Compared with common near space satellite Telemetry,Telecommand,and Communication(TT&C),deep space TT&C presents a more challenging environment such as long distance,very low Signal to Noise Ratio(SNR).How to ...Compared with common near space satellite Telemetry,Telecommand,and Communication(TT&C),deep space TT&C presents a more challenging environment such as long distance,very low Signal to Noise Ratio(SNR).How to acquire main carrier exactly becomes a hot focus for deep space communications.Already there emerged some main carrier acquisition algorithms,but they all require high SNR and small modulation index.In this paper,we develop a new acquire algorithm.First we use the spectral energy center algorithm to shorten the original sequence,filter out some noise and make the spectral more symmetric.Then we adopt the spectral symmetry algorithm to make full use of the whole spectrum information,and utilize FFT to reduce computation complexity.Simulation results show that our algorithm can acquire main carrier successfully under large modulation index and get good performance with low Carrier to Noise Ratio(CNR).展开更多
针对连线干涉测量系统(CEI)在无模型时延或模型时延不准确条件下相位模糊度解算困难的问题,提出了利用伪码测距信号辅助的载波相位模糊解算方法。在测站距离约束下,根据两站所接收伪码信号的相对位置关系计算得到一个时延差作为解载波...针对连线干涉测量系统(CEI)在无模型时延或模型时延不准确条件下相位模糊度解算困难的问题,提出了利用伪码测距信号辅助的载波相位模糊解算方法。在测站距离约束下,根据两站所接收伪码信号的相对位置关系计算得到一个时延差作为解载波相位模糊的时延预报值。为了提高解模糊能力,引入了伪码捕获和跟踪的基本方法。仿真分析了不同信噪比下所能达到的最大精度,结果表明在信噪比高于0 d B时,可直接解算S频段的载波相位模糊;在信噪比较低时,可解算宽带群时延的相位模糊。在0 d B和-30 d B条件下重复试验1 000次,正确率分别达到99.88%和99.91%,证明了算法的有效性。展开更多
航天测控通信网自建成以来,整体运行较为稳定,但在网络安全方面也暴露出了一些问题,为研究和解决目前航天测控通信网中存在的网络安全问题,在分析TCP/IP(Transmission Control Protocol/Intcrnct Protocol,传输控制协议/互联网协议)分...航天测控通信网自建成以来,整体运行较为稳定,但在网络安全方面也暴露出了一些问题,为研究和解决目前航天测控通信网中存在的网络安全问题,在分析TCP/IP(Transmission Control Protocol/Intcrnct Protocol,传输控制协议/互联网协议)分层协议基本原理的基础上,研究了IP网数据链路层、网络层和传输层的协议漏洞及常见攻击方法,详细介绍了当前航天测控通信网的网络安全部署情况,根据网络现状分别对航天测控通信网上数据链路层、网络层和传输层存在的安全问题进行了纵向分析,针对分析出的各类安全问题,进一步给出了有效的防御措施和防护方法。最后,探讨提出了一套航天测控通信网配置维护管理系统的设计方案,通过建立设备配置信息库、检查信息记录库及网络故障库等,实现了对航天测控通信网安全稳定运行的有效管理。展开更多
In this paper, we present a new form of “special relativity” (BSR), which is isomorphic to Einstein’s “special relativity” (ESR). This in turn proves the non-uniqueness of Einstein’s “special relativity” and i...In this paper, we present a new form of “special relativity” (BSR), which is isomorphic to Einstein’s “special relativity” (ESR). This in turn proves the non-uniqueness of Einstein’s “special relativity” and implies the inconclusiveness of so-called “relativistic physics”. This work presents new results of principal significance for the foundations of physics and practical results for high energy physics, deep space astrophysics, and cosmology as well. The entire exposition is done within the formalism of the Lorentz <em>SL</em>(2<em>C</em>) group acting via isometries on <strong>real 3-dimensional Lobachevskian (hyperbolic) spaces</strong> <em>L</em><sup>3</sup> regarded as quotients <span style="white-space:nowrap;"><em>SL</em>(2<em>C</em>)/<em>SU</em>(2)</span>. We show via direct calculations that both ESR and BSR are parametric maps from Lobachevskian into Euclidean space, namely a <strong>gnomonic</strong> (central) map in the case of ESR, and a<strong> stereographic </strong>map in the case of BSR. Such an identification allows us to link these maps to relevant models of Lobachevskian geometry. Thus, we identify ESR as the physical realization of the Beltrami-Klein (non-conformal) model, and BSR as the physical realization of the Poincare (conformal) model of Lobachevskian geometry. Although we focus our discussion on ball models of Lobachevskian geometry, our method is quite general, and for instance, may be applied to the half-space model of Lobachevskian geometry with appropriate “Lorentz group” acting via isometries on (positive) half space, resulting yet in another “special relativity” isomorphic with ESR and BSR. By using the notion of a<strong> homotopy</strong> of maps, the identification of “special relativities” as maps from Lobachevskian into Euclidean space allows us to justify the existence of an uncountable infinity of hybrid “special relativities” and consequently an uncountable infinity of “relativistic physics” built upon them. This is another new result in physics and it states that so called “relativistic physics” is unique only up to a homotopy. Finally, we show that “paradoxes” of “special relativities” in either ESR or BSR are simply common distortions of maps between non-isometric spaces. The entire exposition is kept at elementary level accessible to majority of students in physics and/or engineering.展开更多
基金Supported by the National Natural Science Foundation of China (No. 61032003 and No. 61021001)
文摘Compared with common near space satellite Telemetry,Telecommand,and Communication(TT&C),deep space TT&C presents a more challenging environment such as long distance,very low Signal to Noise Ratio(SNR).How to acquire main carrier exactly becomes a hot focus for deep space communications.Already there emerged some main carrier acquisition algorithms,but they all require high SNR and small modulation index.In this paper,we develop a new acquire algorithm.First we use the spectral energy center algorithm to shorten the original sequence,filter out some noise and make the spectral more symmetric.Then we adopt the spectral symmetry algorithm to make full use of the whole spectrum information,and utilize FFT to reduce computation complexity.Simulation results show that our algorithm can acquire main carrier successfully under large modulation index and get good performance with low Carrier to Noise Ratio(CNR).
