Method and system for detecting multiple radar targets based on joint radar and communication using orthogonal time frequency space (OTFS) signals

Abstract

A method of detecting multiple radar targets based on joint radar and communication using OTFS signals is provided. The method includes: generating a range-Doppler map (RDM) based on a first delay-Doppler (DD) domain signal and a second DD domain signal, whereby a first time domain signal is generated from an OTFS modulation based on the first DD domain signal and transmitted to multiple radar targets, and the second DD domain signal is generated from an OTFS demodulation based on a second time domain signal received and reflected from the multiple radar targets from the first time domain signal transmitted; and detecting a dominant radar target amongst the multiple radar targets based on the RDM. In particular, the method further includes, for each iteration of a plurality of iterations: modifying a correlation intermediate term associated with the RDM associated with the iteration based on the detected dominant radar target to obtain a modified correlation intermediate term, the correlation intermediate term relating to a cyclic correlation between the first and second DD domain signals; modifying the RDM associated with the iteration based on the modified correlation intermediate term; and detecting a dominant radar target (i.e., a next dominant radar target) amongst the multiple radar targets based on the RDM modified based on the modified correlation intermediate term. There is also provided a corresponding system for detecting multiple radar targets and a corresponding joint radar and communication system for detecting multiple targets.

Description

METHOD AND SYSTEM FOR DETECTING MULTIPLE RADAR TARGETS BASED ON JOINT RADAR AND COMMUNICATION USING ORTHOGONAL TIME FREQUENCY SPACE (OTFS) SIGNALSCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority of Singapore Patent Application No.10202403660X filed on 22 November 2024, the content of which being hereby incorporated by reference in its entirety for all purposes.TECHNICAL FIELD

[0002] The present invention generally relates to a method and a system for detecting multiple radar targets based on joint radar and communication (JRC) using orthogonal time frequency space (OTFS) signals, as well as a joint radar and communication system thereof.BACKGROUND

[0003] Joint Radar and Communication (JRC) involves leveraging shared hardware and waveforms to fulfil both sensing and communication tasks. This approach holds promise for significant savings across spectrum utilization, power consumption, and overall costs, thereby offering diverse benefits across various application domains For example, it has the potential to revolutionize technology areas such as assisted or automated driving systems.

[0004] Orthogonal Time Frequency Space (OTFS) modulation represents a modulation scheme designed to overcome the challenges of wireless communication in fast-moving environments. Traditional modulation schemes often struggle to maintain reliability and efficiency when confronted with high mobility, such as in vehicular communication or scenarios involving fast-moving objects. OTFS offers a unique solution by exploiting the timefrequency space, where signals are represented in a joint time and frequency domain. This approach allows OTFS to achieve remarkable performance in highly dynamic environments by effectively decoupling the time and frequency domains, thereby mitigating the impact of Doppler shifts and delay spreads.

[0005] In conventional radar detection, several common challenges arise, particularly in scenarios involving closely spaced and swiftly moving targets. These challenges include:• Difficulty in Detecting Multiple Targets in Close Proximity and Rapid Motion'.Conventional radar systems face difficulty in distinguishing individual targets andaccurately tracking their trajectories when targets are in close proximity and moving rapidly. This complexity often leads to confusion in isolating and monitoring specific targets amidst the clutter of overlapping radar returns.• Masking of Weaker Targets (i.e., weaker target signals) by prominent Targets (i.e., prominent / stronger target signals)'. Conventional radar detection algorithms tend to prioritize the detection of the most prominent targets in scenarios where there is a substantial contrast / difference in target signal strengths. As a result, weaker targets (i.e., weaker target signals) may become obscured or masked by the dominant signals emanating from stronger targets.• Degradation of Detection Performance in Shared Spectrum'. In scenarios where multiple users share the same spectrum and each user is allocated sparse spectrum for radar detection, there is an increased risk of multi-user interference and a reduction in detection performance due to limited bandwidth.

[0006] Existing solutions to address these challenges include:• Strongest Target Detection based on Range or Speed. This existing method operates under the assumption that targets reside within distinct, non-overlapping range areas with known separations. It searches for the strongest target within each range segment. However, this approach has the following limitations:o Restrictive Assumptions'. This method's effectiveness may be limited in scenarios where targets are closely spaced or where range areas are not predetermined. Consequently, weaker targets may go undetected if multiple targets share the same range segment.o Limited Adaptability to Moving Targets. Existing implementations of this method, such as the self-interference cancellation scheme primarily focus on cancelling static targets, rendering them ineffective for moving targets.• Multi-target Detection with Constant False Alarm Rate (CFAR)'. CFAR algorithms, widely employed in radar systems, offer a potential solution for JRC systems These algorithms compare target power levels to estimated noise and surrounding power levels to make detection decisions. Some of the most popular CFAR algorithms are:o Cell Averaging CFAR (CA-CFAR): It is the most basic and commonly used CFAR algorithm. It calculates the noise level by averaging the signal levels in a reference window around the cell under test (CUT). It is effective in homogeneous environments but less robust in non-homogeneous environments.o Order Statistic CFAR (OS-CFAR): It uses the k-th smallest value in the reference window to set the threshold. It is more robust against multiple targets and non- homogeneous backgrounds compared to CA-CFAR. It is suitable for environments with clutter edges and interfering targets.o Greatest Of CFAR (GO-CFAR): It divides the reference window into two halves and uses the maximum of the two average values to set the threshold. It is effective in non-homogeneous environments, particularly where there are clutter edges.o Smallest Of CFAR (SO-CFAR): It is similar to GO-CFAR but uses the minimum of the two average values. It is more sensitive to noise but can be useful in detecting targets in clutter-free regions.o Truncated-Statistics CFAR (TS-CFAR): It removes the high-intensity outliers from the clutter samples with a certain proportion. It elevates the detection probability, but it suffers a heavy computation burden and a high false alarm rate. o Outliers-Robust CFAR (OR-CFAR) and Truncated-Statistics log-normal CFAR (TS-LNCFAR): It develops an adaptive truncation threshold to eliminate the high intensity outliers in the background window, the detection rate in multiple-target backgrounds is greatly enhanced. However, their performance mainly depends on the selection of the fixed trimming depth, which is quite unstable.o Polarimetric Whitening Filtering TS-CFAR (PWF -TS-CFAR): It is based on TS- CFAR and improves the parameter estimation accuracy and the detection probability, but the computational cost is very high.

[0007] The above-mentioned CFAR algorithms can be chosen based on the specific characteristics of the radar environment and the nature of the targets and clutter. Adjusting the CFAR algorithm to the environment ensures better detection performance and lower false alarm rates. However, all the above-mentioned CFAR algorithms present certain challenges:• High Computational Complexity: CFAR algorithms typically involve a computationally intensive two-dimensional (2D) search across the Range-Doppler Map (RDM) to identify potential targets. This process can lead to slower processing times, which may be unsuitable for real-time applications or systems with limited processing capabilities.• Complex Threshold Selection: Determining an appropriate threshold for CFAR detection is non-trivial. It requires balancing detection performance with the probability of false alarms (Pfa). This selection process often necessitates theoretical analysis orMonte Carlo simulations to optimize thresholds for specific scenarios.• Limited Detection of Weak Targets'. CFAR algorithms may prioritize detecting the strongest targets, particularly in scenarios with significant variations in target strengths. This prioritization can pose challenges in detecting weaker targets that may be masked by stronger signals.

[0008] A need therefore exists to provide a method of detecting multiple radar targets based on joint radar and communication (JRC), and as well as a system for detecting multiple radar targets and a JRC system thereof, that seeks to overcome, or at least ameliorate, one or more deficiencies in conventional methods of detecting multiple radar targets, and more particularly, that utilizes OTFS signals and with improved effectiveness in detecting multiple radar targets. It is against this background that the present invention has been developed.SUMMARY

[0009] According to a first aspect of the present invention, there is provided a method of detecting multiple radar targets based on joint radar and communication using OTFS signals, the method comprising:generating a range-Doppler map based on a first delay-Doppler (DD) domain signal and a second DD domain signal, wherein a first time domain signal is generated from an OTFS modulation based on the first DD domain signal and transmitted to multiple radar targets, and the second DD domain signal is generated from an OTFS demodulation based on a second time domain signal received and reflected from the multiple radar targets from the first time domain signal transmitted;detecting a dominant radar target amongst the multiple radar targets based on the range-Doppler map; andfor each iteration of a plurality of iterations:modifying a correlation intermediate term associated with the range-Doppler map associated with the iteration based on the detected dominant radar target to obtain a modified correlation intermediate term, the correlation intermediate term relating to a cyclic correlation between the first and second DD domain signals;modifying the range-Doppler map associated with the iteration based on the modified correlation intermediate term; anddetecting a dominant radar target amongst the multiple radar targets based on the range-Doppler map modified based on the modified correlation intermediate term.

