Low Probability Of Intercept Research Articles

Quantum low probability of intercept

Conventional cryptography—such as the Rivest–Shamir–Adleman public-key infrastructure—may be rendered insecure by the ever-increasing capabilities of classical computers and the emergence of quantum computers. Quantum key distribution and post-quantum cryptography are presently being pursued as solutions to the quantum threat, but they offer no protection against an adversary who has obtained decryption keys by hacking the computer where they are stored, or by bribing a code clerk who has access to them. This paper introduces a protocol, which we call quantum low probability of intercept (QLPI), that has the potential to solve the key-disclosure problem. It transmits a ciphertext in such a way that laws of physics prevent an eavesdropper’s obtaining anything but an error-ridden version of that ciphertext from an individual attack or a restricted class of collective attacks. Consequently, even were an adversary to possess the decryption key, the plain text could not be recovered from such attacks. Furthermore, QLPI is capable of gigabits per second communication rates on optical fiber over metropolitan-area distances without space-division or wavelength-division multiplexing and without the need for any new technology.

An Investigation of LPI Radar Waveforms Classification in RoF Channels

Intensive research has been developed to either design or classify low probability of intercept (LPI) radar signals. These types of signals are used in different sensitive electronic warfare applications such as electronic support, electronic attack, and radar emitter identification. Linear frequency modulation, nonlinear frequency modulation, frequency shift keying, polyphase Barker, polyphase P1, P2, P3, P4 and Frank codes are examples of LPI waveforms. In this paper, we consider the modulation classification problem under the effect of transporting the captured radar signals through radio over fiber channels. Distortions and noise introduced by such channels are likely to affect the performance of LPI classification algorithms. Here, we investigate the accuracy of a recently proposed hierarchical decision-tree automatic modulation classification algorithm for additive white Gaussian noise channels and provide the necessary adjustments when the intercepted radar signals are transmitted over fiber optic channels. The investigation is conducted by simulations and experimental demonstration. The obtained results show that for an 80 km fiber link and noisy intercepted LPI signals, the average identification accuracy reaches more than 98%, at 16 dB optical signal-to-noise ratio.

Adaptive Jamming Waveform Design for Distributed Multiple‐Radar Architectures Based on Low Probability of Intercept

AbstractThis paper investigates the problem of low probability of intercept (LPI)‐based adaptive jamming waveform design for distributed multiple‐radar architectures. Such a smart jammer system adopts a multibeam working mode, where multiple simultaneous jamming beams are synthesized to interfere with multiple radars independently. The primary objective of the smart jammer is to minimize the total jamming power by optimizing the transmitted jamming waveform while the achieved signal‐to‐interference‐plus‐noise ratio (SINR) and mutual information (MI) between the received echoes from the target at each radar receiver and the target impulse responses are enforced to be below specified thresholds. First, the expressions of SINR and MI are derived to characterize target detection and characterization performance, respectively. Then, two different LPI‐based jamming waveform design strategies are proposed to minimize the total noise jamming power by optimizing the jamming waveform while the achieved SINR/MI is enforced to be below a certain threshold. The resulting optimization problems are solved analytically by employing the technique of Lagrange multipliers. With the aid of some numerical examples, it is illustrated that the two schemes result in different jamming waveform design results, which is useful to guide jamming power allocation for various jamming tasks. It is also shown that the LPI performance of the smart jammer can be efficiently improved by exploiting the proposed jamming waveform design criteria.

Low Probability of Intercept Communication Based on Structured Radio Beams Using Machine Learning

A low probability of intercept (LPI) communication system based on structured radio beams using machine learning is proposed. Information symbols can be physically encrypted on the structured radio beam realized by superposition of plane spiral orbital angular momentum (PS-OAM) modes. Performance of decryptor based on support vector machine (SVM) is analyzed. The accuracy achieves higher than 99.5%, which is much better than the interceptor based on k-means. The influence of the deflection angle, number of receiver array elements and the time delay of interceptor are further analyzed. Simulation results shows that the LPI scheme can achieve security communication within practical SNR range.

