bluuebunny/crossref_metadata_2025 huggingface dataset:
Time‐Resolved Investigation of the Ne Luminescence
Authors: Seitfudem G.
Published: July 2007

Solid Ne condensed at a temperature of 7 K is excited with a pulsed electron beam. The resulting emission spectra are recorded during the excitation pulse and in the time range from 0 to 2.3 ms after excitation. Relative contributions from the different vibrational levels are fitted to the Ne emissions, measured at various times after the excitation. A nearly constant contribution from the 0th vibrational level is found which can be explained by complete relaxation of the 0u− excimer state. The degree of relaxation and the decay time of the luminescence contributions from the higher vibrational levels change within the 2.3 ms. It is proposed that the lu state of Ne emits from lattice sites at one vacancy, two vacancies, and from regular lattice sites.
On the Transformation of Collective Modes in a Viscoelastic Medium
Authors: Olemskoi A. I. , Panin V. E. , Petrunin V. A.
Published: July 2007

The transition between „strongly”︁ and „weakly”︁ excited states of the condensed matter is considered. The collective mode, which is connected with the shear components of stress and strain, changes the dispersion law from imaginary to real. This transformation takes place for a boundary wave vector, which is determined by the viscosity of the medium. The reactive and relaxation components of strain perform roles of „breaking and restoring symmetry”︁ variables, consequently. On the base of phenomenological and microscopic approaches a synergetic model of kinetic transformation between strongly and weakly excited states is considered.
Fractal and Percolative Features of Aggregation Processes in NaCl:Eu2+ System Detected by Time‐Resolved Spectroscopy
Authors: Cassi D. , Fava R. , Manfredi M. , Opyrchal H. , Suszyńska M.
Published: July 2007

Time resolved spectroscopy of Eu2+ aggregates in the NaCl system — at different stages of the aggregation process — shows a non‐exponential behaviour of time decay signals that is interpreted in terms of excitation migration and up‐conversion processes in a fractal geometry. Following this model, the spectral dimension of such aggregates is obtained from the time decay profiles. The analysis of experimental results suggests a model (fluctuation‐percolation triggered aggregation, FPTA) for the aggregation process.
Dc electrical conductivity of ultrathin AgSiO superlattices
Authors: Abu El‐Haija A. J. , Madjid A. H.
Published: July 2007

Ultrathin multilayer structures of successive silver and silicon monoxide layer pairs are prepared using evaporation techniques. Small angle X‐ray diffraction and multiple reflection interferometric techniques are used to establish the identity periods of samples. A review of the electrical properties is presented. Both applied voltage and thermally induced resistance switching are observed. These phenomena are described from an empirical vantage.
Image force and stopping power of a fast moving ion near a metal surface
Authors: Bao Tran Thoai Duy
Published: July 2007

The image force on an external ion moving parallel to a metal surface is studied within the hydrodynamic model. Expressions for its longitudinal and transversal components are derived. Retardation effects, spatial dispersion, and diffuseness of the electron density at the surface are included. Results of the longitudinal component of the image force and of the corresponding stopping power are reported numerically for different electron densities. They show a pronounced dependence on the velocity of the moving ion.
Stochastic quantization approach to disordered fermions
Authors: Kolley E. , Kolley W.
Published: July 2007

The method of the stochastic quantization is applied to an electron system described by the random Hubbard model. Two different stochastic calculi are performed corresponding to Euclidean and non‐Euclidean versions of the quantum field theory in terms of Grassmann variables. In averaging over the quenched disorder a nontrivial normalization denominator can be avoided. An averaged, effective two‐time action is given as basis for treating localization.
Investigation of Quantum States of Fast Electrons under Planar Channeling in Silicon Crystals
Authors: Gridnev V. I. , Kaplin V. V. , Khlabutin V. G. , Rozum E. I. , Vorobiev S. A.
Published: July 2007

The angular distributions of (1.87 to 5.7) MeV electrons channeled in 2 μm Si crystals along (100), (110), and (111) atomic planes are measured. The half‐width of measured angular distributions is defined by a critical Lindhard angle. A relation is obtained connecting those energies of electrons at which their angular distributions are similar for various atomic planes. The effect of a “critical energy” under planar channeling of electrons is found and investigated.
Determination of the Distribution Widths of the Spin Hamiltonian Parameters of V4+ Ions from Oxide Glasses
Authors: Nicula Al. , Culea E.
Published: July 2007