文摘针对连线干涉测量系统(CEI)在无模型时延或模型时延不准确条件下相位模糊度解算困难的问题,提出了利用伪码测距信号辅助的载波相位模糊解算方法。在测站距离约束下,根据两站所接收伪码信号的相对位置关系计算得到一个时延差作为解载波相位模糊的时延预报值。为了提高解模糊能力,引入了伪码捕获和跟踪的基本方法。仿真分析了不同信噪比下所能达到的最大精度,结果表明在信噪比高于0 d B时,可直接解算S频段的载波相位模糊;在信噪比较低时,可解算宽带群时延的相位模糊。在0 d B和-30 d B条件下重复试验1 000次,正确率分别达到99.88%和99.91%,证明了算法的有效性。
文摘航天测控通信网自建成以来,整体运行较为稳定,但在网络安全方面也暴露出了一些问题,为研究和解决目前航天测控通信网中存在的网络安全问题,在分析TCP/IP(Transmission Control Protocol/Intcrnct Protocol,传输控制协议/互联网协议)分层协议基本原理的基础上,研究了IP网数据链路层、网络层和传输层的协议漏洞及常见攻击方法,详细介绍了当前航天测控通信网的网络安全部署情况,根据网络现状分别对航天测控通信网上数据链路层、网络层和传输层存在的安全问题进行了纵向分析,针对分析出的各类安全问题,进一步给出了有效的防御措施和防护方法。最后,探讨提出了一套航天测控通信网配置维护管理系统的设计方案,通过建立设备配置信息库、检查信息记录库及网络故障库等,实现了对航天测控通信网安全稳定运行的有效管理。
文摘In this paper, we present a new form of “special relativity” (BSR), which is isomorphic to Einstein’s “special relativity” (ESR). This in turn proves the non-uniqueness of Einstein’s “special relativity” and implies the inconclusiveness of so-called “relativistic physics”. This work presents new results of principal significance for the foundations of physics and practical results for high energy physics, deep space astrophysics, and cosmology as well. The entire exposition is done within the formalism of the Lorentz <em>SL</em>(2<em>C</em>) group acting via isometries on <strong>real 3-dimensional Lobachevskian (hyperbolic) spaces</strong> <em>L</em><sup>3</sup> regarded as quotients <span style="white-space:nowrap;"><em>SL</em>(2<em>C</em>)/<em>SU</em>(2)</span>. We show via direct calculations that both ESR and BSR are parametric maps from Lobachevskian into Euclidean space, namely a <strong>gnomonic</strong> (central) map in the case of ESR, and a<strong> stereographic </strong>map in the case of BSR. Such an identification allows us to link these maps to relevant models of Lobachevskian geometry. Thus, we identify ESR as the physical realization of the Beltrami-Klein (non-conformal) model, and BSR as the physical realization of the Poincare (conformal) model of Lobachevskian geometry. Although we focus our discussion on ball models of Lobachevskian geometry, our method is quite general, and for instance, may be applied to the half-space model of Lobachevskian geometry with appropriate “Lorentz group” acting via isometries on (positive) half space, resulting yet in another “special relativity” isomorphic with ESR and BSR. By using the notion of a<strong> homotopy</strong> of maps, the identification of “special relativities” as maps from Lobachevskian into Euclidean space allows us to justify the existence of an uncountable infinity of hybrid “special relativities” and consequently an uncountable infinity of “relativistic physics” built upon them. This is another new result in physics and it states that so called “relativistic physics” is unique only up to a homotopy. Finally, we show that “paradoxes” of “special relativities” in either ESR or BSR are simply common distortions of maps between non-isometric spaces. The entire exposition is kept at elementary level accessible to majority of students in physics and/or engineering.
