Dual-function Radar-communications Research Articles

Sparse Array Design for Dual-Function Radar-Communications System

The problem of sparse array design for dual-function radar-communications is investigated. Our goal is to design a sparse array which can simultaneously shape desired beam responses and serve multiple downlink users with the required signal-to-interference-plus-noise ratio levels. Besides, we also take into account the limitation of the radiated power by each antenna. The problem is formulated as a quadratically constrained quadratic program with a joint-sparsity-promoting regularization, which is NP-hard. The resulting problem is solved by the consensus alternating direction method of multipliers, which enjoys parallel implementation. Numerical simulations exhibit the effectiveness and superiority of the proposed method which leads to a more power-efficient solution.

Transmit and receive hybrid beamforming design for OFDM dual-function radar-communication systems

This article investigates the design of hybrid digital and analog transmit/receive beamformers for orthogonal frequency division multiplexing dual-function radar-communication system. Specifically, we model the hybrid beamforming design by simultaneously optimizing the spectrum efficiency of communication and approximate output signal-to-interference noise ratio of radar sensing, through a flexible performance tradeoff. Due to the coupling relationship among the beamformers in the hybrid structure and the independence of signals in different frequency bands, the resultant optimization problem is NP-hard. Hence, a consensus alternating direction method of multipliers approach is designed to tackle the difficulty. The transmit hybrid beamformer is obtained by introducing auxiliary variables and exploiting the block continuous upper bound minimization method. Then, the receive beamformer can be optimized via generalized eigenvalue decomposition. Numerical simulations are provided to demonstrate the effectiveness of the proposed scheme.

Dual-use baseband signal design for RadCom with position index and phase modulation

This paper deals with the synthesis of dual-use signal to simultaneously achieve detection and communication for a dual-function radar communication (DFRC) system. A new position index and phase (PIP) modulation is proposed for information embedding, where position index modulation is realized by selecting the information embedding subpulses (InSp) positions. Moreover, differential phase modulation is utilized to distinguish InSp from other available subpulses. As for radar detectability, peak sidelobes level (PSL) of signal auto-correlation function is minimized. Meanwhile, constant-envelope and phases constraints are forced to ensure compatibility with the current hardware technique and modulation demand, respectively. To tackle the resulting nonconvex and NP-hard optimization problem, a spectral majorization-minimization (SM) dual-use baseband signal design method is proposed. In each iteration, the original problem is approximated by a tractable problem with a closed-form solution. Finally, simulation and semi-physical experimental results demonstrate the designed dual-use signal is capable of realizing high data rate communication and ensuring acceptable radar performance.

Estimating the target DOA, range and velocity using subspace methods in a MIMO OFDM DFRC system

Dual-function Radar communication (DFRC) systems implement Radar detection and communication using the same hardware simultaneously. Significant attention has been paid to a multiple-input multiple-output DFRC system based on orthogonal frequency division multiplexing (OFDM). So far, the directions of arrival of the targets have been well estimated using subspace methods. In this paper, the ranges and/or velocities are estimated using the subspace methods. To this end, the Radar waveform must be based on the data symbols that are replicated over a few sub-carriers and/or during a few OFDM symbols. To avoid data replication, the target ranges and velocities can be estimated based on a least-squares (LS) or total LS method. After giving a few practical considerations, simulation results show that the proposed approaches outperform the existing ones based on the Fourier transform and/or Lasso algorithm. The performance of the proposed approaches is compared with the Cramer–Rao bound. Moreover, we show how the performance of the DFRC system (in terms of the accuracy of the estimated target parameters and data rate) evolves when modifying the system parameters, such as the number of sub-carriers and the number of OFDM symbols.

Improved Information Embedding for Frequency Hopping-Based MIMO DFRC System

Dual function radar communication (DFRC) system, which treats the radar as the primary modality and embeds information into the transmitted waveforms, is proposed recently to solve the problem of spectrum congestion. In this letter, we propose an improved information embedding scheme for a frequency hopping (FH) based multiple-input multiple-output (MIMO) DFRC system. First, we develop an FH matrix construction method by taking the radar ambiguity function (AF) into consideration. The constructed FH matrix is able to generate FH waveforms with superior radar detection performance. Then, an offset quadrature phase-shift keying (OQPSK) modulated communication waveform is presented to alleviate the spectral leakage issue caused by canonical modulation schemes, which together with the FH waveform, forms the transmit waveform of the considered DFRC system. Simulation results verify that the proposed scheme achieves lower AF sidelobe levels (SLLs) and better spectral containment as compared with the state-of-the-art.

