Antijam Systems Research Articles

AI-Enabled Compressive Spectrum Classification for Wideband Radios

Cognitive radio is a promising technology that emerged as a potential solution to the spectrum shortage problem by enabling opportunistic spectrum access. In many cases, cognitive radios are required to sense a wide range of frequencies to locate the spectrum white spaces; hence, wideband spectrum comes into play, which is also an essential step in future wireless systems to boost the throughput. Cognitive radios are intelligent devices and therefore can be opted for the development of modern jamming and anti-jamming solutions. To this end, our article introduces a novel AI-enabled energy-efficient and robust technique for wideband radio spectrum characterization. Our work considers a wideband radio spectrum made up of numerous narrowband signals, which could be normal communications or signals disrupted by a stealthy jammer. First, the receiver recovers the wideband from significantly low sub-Nyquist rate samples by exploiting compressive sensing technique to decrease the overhead caused by the high complexity analog-to-digital conversion process. Once the wideband is recovered, each available narrowband signal is given to a cyclostationary feature detector that computes the corresponding spectral correlation function and extracts the feature vectors in the form of cycle and frequency profiles. Then profiles are concatenated and given as input features set to an artificial neural network which in turn classifies each NB signal as legitimate communication with a specific modulation or disrupted by a stealthy jammer. The results show a classification accuracy of about 0.99 is achieved. Moreover, the algorithm highlights significantly high performances in comparison to recently reported spectrum classification techniques. The proposed technique can be used to design anti-jamming systems for military communication systems.

STRUCTURES OF ADAPTIVE SIGNAL PROCESSING SYSTEMS FOR RADAR SENSORS OF EXTERNAL INFORMATION FOR CORRELATION-EXTREME AIRCRAFT NAVIGATION SYSTEMS

During the guidance of the aircraft on the final part of the flight, it is affected, along with other external factors, by interferences of various (artificial or natural) origins. These interferences have various effects on the receiving elements of the antenna array of the radar sensor of external information. Due to the variability and rapidity of the complex interference situation, adaptive interference protection systems are the most effective in combating these interferences. It is known that the use of adaptive processing systems allows for overcoming the practically inevitable a priori uncertainty of statistical characteristics of signals and interference of various origins. At present, due to the development of digital technology, new methods and devices for adaptive signal processing against the back- ground of interference have appeared. Thus, the arsenal of methods of adaptation to Gaussian disturbances has been supplemented by methods involving the inversion (direct or recurrent) of the most plausible estimates of correlation matrices of disturbances or their regularized varieties. Wide possibilities of adaptation are opened up in modern radar stations with multi-element phased antenna ar- rays, which provide for digital information processing. Due to the very high speed of the aircraft during the operation of its correlation- extreme guidance system, as well as due to the dynamic and non-stationary interference environment, an important requirement for adaptive anti-jamming systems is their speed. The effectiveness of adaptive processing of signals against the background of interference can be significantly increased by using reliable a priori information. The paper considers a method of increasing the speed of adaptive protection systems against radar interference of various origins by taking into account a priori information about the central symmetry of the receiving channels of radar sensors of external information of correlation-extreme aircraft navigation systems. It is shown that taking into account such a priori information as the central symmetry of the receiving channels of radar sensors of external informa- tion leads to a corresponding change in the structure of devices for adaptive signal processing in the conditions of interference in these sensors and as a consequence, to an increase in their speed.

A Capacity Enhancement Method for Frequency-Hopping Anti-Jamming Communication Systems

In this paper, we study the enhancement of channel transmission information by expanding the transmission channel in the frequency-hopping rate dimension in a communication system. This is achieved using the frequency-hopping spread spectrum (FHSS) without increasing communication resources, such as power and bandwidth. The anti-jamming capability of the original information is maintained during this process. The spectral characteristics of the extended signal for frequency-hopping (FH) transmission are investigated, a demodulation method based on carrier reconstruction is proposed, the bit error rate performance is simulated, and the capacity enhancement and anti-jamming ability of the extended signal for FH transmission are analyzed.

