Implementation and analysis of spectral subtraction in deterministic wide‐band anti‐jamming scenarios

In this paper, we propose an approach for mitigating deterministic and partially deterministic jamming signals from the received signal space, thus yielding recoverable signal vectors at a target receiver. Aimed at friendly or self‐jamming environments, where enemy communication jamming is paramount. The proposed approach employs a concept called spectral subtraction, where one or more known signals can be removed from the received signal space via the subtraction of their spectral characteristics from the received composite signal. Although spectral subtraction is used in a variety of speech communication scenarios, it has not been extensively employed in wireless applications because of several practical challenges, such as achieving both sufficient time alignment and accurate waveform characterization of the signal to be removed. In order to assess these challenges, as well as analyze the potential benefits of the proposed approach, validation was performed using actual over‐the‐air experimentation using software‐defined radio technology. The feasibility study of the proposed approach for achieving sufficient signal removal was examined for a constrained operating scenario, and experimental results show that spectral subtraction can be achieved in a physical transmission environment. Although physical simulations were limited, they provide baseline results for a previously untested method of jammer suppression. Copyright © 2016 John Wiley & Sons, Ltd.     

An energy‐efficient anti‐jam cognitive system for wireless OFDM communication

In this paper, anti‐jamming capabilities are proposed for a generic OFDM‐based wireless communication system. The performance of a wireless system may severely degrade in presence of jamming or intentional interferences. A malicious entity can send strong interference or noisy signals in the same transmit frequency band thus preventing the intended receiver to correctly decode the transmitted data. As a countermeasure, our work proposes algorithms and techniques to restore the system performance in presence of such malicious entities. Proposed anti‐jamming system consists of an adaptive framework that adapts itself to varying jammer behavior and wireless environment, and then, it chooses an optimal strategy to effectively cancel out the effect of jamming and channel fading. Optimization problem is formulated as a multi‐objective criterion for maximization of system throughput and minimization of energy consumption. Simulation results computed in Rayleigh fading channels with different wideband jamming modes and powers show that the proposed system effectively cancels out the jamming and channel fading effects thus maximizing the system performance and minimizing cost of energy consumption. Copyright © 2013 John Wiley & Sons, Ltd.     

Amplify‐and‐forward‐based cooperative jamming strategy with power allocation for secure communication

This paper deals with the use of jamming transmission for secure amplify‐and‐forward‐based relay networks with total power constraints. An approach that the source and the relay use some of their available power to transmit jamming signals in order to create interference at the eavesdropper is investigated. Assume that the relay and destination have an a priori knowledge of the jamming signals. A power allocation policy that defines how the available power is distributed between the message signal and that of the jamming signal is presented. The results show that the proposed approach can increase the secrecy level and that a positive secrecy rate can be achieved even when the eavesdropper may be near the source. Copyright © 2014 John Wiley & Sons, Ltd.     

Information leakage in bi‐directional IFD communication system with simultaneously transmitted jamming sequence

In this paper, we describe a simultaneously transmitted jamming (ST‐jamming) for bi‐directional in‐band full‐duplex (IFD) system to improve information security at the physical layer. By exploiting ST‐jamming, each legitimate user transmits data samples and jamming samples together in one orthogonal frequency division multiplexing symbol according to given traffic asymmetry. Regardless of the traffic difference in both directions in IFD communication, eavesdropping of confidential information is prevented in both directions simultaneously without the loss of data rate. We first propose an encoding scheme and the corresponding decoding scheme for ST‐jamming to be used by the legitimate users. In addition, we study a transceiver structure of the legitimate users including a baseband modem uniquely designed for the use of ST‐jamming. The leakage of confidential information at an eavesdropper is then quantified by studying the mutual information between the confidential transmit signals and the received signals of the eavesdropper. Simulation results show that the proposed ST‐jamming significantly reduces the leakage of legitimate information at the eavesdropper.     

