可移动低轨道通信卫星地面终端设备的研究

文中结合了低轨道小卫星通信系统的重要理论和关键技术,着重对低轨道小卫星通信的地面站控制系统进行了详细地分析和研究.借鉴国外同类型设备的技术优点和国外设备相结合的研究测试方法,在其设备结构的基础上进行合理的创新与改进.最后,经过系统仿真和实际的测试,达到了与卫星进行数据传输的要求,并实现了对多普勒频移的控制.     

Interference Environment Between High Altitude Platform Networks (HAPN), Geostationary (GEO) Satellite and Wireless Terrestrial Systems

A new broadband telecommunication system has been recently proposed for provision of fixed, mobile and personal services adopting the use of high altitude platform stations placed in a fixed position in the stratospheric layer at heights from 15.5 to 30 km. The International Telecommunication Union (ITU) has allocated a pair of 300 MHz of spectrum in the V band for these services, which is already in use by geostationary satellite and wireless terrestrial systems as co-primary allocations. This paper addresses an in-depth co-channel interference analysis and proposes a C/I (carrier-to-interference) calculation model applicable to all the interference propagation paths as well as sharing criteria between HAPN, GEO satellite and wireless terrestrial systems extracted from simulations performed in urban, suburban and rural environments. By evaluating the interference density cumulative probability distribution functions, sufficient geographical separation distances between the ground stations are proposed which guarantee the harmonic co-existence between the three broadband systems. Maintaining the platform stable in the stratosphere is a key issue, and in this paper the effect of the three different stratospheric platform’s movement models (ITU, HELINET, HALO) appearing in the literature, on C/I levels is estimated.Vasilis F. Milas {received the Diploma in Electrical and Computer Engineering from the National Technical University of Athens, Greece, in 2000. From October 2000 until October 2001 he joined Space Engineering S.P.A in Italy (Rome) as a field practicing engineer where he was mainly involved into the design and realization of satellite telecommunication systems. Since November 2001 he is a member of the Mobile Radiocommunications Laboratory at the National Technical University of Athens working towards his Ph.D. degree with focus on high altitude platform systems and interference characterization on wireless communication systems.Philip Constantinou {received the Diploma in Physics from the National University of Athens in 1972, the Master of Applied Science in Electrical Engineering from the University of Ottawa, Ontario, Canada in 1976 and the Ph.D. degree in Electrical Engineering in 1983 from Carleton University, Ottawa, Ontario, Canada. From 1976 to 1979 was with Telesat Canada. In 1980 he joined the Ministry of Communications in Ottawa, Canada. From 1984 to 1989 he was with the National Research Centre Demokritos in Athens, Greece were he was involved on several research projects in the area of Mobile Communications. In 1989 he joined NTUA where he is currently Professor. His current research interests include Mobile Satellite Communications and Interference Problems on Digital Communications Systems.     

GEO与NGEO卫星频谱共存干扰抑制技术（一）

由于对低延时实时系统和宽带数据的需求日益增加,人们越来越关注如何在几个可用的频带中部署更多的近地轨道（LEO）和中地轨道（MEO）卫星。当可用的非静止轨道（NGEO,即LEO/MEO）卫星数目增多时,其与在轨的地球静止轨道（GEO）卫星频谱共存已经成为了一种必须。在这种情况下,为了使它们的频谱可以共用,探索一项技术来抑制GEO和NGEO系统间的干扰是非常关键的。更具体地说,在GEO和NGEO卫星网络共存的情况下,共线干扰可能是一个严重的问题,特别是在赤道上空。本文提供了几个关于如何在NGEO卫星链路和GEO卫星链路共存情况下频率共用的研究。除此之外,本文提出了几种认知方法来解决共线干扰,也提出了未来研究方向。     

TCRA: a time‐based channel reservation scheme for handover requests in LEO satellite systems

In this paper, we propose a time‐based channel reservation algorithm (TCRA) suitable for handover and call admission control procedures in future mobile satellite systems. These systems are characterized by a high rate of handover attempts which can degrade significantly their performance. Therefore, we propose TCRA, a scheme which guarantees a null handover failure probability by using a channel reservation strategy in the cells to be crossed by the user. The performance of TCRA has been compared to the guaranteed handover (GH) scheme. The TCRA reservation method has the advantage of a better channel utilization by locking the resources only for their expected time of use. A mathematical model has been developed for both schemes, and its results have been validated through simulations. Copyright © 2003 John Wiley & Sons, Ltd.     