[0010] According to a second aspect of the present invention, there is provided a system for detecting multiple radar targets based on joint radar and communication using OTFS signals, the system comprising:at least one memory; andat least one processor communicatively coupled to the at least one memory and configured to:generate a range-Doppler map based on a first delay-Doppler (DD) domain signal and a second DD domain signal, wherein a first time domain signal is generated from an OTFS modulation based on the first DD domain signal and transmitted to multiple radar targets, and the second DD domain signal is generated from an OTFS demodulation based on a second time domain signal received and reflected from the multiple radar targets from the first time domain signal transmitted;detect a dominant radar target amongst the multiple radar targets based on the range-Doppler map; andfor each iteration of a plurality of iterations:modify a correlation intermediate term associated with the range-Doppler map associated with the iteration based on the detected dominant radar target to obtain a modified correlation intermediate term, the correlation intermediate term relating to a cyclic correlation between the first and second DD domain signals;modify the range-Doppler map associated with the iteration based on the modified correlation intermediate term; anddetect a dominant radar target amongst the multiple radar targets based on the range-Doppler map modified based on the modified correlation intermediate term.

[0011] According to a third aspect of the present invention, there is provided a joint radar and communication system for detecting multiple targets using OTFS signals, the joint radar and communication system comprising:one or more antennas; andthe system for detecting multiple radar targets according to the above-mentioned second aspect of the present invention communicatively coupled to the one or more antennas for performing joint radar and communication using OTFS signals.

[0012] According to a fourth aspect of the present invention, there is provided a computer program product, embodied in one or more non-transitory computer-readable storage mediums,comprising instructions executable by at least one processor to perform the method of detecting multiple radar targets according to the above-mentioned first aspect of the present invention.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Embodiments of the present invention will be better understood and readily apparent to one of ordinary skill in the art from the following written description, by way of example only, and in conjunction with the drawings, in which:FIG. 1 depicts a schematic flow diagram of a method of detecting multiple radar targets based on JRC using OTFS signals, according to various embodiments of the present invention;FIG. 2 depicts a schematic block diagram of a system for detecting multiple radar targets based on JRC using OTFS signals, according to various embodiments of the present invention;FIG. 3 depicts a schematic block diagram of a JRC system for detecting multiple targets using OTFS signals, according to various embodiments of the present invention;FIG. 4 depicts a schematic drawing of an example system model for the multi-target OTFS JRC system;FIG. 5 depicts a schematic block diagram of an example OTFS modulation (OFDMbased OTFS modulation) which may be employed to generate a time domain signal based on a DD domain signal, according to various example embodiments of the present invention, FIG. 6 depicts a schematic flow diagram of an example iterative prominent target cancellation (IPTC) method, according to various example embodiments of the present invention;FIG. 7 depicts an example range-Doppler map (RDM) obtained without prominent target cancellation;FIG. 8 depicted the RDM obtained after applying the IPTC method, according to various example embodiments of the present invention;FIGs. 9 and 10 illustrate range and speed detection performances, respectively, of different multiple target detection methods for a same range area scenario;FIGs. 11 and 12 illustrate range and speed detection performances, respectively, of different multiple target detection methods for a same range scenario; andFIGs. 13 and 14 illustrate the range and speed detection performance, respectively, of different multiple target detection methods under two users sharing scenario.DETAILED DESCRIPTION

[0014] Various embodiments of the present invention relate to a method and a system for detecting multiple radar targets based on joint radar and communication (JRC) using orthogonal time frequency space (OTFS) signals, as well as a joint radar and communication system thereof.

[0015] As discussed in the background, conventional radar sensing methods can be ineffective in detecting multiple radar targets, particularly in scenarios where radar targets are in proximity, moving rapidly, and / or when multiple users share the spectrum with sparse subcarriers. In particular, amongst multiple radar targets, signals of weaker targets (or weaker target signals) may be overshadowed or masked by signals of stronger targets (or stronger target signals). As a result, such conventional radar sensing methods are not able to effectively detect multiple targets (including weaker targets). In this regard, various embodiments of the present invention provide a method of detecting multiple radar targets based on JRC, and as well as a system for detecting multiple radar targets and a JRC system thereof, that seeks to overcome, or at least ameliorate, one or more deficiencies in conventional methods of detecting multiple radar targets, and more particularly, that utilizes OTFS signals and with improved effectiveness in detecting multiple radar targets.

[0016] FIG. 1 depicts a schematic flow diagram of a method 100 of detecting multiple radar targets (or objects) based on JRC using OTFS signals, according to various embodiments of the present invention. The method 100 comprises: generating (at 105) a range-Doppler map based on a first delay-Doppler (DD) domain signal and a second DD domain signal, wherein a first time domain signal is generated from an OTFS modulation based on the first DD domain signal and transmitted to multiple radar targets, and the second DD domain signal is generated from an OTFS demodulation based on a second time domain signal received and reflected from the multiple radar targets from the first time domain signal transmitted; and detecting (at 106) a dominant radar target (e.g., having the strongest target signal) amongst the multiple radar targets based on the range-Doppler map. In particular, for each iteration of a plurality of iterations (e.g., each iteration for detecting a respective dominant radar target (e.g., the strongest radar target at the iteration) of the multiple radar targets): modifying (at 112) a correlation intermediate term associated with the range-Doppler map associated with the iteration based on the detected dominant radar target to obtain a modified correlation intermediate term, the correlation intermediate term relating to a cyclic correlation between the first and second DD domain signals; modifying (at 114) the range-Doppler map associated with the iteration based on themodified correlation intermediate term; and detecting (at 116) a dominant radar target (i.e., a next dominant radar target) amongst the multiple radar targets based on the range-Doppler map modified based on the modified correlation intermediate term.

[0017] The method 100 of detecting multiple radar targets based on JRC is advantageously based on OTFS signals and is effective in detecting multiple radar targets. In particular, at each iteration of a plurality of iterations, by modifying the correlation intermediate term associated with the range-Doppler map based on the detected dominant radar target and modifying the range-Doppler map based on the modified correlation intermediate term, effects or signal contribution of the detected dominant radar target in the correlation intermediate term associated with the range-Doppler map can be minimized or removed such that the range-Doppler map can be modified based on the modified correlation intermediate term for also minimizing or removing effects or signal contributions of the detected dominant radar target in the range-Doppler map for significantly enhancing the ability to detect the next dominant radar target based on the range-Doppler map modified. In this manner, signals of weaker targets originally masked by signals of stronger targets can be uncovered or detected iteratively based on the range-Doppler map modified iteratively, thereby significantly improving effectiveness in detecting multiple radar targets. Furthermore, by utilizing or enabling the use of OTFS signals, the method 100 of detecting multiple radar targets has further improved effectiveness in detecting multiple radar targets, especially in environments with fast-moving targets / objects (or fast-moving environments). These advantages or technical effects, and / or other advantages or technical effects, will become more apparent to a person skilled in the art as the method 100 of detecting multiple radar targets, as well as the corresponding system for detecting multiple radar targets and the corresponding a JRC system, is described in more detail according to various embodiments and example embodiments of the present invention.

[0018] In various embodiments, the above-mentioned modifying (at 112) the correlation intermediate term associated with the range-Doppler map associated with the iteration comprises: determining a dominant radar target attributed correlation intermediate term based on the detected dominant radar target, wherein the dominant radar target attributed correlation intermediate term represents a signal contribution of the detected dominant radar target in the correlation intermediate term; and offsetting the dominant radar target attributed correlation intermediate term from the correlation intermediate term to obtain the modified correlation intermediate term.

[0019] In various embodiments, the above-mentioned detecting the dominant radar target (at 106 or 116) comprises: locating a peak in the range-Doppler map as corresponding to the dominant radar target; and determining a range and a speed of the dominant radar target based on the located peak in the range-Doppler map.

[0020] In various embodiments, the above-mentioned determining the dominant radar target attributed correlation intermediate term comprises: compensating the correlation intermediate term associated with the range-Doppler map associated with the iteration based on the detected speed of the dominant radar target to obtain a dominant radar target compensated correlation intermediate term; and determining an average of the dominant radar target compensated correlation intermediate term over a Doppler dimension to obtain the dominant radar target attributed correlation intermediate term.

