基于t检验的星基增强系统完好性数据核验

针对星基增强系统(SBAS)高完好性的服务需求,提出了一种SBAS广播参数用户差分伪距误差(UDRE)的完好性核验方法.利用监测站实测全球定位系统(GPS)和地球静止轨道(GEO)卫星信号,解析GPS电文和SBAS广播差分及完好性信息,对观测量修正误差得到实测UDRE,使用t检验成对二样本分析法验证给定置信区间内广播UDRE'与实测UDRE的符合性,从而完成伪距域完好性参数UDRE的核验.伪距域的核验避免了以往位置域核验计算量大、多卫星故障检测能力差的缺点,有更好的故障检测与隔离能力.采集日本多功能GPS卫星星基增强系统(MSAS)数据并对提出的t检验方法进行验证,结果表明,所建立的统计检测量能有效地反应被监测卫星广播UDRE参数的完好性,通过确定卫星99.9%置信度下的判决门限,对广播UDRE与实测UDRE判别,验证伪距误差的可信度.该结果验证了所提方法应用于UDRE核验的可行性,为SBAS完好性验证提供了技术支撑.     

Multiple gateway placement in large‐scale constellation networks with inter‐satellite links

Multiple gateways are required in large satellite constellation networks (LSCNs) with inter‐satellite links (ISLs), and their placement may greatly affect the system performance. Gateway placement can be optimized to achieve better network performance under the non‐uniform ground demand distribution. This paper formulates a gateway placement optimization model for LSCN with ISLs, aiming at achieving an optimal overall performance including delay, traffic peak, and load balance. The constraints of potential gateway location, gateway‐satellite connectivity, and max hop‐count are considered. A genetic algorithm (GA)‐based method is proposed to solve the integer optimization problem with the help of quasi‐evenly distributed reference layout. A Starlink‐like constellation with ISLs is adopted in the simulation. The simulation results show that the optimized layout has better performance than the reference layout. Additionally, the locations with high user demand or at the middle of ocean are preferred by gateways. The network performance is jointly influenced by gateway placement, demand distribution, constellation configuration, node, and link capacities. The abnormally high ISL hop‐count is found in the south Indian Ocean, which is caused by constellation and ISL configuration.     

SBAS卫星信号的Viterbi译码优化方案

为了减少硬件处理的时间浪费,针对经由卷积编码的SBAS(Satellite-based Augmentation System )卫星信号,提出一种优化的Viterbi译码处理方案.该方案对译码数据流进行截断处理并进行性能补偿,通过Matlab平台对其进行建模仿真.仿真结果表明,该方案能够在节约硬件存储容量和减少数据处理压力的同时,获得与传统译码同等的译码性能,这为硬件实现提供了很好的参考依据.     

Sub-100 nm NMOS Halo工艺优化分析

短沟道效应是MOS器件特征尺寸进入Sub-100nm后必须面对的关键挑战之一。Halo结构能够有效地抑制短沟道效应,合理的Halo区掺杂分布会极大地改善小尺寸器件性能。文中采用器件和工艺模拟工具ISE-TCAD研究形成Halo结构的工艺参数对器件性能的影响,并进行优化。分析表明,Halo注入角度、能量和剂量的增大会提高器件的阈值电压和开关比,降低泄漏电流和阈值漂移,有效抑制SCE、DIBL效应,但同时也会部分地降低驱动能力,即Halo注入参数对器件性能的影响不是简单的线性关系,需要根据具体条件寻求优化值。     

卫星数字电视信号干扰检测与预警实现

随着数字通信技术的发展，广播电视由模拟向数字化全面过渡。卫星数字广播具有诸多优点，受到世界各国的广泛重视，同时也成为不法分子的攻击对象。新型专业卫星数字电视解码器（IRD）通过运行防止非法信号干扰的软件，实时分析卫星数字电视信号的特征，从而提前发现外来非法干扰信号并实施预警。分析卫星数字电视信号在受干扰过程中的信号特征，然后根据此特征提出对恶意干扰进行预警的一种实现算法。     

