Radar Pulse Research Articles

Semi-Blind Post-Equalizer SINR Estimation and Dual CSI Feedback for Radar-Cellular Coexistence

Current cellular systems use pilot-aided statistical-channel state information (S-CSI) estimation and limited feedback schemes to aid in link adaptation and scheduling decisions. However, in the presence of pulsed radar signals, pilot-aided S-CSI is inaccurate since interference statistics on pilot and non-pilot resources can be different. Moreover, the channel will be bimodal as a result of the periodic interference. In this paper, we propose a max-min heuristic to estimate the post-equalizer SINR in the case of non-pilot pulsed radar interference, and characterize its distribution as a function of noise variance and interference power. We observe that the proposed heuristic incurs low computational complexity, and is robust beyond a certain SINR threshold for different modulation schemes, especially for QPSK. This enables us to develop a comprehensive semi-blind framework to estimate the wideband SINR metric that is commonly used for S-CSI quantization in 3GPP Long-Term Evolution (LTE) and New Radio (NR) networks. Finally, we propose dual CSI feedback for practical radar-cellular spectrum sharing, to enable accurate CSI acquisition in the bimodal channel. We demonstrate significant improvements in throughput, block error rate and retransmission-induced latency for LTE-Advanced Pro when compared to conventional pilot-aided S-CSI estimation and limited feedback schemes.

L-Probe 원형 패치 안테나를 이용한 ISO 11452-2 근거리 내성 시험 모사에 대한 연구

ISO 11452-2 is a well-known standard that tests the electromagnetic immunity of a device under test(DUT) in an anechoic chamber. ISO 11452-2 needs a large antenna and high-power amplifier to provide a high electric field in the chamber. In this test setup, finding the root cause and debugging issues is not easy because of varied limitation conditions. In this paper, we suggest two L-probe-fed circular patch antennas that emit a high electric field(over 800 V/m in the radar pulse ranges) on DUTs in the near field. Because the DUT is located 50 mm away from the antenna, the power amplifier consumes a small amount of power for the same electric field in ISO 11452-2. The proposed procedure has the advantage of industry usefulness with fast, handy, and cost-effective radiated immunity debugging of the DUT without considering the environment required by ISO 11452-2 and certain types of monitoring equipment with high immunity.

Deep Reinforcement Learning Control for Radar Detection and Tracking in Congested Spectral Environments

In this paper, dynamic non-cooperative coexistence between a cognitive pulsed radar and a nearby communications system is addressed by applying nonlinear value function approximation via deep reinforcement learning (Deep RL) to develop a policy for optimal radar performance. The radar learns to vary the bandwidth and center frequency of its linear frequency modulated (LFM) waveforms to mitigate mutual interference with other systems and improve target detection performance while also maintaining sufficient utilization of the available frequency bands required for a fine range resolution. We demonstrate that our approach, based on the Deep Q-Learning (DQL) algorithm, enhances important radar metrics, including SINR and bandwidth utilization, more effectively than policy iteration or sense-and-avoid (SAA) approaches in a variety of realistic coexistence environments. We also extend the DQL-based approach to incorporate Double Q-learning and a recurrent neural network to form a Double Deep Recurrent Q-Network (DDRQN). We demonstrate the DDRQN results in favorable performance and stability compared to DQL and policy iteration. Finally, we demonstrate the practicality of our proposed approach through a discussion of experiments performed on a software defined radar (SDRadar) prototype system. Our experimental results indicate that the proposed Deep RL approach significantly improves radar detection performance in congested spectral environments when compared to policy iteration and SAA.

Radar Pulse Compression Methods Based on Nonlinear and Quadratic Optimization

This article addresses the problem of radar pulse compression. First, a matched filter at the receiver is assumed and a method to design a transmit waveform characterized by an autocorrelation function with a narrow mainlobe and low sidelobes is proposed. After that, a mismatched filter is considered and a method to design the optimum linear filter receiver is proposed. In both cases, the pursued objectives are minimum sidelobe energy and peak level through a strategy based on quadratic and nonlinear optimization. In this article, we focus particularly on the case of ground weather radars, where the problem of pulse compression is particularly challenging.