A method is proposed to determine the distribution widths of the spin Hamiltonian parameters g| and A| of V4+ ions from oxide glasses. The basic assumption is that the structural disorder characteristic for such materials determine a distribution of the molecular bonding parameters and of the orbital excitation energies, which lead finally to a distribution of the spin‐Hamiltonian parameters. Estimates of the distribution widths of g| and A| are made for two glasses, As2O3–V2O5 and B2O3–V2O5 with 5% molar V2P5, using EPR and optical data.
The Environment of Muonium in Solids. An Empirical Approach
Authors: Souiri M. , Goltzene A. , Schwab C.
Published: July 2007

Having justified an empirical approach by the study of the correlations between the hyperfine constant value of the Mn2+ ion and bonding parameters in different host matrices, it is applied to muonium. Thus its preference for a cation environment in tetrahedral structures is revealed, which could be partially screened in other ones.
The Nonlinear Theory of the Snoek Relaxation Effect under the Strong and Homogeneous Bias Stress System
Authors: O˘gurtani T. Ö.
Published: July 2007

The nonlinear theory of energy dissipation associated with the mobile paraelastic octahedral interstitial atoms in inhomogeneous interaction fields is applied to the specific problem of the ordinary Snoek relaxation under the influence of the uniform static stress system (an external bias field). In the case of a uniaxial static bias stress system, an extremely accurate and simple analytical expression is deduced for the logarithmic decrement which indicates strong dependence on the magnitude, sign, and direction of the externally applied bias stress with respect to the direction of the excitation field in body centered cubic lattices. It is also demonstrated that by the internal friction measurements in single crystals, utilizing the large on‐line (parallel) and/or off‐line (orthogonal) static bias fields, the direct information about the symmetry, shape and strength of the elastic dipole tensor associated with the equilibrium‐point configurations (intrinsic) can be obtained.
Muon Spin Rotation Spectroscopy in Metallic Spin Glass Systems
Authors: Pinkvos H. , Schwink Ch.
Published: July 2007

An introduction is given into the application of muon spin rotation spectroscopy to spin glass problems. The principles of the μSR method are discussed in connection with basic properties of spin glasses. Important information provided by μSR on the dynamical behaviour of the impurity spins, the spatial structure of the freezing process, and the form of the autocorrelation function for the local fields are reviewed in chosen examples.
Light Absorption and Hyper‐Raman Scattering by Many‐Electron Complexes in Quantum Well Structures
Authors: Bobrysheva A. I. , Russu S. S. , Zaloi V. A.
Published: July 2007

It is shown that in GaAs/AlxGa1‐xAs multiple‐quantum well structures bihole formation is possible. Also the main features of biexciton hyper‐Raman scattering are established.
Infrared Absorption and Anharmonicity of Crystalline Nitrogen
Authors: Fugol I. Ya. , Ratner A. M. , Khashchina L. V. , Pritula I. M.
Published: July 2007

FIR spectra of α‐nitrogen are discussed taking into account optical and mechanical anharmonicities. It is shown that the lattice absorption spectrum is mainly formed due to the optical anharmonicity. The two‐phonon decay rates of IR‐active modes are estimated from measured line halfwidths.
Quantum‐Statistical Approach to Elastic Constants in Metals Influenced by Magnetization
Authors: Cinal M. , Olszewski S.
Published: July 2007

Magnetic contributions to metal compressibility, lattice Grüneisen parameter, and their pressure dependence are calculated with the aid of the Thomas‐Fermi‐Dirac ab initio theory. The magnetic volume obtained on the basis of the same theory makes possible to estimate the volume dependence of the Stoner parameter and the magnetic Grüneisen parameter.
Magnetic Dipole Absorption of Colloidal Ag in Single Crystals of KCl
Authors: Pützler M. , Fischer F.
Published: July 2007

