Adaptive frequency hopping and power control based on spectrum characteristic of error sources in Bluetooth systems

In this paper, we propose a new adaptive frequency hopping (AFH) and power control (PC) scheme to mitigate co-channel interferences and channel noise in the Bluetooth systems. We consider a two-step interference mitigation scheme exploiting the spectrum characteristic of the interference source and channel noise. Good channels without IEEE 802.11x based wireless local area networks (WLAN) interference are first estimated by considering wideband characteristic of WLAN. Then, channel noise and interference from other Bluetooth devices in good channels are, respectively, mitigated by PC and AFH based on narrowband characteristic of Bluetooth. The performance of the proposed scheme is verified by computer simulation. Simulation results show that the proposed mitigation scheme significantly outperforms conventional schemes.     

跳频通信技术研究与仿真

跳频技术具有较强的抗干扰、抗噪声,抗频率选择性衰减的能力和较低的误码率。通过建立跳频通信的仿真模型,实现跳频通信在噪声干扰下的性能分析,用Matlab/Simulink选取不同仿真参数来仿真,对比得出比较好的最佳仿真效果。通过分析跳频通信技术难点,给出相应的最佳方案。     

Highly Robust, Secure, and Perceptual-Quality Echo Hiding Scheme

Audio watermarking using echo hiding has fairly good perceptual quality. However, security and the tradeoff between robustness and imperceptibility are still relevant issues. This paper presents the echo hiding scheme in which the analysis-by-synthesis approach, interlaced kernels, and frequency hopping are adopted to achieve high robustness, security, and perceptual quality. The amplitudes of the embedded echoes are adequately adapted during the embedding process by considering not only the characteristics of the host signals, but also cases in which the watermarked audio signals have suffered various attacks. Additionally, the interlaced kernels are introduced such that the echo positions of the interlaced kernels for embedding "zero" and "one" are interchanged alternately to minimize the influence of host signals and various attacks on the watermarked data. Frequency hopping is employed to increase the robustness and security of the proposed echo hiding scheme in which each audio segment for watermarking is established by combining the fractions selected from all frequency bands based on a pseudonoise sequence as a secret key. Experimental results indicate that the proposed analysis-by-synthesis echo hiding scheme is superior to the conventional schemes in terms of robustness, security, and perceptual quality.     

变频器在力学环境试验设备应用中的干扰及其抑制对策的探讨

变频器在工业生产中的应用越来越广泛,其干扰问题也引起专业人士的日益重视。本文主要介绍了变频器在力学环境试验设备应用系统中干扰产生的来源及其传播途径,提出了抗干扰的实际解决方法,阐述了在变频器应用系统设计和安装中抑制干扰的具体措施。     

一种超低相位噪声频率合成源方案设计

频率合成源是射频发生和频谱分析中最重要的组成之一,评价合成源性能指标的是输出信号的相位噪声、杂散、频率分辨率和频率切换时间.本文通过分析传统锁相环原理,提出一种通用的超低相位噪声合成源设计方案（带宽100MHz以内）.在锁相环基础上,通过引入直接数字合成（Direct digital synthesizer,DDS）混频鉴相技术,使得到的射频信号理论值达到0.1mHz的频率分辨率,同时将带内相位噪声指标优化17dB以上.新方案同时兼顾了杂散和频率切换时间指标,保障合成源的输出信号稳定可靠,使其在自动测试领域拥有广阔的应用前景.     

Modified Nelder-Mead self organizing migrating algorithm for function optimization and its application

In this paper, a modified Nelder Mead Self Organizing Migrating Algorithm (mNM-SOMA) has been presented for solving unconstrained optimization problems. It is based on the hybridization of self organizing migrating algorithm (SOMA) with modified Nelder Mead (mNM) Crossover Operator. SOMA is a low population based technique that has good exploration and exploitation qualities, but sometimes converges premature to local optima solution due to lack of diversity preserve mechanism. In this paper an attempt has been made to improve the efficiency of SOMA using a modified NM crossover operator (mNM) for maintaining the diversity in the search space. mNM-SOMA has been tested on a set of 15 test problems, taken form literature and results are compared with the results obtained by self organizing migrating genetic algorithm (SOMGA), SOMA, genetic algorithm (GA) and particle swarm optimization (PSO). For better presentation, results are also analyzed graphically using a Performance Index. Besides this, mNM-SOMA has also been used to solve Frequency Modulation Sounds Parameter Identification Problem. Analysis of numerical results infers mNM-SOMA as a less expensive robust technique.     