A Bandwidth Efficient Dual-Function Radar Communication System Based on a MIMO Radar Using OFDM Waveforms

A novel dual-function radar communication (DFRC) system is proposed, that achieves high communication rate, and can flexibly trade-off rate for improved sensing performance. The proposed system is a monostatic multiple-input multiple-output (MIMO) radar and transmits wideband, precoded, orthogonal frequency division multiplexing (OFDM) waveforms from its antennas. The system subcarriers are divided into two groups, i.e., shared and private. On a shared subcarrier, all antennas can transmit simultaneously, while on a private one only one antenna can transmit at a time. A novel target estimation approach with low complexity is proposed to overcome the coupling of transmitted symbols and radar target parameters in the target echoes, which arises due to the shared use of subcarriers by the transmit antennas. The proposed method first operates on all (shared and private) subcarriers to obtain coarse angle estimates, and then fine-tunes those estimates based on the signal received on the private subcarriers. The resolution of the coarse angle estimates is limited by the physical receive array, while the fine-tuning is enabled by effectively constructing a virtual array that has larger aperture than the receive array. The precoding matrix is optimally designed to optimize a weighted combination of the beampattern error with respect to a desirable beampattern, and the signal-to-noise ratio at the communication receiver.

Bistatic MIMO DFRC System Waveform Design via Fractional Programming

The Cramér-Rao lower bound (CRLB) and sum-rate (SR) are widely-used metrics in the radar parameter estimation performance evaluation and communication quality-of-service (QoS) assessment, respectively. In this paper, we adopt these two metrics in waveform design for bistatic multiple-input multiple-output dual-function radar-communication (MIMO DFRC) systems, which is different from existing methods where only suboptimal optimization criteria are employed. However, both of the design formulations result in nonconvex and nonlinear fractional programming (FP) problems with complex fractional constraint and objective function. Especially, the CRLB for direction-of-departure (DOD) and direction-of-arrival (DOA) in bistatic DFRC MIMO system is a fraction with quadratic polynomial in the numerator and quartic polynomial in the denominator; whereas the SR expression corresponds to a summation-log-fraction function. By fractional function transformation and convexification, complex function design and simplification, and summation-log-fraction function separation, this paper derives an FP framework to solve these complicated problems. Numerical results demonstrate the excellent performance of our design solutions.

Transmit Waveform Design for Dual-Function Radar-Communication Systems via Hybrid Linear-Nonlinear Precoding

This paper develops a transmit (Tx) waveform de- sign technique for dual-function radar-communication systems that provide both multiple-input multiple-output (MIMO) radar and multi-user multiple-input single-output (MU-MISO) com- munication functionalities. We propose a hybrid linear-nonlinear precoding (HLNP) signaling scheme, in which the dual-use waveform is the superposition of linearly-precoded communica- tion symbols and a nonlinearly-precoded waveform that improves the radar performance. To attain good radar Tx beampattern and waveform ambiguity properties, we focus on optimizing a weighted sum of the integrated main-lobe-to-sidelobe ratio (IMSR) of the Tx beampatttern and a novel angular waveform similarity metric, while ensuring a predefined signal-to-interference-plus- noise ratio (SINR) for each communication user. Practical con- straints are imposed on the Tx waveform, including per-antenna power and peak-to-average-power ratio (PAPR) constraints. We propose an extended feasible point pursuit successive convex ap- proximation (EFPP-SCA) algorithm to solve the resultant non- convex problem and establish its convergence properties. To re- duce the computational cost of designing a long Tx waveform, we further introduce a sub-block design technique. Numerical ex- amples indicate that the proposed HLNP provides a superior performance tradeoff between sensing and communication com- pared to conventional nonlinear precoding.

