Diversity and coding for FH/MFSK systems with fading and jamming.II. Selective diversity

For pt.1 see ibid., vol.COM-35, p.1329-41 (1987). A performance evaluation is presented for selective diversity with feedback for frequency-hopping M-ary frequency-shift-keyed systems operating over Rayleigh faded channels in the presence of partial-band noise and partial-band tone jamming. The behavior of uncoded and coded systems is studied. For coded systems, the performance is evaluated for hard-decision receivers without channel state information and soft-decision receivers with perfect jammer state information. The results demonstrate that the performance of uncoded FH/MFSK with selective diversity is unacceptable. However, this diversity technique can offer definite improvements for coded FH/MFSK systems. Specifically, the effectiveness of selective diversity signaling depends on the provision of a feedback channel between the transmitter and receiver to provide the transmitter with the fading gains of the independently faded channels. To obtain an improvement from the selective diversity signaling scheme described here, there must be multiple independently faded channels between the transmitter and receiver. If not, the performance of the selective diversity signaling scheme will be identical to the performance of FH/MFSK without diversity     

动态频谱抗干扰系统在部分频带干扰下的性能

为了评估动态频谱抗干扰新体制在抗干扰通信中的性能,采用理论分析与仿真相结合的方法,研究了动态频谱抗干扰系统在部分频带干扰下的信道容量及比特误码率,并将其与常规跳频系统在部分频带干扰下的信道容量及比特误码率进行了比较.结果表明:在很宽的部分频带干扰因子取值范围内,动态频谱抗干扰系统的信道容量均大于常规跳频系统的信道容量,...     

Diversity and Coding for FH/MFSK Systems with Fading and Jamming--Part I: Multichannel Diversity

The performance of diversity and/or coding is evaluated for FH/MFSK signaling over Rayleigh fading channels in the presence of jamming. The effects of partial-band tone and partial-band noise jamming on uncoded and coded systems are considered. The results indicate that FH/MFSK signaling with diversity provides satisfactory performance for jammed fading channels. For coded FH/MFSK signaling over fading channels, noise jamming may be more effective than tone jamming. The amount of improvement resulting from the use of diversity in conjunction with coding depends upon many factors, including the nature of the channel, the degree of channel state information available at the decoder, the type of decoding, and the modulation alphabet size.     

Strategies for FH/MFSK Signaling with Diversity in Worst-Case Partial-Band Noise

Optimum diversity and worst-case partial-band noise jamming conditions have been derived for noncoherent energy detection of frequency-hopped (FH)M-ary frequency-shift keyed (MFSK) signals using a soft-chip decision suboptimum linear combining metric with perfect jamming-state side information. However, the assumption implicit in previous publications is that the error rate is first maximized over the jammer's partial-band duty factor for arbitrary diversity, and the result is then minimized over the amount of diversity. This paper shows that if the order of optimization is reversed, different conditions and performance are produced; that is, the previous solution is not a saddlepoint. This introduces some game-theoretic considerations for the communicator and the jammer, the risks and advantages of which are explored.     

自适应调零天线对快速跟踪干扰抑制的研究

为了有效地抑制来自跳频卫星通信系统上行链路的快速跟踪干扰,本文提出了一种数字波束形成与跳频相结合的新型干扰抑制技术(AJDBFFH).基于AJDBFFH技术,本文较好地解决了快速跟踪干扰与跳频有用信号相关所带来的干扰抑制问题.通过对快速跟踪干扰抑制的计算机仿真,其结果表明,AJDBFFH技术可以有效地抑制快速跟踪干扰,系统的误码率性能得到了明显的改善.     

