There is an increasing demand on wireless communications in subway tunnels to provide video surveillance and sensory data for security,maintenance and train control,and to offer various communication or entertainment ...There is an increasing demand on wireless communications in subway tunnels to provide video surveillance and sensory data for security,maintenance and train control,and to offer various communication or entertainment services(e.g.,Internet,etc.) to passengers as well.The wireless channel in tunnels is quite unique due to the confined space and the waveguide effects.Therefore,modeling the radio channel characteristics in tunnels is critically important for communication systems design or optimization.This paper investigates the key radio channel characteristics of a subway tunnel at 2.4 GHz and 5 GHz,such as the path loss,root mean square(RMS) delay spread,channel stationarity,Doppler shift,and channel capacity.The field measurements show that channel characteristics in tunnels are highly location-dependent and there exist abundant components in Doppler shift domain.In the straight section of the subway tunnel,the measured path loss exponents are close to1.6,lower than that in free space.展开更多
隐蔽信道能够以危害系统安全策略的方式传输信息,目前,基于网络协议的隐蔽信道研究已成为热点。域名系统协议(Domain Name System,DNS)用于将主机名字和IP地址之间的转换,是双向协议,互联网正常运行离不开DNS协议,因此可以基于DNS协议...隐蔽信道能够以危害系统安全策略的方式传输信息,目前,基于网络协议的隐蔽信道研究已成为热点。域名系统协议(Domain Name System,DNS)用于将主机名字和IP地址之间的转换,是双向协议,互联网正常运行离不开DNS协议,因此可以基于DNS协议建立隐蔽信道。文中首先介绍隐蔽信道、DNS隐蔽信道的概念和原理,搭建DNS隐蔽信道系统,然后演示了DNS隧道工具的使用方法,最后针对现有的DNS隐蔽信道工具提出了几点改进措施,使DNS隐蔽信道数据传输更加高效。展开更多
针对车-车(vehicle to rechicle,V2V)通信系统对无线电信道衰落特性和模型的需求,分别在两种隧道场景中5.9 GHz和5.2 GHz频段下进行了V2V无线电信道测量活动,并对隧道外、隧道内和两者之间的连接部分场景进行了小尺度衰落特性分析.基于...针对车-车(vehicle to rechicle,V2V)通信系统对无线电信道衰落特性和模型的需求,分别在两种隧道场景中5.9 GHz和5.2 GHz频段下进行了V2V无线电信道测量活动,并对隧道外、隧道内和两者之间的连接部分场景进行了小尺度衰落特性分析.基于近距离(close-in,CI)对数模型和ABG(α-β-γ)模型建立了基于距离的接收功率模型,对两种场景隧道内外的接收功率进行了评估和比较,路径损耗指数分别为1.83和1.9,结果表明参考距离为1 m的CI对数模型具有更高的拟合度.此外,将测量数据幅度的衰落分布与五种典型的理论衰落分布进行比较分析,发现其特征更接近于具有最小拟合优度值的莱斯分布,且隧道内的莱斯K因子小于隧道外.同时,给出了隧道内和隧道外之间连接处基于距离的莱斯K因子模型,发现连接处的K因子与距离无关,而隧道内的K因子随距离增大而减小.展开更多
In recent years,high-speed railways(HSRs)have developed rapidly with a high transportation capacity and high comfort level.A tunnel is a complex high-speed rail terrain environment.It is very important to establish an...In recent years,high-speed railways(HSRs)have developed rapidly with a high transportation capacity and high comfort level.A tunnel is a complex high-speed rail terrain environment.It is very important to establish an accurate channel propagation model for a railway tunnel environment to improve the safety of HSR operation.In this paper,a method for finite-state Markov chain(FSMC)channel modeling with least squares fitting based on non-uniform interval division is proposed.First,a path loss model is obtained according to measured data.The communication distance between the transmitter and receiver in the tunnel is non-uniformly divided into several large non-overlapping intervals based on the path loss model.Then,the Lloyd-Max quantization method is used to determine the threshold of the signal-to-noise ratio(SNR)and the channel state quantization value and obtain the FSMC state transition probability matrix.Simulation experiments show that the proposed wireless channel model has a low mean square error(MSE)and can accurately predict the received signal power in a railway tunnel environment.展开更多
Long undersea tunnels, and particularly those that are built for transportation purposes, are not commonplace infrastructure. Although their planning and construction take a considerable amount of time, they form impo...Long undersea tunnels, and particularly those that are built for transportation purposes, are not commonplace infrastructure. Although their planning and construction take a considerable amount of time, they form important fixed links once in operation. The fact that these tunnels are located under the sea gen- erally involves unique challenges including complex issues with construction and operations, which relate to the lack of intermediate access points along the final route of the tunnel. Similar issues are asso- ciated with long under-land tunnels, such as those under mountain ranges such as the Alps. This paper identifies the key issues related to the design and construction of such tunnels, and suggests a potential solution using proven technology from another engineering discipline.展开更多