Experimental evidence for magnetic dipole absorption of Ag particles, produced by solid state reaction in a KCl single crystal, is given for the first time. Absorption in the FIR better follows a ω4 than ω2 law. A maximum absorption at 65 cm−1 is up to five times as high as the absorption plateau in the MIR. Therefore the low temperature scattering rate of electrons is clearly lower than for electric dipole absorption. A quantitative comparison shows absorption still 10 to 50 times higher than predicted by current quantum mechanical theories.
Optical and Electrical Bistability Induced by Exciton Ionization Processes
Authors: Ashkinadze B. M. , Belkov V. V. , Subashiev A. V.
Published: July 2007

Nonlinear optical effects in the luminescence and the microwave absorption which are induced by heating of electrons in a microwave electric field are revealed in silicon: (1) Hysteresis in the exciton condensation process at T = 2 K which results in the bistability of the recombination radiation, with a hysteresis lifetime of 3 × 10−2s. (2) Self‐oscillations in the electron density during impact ionization of excitons, the frequency of the self‐oscillations varies over the range 0.5 to 5 MHz while changing the light excitation or microwave power. (3) Thermal exciton breakdown which is accompanied by jumps and hysteresis of the sample temperature as the excitation is varied.
Nonlinear Absorption in Quantum‐Size Heterostructures
Authors: Kononenko V. K.
Published: July 2007

A theory is developed of absorption saturation on filling the subbands appearing in quantum wells. It is shown that the bleaching spectrum of quantum‐size heterostructures has a resonant, sawtooth shape. The transformation of nonlinear absorption spectra is analyzed depending on the layer thickness, temperature, excitation power, and the character of optical transitions between the electronic states in the quantum wells.
Fast and Strong Nonlinearity of Thin‐Film Semiconductor Interferometers Due to Intrinsic Photo‐ and Electrooptical Effects of the Semiconductor Interlayer
Authors: Karpushko F. V.
Published: July 2007

The electron nature mechanism of optical nonlinearity in thin‐film semiconductor interference systems is considered. It is shown that due to the boundary barrier photo‐ and electrooptic effects in thin‐film system there is the fast and low‐energy photoinduced charges of refractive index. The estimates of switching energy and operation rates of the OB devices based on this nonlinear mechanism are close to the fundamental limits.
Optical Nonlinearity Due to the Excitonic System in CuCl
Authors: Nagasawa N.
Published: July 2007

The optical nonlinearity associated with the giant two‐photon absorption, GTA, of excitonic molecules in CuCl is discussed. The metamorphoses of the four‐wave mixing spectra due to the generation of the exciton grating are demonstrated by the observation of their polarization characteristics. The propagation characteristics of the excitation around the GTA resonance are observed by micro‐Raman spectroscopy. The two‐photon Raman scattering light is used as a probe to monitor the spatial character of the excitation. The propagation characteristics show a drastic change in the very narrow spectral range around the GTA resonance energy.
Complex Centres in Additively Coloured RbCl: Li+
Authors: de Matteis F. , Scacco A. , Somma F. , Baldacchini G. , Giovenale E. , Grassano U. M.
Published: July 2007

Complex colour centres in RbCl and RbCl:Li+ are extensively studied. (F2)A centres, never observed so far in this system, are formed and their optical absorption and emission determined. The kinetics of the equilibria among aggregate and associate defects are investigated in order to obtain the highest concentration of (F2)A centres.
Core Hole Relaxation Energy in Semiconductors. Using a Pseudopotcntial Description of the Core Hole Perturbation
Authors: Castellani N. J. , Lambrecht W. R. L.
Published: July 2007

Core hole relaxation energies in semiconductors are calculated by means of a linear response method, combining a model dielectric function with a pseudopotential description of the core hole perturbation. The latter incorporates the core‐orthogonality constraints on the valence electron screening charge density. Both, norm‐conserving pseudopotentials and Ashcroft‐like model pseudopotentials are used. The latter allow to obtain the results in closed analytical form. Atomic local density functional calculations are performed for the intra‐core contribution and combined with the valence electron contribution in the semiconductor, provide total relaxation energies.
Slocum Gliders: Robust and ready
Authors: Schofield Oscar , Kohut Josh , Aragon David , Creed Liz , Graver Josh , Haldeman Chip , Kerfoot John , Roarty Hugh , Jones Clayton , Webb Doug , Glenn Scott
Published: July 2007