Device decapsulated (and/or depassivated) – Retest ok – What happened?

One of the very first steps to enter into physical device failure analysis is the device decapsulation. In some cases, an additional depassivation follows to give access to contact needles for internal probing. However, it happens from time-to-time that the device has been cured from its failure behaviour. Such cases often end as non-conclusive analysis result. Our principle investigations and results, however, will help to understand the mechanisms and allow in many “hopeless” cases to draw useful conclusions on the root causes. These are linked in most cases to metal related failures. Besides the “classical case” of touching bond wires, typical root causes are metal filament shorts in the nanometer-order-of magnitude, which can be removed easily by mechanical and/or chemical effects of any delayering procedure. Surface metal shorts may also be generated by bump metal or pad-interface-metallisation-redeposition onto the passivation surface and by metal residue-related recombinations of trimming fuses. In both latter cases, nanometer metal films short-circuit neighbouring pads or fuses in trimming-fuse-arrays. This paper describes these and some second-order mechanisms in detail, which sometimes let the chip recover after decapsulation and/or depassivation.     

Correlation analysis between pattern and non-pattern wafer for characterization of shallow trench isolation–chemical–mechanical polishing (STI–CMP) process

This study is about control of oxide removal amounts on the shallow trench isolation (STI) patterned wafers using removal rate and thickness of blanket (non-patterned) wafers. At first, the removal properties of plasma enhanced tetra-ethyl ortho-silicate (PETEOS) blanket wafers was investigated, and then it was compared with the removal properties and the planarization (step height) as a function of polishing time of the specific STI patterned wafers. We found that there is a relationship between the amount of oxide removal by blanket and patterned wafers. We analyzed this relationship, and the post-CMP thickness of patterned wafers could be controlled by removal rate and removal target thickness of blanket wafers. As the result of correlation analysis, we confirmed that there was the strong correlation between patterned and blanket wafers (correlation factor: 0.7109). So, we could confirm the repeatability as applying to STI CMP process from the linear formula obtained.     

Globalization and heterogenization: Cultural and civilizational clustering in telecommunicative space (1989–1999)

The globalization of telecommunicative ties between nations is studied from a heterogenization perspective. A theoretical model inspired by Appadurai’s “disjuncture hypothesis,” which stipulates that global flows of communication are multidimensional and reinforce regional/local identities, is tested empirically on an international voice traffic dataset. Spatial-statistical measures (global and local versions of Moran’s I) indicate that countries that share the same linguistic (English, Spanish, or French) or civilizational (Catholic, Protestant, and Buddhist–Hindu) background are more likely to be each other’s “telecommunicative neighbors” and that this tendency has increased over time (1989–1999).     

Percolation Mechanism and Characterization of (CdO)y(ZnO)1–y Thin Films

(CdO)_y(ZnO)_1–y thin films have been prepared by the sol–gel process, based on precursor solutions used separately for such oxides. The Cd/(Cd + Zn) atomic ratio in solution ranged from 0 to 0.32. These compositions were selected on the basis of an observed abrupt fall, of ca. four orders of magnitude, in the resistivity of the films within this range. Such a resistivity drop, with a threshold value of around y = 0.17, is consistent with a percolation mechanism in a three‐dimensional, random, two‐phase system composed of isotropic, sphere‐like, conducting CdO regions embedded in a highly resistive ZnO matrix. Optical measurements show that the films are highly transparent, above 90 % transmission, for wavelengths ≥600 nm. The optical absorption edge shifts to longer wavelengths as the Cd content in the film increases. On the basis of the percolation mechanism observed in the multicomponent system (CdO)_y(ZnO)_1–y, possible future pathways are proposed for the design and construction of highly efficient, transparent, conducting oxides.     

