Prinzipien der Powerline Communication

The liberalization of the electricity and telecommunications markets has paved the way for harnessing existing electricity supply networks to transfer data from the low-voltage transformer station right through to every mains socket in a building. Powerline communication (PLC) allows for coupling power supply with data transmission. The modulation or demodulation calls for state-of-the-art, fast chip technologies as well as algorithms. According to powerline companies, the first generation of products is to be launched in the year 2001. Further development of this system depends completely on the regulation of the respective frequency levels. If regulatory measures and the market were to favor powerline technology, electric utility companies could come to play a role as telecom providers.     

Efficient Wireless Network Simulations with Detailed Propagation Models

Accurate simulation of wireless networks requires realistic models of the channel propagation medium. The widely used free space model is computationally efficient but ignores many attenuation components which affect wireless signal propagation. This paper describes the impact of the accuracy of the wireless channel model on the accuracy of the results and on the execution time of large-scale network models. It then introduces means to reduce the runtime execution when deploying such detailed propagation models.     

On the Effects of Frequency Scaling Over Capacity Scaling in Underwater Networks—Part I: Extended Network Model

In this two-part paper, information-theoretic capacity scaling laws are analyzed in an underwater acoustic network with n regularly located nodes on a square, in which both bandwidth and received signal power can be limited significantly. Parts I and II deal with an extended network of unit node density and a dense network of unit area, respectively. In both cases, a narrow-band model is assumed where the carrier frequency is allowed to scale as a function of n, which is shown to be crucial for achieving the order optimality in multi-hop (MH) mechanisms. We first characterize an attenuation parameter that depends on the frequency scaling as well as the transmission distance. Upper and lower bounds on the capacity scaling are then derived. In Part I, we show that the upper bound on capacity for extended networks is inversely proportional to the attenuation parameter, thus resulting in a highly power-limited network. Interestingly, it is shown that the upper bound is intrinsically related to the attenuation parameter but not the spreading factor. Furthermore, we propose an achievable communication scheme based on the nearest-neighbor MH transmission, which is suitable due to the low propagation speed of acoustic channel, and show that it is order-optimal for all operating regimes of extended networks. Finally, these scaling results are extended to the case of random node deployments providing fundamental limits to more complex scenarios of extended underwater networks.     

Characterizing 802.11 wireless link behavior

Since wireless signals propagate through the ether, they are significantly affected by attenuation, fading, multipath, and interference. As a result, it is difficult to measure and understand fundamental wireless network behavior. This creates a challenge for both network researchers, who often rely on simulators to evaluate their work, and network managers, who need to deploy and optimize operational networks. Given the complexity of wireless networks, both communities often rely on simplifying rules, which frequently have not been validated using today’s wireless radios. In this paper, we undertake a detailed characterization of 802.11 link-level behavior using commercial 802.11 cards. Our study uses a wireless testbed that provides signal propagation emulation, giving us complete control over the signal environment. In addition, we use our measurements to analyze the performance of an operational wireless network. Our work contributes to a more accurate understanding of link-level behavior and enables the development of more accurate wireless network simulators.     

10kV中压配电线载波信道的建模

近年来，利用中压配电网作为电力自动化的载波通信媒介日益受到人们的关注，对其传输特性的研究也成为了热点问题。论文针对中压配电网的网络结构及由此产生的阻抗不匹配和传输衰减等问题，提出了一种仿真模型。该模型对于信道中的不同噪声给出了不同的模型，特别是采用Middleton的A类噪声模型作为脉冲干扰的模型。对于信道的多径衰减给出了详尽的计算模型。在此基础上考虑了信道的时变性，提出利用信道的阻抗调制特性实现对不同信道状态的转换。相对于前人的模型，该模型更符合中压配电线信道实际特点，为研究克服电力线信道恶劣传输特性的信号处理方法提供了参考模犁，因而更具实用价值。     