Buoyancy driven Slocum Gliders were a vision of Douglas Webb, which Henry Stommel championed in a futuristic vision published in 1989. Slocum Gliders have transitioned from a concept to a technology serving basic research and environmental stewardship. The long duration and low operating costs of Gliders allow them to anchor spatial time series. Large distances, over 600 km, can be covered using a single set of alkaline batteries. Since the initial tests, a wide range of physical and optical sensors have been integrated into the Glider allowing measurements of temperature, salinity, depth averaged currents, surface currents, fluorescence, apparent and inherent optical properties. A command/control center, entitled Dockserver, has been developed that allows users to fly fleets of gliders simultaneously in multiple places around the world via the Internet. Over the last 2.5 years, Rutgers Gliders have logged 27 056 kilometers, and flown 1357 days at sea. Gliders call into the automated Glider Command Center at the Rutgers campus via satellite phone to provide a status update, download data, and receive new mission commands. The ability to operate Gliders for extended periods of time are making them the central in situ technology for the evolving ocean observatories. Off shore New Jersey Gliders have occupied a cross shelf transect and have documented the annual variability in shelf wide stratification on the Mid‐Atlantic Bight and the role of storms in sediment resuspension. The sustained data permits scientists to gather regional data critical to addressing if, and how, the oceans are changing. © 2007 Wiley Periodicals, Inc.
Intelsat VI. A new satellite generation for 1986–2000
Authors: Thompson P. T. , Johnston E. C.
Published: July 2007

Following three years of conceptual studies, and a competitive procurement contract, construction of the INTELSAT VI series of satellites is now under way. The design represents a major step forward in satellite size and technical complexity. Sixfold frequency reuse and on‐board satellite switching are particularly important developments.
Subjective evaluation of companded frequency modulation and continuously variable slope delta modulation single channel per carrier satellite communication systems
Authors: Abachi N. , Evans B. G.
Published: July 2007

A comprehensive series of subjective tests are carried out on narrow‐band companded F.M. and continuously controlled delta modulation SCPC satellite systems. In order to resolve discrepancies reported in the literature both Youden square and mean opinion scale listening tests have been applied. Both white noise and modulated noise reference conditions are employed and the performance of the systems, in terms of signal to noise and equivalent Q factor are given for various C/N0 fixed and mobile‐maritime performance requirements.
Telematic services via satellite in Europe
Authors: Goumy C. , Golden E.
Published: July 2007

The word ‘telematics’ was used for the first time in France in 1978 by Simon Nora and Alain Minc; it is a contraction of the French words ‘tétécommunications’ and ‘informatique’, and defines a marriage between computers and data transmission networks. This paper describes the five systems which will be implemented to provide telematic services via satellite in Europe during the next few years: EUTELSAT, TELECOM 1, UNISAT, DFS and ITALSAT. The main characteristics of the ‘special service’ transponders are presented, showing that, in Europe, (a) 2 to 5 transponders per satellite will be devoted to the special (telematic) services; (b) 4 satellites out of the 5 use the 12.5–12.75 GHz down‐link band for this purpose (only ITALSAT uses the 20 GHz down‐link for the same purpose), and (c) e.i.r.p.s at 12 GHz are in the range 40–49 dBW.

The ground and space segments corresponding to this new service are presented. The main peculiarity of the ground segment is the exclusive use of ‘small’ earth‐stations equipped with fixed antennas and SCPC or 25–60 Mb/s TDMA multiple access equipment. Telematic services include videoconference at 2048 kb/s, voice services, computer‐to‐computer transfer of data, data distribution, remote printing, electronic mail, high‐speed facsimile, offshore voice and data services, digital network overflow, transatlantic digital business etc…

Customer bit rates start from 2.4, 4.8, 9.6 and 32 kb/s (for TELECOM 1) up to 2048 kb/s by 64 kb/s steps. Bit error rates are maintained below 10−6 (standard) or 10−10 (higher grade) during 99 per cent of the year using FEC. The five networks for telematics via satellite in Europe are independent. A large efficiency improvement of the different services should be obtained through a future interconnection of the various networks via intersatellite links.
Leased services on the intelsat system. Part 1: Domestic service and international television
Authors: Kelley T. Michael
Published: July 2007

This is Part One of a two‐part article on the current status of INTELSAT's leased services, a relatively unfamiliar subject when compared with INTELSAT's standard communications services.