General switch‐and‐examine relaying for demodulate‐and‐forward cooperative diversity

Two new demodulate‐and‐forward schemes of multi‐relay cooperative diversity with switch‐and‐examine relaying (SER) are analyzed. To reduce relay usage and enhance bandwidth efficiency, the two new cooperative diversity schemes employ a switch‐based relay selection. The proposed schemes consume less communication resource than regular relaying schemes, such as the selection combining (SC) or maximal ratio combining (MRC) schemes that always use all relays, and also achieve better performance than distributed switch‐and‐stay schemes. In the first scheme, the decision statistic for relay usage and selection is based on the signal‐to‐noise ratio (SNR). In the second scheme, the log‐likelihood ratio (LLR) of received signals is used for the decision of relay usage and selection. With the two SER schemes, the bit error probability (BEP) of binary phase shift keying (BPSK) and the average number of used paths are derived and expressed in closed‐form for the independent and identically distributed (i.i.d.) Rayleigh fading channels. Numerical and simulation results are presented for performance illustrations. According to the numerical results, the LLR‐based SER not only achieves a lower BEP but also consumes less relay resource than the SNR‐based SER. Furthermore, the LLR‐based SER scheme even outperforms the corresponding SNR‐based SC scheme for a range of average SNR. Copyright © 2014 John Wiley & Sons, Ltd.     

对V-调频信号的间歇采样转发干扰研究

间歇采样转发是一种新型的干扰式样,可以产生相干假目标串的干扰效果。研究了对V-调频信号的间歇采样干扰方法。在阐述了间歇采样转发干扰的基本原理后,分析了间歇采样转发信号的时频和频域特性,在理论上推导了干扰信号经匹配滤波后输出的信号模型;在此基础上,根据低阶假目标的幅相特性,提出了一种使假目标回波和真实目标回波的反相对消方法,并进一步推导了为实现反相对消对转发时延、转发频率、转发功率的要求。仿真结果表明这种方法能实现目标回波的有效对消。该文研究成果对于间歇采样转发干扰机的原理设计及使用具有指导意义。     

Nelder‐Mead–based power optimization for secrecy enhancement in amplify‐and‐forward cooperative relay networks

Cooperative communication based on relaying nodes has been considered as a promising technique to increase the physical layer security (PLS) performance in wireless communications. In this paper, an optimal power allocation (OPA) scheme based on Nelder‐Mead (NM) algorithm is proposed for improving the secrecy rate of amplify‐and‐forward (AF) cooperative relay networks employing cooperative jamming (CJ) scheme. The proposed hybrid jamming scheme allows the source and selected relay to transmit the jamming signal along with the information to confound the eavesdropper. The path selection probability of ant colony optimization (ACO) algorithm is used for selecting the relay for transmission. The performance based on secrecy rate is evaluated for “n” trusted relays distributed dispersedly between the source and destination. Gradient‐based optimization and three‐dimensional exhaustive search methods are used as benchmark schemes for comparison of the proposed power optimization algorithm. The secrecy performance is also compared with conventional AF scheme and CJ scheme without power optimization (EPA). The impact of single and multiple relays on secrecy performance is also evaluated. Numerical results reveal that, compared with the gradient method and exhaustive search algorithm, the proposed power allocation strategy achieves optimal performance. Also, the derived OPA results show a significantly higher secrecy rate than the EPA strategy for both CJ and AF schemes.     

SAR二维余弦调相转发散射波干扰原理

本文提出一种新的合成孔径雷达(SAR)干扰方法:SAR二维余弦调相转发散射波干扰.该方法将SAR二维余弦调相转发干扰同散射波干扰结合,利用二维余弦调相转发干扰实现多假目标干扰,再通过散射波干扰使干扰回波携带真实目标的散射信息,二者的结合相得益彰,为实现多假目标干扰和假目标携带真实目标散射信息提供了一种可行途径,实现了对SAR在时域、频域和极化域都较为逼真的多假目标欺骗干扰.理论分析和仿真实验验证了该干扰方法的可行性和有效性.     