Frequency-hopped spread spectrum in the presence of a followerpartial-band jammer

A countermeasure to a partial-band follower jammer is proposed for frequency-hopped spread-spectrum communications. This technique randomizes the transmission technique used by the transmitter (and receiver). Either the information is carried by M tones which are transmitted in a frequency slot, or by M frequency slots which contain signal energy. As a counter-countermeasures, the jammer randomizes between jamming the same frequency slot being used by the communicator, or jamming a subset of the slots not being used by the communicator. The performance for randomized strategies for the communicator and jammer is investigated. It is shown that the proposed technique enhances the system's performance     

战术跳频系统智能抗干扰决策

作为一种有效的抗干扰方法,跳频（Frequency hopping, FH）技术已被广泛应用于战术通信系统来提高在强对抗环境下军事通信网络的可靠性。跳频通信网络面临的主要威胁是具有灵敏的频谱侦察和频率捷变能力的跟踪干扰机。为提高战术跳频通信系统在跟踪干扰攻击环境中的抗脆性和吞吐量,本文提出了一种基于双深度Q网络（Double deep Q-network, DDQN）的功率和跳速联合抗干扰决策方法。该算法将战术电台发射机与跟踪干扰机之间的对抗建模为马尔可夫决策过程（Markov decision process, MDP）,其中干扰器通过调整频谱扫描速率提高干扰效能,战术电台终端则将接收状态反馈信息作为算法输入,根据决策网络的输出调整数据传输的发射功率和跳频速率。该算法模型在未知环境状态和干扰参数的情况下,通过与环境的交互学习更新网络参数,逐渐收敛于最佳功率和跳速联合控制策略,以使跳频通信系统的平均吞吐量最大化。仿真结果表明,相比传统的无模型抗干扰方法,本文所提算法在跟踪干扰环境下能够更有效改善跳频系统的抗干扰性能。     

Concatenated combined modulation and coding of frequency hoppingmultiaccess systems

A spread-spectrum system that does not have a separate state for initial code acquisition is presented. A uniform random variate selects one of several Gold codes for transmission, thus removing the notion of pseudorandom codes from spread-spectrum systems, making the effective code length infinite, and leading to acquisitionless systems. Because coding is critical to the proposed multiaccess frequency-hopping (FH) system, more powerful codes are needed. The performance of the proposed multiaccess system using the combined modulation and coding technique (trellis) concatenated with Reed-Solomon codes in partial-band jamming is investigated. The FH multiaccess performance of noncoherent soft detection of MFSK in association with trellis coding is introduced and the performance compared to that using RS outer/RS inner concatenated codes     

Independent multitone jamming of FH/MFSK in Rician channels

We derive exact expressions of the symbol error rate (SER) performance of orthogonal, frequency-hopped, noncoherent M-ary frequency-shift-keying (FH/MFSK) receivers in the presence of independent multitone jamming (MTJ), as well as thermal and other wideband Gaussian noises. Both the signal tones and the multiple jamming tones are affected independently by Rician fading. Both the slow-hopping and fast-hopping systems are considered. In our derivation, we exploit the fact that the multipath components of the signal and jamming tones can be combined with the other Gaussian noises to form a single Gaussian process. Using this technique, we are able to obtain compact exact SER expressions which can be computed efficiently. From the computation results we provide physical explanations on the effects of several system parameters, such as jamming fraction, fading conditions and number of hops per symbol, on the SER performance of slow and fast FH/MFSK systems under independent MTJ     

The Analyses of Uncoded Performances for Certain ECCM Receiver Design Strategies for Multihops/Symbol FH/MFSK Waveforms

Frequency-hopping (FH)M-ary FSK (MFSK) spread-spectrum modulation is an effective choice for an electronic counter-countermeasures (ECCM) system. When the power efficient MFSK (M > 2) baseband orthogonal waveform is transmitted withL-fold diversity under constrained symbol energy, the resultant multiple (L) hops/symbol FH/ MFSK becomes a most viable low probability of intercept (LPI) waveform. In this paper, analyses are presented for the uncoded performance of such a waveform for two types of square-law nonlinear combining soft-decision receiver strategies under the assumption of worst-case partial-band noise jamming (countermeasures). The receivers employ, prior to combining, nonlinear weighting strategies of 1) adaptive gain control and 2) soft limiting (clipping) of the detector output of each channel of the dehopped waveform. The primary focus is on exact analytical results and, as such, the system's thermal noise is not neglected in the analyses. Numerical results of the error rates are graphically displayed as a function of signal-to-jamming power ratio withLandMas parameters under assumed values of signal-to-noise ratio. It is shown that. a diversity gain for error-rate improvement is realized for the nonlinear diversity combining receiver strategies. No attempt is made in this paper to compare the diversity performance to any error-control coding schemes.     