An improved de-interleaving algorithm of radar pulses based on SOFM with self-adaptive network topology

As a core part of the electronic warfare (EW) system, de-interleaving is used to separate interleaved radar signals. As interleaved radar pulses become more complex and denser, intelligent classification of radar signals has become very important. The self-organizing feature map (SOFM) is an excellent artificial neural network, which has huge advantages in intelligent classification of complex data. However, the de-interleaving process based on SOFM is faced with the problems that the initialization of the map size relies on prior information and the network topology cannot be adaptively adjusted. In this paper, an SOFM with self-adaptive network topology (SANT-SOFM) algorithm is proposed to solve the above problems. The SANT-SOFM algorithm first proposes an adaptive proliferation algorithm to adjust the map size, so that the initialization of the map size is no longer dependent on prior information but is gradually adjusted with the input data. Then, structural optimization algorithms are proposed to gradually optimize the topology of the SOFM network in the iterative process, constructing an optimal SANT. Finally, the optimized SOFM network is used for de-interleaving radar signals. Simulation results show that SANT-SOFM could get excellent performance in complex EW environments and the probability of getting the optimal map size is over 95% in the absence of priori information.

Methodology of classification and recognition of the radar emission sources based on Bayesian programming

This study considers the Bayesian programming methodology for recognition and classification of radio emission sources. A mathematical model of Bayesian programming proposes forming a family of probability distributions based on known parameters contained in a training sample (database). The correlations between the object classes have been estimated according discussed methodology. The received assessment has been used to separate procedures of recognition and classification of radar emission sources. The simulation of methodology has carried out for four parameters of radar signals (frequency range, pulse width, pulse repetition interval and radar rotation frequency) by used database with 346 classes and 16 types of radar. Based on the existing database of radar emission sources, it is possible to predict the probability of class recognition for the general population of objects, if its distribution is known. This study demonstrates the consistency of the Bayesian programming methodology for object identification in ELINT systems.

Active Normal Faulting, Diking, and Doming Above the Rapidly Inflating Laguna del Maule Volcanic Field, Chile, Imaged With CHIRP, Magnetic, and Focal Mechanism Data

AbstractThe Laguna del Maule volcanic field (LdMVF) in Chile, a rapidly inflating silicic volcanic system without historical eruption, is intersected by active regional faults. The LdMVF provides an opportunity to observe how faults influence, accommodate, or are driven by an actively deforming large silicic system. Here we use Compressed High Intensity Radar Pulse (CHIRP) acoustic reflection data to map the fault network in sediments captured within the eponymous lake at the LdMVF and combine our fault maps with the volcanic history, earthquake locations, focal mechanisms, and lacustrine magnetic data to interpret how faults and magmatism interact. Our seismic data image dominantly dip‐slip faults forming grabens within the lake, subparallel to regional faults. No indications exist in the seismic data to suggest that fault patterns were created by the volcanic system, either ring or radial faults. Fault strikes interpreted from seismic and magnetic data are consistent with mapped dike and fault orientations on land. We therefore interpret that active faults at the LdMVF are tectonic rather than volcanic in origin, forming a transtensional zone that hosts the magmatic system. However, vertical motion along a NS‐striking fault near the center of uplift suggests trapdoor‐style faulting above the volcanic center in which tectonic faults are reactivated to accommodate magmatic inflation and overlying deformation. Magnetic anomalies follow regional faults, suggesting that faults also provide migration pathways. Depositional patterns indicate a prior episode of uplift followed by quiescence, indicating that significant magmatically related uplift at the LdMVF can occur without an associated major eruption.

Probability of Pilot Interference in Pulsed Radar-Cellular Coexistence: Fundamental Insights on Demodulation and Limited CSI Feedback

This letter considers an underlay pulsed radar-cellular spectrum sharing scenario, where the cellular system uses pilot-aided demodulation, statistical channel state information (S-CSI) estimation and limited feedback schemes. Under a realistic system model, upper and lower bounds are derived on the probability that at least a specified number of pilot signals are interfered by a radar pulse train in a finite CSI estimation window. Exact probabilities are also derived for important special cases which reveal operational regimes where the lower bound is achieved. Using these results, this letter (a) provides insights on pilot interference-minimizing schemes for accurate coherent symbol demodulation, and (b) demonstrates that pilot-aided methods fail to accurately estimate S-CSI of the pulsed radar interference channel for a wide range of radar repetition intervals.