In Part One, domestic service and international television service will be covered. For both services, statistics on existing and planned levels of use will be provided. Key aspects of the terms and conditions governing the lease will be outlined, and the annual charges summarized. The variety of services possible when using these leases, and the earth station networks chosen by users to meet their communications goals are also described.

A brief look at the future of these two services will be given, and the topics of Part Two. INTELSAT Business Service (IBS), and the low‐density telephony service (VISTA) will be introduced.
Multiple‐beam antennas for contiguous coverage of europe for business service applications
Authors: Claydon B. , Dinwiddy S. E. , Adatia N.
Published: July 2007

Demands for increased channel capacity in future communication satellite systems coupled with basic limitations in terms of satellite power and frequency spectrum will lead to requirements for advanced multiple‐beam antenna systems with frequency re‐use capability.

This paper describes the results of a study of multiple‐beam antenna systems suitable for an advanced European business services satellite. Initially, background work is described which serves to define the overall system, analyse the link performance and specify the antenna requirements. A generalized parametric study of the capabilities of a model antenna is discussed to set the bounds of feasibility, as it was appreciated that some specification targets might prove impossible to attain. In parallel, a comparative survey of a wide range of antenna types is presented to determine the most promising configurations. Based on these two outputs, candidate antenna configurations are analysed in detail to predict accurately the capability of the more promising antenna types to meet the range of performance objectives. Finally, detailed electrical design studies are performed for specific example missions.
Depolarization properties of metal space frame radomes for use in satellite communication systems
Authors: Rwabona‐Katashaya S. , Evans B. G.
Published: July 2007

Radomes have traditionally only been used in military satellite systems. However, higher availability civil applications are demanding their consideration in the higher frequency bands and for dualpolarization frequency re‐use systems. This paper investigates the depolarization performance of metal space frame radomes and presents results of XPD for radome covered antennas in the 4/6 and 11/14 GHz bands and for antennas of 30, 11, 5 and 3 m diameters. It is demonstrated that current polarization specifications adopted in the INTELSAT system should be able to be met by radome covered earth‐stations using conventional antennas.
A reassessment of satellite communications in the 20 and 30 GHz bands
Authors: Bargellini Pier L.
Published: July 2007

Notwithstanding the additional spectrum allocations of the 1979 World Administrative Radio Conference (WARC '79) and the ever‐increasing sophistication of spacecraft antennas which allow more intensive spectrum reuse, saturation of the 6/4 and 14/11 GHz bands is foreseeable by the late‐1990s.

The next available frequency bands at 30/20 GHz were allocated at WARC '71, when knowledge of propagation phenomena and their effect on satellite communications systems performance was fragmentary. During the past 8 years, numerous experimental programmes have led to the acquisition of more precise information about hydrometeor‐induced propagation disturbances. Analysis of the data reveals that even with corrective means such as diversity and coding, service reliability of satellite communications systems with up‐links at 30 GHz and down‐links at 20 GHz could not reach 99.99 per cent as currently available at the lower frequencies and could be 98.0 per cent, or lower, in certain parts of the world. Since the conventionally proposed use of the 30/20 GHz bands does not lead to optimal solutions, alternative approaches are needed.

An approach which would involve a revision of the spectrum allocations at 30/20 GHz is proposed. Placing both up‐ and down‐links around 20 GHz and redistributing the spectrum available at 20 GHz would prevent the intrinsic imbalance of the up‐ and down‐links with consequent higher reliability, reduced earth‐station transmitter power, reduced construction and operational costs, and simplification of the spacecraft transponders and antenna design.