[0021] In various embodiments, the correlation intermediate term associated with the range-Doppler map associated with the iteration is compensated based on a phase compensation factor corresponding to the detected speed of the dominant radar target to obtain the dominant radar target compensated correlation intermediate term.

[0022] In various embodiments, the above-mentioned generating (at 105) the range-Doppler map comprises: obtaining a first Time-Frequency (TF) domain signal associated with the first DD domain signal based on determining a 2D fast Fourier transform (FFT) of the first DD domain signal; obtaining a second TF domain signal associated with the second DD domain signal based on determining a 2D FFT of the second DD domain signal; determining the correlation intermediate term based on a multiplication (e.g., element-wise multiplication) of the first and second TF domain signals; and determining a cyclic correlation (e.g., 2D cyclic correlation) of the first and second DD domain signals based on the correlation intermediate term for generating the range-Doppler map.

[0023] In various embodiments, one of the first and second TF domain signals is a complex conjugate thereof (e.g., the above-mentioned obtaining the first TF domain signal may further comprises determining a complex conjugate of the first TF domain signal (therefore, in the above-mentioned multiplication, the first TF domain signal associated with the first time domain signal transmitted serves as the conjugate)); and the above-mentioned determining the cyclic correlation of the first and second DD domain signals comprises determining a 2D inverse FFT of the correlation intermediate term to generate the range-Doppler map.

[0024] In various embodiments, the above-mentioned modifying (at 114) the range-Doppler map associated with the iteration based on the modified correlation intermediate termcomprises determining a 2D inverse FFT of the modified correlation intermediate term to recompute the range-Doppler map.

[0025] In various embodiments, the first DD domain signal comprises data symbols for transmission.

[0026] FIG. 2 depicts a schematic block diagram of a system 200 for detecting multiple radar targets based on JRC using OTFS signals, according to various embodiments of the present invention, corresponding to the above-mentioned method 100 of detecting multiple radar targets as described hereinbefore with reference to FIG. 1 according to various embodiments of the present invention. The system 200 comprises: at least one memory 202; and at least one processor 204 communicatively coupled (e.g., connected) to the at least one memory 202 and configured to perform the method 100 of detecting multiple radar targets according to various embodiments of the present invention. Accordingly, the at least one processor 204 is configured to: generate a range-Doppler map based on a first DD domain signal and a second DD domain signal, wherein a first time domain signal is generated from an OTFS modulation based on the first DD domain signal and transmitted to multiple radar targets, and the second DD domain signal is generated from an OTFS demodulation based on a second time domain signal received and reflected from the multiple radar targets from the first time domain signal transmitted; and detect a dominant radar target amongst the multiple radar targets based on the range-Doppler map. In particular, for each iteration of a plurality of iterations: the at least one processor 204 is further configured to: modify a correlation intermediate term associated with the range-Doppler map associated with the iteration based on the detected dominant radar target to obtain a modified correlation intermediate term, the correlation intermediate term relating to a cyclic correlation between the first and second DD domain signals; modify the range-Doppler map associated with the iteration based on the modified correlation intermediate term, and detect a dominant radar target (i.e., a next dominant radar target) amongst the multiple radar targets based on the range-Doppler map modified based on the modified correlation intermediate term.

[0027] It will be appreciated by a person skilled in the art that the at least one processor 204 may be configured to perform various functions or operations through set(s) of instructions (e.g., software modules) executable by the at least one processor 204 to perform various functions or operations. Accordingly, as shown in FIG. 2, the system 200 may comprise: a range-Doppler map module (or a range-Doppler map circuit) 205 configured to generate a range-Doppler map based on a first DD domain signal and a second DD domain signal, whereina first time domain signal is generated from an OTFS modulation based on the first DD domain signal and transmitted to multiple radar targets, and the second DD domain signal is generated from an OTFS demodulation based on a second time domain signal received and reflected from the multiple radar targets from the first time domain signal transmitted; a dominant radar target detecting module (or a dominant radar target detecting circuit) 206 configured to detect a dominant radar target amongst the multiple radar targets based on the range-Doppler map, and a correlation intermediate term modifying module (or a correlation intermediate term modifying circuit) 212 configured to, for each iteration of a plurality of iterations, modify a correlation intermediate term associated with the range-Doppler map associated with the iteration based on the detected dominant radar target to obtain a modified correlation intermediate term, the correlation intermediate term relating to a cyclic correlation between the first and second DD domain signals The range-doppler map module 205 is further configured to, for each iteration of the plurality of iterations, modify the range-doppler map associated with the iteration based on the modified correlation intermediate term. The dominant radar target detecting module 206 is further configured to, for each iteration of the plurality of iterations, detect a dominant radar target (i.e., a next dominant radar target) amongst the multiple radar targets based on the range-Doppler map modified based on the modified correlation intermediate term.

[0028] It will be appreciated by a person skilled in the art that the above-mentioned modules are not necessarily separate modules, and two or more modules may be realized by or implemented as one functional module (e.g., a circuit or a software program) as desired or as appropriate without deviating from the scope of the present invention. For example, two or more of the range-Doppler map module 205, the dominant radar target detecting module 206 and the correlation intermediate term modifying module 212 may be realized (e g., compiled together) as one executable software program (e g., embedded control firmware), which for example may be stored in the at least one memory 202 and executable by the at least one processor 204 to perform the corresponding functions or operations as described herein according to various embodiments of the present invention.

[0029] In various embodiments, the system 200 for detecting multiple radar targets corresponds to the method 100 of detecting multiple radar targets as described hereinbefore with reference to FIG. 1, therefore, various operations, functions or steps configured to be performed by the least one processor 204 may correspond to various operations, functions or steps of the method 100 described hereinbefore according to various embodiments, and thus need not be repeated with respect to the system 200 for clarity and conciseness. In other words,various embodiments described herein in context of methods (e.g., the method 100 of detecting multiple radar targets) are analogously valid for the corresponding systems or devices (e.g., the system 200 for detecting multiple radar targets), and vice versa. For example, in various embodiments, the at least one memory 202 may have stored therein the range-Doppler map module 205, the dominant radar target detecting module 206 and / or the correlation intermediate term modifying module 212, which respectively correspond to various operations, functions or steps of the method 100 of detecting multiple radar targets as described hereinbefore according to various embodiments, which are executable by the at least one processor 204 to perform the corresponding operations, functions or steps as described herein.

[0030] A computing system, a controller, a microcontroller or any other system providing a processing capability may be provided according to various embodiments in the present invention. Such a system may be taken to include one or more processors and one or more computer-readable storage mediums. For example, the system 200 for detecting multiple radar targets described hereinbefore may include at least one processor 204 and at least one computer-readable storage medium (or memory) 202 which are for example used in various processing carried out therein as described herein. A memory or computer-readable storage medium used in various embodiments may be a volatile memory, for example a DRAM (Dynamic Random Access Memory) or a non-volatile memory, for example a PROM (Programmable Read Only Memory), an EPROM (Erasable PROM), EEPROM (Electrically Erasable PROM), or a flash memory, e.g., a floating gate memory, a charge trapping memory, an MRAM (Magnetoresistive Random Access Memory) or a PCRAM (Phase Change Random Access Memory).

[0031] In various embodiments, a “circuit” may be understood as any kind of a logic implementing entity, which may be special purpose circuitry or a processor executing software stored in a memory, firmware, or any combination thereof Thus, in an embodiment, a “circuit” may be a hard-wired logic circuit or a programmable logic circuit such as a programmable processor, e.g., a microprocessor (e.g., a Complex Instruction Set Computer (CISC) processor or a Reduced Instruction Set Computer (RISC) processor). A “circuit” may also be a processor executing software, e.g., any kind of computer program, e.g., a computer program using a virtual machine code, e.g., Java. Any other kind of implementation of various functions or operations may also be understood as a “circuit” in accordance with various other embodiments. Similarly, a “module” may be a portion of a system according to various embodiments in the present invention and may encompass a “circuit” as above, or may be understood to be any kind of a logic-implementing entity therefrom.

[0032] Some portions of the present disclosure may be explicitly or implicitly presented in terms of algorithms and functional or symbolic representations of operations on data within a computer memory. These algorithmic descriptions and functional or symbolic representations are the means used by those skilled in the data processing arts to convey most effectively the substance of their work to others skilled in the art. An algorithm may be, and generally, conceived to be a self-consistent sequence of steps leading to a desired result.100331 The present specification also discloses a system (e.g., which may also be embodied as one or more devices or apparatuses), such as the system 200 for detecting multiple radar targets, for performing various operations, functions or steps of various methods described herein. Such a system may be specially constructed for the required purposes or may comprise a general purpose computer system selectively activated or reconfigured by a computer program stored in the computer system. In general, various algorithms that may be presented herein are not limited to being implemented or executed by any particular computer system. Alternatively, the construction of more specialized computer system to perform various operations, functions or steps of various methods described herein may be provided as desired or as appropriate without going beyond the scope of the present invention.

