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The sharing waveform based integrated radar and communication (IRC) has great potential to apply in Internet of Things (IoT) devices due to its equipment miniaturizing and high efficiency of spectrum and energy, etc. However, the sharing waveform scheme demands a trade-off between radar and communication performances. In this paper, we focus on the design of multiple phase shift keying (MPSK) based linear frequency modulation (LFM) sharing waveform by exploring the trade-off among energy leakage, peak-to-side lobe ratio (PSLR) and symbol rate. First, we derive the energy leakage and PSLR with respect to the symbol rate. Next, a novel LFM-MPSK waveform design is carried out by formulating a communication frame based optimization, where the symbol rate is maximized with the constraints of the energy leakage and PSLR. Then, a branch and reduce algorithm is proposed to solve the optimization. Compared with the conventional one, the proposed LFM-MPSK waveform has a higher symbol rate with the same energy leakage and PSLR. Besides, the proposed waveform design alleviates the difficulty of the trade-off among the energy leakage, PSLR and symbol rate due to more Pareto solutions. Finally, all the analytical results are validated by simulations.

In current wireless communication and electronic systems, digital signals and electromagnetic (EM) radiation are processed by different modules. Here, we propose a mechanism to fuse the modulation of digital signals and the manipulation of EM radiation on a single programmable metasurface. The programmable metasurface consists of massive subwavelength-scale digital coding elements. A set of digital states of all elements forms simultaneous digital information roles for modulation and the wave-control sequence code of the programmable metasurface. By designing digital coding sequences in the spatial and temporal domains, the digital information and far-field patterns of the programmable metasurface can be programmed simultaneously and instantly in desired ways. For the experimental demonstration of the mechanism, we present a programmable wireless communication system. The same system can realize transmissions of digital information in single-channel modes with beam-steerable capability and multichannel modes with multiple independent information. The measured results show the excellent performance of the programmable system. This work provides excellent prospects for applications in fifth- or sixth-generation wireless communications and modern intelligent platforms for unmanned aircrafts and vehicles.

Femtocell access point gives an efficient solution to furnish peak data rates in indoor wireless access systems. Propagation of the signal will get up-shot because of few considerations in advanced communication appliances. The maximum simulation reflection coefficient ( S 11 ) of proposed antenna is 45.12 dB, directivity is 6.54 dBi with the efficiency of 60% and at 60 GHz, and the measurement value of 36.35 is observed which covers the complete RADAR applications which have an unlicensed bandwidth. The proposed tree-shaped unequal slotted antenna is well suited for millimeter-wave applications because of its good bandwidth and less dimension.

The advantages of optical fiber as a transmission medium for microwave signals have led to an increasing interest in implementing RF photonic links in radar frontends. Many critical radar applications, such as those found in modern military systems, often require a large spur-free dynamic range (SFDR) that is beyond the reach of conventional intensity modulated-direct detection (IM-DD) fiber-optic links. For a solution, we propose a coherent amplitude-modulated link with optical down-conversion that can achieve high dynamic range by employing a receiver with balanced detection and digital linearization. The link is presented along with experimental validation. The measurements show notable dynamic range enhancements over prior arts in down-conversion RF photonic links.

Electronic beam steering is an essential feature of state-of-the-art radar systems. Conventional phased array (PA) radars with fixed carrier frequencies are well-known for electronically steering their beam with high directivity. However, the resulting beampattern is angle-dependent but range-independent. Recently, a new electronic beam steering concept, referred to as frequency diverse array (FDA) radar, has attracted increasing attention due to its unique range-angle dependent beampattern. More importantly, the FDA radar employs a small frequency increment across the array elements to achieve beam steering as a function of angle, range, and time. In this paper, we review the development of the FDA radar since its inception in 2006. Since the frequency offset attaches great importance in FDAs to determine the beampattern shape, initially much of the research and development were focused on designing the optimal frequency offsets for improved beampattern synthesis. Specifically, we analyze characteristics of the FDA beampattern synthesis using various frequency offsets. In addition to analyzing the FDA beampattern characteristics, this study also focuses on the neglected propagation process of the transmitted signals in the early FDA literature, and discuss the time-variant perspective of FDA beampatterns. Furthermore, FDA can also play a significant role in wireless communications, owing to its potential advantages over the conventional PAs. Therefore, we highlight its potential applications in wireless communication systems. Numerical simulations are implemented to illustrate the FDA beampattern characteristics with various frequency offset functions.

Robust channel estimation in time-varying channels is used to guarantee the quality of communication services, especially for Vehicle-to-Everything (V2X) scenarios. To improve the channel estimation accuracy and reduce the pilot overhead, multi-input multi-output (MIMO) radar is deployed to assist millimeter wave (mmWave) channel estimation. In this paper, we propose a MIMO radar aided channel estimation scheme using deep learning (DL) for the uplink mmWave multiuser (MU)-MIMO communications. To allocate pilot resources reasonably, we design a transmission frame structure of joint radar module and communication module, which divides the estimation scheme into two stages, i.e., the arrival/departure (AoA/AoDs) estimation stage and the gain estimation stage. In view of the imperfections of array elements in practice, we propose an AoA/AoDs estimation algorithm based on subspace reconstruction in the AoA/AoDs estimation stage named two-step angle estimation (TSAE) algorithm. In the gain estimation stage, a DL based channel gain estimator is designed. An autoencoder combined with residual structure named residual denoising autoencoder (RDAE) is proposed to eliminate the noise on wireless signals, which is passed into the least square (LS) estimation module to obtain gains. Simulation results demonstrate that the MIMO radar aided and DL-based channel estimator provides the efficient estimation performance of the high-mobility mmWave channel with fewer training resources.