A new FQPSK modem/radio architecture for PCS and mobile satellitecommunications

A newly developed constant envelope FQPSK modem/radio architecture, which employs a modified double-jump (DJ) filter in the cross-correlated FQPSK system, is proposed for personal communications systems (PCS) and mobile satellite applications. The power efficiency and spectrum efficiency of this system are investigated in a nonlinear amplified (NLA) environment. The bit error rate (BER) performance is evaluated in a noisy Rayleigh fading channel. We demonstrate that with the simplest threshold detectors (binary robust eye diagrams in I and Q channels), this system is 4-7 dB more power efficient than the US digital cellular and Japanese Handyphone standard π/4-QPSK (50%-100% more spectrally efficient than the recently adopted wireless local area network (LAN) standard GFSK and the European standard GMSK). The results indicate that the proposed DJ filtered FQPSK is a power and spectrally efficient modem/radio technique. By selecting different system parameters, this system can be optimized for a wide range of applications in PCS and mobile satellite communications     

Dual-Space Diversity over Land Mobile Satellite Channels Operating in the L and K Frequency Bands

Land mobile satellite communication systems at Ka/K band (30/20 GHz) are attracting more and more attention to researchers because of its frequency band availability and the possibility of using small earth stations and satellite antennas for the systems. However, the Ka/K-band communications also give significant challenges in the system design due to severe channel impairments expected from the satellite links. In this paper, K-band channel characteristics are studied and compared with those at L band. The channel is modeled as Rayleigh multipath fading with the line-of-sight (LOS) component following a lognormal distribution. The first and second-order statistics of the fading channel are studied. Dual-space diversity reception is investigated to combat the flat channel fading. The bit error rate performance of coherent binary phase shift keying (BPSK) with ideal bit and carrier phase synchronization over the fading channel at K band is evaluated theoretically and verified by computer simulations in the case with and without diversity reception.     

星基增强系统接收机中的导航比特同步设计与性能仿真

星基增强系统(SBAS)中导航电文速率为500符号/秒,针对其弱信号时找导航比特边界难的特点,提出了基于最大似然算法的比特同步算法,给出了在SBAS接收机中比特同步的应用公式和实现方法,并进一步创新性地设计了包含有软判决和多次判决的比特同步综合流程;最后在多种导航比特分布的情形下,对最大似然比特同步算法进行了不同载噪比下的性能仿真,确认了此算法在接收信号很弱时仍然有效。     

Maximum cross correlation automatic satellite image navigation and attitude corrections for open-ocean image navigation

To enable "automated" image navigation (without human intervention) a base image is defined, and the maximum cross correlation (MCC) method is used to automatically compute the satellite attitude parameters required to geometrically correct images to this base image. Several levels of filters insure that contamination from cloudy pixels is minimized. The MCC method produces displacement vectors, which are translated into satellite attitude corrections to be added to the orbital image navigation corrections. The auto attitude corrections are shown to be more accurate than the traditional linear translation methods. A further application of the attitude corrections is demonstrated whereby attitude corrections computed over land can be carried forward in the satellite's orbit to accurately navigate imagery over the open ocean where no map reference points are available. Tested for two land sites well separated in a single orbit this method is shown to be as accurate as when applied to an individual image.     

A generalized N-state model to characterize satellite diversity forarbitrary number of satellites in case of uncorrelated channels

To mitigate the main impairments due to the mobile satellite channel, satellite systems adopting code-division multiple access (CDMA) can exploit diversity. Each signal can flow through more than one path, increasing link availability or improving signal-to-noise ratio (SNR). This letter presents a general mobile satellite channel model for an arbitrary diversity order assuming that all the links are statistically independent. A diversity availability improvement upper bound is calculated     

Dynamic fade restoration in Ka‐band satellite systems

Atmospheric precipitation can seriously affect the propagation of centimeter and millimeter electromagnetic waves. As a consequence, in some applications, it is necessary to make use of a fade countermeasure technique in order to satisfy the system availability and quality requirements. This study analyses the performance of a satellite‐based system in geo‐stationary orbit operating at 20 GHz, dynamically assigning the antenna directivity pattern to counteract tropospheric attenuation. The on‐board power is spatially distributed over the covered region to minimize, at any time, the number of users undergoing outage because of the tropospheric attenuation. Both the aspects of broadcasting and telecommunication services are addressed. The reflector antenna of the system is supposed to be illuminated by a cluster of feeds driven by a set of excitation coefficients, continuously modified and optimized according to the meteorological information derived by processing METEOSAT satellite data and ECMWF (European Centre for Medium‐Range Weather Forecasts) data. Copyright © 2002 John Wiley & Sons, Ltd.     