基于改进型最大信噪比算法的抗压制性干扰研究

自雷达诞生以来,抗干扰能力一直是评价一部雷达性能的关键性指标,特别是随着战场电磁环境的日益复杂,雷达抗干扰问题变得尤其重要。针对抗压制性干扰,改进了传统意义上基于最大信噪比的盲源分离算法,提出了使用干扰重构算法取代滑动平均处理的方法,获得了比传统方法分离出质量更高的雷达信号,输出信号与源信号相关性更强。     

Low‐Cost High‐Performance TDD Synchronizer for WiBro RF Repeater

WiBro radio frequency (RF) repeater is used for solving the problem of partial shadow areas in the wireless communication field that uses time‐division duplexing (TDD) mode. In this paper, a method to efficiently generate TDD signals for WiBro RF repeater is proposed and its digital circuit is implemented. A TDD signal is detected from RF signals transmitted/received to/from RF repeater and then inputted again into the RF repeater, so that it can operate normally. First, the envelope of downlink signals is detected and then clamped to extract the basic form of a TDD signal using an operational amplifier circuit. Next, the TDD signal is generated by restoring and filtering the shape which has been distorted by the wireless channel. The algorithm and system to acquire TDD signal are developed with a goal to have simple but powerful functions with as little cost as possible. The proposed method is implemented as an RF‐digital integrated system and verified through the experiments under the same condition as actual WiBro service environment.     

Jamming detection approach based on fuzzy assisted multicriteria decision‐making system for wireless sensor networks

The jamming detection approach based on fuzzy assisted multicriteria decision‐making system (JDA) is proposed to detect the presence of jamming in downstream communication for Cluster based Wireless Sensor Network (CWSN). The proposed approach is deployed in cluster head (CH). The JDA functions in two aspects: First, the CH periodically measures the jamming detection metrics namely Packet Delivery Ratio (PDR) and Received Signal Strength Indicator (RSSI) of every node in the cluster to determine the behavior of the sensor nodes. In order to determine the behavior of members in the cluster, the CH compares the measured PDR with the PDR threshold. If the measured PDR is lesser than the PDR threshold, then CH applies the TOPSIS method on the PDR and RSSI metrics to determine the presence of jamming. These metrics are considered as the criteria and the nodes or the members are considered to be the alternatives. Next, the fuzzy logic is applied on the results obtained from the TOPSIS method to optimize the jamming detection metrics and identify the presence of jamming accurately. The proposed jamming detection approach detects well and arrives at 99.6% jamming detection rate as shown in simulation.     

间歇采样转发干扰参数分析

间歇采样转发干扰的参数设置对干扰效果有较大影响,干扰参数决定了间歇采样转发干扰信号进入雷达接收机后的脉压结果。通过数学理论推导给出了间歇采样周期和干扰信号占空比两类干扰参数与干扰效果的明确数学对应关系,并通过数字仿真验证了数学推导和理论分析的正确性。     

基于压缩感知的间歇采样转发干扰方法

针对现代雷达信号带宽大、频率高,相干干扰实现困难的问题,提出了基于压缩感知的间歇采样转发干扰方法.研究了压缩感知基本原理及其对模拟信号处理的实现方法,分析了压缩感知对线性调频信号的间歇采样实现方法及其转发干扰效果.仿真结果表明,压缩感知理论对宽带雷达信号间歇采样具有较好的适用性,对宽带雷达能够实现较好的干扰效果.     

分布式多站雷达转发式欺骗干扰研究

作为一种重要的欺骗干扰样式,转发式干扰通过对雷达发射信号存储转发,形成的距离欺骗假目标在空间上是分散的。而分布式多站雷达进行空间配准时,会将未分布于一个空间分辨单元内的假目标剔除,使之失去干扰效果。因此,有必要研究转发式干扰对分布式多站雷达的干扰能力。该文在多站雷达中各雷达站相距不远的条件下,从空间分辨单元的物理含义入手,导出了多站雷达在一定空间分辨率下,转发式干扰能对其进行有效干扰的条件。当干扰机位于远场区域时,证明了相同时延产生的假目标必然可对多站雷达实现有效欺骗;当干扰机位于近场区域时,推导出有效干扰的欺骗距离范围,通过控制转发延迟量,可保证对多站雷达的欺骗效果。该结论对多站雷达的干扰和抗干扰均具有重要的指导意义。     