[0034] In addition, the present specification also at least implicitly discloses computer program(s) or software / functional module(s), in that it would be apparent to a person skilled in the art that various operations, functions or steps of various methods described herein may be put into effect by computer code. The computer program(s) is not intended to be limited to any particular programming language and implementation thereof, and it will be appreciated by a person skilled in the art that a variety of programming languages and coding thereof may be used to implement the computer program(s). Moreover, the computer program(s) is not intended to be limited to any particular control flow as there are a variety of programming languages which can use different control flows. It will be appreciated by a person skilled in the art that a computer program may be stored on any computer-readable storage medium (non-transitory computer-readable storage medium), such as but not limited to, a magnetic disk, an optical disk or a memory chip. For example, a computer program stored on a computer-readable storage medium may be loaded and executed on a computer system to implement various operations, functions or steps of various methods described herein according to various embodiments of the present invention.

[0035] Accordingly, in various embodiments, there is provided a computer program product, embodied in one or more computer-readable storage mediums (non-transitorycomputer-readable storage medium), comprising instructions (e.g., the range-doppler map module 205, the dominant radar target detecting module 206, and / or the correlation intermediate term modifying module 212) executable by one or more computer processors to perform a method 100 of detecting multiple radar targets as described hereinbefore with reference to FIG. 1 according to various embodiments of the present invention Accordingly, various computer programs or software modules described herein may be stored in a computer program product receivable by a system therein, such as the system 200 for detecting multiple radar targets as shown in FIG. 2, for execution by at least one processor 204 of the system 200 to perform various operations, functions or steps of various methods described herein according to various embodiments of the present invention.

[0036] It will be appreciated by a person skilled in the art that various modules described herein (e g, the range-doppler map module 205, the dominant radar target detecting module 206 and / or the correlation intermediate term modifying module 212) may be software module(s) realized by computer program(s) or set(s) of instructions executable by a computer processor to perform various functions or operations. Various modules described herein (e.g., the range-doppler map module 205, the dominant radar target detecting module 206 and / or the correlation intermediate term modifying module 212), together with the at least one processor 204 and the at least one memory 202, may also be implemented as hardware module(s) being functional hardware unit(s) designed to perform various functions or operations. More particularly, in the hardware sense, a module is a functional hardware unit designed for use with other components or modules. For example, a module may be implemented using discrete electronic components, or it can form a portion of an entire electronic circuit such as an Application Specific Integrated Circuit (ASIC) or a Field Programmable Gate Array (FPGA). Numerous other possibilities exist. It will also be appreciated by a person skilled in the art that a combination of hardware and software modules may be implemented. Furthermore, various operations, functions or steps of various methods described herein may be performed in parallel rather than sequentially as desired or as appropriate (e.g., as long as it does not render the method(s) inoperable or unsatisfactory for its intended purpose).

[0037] FIG. 3 depicts a schematic block diagram of a IRC system 300 for detecting multiple targets using OTFS signals, according to various embodiments of the present invention. The joint radar and communication system 300 comprises: one or more antennas 312, 314; and the system 200 for detecting multiple targets as described hereinbefore according to various embodiments of the present invention communicatively coupled (e g., connected) to the one ormore antennas 312, 314 for performing joint radar and communication using OTFS signals. In various embodiments, the joint radar and communication radar 300 may further comprise a radar transmitter 302 comprising a transmitter antenna 312 and is configured to perform signal modulation (OTFS modulation) on a signal (e.g., the first DD domain signal comprising data symbols for transmission as described hereinbefore according to various embodiments of the present invention) for transmission via the transmitter antenna 312. The joint radar and communication radar 300 may further comprise a radar receiver 304 comprising a receiver antenna 314 and is configured to perform signal demodulation (OTFS demodulation) on a received signal (e.g., the second time domain signal as described hereinbefore according to various embodiments of the present invention) via the receiver antenna 314 As shown in FIG.3, the system 200 for detecting multiple targets may be communicatively coupled (connected) to the radar transmitter 302 and the radar receiver 304, for example, for obtaining the transmitted signal and the received signal. In various embodiments, the joint radar and communication radar 300 may be a monostatic radar. In the case of a monostatic radar, it will be appreciated by a person skilled in the art that one antenna may be provided or configured to function or serve to transmit and receive radio signals (i.e., function as transmitter and receiver (transceiver) antenna), although separate antennas for transmitting and receiving radio signals may be preferred for various technical purposes. It will be appreciated by a person skilled in the art that the present invention is not limited to a monostatic radar. For example, the present invention may also be applied to a bistatic radar. In the case of a bistatic radar, the system 200 for detecting multiple targets may be located at the radar receiver 304 side and may thus be communicatively coupled (connected) to the radar receiver 304, for example, for obtaining the received signal. In this regard, for example, the transmitted signal may be estimated at the receiver side. For example, the radar receiver 304 may perform demodulation or decoding to obtain the estimated transmitted signal. In various embodiments, the system 200 for detecting multiple targets may be comprised in (e.g., integrated in) the receiver 304.

[0038] It will be appreciated by a person skilled in the art that the terminology used herein is for the purpose of describing various embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and / or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components,but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0039] Any reference to an element or a feature herein using a designation such as “first”, “second” and so forth does not limit the quantity or order of such elements or features, unless stated or the context requires otherwise For example, such designations may be used herein as a convenient way of distinguishing between two or more elements or instances of an element. Thus, a reference to first and second elements does not necessarily mean that only two elements can be employed, or that the first element must precede the second element, unless stated or the context requires otherwise. In addition, a phrase referring to “at least one of’ a list of items refers to any single item therein or any combination of two or more items therein.

[0040] In order that the present invention may be readily understood and put into practical effect, various example embodiments of the present invention will be described hereinafter by way of examples only and not limitations. It will be appreciated by a person skilled in the art that the present invention may, however, be embodied in various different forms or configurations and should not be construed as limited to the example embodiments set forth hereinafter. Rather, these example embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art.

[0041] According to various example embodiments, there is provided an iterative prominent (or dominant) targets cancellation (IPTC) method for multi -targets detection for joint radar and communication (JRC) systems using OTFS signals (which may also be referred to as OTFS JRC systems) (e.g., corresponding to the method 100 of detecting multiple radar targets as described hereinbefore according to various embodiments of the present invention). The IPTC method is designed to mitigate the influence of dominant radar targets iteratively, which is particularly crucial in scenarios where robust interference may overshadow fainter / weaker targets (i.e., fainter / weaker target signals), thus posing challenges for conventional detection methods such as range or speed-based search and constant false alarm (CFAR) algorithms. According to various example embodiments, by systematically cancelling dominant targets, the IPTC method strengthens the JRC system's capability to identify and isolate weaker targets of interest, thereby enhancing overall radar target detection efficacy. Furthermore, conventional methods may encounter difficulty in detecting weak targets when sparse spectrum is available for radar sensing due to spectrum sharing with multiple users. In contrast, the IPTC method for multi-targets detection for joint radar and communication (JRC) systems using OTFS signals,with its adaptability and robustness, enables accurate detection even under resource-constrained conditions.

[0042] The IPTC method for cancelling prominent / dominant targets iteratively advantageously addresses a number of limitations / problems encountered in radar sensing / detection scenarios. For example, unlike existing approaches relying on predefined non-overlapping range areas or target speeds, the IPTC method dynamically minimizes or cancels the influence of dominant targets (dominant target signals) to progressively unveil weaker targets (weaker target signals). This adaptability, along with the use of OTFS signals, enables target detection even in scenarios with closely spaced or overlapping range areas, as well as high-speed targets. The IPTC method for detecting multiple radar targets according to various example embodiments provides a number of technical advantages, such as:• Reduced Complexity. The IPTC method significantly reduces detection complexity by eliminating the need for exhaustive 2D searches.• Addressing Close-Distance and High-Speed Scenarios. The IPTC method demonstrates effectiveness in scenarios characterized by closely spaced multiple targets, potentially even occupying the same location, and exhibiting high relative velocities. This adaptability renders it well-suited for dynamic environments where targets may be in close proximity to each other and moving rapidly.• Enhanced Weak Target Detection'. Through the utilization of prominent target cancellation, the IPTC method significantly improves the system’s capability to detect weaker targets (weaker target signals), particularly in environments characterized by strong interference. For example, this enhanced detection capability is found to be particularly advantageous in crowded or challenging scenarios where strong targets from nearby sources may otherwise obstruct the detection of weaker targets.• Iterative Detection for Weak Targets. Leveraging its iterative nature, the IPTC method systematically cancels prominent / dominant targets iteratively (e.g., cancels the strongest target (strongest target signal) at each iteration) to uncover each weaker target (e.g., next prominent / dominant target) one by one. This iterative process significantly enhances the ability of detecting weaker targets previously obscured by strong interference (by stronger target signals).• Strong Performance in Multi-user Sharing Scenarios'. By mitigating the influence of dominant targets through cancellation iteratively, the IPTC method significantly improves weak target signal detection even when sparse spectrum is available due tomulti-user sharing.