短波FH/OFDM通信系统抗跟踪式干扰性能分析

对于短波多载波跳频通信系统,跟踪式干扰是一种有效的干扰模式。分析了正交频分复用( OFDM)部分子信道干扰与符号误码率的关系,通过仿真获得了最佳跟踪干扰的部分时间参数,结合OFDM频谱结构与干扰频谱关系,推导了高斯信道条件下部分频带干扰和多音干扰时系统误码率,分析了短波FH/OFDM通信系统抗跟踪式干扰的误码率性能,仿真结果表明：跟踪干扰时间窗口对误码率的影响与部分频带干扰因子和信干比有关;在部分频带干扰与部分时间干扰之间,存在等效的干扰效果区域;多音干扰因子越大,系统所受影响越大,跟踪干扰时间窗口对误码率的影响与多音干扰因子和信干比有关,针对OFDM符号的多音干扰影响要远大于部分频带干扰的影响;跳频与OFDM技术的结合、提高载波跳速、减小跟踪式干扰对OFDM符号的影响,也是消除多音干扰的重要手段。     

Coherent Detection of Frequency-Hopped Quadrature Modulations in the Presence of Jamming--Part I: QPSK and QASK Modulations

This paper examines the performance of coherent QPSK and QASK systems combined with FH or FH/PN spread spectrum techniques in the presence of partial-band multitone or noise jamming. The worst-case jammer and worst-case performance are determined as functions of the signal-to-background noise ratio (SNR) and signal-to-jammer power ratio (SJR). Asymptotic results for high SNR are shown to have a linear dependence between the jammer's optimal power allocation and the system error probability performance.     

Effect of worst case multiple partial-band noise and tone jammerson coded FH/SSMA systems

The author characterizes and evaluates the effect of simultaneous multiple partial-band noise or tone jammers and other user interference on a single communication link employing frequency-hopped spread-spectrum (FH/SS) signaling, M-ary frequency-shift keying (FSK) modulation with noncoherent demodulation, and Reed-Solomon coding. For the symbol error probability of these systems, the author derives exact expressions in the absence of multiple-access interference and tight upper bounds in the presence of other-user interference. Although the analytical methods are valid for any number of multiple jammers, the numerical study is restricted to the cases of two and three-partial-band noise and tone jammers. For fixed values of the spectral densities of noise jammers, or the energies per symbol of tone jammers, the worst-case fraction of the band that each jammer should use in order to maximize the error probability of the FH/SS or FH/SSMA system is evaluated. For the range of the signal-to-jammer power ratios examined, multiple-noise or multiple-tone jammers appear to have no advantage over single-tone jammers of equivalent spectral density or energy per symbol, but achieve approximately the same worst-case performance by jamming smaller fractions of the band     

Optimization of a hybrid SFH/DS MFSK link in the presence of worstcase multitone jamming

The performance of a hybrid slow frequency hopped direct sequence multiple frequency shift keyed (SFH/DS MFSK) communication link in the presence of partial band multitone jamming is considered. The communication signal is characterized by a DS-spread MFSK signal bandwidth that may exceed the FH slot spacing, and the signal consists of multiple M-ary symbols per DS code period. An equation for the bit error rate (BER) is developed for the signal in the presence of multitone jamming. The equation is flexible enough to allow examination of optimization of jamming strategy. It is shown that the jamming strategy may be optimized by varying the number of tones, their placement, or both. It is shown that in the presence of optimized jamming, overlapping systems are more resistant to jamming than nonoverlapping systems with equal parameters (except for the number of FH slots). It is also demonstrated that, in some cases, the addition of DS spreading to an FH system, without increasing the total system bandwidth, can significantly improve the system's resistance to partial band multitone jamming     

音调高跳速碰撞干扰对FH／MFSK系统的干扰性能分析

针对跳频／多路频移键控（FH／MFSK）通信系统的特点和较强的抗干扰能力,研究了一种动态阻塞干扰样式——高跳速碰撞干扰,分析了高跳速碰撞干扰的基本特性和优点,建立了一种音调高跳速碰撞干扰模型,分析了对FH／MFSK系统的干扰性能,并进行了FH／MFSK系统在高跳速碰撞干扰下的误码率性能仿真。仿真结果表明,高跳速碰撞干扰对跳频体制能构成较大的威胁。     

