Signal propagation techniques for wireless underground communication networks

Wireless Underground Communication Networks (WUCNs) consist of wireless devices that operate below the ground surface. These devices are either (i) buried completely under dense soil, or (ii) placed within a bounded open underground space, such as underground mines and road/subway tunnels. The main difference between WUCNs and the terrestrial wireless communication networks is the communication medium. In this paper, signal propagation characteristics are described in these constrained areas. First, a channel model is described for electromagnetic (EM) waves in soil medium. This model characterizes not only the propagation of EM waves, but also other effects such as multipath, soil composition, water content, and burial depth. Second, the magnetic induction (MI) techniques are analyzed for communication through soil. Based on the channel model, the MI waveguide technique for communication is developed to address the high attenuation challenges of MI waves through soil. Furthermore, a channel model, i.e., the multimode model, is provided to characterize the wireless channel for WUCNs in underground mines and road/subway tunnels. The multimode model can characterize two cases for underground communication, i.e., the tunnel channel and the room-and-pillar channel. Finally, research challenges for the design communication protocols for WUCNs in both underground environments are discussed based on the analysis of the signal propagation.     

Analysis of plasma sheath propagation attenuation based on ray tracing

Based on the complex Snell's law of lossy media, a ray tracing method is proposed to study the propagation attenuation characteristics of electromagnetic (EM) waves in plasma sheaths. The plasma sheath is modelled as layered media. This method considers the complex ray characteristics of inhomogeneous plane EM waves, tracks the propagation rays of EM waves in each layer of media, and calculates the propagation attenuation of EM waves in each layer of media according to the propagation direction of the complex rays. The attenuation during numerical cumulative propagation is the total attenuation of EM waves through the plasma sheath. By comparing the results with that obtained from the WKB method, the accuracy of the ray tracing algorithm is proved. The results of the propagation attenuation of a blunt cone model are calculated by the proposed method, and the effects of different parameters on the EM wave propagation attenuation in the plasma sheath are analysed at different heights, velocities, incident angles, and incident positions. Studying the propagation characteristics of EM waves in the plasma sheath is of importance in application for radar target tracking, blackout communication, and other issues.     

Overview of channel models for underwater wireless communication networks

Acoustic communication in Underwater Wireless Communication Networks (UWCNs) has several challenges due to the presence of fading, multipath and refractive properties of the sound channel which necessitate the development of precise underwater channel models. Some existing channel models are simplified and do not consider multipath or multipath fading. In this paper, a detailed survey on ray-theory-based multipath Rayleigh underwater channel models for underwater wireless communication is presented and the research challenges for an efficient communication in this environment are outlined. These channel models are valid for shallow or deep water. They are based on acoustic propagation physics which captures different propagation paths of sound in the underwater and consider all the effects of shadow zones, multipath fading, operating frequency, depth and water temperature. The propagation characteristics are shown through mathematical analysis. Transmission losses between transceivers are investigated through simulations. Further simulations are carried out to study the bit error rate effects and the maximum internode distances for different networks and depths considering a 16-QAM modulation scheme with OFDM as the multicarrier transmission technique. The effect of weather season and the variability of ocean environmental factors such as water temperature on the communication performance are also shown. The mathematical analysis and simulations highlight important considerations for the deployment and operation of UWCNs.     

基于ZigBee的温室环境无线测控系统

为了实现温室大棚环境的无线、远程实时监控,提出了一种以CC2430芯片为核心的ZigBee温室环境无线测控系统。描述了终端节点、路由节点和协调器节点的硬件组成和软件流程,并应用改进的Cluster-Tree路由算法组成ZigBee无线传感网络,实现数据的无线传输。利用串口通信技术实现无线传感网络与Yeelink物联网平台的通信,管理者可远程登陆Yeelink平台和手机APP查看温室环境信息以及控制节点状态。经实验测试,大棚内无线节点间的通信距离约80米,并且实现了光强、空气温湿度及土壤湿度的监控。测试表明系统构建简单,稳定可靠,为智能农业的设计提供了参考。     

Characterization,modeling and simulation of the MIMO propagation channel

This article deals with several aspects relative to the MIMO propagation channel. Based on simulations and/or measurements, different approaches are used to model the propagation channel. These models are useful for the MIMO system design. Several studies are performed in order to realize realistic simulation of MIMO channel. Different measurement techniques are used in characterizing the propagation channel in various environments. Measurement campaigns made in different situations have been analyzed to obtain the relevant statistical parameters of the channel. Simulation of MIMO channel is then presented. Measurement and simulation results provide an evaluation of the capacity of MIMO channel. Obtained results show feasibility in the integration of MIMO techniques in practical wireless communication systems.     