[0043] FIG. 4 depicts a schematic drawing of an example system model for the multi-target OTFS JRC system. The OTFS JRC system comprises a transmitter (TX) configured to generate a communication signal based on OTFS modulation (e g., a standard OTFS protocol). Subsequently, this OTFS signal is transmitted to targets via a TX antenna (ANT). The receiver (RX) in the OTFS JRC system serves dual functions: radar detection and conventional communication but with a primary focus on radar detection according to various example embodiments of the present invention. By capturing and analyzing the reflected signals from radar targets, the receiver can execute the radar detection process to estimate both the range (distance) and speed of the targets. It will be appreciated by a person skilled in the art that while FIG. 4 illustrates only two radar targets (one strong and one weak) for simplicity, the present invention is not limited to detecting only two targets In other words, the present invention may be employed to detect any number of targets as desired or as appropriate. For example, it will be appreciated by a person skilled in the art that in real-world scenarios, there can be any number of multiple radar targets. In this regard, the IPTC method is designed to detect each target iteratively, even in cases with numerous targets present.

[0044] FIG. 5 depicts a schematic block diagram of an example OTFS modulation (OFDMbased OTFS modulation) which may be employed to generate a time domain signal s(t) based on a DD domain signal X(m, ri) comprising data symbols for transmission according to various example embodiments of the present invention. For example, it is assumed that there are P radar targets and the data is placed in DD domain (N subblocks of length AT). For the 7-length rectangular pulses (T is the length of a subblock), the DD domain received signal Y(m, n) (e.g., corresponding to the “second DD domain signal” described hereinbefore according to various embodiments of the present invention) that passed through the channel can be approximated as:p hpe 'M7 — ctp(m, n)X(< m - lp>m, < n — kp>N) + r](m,n)p=i (Equation 1) where X(m,n) is the DD domain transmitted signal samples (e g., corresponding to the “first DD domain signal” described hereinbefore according to various embodiments of the present invention); m and n denote the m-th delay and n-th Doppler, respectively; lp=p / Ts, (0 < lp< M — 1) is the normalized range for p-Lh radar target;pis the delay of the p-th path; Ts= 1 / (Mδf); Mδf is the sampling rate of the OTFS signal, leading to the delay resolution of the signal being 1 / (Mδf); kp= NfpT = Nfp / δf, (0 < kp< N — 1) is the normalized Dopplerfrequency of p-th path; NT is the total OTFS frame duration, leading to the Doppler resolution of the signal be 1 / NT; and1, lp< m < M - 1a.p (m, ri) =0 < m < lp— 1(Equation 2)

[0045] As illustrated in FIG. 5, according to the example OTFS modulation at the transmitter side, the DD domain signal X(m,n) is converted to a Time-Frequency (TF) domain signal (TF domain data) through an inverse symplectic fast Fourier transform (ISFFT). The TF domain signal is then converted to a time domain signal s(t) and transmitted from a transmitter antenna. Correspondingly, according to an example OTFS demodulation at the receiver side, the time domain signal s(t) received by a receiver antenna is converted to a TF domain signal (TF domain data). The TF domain signal is then converted to a DD domain signal (DD domain data) Y (m, n) using a symplectic fast Fourier transform (SFFT).

[0046] An example existing fast radar sensing algorithm for OTFS waveform (or fast algorithm OTFS radar (FAOR)) will now be described.

[0047] 1. Perform 2D-FFT on received signal and transmitted signal on DD domain (T (m, ri) and X(m, n)) to obtain received TF domain signal Y (a, ft) and transmitted TF domain signal X(a, b), respectively, as follows:M-l N-l 1 v-1v-1 / —j2irma\ / —J2nbn\y(a'b) =v^ ^ ^Y(m'n) expHir- )expm-0 n-0(Equation 3) M-l N-l 1 v-1v-1(—j2mna\ / —j2-nbn\ X(a, h) = y y X(m,n)exp - exp - 4MN V M / \ N )m-0 n-0(Equation 4)

[0048] 2. Calculate 2D Cyclic Correlation to obtain range-Doppler map (RDM): The received TF domain signal Y (a, b) is correlated with the transmitted TF domain signal X(a, b) to obtain the cyclic correlation. To obtain the RDM R(m, n), the cyclic correlation of the received TF domain signal Y(a, b) and transmitted TF domain signal X(a, b) is calculated using 2-D IFFT as follows:M—1N—11 y y / 2rrma\ / 2rrbn\=x / MN t—i / D(“'h)exP \ M / exPp \'n Nr / a=o b=0(Equation 5) where D(a, b) = Y (a, b)X(a, b)*.

[0049] 3 Multi-target detection based on the RDM: CFAR algorithms or any other conventional methods known in the art may be used as appropriate to detect the range and speed of the targets based on the obtained RDM, and thus need not be described in detail herein for clarity and conciseness.

[0050] Accordingly, the example existing FAOR provides a fast algorithm to generate the RDM. However, the example existing FAOR still uses conventional methods based on the RDM for multi-target detection. In contrast, according to various example embodiments of the present invention, a unique multi -target detection based on a special property of OTFS signals and FAOR algorithm is provided. An overview of the iterative prominent target cancellation (IPTC) method with FAOR according to various example embodiments of the present invention will now be described below.

[0051] Initial Detection'. The IPTC method may commence by utilizing an existing Fast algorithm OTFS radar (FAOR) to detect the range and speed of the dominant (e.g., strongest target) within the environment. Various OTFS-based radar sensing methods (the corresponding algorithm of which may be referred to as fast algorithm OTFS radar (FAOR)) have been described in International Application no. PCT / SG2025 / 050205 (Publication no. WO / 2025 / 198539), entitled “ORTHOGONAL TIME FREQUENCY SPACE (OTFS)-BASED RADAR SENSING”, the content of which being hereby incorporated by reference in its entirety for all purposes. The present invention is not limited to any particular or specific OTFS-based radar sensing method (or FAOR), for example, any OTFS-based radar sensing method (or any FAOR) described in International Application no. PCT / SG2025 / 050205 may be employed in the IPTC method according to various example embodiments of the present invention. This initial detection furnishes crucial information regarding the position and motion characteristics of the dominant target

[0052] Cancellation of Prominent / Dominant Targets. Following the identification of the dominant (e.g., strongest target), the IPTC method proceeds to mitigate its influence in the correlation intermediate term D(a, b) associated with the range-Doppler map (RDM), which is used to calculate the correlation term of transmitted and received signal on the DD domain (i.e, the transmitted and received DD domain signals X(m, ri) and Y(m, n)). In various example embodiments, this is accomplished by averaging the correlation intermediate term D(a, bj (or more specifically, the dominant target compensated correlation intermediate term) across Doppler domain, adjusted by the detected speed of the dominant target (e.g., the correlation intermediate term D(a, b) is compensated by a phase compensation factor corresponding to thedetected speed of the dominant target). This process is surprisingly found to effectively diminish or remove the signal contribution of the detected dominant radar target in the correlation intermediate term associated with the RDM, and which also minimizes or removes signal contributions of the detected dominant radar target in the RDM, thereby significantly enhancing the visibility or the detection of weaker radar targets.

[0053] Iterative Detection. The dominant target cancellation process is iteratively executed to sequentially neutralize the effects of the prominent / dominant target (e.g., strongest target signal) at each iteration one by one. Each iteration aims to unveil weaker targets (e g., next dominant target after the current dominant target has been removed) previously obscured by the dominance of stronger signals.

[0054] Range and Speed Detection. At each iteration, with the interference from the dominant target mitigated or removed, the IPTC method re-engages in range and speed detection. This time, the IPTC method utilizes the RDM computed based on the updated correlation (updated or modified correlation intermediate term) obtained post-cancellation of the prominent target. For example, this iterative cycle may continue until all radar targets have been detected, including weaker targets previously obscured by the dominance of stronger signals.