Cognitive Anti-Deception-Jamming for Airborne Array Radar via Phase-Only Pattern Notching With Nested ADMM

Deceptive jamming may not only induce a large amount of false alarms and deteriorate the target detection performance, but also lead to degraded space-time adaptive processing (STAP) performance in an airborne radar. To tackle these issues, this paper proposes a cognitive transmitting scheme to counter the deceptive jamming for airborne array radar. The proposed approach is composed of two steps. The first step is the deceptive jamming perception. A specially designed high pulse repetition frequency (PRF) waveform is transmitted, and then the deceptive jamming is identified according to the angle clustering feature of the false targets. In the second step, the phase-only transmit pattern with notches at the jammers' directions is designed. The encountered pattern synthesis problem is nonconvex due to the fixed excitations constraint. To solve this problem, a nested alternating direction method of multipliers (N-ADMM) is proposed. With the developed approach, the radiated power at the jammers' directions is attenuated significantly. Therefore, the probing signal possesses the characteristic of low probability of intercept (LPI). Numerical examples are given to demonstrate the effectiveness of the proposed approach.

The Modulation Technology of Chaotic Multi-Tone and its Application in Covert Communication System

With the development of communication countermeasure technology, the existing communication mode is exposed to intercept or decipher in the covert transmission of information. Therefore, the development of a new concept and principle covert communication technology with low interception probability and anti-non-cooperative demodulation has drawn increasing attention. In this treatise, we propose a chaotic multi-tone modulation and demodulation technology thus present a method to construct the covert communication system. The technology constructs chaotic multi-tone sets to express the baseband information with the multi-value mapping based on the dynamics principle, which can express the same baseband information with different multi-tone groups. Signal modulation is accomplished by combining frequency hopping and baseband information scrambling technology. Multi-value mapping is adopted to complete chaotic multi-tone modulation. Specifically it has strong information concealment and anti-non-cooperative demodulation characteristics. In order to solve the demodulation problem of the cooperative party, we present a demodulation scheme based on chaotic multi-tone and provide a complete chaotic multi-tone communication system construction scheme. Simulation results verify the performance of the proposed method.

The Background and Significance of Radar Signal Sorting Research in Modern Warfare

As an important part of electronic intelligence (ELINT) and electronic support measure (ESM) system, radar signal sorting affects the performance of electronic reconnaissance equipments directly, and is a key technology to campaign decision-making. However, as the radar systems are becoming more and more complicated, as the countermeasure activities in modern electronic warfare are becoming more and more drastic, and as the development of low-probability of intercept (LPI), the regularities of signal sorting are heavily destroyed. This leads to the results of radar signal sorting based on common five parameters are not well. At present, the deinterleaving of advanced radar signals has become the primary bottleneck of signal processing in ELINT and ESM system, and confined farther improvement of the performance of electronic countermeasure equipment. So this paper analyzes and studies the background and significance of radar signal sorting in complex systems.

Hybrid Chaos Communication With Code Index Modulation

Hybrid chaos communication (HCC) is promising for covert transmission by delivering confidential information via chaotic signals. To enhance the transmission rate and the energy efficiency while maintaining a low probability of interception, in this paper, we propose a code index modulation-aided HCC (CIM-HCC) scheme. Specifically, the input bit stream is split into the chaotic signaling stream, the modulating stream, and the code indexing stream. The chaotic signaling stream is modulated by the hybrid chaos signal and the code indexing stream is mapped onto the Walsh codes. The modulating stream is multiplied to the Walsh codes. Thus, the proposed CIM-HCC achieves higher data rate and lower power consumption than that of the conventional HCC. Another advantage is that, since part of the information bits are conveyed by the indices of the Walsh codes, the CIM-HCC outperforms the conventional HCC, and binary phase-shift keying (BPSK) in terms of reliability. In particular, when the number of indexing bits equals to that of the signaling bits, the proposed CIM-HCC doubles the data rate and saves about 50% power consumption. In addition, the numerical results show that the proposed scheme outperforms the code index modulation differential chaos shift keying in terms of bit error rate over both the additive white Gaussian noise channel and the multipath Rayleigh fading channels.