近水面2.4GHz信号传播损耗模型的校正研究

无线传感器网络的性能很大程度上受限于无线信道的特性。随着物联网事业飞速发展,近水面环境下2.4 GHz信号传播路径损耗模型的研究已成为无线传感器网络研究的重要课题之一。在近水面的环境下,针对基于IEEE802.15.4标准的2.4 GHz信号传播特性进行了实测研究,并利用最小二乘法对双射线模型进行拟合分析得到经验公式。研究结果表明:校正后的经验公式更符合实际环境中的信号传播路径损耗特点,这也为未来大规模铺设近水面无线传感器网络提供理论指导作用。     

Interference Studies Between Adjacent Satellite Communications Systems operating Above 10 GHz and Using Power Control as Fade Mitigation Technique

Interference problems are arising from the spectral coexistence between satellite communication networks that operate at frequencies above 10 GHz and particularly when they employ power control as fade mitigation technique. This situation is aggravated due to tropospheric propagation phenomena. In this frequency range, rain attenuation is considered to be the dominant tropospheric fading mechanism. The conditional acceptable intersystem interference probability of the Carrier-to-Interference Ratio of a satellite terminal interfered by an adjacent satellite network is defined as a figure of merit and analytically calculated taking into account a physical-mathematical model for the rainfall medium. The correlated propagation fading phenomena over multiple slant paths are accurately incorporated. The proposed model is flexible and can be applied on a global scale since it incorporates the local climatic conditions concerning the point rainfall rate and the spatial rainfall inhomogeneity. Useful numerical results of the proposed model are obtained and the impact of various crucial operational and geometrical parameters of satellite networks’ coexistence is examined. The numerical results have been also verified through simulations using a multi-dimensional rain attenuation synthesizer. Finally, simple and easy-calculated formulas for the satellite communication designers for back of the envelope computations are given.     

Real-world environment models for mobile network evaluation

Simulation environments are an important tool for the evaluation of new concepts in networking. The study of mobile ad hoc networks depends on understanding protocols from simulations, before these protocols are implemented in a real-world setting. To produce a real-world environment within which an ad hoc network can be formed among a set of nodes, there is a need for the development of realistic, generic and comprehensive mobility, and signal propagation models. In this paper, we propose the design of a mobility and signal propagation model that can be used in simulations to produce realistic network scenarios. Our model allows the placement of obstacles that restrict movement and signal propagation. Movement paths are constructed as Voronoi tessellations with the corner points of these obstacles as Voronoi sites. Our mobility model also introduces a signal propagation model that emulates properties of fading in the presence of obstacles. As a result, we have developed a complete environment in which network protocols can be studied on the basis of numerous performance metrics. Through simulation, we show that the proposed mobility model has a significant impact on network performance, especially when compared with other mobility models. In addition, we also observe that the performance of ad hoc network protocols is effected when different mobility scenarios are utilized.     

OFDM在电力线通信中的同步技术

研究了电力线上OFDM通信中的同步技术。利用OFDM信号模型,分析了各种同步误差的来源。并且针对使用电力线作为传输媒介实现逆变电源间通信的要求,着重对符号同步和载波同步算法进行研究,并在原有的ML(MaximumLikelihood)算法上进行了改进。从仿真结果看,此改进算法能够明显改善同步的性能。     

Adaptive digital notch filter design on the unit circle for theremoval of powerline noise from biomedical signals

Investigates adaptive digital notch filters for the elimination of powerline noise from biomedical signals. Since the distribution of the frequency variation of the powerline noise may or may not be centered at 60 Hz. Three different adaptive digital notch filters are considered. For the first case, an adaptive FIR second-order digital notch filter is designed to track the center frequency variation. For the second case, the zeroes of an adaptive IIR second-order digital notch filter are fixed on the unit circle and the poles are adapted to find an optimum bandwidth to eliminate the noise to a pre-defined attenuation level. In the third case, both the poles and zeroes of the adaptive IIR second-order filter are adapted to track the center frequency variation within an optimum bandwidth. The adaptive process is considerably simplified by designing the notch filters by pole-zero placement on the unit circle using some suggested rules. A constrained least mean-squared algorithm is used for the adaptive process. To evaluate their performance, the three adaptive notch filters are applied to a powerline noise sample and to a noisy EEG as an illustration of a biomedical signal     

A simplified analytical model for predicting path loss in urban andsuburban environments