Routing protocol for wireless quantum multi-hop mesh backbone network based on partially entangled GHZ state

Quantum multi-hop teleportation is important in the field of quantum communication. In this study, we propose a quantum multi-hop communication model and a quantum routing protocol with multihop teleportation for wireless mesh backbone networks. Based on an analysis of quantum multi-hop protocols, a partially entangled Greenberger–Horne–Zeilinger (GHZ) state is selected as the quantum channel for the proposed protocol. Both quantum and classical wireless channels exist between two neighboring nodes along the route. With the proposed routing protocol, quantum information can be transmitted hop by hop from the source node to the destination node. Based on multi-hop teleportation based on the partially entangled GHZ state, a quantum route established with the minimum number of hops. The difference between our routing protocol and the classical one is that in the former, the processes used to find a quantum route and establish quantum channel entanglement occur simultaneously. The Bell state measurement results of each hop are piggybacked to quantum route finding information. This method reduces the total number of packets and the magnitude of air interface delay. The deduction of the establishment of a quantum channel between source and destination is also presented here. The final success probability of quantum multi-hop teleportation in wireless mesh backbone networks was simulated and analyzed. Our research shows that quantum multi-hop teleportation in wireless mesh backbone networks through a partially entangled GHZ state is feasible.     

Intensity depending on object distance in a two-dimensional photonic crystal

The propagation of electromagnetic (EM) waves in two-dimensional triangular-lattice photonic crystals (PCs) is investigated through dispersion characteristics analysis and numerical simulation of field pattern. The designed PC structure can exhibit all angle negative refraction in the second band. A flat superlens formed from such a PC has been designed and its imaging properties have been investigated systematically. Good-quality images and focusing, with relative refractive index of ?1, have been observed in this system for TE mode waves. In contrast to the images in near-field region for the lowest valence band, non-near-field images, explicitly following the well-known wave-beam negative refraction law, have been demonstrated. The relation between the intensity of the image and the object distance has also been discussed in this paper. The extensive applications of such a phenomenon to optical devices are anticipated.     

Imaging properties of triangular lattice photonic crystal at multi-bands

The propagation of electromagnetic (EM) waves in two-dimensional triangular-lattice photonic crystals (PCs) is investigated through dispersion characteristics analysis and numerical simulation of field pattern. The designed PC structure can exhibit all angle negative refraction in the second and the eighth band. A flat superlen formed from such a PC has been designed and its imaging properties have been investigated systematically. Both in band 2 and band 8, a quite high quality image in the opposite side of the slab can be found.     

Modeling the propagation of electromagnetic waves over the surface of the human body

The results of modeling and an experimental study of electromagnetic (EM) waves in microwave range propagating along the surface of the human body have been presented. The parameters of wave propagation, such as the attenuation and phase velocity, have also been investigated. The calculation of the propagation of EM waves by the numerical method FDTD (finite difference time domain), as well as the use of the analytical model of the propagation of the EM wave along flat and curved surfaces has been fulfilled. An experimental study on a human body has been conducted. It has been shown that creeping waves are slow and exhibit a noticeable dispersion, while the surface waves are dispersionless and propagate at the speed of light in free space. A comparison of the results of numerical simulation, analytical calculation, and experimental investigations at a frequency of 2.55 GHz has been carried out.     

A Resiliency-Connectivity metric in wireless sensor networks with key predistribution schemes and node compromise attacks

Applications for wireless sensor networks require widespread, highly reliable communications even in the face of adversarial influences. Maintaining connectivity and secure communications between entities are vital networking properties towards ensuring the successful and accurate completion of desired sensing tasks. We examine the required communication range for nodes in a wireless sensor network with respect to several parameters. Network properties such as key predistribution schemes and node compromise attacks are modelled with several network parameters and studied in terms of how they influence global network connectivity. These networks are physically vulnerable to malicious behavior by way of node compromise attacks that may affect global connectivity. We introduce a metric that determines the resilience of a network employing a key predistribution scheme with respect to node compromise attacks. In this work,we provide the first study of global network connectivity and its relationship to node compromise attacks. Existing work considers the relationship between the probability of node compromise and the probability of link compromise and the relationship of the probability of secure link establishment and overall network connectivity for the Erdős network model. Here, we present novel work which combines these two relationships to study the relationship between node compromise attacks and global network connectivity. Our analysis is performed with regard to large-scale networks; however, we provide simulation results for both large-scale and small-scale networks. First, we derive a single expression to determine the required communication radius for wireless sensor networks to include the effects of key predistribution schemes. From this, we derive an expression for determining required communication range after an adversary has compromised a fraction of the nodes in the network. The required communication range represents the resource usage of nodes in a network to cope with key distribution schemes and node compromise attacks. We introduce the Resiliency-Connectivity metric, which measures the resilience of a network in expending its resources to provide global connectivity in adverse situations.     

