Effects of fading and partial-band noise jamming on a fast FH/BFSKacquisition receiver with noise-normalization combination

We present the performance analysis of a fast frequency-hopped (FH) binary orthogonal frequency-shift keying acquisition receiver for communication against adverse environments. The receiver employs noncoherent, noise-normalized, matched-filtered (MF) correlation detection for rapid acquisition in the search mode. Our analysis includes four types of communication environments, namely additive white Gaussian noise (AWGN) channel, AWGN channel with partial-band noise jamming, fading channels, and fading channels with partial-band noise jamming. The considered fading channels include Nakagami-m, Rician, and Rayleigh amplitude models. Based on Beaulieu's (see ibid., vol.38, no.9, p.1463, 1990) convergent series approach, efficient analytical formulas are developed for performance evaluation. Example performance results for various environments are presented in terms of two acquisition probabilities, namely the detection probability and the false alarm probability of the noise-normalized MF detector. It is analytically shown that with a short MF correlation length and with a sufficiently large ratio of signal power to noise power the fast FH diversity combining yields noticeable performance improvement for environments with strong fading. When the MF correlation is lengthened, this improvement tends to fade away and the diversity combining results in performance loss     

Vector similarity-based detection scheme for multi-antenna FH/MFSK systems in the presence of follower jamming

Follower partial band jamming has been recognised as an efficient strategy to degrade the performance of frequency hopping (FH) systems. To alleviate this detrimental effect, a novel detection scheme for slow FH/Mary frequency shift keying systems, which use two receive antennas in a quasi-static flat fading channel, is proposed. Specifically, using the principle of vector similarity, an area-based vector similarity metric is formulated to give an estimate of the unknown spatial correlation of the received jamming components at the two receive antennas. The jamming signal can then be removed in the symbol detection process. The improved performance of the new scheme is verified by using an analysis under a jamming dominant environment as well as simulated bit error rate results.     

Performance analysis of two serial-search acquisition schemes for FH spread spectrum signals

Initial synchronization (acquisition) schemes of frequency hopped (FH) spread spectrum signals often make use of serial-search acquisition techniques. Two FH serial-search acquisition schemes are introduced and analysed. These schemes are the fixed dwell-time with false alarm memory (FDT/FAM) and the double dwell-time with binary integration (DDT/BI) scheme. Statistical properties namely, probability density function, characteristic function and mean value of the random acquisiton time of each acquisition scheme are obtained. The performances of the FDT, FDT/FAM and DDT/BI acquisition schemes are established and compared in the presence of partial band noise jamming, partial band tone jamming and additive white gaussian noise (AWGN). The results indicate that the DDT/BI acquisition scheme outperforms the FDT and FDT/FAM acquisition schemes.     

New robust threshold setting method for frequency-hopping acquisition

A new, very robust threshold setting method for the serial search acquisition of frequency hopping (FH) waveforms, the 'reference channel detector' (RCD), is proposed and analysed. It is shown that this detector has considerable immunity when subjected to large signal dynamics and pulse jamming. Especially in pulse jamming, this procedure is a much more appropriate solution than the constant and adaptive threshold setting methods reported previously.<>     

多序列跳频系统及其在AWGN信道下误码率性能分析

常规跳频系统发送的调制信号易被干扰损伤。本文提出一种新的多序列跳频系统,无需对载波进行调制,数据分组从一簇相互正交的跳频序列中选出某一跳频序列,该跳频序列的当前频率由射频端直接发送。相比差分跳频,多序列跳频的发送频率不仅是用户数据的函数,也是跳频序列的函数,增加了对发送频率的约束,因此可以采用窄带接收,更好地抑制了带外干扰。在AWGN信道下简要讨论了多序列跳频抗跟踪干扰性能,重点分析了其抗部分频带干扰性能。计算和仿真表明,多序列跳频受跟踪干扰影响不大;最坏部分频带干扰下,误码率为10^-5要求的信干比,MSFH比DFH低约1.5dB,比常规跳频低约2.5dB。      