This work presents a cross correlation-based true-speed-over-ground estimation approach based on experiences from an earlier system. The radar system parameters as well as the antenna configuration were adapted to fit the requirements of the presented application. Also, challenges regarding the previously limited velocity range are addressed and an appropriate solution is proposed. The entire system was thoroughly tested in a train scenario over a wide range of velocities. Very promising measurement results are presented and compared to related approaches.

Wireless communications and sensing at terahertz (THz) band are increasingly investigated as promising short-range technologies because of the availability of high operational bandwidth at THz. In order to address the extremely high attenuation at THz, ultra-massive multiple-input multiple-output (MIMO) antenna systems have been proposed for THz communications to compensate propagation losses. However, the cost and power associated with fully digital beamformers of these huge antenna arrays are prohibitive. In this paper, we develop wideband hybrid beamformers based on both model-based and model-free techniques for a new group-of-subarrays (GoSA) ultra-massive MIMO structure in low-THz band. Further, driven by the recent developments to save the spectrum, we propose beamformers for a joint ultra-massive MIMO radar-communications system, wherein the base station serves multi-antenna user equipment (RX), and tracks radar targets by generating multiple beams toward both RX and the targets. We formulate the GoSA beamformer design as an optimization problem to provide a trade-off between the unconstrained communications beamformers and the desired radar beamformers. To mitigate the beam split effect at THz band arising from frequency-independent analog beamformers, we propose a phase correction technique to align the beams of multiple subcarriers toward a single physical direction. To further decrease the ultra-massive MIMO computational complexity and enhance robustness, we also implement deep learning solutions to the proposed model-based hybrid beamformers. Numerical experiments demonstrate that both techniques outperform the conventional approaches in terms of spectral efficiency and radar beampatterns, as well as exhibiting less hardware cost and computation time., 17pages14figures. Accepted in IEEE Journal of Selected Topics in Signal Processing

Multiple-input multiple-output (MIMO) has been used in wireless communications to increase data rates via multiplexing or improve performance via diversity. Additionally, in radar systems, MIMO promises improved parameter identifiability and target resolution. Frequency diverse (FD)-MIMO radar can effectively distinguish targets that are closely spaced in the same angle cell by exploiting its range-angle-dependent transmit beamform. Therefore, in this paper, we first propose an integrated waveform design by embedding weighted, phase-modulated communication signals in the FD-MIMO radar waveform. Then, we derive the Cramer-Rao lower bound (CRLB) of the location estimation and analyze the communication performance achieved when the communication receiver extracts information from the integrated signals. Next, transmit beamforming is optimized to achieve the best tradeoff between the radar and communication performances of the system. Due to the nonconvexity of the optimization problem, we apply sequential parametric convex approximation (SPCA) and semidefinite relaxation (SDR) methods to solve the problem. The simulation results reveal the effects of some parameters, such as the frequency interval, symbol period, and communication symbol sequence, on radar and communication performance and demonstrate the tradeoff between radar and communication obtained by optimizing the transmit beamforming vector.

Microwave photonic (MWP) radar has the advantages of generating and processing wide bandwidth microwave signals, reconfigurability, high immunity to electromagnetic interference compared to microwave electronic radar. It has the potential to be used in applications such as intelligent autonomous and cyber-physical systems. Recent advances in microwave photonic technology led to the generation, fast processing, and control of broadband signals. Because of the advancements in photonic technologies, next-generation microwave photonic radar is becoming more prominent. This article reviews the most recent advancements and future directions in MWP radars. This review article overviews the different components of microwave photonic radar, different design challenges, and issues pertaining to it. We present a comparative study of different MWP radars on different applications. It also discusses possible future research directions of MWP radar.

The detection and tracking performance of passive radar systems can be enhanced by exploiting multiple emitters and one receiver site by allowing for multiple bistatic geometries. This article investigates the measurement accuracy of passive radar systems that employ the advanced television system committee (ATSC 1.0) signal as a signal of opportunity. The monostatic and bistatic modified Cramer–Rao lower bound for the range and velocity measurements are derived as a quantitative way to evaluate the performance variation when exploiting multiple transmitters. The effect of 3D target position on the signal-to-noise ratio, with respect to stationary transmitters and receiver, is highlighted. Furthermore, signal-to-interference-and-noise ratio modeling is included by considering the direct signal interference suppression performance for a set of transmitters. An example in Columbus, Ohio, for a single receiver and multiple digital television transmitters that are spatially distributed is presented to find the optimal emitter that yields the best range and velocity measurement in the analyzed area. Target-tracking experiments show an agreement between the optimal emitter map and the tracking quality for the set of transmitters.