Synthesis of Microscale Raft‐shaped Zinc(II)–Phenylalanine Complexes and Zinc(II)–Phenylalanine/dye Hybrid Bundles with New Optical Properties

Novel raft‐like zinc(II)–phenylalanine complexes and zinc(II)–phenylalanine/acid green 27 (AG27) hybrid radial bundles have been successfully synthesized by a simple refluxing reaction. The formation processes of the morphologies and the superstructures of the hybrid bundles were proposed based on the time‐dependent evolution process. The AG27 molecules act as both the inclusion compound and the controller of the morphologies and the superstructures of the final hybrid. The combination of the zinc(II)–phenylalanine complex and AG27 leads to distinct optical properties compared with the individual component materials. This approach opens a new and effective way for the fabrication of amino acid/dye hybrid materials with unique optical properties and is expected to allow access to other organic/organic hybrid materials with structural specificity and functional novelty.     

Brief Overview of Recent Developments on Negative Phase–Velocity Mediums (alias Left–Handed Materials)

This brief overview covers a rapidly occurring development in the area of microwave composite materials: isotropic dielectric–magnetic mediums wherein the phase velocity vector and the time–averaged Poynting vector are oppositely directed. Such materials have also been inappropriately designated as left–handed materials. Ramifications for aberration–free lenses, homogenization approaches, and complex mediums are also presented.     

Synthesis,Morphology, and Properties of Poly(3‐hexylthiophene)‐block‐Poly(vinylphenyl oxadiazole) Donor–Acceptor Rod–Coil Block Copolymers and Their Memory Device Applications

Novel donor–acceptor rod–coil diblock copolymers of regioregular poly(3‐hexylthiophene) ( P3HT )‐block‐poly(2‐phenyl‐5‐(4‐vinylphenyl)‐1,3,4‐oxadiaz‐ole) ( POXD ) are successfully synthesized by the combination of a modified Grignard metathesis reaction ( GRIM ) and atom transfer radical polymerization ( ATRP ). The effects of the block ratios of the P3HT donor and POXD pendant acceptor blocks on the morphology, field effect transistor mobility, and memory device characteristics are explored. The TEM, SAXS, WAXS, and AFM results suggest that the coil block fraction significantly affects the chain packing of the P3HT block and depresses its crystallinity. The optical absorption spectra indicate that the intramolecular charge transfer between the main chain P3HT donor and the side chain POXD acceptor is relatively weak and the level of order of P3HT chains is reduced by the incorporation of the POXD acceptor. The field effect transistor (FET) hole mobility of the system exhibits a similar trend on the optical properties, which are also decreased with the reduced ordered P3HT crystallinity. The low‐lying highest occupied molecular orbital (HOMO) energy level (–6.08 eV) of POXD is employed as charge trap for the electrical switching memory devices. P3HT‐ b ‐POXD exhibits a non‐volatile bistable memory or insulator behavior depending on the P3HT / POXD block ratio and the resulting morphology. The ITO/ P3HT₄₄ ‐b‐ POXD₁₈ /Al memory device shows a non‐volatile switching characteristic with negative differential resistance (NDR) effect due to the charge trapped POXD block. These experimental results provide the new strategies for the design of donor‐acceptor rod‐coil block copolymers for controlling morphology and physical properties as well as advanced memory device applications.     