对地域通信网跳频通信干扰及仿真研究

由于跳频通信的抗干扰性和保密性强,在地域通信网组网过程中得到了广泛的应用。分析了跳频通信的特点和抗干扰性,介绍了对其进行干扰的多种方法,提出了对跳频通信进行跟踪干扰时干扰机的有效配置区域,并对干扰机的配置区域进行了计算机仿真。     

对SAR的方位向间歇采样转发干扰

立足于干扰机天线收发分时体制,研究了方位向间歇采样转发干扰方法。其核心思想是对SAR发射的脉冲串信号进行间歇采样和存储,再经一定处理后恢复为模拟信号在下一个或数个脉冲重复周期转发出去形成干扰,然后利用SAR方位向匹配滤波特性,就可以形成方位向多假目标欺骗的效果,避开了高速采样和同时收发高度隔离的难题。理论分析了方位向间歇采样转发干扰的原理和干扰效果,指出了间歇采样周期、占空比及干扰组数等关键参数对干扰效果的影响,通过仿真实验进行了验证。研究结果表明,方位向间歇采样转发干扰是种有效的、易于工程实现的干扰样式。      

逆合成孔径雷达散射波干扰技术研究

针对传统转发干扰对ISAR只能形成点斑干扰的不足,提出了ISAR散射波干扰方法,该方法将截获的ISAR发射信号直接转发至目标,经目标散射后形成散射波干扰信号,获得了更为丰富的干扰信息。文中根据双基地ISAR的成像理论,将干扰机与ISAR接收机分别等效为双基地ISAR的发射站和接收站,建立了ISAR散射波干扰模型,分析了散射波干扰的功率以及对ISAR的干扰效果。研究结果表明通过控制干扰机的转发时延和等效双基地角,散射波干扰可以对ISAR形成单个或多个不同位置的假目标欺骗干扰,而且实现简便,是一种对ISAR形成假目标数量欺骗干扰的有效手段。     

基于运动干扰站的SAR-GMTI相干噪声调频干扰

合成孔径雷达-地面动目标指示(SAR-GMTI)系统通常采用多个通道对杂波和干扰进行抑制和对消,传统的合成孔径雷达(SAR)噪声调频压制干扰难以对SAR-GMTI实施有效干扰。文中针对多通道SAR-GMTI提出基于运动干扰站的相干噪声调频干扰。该方法利用运动干扰站转发式干扰的成像特性实现方位向扩展,利用方位向相干噪声调频实现距离向扩展,将二者有机结合,可同时实现干扰目标在方位向和距离向的二维扩展。研究结果表明:该方法可获得部分方位向处理增益,有效降低了干扰功率需求,对SAR和SAR-GMTI均可产生灵活可控的干扰条带,可同时保护地面分布式静止目标和运动目标。理论分析和仿真实验验证了该干扰方法的可行性和有效性。     

间歇采样转发干扰压制效果分析

分析了间歇采样转发干扰原理及其不同形式,由于间歇采样转发干扰机理不同于传统的噪声压制干扰,提出了一种基于恒虚警检测的间歇采样转发干扰压制效果分析方法,并利用仿真实验进行了验证。实验表明,该方法能够正确分析间歇采样干扰压制效果。     

Fuzzy logic–based jamming detection algorithm for cluster‐based wireless sensor network

In this paper, a fuzzy logic–based jamming detection algorithm (FLJDA) is proposed to detect the presence of jamming in downstream data communication for cluster‐based wireless sensor networks. The proposed FLJDA keeps an eye on the existing nodes and new node to determine their behavior by applying fuzzy logic on measured jamming detection metrics. To monitor the behavior of the nodes, the FLJDA computes the jamming detection metrics, namely, packet delivery ratio and received signal strength indicator. The major features of this paper are the following: (1) The jamming detection algorithm is specifically implemented for downstream data communication, (2) cluster head estimates jamming detection metrics for detecting the jamming unlike the existing algorithms where individual nodes explicitly collect the jamming detection metrics, and (3) the proposed algorithm optimizes the jamming detection metrics on the basis of fuzzy logic unlike the existing approaches, which uses merely jamming detection threshold alone for jamming detection. The simulation results of the proposed system provide the true detection ratio as high as 99.89%.