Accurate and stable time and frequency transfer (TFT) is typically required in distributed sensing. While this has historically been a limiting factor in the design of netted radars, the rise of modern TFT techniques has paved the way to nanosecond level time accuracy, absolute phase synchronization, and sub-Hertz frequency accuracy. In particular, netted systems composed of mobile nodes have benefited immensely from TFT based on global navigation satellite systems (GNSS). However, GNSS systems are liable to denial of service interruption. This article demonstrates the use of a fiber-optic White Rabbit (WR) network in an operational multistatic radar—NeXtRAD, and directly compares the results to one-way multichannel GPS disciplined oscillators acting under common-view TFT.

Photonics-based radar technologies can implement better performance in some main functionalities of the radar systems. The outstanding question is whether these technologies are suitable for the practical application of modern or future radars. Here, we comprehensively analyze key radar parameters and summarize the requirements for the practical applications. Then, we present the corresponding photonics-based technologies capable of meeting actual radar needs. From the aspect of radar signal requirements, we compare the typical microwave photonic technologies for the radar signal generation at this stage and guide the improvement direction. The paper reviews the photonics-based radar signal generation based on a phase-locked dual-comb in detail. Further, the innovative and scalable capabilities of the scheme are presented, including the multi-band radar signal generation for multiple functions radar, and high accuracy beamforming for advanced active phased array radar. The enhanced performances include more flexible carrier frequency, large modulation bandwidth, tunable pulse duration, configurable pulse repetition frequency, full coherence, and continuous phase shift with ultra-high accuracy. The proposed novel photonics-based technology will greatly push forward the application of microwave photonics technologies in actual radar systems.

The increasing bandwidth requirement of new wireless applications has lead to standardization of the millimeter wave spectrum for high-speed wireless communication. The millimeter wave spectrum is part of 5G and covers frequencies between 30 and 300 GHz corresponding to wavelengths ranging from 10 to 1 mm. Although millimeter wave is often considered as a communication medium, it has also proved to be an excellent 'sensor', thanks to its narrow beams, operation across a wide bandwidth, and interaction with atmospheric constituents. In this paper, which is to the best of our knowledge the first review that completely covers millimeter wave sensing application pipelines, we provide a comprehensive overview and analysis of different basic application pipeline building blocks, including hardware, algorithms, analytical models, and model evaluation techniques. The review also provides a taxonomy that highlights different millimeter wave sensing application domains. By performing a thorough analysis, complying with the systematic literature review methodology and reviewing 165 papers, we not only extend previous investigations focused only on communication aspects of the millimeter wave technology and using millimeter wave technology for active imaging, but also highlight scientific and technological challenges and trends, and provide a future perspective for applications of millimeter wave as a sensing technology., 36 pages, submitted to IEEE Sensors Journal

Unified waveform design for automotive joint radar-communications (JRC) leverages the scarce spectrum efficiently and has become a key topic for investigation of late. Designing such a waveform necessitates meeting the requirements of both systems, thereby making it a challenging task. The contribution of this paper is to formulate the JRC design problem into an optimization problem and propose an algorithm to maximize the signal-to-clutter-plus-noise-ratio (SCNR) of radar system and signal-to-noise-ratio (SNR) at communicating vehicle, simultaneously. Central to this are the exploitation of the communication link to acquire environment/ channel information and enhance radar tasks, flexibility to impart trade-off between the two systems during design as well the formulation of the optimization problem to include sidelobe constraints and yield solutions robust to Doppler shifts. The designed waveforms exhibit enhanced radar performance in terms of probability of detection and communication performance in terms of bit error rate (BER), while taking into account the trade-off between two systems. The numerical simulations corroborate the claim of optimized performance with environment/ channel information, ease of effecting trade-off and the use of design flexibility.

Fast Fourier transform (FFT) is one of the fundamental signal processing algorithms widely used in radar applications. The Radon–Fourier transform (RFT) can be seen as an FFT generalization that can overcome some of its limitations. This work derives three spectral RFT (SRFT) based approaches to address major challenges of the multiple-input multiple-output automotive radars. First, two SRFT-based approaches are derived to increase maximal target detection range by mitigation of target migration in range and direction of arrival, jointly, and by multidwell integration processing, which increases the radar coherent integration time without compromising its detection update rate. Next, SRFT-based approach is proposed to address the cluster-to-track association problem that arises in multiple distributed target tracking scenarios that characterize automotive radar operation in dense urban environments.

Recently, the photonics-radar technology comes out as an attractive candidate in the arena of smart autonomous transportation, surveillance, and navigation-related applications owing to provide wide-spectra to attain improved and precise radar-resolutions. On the other hand, microwave radars, due to limited bandwidth, are incapable of coping with the demands of next-generation radar technology. Moreover, the atmospheric fluctuations become more prominent at higher frequencies and affect the radar’s performance significantly. Subsequently, the authors develop a 2 × 2 multi-input multi-output (MIMO) employed linear frequency-modulated continuous-wave coherent photonic-radar system (MIMO-Co-PHRAD) using OptiSystem™ and MATLAB™ to attain a prolonged detection-range with an enhanced visibility. The developed MIMO-Co-PHRAD is investigated with heterodyne- and homodyne-detection approaches under weak-to-strong regimes of the atmospheric fluctuations like Rain and Fog. A comparison is also drawn for both the demonstrated MIMO-equipped laser-driven coherent photonic-radar systems. The performance of both the developed MIMO-Co-PHRAD systems is evaluated by measuring the intensity of reflected-echoes, signal-to-noise ratio, and range-Doppler patterns. A contrast with the single-input single-output coherent photonic-radar (SISO-Co-PHRAD) is also established to validate the robustness of the demonstrated MIMO-Co-PHRAD.