Machine-Learning-Assisted Cyclostationary Spectral Analysis for Joint Signal Classification and Jammer Detection at the Physical Layer of Cognitive Radio.

Cognitive radio technology was introduced as a possible solution for spectrum scarcity by exploiting dynamic spectrum access. In the last two decades, most researchers focused on enabling cognitive radios for managing the spectrum. However, due to their intelligent nature, cognitive radios can scan the radio frequency environment and change their transmission parameters accordingly on-the-fly. Such capabilities make it suitable for the design of both advanced jamming and anti-jamming systems. In this context, our work presents a novel, robust algorithm for spectrum characterisation in wideband radios. The proposed algorithm considers that a wideband spectrum is sensed by a cognitive radio terminal. The wideband is constituted of different narrowband signals that could either be licit signals or signals jammed by stealthy jammers. Cyclostationary feature detection is adopted to measure the spectral correlation density function of each narrowband signal. Then, cyclic and angular frequency profiles are obtained from the spectral correlation density function, concatenated, and used as the feature sets for the artificial neural network, which characterise each narrowband signal as a licit signal with a particular modulation scheme or a signal jammed by a specific stealthy jammer. The algorithm is tested under both multi-tone and modulated stealthy jamming attacks. Results show that the classification accuracy of our novel algorithm is superior when compared with recently proposed signal classifications and jamming detection algorithms. The applications of the algorithm can be found in both commercial and military communication systems.

Polarization-mismatching transmissive metasurface for independent amplitude and phase control of circular polarization.

This work presents a strategy for independent control of the amplitude and phase of transmissive circular-polarization (CP) waves. The designed meta-atom consists of an elliptical-polarization receiver and a CP transmitter. By changing the axial ratio (AR) and polarization of the receiver, amplitude modulation can be realized based on polarization mismatching theory, with negligible cumbrous components. While by rotating the element, a full phase coverage enabled by the geometric phase is achieved. Subsequently, a CP transmitarray antenna (TA) with high gain and low side-lobe level (SLL) is implemented to experimentally validate our strategy, and the tested results match well with the simulated ones. During the operating band from 9.6 to 10.4 GHz, the proposed TA obtains an average SLL of -24.5 dB, a lowest SLL of -27.7 dB at 9.9 GHz, and a maximum gain of 19 dBi at 10.3 GHz, with the measured AR lower than 1 dB, which mainly benefits from high polarization purity (HPP) of the proposed elements. The proposed strategy for full amplitude-phase manipulation of CP waves together with HPP paves a way for complicated field manipulations and indicates a promising candidate in antenna applications, such as anti-jamming systems and wireless communications.

Radar Anti-Jamming Countermeasures Intelligent Decision-Making: A Partially Observable Markov Decision Process Approach

Current electronic warfare jammers and radar countermeasures are characterized by dynamism and uncertainty. This paper focuses on a decision-making framework of radar anti-jamming countermeasures. The characteristics and implementation process of radar intelligent anti-jamming systems are analyzed, and a scheduling method for radar anti-jamming action based on the Partially Observable Markov Process (POMDP) is proposed. The sample-based belief distribution is used to reflect the radar’s cognition of the environment and describes the uncertainty of the recognition of jamming patterns in the belief state space. The belief state of jamming patterns is updated with Bayesian rules. The reward function is used as the evaluation criterion to select the best anti-jamming strategy, so that the radar is in a low threat state as often as possible. Numerical simulation combines the behavioral prior knowledge base of radars and jammers and obtains the behavioral confrontation benefit matrix from the past experience of experts. The radar controls the output according to the POMDP policy, and dynamically performs the best anti-jamming action according to the change of jamming state. The results show that the POMDP anti-jamming policy is better than the conventional policy. The POMDP approach improves the adaptive anti-jamming capability of the radar and can quickly realize the anti-jamming decision to jammers. This work provides some design ideas for the subsequent development of an intelligent radar.

