基于皮肤-脂肪模型的太赫兹体内多输入多输出信道特性分析与建模

为探究太赫兹(THz)频段体内多输入多输出(MIMO)通信系统的传输特性,该文在0.8～1.2 THz下构建了精确的皮肤-脂肪模型,对皮肤-脂肪模型中垂直方向和水平方向的链路进行全波电磁仿真,分析太赫兹体内信道特性,建立路径损耗模型。首先,结合太赫兹频段人体组织的介电特性和人体皮肤的解剖学结构构建皮肤-脂肪模型。其次,对比分析了3条链路的路径损耗和阴影衰落,提出带有等效吸收因子的太赫兹体内路径损耗模型。最后,对3条链路的莱斯K因子、均方根时延扩展、MIMO容量进行分析。仿真分析表明,带有等效吸收因子的太赫兹体内路径损耗模型可以更准确地描述加长距离垂直链路2的路径损耗,发射端在体表可以增强MIMO容量。该文的工作可以为太赫兹体内通信系统的设计和优化提供参考。     

一种基于人体通信的路径损耗模型

随着智能可穿戴设备的发展,人体通信(Human Body Communication,HBC)为体域网智能传感器及传感器网络在医疗领域的发展提供了新的思路。针对体域网发展的实际应用,对人体周围的信道特性进行完整的研究十分必要。在采用完整人体模型的基础上,应用时域有限差分法,对HBC频段人体信道特性进行了仿真,得出频率和距离对路径损耗特性的关系。同时针对颈部、背部非直射链路进行了仿真研究。结果表明,人体表面5条主要链路中左胸-右胸链路通信性能最佳。在整个HBC频段,路径损耗特性与频率及距离密切相关,随着频率增加,路径损耗逐渐降低,而路径损耗特性与距离间具有定量的数学关系。在体表的非直视链路,路径损耗和相同表面距离的直射链路路径损耗相同,路径损耗仍与体表距离存在定性的数学关系,同时信号的到达前后也与体表距离密切相关。     

植入式生物医学电子的UWB无线通信可行性建模研究

为考察超宽带(UWB)实现植入式生物医学电子设备无线通信的可行性及信道传播特性,基于男性活体CT及MRI切片图像,构建了一个频率范围在1～10.8 GHz的高分辨率三维人体电磁模型,考虑了85种不同人体组织或器官的电磁特性参数;将模型嵌入基于有限积分法(FIT)的三维电磁仿真软件进行电磁计算,考察电磁波在人体内的路径损耗及比吸收率特性。实验结果表明:该模型能较好地描绘真实人体的电磁特性,信号在人体内的衰减随频率的升高及植入深度的加深而加重;在植入深度达160mm时,3.5 GHz信号的路径损耗为75 dB;参考功率为27 dBm时,人体对3.5 GHz信号的比吸收率在安全值范围内;证实了采用UWB频段内的3.5 GHz实现植入式生物医学电子无线通信的可行性和安全性。     

基于平面波斜入射的人体信道远场路径损耗建模

人体信道路径损耗计算对植入式通信链路预估具有重要意义。文章利用有耗媒质的电磁场边界条件、反射和透射定理并引入切向等效波阻抗定义,推导出平面波向人体斜入射时各人体组织分界面上的入射角、透射角、反射系数、透射系数、切向等效波阻抗以及各人体组织中的电磁合成波,提出了一种基于平面波向多层有耗媒质斜入射的人体信道远场路径损耗解析模型。然后以植入在肌肉为例,计算了TM波和TE波在5个常用工业通信频率以不同角度斜入射的人体信道电磁场分布与路径损耗,结果显示,电磁波在入射面的反射是影响人体信道路径损耗的关键因素,当频率在1.4 GHz附近时总路径损耗最小,TM波性能优于TE波,且当入射角小于等于30°时,总路径损耗基本保持不变。最后采用COMSOL Multiphysics建立了有限元仿真模型验证解析模型,二者结果高度吻合,最大误差仅为0.039,有力证明了解析模型的正确性和有效性。     

室内X波段离体信道传播特性的测量与建模

研究了在X波段以人体为中心环境的无线信道衰落模型建模方法，围绕可穿戴天线在体表不同部位的无线信道进行了实验和分析.分别在离体与无体场景下测量视距（line-of-sight, LoS）和非视距（non-lineof-sight, NLoS）两种路径的信道衰落，对比分析人体不同部位的阴影效应和穿透损耗，结果表明改变天线穿戴部位，信道衰落曲线的损耗指数和截距均会发生变化；人体穿透损耗与信道频率、收发端天线之间的距离无关.基于现有的模型对实验数据进行拟合，提出一种与人体不同部位相关的带有体表阴影效应、穿透损耗修正因子的离体信道衰落模型.该模型细化了人体不同部位的信道特性，与通用模型相比能更加精地确描述离体信道传播环境.     