In the present century, digital signal processing (DSP) approaches are considered to be one of the most powerful technologies which may shape the science and technology in coming decades. From 1970 onwards, a drastic revolution took place in a wider domain of DSP which has made it popular in several studies such as radar and sonar signal processing, digital televisions, wireless communication scenarios and other multimedia setup etc. Digital filters form the backbone of this DSP architecture and in point of fact the field of digital filter design has drawn justified recognition from the researchers throughout the world for the last 50 years. In connection to this, thousands of research articles may be found from the literature which had extensively addressed on the design of such filters. In order to meet the requirement of narrow transition-band, finite impulse response (FIR) filters are commonly assumed to be of higher order and accordingly it significantly enhances computational complexity. In regard to this, construction of hardware efficient digital filters had drawn significant consideration which aims to include minimum hardware elements during its application and consequently consumes less power. This review paper illustrates various techniques for the implementation of hardware efficient narrow transition-band FIR filter and investigates a number of favourable attributes which are capable in sustaining the stringent requirements of communication standards. A good number of relevant articles are taken from the literature so as to make a robust and complete review.

The use of chipless RFID is rapidly growing with applications for both identification and sensing purposes. In existing chipless RFID technology for identification purposes, radar cross-section (RCS) vs. frequency information is often used to create a unique identification (binary) code of 1's and 0's. In contrast, for purposes such as environmental sensing (i.e., temperature, humidity, gas concentration, etc.), a shift in the RCS frequency response is then correlated to the sought-for information. In this paper the utility of embedding chipless RFID sensors in various dielectric materials is investigated, where changes in the material properties cause a shift in the RFID frequency response and the changes are translated to a change in its original binary code. To illustrate the efficacy of this unique technique for materials characterization, electromagnetic simulations and measurements were conducted, the result of which are presented in this paper.

In-band full duplex (IBFD) radio represents one of the key technologies for future wireless communication and radar applications. A major challenge of this technology is to mitigate the strong self-interfer-ence (SI) so that the residual SI level falls below the receiver's noise floor. Radio frequency (RF) self-inter-ference cancellation (SIC) is essential for preventing an IBFD receiver from becoming saturated by the SI. We commence with an in-depth review of the promising analog least mean square (ALMS) adaptive filtering architecture, conceived for RF SIC in the IBFD radio RF front-end. The cancellation circuits employing this architecture can be implemented purely by analog components without any involvement of more power-thirsty digital signal processing. The behaviors, performance, and implementation of the ALMS loop are presented. Finally, their applications in various IBFD radios are discussed, and future research directions are provided.

An ultra-wideband chaotic radar with wireless synchronization command is proposed and experimentally demonstrated for target localization and tracking. This radar uses the wideband chaotic pulse position modulation (CPPM) signal as the probe signal and the radar structure of single-transmitting-dual-receiving. The echo signal scattered from a target is collected by two receivers. The target is located and tracked accurately in two-dimensional space using the signal processing scheme. In particular, the radar receivers can directly generate the CPPM reference signals through a wireless synchronization command, so that the transceivers can be physically separated without cable or optical fiber connection. Experimental results demonstrate the proposed chaotic radar can locate and track the target accurately. A localization error of 11 cm and a detection resolution of 17 cm can be both achieved. Moreover, this radar possesses the excellent immune performance to the external electromagnetic interferences, which makes it suitable in the complex electromagnetic environment caused by the cooperative work of multiple radars.

An adaptive ranging technique for maintaining high-accuracy ranging between nodes in coherent distributed antenna arrays is presented. Coherent distributed antenna arrays are networks of wireless systems coordinated coherently at the level of the wavelength of the wireless signal. Enabling coherent operation between separate mobile nodes for active and passive microwave remote sensing requires accurate knowledge of the relative positions of the nodes in the array. In this article, a novel adaptive ranging technique based on the near-optimal waveform for high-accuracy ranging, a two-tone waveform, is designed and demonstrated in software-defined radio platforms representing array nodes. Ranging accuracy is dependent on both signal-to-noise ratio and the separation of the two tones in the waveform; however, in realistic environments, factors such as attenuation or antenna misalignment are not easily predicted, which can lead to degradation of the ranging measurement. Selecting one appropriate waveform for range measurements is, thus, not feasible unless the bandwidth assigned to it is always higher than required for the needed range accuracy. Rather than allocating such an unnecessarily wide bandwidth, this article presents a controller that regulates the spectral resources adaptively to meet the desired reference accuracy while minimizing the total occupied bandwidth. The controller continuously monitors the statistical parameters of the received signal, such as signal-to-noise ratio, in a perception stage and adapts the spectral characteristics of the transmitted waveform in an action stage. The adaptive action, based on a Cramer–Rao lower bound analysis, maintains the signal statistical characteristics below a specified bound to maintain high coherent gain. Experimental results demonstrate the ability to maintain ranging standard deviation of 1.5 mm (standard deviation of time delay estimates equals $10^{-11}$ s), which yields 90% or more of the possible achievable coherent gain at carrier frequencies up to 13.33 GHz.