A multi‐agent reinforcement learning anti‐jamming method with partially overlapping channels

This paper investigates the problem of multi-user anti-jamming channel access with partially overlapping channels (POC). Compared with traditional anti-jamming systems that use non-overlapping channels, POC improve the spectral efficiency. However, the partial overlap of channels also brings more serious interference. For this, physical distance and channel separation on the interference intensity under partially overlapping channels are first considered and the malicious jamming and interference among users are formulated as a hierarchical binary model. Secondly, to cope with multi-user decisions under dynamic jamming conditions, the Markov game framework is adopted to analyse the problem. Thirdly, a multi-user collaborative anti-jamming channel selection algorithm based on reinforcement learning is proposed as well as the optimal anti-jamming strategy can be obtained. Finally, the simulation results validate that the proposed algorithm helps users cope with jamming and eliminate mutual interference. Compared with the non-overlapping channel access scheme, the POC access scheme achieves higher network throughput.

A New Optimization Algorithm Based on the Fungi Kingdom Expansion Behavior for Antenna Applications

This paper presents a new optimization algorithm based on the behavior of the fungi kingdom expansion (FKE) to optimize the radiation pattern of the array antenna. The immobile mass expansion of the fungi is mimicked in this work as a chaotic behavior with a sinusoidal map function, while the mobile mass expansion is realized by a linear function. In addition, the random germination of the spores is utilized for randomly distributing the variables that are far away from the best solution. The proposed FKE algorithm is applied to optimize the radiation pattern of the antenna array, and then its performance is compared with that of some well-known algorithms. The MATLAB simulation results verify the superiority of the proposed algorithm in solving 20-element antenna array problems such as sidelobe reduction with sidelobe ratio (SLR = 25.6 dB), flat-top pattern with SLR = 23.5 dB, rectangular pattern with SLR = 19 dB, and anti-jamming systems. The algorithm also results in a 100% success rate for all of the mentioned antenna array problems.

Anti-Interference Design Based on Prime Interleaving for a Combined FH and DS Spreading Spectrum System

A combined prime interleaving design is proposed for a spreading spectrum system with frequency hopping (FH), direct sequence (DS), and coherent detection. Obtaining a lower bit error rate (BER) is the object of classical anti-jamming communication systems. By employing combined prime interleaving, we get lower BER results compared with conventional block interleaving under the same signal-to-noise ratio (SNR) level by merit of superior storage and interleaving effects. Prime interleaving requires only one row to interleave while both block and random interleaving require the whole interleaving matrix, which results in lower latency time. Simulations reveal that the proposed combined interleaving design has comparative performance with random interleaving, and has advantages in transmission reliability and system delay. Moreover, the prime interleaving outputs slightly worse BER compared with random interleaving over the same SNR. Compared with random interleaving, the proposed combined interleaving has 0.25 dB worse SNR over the same average BER.

GNSS and LNSS Positioning of Unmanned Transport Systems: The Brief Classification of Terrorist Attacks on USVs and UUVs

As the demand for precision positioning grows around the world and spreads across various industries, initiatives are being taken to increasingly protect Global Navigation Satellite System (GNSS) receivers from intruders of all kinds, from unintentional industrial interference to advanced GNSS spoofing systems. The timing and cost of these forthcoming satellite navigation safety efforts are difficult to decipher due to the large number of new signals and constellations being deployed. However, it is safe to say that the newly designed anti-jamming and anti-spoofing GNSS systems open up new opportunities for innovative technologies. The false acoustic signal delay is equal to the sum of the spoofer receiving antenna delay, processing delay, and propagation delay from the spoofer to the victim. The victim finds the same location as the spoofer’s receiving antenna, and receivers located in different locations will have the same XYZ. The article presents classifications of terrorist attacks of this type.

Friction Torque Analysis of Planetary Roller Screw Mechanism in Roller Jamming

The load distribution model of the planetary roller screw mechanism (PRSM) is established on the basis of Hertz contact theory. The objective is to obtain a friction torque model of the PRSM in roller jamming. An example is provided to calculate the friction torque of the PRSM in roller jamming. Thereafter, the transmission efficiency is calculated. A static structural analysis is performed using the finite element method to estimate the contact stress between the threads of the PRSM components. Computational results indirectly reveal that roller jamming exerts considerable influence on the friction torque of the PRSM. Results show that the friction torque of the planetary roller screw increases when the roller is jammed and the wear of the parts is accelerated. This condition leads to structural failure. The results of this study can serve as a foundation for electromechanical actuation systems, which can be useful in designing antijamming systems for safety-critical aircraft applications.