Analysis of an antijam FH acquisition scheme

An easily implemented matched filter scheme for acquiring hopping code synchronization of incoming frequency-hopping (FH) signals is analyzed, and its performance is evaluated for two types of jamming: partial-band noise jamming and partial-band multitone jamming. The system is designed to reduce jammer-induced false alarms. The system's matched filter output is compared to an adaptive threshold that is derived from a measurement of the number of acquisition channels being jammed. Example performance calculations are given for the frequency coverage of the jamming either fixed over the entire acquisition period or hopped, that is, changed for each acquisition pulse. It is shown that the jammer's optimum strategy (the worst case) is to maximize the false alarm probability without regard for the effect on detection probability, for both partial-band noise and multitone jamming. It is also shown that a significantly lower probability of false acquisition results from using an adaptive matched filter threshold, demonstrating that the strategy studied here is superior to conventional nonadaptive threshold schemes     

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     

基于附加频移的跳频同步组网设计与分析

为了提高跳频同步组网的频点利用率,提出了一种基于附加频移的跳频同步组网方案。首先,给出了基于附加频移跳频通信的基本模型和收发双方的实现方案;然后,基于该跳频通信模型,给出了同步组网的网络拓扑结构。该方案在整个工作频段内能够使用所有可用频点进行同步组网,提高了频点利用率。分析结果表明,在相同子网数下,该方案较常规跳频同步组网还具有更小的碰撞概率和比特差错率,同时该方案还增加了敌方的侦察分选难度和干扰难度。     

跳频通信中阻塞干扰样式的自动识别

对跳频通信系统所处的干扰环境进行分析,可以使通信双方针对不同的干扰选择正确的抗干扰措施,对于跳频通信系统,跟踪干扰和阻塞干扰是非常有效的干扰方法。现有的干扰抑制算法只对某一类型的干扰有效,在干扰抑制之前,需要对干扰类型进行识别。本文以 FH-GMSK （frequency hopping-gaussian filtered minimum shift keying）通信系统为载体,对跳频通信中常见的阻塞干扰样式识别进行了研究,从接收信号中联合提取干扰的时域、频域和时频域特征,得到了一组稳定性好、对识别信噪比不敏感的特征参数,在不需要干扰先验知识的情况下对FH-GMSK通信系统中常用的阻塞干扰样式进行自动识别。仿真结果表明,对于跳频通信中常见的阻塞干扰信号,本方法在不同识别信噪比的情况下能获得很高的正确识别率。     

基于重叠缓冲预解跳的DS/FH扩频信号快速捕获

DS/FH(Direct Sequence/Frequency Hopping)扩频信号捕获相对直接序列扩频(Direct Sequence Spread Spectrum,DSSS)需要更多维度的搜索,捕获电路复杂。针对现有DS/FH扩频信号捕获算法复杂度高、电路结构与波形参数强相关,以及通用性差、灵活度低的问题,提出了一种基于重叠缓冲预解跳的DS/FH扩频信号快速捕获方法,利用双缓冲补零(Double Block Zero Padding,DBZP)缓冲单元与预解跳单元的灵巧结合,将时域-频域-多普勒域高度耦合的扩跳频图案搜索进行降维分离,在保证积分增益的同时降低了捕获实现的复杂度。数值分析与仿真结果表明,所提方法兼顾了捕获性能与运算资源,相比现有基于预解跳方法的DS/FH扩频信号捕获算法的运算量减小了50%。     

跳频通信系统抗干扰性能分析

在介绍跳频通信基本原理的基础上,分析了在部分频带干扰和宽带阻塞干扰这两种常见干扰下的跳频通信系统的抗干扰性能,并借助计算机仿真工具MATLAB进行程序仿真,得到了在两种干扰下的误码率—信噪比曲线,从而验证了由理论分析而来的结果。同时,提出了用信号分集来克服部分边带干扰,并分析了其效果。     

ML-based follower jamming rejection in slow FH/MFSK systems with an antenna array

The jamming robustness of frequency hopping (FH) systems with M-ary frequency shift keying (MFSK) modulation may be potentially neutralized by a follower partial-band jammer. In this paper, a maximum likelihood (ML)-based algorithm that uses a two-element array is proposed for joint follower jamming rejection and symbol detection in slow FH/MFSK systems over quasi-static flat Rayleigh fading channels. The algorithm is derived by treating both the received jamming components and the unknown data symbols as deterministic quantities to be jointly estimated in an integrated ML operation. In addition, an approximate expression for the symbol error rate (SER) of the proposed scheme is derived when BFSK signaling is employed in a jamming dominant scenario. Analytical and simulated results show that the proposed approach is able to remove jamming and outperform the conventional and sample matrix inversion (SMI)-based beam-formers in the presence of a follower partial-band jammer.     

