidth transmission, it is capable of detecting and tracking short-range targets with high-range resolution.
[0051] The short-range high update rate channel processes aim at detecting short-range targets with high update rates. The short-range targets require less integration time due to better power returns. Thus, update rates can be improved. Also, the time/resource required to process lower amount of data is less. This channel takes clutter-suppressed data and extracts the Range Doppler map as per the above explanation and the targets are extracted using data detection and data clustering mechanisms. The above-said process runs independently on each 𝑆𝑏𝑒𝑎𝑚 and the measurements from each beam are stitched together. The output plots/measurements of this data are sent to data processing and a long range channel.
[0052] The long-range channel uses a longer duration of data to extract long-range targets. Long integration time is used to improve the SNR of Far range targets. Since the received power from far range targets is weak, thus they may be buried in side-lobes of the nearby strong targets. To mitigate this problem, the detection from short-range channel is used. The returns corresponding to measurements from short-range channel are suppressed from the surveillance channel. This is done by first adaptively calculating the weight vectors for different delays and Doppler of reference signals corresponding to the range and Doppler detected by the short-range channel and then removing it by subtracting the weighted delayed and doppler shifted versions of reference from the surveillance channel. This surveillance signal after suppression is then used to extract a range-doppler map and targets are extracted by CFAR detection and data clustering. The above said process runs independently on each 𝑆𝑏𝑒𝑎𝑚 and the measurements from each beam are stitched together. The measurements are sent to data processing.
[0053] Tracker-based adaptive plot extraction channel receives requests from the tracker in data processing module (112). Tracks which to coasting mode (when measurements are not received for an already formed track), the tracker request this channel to investigate a specific range, doppler and beam. The channel decides on the integration time based on range, doppler and previously detected SNR and scans for the target using digital beamforming with the previously detected beams and its neighbouring beams. Once the detection is established, it is reported back to data processing. If this channel cannot establish a presence of the target after a maximum integration time based on range bin size and range migration of the target, then the processing is aborted and reported back to the data processing unit.
[0054] The DVB-T2 signals follow Orthogonal Frequency Division Multiplexing (OFDM) and is designed for broadcast transmission. The given signal is constructed based on international standards and contains both data and extra overhead. The overhead part consists of guard interval, pilot signals etc. tasked for operations like synchronization, error correction and channel estimation at the communication receiver end. While the given signal design is essential for broadcast communication, it is less optimal for robust target detection and tracking in PCL. The structure of the signal can cause periodic spikes in the final correlation computation. These can cause unnecessary false alarms in the final detection. In addition to this, they can also mask the reflections from the weak targets. Hence, the detection and tracking performance will be deteriorated significantly unless the reference signal is cleaned.
[0055] The already-known structure of the signal according to the DVB-T2 standard can be utilized in the reference signal cleaning. Properties such as pilot signal structure, timing etc. are already fixed for a particular DVB-T2 transmitter depending on its operating mode. Since the pilot symbols are generated from a known function and also since the carrier frequency locations and timings are known, the pilot carriers can be suppressed using a simple subtraction of the scaled version of the already collected reference signal from itself. The shifting and scaling factor of the reference signal varies according to the operating mode of the given transmitter. The cleaned reference signal can be used for further target detection through matched filtering.
[0056] The fusion stage consolidates all the incoming extracted plots from channels. The incoming plots are updated at different time intervals providing information at various range resolutions and maximum ranges. Since the module in a short range high update rate channel is processing FM signal at a lower integration time, it may be able to provide plots at a faster update rate but only for shorter-range targets with low-resolution capability. The module detects the fast-moving targets, which are coming towards the area of interest but with a very high update. Hence, the module may aid in tasks that need quick decision-making. The long-range channel helps in improving the detection performance of long-range targets but at the expense of less update rate. The tracker-based detection channel provides an even more refined plot giving importance to high-priority targets. Since the above channels use the FM signal, the plots may be at less range resolution. To complement this limitation, the DVB-T module provides very high-resolution plots but at a very slow rate. All the above bi-static plots are fused together to form consolidated tracks. Measurements from each channel are used by the track to generate and maintain tracks. The existing track may start to lose targets due to the absence of detection at this stage the target gives feedback to the tracker-based adaptive plot extraction channel. The fused tracks are sent out for multi–static localization.
[0057] Thus, the present invention overcomes the drawbacks, shortcomings, and limitations associated with existing solutions, and improves the probability of detection, enhances target localization and tracking, enables high-resolution target detection, and provides practical benefits for passive surveillance systems operating on non-cooperating opportunity transmissions.