Pulse state interval modulation and open loop communication experiment in the hostile environments

Based on several atmospheric channel field tests and analyses, the modulation model of wireless laser communication in hostile weather is investigated, for enhancing the link rate of wireless laser communication. Firstly, the conversion relationship between SER and BER under different conditions is studied. Afterwards, by analyzing atmospheric channel tests result, the importance of atmospheric channel bandwidth was featured during test. On the basis of this, an efficiency pulse state-interval coded modulation is present for the first time and its characteristics are analyzed. In order to verify whether this modulation model is feasible and effective as well as its robustness, a wireless laser communication feasibility experiment in the hostile environments was launched. According to the results, a prospect is pointed out that atmospheric channel properties feedback technique in real time may be a key and precondition in all-weather wireless optical communication.     

二元决策图和故障树相融合的无线传感器网络可靠性分析

为了提高无线传感器分析网络可靠性,提出一种基于二元决策图和故障树相融合的无线传感器网络可靠分析方法;首先根据无线传感器网络拓扑结构建立了故障树模型,然后将无线传感器网络故障树转化为二元决策图结构,最后采用仿真实验分析了不同节点冗余度、不同跳数条件下无线传感器网络的可靠性;仿真结果表明,文章方法的分析结果可以帮助无线传感器网络性能的优化,可以提高无线传感器网络的可靠性。     

A Thin Self-Feeding Janus Metasurface for Manipulating Incident Waves and Emitting Radiation Waves Simultaneously

A thin metasurface has shown powerful capabilities in controlling either incident electromagnetic (EM) waves or radiation waves, but is difficult for both. Here, a self-feeding Janus metasurface (SFJ-MS) is proposed to manipulate the incident EM waves and emit the radiated waves simultaneously, which can realize the polarization conversion of incident waves, scattering control, EM wave radiation, and radiation-beam steering. On the upper of SFJ-MS, a diagonal-split square ring and a rectangular patch with rotation for radiation are designed to introduce anisotropy in the meta-atom for converting the polarization of incident EM waves. On the bottom of SFJ-MS, a self-feeding microstructure converts the alternating current into the excitation of SFJ-MS to emit the EM waves to free space. The multiple functions of SFJ-MS are comprehensively substantiated by measured results, which are in agreements with the stringent simulations. This SFJ-MS, with lightweight, compact, low profile, and power-efficient features, can find potential applications in phased array radar systems, wireless communication systems, polarimetric radar imaging systems, and target detection systems.     

基于矢量传感器的水下双址接入研究

针对水声信道的特殊性,提出一种适用于水声通信的双址接入方法。旋转矢量传感器的组合指向性,使其零点对准某一信源,则该信源被屏蔽,此时信宿可以与另一信源进行通信,反之亦然。矢量传感器的空间指向性不随频率变化,该方法可以实现宽带双址异步通信。此外,当两信源之间的开角大于34.8°时,通过对矢量传感器声压和振速输出的联合处理,可以使分离出的不同信源所发射的信号获得一定的信噪比增益。理论分析、数值仿真和湖上实验结果表明:基于矢量传感器的双址通信算法实现简单,信道资源利用率高,可以与其它多址接入技术结合使用,并且矢量传感器的空间增益可以有效降低系统的误码率。由于水声信道的特殊性,水下信息网须采用多种多址接入技术,本文所提出的双址通信方案将是其它多址接入技术的有益补充。     

Theoretical study of two-element array of equilateral triangular patch microstrip antenna on ferrite substrate

The radiation characteristics of a two-element array of equilateral triangular patch microstrip antenna on a ferrite substrate are studied theoretically by considering the presence of bias magnetic field in the direction of propagation of electromagnetic waves. It is found that the natural modes of propagation in the direction of magnetic field are left- and right-circularly polarized waves and these modes have different propagation constants. In loss-less isotropic warm plasma, this array antenna geometry excites both electromagnetic (EM) and electroacoustic plasma (P) waves in addition to a nonradiating surface wave. In the absence of an external magnetic field, the EM- and P-waves can be decoupled into two independent modes, the electroacoustic mode is longitudinal while the electromagnetic mode is transverse. The far-zone EM-mode and P-mode radiation fields are derived using vector wave function techniques and pattern multiplication approaches. The results are obtained in both plasma medium and free space. Some important antenna parameters such as radiation conductance, directivity and quality factor are plotted for different values of plasma-to-source frequency.     