Interference avoidance will be an essential feature of wireless communication systems in the future. Interference avoidance to narrowband users is particularly difficult with Orthogonal Frequency Division Multiplexing (OFDM) due to the side lobes of the subcarriers. Spectrum-nulling algorithms based on cancellation signals have been studied in the literature. In this letter, we describe a general technique to design spectrum nulls for arbitrary signal and canceler bases. Appropriately chosen nonorthogonal canceler bases can result in data rate- and energy-efficient design of spectrum nulls. We also describe an iterative algorithm to cancel the resulting inter-carrier interference at the receiver. Spectrum nulls that meet requirements for avoiding interference to weather radars in the 5 GHz band can be designed using this technique. Bit error rates have been evaluated using simulations.

In this paper, we investigate the hybrid beamforming problem in joint radar-communications at terahertz (THz) bands. In order to address the extremely high attenuation at THz, ultra-massive multiple-input multiple-output (UM-MIMO) antenna systems have been proposed for THz communications to compensate propagation losses. Further, we propose a new group-of-subarrays (GoSA) UM-MIMO structure to reduce the hardware cost. We formulate the GoSA beamformer design as an optimization problem to provide a trade-off between the unconstrained communications beamformers and the desired radar beamformers. Numerical experiments demonstrate that the proposed approach outperforms the conventional approaches in terms of spectral efficiency and hardware costs.

We compute the minimum cost for an optimal quantum radar, and we compare it with the cost of actual real world classical radars as a function of range. Our calculations show that the minimum cost quantum radar at X-band is many orders of magnitude more expensive than the corresponding classical radar, even assuming the most optimistic wideband-phased array radar architecture. We also assume that the quantum radar is optimal; that is, the effective signal-to-noise ratio is 6 dB better than for a classical radar with the same transmit power and bandwidth at low photon flux per mode. Finally, we discuss many practical issues and potential solutions.

Compared with conventional phased array radar, the collocated multiple-input multiple-out (C-MIMO) radar is envisioned to offer greater freedom in waveform design and can simultaneously manage different beams to track multiple targets in the simultaneous multi-beam (SM) working mode. In this study, aiming at the multiple targets tracking (MTT) problem, a joint beam selection integrated with power and bandwidth allocation (JSPBA) scheme for the C-MIMO radar is proposed in the SM mode. By incorporating the modified particle filter, the predicted conditional Cramer–Rao lower bound (PC-CRLB) is calculated, which gives a measure of the best achievable performance for targets tracking. Then, the optimisation model is established with the aim of improving the worst case of PC-CRLB to achieve better performance of the worst-case tracking. Next, a three-step solution method is proposed to solve the JSPBA problem by converting the non-convex problem into a series of convex problems. At last, after the solutions are fed back to the control centre to guide the beam generation in the next tracking epoch, a cognitive tracking system is established. Simulation results confirm the superiority of the proposed method in improving the MTT performance in C-MIMO radar system.

Spectrum sharing of wireless vehicle-to-vehicle (V2V) communication and automotive radar in intelligent transportation systems (ITS) can provide higher spectrum utilization efficiency. However, spectrum sharing between two systems might bring severe interference, which needs to be well solved. To address the communication-radar spectrum sharing (CRSS) and inter-system interference issue, we first model the radar interference estimation as an off-grid compressed sensing problem. Then, we propose an interference cancellation algorithm based on the atomic norm (AN) minimization theory. Simulation results show that the proposed algorithm facilitates the coexistence between radar and communication and improves the V2V communication performance efficiently in the presence of automotive radar interference.

As the only method for all-weather, all-time and long-distance target detection and recognition, radar has been intensively studied since it was invented, and is considered as an essential sensor for future intelligent society. In the past few decades, great efforts were devoted to improving radar's functionality, precision, and response time, of which the key is to generate, control and process a wideband signal with high speed. Thanks to the broad bandwidth, flat response, low loss transmission, multidimensional multiplexing, ultrafast analog signal processing and electromagnetic interference immunity provided by modern photonics, implementation of the radar in the optical domain can achieve better performance in terms of resolution, coverage, and speed which would be difficult (if not impossible) to implement using traditional, even state-of-the-art electronics. In this tutorial, we overview the distinct features of microwave photonics and some key microwave photonic technologies that are currently known to be attractive for radars. System architectures and their performance that may interest the radar society are emphasized. Emerging technologies in this area and possible future research directions are discussed.