无线网宽间隔跳频及其性能研究

论文主要对宽间隔跳频进行了介绍,给出了实现方法,针对我们常用的宽间隔跳频增益算法存在的问题,采用修正算法对宽间隔跳频增益进行了计算,同时分析了误码率及抗干扰能力,指出了和传统跳频相比较存在的优势和不足。     

一种改进的混沌跳频序列的设计方法

现有混沌跳频序列在混沌迭代次数、通信保密性和安全性等方面存在着不足.为解决上述问题,本文通过给出优化的Logistic映射函数,采用了一种改进的利用伪随机序列控制比特抽取来生成混沌跳频序列的方法.该方法各项跳频性能指标与已有研究成果相当,但其混沌迭代次数减少,序列安全性增强.     

高速／变速跳频同步技术

跳频通信具有很强的抗干扰、抗衰落、抗截获能力。跳频速率、跳频带宽和跳频频点数是跳频通信主要的性能参数,而跳频同步则是跳频通信的关键技术。为了提高抗干扰能力,必须采用较高的跳频速率,采用可靠快速的跳频同步方法。以DSP＋DDS为支撑的宽带高速／变速跳频系统的跳频器可输出直接射频调制信号。基于相关码联合差错控制的快速跳频同步方法,有较短的初始同步时间及迟入网进入时间,具有较强的抗噪声干扰性能。     

跳频异步组网捕获新技术研究

由于跳频异步组网使用同一频率集,跳频异步组网的用户在入网捕获时会受到多址效应的影响。在详细分析了现有跳频组网的方式、多址效应对捕获的影响、传统捕获方法的不足的基础上,提出了跳频异步组网捕获的新算法,很好的解决了用户入网捕获时受多址效应影响的难点问题。通过对比实验,证明了这个新方法的有效性和实用性,为跳频组网系统的建设提供了新思路和新方法。     

Spectrum Sharing in Competing Wireless Systems: A Simulation Study Using WLAN and WMAN

Worldwide, spectrum regulators are reducing the amount of radio spectrum they directly license. Consequently mechanisms are required to permit co-existence of non-cooperative technology. The purpose of this paper is to bring our experiences of this problem to the wireless area, by presenting a simulation system constructed to investigate the effects of imposing various spectrum sharing schemes upon wireless networks operating in the same spectrum band. In particular, wireless metropolitan and local area networks are considered operating in the 5 GHz band using two common sharing schemes—simple frequency hopping and move if interfered, both of which are compared against a spectrum commons approach (free for all). The system’s design and operation is explained, as are the sharing schemes that have been incorporated. Results indicate that significant performance improvements can be obtained compared to a free-for-all approach and that differences occur depending on whether a planned or random frequency allocation is initially used.     

A comparative study on the performance of dissortative mating and immigrants-based strategies for evolutionary dynamic optimization

Traditional Genetic Algorithms (GAs) mating schemes select individuals for crossover independently of their genotypic or phenotypic similarities. In Nature, this behavior is known as random mating. However, non-random protocols, in which individuals mate according to their kinship or likeness, are more common in natural species. Previous studies indicate that when applied to GAs, dissortative mating - a type of non-random mating in which individuals are chosen according to their similarities - may improve their performance (on both speed and reliability). Dissortative mating maintains genetic diversity at a higher level during the run, a fact that is frequently observed as a possible cause of dissortative GAs’ ability to escape local optima. Dynamic optimization demands a special attention when designing and tuning a GA, since diversity plays an even more crucial role than it does when tackling static ones. This paper investigates the behavior of the Adaptive Dissortative Mating GA (ADMGA) in dynamic problems and compares it to GAs based on random immigrants. ADMGA selects parents according to their Hamming distance, via a self-adjustable threshold value. The method, by keeping population diversity during the run, provides an effective means to deal with dynamic problems. Tests conducted with dynamic trap functions and dynamic versions of Road Royal and knapsack problems indicate that ADMGA is able to outperform other GAs on a wide range of tests, being particularly effective when the frequency of changes is low. Specifically, ADMGA outperforms two state-of-the-art algorithms on many dynamic scenarios. In addition, and unlike preceding dissortative mating GAs and other evolutionary techniques for dynamic optimization, ADMGA self-regulates the intensity of the mating restrictions and does not increase the set of parameters in GAs, thus being easier to tune.     