Capacity and cutoff rate of coded FH/MFSK communications withimperfect side information generators

When JSI (jamming state information) is imperfect due to thermal noise, the capacities and cutoff rates of the channels are calculated as a function of the signal-to-jamming-noise ratio for memoryless, noncoherent FH/MFSK (frequency-hopped M-ary frequency-shift-keying) systems under partial-band noise jamming (PBNJ). Both soft- and hard-decision metrics with perfect, imperfect, and no JSI are considered. The first of three imperfect JSI generator uses the maximum a posteriori (MAP) decision rule based on the energy from an FH tone frequency which is near the M-signaling FH tone frequencies. The second decision rule utilizes the MAP rule, but it is based on the total energy received at the M-signaling FH tone frequencies. The third generator has the same decision statistics as the second generator, but its decision rule is an easily implementable suboptimum rule. If hard decision are made and code rates are high, then the differences between the imperfect JSI generators and perfect JSI generator can be larger than 1 dB. If soft decisions are made, then the differences between the imperfect and perfect JSI cases are negligible     

存在检测误差的抗跟踪干扰最优跳速设计

跟踪干扰对跳频通信构成严重威胁。首先采用Stackelberg博弈模型对存在检测误差条件下的通信干扰与抗干扰进行建模,在该模型中,存在一个先行者和一个跟随者,其中,通信方作为先行者进行跳频通信,跟踪干扰方作为跟随者检测跳频通信信号并实施干扰。分别推导了通信方的最优跳速,以及干扰方最优检测时间与干扰时间的分配策略,证明了当信噪比小于一定门限时,干扰方的最优干扰策略是盲干扰,通信方的最优抗干扰策略是慢速跳频。最后,对理论分析结果进行了计算机仿真验证,并将所提算法与盲跳频和变速跳频进行了比较,结果表明,所提算法的抗跟踪干扰性能显著优于已有算法。      

一种新的部分频带噪声干扰模型下的FH/MFSK系统性能分析

部分频带噪声干扰(PBNJ)是一种主要的窄带干扰,它对通信系统性能的影响十分突出。该文针对FH/ MFSK系统中,传统的部分频带干扰模型的干扰带宽最小分辨率是一个跳频子带带宽(即MFSK信号的带宽),研究了更具有实际价值的新的部分频带干扰模型,即将干扰带宽最小分辨率精确到MFSK信号带宽的1/M。该文推导了莱斯衰落信道下的误比特率(BER)公式,给出了其闭合表达式,并通过计算机仿真验证了理论推导的正确性。理论分析与仿真结果表明,M,Nh,越小,传统与新PBNJ模型下FH/MFSK信号的BER性能差异就越大。     

Mathematical Models for Cochannel Interference in FH/MFSK Multiple-Access Systems

FH/MFSK has been Proposed for a multiuser spread spectrum digital communication system to combat both self-jamming and intentional jamming. An independence assumption at the energy detector outputs is used to evaluate such a system for a digitized voice mobile radio system [11]. This paper presents a correlated model and compares its performance to an independence model under the symbol error probability criterion. A Gaussian process model is also developed for comparison. It is found that the conventional Gaussian approximation is inadequate in predicting the number of users that can be accommodated by an FH/MFSK system using the conventional receiver. Furthermore, for the cases we evaluated, the independence model provides an excellent approximation to the correlated model. Additionally, a conditional Chernoff bound is presented for the more general case of frequency-hopping systems with multiple hops per symbol.     

宽带MFSK/DFH系统抗部分频带噪声干扰性能分析

本文提出一种宽带MFSK/DFH系统模型,与常规差分跳频系统相比,在跳频点数一定条件下,通过增加多进制编码器复杂度,提高编码增益的方法提高系统抗干扰性能。对基于FFT的宽带MFSK/DFH系统接收机抗干扰性能进行了理论分析和计算机仿真验证。结果表明:在相同条件下,提出方法通过增加多进制编码器约束长度提高了系统抗干扰能力,实现方法简单有效,具有一定的实际应用价值。