[0055] An example IPTC method with FAOR will now be described in further detail with reference to FIG. 6 according to various example embodiments of the present invention. In particular, FIG. 6 depicts a schematic flow diagram of the example IPTC method according to various example embodiments of the present invention.1. Prominent / Dominant Target Detection

[0056] A range-Doppler map (RDM) R(m, n) is generated based on a first DD domain signal X(m, n) (comprising data symbols for transmission) (which may herein be referred to as a transmitted DD domain signal) and a second DD domain signal Y(m, n) (which may herein be referred to as a received DD domain signal). In this regard, a first time domain signal s(t) (which may herein be referred to as a transmitted time domain signal) is generated from an OTFS modulation based on the first DD domain signal and transmitted to multiple targets. The second DD domain signal is generated from an OTFS demodulation based on a second time domain signal received (which may herein be referred to as a received time domain signal) and reflected from the multiple targets from the first time domain signal transmitted. Adominant / prominent target (e.g., the strongest target) amongst the multiple targets may then be detected based on the RDM R(m, n).

[0057] In various example embodiments, to generate the RDM R(m, n), a first Time-Frequency (TF) domain signal X(a, b) associated with the first DD domain signal X(m,n) is obtained based on determining a 2D fast Fourier transform (FFT) of the first DD domain signal X(m, n), and a second TF domain signal Y(a, b) associated with the second DD domain signal is obtained based on determining a 2D FFT of the second DD domain signal Y(m, n). In various example embodiments, one of the first and second TF domain signals is a complex conjugate thereof (i.e., the first TF domain signal is X(a, b)* (a complex conjugate of the first TF domain signal X(a, b) or the second TF domain signal is Y(a, b)* (a complex conjugate of the second TF domain signal Y(a, b)). The correlation intermediate term D(a, b) may then be determined based on a multiplication of the first and second TF domain signals (Y(a, b)X(a, b)* or X(a, b)Y(a, b)*). In this regard, the correlation intermediate term D(a, b) relates to a cyclic correlation between the first and second DD domain signals X(m,n), Y(m,n). Accordingly, a 2D-FFT is performed on both the received and transmitted signals in the Delay-Doppler (DD) domain Y(m,n), X(m,n) to derive received and transmitted TF signals Y(a, b), X(a, b), respectively, and the correlation intermediate term may be determined by, for example, D(a, b) = Y(a, b)X(a, b)* (in the case of the first TF domain signal serving as the complex conjugate). A cyclic correlation of the first and second DD domain signals X(m,n), Y(m, n) may then be determined based on the correlation intermediate term D(a, b) for generating the RDM R(m, n) In various example embodiments, the cyclic correlation of the first and second DD domain signals X(m,n), Y(m,n) is determined based on a 2D inverse FFT of the correlation intermediate term D(a, b) to generate the RDM R(m, n). Accordingly, in various example embodiments, the 2D cyclic correlation of the transmitted and receive signals on the DD domain X(m, n), Y (m, n) is computed to generate the RDM R(m, n) using 2-D IFFT (i.e., compute 2D IFFT of D(a, b), adhering to the cyclic convolution theorem. Thereafter, for detecting the dominant target, a peak in the RDM R(m, n) is located or identified as corresponding to the dominant target, and a range l1and a speed v1of the dominant target are then determined based on the located peak in the RDM. For example, the peak of the RDM R(m, n) may be identified according to Equation (6) below for determining the range l1and speed v1of the dominant / prominent target (e.g., strongest target). Accordingly, the dominant target's position and motion characteristics can be identified.(m1, n1) = arg maxm,n|R(m,n)|(Equation 6) where the normalized range and speed are then obtained as: Jl1= m1, k1= n1.2. Determining Dominant Target Attributed Correlation Intermediate Term

[0058] For each iteration of a plurality of iterations (each iteration for detecting a respective dominant target (e.g., the strongest target at the iteration)), the correlation intermediate term D(a, b) associated with the RDM associated with the iteration is modified based on the detected dominant target to obtain a modified correlation intermediate term D(a, b). In various example embodiments, a dominant target attributed correlation intermediate term D(a) is determined based on the detected dominant target, whereby the dominant target attributed correlation intermediate term D (a) represents a signal contribution of the detected dominant target in the correlation intermediate term D (a, b). The dominant target attributed correlation intermediate term D(a) is then offset from the correlation intermediate term D(a,b) to obtain the modified correlation intermediate term D (a, b). In various example embodiments, to determine the dominant target attributed correlation intermediate term D(a), the correlation intermediate term D(a, b) associated with the RDM associated with the iteration is compensated based on the detected speed k1of the dominant target to obtain a dominant target compensated correlation intermediate term (e.g., corresponding to D(a, b) exp(j2πbk₁ / N) in Equation 7 below), and anaverage of the dominant target compensated correlation intermediate term is determined over a Doppler dimension to obtain the dominant target attributed correlation intermediate term D̄(a). In various example embodiments, the correlation intermediate term associated with the RDM associated with the iteration is compensated based on a phase compensation factor (e.g., corresponding to exp(j2πbk₁ / N) in Equation 7 below) corresponding to the detected speed k1ofthe dominant target to obtain the dominant target compensated correlation intermediate term.

[0059] For example, the correlation intermediate term D(u, b) obtained in step 1 shown in FIG. 6 may be averaged over the Doppler dimension with compensation (e g., corresponding to exp(j2πbk₁ / N) in Equation 7 below) of the detected speed k1of the detectedprominent / dominant target. In this regard, various example embodiments surprisingly found that averaging the correlation intermediate term with the speed (Doppler) compensation of the detected prominent / dominant target advantageously enables to the isolation of the detected prominent / dominant target’s signal contribution in the correlation intermediate term Once thedetected prominent / dominant target’s signal contribution is isolated (corresponding to the dominant target attributed correlation intermediate term D (a)), this signal contribution can then be subtracted from the current correlation intermediate term associated D(a, b) with the RDM associated with the iteration to remove the effect of the prominent / dominant target. Accordingly, determining the dominant target attributed correlation intermediate term D(a) aims to isolate the influence of the most prominent target. For example, the average of the correlation intermediate term D(a,b) after compensating for the speed k1of the most prominent target (exp(j2πbk₁ / N)) is expressed as:N—l_ 1 v fi^itbkiXD (a) = — y D (a, b) exp ( — — — ), Va = 0,... M — 16 = 0(Equation 7) For example, the original correlation intermediate term contains signal contributions from all of the multiple targets. By multiplying this correlation intermediate term with the above-mentioned phase compensation factor (expcorresponding to the detected Doppler (speed) / q of the most dominant target, the phase variation along the Doppler dimension n for that dominant target is effectively removed. After this compensation, the signal contribution from the dominant target becomes a constant across the Doppler dimension n. When subsequently averaged over n, the signal contribution from the dominant target is preserved, while the signal contributions from the remaining targets - whose phases continue to vary with n - average out to nearly or substantively zero. In this manner, the detected prominent / dominant target’s signal contribution in the correlation intermediate term can advantageously be isolated.3. Cancel Prominent / Dominant Target Influence in Correlation Intermediate Term

[0060] As described above, the dominant target attributed correlation intermediate term D (a) is offset from the correlation intermediate term D (a, b) to obtain the modified correlation intermediate term D(a, b). Therefore, to mitigate the impact of the detected prominent / dominant target in the correlation intermediate term, its effects or signal contributions are nullified across the Doppler domain. The resulting residual correlation intermediate term (i.e., the modified correlation intermediate term Z)(a, b)), post-cancellation of the prominent target signal, may be determined by:~ _ / i2ivbki\D̃(a, b) = D(a, b) − D̄(a) exp(−j2πbk₁ / N), ∀a = 0,... M − 1(Equation 8) For example, the isolated contribution of the prominent / dominant target obtained above has been compensated by the Doppler (speed) of the dominant target. According to various example embodiments, to effectively remove the influence of this dominant target from the original / current correlation intermediate term, the inverse (i.e., compensate back) of the Doppler compensation is applied before performing the subtraction in Equation 8 above. This ensures that both the original and the modified correlation intermediate terms are in the same phase reference, allowing accurate cancellation of the dominant target’s contribution.4. Recompute RDM based on Updated / Modified Correlation