自适应频率测量方法(AMF)及其在涡街流量计中的应用

本文研究了用于涡街流量计信号处理的自适应频率测量方法(AMF).这种方法将自适应 滤波和功率谱分析结合在一起,特别适合于测量或估计涡街流量计这类受随机噪声和干扰影 响了的信号频率.理论分析和实验结果证明,此法对提高涡街流量计应用中的测量精度是有 效的,同时,也适用于其他仪表测量系统.     

低能耗最小阻力组播路由算法研究

阐述了跳频无线传感器网络的概念;综合考虑无线链路阻力和数据转发跳数因素,设计了一种适用于跳频无线传感器网络的组播路由算法,即低能耗最小阻力组播路由算法;最后对该组播路由算法的性能进行了分析。     

基于神经网络非线性系统辨识和控制的研究

本文提出了由静态的前馈网络和稳定的滤波器构成的非线性系统的辨识模型，在神经网络固有的逼近误差存在的情况下，从理论上讨论了神经网络应用于辨识控制过程中系统的稳定性问题，最后研究了在非线性系统的轨迹跟踪过程中增加滑动控制来偿神经网络的逼近误差，从而提高系统跟踪性能。     

宽带RF功率放大器的预失真线性化技术综述

随着无线需求和无线业务的不断增加,传输信号必将不断向高速率宽带宽发展。在宽带应用中,由于传输信号带宽增加,RF功率放大器不同于窄带输入下的无记忆特性,将表现出与频率有关的记忆非线性特性。针对宽带功率放大器线性化的记忆预失真技术成为当前研究的一个热点,综述了宽带RF功率放大器的预失真线性化技术的研究进展,详细介绍和分析了目前最主要的几种记忆预失真器的模型和对应的自适应预失真方案,最后给出了今后的研究方向。     

文本分类特征权重改进算法

TF-IDF是一种在文本分类领域获得广泛应用的特征词权重算法,着重考虑了词频与逆文档频等因素,但无法把握特征词在类间与类内的分布情况。为提高在同类中频繁出现、类内均匀分布的具有代表性的特征词权重,引入特征词分布集中度系数改进IDF函数、用分散度系数进行加权,提出TF-IIDF-DIC权重函数。实验结果表明,基于TF-IIDF-DIC权重算法的K-NN文本分类宏平均F1值比TF-IDF算法提高了6.79%。     

Performance evaluation of complementary code combining diversity in DVB-SH

In this paper, the application of code combining diversity in Digital Video Broadcasting Satellite to Handheld (DVB-SH) systems is analyzed. The complementary code combining diversity is a simple and efficient technique that exploits the advantages of a hybrid satellite/terrestrial system. A meaningful diversity gain can be obtained in multiple frequency networks, allowing an improvement of the receiver robustness in both static and mobile scenarios. Furthermore, for typical DVB-SH terminals with two receiver branches, this gain can be easily obtained without increasing the hardware complexity.     

文本分类特征权重改进算法

TF-IDF是一种在文本分类领域获得广泛应用的特征词权重算法,着重考虑了词频与逆文档频等因素,但无法把握特征词在类间与类内的分布情况。为提高在同类中频繁出现、类内均匀分布的具有代表性的特征词权重,引入特征词分布集中度系数改进IDF函数、用分散度系数进行加权,提出TF-IIDF-DIC权重函数。实验结果表明,基于TF-IIDF-DIC权重算法的K-NN文本分类宏平均F1值比TF-IDF算法提高了6.79%。     

自适应跳频MF-TDMA抗干扰卫星通信技术

MF-TDMA卫星通信系统中,网内终端本身具有频率跳变的能力,可以与跳频相结合实现抗干扰的目的。文章分析了MF-TDMA卫星通信和自适应跳频技术的特点,比较了两种常用的自适应跳频技术,并根据分析结果提出了一种基于分布式干扰检测、频点集中规划的自适应跳频MF-TDMA(AFH-MF-TDMA)卫星通信技术,该技术具有干扰检测准确、频率资源综合利用率高的特点,可以有效增强MF-TDMA卫星通信系统的抗干扰能力。