基金国家自然科学基金(70471004和70731160634)Research Grants Council of the Hong Kong Special Administrative Region,China(RGC Project No.PolyU 511405&N_PolyU 514/07)
基金supported in part by the NSFC project under grant No.61132003the Fundamental Research Funds for the Central Universities(2013JBZ002)the Ph.D.Program Foundation of Ministry of Education of China under grant No.20120009130002
文摘There is an increasing demand on wireless communications in subway tunnels to provide video surveillance and sensory data for security,maintenance and train control,and to offer various communication or entertainment services(e.g.,Internet,etc.) to passengers as well.The wireless channel in tunnels is quite unique due to the confined space and the waveguide effects.Therefore,modeling the radio channel characteristics in tunnels is critically important for communication systems design or optimization.This paper investigates the key radio channel characteristics of a subway tunnel at 2.4 GHz and 5 GHz,such as the path loss,root mean square(RMS) delay spread,channel stationarity,Doppler shift,and channel capacity.The field measurements show that channel characteristics in tunnels are highly location-dependent and there exist abundant components in Doppler shift domain.In the straight section of the subway tunnel,the measured path loss exponents are close to1.6,lower than that in free space.
文摘隐蔽信道能够以危害系统安全策略的方式传输信息,目前,基于网络协议的隐蔽信道研究已成为热点。域名系统协议(Domain Name System,DNS)用于将主机名字和IP地址之间的转换,是双向协议,互联网正常运行离不开DNS协议,因此可以基于DNS协议建立隐蔽信道。文中首先介绍隐蔽信道、DNS隐蔽信道的概念和原理,搭建DNS隐蔽信道系统,然后演示了DNS隧道工具的使用方法,最后针对现有的DNS隐蔽信道工具提出了几点改进措施,使DNS隐蔽信道数据传输更加高效。
基金partially supported by Nation Science Foundation of China (61661025, 61661026)Foundation of A hundred Youth Talents Training Program of Lanzhou Jiaotong University (152022)
文摘In recent years,high-speed railways(HSRs)have developed rapidly with a high transportation capacity and high comfort level.A tunnel is a complex high-speed rail terrain environment.It is very important to establish an accurate channel propagation model for a railway tunnel environment to improve the safety of HSR operation.In this paper,a method for finite-state Markov chain(FSMC)channel modeling with least squares fitting based on non-uniform interval division is proposed.First,a path loss model is obtained according to measured data.The communication distance between the transmitter and receiver in the tunnel is non-uniformly divided into several large non-overlapping intervals based on the path loss model.Then,the Lloyd-Max quantization method is used to determine the threshold of the signal-to-noise ratio(SNR)and the channel state quantization value and obtain the FSMC state transition probability matrix.Simulation experiments show that the proposed wireless channel model has a low mean square error(MSE)and can accurately predict the received signal power in a railway tunnel environment.
文摘Long undersea tunnels, and particularly those that are built for transportation purposes, are not commonplace infrastructure. Although their planning and construction take a considerable amount of time, they form important fixed links once in operation. The fact that these tunnels are located under the sea gen- erally involves unique challenges including complex issues with construction and operations, which relate to the lack of intermediate access points along the final route of the tunnel. Similar issues are asso- ciated with long under-land tunnels, such as those under mountain ranges such as the Alps. This paper identifies the key issues related to the design and construction of such tunnels, and suggests a potential solution using proven technology from another engineering discipline.