[0061] The RDM associated with the iteration is modified based on the modified correlation intermediate term D(a, b). In various example embodiments, the RDM is recomputed by determining a 2D inverse FFT of the modified correlation intermediate term D(a, b). For example, the RDM R(m, n) may be recomputed based on the updated / modified correlation intermediate term as follows:M—l IV— 1R̃(m, n) = (1 / √MN) Σ Σ D̃(a,b) exp(j2πma / M) exp(j2πbn / N)a=0 b=0(Equation 9)5. Detection Range and Speed, of the Next Prom.in.ent / Dom.inant Target

[0062] A dominant target (i.e., a next dominant target) amongst the multiple targets may be determined based on the RDM modified R̃(m, n) based on the modified correlation intermediate term D̃(a, b) In the same or corresponding manner as described hereinbefore in the above-mentioned step 1, the range and speed of the next prominent / dominant target may be detected by identifying the peak in the updated / modified RDM R(m, n) following the cancellation of the previous dominant signal (e g., previous most prominent or strongest signal). Accordingly, an accurate determination or estimation of the prominent target's range and speed can be achieved. For example, the peak in the updated / modified RDM R(m, n) may be determined as follows:(m2,n2) = arg maxm,n|R̃(m,n)|(Equation 10) where the normalized range and speed of the detected dominant target are then obtained as: l2= m2, k2= n2.6. Iterative Cancellation and Detection

[0063] As described hereinbefore, the example IPTC is performed iteratively. In this regard, after each iteration, the example IPTC method may loop back to step 2, where the next prominent / dominant target cancellation is carried out. This iterative approach enables the gradual or sequential detection of weaker targets by eliminating one prominent / dominant target at a time, for example, until all anticipated radar targets are detected.

[0064] Without wishing to be bound by theory but for better understanding, an example technical derivation of the IPTC method will now be described below.Strongest Target Signal Cancellation

[0065] Apply a 2-D FFT to the DD domain signal Y (m, n) to obtain the TF domain signal Ỹ(a, b) as follows:pV ~ / LnCC / kr>b\ Y(a,b) = f hpX(a,b) exp[—j2TV-j^] exp[—j2Ti—^-) + W(a, b),p=i(Equation 11) where X̃(a, b) is the 2-D FFT of the DD domain signal X(m, n), and W(a, b) denotes the noise term. For simplicity and clarity, the noise term is ignored in the following derivation.100661 Next, the TF domain signal Y(a, b) is multiplied with the conjugate of the TF domain signal X(a, b) to obtain the correlation intermediate term D(a, b):D(a,b) = Ỹ(a,b) ⊙ X̃(a, b)*(Equation 13) Z p, lpa\ / kpb\hpF(a, b) exp ^-J2TT— j exp ( -J2TT— J(Equation 14) where F(a, b) = X̃(a, b) ⊙ X̃(a,b)H≈ F̄(a) which varies slowly over Doppler dimension, and representing the self-correlation of the transmitted OTFS frameStrongest Target Compensation

[0067] To isolate the dominant target, various example embodiments compensate for its Doppler shift (speed) k1and average D(a, b) along the Doppler dimension:D̄(a) = (1 / N) Σ_{b=0}^{N-1} D(a,b) exp(j2πbk₁ / N).(Equation 15)

[0068] Substituting D (a, b), the dominant target attributed correlation intermediate term D(a) may be obtained as follows:N-l N—l P,,,,,, 1 \ i Zi a 1 \ i \ i l-nCi \k-n~ 5(a) = / 1iF<a)e’72ll7r +N 22 e“72nTEe-^ Nb = 0 b=0 p=2(Equation 16)

[0069] Since the cross terms average out due to their Doppler mismatch, the following can be obtained:D̄(a) ≈ h₁F̄(a)e^{-j2π(l₁a / M)}(Equation 17) which corresponds to the signal contribution of the dominant target.Residual Correlation and Range- -Doppler Map

[0070] To remove this dominant component, its contribution D(a) is subtracted from D(a, b) to obtain the modified (or residual) correlation intermediate term D(a, by.~ _ / j2itbki\ D(a, b) = D(a, b) — D(a) exp ( - — — I p= Σ_{p=2}^{P} h_p F̄(a) exp(−j2π(l_p a / M)) exp(−j2π(k_p b / N))p = 2(Equation 18)

[0071] Finally, performing a 2-D inverse FFT on D̃(a, b) yields the RDM corresponding to the residual targets (remaining targets), from the range and velocity of the next prominent target can be accurately estimated.

[0072] Simulation results of the IPTC method or algorithm for multi-target detection with FAOR according to various example embodiments of the present invention will now be described. Its performances are compared with other existing multi-target detection algorithms, including the range-based search and the CA-CFAR algorithm. While there are various CFAR algorithms, CA-CFAR was chosen to compare with the PTC method since it is the most used, and other CFAR algorithms typically exhibit similar performance. The simulation settings are provided in Table 1 below. The simulations performed primarily evaluate the ability of various algorithms to detect weak targets (weak target signals), as there are typically no problems indetecting prominent targets (e g., strongest targets). It is assumed that the power of the weak target is 10 dB lower than that of the prominent target.Table 1: Simulation ParametersChannel bandwidth 122.8 MHzCarrier frequency 60 GHzSubcarrier spacing 30 KHzModulation scheme QPSKFFT size 4096Symbols per slot 14Slots per subframe 1Slots per frame 10Number of transmit antennas 1Number of receive antennas 1Relative path gains of two reflected signals

[0100] dBRange of radar objects [120300] mSpeed of radar objects

[0100] km / h

[0073] To provide a clear illustration of the impact of the IPTC algorithm according to various example embodiments of the present invention, a comparison of RDM obtained with and without prominent target cancellation when the Signal -to-Noise Ratio (SNR) is set to -20 dB is presented. In the original RDM without prominent target cancellation as depicted in FIG.7, there are two peaks corresponding to the two targets. The strong target exhibits significantly higher power compared to the weak target. Without prior knowledge of the range or speed separation between the two targets, only the strong target can be detected using the existing FAOR algorithm or CFAR algorithm. FIG. 8 depicted the RDM obtained after applying the IPTC algorithm. Notably, the prominent target is effectively eliminated, leaving only the weak target visible in the RDM. Accordingly, this refined / modified RDM enables effective detection of the weak target.

[0074] To provide comprehensive evaluation of the IPTC algorithm performance under various conditions, three specific scenarios were considered in the simulation as follows:• Same Range Area. Targets are situated within the same range area, allowing for assessment of algorithms' performance in distinguishing closely spaced targets.• Same Range. Both strong and weak targets share the same range value, challenging thealgorithms to differentiate between targets with identical range values and detect the weaker one.• Multiple Users Sharing the Spectrum'. In this scenario, multiple users share the spectrum, introducing interference and making target detection more challenging.

[0075] In the Same Range Area Scenario, both the strong and weak targets are situated within the same range area, specifically between 120 and 300 meters. Although they vary in distance from the radar, their range values fall within a defined region. This scenario serves to evaluate the algorithms' ability to distinguish and detect targets that are closely spaced in range. FIGs. 9 and 10 illustrate the performance of range and speed detection, respectively, in this context. It becomes apparent that the range-based search method struggles to differentiate between the targets, leading to poor performance in detecting the weaker target. Similarly, the CFAR method, which relies on thresholding based on noise estimates and surrounding signal strengths, may prioritize the stronger target, thereby failing to effectively detect the weaker one. However, the IPTC method of canceling strong targets demonstrates accurate range and speed detection for the weak target when the SNR exceeds approximately -26 dB. This outcome highlights the efficacy of the IPTC method in enhancing weak signal detection under challenging conditions characterized by strong interference.

[0076] In the Same Range Scenario, both the strong and weak targets are positioned equidistant from the radar, sharing identical range values. This situation presents a significant challenge for algorithms tasked with distinguishing between targets and accurately detecting the weaker one. FIGs. 11 and 12 illustrate the clear superiority of the IPTC algorithm method over traditional range-based search and CFAR methods in terms of both range and speed detection. In this scenario, conventional range-based search methods may mistakenly identify the strong target as the weak one, given their shared range value. Consequently, while range detection may seem effective, it leads to inaccurate speed detection, as the method attributes the speed of the strong target to the weaker one. Similarly, the CFAR method faces difficulties in this context, potentially favoring the stronger target and thus failing to detect the weaker one accurately. However, the IPTC method, incorporating robust target cancellation techniques, exhibits exceptional performance even in this challenging scenario. By mitigating the influence of the dominant target, the IPTC method maintains its ability to accurately detect the range and speed of the weaker target. This capacity to correctly identify the weaker target despite it sharing the same range value with the strong target underscores the resilience and effectiveness of the IPTC approach.