Directional modulation based on dual-function radar-communication system

Dual-function radar-communication (DFRC) system has recently been proposed to enable the co-design of radar and wireless communications, which in turn alleviates the increased spectrum congestion crisis. DFRC system exploits the transmit beamforming technique and waveform diversity, the combination of which enables the system to embed information in radar emission. In this paper, directional modulation (DM) based on dual-function radar communication system is proposed. To achieve the security of information transmission, a beam weight vector set is established. The reference beam weight vector is initially designed and the remaining weight vectors are derived from it, by minimizing the differences between them. The transmitting beams shaped by the designed weight vectors are almost the same in radar main lobe, but differ in the amplitudes and phases towards the direction of intended communication receivers. The communication receivers decode the data based on its radiated beam. The proposed communication process is secure against intercept from directions other than the pre-assigned communication directions. Simulation results are provided for performance evaluation and to demonstrate the effectiveness of the proposed scheme.

Joint Secure Communication and Radar Beamforming: A Secrecy-Estimation Rate-Based Design

This paper considers transmit beamforming in dual-function radar-communication (DFRC) system, where a DFRC transmitter simultaneously communicates with a communication user and detects a malicious target with the same waveform. Since the waveform is embedded with information, the information is risked to be intercepted by the target. To address this problem, physical-layer security technique is exploited. By using secrecy rate and estimation rate as performance measure for communication and radar, respectively, three secrecy rate maximization (SRM) problems are formulated, including the SRM with and without artificial noise (AN) and robust SRM. For the SRM beamforming, we prove that the optimal beamformer can be computed in closed form. For the AN-aided SRM, by leveraging alternating optimization, similar closed-form solution is obtained for the beamformer and the AN covariance matrix. Finally, the imperfect CSI of the target is also considered under the premise of a moment-based random phase-error model on the direction of arrival at the target. Simulation results demonstrate the efficacy and robustness of the proposed designs.

Integrated Sensing and Communications (ISAC) for Vehicular Communication Networks (VCN)

With the unprecedented development of smart vehicles and roadside units equipped with wireless connectivity, the transportation system is undergoing revolutionary changes in the past decade or two. Bearing safety and efficiency as the utmost objectives, the vehicular environments are witnessing explosive increase of various sensors onboard vehicles and equipped at transportation infrastructures. On the one hand, these sensors are destined to be wirelessly connected to provide more comprehensive situational awareness for transportation purposes. On the other hand, the abundance of sensor data of the environment can potentially shed light on the channel propagation characteristics that lie at the core of any communications system design. The integrated sensing and communications (ISACs) is henceforth both necessary and natural in vehicular communications networks (VCN). Different from existing ISAC works that target generic environments but are limited to dual-function radar-communications (DFRC), in this article we focus on transportation scenarios and applications but take a wholistic view of ISAC possibilities. First, we argue that, even though many sensors in transportation settings are nonradio-frequency (RF)-based, functional ISAC (fISAC) is feasible and necessary, in both communication-centric (CC) or sensing-centric (SC) modes. To facilitate this, the concept of synesthesia is introduced to ISAC to accommodate “machine senses” in the RF and non-RF formats. We then zoom in to RF-based sensors and propose the so-termed signaling ISAC (sISAC), with either unified-hardware (UH) or separate-hardware (SH) platforms, and delineate the unique issues arising in transportation settings. Several transportation-specific case studies are included to demonstrate these various ISAC regimes. Toward the end, the relationships of these ISAC subcategories are discussed with a roadmap laid out.

Generalized Fully Coherent Closed-Form Receiver Design for Joint Radar and Communication System

Conventional radars repeat the transmission of the same waveform after a predefined interval of time called pulse-repetition-interval (PRI). This technique helps estimate the range and Doppler shift of the targets and suppress clutter. However, in dual-function radar communication (DFRC), a different symbol waveform is transmitted after each PRI. Depending on the number of targets, radar receiver output yields several peaks representing different targets’ ranges. Each peak comes with its side-lobes called range-side-lobes (RSL). In DFRC, due to different symbol waveform transmission, peaks and RSLs do not remain coherent, making Doppler shift estimation and clutter suppression challenging tasks. In most of the available literature, iterative receive filters have been designed for DFRC to minimize RSLs and achieve coherent output for different waveforms. However, the proposed receive filter does not guarantee coherent output for more than two waveforms. In contrast, we proposed two novel closed-form algorithms to design receive filters for DFRC that guarantee coherent output response for several waveforms and suppress RSLs. Simulation results demonstrate that the proposed receivers achieve full coherency, and the RSLs are significantly lower than the conventional method. Furthermore, the advantage of achieving coherent output response is shown in target detection and bit-error-rate improvement.