[0058] FIG. 2 illustrates the RF front-end block that contains a low noise amplifier and band pass filter to block the unwanted signals and noise into the system, in accordance with an embodiment of the present disclosure.
[0059] Referring to FIG.2, the RF front end includes several modules that play crucial roles in signal reception and conditioning. The RF front end can include Low Noise Amplifier (LNA) 202, RF filter 204, variable gain amplifier/attenuator 206 and analog-to-digital converter (ADC) module 208.
[0060] The LNA 202 amplifies the weak signals received by the antenna while introducing minimal noise into the system. This amplification stage helps to improve the overall signal strength and quality. The RF filter 204 is responsible for removing unwanted signals and noise from the received signal. It is designed to allow only signals within a specific frequency range to pass through, while blocking signals outside of this range. Two parallel RF front ends with different bandpass filters are implemented to filter different broadcast signals such as FM radio and DVBT.
[0061] Variable Gain Amplifier/Attenuator 206 includes a feedback mechanism that connects it to the analog-to-digital converter (ADC) module 208. The feedback mechanism adjusts the gain of the signals to match the dynamic range of the ADC. This adaptive gain adjustment technique ensures that the system operates within permissible limits even when the passive surveillance receiver is physically relocated. These modules within the RF front-end stage work together to amplify weak signals, filter out unwanted noise, and adjust signal gain adaptively. By doing so, they contribute to optimizing the reception and conditioning of signals before further processing stages in the passive bistatic receiver architecture.
[0062] FIG. 3 illustrates target detection module consists of cross ambiguity function and range doppler map generation followed by CFAR for the detection of targets, in accordance with an embodiment of the present disclosure. The cross-correlation and detection block in the passive bistatic receiver architecture can include cross-correlation, where the reference signal (Sref) and surveillance signal from each beam (Sbeam) are correlated in the cross-correlation and detection block 302. This correlation process aims to detect the echoes of targets in the received signals. Both signals are divided into multiple blocks based on parameters such as the maximum range of detection required and the desired Doppler ambiguity, considering the length of the data.
[0063] The correlation results generate a range-doppler map, which represents the scenario under surveillance. This map provides information about the range (distance) and doppler (velocity) characteristics of potential targets within the surveillance area. The range-doppler map is then processed through a two-dimensional Constant False Alarm Rate (CFAR) detection block 304. This block analyzes the map to detect the presence of targets. It generates a hit map or detection map that identifies potential target locations.
[0064] The groups of detections that belong to the same target are consolidated using a data clustering algorithm. The algorithm combines the detections to form centroids or measurements represented as single points. These centroids contain parameters such as range, doppler, azimuth, and time stamp, providing information about the target's location and movement. Additional parameters like range spread, doppler spread, amplitude, and signal-to-noise ratio (SNR) can be incorporated to facilitate further data processing.
[0065] The cross-correlation and detection block plays a critical role in extracting the range-doppler map, detecting targets using CFAR, and consolidating target detections through data clustering and centroiding techniques. These processes contribute to the localization and tracking of targets within the passive surveillance system.
[0066] FIG. 4 illustrates a flow chart of a method for target extraction in surveillance using opportunistic multi-broadcast transmissions, in accordance with an embodiment of the present disclosure.
[0067] Referring to FIG. 4, the method 400 involves at block 402, the radio frequency (RF) front end can provide having two different antenna array structures adapted for different broadcast signals, the broadcast signals pertain to FM radio and DVBT.
[0068] At block 404, amplify by the low noise amplifier (LNA) (202), received signals while minimizing noise. At block 406, filter, by an RF filter (204), different broadcast signals, removes unwanted signals and noise outside the desired frequency range and selectively allows signals within a specific frequency range to pass through. At block 408, post amplifies, by the variable amplifier, the filtered signals.
[0069] At block 410, convert, by a digitizer and down conversion module, the conditioned analog signals are into digital form through analog-to-digital converters (ADCs) 208, wherein the digitized signals are down-converted to baseband, undergo digital filtering for removing noise and extracting various FM channels and DVB-T2 signal from the digitized signals, and are decimated to reduce the sampling data rate of the digitized signals.
[0070] At block 412, control, by an adaptive gain control module, the gain of the variable amplifier and capturing data directly from the digitizer and down conversion module and calculating an appropriate gain level.
[0071] It will be apparent to those skilled in the art that the system 100 of the disclosure may be provided using some or all of the mentioned features and components without departing from the scope of the present disclosure. While various embodiments of the present disclosure have been illustrated and described herein, it will be clear that the disclosure is not limited to these embodiments only. Numerous modifications, changes, variations, substitutions, and equivalents will be apparent to those skilled in the art, without departing from the spirit and scope of the disclosure, as described in the claims.