Probing Bias‐Dependent Electrochemical Gas–Solid Reactions in (LaxSr1–x)CoO3–δ Cathode Materials

Spatial variability of bias‐dependent electrochemical processes on a (La_0.5Sr_0.5)₂CoO_4±δ modified (La_xSr_1–x)CoO_3–δ surface is studied using first‐order reversal curve method in electrochemical strain microscopy (ESM). The oxygen reduction/evolution reaction (ORR/OER) is activated at voltages as low as 3–4 V with respect to bottom electrode. The degree of bias‐induced transformation as quantified by ESM hysteresis loop area increases with applied bias. The variability of electrochemical activity is explored using correlation analysis and the ORR/OER is shown to be activated in grains at relatively low biases, but the final reaction rate is relatively small. At the same time, at grain boundaries, the onset of reaction process corresponds to larger voltages, but limiting reactivity is much higher. The reaction mechanism in ESM of mixed electronic‐ionic conductor is further analyzed. These studies both establish the framework for probing bias‐dependent electrochemical processes in solids and demonstrate rich spectrum of electrochemical transformations underpinning catalytic activity in cobaltites.     

Electrochromic Window Based on Conducting Poly(3,4‐ethylenedioxythiophene)–Poly(styrene sulfonate)

A short survey of technological aspects of electrochromism with various electroactive species is given. Different approaches with inorganic and organic materials have been pursued in the past. So far widespread usage of this technology for large area applications has not been achieved. Nevertheless one major technical product, self‐darkening rear‐view mirrors for cars, is already well established. This article reviews some research results on electroactive polythiophenes, especially poly(3,4‐alkylenedioxythiophenes). Some promising results with the commercially available electrically conducting polymer Baytron P (PEDT/PSS) are presented. It is demonstrated that an all solid‐state electrochromic multilayer assembly based on a polymeric electrochromic material might be close to technical realization. The coating of large area substrates with aqueous poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) dispersion can be a way to an economically viable product.     

Epitaxy of Layered Orthorhombic SnS–SnSxSe(1−x) Core–Shell Heterostructures with Anisotropic Photoresponse

Vertical and in‐plane heterostructures based on van der Waals (vdW) crystals have drawn rapidly increasing attention owning to the extraordinary properties and significant application potential. However, current heterostructures are mainly limited to vdW crystals with a symmetrical hexagonal lattice, and the heterostructures made by asymmetric vdW crystals are rarely investigated at the moment. In this contribution, it is reported for the first time the synthesis of layered orthorhombic SnS–SnS_xSe_(1?x) core–shell heterostructures with well‐defined geometry via a two‐step thermal evaporation method. Structural characterization reveals that the heterostructures of SnS–SnS_xSe_(1?x) are in‐plane interconnected and vertically stacked, constructed by SnS_xSe_(1?x) shell heteroepitaxially growing on/around the pre‐synthesized SnS flake with an epitaxial relationship of (303)_SnS//(033)_SnSxSe(1?x), [010]_SnS//[100]_SnSxSe(1?x). On the basis of detailed morphology, structure and composition characterizations, a growth mechanism involving heteroepitaxial growth, atomic diffusion, as well as thermal thinning is proposed to illustrate the formation process of the heterostructures. In addition, a strong polarization‐dependent photoresponse is found on the device fabricated using the as‐prepared SnS?SnS_xSe_(1?x) core–shell heterostructure, enabling the potential use of the heterostructures as functional components for optoelectronic devices featured with anisotropy.     

Partial feedback schemes for MIMO–OFDMA systems using random beamforming: analysis and optimization

In this paper, partial feedback schemes for a multiple input multiple output orthogonal frequency division multiple access system using a random beamforming are analyzed and optimized. For partial feedback schemes, the partial channel quality indicator feedback schemes and the partial channel quality rank indicator feedback schemes are considered. For these schemes, we first derive the effective downlink spectral efficiencies by considering the required uplink resource for feedback together over block fading channels. Then, by using the analysis, the amount of feedback overhead per user is optimized to maximize the effective downlink spectral efficiency according to the system and channel parameters. From the analysis and numerical examples, we show that the partial channel quality rank indicator feedback scheme provides better performance than the partial channel quality indicator feedback scheme unless the channel rapidly varies owing to its feedback efficiency, and the proposed adaptive control of the feedback overhead can improve the performance of practical systems, such as the 3rd generation partnership project (3GPP) long term evolution, in practical scenarios. Copyright © 2012 John Wiley & Sons, Ltd.