Exploiting Constructive Interference in Symbol Level Hybrid Beamforming for Dual-Function Radar-Communication System

In this letter, we study the Hybrid Beamforming (HBF) design for a Dual-Function Radar-Communication (DFRC) system, which serves Multiple Users (MUs) and detects a target in the presence of signal-dependent clutters, simultaneously. Unlike conventional beamforming strategies, we propose a novel one on the symbol level, which exploits Constructive Interference (CI) to achieve a trade-off between radar and communication using one platform. To implement this novel strategy, we jointly design the DFRC transmit HBF and radar receive beamforming by maximizing the radar Signal to Interference plus Noise Ratio (SINR) while ensuring the Quality of Service (QoS) of downlink communication. To tackle the formulated non-convex problem, we propose an iterative algorithm, which combines the Majorization-Minimization (MM) and Alternating Direction Method of Multipliers (ADMM) judiciously. The numerical experiments indicate that our algorithm yields the CI properly for robust communications and achieves better performance than the conventional HBF benchmarks in both communication bit error rate and radar SINR.

Manifold optimization for hybrid beamforming in dual-function radar-communication system

Manifold optimization for hybrid beamforming in dual-function radar-communication system

Integrating Secure Communications Into Frequency Hopping MIMO Radar With Improved Data Rate

Dual-function radar-communication (DFRC) based on frequency hopping (FH) MIMO radar (FH-MIMO DFRC) achieves symbol rate much higher than radar pulse repetition frequency. Such DFRC, however, is prone to eavesdropping due to the spatially uniform illumination of an FH-MIMO radar. In this paper, we reveal the potential of using permutations of hopping frequencies to achieve secure and high-speed FH-MIMO DFRC. Specifically, we identify the angle-dependent issue in detecting permutations and develop an element-wise phase compensation (EPC) to solve the issue for a legitimate user (Bob). EPC makes the demodulation at an eavesdropper (Eve) conditioned on knowing the angle-of-departure (AoD) of Bob. We also propose the random sign reversal (RSR) technique which randomly selects several antennas over hops and reverses their signs. Owing to EPC, there is a sign rule available for Bob. We employ the rule and develop a low-complexity algorithm for Bob to remove RSR. We further prove that, given the same signal-to-noise ratio, RSR plus EPC make the demodulation performance of Eve inferior to that of Bob in most angular regions. Confirmed by simulation, our design achieves substantially high physical layer security for FH-MIMO DFRC, improves demodulation performance compared with existing designs, and reduces mutual interference among radar targets.

Min-Max Latency Optimization Based on Sensed Position State Information in Internet of Vehicles

The dual-function radar communication (DFRC) is an essential technology in Internet of Vehicles (IoV). Consider that the road-side unit (RSU) employs the DFRC signals to sense the vehicles’ position state information (PSI), and communicates with the vehicles based on PSI. The objective of this paper is to minimize the maximum communication delay among all vehicles by considering the estimation accuracy constraint of the vehicles’ PSI and the transmit power constraint of RSU. By leveraging convex optimization theory, two iterative power allocation algorithms are proposed with different complexities and applicable scenarios. Simulation results indicate that the proposed power allocation algorithm converges and can significantly reduce the maximum transmit delay among vehicles compared with other schemes.