Improved algorithm for de‐interleaving radar signals with overlapping features in the dynamically varying electromagnetic environment

As an indispensable part of electronic support measure, the de-interleaving technique is used to separate interleaved radar pulse streams. At present, clustering based on radar features is one of the most effective de-interleaving methods. In a dynamically varying electromagnetic environment, the features of intercepted radar pulses overlap each other. Compared with other de-interleaving algorithms, the fuzzy adaptive resonance theory (Fuzzy ART) has obvious advantages in classifying such radar features. However, it still faces several problems: (i) the vigilance parameter used to regulate de-interleaving performance is difficult to reach its optimal value and (ii) since the unified discrimination threshold is selected for different regions, the algorithm suffers from category proliferation problem. This study addresses these problems by constructing a new vigilance model to replace the unified vigilance parameter and introducing a dual-vigilance mechanism to ART-based de-interleaving systems. It demonstrates this idea in the context of Fuzzy ART, presented as Fuzzy ART based on a 3D fuzzy model with two vigilance thresholds (2VT-3DFA). 2VT-3DFA suppressed the excessive proliferation of categories, and its clustering quality was 20% higher than that of conventional algorithms in dynamically varying signal environment.

The Global Search for Liquid Water on Mars from Orbit: Current and Future Perspectives.

Due to its significance in astrobiology, assessing the amount and state of liquid water present on Mars today has become one of the drivers of its exploration. Subglacial water was identified by the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) aboard the European Space Agency spacecraft Mars Express through the analysis of echoes, coming from a depth of about 1.5 km, which were stronger than surface echoes. The cause of this anomalous characteristic is the high relative permittivity of water-bearing materials, resulting in a high reflection coefficient. A determining factor in the occurrence of such strong echoes is the low attenuation of the MARSIS radar pulse in cold water ice, the main constituent of the Martian polar caps. The present analysis clarifies that the conditions causing exceptionally strong subsurface echoes occur solely in the Martian polar caps, and that the detection of subsurface water under a predominantly rocky surface layer using radar sounding will require thorough electromagnetic modeling, complicated by the lack of knowledge of many subsurface physical parameters. Higher-frequency radar sounders such as SHARAD cannot penetrate deep enough to detect basal echoes over the thickest part of the polar caps. Alternative methods such as rover-borne Ground Penetrating Radar and time-domain electromagnetic sounding are not capable of providing global coverage. MARSIS observations over the Martian polar caps have been limited by the need to downlink data before on-board processing, but their number will increase in coming years. The Chinese mission to Mars that is to be launched in 2020, Tianwen-1, will carry a subsurface sounding radar operating at frequencies that are close to those of MARSIS, and the expected signal-to-noise ratio of subsurface detection will likely be sufficient for identifying anomalously bright subsurface reflectors. The search for subsurface water through radar sounding is thus far from being concluded.

Work modes recognition and boundary identification of MFR pulse sequences with a hierarchical seq2seq LSTM

Recognition of multi-function radar (MFR) work mode in an input pulse sequence is a fundamental task to interpret the functions and behaviour of an MFR. There are three major challenges that must be addressed: (i) The received radar pulses stream may contain an unknown number of multiple work mode class segments. (ii) The intra-mode and inter-mode knowledge of a modern MFR may be too flexible and complicated to be represented and learned through traditional hand-crafted features and learning models. (iii) The variable duration of each enclosed work mode makes the identification of the transition boundaries of adjacent modes difficult. To address these challenges and implement automatic recognition of MFR work mode sequences at a pulse-level, this study develops a novel processing framework based on a time series representation of MFR work mode sequence and sequence-to-sequence (seq2seq) long short-term memory network. The proposed method can not only automatically recognise multiple complexes modulated work mode classes in a pulse sequence. Still, it can also accurately identify the transition boundaries between each class by labelling the class information for each pulse. The experimental results showed the extended capabilities and improved performance of the proposed method over the state-of-the-art work mode classification methods.