基于无线传感器网络的智能LED灯控制系统设计

针对无线传感器网络为基础的控制系统中其板载电池的能量有限,从而影响无线传感器节点的运行寿命问题。本文设计并采取了嵌入式与分布式智能无线传感器网络（WSN）,目的是优化和使控制照明系统更加高效,为了克服这个问题,基于能量感知的通信协议被引入,以减少为了延长其使用时间的无线传感器网络的功耗。本文中的以智能无线传感器网络为基础的LED照明系统,经过实验结果表明,无线传感器节点都能够运行的时间较长,从87天至102天,而增加了约20％的工作寿命。     

Transmission characteristics of electromagnetic waves in a semicircular plasma filament layer generated by a femtosecond laser

The transmission characteristics of electromagnetic (EM) waves in a semicircular plasma filament layer generated by a femtosecond laser were studied in a wide frequency band including radar waves. We have focussed on the influence of plasma parameters and filament arrangement based on the diffraction and superposition theory of EM waves on the transmittance. A numerical simulation model using the current density convolution finite-difference time-domain method was constructed in a semicircular multilayer filament structure, and the transmission characteristics of spherical EM waves were examined. The simulation results showed that in this semicircular structure, the transmittance was periodically changed at a frequency interval corresponding to the thickness of the filament channel. This phenomenon was more pronounced as the number of the filament layers increased. In the lower band (<30 GHz), there was little change in the transmittance according to layer-to-layer distance, but in the higher band (>30 GHz), it changed irregularly. On the contrary, for the electron number density, it changed regularly in the lower frequency and hardly changed in the higher frequency. When the number of layers was 3 or more, the transmittance became 0 at the centre of the channel, and a discontinuous interference pattern appeared more clearly as the frequency increased.     

基于车载通信标准街道场景的电磁散射信道模型

针对室外无线信道视距(line of sight,LOS)/非视距(non-line of sight,NLOS)传输环境下的车到车(vehicular-to-vehicular,V2V)通信系统,本文提出了一种基于标准街道散射的统计信道模型,其移动发射机(mobile transmitter,MT)与移动接收机(mobile receiver,MR)处于运动状态,街道两旁分布的散射体固定.由几何模型出发又引入了一种随机的参考信道模型,其散射体有无穷多个,均以平行于街道两侧的散射条纹形式均匀分布在三维(three dimensional,3D)空间的一个二维(two dimensional,2D)矩形内部.在室外街道通信环境下,模型推导了散射信道中发射角(angle of departure,AOD)以及到达角(angle of arrival,AOA)的概率密度函数(probability density functions,PDFs)解析式;研究了多普勒功率谱密度(power spectral density,PSD)及其时间自相关函数(autocorrelation function,ACF);分析了模型多普勒参数以及街道散射体等因素对V2V通信系统性能的影响.与城市、农村的测量信道对比分析,表明本模型仿真的统计特性符合理论与实际,拓宽了室外V2V无线通信信道建模的研究.为评估室外V2V通信系统的传输特性、仿真无线通信系统提供了有力的研究工具.     

室内直达与非直达环境无线传播综合信道建模

本文主要针对室内无线传播信道直达(line of sight, LOS)与非直达(no line of sight, NLOS)环境, 引入参考模型研究其建模设计及其相关统计特性. 文中提出了一种基于几何散射模型的综合改进室内参考信道模型, 假设将无限数量的散射体均匀分布在三维空间的一个二维(two dimensional, 2D)水平面上. 本文推导了电磁波达信号到达角(angle of arrival, AOA) 概率分布函数(probability density function, PDF)、多普勒功率谱密度(power spectral Density, PSD)、 时间自相关函数(autocorrelation function, ACF)的解析表达式, 并分析其重要参数对函数的影响. 此外, 本文还通过非现实参考模型提出了一种高效的SOC(Sum of Cisoids) 信道仿真模型, 同时提出了设计SOC信道仿真模型的两种有效参数计算方法, 并比较两者的计算性能. 仿真结果表明, 信道仿真模型的统计特性与参考模型相匹配, 即室内参考模型可以通过的SOC信道仿真模型来近似, 同时信道仿真模型可以很好的应用于评估室内无线通信系统的性能, 拓宽了室内无线信道建模的研究, 同时减少实现开支.