An energy balance and mobility prediction clustering algrithm for large-scale UAV ad hoc networks

Creating a clustering structure is considered the performance of radio frequency (RF) stealth for data link in the battlefield environment and the dynamic topology characteristic for larger-scale unmanned aerial vehicle (UAV) ad hoc networks. This problem is of a great importance-to get low intercept probability of the data link and low randomness of clustering structure. An energy balance and mobility prediction (EBMP) clustering algorithm is proposed. In the initial clustering stage, the power management for information transmission is conducted in the network layer and the MAC layer. The Doppler shift is implemented to estimate the relative speeds stability degree between neighboring UAVs when they exchange Hello packets. It can be selected as cluster head (CH) where one UAV associateslower energy consumption with higher relative stability. In the cluster maintaining stage, a CH rotation process for the dynamic topology to improve resource utilization efficiency. The inter-cluster communication is enhanced by dynamic packet forwarding gateway. The simulations and analysis show that this scheme can provide better results for larger-scale UAV ad hoc networks compared to MPBC and MPCR in terms of improving CH lifetime and throughput, reducing average delay.

Radar Selection Method Based on an Improved Information Filter in the LPI Radar Network

In order to save the radar resources and obtain the better low probability intercept ability in the network, a novel radar selection method for target tracking based on improved interacting multiple model information filtering (IMM-IF) is presented. Firstly, the relationship model between radar resource and tracking accuracy is built, and the IMM-IF method is presented. Then, the information gain of every radar is predicted according to the IMM-IF, and the radars with larger information gain are selected to track target. Finally, the weight parameters for the tracking fusion are designed after the error covariance prediction of every working radar, in order to improve the IMM-IF. Simulation results show that the proposed algorithm not only saves much more radar resources than other methods but also has excellent tracking accuracy.

LPI time‐based TMS against high‐sensitivity ESM

Low probability of interception (LPI) time refers to a time during which a certain airborne radar system is tracking the target without being intercepted by a high-sensitivity electronic support measurement (HSESM) on the target. LPI time is determined by the tracking process of the certain airborne radar system and the interception performance of an HSESM. This study proposes a track mission shifting (TMS) tactic of the distributed airborne radar system (DARS) or distributed airborne formation radar system (DAFRS) based on LPI time. First, this study defines a short-time average interception probability of HSESM on frequency search mode. Then, with adaptive dwell time design and the maximum illumination interval algorithm based on predicted tracking error covariance matrix, this study proposes to take interactive multiple models Kalman filter to describe target tracking process and introduces binary hypothesis test of chi-square and non-central chi-square distributions as target detection criterion during target tracking. Finally, with a partial prior knowledge of the opposed HSEMS on the target, this study proposes a TMS tactic model based on LPI time. Simulations show that LPI time is a significant reference value for DARS or DAFRS to turn over track mission against an opposed HSEMS.

The architecture and technology of cognitive electronic warfare

Development and applications of technologies of cognitive radio, software-defined network, cognitive network as well as anti-jamming and low intercept probability in radar and other communication systems have led to an exponential increase in the complexity of the electromagnetic environment. When confronted with the challenges in the future complicated battlefield environment, how to speed up the loop of “observe-orient-decide-act (OODA)” and realize electromagnetic agility is the key problem for electronic warfare system. To make the system more cognitive, we combine the theory of artificial intelligence with electronic warfare, which can significantly enhance the ability to sense a threat signal, make a jamming decision, and evaluate the jamming effect. Moreover, this will shorten the reaction time to unknown threats, speed up the OODA loop, and strengthen the operational capability of the system.