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。     

Adaptive multichannel detection of frequency-hopping signals

An adaptive multichannel radiometer designed to detect frequency-hopping (FH) signals in complex signal environments is presented. Each channel updates its hop threshold to reflect the current environment and excise any persistent hop activity inconsistent with an FH signal from subsequent processing. This strategy allows the receiver to discriminate FH signals from any random noise or interference activity with relatively small degradations as compared to operation in stationary additive white Gaussian noise. Two data collection schemes are considered for the proposed receiver, both of which attempt overall decisions using fixed-length blocks of data. In the first scheme, block detection, successive decisions are based on consecutive, nonoverlapping blocks of data, whereas in the second, block-sequential detection, decisions are made each time a new datum is collected. The block-sequential scheme is shown to offer greatly reduced average signal detection times and, thus, is the preferred approach     

一种MFSK/FFH系统差动抗干扰接收机

在最坏情况多音干扰环境中,一种应用于MFSK/FFH系统的差动干扰抑制(DJR)接收机被提出。该方法无需任何干扰信号副信息,利用接收端对跳频图案和跳频速率的先验知识,通过提前检测跳频频点频谱特征完成对干扰信号的差动抑制。数据分析和仿真表明了该方法有效性。     

基于编码跳频图案的DS/FH测控信号性能分析

为了研究跳频图案的不同编码方式对DS/FH测控信号的性能影响,从模糊函数的角度出发,推导了DS/FH测控信号的模糊函数表达式,得到了不同切面的距离模糊图和速度模糊图。仿真结果表明,采用步进编码形式跳频图案的DS/FH测控信号,出现距离和速度耦合;采用随机编码形式跳频图案,则没有距离和速度耦合,且具有良好的目标分辨性能和测量精度性能。     

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     

A parameter estimation method for time‐frequency‐overlapped frequency hopping signals based on sparse linear regression and quadratic envelope optimization

The frequency hopping (FH) signals have well‐documented merits for commercial and military fields due to near‐far resistance and robustness to jamming. Therefore, the parameter estimation of FH signals is an important task for subsequent information acquisition and autonomous electronic countermeasure or attack. However, under the complex electromagnetic environment, there always exist overlaps in the time‐frequency domain among multiple signals, which bring poor signal sparsity and make the estimation more challenging. In this paper, a novel parameter estimation approach is developed for the time‐frequency‐overlapped FH signals under single‐channel reception. The exact solution is mainly composed of the sparse linear regression‐based matrix optimization (SLR‐MO) and quadratic envelope optimization (QEO). SLR‐MO highlights the removal of noise and distortion features for improving the overall sparsity and time‐frequency resolution. QEO further eliminates parts of the interfering signal features and outliers and then extracts and optimizes the average time‐frequency ridge to complete the parameter estimation (hopping instants, period, and carriers). Simulation results demonstrate that the developed estimator outperforms the traditional methods in the scope of application, estimation accuracy, and the robustness under low signal‐to‐noise ratio (SNR).     

超短波跳扩频电台抗扫频干扰的性能仿真研究

依据超短波跳扩频电台的工作机理,采用Matlab中的Simulink分别建立了直扩、跳频、跳扩结合三种通信方式下的仿真模型以及扫频干扰模型。不仅研究了当存在扫频干扰时,改变扩频增益和跳频速度的参考值,仿真得出三种扩频方式下的误码率并进行了比较,还进一步探讨了改变扫频干扰参数（如扫频周期、扫频带宽等）情况下,计算各种通信方式下的干扰容限,比较得出跳扩结合模式抗扫频干扰性能最佳的结论。     

基于HLA/Simulink的跳频通信对抗仿真系统开发

以建立超短波跳频通信对抗分布式仿真系统为目的,首先给出了联邦的体系结构及跳频发信机、接收机成员的复包络仿真框图。其次,讨论了仿真系统实现的关键技术,包括帧处理结构、跳频序列发生器、路径损耗与多径信道仿真模型、信号传播延时及干扰信号的仿真等。最后,给出了仿真系统实例,分析并仿真了频率偏移对多频连续波干扰性能的影响。联邦开发实践表明,该系统具有良好的可扩充性和可重用性。