The First IEEE Milestone in Ukraine Celebrates "Zenit Parabolic Reflector L-Band Pulsed Radar, 1938" in Kharkiv [Around the Globe

On 21 November 2019, a commemorative plaque recognizing the IEEE Milestone “Zenit Parabolic Reflector L-band Pulsed Radar, 1938” was unveiled at the School of Radiophysics, Biomedical Electronics, and Computer Systems at the V.N. Karazin Kharkiv National University (KhNU).

A time-delay estimation approach for coherent GPR signals by taking into account the noise pattern and radar pulse

In this paper, we propose to perform time-delay estimation (TDE) of coherent GPR signals by taking into account the radar pulse and noise pattern. The proposed method can process raw GPR data without whitening procedure and decorrelate coherent signals properly with a Hankel matrix which contains the signal eigenvector, the radar pulse and the noise characteristics. Simulations and a field experiment show the effectiveness of the proposed method.

Method for Recognition and Generation of High Precision Range Delay in High Range Resolution Pulse Radar

Method for Recognition and Generation of High Precision Range Delay in High Range Resolution Pulse Radar

A Signal Model for PRF Dithering in Wide-Swath, Fine-Resolution InSAR

Wide-swath radar imaging requires that the time interval to collect each radar pulse echo is large and can often exceed the interpulse period. As it is difficult to both transmit and receive from the same antenna simultaneously, there will be “blind ranges” when the receive and transmit times overlap. This leads to gaps in the radar echo and thus degradation of system performance. Today, most wide-swath systems address this by segmenting the swath in range, such as in the ScanSAR or Terrain Observation with Progressive Scan (TOPS) mode operation, so that each subswath is within the range ambiguity limit. Some groups have started experimenting with the variations in the sweepSAR technology, in which the receive antenna tracks the radar echo across the swath, realizing a complete wide-swath range scan but leading to the echo gaps. Here, we look at minimizing the effect of blind ranges by varying the radar pulse-repetition frequency (PRF) and interpolating across the gaps to preserve azimuth signal continuity. If the pulse times are selected properly, the main effect is to raise the noise floor of the echoes. Geocoded magnitude images, interferograms and correlation images, and deformation time series show strong robustness with respect to dithering, demonstrating that choosing essentially random PRFs allows for accurate generation of SAR and Interferometric Synthetic Aperture Radar (InSAR) data products while retaining wide-swath, fine-resolution coverage.

단일 펄스 LFM 파형에서 표적 속도 추정 방법

Linear frequency modulation(LFM) waveforms in pulsed radars are extensively used owing to their excellent Doppler tolerance and low side-lobe level characteristics after pulse compressions. On the contrary, it is difficult to determine target Doppler velocity from single-pulse LFM waveforms because of their excellent Doppler tolerance. If it is possible to detect the range and velocity of targets with only single-pulse transmission and reception, multi-function radars can gain advantages in terms of resource management. In this paper, we propose a method of estimating target velocity using single-pulse LFM waveforms. The proposed method uses range-Doppler coupling and signal to noise ratio loss effects due to Doppler frequency inconsistency between the matched filter and signal during pulse compressions. The proposed method can estimate the target velocity from a few computations through two additional matched filtering processes after the target range detection, and its function and performance are verified via simulations.

Nonlinear Transformations of Pulsed Signals in Radar Tomography

This paper considers two methods for improving the visibility of hidden objects in radar tomography using nonlinear time transformations of short ultra-wideband (UWB) pulses. The first method is based on selection of a digital coherent jitter formed by special nonlinear signal transformation. The resulting increase in the contribution of high-frequency components to the reflected signal spectrum improves the spatial resolution of images of hidden objects. The second method uses relatively powerful monochromatic side irradiation in the clocked mode to detect a target. This leads to a characteristic distortion of the radar sensing pulse reflected from nonlinear radio-electronic elements – parts of the target being located. The observed change in the radar pulse waveform allows selective tomography of nonlinear radio-electronic elements to be carried out.