Non‐cooperative game‐theoretic distributed power control technique for radar network based on low probability of intercept

Here, the problem of non-cooperative game-theoretic distributed power control is studied in a radar network system based on low probability of intercept (LPI) subject to the signal-to-interference-plus-noise ratio (SINR) constraint and the transmit power constraint of each radar, where all the radars in the network share the same frequency band. The objective is to improve the LPI performance by reducing the transmit power caused by some radars' SINRs over the specified threshold. First, a novel LPI performance-oriented utility function is defined as a metric to evaluate power control. Then, consider that radars in the network are self-interested to maximise their own utilities, the distributed power control problem is formulated as a non-cooperative game, and an iterative power control algorithm is proposed that converges quickly to the Nash equilibrium (NE) of the non-cooperative game. Finally, the existence and uniqueness of NE are proved analytically. Numerical simulation results are provided to demonstrate that, compared with other methods, the presented algorithm not only guarantees the minimum SINR requirements of all radars but also improves the LPI performance for radar network.

Spread-Spectrum Method Using Multiple Sequences for Underwater Acoustic Communications

Direct-sequence spread-spectrum-based approaches have been adopted in underwater acoustic communications. In this paper, multiple sequences utilizing the periodic correlation characteristics of an original spreading waveform are superimposed, modulating multiple distinct symbols simultaneously within each block at the transmitter. Among those superimposed symbols, one is used as the pilot for channel estimation on chip level and others carry data. Similar to existing superposition schemes, the proposed approach also has low receiver complexity, only requiring matched filtering operations. However, the innovation of the proposed approach is perfect interference suppression, cyclic prefix (CP) is inserted to eliminate the interblock interference totally. Combined CP operation leading to an equivalent cyclic channel matrix with circularly shifted versions of spreading sequences, interferences can be solved considerably. The proposed technique is evaluated with both simulation and experimental data analysis. Data processing gives a brief discussion about low probability of detection and low probability of interception.

LPI radar network optimization based on geometrical measurement fusion

The power optimization problem and target assignment are investigated to improve low probability of interception (LPI) in a distributed radar network system. The target geometrical localization error and probability of detection are considered as QoS metrics of the network. We introduce geometrical fusion gain as a metric to fuse information for measuring target localization by multiple radars. The problem is then considered as an optimization challenge based on measurement error covariance ellipses, which satisfy detection and localization accuracy of the network. The LPI problem can be solved with two different objectives for the optimization as it minimizes the maximum power and cuts down on total power. Due to the combinatorial nonconvex and nonlinear nature of the optimization problems, relaxations are considered to make the problems more tractable. They can be efficiently solved by dividing them into two subproblems. Firstly, there is the power allocation in which a framework is proposed to compute minimum required power for a radar assignment scheme by applying a numerical method. Secondly, there is the radar assignment in which a heuristic assignment algorithm is suggested to acquire sufficient radar-to-target assignment based on calculated power. The simulation results show that the proposed algorithms considerably improve LPI performance while detection probability and target localization error constraints can be satisfied.

Joint Transmitter Selection and Resource Management Strategy Based on Low Probability of Intercept Optimization for Distributed Radar Networks

AbstractIn this paper, a joint transmitter selection and resource management (JTSRM) strategy based on low probability of intercept (LPI) is proposed for target tracking in distributed radar network system. The basis of the JTSRM strategy is to utilize the optimization technique to control transmitting resources of radar networks in order to improve the LPI performance while guaranteeing a specified target‐tracking accuracy. The weighted intercept probability and transmit power of radar networks is defined and subsequently employed as the optimization criterion for the JTSRM strategy. The resulting optimization problem is to minimize the LPI performance criterion of radar networks by optimizing the revisit interval, dwell time, transmitter selection, and transmit power subject to a desired target‐tracking performance and some resource constraints. An efficient and fast three‐step solution technique is also developed to solve this problem. The presented mechanism implements the optimal working parameters based on the feedback information in the tracking recursion cycle in order to improve the LPI performance for radar networks. Numerical simulations are provided to verify the superior performance of the proposed JTSRM strategy.