Protection of Coherent Pulse Radars against Combined Interferences. 1. Modifications of STSP Systems and their Ultimate Performance Capabilities

This paper is the first paper of the sequence devoted to modern methods of protection of coherent pulse radars against combined interferences (additive internal noise mixture masking the active jamming and clutter (passive jamming)). It compares the ultimate capabilities of the known and relatively new varieties of the interference protection (anti-jam and anti-clutter) systems under the hypothetical conditions of exact knowledge of statistical characteristics of signals and interferences. The ultimate capabilities of systems are understood in the sense that their efficiency is calculated for the hypothetical conditions of exact knowledge of statistical characteristics of input actions. The obtained estimates determine the upper bounds of efficiency in the real conditions of a priori uncertainty of parameters of signals and interferences. The losses of efficiency related to the transition to simplified systems of space-time signal processing (STSP) are also analyzed. The second paper deals with peculiarities (high-speed) of the considered anti-jam and anti-clutter systems in real conditions of parametric a priori uncertainty that is overcome by using different kinds of estimates of a priori unknown parameters of interferences. The third paper is devoted to the substantiation of general-purpose STSP system based on adaptive lattice filters.

TH-NRDCSK: A Non-Coherent Time Hopping Chaotic System for Anti-Jamming Communications

Time hopping spread spectrum (THSS) system and chaotic system have been studied as candidates of the anti-jamming (AJ) systems with substantial advantages. However, THSS systems suffer from the strict synchronization prerequisite. In order to overcome the shortcomings of the THSS system and utilize the profits of the non-coherent chaotic system, we first propose a novel TH-NRDCSK system to enhance the bit error rate (BER) performance of the conventional non-coherent THSS system and relieve the strict synchronization issue of coherent THSS systems. Then, we analyze the performance of the proposed system under additive white Gaussian noise (AWGN) channel and jamming environment. Finally, we implement the simulation to demonstrate the consistency of the analysis and the simulation results and to disclose the effects of the system parameters on system's AJ performance. Moreover, the performance of the proposed system is compared to that of conventional counterparts to look at the benefits of integrating chaotic and THSS systems. The simulation results show that the proposed system significantly outperforms conventional counterparts in a practical environment.

Power Control in Relay-Assisted Anti-Jamming Systems: A Bayesian Three-Layer Stackelberg Game Approach

This paper investigates the multi-user power control problem in relay-assisted anti-jamming systems. Because of the hierarchical confrontation characteristics between users and jammer, we take the incomplete information and observation error into consideration and formulate an anti-jamming Bayesian three-layer Stackelberg game, in which primary users act as leaders, relay users act as vice-leaders, and jammer acts as a follower. Both users and jammer have the ability to sense others' transmission power and choose optimal power to realize the maximum of utility. Based on the backward induction method, we propose a multi-user hierarchical iterative algorithm to obtain the Stackelberg equilibrium (SE) and prove the existence and uniqueness of SE. Finally, simulation results are compared with the Nash equilibrium to verify the effectiveness of the proposed game. Moreover, both the influence of incomplete information and the observation error on utility are analyzed.

Preliminary Research on Possibilities of Drilling Process Robotization

Nowadays, drilling & blasting is crucial technique for deposit excavation using in hard rock mining. Unfortunately, such approach requires qualified staff to perform, and consequently there is a serious risk related to rock mechanics when using explosives. Negative influence of explosives usage on safety issues of underground mine is a main cause of mining demands related to elimination of people from production area. Other aspects worth taking into consideration are drilling precision according to drilling pattern, blasting effectiveness, improvement of drilling tool reliability etc. In the literature different drilling support solutions are well-known in terms of positioning support systems, anti-jamming systems or cavity detection systems. For many years, teleoperation of drilling process is also developed. Unfortunately, available technologies have so far not fully met the industries expectation in hard rock. Mine of the future is expected to incorporate robotic system instead of current approaches. In this paper we present preliminary research related to robotization of drilling process and possibilities of its application in underground mine condition. A test rig has been proposed. To simulate drilling process several key assumptions have been accepted. As a result, algorithms for automation of drilling process have been proposed and tested on the test rig. Experiences gathered so far underline that there is a need for further developing robotic system for drilling process.