Cooperative Hybrid Land Mobile Satellite–Terrestrial Broadcasting Systems: Outage Probability Evaluation and Accurate Simulation

Next generation communication networks incorporate Land Mobile Satellite (LMS) systems in order to provide greater areas of coverage and higher throughput for specific applications. Cooperation between satellite communication networks and terrestrial relays is or increasing the system’s performance and availability. In this paper, the outage performance of a cooperative hybrid satellite and terrestrial system configuration is analytically evaluated assuming that the satellite links suffer from shadowed Rician fading, while the terrestrial link suffers from the Nakagami-m fading. Two cooperative relaying strategies are examined and the final formulas for the calculation of the outage probability are given. Moreover, a block diagram for the generation of time series for the reliable simulations of the outage probability of the cooperative hybrid land mobile satellite systems is given. The theoretical results and the simulation results almost coincide. Moreover, extended numerical results investigate the impact, of different shadowing conditions and more generally of the satellite links elevation angles, on the overall cooperative LMS system performance.     

The Bayesian Assessment of System Availability: Advanced Applications and Techniques

The statistical assessment of system availability within a Bayesian framework is extended here to consider four additional areas: 1) applications to more complicated availability definitions than considered in an earlier paper; 2) applications to measures of performance other than availability; 3) the use of prior distributions on the failure and repair rates more general than the gamma form; and 4) the use of a model involving nonexponential repair intervals. Under category 1) we consider applications involving: a) a demand for system performance which occurs at a random time within an initial interval; b) a situation involving demands upon a system repeated at intervals; and c) the availability statistics of a redundant configuration. Under category 2) we develop: a) the moment and distributional statistics for the accumulated repair time in a given real-time interval when the rate parameters are uncertain; and b) additional measures of performance in a repeated demand situation. Under category 3) we treat fully the case of a prior distribution composed of a linear combination of gamma distributions; this allows multimodal priors. Under category 4) we treat the case of gamma-distributed repair intervals where both the location and shape parameters are uncertain. The results obtained under all four categories can be expressed in terms of the basic measures for the Euler distribution developed in an earlier paper [1].     

A satellite system for CATV

The increasing capacity of CATV systems has generated a demand for more program material than can be economically generated with local facilities. A possible solution is a nationwide satellite distribution system dedicated to CATV which would provide the additional material directly to the CATV head-end. This paper presents a satellite system design that would distribute six TV channels to 10 ft antenna terminals located at the head-end. Since such a system requires thousands of receiving terminals, their cost must be minimized to produce an economically viable system. The system addressed in this paper requires a ground terminal that is comparable to a standard microwave relay terminal in both cost and complexity. The system consists of three satellites, covering the Eastern, Central, and Western portions of the United States. Based on tradeoffs of spectrum availability and low-noise amplifiers, the 12 GHz frequency band has been selected for the satellite to terminal link. The proposed terminal uses a fixed high-efficiency 10 ft antenna with extremely simple but rigid construction. A low-cost tunnel diode amplifier is used for the receiver front end. After the necessary down-conversion, detection of each channel is performed at the standard 70 MHz IF frequency. The required satellites could be launched on an Atlas Centaur launch vehicle using present technology. The satellites would weigh an approximate 1500 Ib and generate 5 kW of dc power.     