The interference between wind turbine generators and radar is now being considered as one of the major deterrents towards seeking clearance for new wind energy project. The windfarm developers have to seek clearance from Civil Air Traffic Control and Defence Department certifying that the windfarms will not create interference with radars. The tower of wind turbine generator along with blades presents a large radar cross section to radars, thus creating static clutter; moreover, rotation of wind turbine generator blades creates Doppler ambiguities which confuse radar operators. Many radar designers have proposed mitigation techniques to overcome this issue; however, each technique has its own limitation. The study takes a two-pronged approach to address the issue of wind turbine generator static clutter due to tower and blades and the resolution of Doppler ambiguities through signal processing–based mitigation techniques. In addition, the study also suggests the use of micro-Doppler techniques for signature identification of wind turbine generator blades for eliminating their effect during the radar signal processing. The article presents a step-by-step mitigation technique to resolve the wind turbine generator and radar interference issue.

Over the past few years, Radio Frequency IDentification (RFID) has stridden significantly due to its adoption in many business and daily life activities. RFID empowers end-to-end and item-by-item visibility, letting the customers or decision-makers effectively trail the personnel and resources for improved management. Significant research and development in this area have transformed the inexpensive, miniaturized technology of RFIDs without chip inside. Chipless Radio Frequency IDentification (CRFID) is a unique wireless technology based on radar principle to sense, identify, and track the objects. CRFIDs are simplified and miniaturized tags of traditional RFID, which can widely be used in small and cheap objects/applications in our daily life. This paper reviews the definition, principle, and most recent development in CRFIDs. Based on the reported researches, the ElectroMagnetic Spectrum (EMS) method is typical, which has been concerned by many RFID researchers. Therefore, this paper reviews different types of EMS CRFID tag and classifies these tags based on structure design emphasizing their significant geometries in comparison with performance parameters. Antenna and coding methods of the EMS CRFID are also elaborated, contrasting the tag capacity and coding performance. Finally, we briefly summarize the challenges and limitations in this emerging field and look forward to the prospects of future CRFID.

This article presents a design for implementing an ultrawideband (UWB) software-defined radar (SDRadar) using a bandwidth reconstruction technique, called frequency stacking, for a stepped frequency signal to create a synthetic wideband waveform (SWW). Practical methods of overcoming traditional limitations of SDRadar and stepped chirp radar are introduced, and the performance is demonstrated using a commercial battery-powered universal software radio peripheral (USRP) software-defined radio (SDR). Application-specific considerations are made and performance tradeoffs are demonstrated. Furthermore, the method is shown to be the coherence solution for otherwise noncoherent low-cost communications’ SDR systems. The proposed design has multiple applications in low-cost, reconfigurable ground-penetrating radar (GPR) and small unmanned aerial vehicle (UAV) synthetic aperture radar (SAR) platforms.

The use of existing hardware (e.g. software defined radio) above given frequency range and resulting undersampling necessity is and will represent very often practical question. In this article our concern is to describe most critical details of the radar digital signal processing modelling, micro-Doppler detection of small unmanned aerial vehicle motion in particular. Mathematical model of the radar echo signal generation, undersampling theoretical analysis and preconditions definition for digital signal processing model in MATLAB-Simulink represents the core work. This step is very important for further programming - software implementation with software defined radio. The digital signal processing model as the output shows practical limits that demonstrates realistic micro-Doppler detection of small unmanned aerial vehicle motion. Theoretical results and practical example can be used in other software defined radio applications with respect to given practical hardware parameters.

Photonics-based radar expands the bandwidth of traditional radars and enhances the radar range resolution. This makes it possible to recognize small-size targets using the high resolution range profiles (HRRPs) acquired by a photonics-based broadband radar. In this paper, we investigate the performance of small target recognition using HRRPs of a photonics-based radar with a bandwidth of 8 GHz (28-36 GHz), which is built based on photonic frequency multiplication and frequency mixing. A convolutional neural network (CNN) is used to extract features of the HRRPs and classify the targets. In the experiment, recognition of four types of small-size targets is demonstrated with an accuracy of 97.16%, which is higher than target recognition using a 77-GHz electronic radar by 31.57% (2-GHz bandwidth) and 8.37% (4 GHz-bandwidth), respectively. Besides the accuracy, target recognition with photonics-based radar HRRPs is proved to have good generalization capability and stable performance. Therefore, photonics-based radar provides an efficient solution to small target recognition with one-dimension HRRPs, which is expected to find import applications in air defense, security check, and intelligent transportation.

Based on the long-known and well-described radar design techniques, this paper introduces a four-channel FMCW (Frequency Modulated Continuous Wave) radar system built from COTS (Commercial-Off-The-Shelf) elements for imaging purposes. Starting with a short historical view of the matter in question, general advantages, and motivations for the developed solution, the article presents the theory of operation of FMCW radar, as well as the construction of the analog part, the digital part, and the developed software. The most fundamental signal processing algorithms are also covered as a starting point for more advanced techniques, which may be further implemented. The developed radar system allows for the use of wide bandwidth - up to 1 GHz - which gives resolutions up to tenths of centimeters, and a high rate of pulse repetition frequency (8 kHz), which gives the opportunity to detect high-speed objects. The paper does not aim to provide any scientific novelties but rather to present the possibility of creating a simple and effective solution.