ADVANTAGES OF THE PRESENT INVENTION
[0072] The present invention provides a system that enhances the probability of detecting targets. This optimization ensures that each channel is tailored to maximize target detection capability and update rates, thereby increasing the overall effectiveness of the surveillance system.
[0073] The present invention provides a system that provides enhanced target localization and tracking. The system can more accurately determine target positions, movements, and other relevant parameters. This contributes to better situational awareness and tracking capabilities.
[0074] The present invention provides a system to achieve high-resolution target detection in short-range scenarios. This capability allows for enhanced precision in detecting and tracking targets within close proximity, further improving the effectiveness of the surveillance system.
[0075] The present invention provides a system that addresses real-world challenges and enhances the performance of passive surveillance systems.
, Claims:
1. A system (100) for target extraction in surveillance using opportunistic multi-broadcast transmissions, the system comprising:
a radio frequency (RF) front end (102-1, 102-2) having two different antenna array structures adapted for different broadcast signals, the broadcast signals pertain to frequency modulation (FM) radio and digital video broadcasting – terrestrial (DVBT2), the RF front end comprises:
a low noise amplifier (LNA) (202) that amplifies received signals while minimizing noise;
an RF filter (204) filters different broadcast signals, removes unwanted signals and noise outside the desired frequency range and selectively allows signals within a specific frequency range to pass through;
a variable amplifier (206) adapted for post-amplification of the filtered signals;
a digitizer and down conversion module configured to convert the conditioned analog signals into digital form through analog-to-digital converters (ADCs) (208), wherein the digitized signals are down-converted to baseband, undergo digital filtering for removing noise and extracting various FM channels and DVB-T2 signal from the digitized signals, and are decimated to reduce the sampling data rate of the digitized signals; and
an adaptive gain control module configured to control the gain of the variable amplifier and capturing data directly from the digitizer and down conversion module and calculating an appropriate gain level.