星座组网中直扩信号快速同步改进算法

基于直扩体制的时分多址(TDMA)卫星星座组网,信号帧前导段长度越短、净荷长度越长,数据传输的效率就越高.但是,直扩体制信号帧前导段长度越短意味着接收信号捕获增益就越低,捕获概率就越低.另外,前导段长度越短要求锁相环信号跟踪收敛速度越快.星座组网整网数据传输效率受到卫星信号同步算法性能的制约.为了提高直扩信号同步算法的性能,从捕获与跟踪两个部分对同步算法进行了改进,提出了一种直扩信号快速同步改进算法.针对捕获部分,分析了前置低通滤波器带宽对扩频信号的自相关函数的影响,通过选择滤波器参数在保证相关主峰无明显恶化情况下提升1/4码片偏差相关峰能量1 dB以上.针对跟踪部分,提出了一种调整闭环控制系统的零极点分布优化锁相环时域响应的锁相环设计方法,给出了基于控制理论优化锁相环闭环系统的零极点分布的四点原则,利用该方法设计的锁相环能大大降低信号跟踪的收敛时间.仿真结果表明,所提改进算法与传统同步方法相比能有效提高信号的捕获概率,加快信号跟踪的收敛速度,明显减少信号的同步时间.     

Adaptive Control of Satellite EIRP to Reduce Outage Caused by Fading

The output EIRP or the available bandwidth of a satellite in general limits the amount of traffic which can be handled by SATCOM systems. As the frequency congestion drives future SATCOM systems to higher frequencies, the former constraint will be the more important one because of the severe fades caused by precipitation. Rather than using fixed fade margins, the link power can be dynamically allocated from a common pool of satellite EIRP. By judicious, adaptive allocation of the satellite EIRP among the various users, the traffic supported can be maximized while maintaining the link availability. This paper reports techniques and statistical results of four different ways of allocating the EIRP. By using adaptive centralized control of the terminals transmit power and a variable satellite transmit antenna adaptively controlled by ground commands to compensate for link fades, most efficient use of the satellite EIRP is made. The performance of this technique is derived and compared with others of less complexity and that of a system with fixed satellite antenna and transmit power levels.     

A Wide-Band Satellite Microwave Switch Matrix for SS/TDMA Communications

A lightweight, broad-band, 8 × 8 crossbar microwave switch matrix (MSM) has been developed for satellite-switched timedivision multiple-access (SS/TDMA) operation anywhere in the 6 GHz up-link and/or 4 GHz down-link bands. The nearly transparent performance characteristics in the 3.5-6.5 GHz band, for any of the highly flexible interconnect possibilities, have been facilitated by the design of a low-power-consuming resistively matched PIN diode switch. Broad-band push-pull connectors are used to simplify assembly and disassembly of this modular three-dimensional matrix. The switch control electronics (SCE) circuits have been implemented as custom-designed LSI chips for integration within the MSM input distribution networks. Design considerations and performance characteristics of the satellite switch matrix are presented.     

卫星S频段下行链路频谱占用建模与预测

目前提出的频谱占用模型能够在时域上描述和重现基本的统计特征，如传统的地面移动通信的频谱占用/空闲周期长度可以用经典的广义帕累托(GP)分布、指数分布等分布来拟合。然而在某些复杂的如卫星链路频谱占用场景中，传统的参数估计分布无法给出良好的拟合。为此提出了用核密度估计(KDE)的方法来进行概率密度分布的拟合，在此基础上，分别采用差分整合移动平均自回归模型(ARIMA)和模糊神经网络对频谱占用模型的时间序列进行预测并进行对比。结论表明，核密度估计的使用可以更加准确地描述并再现卫星下行链路所使用S频段的占用时间序列的统计特征，而模糊神经网络的预测比ARIMA模型预测更加精确。     

多卫星系统组合导航的可用性分析

在航空应用中,多卫星导航系统组合导航是未来的发展趋势,可用性是航空应用的主要性能要求之一。但是在截止角增大时,GPS单系统的可用性却达不到航空性能标准。针对该问题,对GPS/Galileo/BD组合系统在中国境内的可用性进行仿真分析,与GPS单系统相比,组合系统的可用性相对单系统有所提高,且截止角较大时,仍能达到可用性要求。