THE INFLUENCE OF STATISTICAL CHARACTERISTICS OF THE FLUCTUATIONS OF THE RADIATION SIGNAL INITIAL PHASES ON THE ACCURACY OF THE MEASUREMENT AERODYNAMIC OBJECT RADIAL VELOCITY

The article deals with the estimation of radial velocity when using a coherent packet of radio pulses regarding the case of the presence of correlated fluctuations of the initial phases in the reflected from the aerodynamic object pulses. The subject of the research is the accuracy of measuring the frequency of the received packet for the case of concerted processing without taking into account the phase fluctuations of its radio pulses. The purpose is a numerical analysis of the influence of the statistical characteristics of the fluctuations of the received pack’s initial phases on the decrease in the accuracy of measuring the radial velocity of the aerodynamic object. The task : to estimate the possible values of fluctuation constituent middling quadratic error of measuring of radial speed of aerodynamic object. Consideration is given to the assumption that an additive mixture of deflected signal and uncorrelated Gaussian noise is input to the radar receiver. It is considered that the phase fluctuations of the received packet are distributed according to the normal law with zero mean, and the correlation of phase fluctuations with the increase of the interval between the packet radio pulses decreases according to the alternating law. Methods used: methods of probability theory and mathematical statistics. The following results are obtained: the accuracy of frequency measurement of the pack had been estimated in the presence of correlated phase fluctuations of its radio pulses. Conclusions . The results indicate that for modern radars in the conditions of regular measurement the accuracy of estimating the frequency of the packet of radio pulses is much more influenced by the statistical characteristics of the phase fluctuation than the signal-to-noise ratio. Due to the phase fluctuations of the radio pulses of the received packet, the mean-square error (MSE) of radial velocity measurement of the aerodynamic object is able to exceed the values determined by the requirements for coherent pulse radar.

Jamming Analysis and Simulation of Active Jamming on Pulse Radar Fuze

Pulse radar fuze is widely used at present. The jamming and anti-jamming of radar fuze have always been the focus of modern electronic countermeasures. The working principle of pulse radar fuze and the jamming mechanism of three typical active jamming to radar fuze is analyzed, and the jamming effect is simulated. The simulation results show that the pulse radar fuze has a certain anti-jamming ability to suppress radio frequency noise; The anti-jamming measures of variable period has a good anti-jamming effect to range deception jamming; After the density of dense false target jamming reaches a certain degree, it can exert an effective influence on the pulse radar fuze.

Mind the gap – Part 1: Accurately locating warm marine boundary layer clouds and precipitation using spaceborne radars

Abstract. Ground-based radar observations show that, over the eastern North Atlantic, 50 % of warm marine boundary layer (WMBL) hydrometeors occur below 1.2 km and have reflectivities of < −17 dBZ, thus making their detection from space susceptible to the extent of surface clutter and radar sensitivity. Surface clutter limits the ability of the CloudSat cloud profiling radar (CPR) to observe the true cloud base in ∼52 % of the cloudy columns it detects and true virga base in ∼80 %, meaning the CloudSat CPR often provides an incomplete view of even the clouds it does detect. Using forward simulations, we determine that a 250 m resolution radar would most accurately capture the boundaries of WMBL clouds and precipitation; that being said, because of sensitivity limitations, such a radar would suffer from cloud cover biases similar to those of the CloudSat CPR. Observations and forward simulations indicate that the CloudSat CPR fails to detect 29 %–43 % of the cloudy columns detected by ground-based sensors. Out of all configurations tested, the 7 dB more sensitive EarthCARE CPR performs best (only missing 9.0 % of cloudy columns) indicating that improving radar sensitivity is more important than decreasing the vertical extent of surface clutter for measuring cloud cover. However, because 50 % of WMBL systems are thinner than 400 m, they tend to be artificially stretched by long sensitive radar pulses, hence the EarthCARE CPR overestimation of cloud top height and hydrometeor fraction. Thus, it is recommended that the next generation of space-borne radars targeting WMBL science should operate interlaced pulse modes including both a highly sensitive long-pulse mode and a less sensitive but clutter-limiting short-pulse mode.