A full measurement system for automotive radar at 77GHz is presented in this study. Radar applications require particularly outstanding quiet-zone performance for its measurement uncertainty and calibration, especially at millimeter wave (mmWave) frequency range. Therefore, this system employs compact antenna test range (CATR) to generate its quiet zone. In addition, a Radar Test Simulator (RTS) is used to test DUT with broad ranges of distance and speed range. Software is also developed to coordinate with the hardware so the system is ready for commercial automotive radar test and calibration. An example design is also proposed in this paper to explain the whole system configuration and performance of a practical automotive radar test system.

In this article, we study the joint communication and sensing (JCAS) paradigm in the context of millimeter-wave (mm-wave) mobile communication networks. We specifically address the JCAS challenges stemming from the full-duplex operation and from the co-existence of multiple simultaneous beams for communications and sensing purposes. To this end, we first formulate and solve beamforming optimization problems for hybrid beamforming based multiuser multiple-input and multiple-output JCAS systems. The cost function to be maximized is the beamformed power at the sensing direction while constraining the beamformed power at the communications directions, suppressing interuser interference and cancelling full-duplexing related self-interference (SI). We then also propose new transmitter and receiver beamforming solutions for purely analog beamforming based JCAS systems that maximize the beamforming gain at the sensing direction while controlling the beamformed power at the communications direction(s), cancelling the SI as well as eliminating the potential reflection from the communication direction and optimizing the combined radar pattern (CRP). Both closed-form and numerical optimization based formulations are provided. We analyze and evaluate the performance through extensive simulations, and show that substantial gains and benefits in terms of radar transmit gain, CRP, and SI suppression can be achieved with the proposed beamforming methods.

Non-touch interface technology will be used more and more in future electronic systems. This paper describes the development of a novel sensor element for such interfaces. In this work, we apply a systematic approach, the M3-approach (methodologies, models, measures), to design miniaturized, scalable and low-cost 60 GHz MIMO (Multiple Input Multiple Output) radar front-ends for the integration of a novel non-touch human interface into a table. The packaging technology applied for the development of this radar module is suitable for mass production. The complete application of the M3-approach requires the implementation of three key steps, namely methodologies, models and measures. However, in this paper, we focus on the first two steps (i.e., methodologies and models) and describe these steps in detail.

In this paper, we propose a deep learning-based indoor two-dimensional (2D) localization scheme using a 24 GHz frequency-modulated continuous wave (FMCW) radar. In the proposed scheme, deep neural network and convolutional neural network (CNN) models that use different numbers of FMCW radars were employed to overcome the limitations of the conventional 2D localization scheme that is based on multilateration methods. The performance of the proposed scheme was evaluated experimentally and compared with the conventional scheme under the same conditions. According to the results, the 2D location of the target could be estimated with a proposed single radar scheme, whereas two FMCW radars were required by the conventional scheme. Furthermore, the proposed CNN scheme with two FMCW radars produced an average localization error of 0.23 m, while the error of the conventional scheme with two FMCW radars was 0.53 m.

In recent years, there have been plenty of demands and growth in the autonomous vehicle industry, and thus, challenges of designing highly efficient photonic radars that can detect and range any target with the resolution of a few centimeters have been encountered. The existing radar technology is unable to meet such requirements due to limitations on available bandwidth. Another issue is to consider strong attenuation while working under diverse atmospheric conditions at higher frequencies. The proposed model of photonic radar is developed considering these requirements and challenges using the frequency-modulated direct detection technique and considering a free-space range of 750 m. The result depicts improved range detection in terms of received power and an acceptable signal-to-noise ratio and range under adverse climatic situations.

An inherent disadvantage of a Microstrip Patch Antenna (MPA) is its narrow bandwidth and low gain. There are various techniques in the market that either enhances gain or bandwidth of the MPA. The proposed system uses a novel technique which proves to enhance both the bandwidth, as well as the gain up to a great extent, simultaneously. We have tried to overcome these limitations by inserting slots in the proposed Rectangular Microstrip Patch Antenna (RMPA), also known as the slotted array technique. The proposed antenna has been designed for an operating frequency of 9 GHz which lies in the X-band of an electromagnetic system. It has been simulated over an RT Roger/duroid 5880 material that has a dielectric constant of 2.2, using HFSS software. It was observed that the RMPA has a bandwidth of 425.2 MHz, whereas, a bandwidth of 920 MHz has been achieved for slotted RMPA, that means 494.8 MHz of bandwidth enhancement. In addition to this, a gain of 6.92 dB has been achieved for RMPA, whereas, by introducing slots, the gain becomes 19.88 dB, i.e., an enhanced value of 12.96 dB has been achieved. This antenna can be used in various wireless applications such as: Wi-Fi, Bluetooth, and wireless LAN, and satellite and radar communication.

In recent years, software defined radio and digital signal processing have been widely used in communication and radar. As a result, the hardware and RF front-end for radar and wireless communication tends to be similar. Thus, using the same RF and hardware platform for joint radar-communication becomes viable. Joint radar-communication would bring more efficient plan and usage for the radio spectral resource. Furthermore, it could enable new applications that require information exchange and precise localization at the same time. In this paper, cyclic prefixed single carrier (CP-SC) and its variations are chosen as the waveforms for joint radar-communication. CP-SC waveform and its variations are popular in wireless communication and have been chosen by a few standards like IEEE 802.11ad and LTE-advanced. Efficient algorithms are proposed to use such waveforms for range and speed detection/estimation of targets. The proposed algorithms are derived from the maximum likelihood (ML) principle and have low computational complexity. Simulations show that the estimation performance of the proposed method is almost the same as that of ML and is much better than that of the channel estimation based method.