Energy-Efficient Resource Allocation Strategy for Low Probability of Intercept and Anti-Jamming Systems

Energy-Efficient Resource Allocation Strategy for Low Probability of Intercept and Anti-Jamming Systems

Need a Change? Try GeTe: A Reconfigurable Filter Using Germanium Telluride Phase Change RF Switches

There is an increasingly high demand for compact, low-loss reconfigurable filters in various advanced wireless applications: cognitive radios, modern transceivers, and antijamming communication systems, to name a few [1]. With reconfigurable filters, wireless communication systems that require multiple operating frequency bands can be implemented in a smaller size and at a reduced cost compared to conventional systems using multiple single-frequency filters. Bandpass filters provide a better RF performance compared to low-pass or high-pass filters, resulting in improved signal-to-noise ratio and out-of-band performance [2].

Sparse Arrays and Sampling for Interference Mitigation and DOA Estimation in GNSS

This paper establishes the role of sparse arrays and sparse sampling in antijam global navigation satellite systems (GNSS). We show that both jammer direction of arrival estimation methods and mitigation techniques benefit from the design flexibility of sparse arrays and their extended virtual apertures or coarrays. Taking advantage of information redundancy, significant reduction in hardware and computational cost materializes when selecting a subset of array antennas without sacrificing jammer nulling or localization capabilities. In addition to the spatial array sparsity, antijam can utilize sparsity of jammers in the spatio–temporal frequency domains. By virtue of their finite number, jammers in the field of view are sparse in the azimuth and elevation directions. For the class of frequency modulated jammers, sparsity is also exhibited in the joint time-frequency signal representation. These spatial and signal characteristics have called for the development of sparsity-aware antijam techniques for the accurate estimation of jammer space-time-frequency signature, enabling its effective sensing and excision. Both theory and simulation examples demonstrate the utility of coarrays, sparse reconstructions, and antenna selection techniques for antijam GNSS.

Design of GPS Anti-Jamming Systems Using Adaptive Notch Filters

Continuous wave interferences (CWIs) can reduce the positioning accuracy of a Global Positioning System (GPS) receiver and even paralyze its normal operation. Therefore, we have designed a low-cost anti-jamming system to combat CWIs for GPS receivers. The anti-jamming system comprises cascaded CWI-detectable adaptive notch filter (ANF) modules, and each module is able to mitigate one CWI. The ANF module is composed of a second-order infinite-impulse response (IIR) filter with a lattice structure. The proposed ANF detects the existence of the CWI and estimates its power by exploiting the statistic value and internal state associated with the IIR filter, respectively. The impact of the ANF module on the acquisition and tracking loops is analyzed. Properly controlling the $-$ 3-dB bandwidth of the ANF module allows its impact to be neglected. Moreover, more modules can be cascaded to deal with multiple CWIs. We have also designed an adaptation algorithm for the ANF modules and proven that the module can adaptively notch the strongest CWI at its input. This merit enables us to notch the primary CWIs with a limited number of ANF modules. Simulation results show that our approach considerably outperforms related works in both CWI detection and rejection capabilities.

Design of an Array Antenna Hood for Jamming Simulator

In this study, due to the necessity of the equipment for inspecting an anti-jamming function depending on the expansion of the development of anti-jamming systems, an array antenna hood that can inspect the anti-jamming function of an anti-jamming system while being installed at the system was designed and manufactured. The manufactured array antenna hood plays a role in radiating GNSS signals and jamming signals. Based on an experiment, it was demonstrated that using a near-field radiation method, the manufactured array antenna hood could be used for examining the normal operation of an anti-jamming system function in outdoor or indoor environments rather than an anechoic chamber.