基于波导耦合型无线人体通信技术研究

为了研究无线人体通信中信道的特征及其影响因素,建立了五层组织手臂通信模型,并据此设计了两种基于空气介质和FR-4介质的收发器。采用基于FDTD算法的CST软件进行了仿真分析和实验测试。结果表明,两种通信模型中适于人体通信的频段均在630MHz~1200MHz范围内,且在700MHz附近人体通信信道损耗最小;通过改变收发机的结构参数会引起人体通信信道内损耗的变化。     

无线体域网信道特性研究

无线体域网(WBAN)包含一系列低功耗、微型化、侵入式或非侵入式无线传感器节点,通过短距离无线通信技术实现与外界的通信,提供医疗保健、消费电子、个人娱乐等多项服务。由于WBAN应用于人体,WBAN信道的传播特性与其他传统的无线信道特性有着显著的不同。本文从频点、环境和人体状态3个方面详细研究了WBAN的信道特性。UWB频段采用了冲激响应模型,而路径损耗模型适用于所有频段;在不同环境下,多径效应是影响信号在体外空间传播的主要因素;此外,天线的位置和人体的运动状态,也是WBAN信道建模和仿真时考虑的关键因素。     

超短波电波传播路径损耗中值公式的数值实验建模

在超短波30~88 MHz波段,路径损耗中值公式Okumura-Hata模型已远远不能满足实际工程对损耗计算的高精度需求,本文利用电磁数值仿真方法,建立真实城市环境中的电波传播模型,通过大量的多种背景模型和收发条件下的数值实验,拟合出适用于30~88 MHz波段的电波传播路径损耗中值公式,弥补Okumura-Hata公式在低端频段的空缺,有效地扩展了Okumura-Hata公式的应用范围,提高了它的实用性。     

人体通信模型与信道特性研究

建立了基于人体多层组织结构的人体通信系统模型.利用人体的波导效应,直接将电磁信号耦合到人体.采用FDTD算法从电磁场与人体交互作用的角度仿真了人体通信的信道特性.结果表明,450～750 MHz和1～1.2 GHz是人体通信的两个最佳通信频段;合理选择收发机的结构,包括电路板尺寸、电极距离和大小,可以有效提高通信效率.分析人体通信电场的传输机制发现,信号沿着人体表面向四周爬行,因此接收机放在人体表面的任何一个位置均可接收信号.     

人体通信信道相位特性研究

采用实验统计方法研究人体信道在1~200 MHz频段下的传播延时和相位特性。实验采用13名志愿者分别进行4个传播路径的群延时测量,并将测试频段划分为1~100 MHz和100~200 MHz两个子频段进行研究,探讨4个传播路径和两个子频段下的延时特性。统计分析表明:信号在人体通信信道的传播延时和传播路径无关;100~200 MHz频段内的传播延时均比1~100 MHz内的传播延时大。1~200 MHz频段内相位归一化曲线表明:在20~40 MHz频段信号畸变较大。根据最大似然估计算法(Maximum Likelihood Estimation,MLE)和Akaike信息量准则(Akaike Information Criterion,AIC),信号相位归一化偏差值符合Lognormal分布。     

Path loss model for in-body communication in homogeneous human muscle tissue

Proposed is the first in-body path loss model in homogeneous human muscle tissue at 2.4 GHz for implants in the human body. This model is valid for insulated dipole antennas up to a distance of 8 cm. Excellent agreement is obtained between measurements, simulations and the models. The path loss model can be used to design an in-body communication system.     

Human Body Communication In-Vivo Measurement Using Different Test Equipment

Human body communication is non-radio frequency technique of wireless body area network, wherein the human body is used as a communication medium in two coupling methods namely: capacitive and galvanic coupling. HBC is relatively new method and in full development, given the large number of scientific publishing works depending on different setup and equipment. Even that it remains controversial with no consensus in terms of propagation characteristics and behavior mechanism. This paper deals with the common used test equipment and configuration attempting to provide a complementary information about HBC channel characterization issue. For that, in vivo measurements were carried out using several assembling of equipment in different scenarios, considering the conventional inspected parameters (channel length, transverse distance and balun insertion scenarios). The measurements were conducted in both frequency and time domain using primarily spectrum/vector network analyzer and digital oscilloscope respectively. Thus, in addition to transmission losses between transceivers across the channel (calculated path loss factor), phase angle information are considered over the operating frequency band to assert the non-dispersive HBC channel nature. Further harmonic distortion effect is shown, then high transmission power for the signal of interest is attributed to HBC methods according to the calculated total harmonic distortion THD metric, even harmonics resulting from the channel non-linearity characteristics or transceivers signal/apparatus imperfections. The experimental setups highlights the important to consider the precise criteria for measurement purpose, thus leading using the most appropriate test apparatus.