Joint MIMO Precoding and Computation Resource Allocation for Dual-Function Radar and Communication Systems With Mobile Edge Computing

In this paper, an integrated communication, radar sensing, and mobile-edge computing (CRMEC) architecture is developed, where user terminals (UTs) perform radar sensing and computation offloading simultaneously at the same spectrum by using multiple-input and multiple-output (MIMO) arrays and dual-function radar-communication techniques. We formulate a multi-objective optimization problem to jointly consider the performance of multi-UT MIMO radar beampattern design and computation offloading energy consumption while jointly optimizing individual transmit precoding for radar and communication and computation resource allocation. To address the optimization problem, we first decompose the it into three subproblems and adopt an iterative optimization algorithm. Specifically, quadratic transform based fractional programming methods are used to minimize the offloading energy consumption. The design objective of MIMO radar beampattern is handled by the first-order Taylor expansion. Transmit precoding is designed to optimize radar sensing and computation task offloading. The local and edge computation resource allocation are obtained in closed-form. Numerical results verify the effectiveness of the proposed algorithms. The proposed CRMEC architecture can generate the desired multi-UT MIMO radar beampattern and perform computation offloading simultaneously.

Dual-Function Frequency-Hopping MIMO Radar System With CSK Signaling

We consider a dual-function radar communication (DFRC) system employing frequency hopping (FH) radar waveforms. Each communication symbol is represented by a phase-modulated pulse sequence that multiplies the radar hops in fast-time and transmitted from a multiple-input multiple-output radar platform. In this respect, the DFRC system considered follows the code-shift keying (CSK) signal embedding strategy. The phase modulations include phase-shift keying (PSK), derivative PSK, and continuous phase modulation. The CSK pulse sequences and the FH code are jointly designed to reduce range sidelobe levels (RSLs) and combat range sidelobes modulation. It is shown that the joint optimization using the genetic algorithm yields desired CSK sequences and FH code matrix with less computational complexity compared to the exhaustive search algorithm. The power spectral density and detection performance of various DFRC systems are analyzed, underscoring the tradeoff between RSLs and spectral sidelobe levels. The proposed DFRC system with optimum phase sequences and hopping code achieves high data communication rates by permitting frequencies to be reused in the radar hops.

Joint Waveform and Filter Designs for STAP-SLP-Based MIMO-DFRC Systems

Dual-function radar-communication (DFRC), which can simultaneously perform both radar and communication functionalities using the same hardware platform, spectral resource and transmit waveform, is a promising technique for realizing integrated sensing and communication (ISAC). Spacetime adaptive processing (STAP) in multi-antenna radar systems is the primary tool for detecting moving targets in the presence of strong clutter. The idea of joint spatial-temporal optimization in STAP-based radar systems is consistent with the concept of symbol-level precoding (SLP) for multi-input multi-output (MIMO) communications, which optimizes the transmit waveform for each of the transmitted symbols. In this paper, we combine STAP and SLP and propose a novel STAP-SLP-based DFRC system that enjoys the advantages of both techniques. The radar output signal-to-interference-plus-noise ratio (SINR) is maximized by jointly optimizing the transmit waveform and receive filter, while satisfying the communication quality-of-service (QoS) constraint and various waveform constraints including constant-modulus, similarity and peak-to-average power ratio (PAPR). An efficient algorithm framework based on majorization-minimization (MM) and nonlinear equality constrained alternative direction method of multipliers (neADMM) methods is proposed to solve these complicated non-convex optimization problems. Simulation results verify the effectiveness of the proposed STAP-SLP-based MIMO-DRFC scheme and the associate algorithms.

MIMO OFDM Dual-Function Radar-Communication Under Error Rate and Beampattern Constraints

In this work we consider a multiple-input multiple-output (MIMO) dual-function radar-communication (DFRC) system, which senses multiple spatial directions and serves multiple users. Upon resorting to an orthogonal frequency division multiplexing (OFDM) transmission format and a differential phase shift keying (DPSK) modulation, we study the design of the radiated waveforms and of the receive filters employed by the radar and the users. The approach is communication-centric, in the sense that a radar-oriented objective is optimized under constraints on the average transmit power, the power leakage towards specific directions, and the error rate of each user, thus safeguarding the communication quality of service (QoS). We adopt a unified design approach allowing a broad family of radar objectives, including both estimation- and detection-oriented merit functions. We devise a suboptimal solution based on alternating optimization of the involved variables, a convex restriction of the feasible search set, and minorization-maximization, offering a single algorithm for all of the radar merit functions in the considered family. Finally, the performance is inspected through numerical examples.