2. The system as claimed in claim 1, wherein the system comprises a signal processing unit (112) separates reference and surveillance signals using array processing techniques, wherein the reference signal corresponds to the FM radio direct path signal and the surveillance signal corresponds to signals from desired surveillance directions.

3. The system as claimed in claim 1, wherein the signal processing unit (112) receives the digitized signals from opportunistic FM radio transmitters and are processed to extract targets for surveillance, the signal processing unit configured to:
remove unwanted reflections from the reference signal by leveraging known properties of the signals, wherein the FM radio direct signal is cleaned based on properties such as constant amplitude; and
suppress ground clutter in the surveillance signal using information from the reference signal, thereby preventing masking of weak targets of interest by strong clutter side-lobes, wherein the surveillance signal, after ground clutter suppression, is processed using three separate signal processing chains.

4. The system as claimed in claim 3, wherein the three separate signal processing chains comprising:
a short-range high update rate channel for detecting short-range targets with a high update rate;
a long-range channel for detecting long-range targets while suppressing nearby strong targets; and
a tracker-based adaptive plot extraction channel for targeted investigation based on input from a tracker.

5. The system as claimed in claim 4, wherein the short-range high update rate channel for target extraction in surveillance configured to:
integrate short durations of data to form a range doppler map;
perform detection and plot extraction using the integrated short-duration data; and
obtain high update rate by utilizing short durations of data, which require less processing resources.

6. The system as claimed in claim 1, wherein the long-range channel for target extraction in surveillance configured to:
extract the plot from the high update rate obtained from the short-range high update rate channel;
clean the surveillance signal by suppressing short-range strong targets, preventing masking of weak targets of interest in the long-range by strong nearby target side-lobes;
integrate long durations of data to form a range doppler map; and
perform detection and plot extraction using the integrated long-duration data.

7. The system as claimed in claim 1, wherein the tracker-based adaptive plot extraction channel for target extraction in surveillance is configured to:
receive input from data processing to improve the current detection performance;
utilize parameters based on high-priority target tracks to determine the direction of gain of the antenna array;
adjust the duration of data for processing to obtain refined measurements; and
incorporate adaptive techniques to enhance target extraction based on real-time input and track priorities, wherein the tracks based on the health are sent as feedback to channel to improve detection performance.

8. The system as claimed in claim 1, wherein the signal processing unit (112) receives the digitized signals from opportunistic DVB-T2 transmitters and are processed to extract targets for surveillance, the signal processing unit configured to:
remove unwanted reflections from the reference signal by leveraging known properties of the signals, wherein the DVB-T2 signals are cleaned based on known pilot signal information;
suppress ground clutter in the surveillance signal using information from the reference signal, thereby preventing masking of weak targets of interest by strong clutter side-lobes; and
a predetermined duration of data is integrated to form a range doppler map and perform target detection and extraction of high-resolution short-range target measurements.

9. The system as claimed in claim 1, wherein the signal processing unit (112) combines the plots obtained from different channels, each with distinct update rates and range resolutions are fused together to form a consolidated bi-static tracks, wherein the consolidated bi-static tracks are formed based on the fused plots, providing a comprehensive representation of the targets and wherein the consolidated bi-static tracks are then transmitted for multi-static localization facilitating target localization.

10. A method (400) for target extraction in surveillance using opportunistic multi-broadcast transmissions, the method comprising:
providing (402) a radio frequency (RF) front end having two different antenna array structures adapted for different broadcast signals, the broadcast signals pertain to frequency modulation (FM) radio and digital video broadcasting – terrestrial (DVBT2);
amplifying (404), by a low noise amplifier (LNA) (202), received signals while minimizing noise;
filtering (406), by an RF filter (204), different broadcast signals, removes unwanted signals and noise outside the desired frequency range and selectively allows signals within a specific frequency range to pass through;
post amplifying (408), by a variable amplifier, the filtered signals;
converting (410), by a digitizer and down conversion module, the conditioned analog signals into digital form through analog-to-digital converters (ADCs) 208, wherein the digitized signals are down-converted to baseband, undergo digital filtering for removing noise and extracting various FM channels and DVB-T2 signal from the digitized signals, and are decimated to reduce the sampling data rate of the digitized signals; and
controlling (412), by an adaptive gain control module, the gain of the variable amplifier and capturing data directly from the digitizer and down conversion module and calculating an appropriate gain level.