An analytical propagation model has recently been developed to predict radio signal attenuation in urban and suburban environments. This analytical model explicates the path loss as a result of signal reduction due to free space wavefront spreading, multiple diffraction past rows of buildings, and building shadowing. It is applicable for cellular mobile services as well as personal communications services (PCS) in both macro- and microcellular environments. Good accuracy was found for this analytical model by comparing the predictions with numerous measurements made in various propagation environments. However, since the analytical model involves multiple-dimension integration to calculate the signal attenuation due to multiple diffraction past rows of buildings, the model in its original format does not lend itself to easy implementation into a radio system planning tool. A simplified version of the analytical model is developed in this paper, which can be used for three different propagation scenarios with base-station antenna above, below, and near the average rooftop level     

典型风沙环境对电磁信号衰减的规律研究

风沙天气对人们生活有很大影响,其中一方面就是对电磁信号传播的干扰,文中通过建立基本地形模型,将风沙天气进行建模处理,加入到基本地形模型中,然后研究其电磁特征参数得到电磁模型,对比研究了在没有风沙情况下的电磁传播衰减以及不同严重程度风沙天气中的电磁传播衰减。所得规律既可以为进一步研究风沙区域电磁信号衰减问题提供技术参考,也可以由衰减情况反推出风沙天气的严重程度。     

室内场强预测理论研究及工程应用

在数字移动通信网络工程建设中,希望对网络覆盖区域的接收信号场强进行预测,尽可能减少大量的实测工作。首先介绍场强预测理论,然后根据工程实际应用,介绍了目前常用的几种室内传播模型;最后在实际环境下,利用TEMS模拟测试对Chan传播模型和衰减因子传播模型进行比较,提出了较为实用的衰减因子模型,以利于工程实践中对室内场强传播的预测。     

Channel Capacity Statistics of an Interfered Broadband Satellite Link

Satellite communication networks play an important role in the “digital divide” problem, by offering broadband services everywhere in the world. The ever increasing demand for multimedia services has led to the use of Ku, Ka and V band in modern satellite communication networks. In these frequency bands, rain attenuation is the most dominant propagation fading mechanism. Moreover, interference due to propagation phenomena deteriorates the performance of the satellite links and should be taken into account for the reliable design of satellite communication networks. In this paper, an analytical physical mathematical propagation model is presented for the prediction of channel capacity statistics of a dual-polarized interfered broadband satellite link. Rain attenuation spatial inhomogeneity is incorporated in the analysis with the employment of correlated slant paths. The obtained numerical results show the significance of these effects to channel capacity estimation. Finally, the proposed model may be used towards the optimum utilization of the satellite channel capacity by means of adaptive fade mitigation schemes.     

基于人工神经网络的通信信号分类识别

通信信号的分类识别是一种典型的统计模式识别问题。系统地论述了通信信号特征选择、特征提取和分类识别的原理和方法。设计了人工神经网络分类器,包括神经网络模型的选择、分类器的输入输出表示、神经网络拓扑结构和训练算法,并提出了分层结构的神经网络分类器。     

Effects of buildings and trees on satellite mobile communications

A propagation model for lossy building with tree attenuation in urban and residential areas is developed for satellite mobile communications. This model is used to characterize the signal transmitted from medium earth orbit (MEO) satellite when there are buildings and trees in the path of the signal. The analysis is performed using the uniform theory of diffraction (UTD). The tree attenuation is evaluated through the modified exponential decay model (MED).

The normalized signal level and signal attenuation rate are computed. Such information is useful in developing the mobile system's hand-off algorithm. In narrowband systems, the propagation attenuation and fading statistics are the main causes of signal degradation. So, the probability of error is calculated with and without the existence of the tree. Also the axial ratio (AR) is computed as function of satellite elevation angle. In wide band systems, the delay-spread is dominant because of the inter-symbol interference. For such case, the coherence bandwidth and impulse response are computed. Along with that, computed results are compared with actual measured data.     

Long polyphase sequences for adaptive MMSE detector in asynchronous CDMA PLC system

An adaptive receiver solution for an asynchronous DS-CDMA system in an indoor powerline network is proposed. A combination of different receiver structures with binary and complex-polyphase sequences is evaluated and compared in terms of bit error rate. The simulation results based on a complete powerline channel model are reported.