[0077] In the scenario where multiple users share the spectrum, the spectrum is utilized by multiple users simultaneously, potentially causing interference and complicating target detection. FIGs. 13 and 14 illustrate the range and speed detection performance, respectively, of various algorithms under two users sharing scenarios. In this intricate environment, each user is allocated only half of the spectrum for radar detection, and the presence of other users may further impede the detection of weak targets. From FIGs. 13 and 14, it becomes apparent that the IPTC approach demonstrates exceptional performance in both range and speed detection, even in scenarios with multiple users sharing the spectrum. Specifically, as depicted in FIGs.13 and 14, accurate range and speed detection can be achieved when the SNR exceeds approximately -22 dB In contrast, traditional methods such as range-based search and CFAR methods may encounter challenges in effectively detecting weak targets in this scenario. These methods utilize only a portion of the spectrum for radar detection, and the presence of interference from other users exacerbates the difficulty. In summary, the IPTC approach proves highly effective in facilitating accurate range and speed detection in scenarios where multiple users share the spectrum, even under resource constraints.

[0078] While embodiments of the invention have been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the invention as defined by the appended claims. The scope of the invention is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.

Claims

CLAIMS1. A method of detecting multiple radar targets based on joint radar and communication using orthogonal time frequency space (OTFS) signals, the method comprising:generating a range-Doppler map based on a first delay-Doppler (DD) domain signal and a second DD domain signal, wherein a first time domain signal is generated from an OTFS modulation based on the first DD domain signal and transmitted to multiple radar targets, and the second DD domain signal is generated from an OTFS demodulation based on a second time domain signal received and reflected from the multiple radar targets from the first time domain signal transmitted;detecting a dominant radar target amongst the multiple radar targets based on the range-Doppler map; andfor each iteration of a plurality of iterations:modifying a correlation intermediate term associated with the range-Doppler map associated with the iteration based on the detected dominant radar target to obtain a modified correlation intermediate term, the correlation intermediate term relating to a cyclic correlation between the first and second DD domain signals;modifying the range-Doppler map associated with the iteration based on the modified correlation intermediate term; anddetecting a dominant radar target amongst the multiple radar targets based on the range-Doppler map modified based on the modified correlation intermediate term.

2. The method according to claim 1, wherein said modifying the correlation intermediate term associated with the range-Doppler map associated with the iteration comprises:determining a dominant radar target attributed correlation intermediate term based on the detected dominant radar target, wherein the dominant radar target attributed correlation intermediate term represents a signal contribution of the detected dominant radar target in the correlation intermediate term; andoffsetting the dominant radar target attributed correlation intermediate term from the correlation intermediate term to obtain the modified correlation intermediate term.

3. The method according to claim 2, wherein said detecting the dominant radar target comprises:locating a peak in the range-Doppler map as corresponding to the dominant radar target; anddetermining a range and a speed of the dominant radar target based on the located peak in the range-Doppler map.

4. The method according to claim 3, wherein said determining the dominant radar target attributed correlation intermediate term comprises:compensating the correlation intermediate term associated with the range-Doppler map associated with the iteration based on the detected speed of the dominant radar target to obtain a dominant radar target compensated correlation intermediate term; anddetermining an average of the dominant radar target compensated correlation intermediate term over a Doppler dimension to obtain the dominant radar target attributed correlation intermediate term.

5. The method according to claim 4, wherein the correlation intermediate term associated with the range-Doppler map associated with the iteration is compensated based on a phase compensation factor corresponding to the detected speed of the dominant radar target to obtain the dominant radar target compensated correlation intermediate term.

6. The method according to claim 1, wherein said generating the range-Doppler map comprises:obtaining a first Time-Frequency (TF) domain signal associated with the first DD domain signal based on determining a 2D fast Fourier transform (FFT) of the first DD domain signal;obtaining a second TF domain signal associated with the second DD domain signal based on determining a 2D FFT of the second DD domain signal;determining the correlation intermediate term based on a multiplication of the first and second TF domain signals; anddetermining a cyclic correlation of the first and second DD domain signals based on the correlation intermediate term for generating the range-Doppler map.

7. The method according to claim 6, whereinone of the first and second TF domain signals is a complex conjugate thereof; andsaid determining the cyclic correlation of the first and second DD domain signals comprises determining a 2D inverse FFT of the correlation intermediate term to generate the range-Doppler map.

8. The method according to claim 1, wherein said modifying the range-Doppler map associated with the iteration based on the modified correlation intermediate term comprises determining a 2D inverse FFT of the modified correlation intermediate term to recompute the range-Doppler map.

9. The method according to claim 1, wherein the first DD domain signal comprises data symbols for transmission.

10. A system for detecting multiple radar targets based on joint radar and communication using orthogonal time frequency space (OTFS) signals, the system comprising:at least one memory; andat least one processor communicatively coupled to the at least one memory and configured to:generate a range-Doppler map based on a first delay-Doppler (DD) domain signal and a second DD domain signal, wherein a first time domain signal is generated from an OTFS modulation based on the first DD domain signal and transmitted to multiple radar targets, and the second DD domain signal is generated from an OTFS demodulation based on a second time domain signal received and reflected from the multiple radar targets from the first time domain signal transmitted;detect a dominant radar target amongst the multiple radar targets based on the range-Doppler map; andfor each iteration of a plurality of iterations:modify a correlation intermediate term associated with the range-Doppler map associated with the iteration based on the detected dominant radar target to obtain a modified correlation intermediate term, the correlation intermediate term relating to a cyclic correlation between the first and second DD domain signals;modify the range-Doppler map associated with the iteration based on the modified correlation intermediate term; anddetect a dominant radar target amongst the multiple radar targets based on the range-Doppler map modified based on the modified correlation intermediate term.

11. The system according to claim 10, wherein said modify the correlation intermediate term associated with the range-Doppler map associated with the iteration comprises:determining a dominant radar target attributed correlation intermediate term based on the detected dominant radar target, wherein the dominant radar target attributed correlation intermediate term represents a signal contribution of the detected dominant radar target in the correlation intermediate term; andoffsetting the dominant radar target attributed correlation intermediate term from the correlation intermediate term to obtain the modified correlation intermediate term.

12. The system according to claim 11, wherein said detect the dominant radar target comprises:locating a peak in the range-Doppler map as corresponding to the dominant radar target; anddetermining a range and a speed of the dominant radar target based on the located peak in the range-Doppler map.

13. The system according to claim 12, wherein said determining the dominant radar target attributed correlation intermediate term comprises:compensating the correlation intermediate term associated with the range-Doppler map associated with the iteration based on the detected speed of the dominant radar target to obtain a dominant radar target compensated correlation intermediate term; anddetermining an average of the dominant radar target compensated correlation intermediate term over a Doppler dimension to obtain the dominant radar target attributed correlation intermediate term.

14. The system according to claim 13, wherein the correlation intermediate term associated with the range-Doppler map associated with the iteration is compensated based on a phase compensation factor corresponding to the detected speed of the dominant radar target to obtain the dominant radar target compensated correlation intermediate term.

15. The system according to claim 10, wherein said generate the range-Doppler map comprises:obtaining a first Time-Frequency (TF) domain signal associated with the first DD domain signal based on determining a 2D fast Fourier transform (FFT) of the first DD domain signal;obtaining a second TF domain signal associated with the second DD domain signal based on determining a 2D FFT of the second DD domain signal;determining the correlation intermediate term based on a multiplication of the first and second TF domain signals; anddetermining a cyclic correlation of the first and second DD domain signals based on the correlation intermediate term for generating the range-Doppler map.

16. The system according to claim 15, whereinone of the first and second TF domain signals is a complex conjugate thereof; and said determining the cyclic correlation of the first and second DD domain signals comprises determining a 2D inverse FFT of the correlation intermediate term to generate the range-Doppler map.

17. The system according to claim 10, wherein said modify the range-Doppler map associated with the iteration based on the modified correlation intermediate term comprises determining a 2D inverse FFT of the modified correlation intermediate term to recompute the range-Doppler map.

18. The system according to claim 1, wherein the first DD domain signal comprises data symbols for transmission.

19. A joint radar and communication system for detecting multiple targets using orthogonal time frequency space (OTFS) signals, the joint radar and communication system comprising:one or more antennas; andthe system for detecting multiple radar targets according to claim 10 communicatively coupled to the one or more antennas for performing joint radar and communication using OTFS signals.

20. A computer program product, embodied in one or more non-transitory computer-readable storage mediums, comprising instructions executable by at least one processor to perform the method of detecting multiple radar targets according to claim 1.

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