Subarray‐based time‐delay low sidelobes methods for space‐time coding array

A space-time coding array (STCA) system transmits an identical waveform with a small time offset across the array elements. It shares the characteristics of high angular resolution and instant wide angular coverage, leading to the low probability of interception as seen in the traditional multiple-input and multiple-output radar. Angle-time two-dimensional matched filter is required in the STCA. However, the sidelobe level (SLL) of the multi-dimensional ambiguity function in the range and angle domains is not as low as that desired in practical applications and the range resolution decreases as the number of elements increases. Here, two kinds of subarray-based time-delay methods are proposed to improve the resolution and reduce the SLL of the ambiguity function for STCA. Both the regular and irregular subarrays are considered, which increase the degrees of freedom and thus enhance the range resolution. Moreover, the SLL of the ambiguity function is reduced. Simulation results are provided to demonstrate the effectiveness of the proposed methods.

Design and Processing of a Novel Chaos-Based Stepped Frequency Synthesized Wideband Radar Signal.

The linear stepped frequency and linear frequency shift keying (FSK) signal has been widely used in radar systems. However, such linear modulation signals suffer from the range–Doppler coupling that degrades radar multi-target resolution. Moreover, the fixed frequency-hopping or frequency-coded sequence can be easily predicted by the interception receiver in the electronic countermeasures (ECM) environments, which limits radar anti-jamming performance. In addition, the single FSK modulation reduces the radar low probability of intercept (LPI) performance, for it cannot achieve a large time–bandwidth product. To solve such problems, we propose a novel chaos-based stepped frequency (CSF) synthesized wideband signal in this paper. The signal introduces chaotic frequency hopping between the coherent stepped frequency pulses, and adopts a chaotic frequency shift keying (CFSK) and phase shift keying (PSK) composited coded modulation in a subpulse, called CSF-CFSK/PSK. Correspondingly, the processing method for the signal has been proposed. According to our theoretical analyses and the simulations, the proposed signal and processing method achieve better multi-target resolution and LPI performance. Furthermore, flexible modulation is able to increase the robustness against identification of the interception receiver and improve the anti-jamming performance of the radar.

Low Probability of Intercept-Based Radar Waveform Design for Spectral Coexistence of Distributed Multiple-Radar and Wireless Communication Systems in Clutter.

In this paper, the problem of low probability of intercept (LPI)-based radar waveform design for distributed multiple-radar system (DMRS) is studied, which consists of multiple radars coexisting with a wireless communication system in the same frequency band. The primary objective of the multiple-radar system is to minimize the total transmitted energy by optimizing the transmission waveform of each radar with the communication signals acting as interference to the radar system, while meeting a desired target detection/characterization performance. Firstly, signal-to-clutter-plus-noise ratio (SCNR) and mutual information (MI) are used as the practical metrics to evaluate target detection and characterization performance, respectively. Then, the SCNR- and MI-based optimal radar waveform optimization methods are formulated. The resulting waveform optimization problems are solved through the well-known bisection search technique. Simulation results demonstrate utilizing various examples and scenarios that the proposed radar waveform design schemes can evidently improve the LPI performance of DMRS without interfering with friendly communications.

Poly-phase signal generation and optimizationof LPI Radar: A new approach

Low Probability of Intercept (LPI) Radar own certain positive characteristics make them nearly undetectable by Intercept Receivers. In a battle field, this present a considerable strategic problem. New digital receivers required complex signal processing techniques to detect these types of Radar. This paper address the problem of constructing a new hybrid waveform design using Poly-Phase modulation technique to optimize the detection performance of LPI Radar. Phase coded Pulse compression waveforms using Frequency Hopping Spread Spectrum (FHSS) are designed to evaluate the detection performance of LPI radar in terms of Discrimination factor (DF).The difference in DF of the Poly-phase coded and Binary phase coded signals is increasing with the increase in the phase values.The effect of noise on Hybrid Poly-Phase waveforms examined using the signal to noise ratios of -10dB,-15dB and -20dB and extract the parameter necessary for the LPI Radar system.