     

Compact broadband stacked implantable antenna for biotelemetry with medical devices

A compact stacked implantable antenna for biotelemetry in medical implant communication services band (MICS band: 402-405 MHz) is proposed. Using a stacked planar inverted-F antenna (PIFA) structure can enhance bandwidth and reduce the effect of frequency shift in human tissue giving complex and highly variable characteristics. The antenna looks like one dime (US currency) and has a 7.5 mm radius, 1.9 mm thickness, operating frequency at 402 MHz and a bandwidth of 50 MHz at return loss of 10 dB. A miniature, broadband stacked implantable antenna for biotelemetry with medical devices is provided     

Channel Modeling of Wireless Sensor Networks in Oil

Electromagnetic (EM) techniques enable efficient wireless communications in different media with high material absorptions, such as underground soil, water and oil medium. A wide range of novel and important applications in such challenged environments can be realized based on the EM communication mechanism. In this paper, the propagation based on EM waves in the megahertz (MHz) and gigahertz (GHz) band through a different types of oil is analyzed in order to explore its applicability in pipelines and oil sands. The developed model evaluates the total path loss and the transmission characteristics. Moreover, based on the proposed channel model, the resulting bit error rate (BER) is analyzed that an EM wave experiences when propagating through the oil medium. The propagation characteristics are investigated through simulation. The theoretical analysis and the simulation results prove the feasibility of wireless communication in the MHz and GHz band in oil environment and highlight several important aspects in this field.

     

人体阻抗模型与人体域通信信道特性分析

基于人体柱体模型分析了输入阻抗与人体形状大小的关系,就人体信道的频率传输特性进行了讨论,在3～5GHz 的频率范围内,人体对传输信号具有良好的响应。考虑到多径传输环境下的信噪比和误码率,采用二相相移键控(BPSK)的调制方式,对人体域无线传输信道具有更好的性能。     

Channel Models for Body Surface Communications in Ultra Wideband-Based Wireless Body Area Networks

Body area networks are being developed to serve a wide range of purposes ranging from providing health care to patients on the move to tracking patients and motion sensing for gaming controls. There has been significant and sizeable amount of research in the various areas and applications of body area networks. Ultra wideband which operates in the 3.1–10.6 GHz band is slowly being preferred for high data rate communication in body area networks. The development of suitable applications and techniques for communication depends significantly on the channel models. The wireless channel is a crucial parameter as it provides significant information about the propagation characteristics and losses involved in the transmission medium. The existing channel models proposed are mostly in the spectra involving the wideband 3.1–10.6 GHz bands or the 3.1–6 GHz bands. However, the IEEE 802.15.6 specifies operation in various sub-bands of 499.2 MHz width. And the channel characteristics are significantly different for wideband and narrowband channels. In this article, we propose empirical channel models for body surface communication in the various sub-bands specified by the IEEE 802.15.6. The body surface scenario is chosen as the combination of propagation through wireless media and losses due to absorption from body tissues make it challenging. The proposed path loss models are developed from more than 300,000 received power measurements collected over a span of hours.     

Propagation Path Loss and Materials Insertion Loss in Indoor Environment at WiMAX Band of 3.3 to 3.6?GHz

The purpose of this study is to characterize the indoor channel for IEEE 802.16 (WiMAX) at 3.3?C3.6?GHz frequency. This work presents a channel model based on measurements conducted in commonly found scenarios in buildings. These scenarios include closed corridor, wide corridor and semi open corridor. Path loss equations are determined using log-distance path loss model and a Rayleigh multipath induced fading, Normal multipath induced fading or a combination of both. A numerical analysis of measurements in each scenario was conducted and the study determined equations that describe path loss for each scenario. Propagation loss is given for 300?MHz bandwidth. This work also represents the insertion loss of different materials and the obstruction loss due the existence of human beings between the transmitting antenna and the receiving one.     

Analysis on Co‐channel Interference of Human Body Communication Supporting IEEE 802.15.6 BAN Standard

Human body communication (HBC) is being recognized as a new communication technology for mobile and wearable devices in a body area network (BAN). This paper presents co‐channel interference experienced by HBC supporting the physical layer in the IEEE 802.15.6 BAN standard. To analyze the co‐channel interference, a co‐channel interference model is introduced, and space‐domain and time‐domain parameters representing an interference environment are generated using the co‐channel interference model. A new signal‐to‐interference ratio (SIR) parameter depending on the peak amplitudes of the data signals causing co‐channel interference is defined; co‐channel interference can be easily analyzed and modelled using the newly defined SIR. The BER degradation model derived using the co‐channel interference model and SIR in this paper can be effectively used to estimate the performance.