Coexisting radar and communication (CRC) systems on the same spectrum band have been recently recognized as a promising approach to solve the spectrum scarcity problem. Additionally, with the new requirements of achieving higher energy efficiency and restoring the consumed power, an initiative has been exploited to embed both information and energy within the same signal. Motivated by that, this paper presents a unified model to implement the concept of simultaneous wireless information and power transfer (SWIPT) in the coexistence environment between radar and communication systems. Specifically, we propose a novel energy harvesting based CRC model (CRCEH), in which the signals transmitted from both the communication and radar transmitters are precoded towards their conventional targets, communication receiver and radar targets respectively, as well as to an energy harvesting receiver. This system is capable of solving the spectrum scarcity problem as well as supporting low power devices with their energy requirements from the energy harvested at the energy harvesting receiver. The design problem is formulated as maximizing the radar detection probability subject to communication capacity and energy harvesting constraints. However, directly processing the data from the radar receiver requires high computational complexity and hardware costs. In order to circumvent this issue, this paper also proposes to deploy lens antenna array (LNA) to CRCEH system to sharply direct the signals to the energy harvesting receiver together with their respective destinations. Since LNA is able to focus the signal power on a subset of antennas, we may only deal with the data from the selective antenna subset associated with the maximal power. Numerical results show that the proposed method is able to achieve improved performance in terms of radar detection under communication capacity constraints compared to the conventional approaches besides the great benefit of harvesting the energy to feed some limited energy devices.

Fully autonomous driving, even under bad weather conditions, requires use of multiple sensor systems including radar imaging. Microwave photonics, especially the optical generation and distribution of radar signals, can overcome many of the electronic disadvantages. This article will give an overview about several photonic components and how they could be incorporated into a photonic synchronized radar system, where all the complexity is shifted to a central station. A first proof-of-concept radar experiment with of the shelf telecommunication equipment shows an angular resolution of 1.1°. Furthermore an overview about possible photonic electronic integration is given, leading to comprising low complexity transmitter and receiver chips.

A microwave photonic (MWP) video imaging radar with a bandwidth tuning range of 0–10 GHz is proposed and experimentally demonstrated. In the transmitting path, high-frequency radar transmission signals with varied bandwidths are generated by optical frequency multiplication of an electrical low-frequency signal with tunable bandwidth, which enables radar to image targets with proper resolution and thus optimizes the balance between the observation distance and resolution. In the receiving path, in order to realize video imaging, the high-frequency echo signals with large bandwidth, after being subjected to MWP down-conversion technology for de-chirping, can be sampled by a low-speed and high-precision analog-to-digital converter Then, a digital signal processor is employed for processing the sampled echo data to realize video imaging. In field experiments, imaging ability with varied resolution is firstly verified by imaging Boeing 737 airliner with different-bandwidth radar signals. Moreover, continuous monitoring the flight process of non-cooperative Boeing 737 airliner and unmanned aerial vehicle also successfully demonstrates the video imaging ability of the proposed MWP radar. The capturing of detail structures and the recognition of target flight posture changes all indicate a great potential of the MWP radar for observing distant-range targets of interest.

A unified data communication and radar sensing system towards millimeter-wave (mm-wave) applications with extended coverage is proposed and experimentally demonstrated. In the unified system, the transmission and reception of mm-wave signals are implemented by microwave photonics technologies, and the orthogonal frequency division multiplexing (OFDM) signal is employed for communications and radar sensing simultaneously. The superheterodyne optical carrier suppression (HeteroOCS) is used to up-convert the intermediate frequency (IF) OFDM signal to the mm-wave band in the central office (CO). The optical mm-wave signal is transmitted to the remote antenna units (RAUs) via optical fibers. The echo signal is received by the RAU which is remotely connected to the CO by an analog photonic link based on a polarization modulator (PolM). In the transmitter and receiver links, the chromatic dispersion of optical fibers is overcome by the HeteroOCS and the PolM, respectively. The baseband units (BBU) centralized in the CO is used to process the radar sensing signal. A pre-delayed trigger signal is proposed to overcome the fiber length limitation. A proof-of-concept experiment is performed. Two targets with distances of 1.64 m and 3.40 m are successfully detected separately. The communication function of the system is also verified. 1 m wireless transmission of 1.56 Gb/s data rate is achieved below the forward error correction limit.

Acoustic noise can be reduced by active noise cancellation (ANC) and passive noise cancellation (PNC) algorithm. The PNC can effectively attenuate the noise with high frequency, but not the noise with low frequency. ANC is one of the promising solution to reduce the low frequency noise. Commercial ANC headphones often use the digital signal processor (DSP) to perform the noise cancellation algorithm to cancel the annoying acoustic noise, but the cost is relatively high. A low-cost ANC solution is urgently needed to reduce the acoustic noise. The relationship between the frequency, distance and degree of magnitude of the noise level are also evaluated in this paper.