The use of frequencies around 30 GHz could be postponed until the 20 GHz bands became saturated. When the 30 GHz bands would eventually be used, there would be no imbalance of up‐ and down‐links.
High speed receiver designs based on surface acoustic wave devices
Authors: Nanayakkara S. , Anderson J. B.
Published: July 2007

The principles of operation and several types of surface acoustic wave devices are reviewed. One device, the interdigital transducer device, can accomplish matched filtering for complex bandwidth‐efficient phase modulations. Data speeds in excess of 120 Mb/s are accomplished with existing thin film lithography. Filters are cheap and small, and show little mismatch to the desired response. A number of receiver designs are proposed that are based on these filters. A bank‐of‐matched‐filters approach seems superior to the Viterbi algorithm at high speeds.
Experimental study and empirical evaluation of carrier compression and third order intermodulation products of unequal carriers in a communication satellite transponder
Authors: Rustogi Dipti , Sengupta N.
Published: July 2007

Carrier compression and third order intermodulation products of two and three unequal carriers have been studied experimentally using a 36 MHz wide C‐band transponder of INSAT‐1B satellite. From the experimental data, empirical relations for carrier compression for two unequal carriers have been derived, which agree with the measured data within ±0.5 dB. The empirical relations for carrier compression derived for two unequal carriers have been extended to three unequal carriers and good correlations with measured data have been obtained. Empirical relations for third order intermodulation products of two and three (f1+f2‐f3 type) unequal carriers have also been derived.
An interactive computer program for elliptical beam optimization
Authors: Richharia M.
Published: July 2007

Elliptical antenna beams are used for planning of direct broadcast satellite systems. In this paper concepts of the beam optimization process are described briefly. A method of plotting the optimized beam on a suitable map projection is discussed. An interactive computer program, which can be used for the optimization and plotting of beams on a given territory, is described with the help of examples.
Intelsat tdma/dsi system: implementation and system management
Authors: Parthasarathy R.
Published: July 2007

This paper presents an overview of the concepts underlying the implementation of the TDMA/DSI technique in the INTELSAT satellite system, together with a description of preliminary ideas on the system management of TDMA networks. The TDMA project is an INTELSAT response to steady growth in international services, and the TDMA system uses digital techniques for enhancing capacity on a satellite. The establishment of the system requires international co‐operation on an extensive scale; all the decision‐making components in INTELSAT's structure have contributed to the planning and implementation of the system. Preliminary ideas on network management are discussed. The methods used for establishing internationally agreed procedures and for orchestrating the maintenance of reference stations are described.
The acquisition and synchronization control procedures for the intelsat tdma system
Authors: Bedford R. , Ishi Y.
Published: July 2007

Control of all bursts in the TDMA system is achieved by the use of complementary controlled and controlling procedures. Controlled procedures operate in traffic terminals and reference terminals alike, whereas controlling procedures operate only in reference terminals. Controlling procedures are the subject of this paper. These procedures govern the acquisition, synchronization and monitoring of all bursts, including reference bursts, in the TDMA system.

To perform the acquisition and synchronization control function, each reference burst contains a control and delay channel (CDC) in which control information is transmitted to controlled terminals on a constant repetitive basis. The structure and timing of this control cycle will be discussed, assuming that the basic control frame and multiframe structure is familiar.

Acquisition and synchronization control is performed only on the principal burst transmitted by each terminal; all other bursts are monitored by the reference terminals and controlled by the SDNTX (selective do not transmit) message which is transmitted in the reference burst service channel on an as‐needed basis. The procedure which governs the generation of these messages will also be discussed.
Intelsat tdma system monitor
Authors: Barnett Jerry , Phiel John F.
Published: July 2007

The INTELSAT 120 Mb/s TDMA/DSI system consists of reference stations and traffic terminals which access the INTELSAT V satellites as a multiple beam network. Two reference stations located within each satellite beam serve the network by controlling the acquisition and synchronization of the traffic terminals and by performing TDMA system monitoring. Within the reference stations, the acquisition and synchronization control functions are performed by the reference terminal equipment and the monitoring functions are performed by the TDMA system monitor. This paper provides a discussion of the TDMA system monitor, including its configuration, measurement techniques, and an assessment of its measurement.
The french tdma terminal
Authors: Bernard A. , Kerromes L. , Meunier J. , Rancy F. , Bareyt C. , Vautier D. , Beaucent A. , Salomon J. , Sergent C.
Published: July 2007

The paper describes the TDMA terminal manufactured by the French consortium regrouping TEL‐SPACE, SAT and CIT‐ALCATEL. Details on terminal organization, equipment modularity and operational aspects are first presented. The constituent parts of the terminal (common TDMA terminal equipment, DSI/DNI module, order wire module) are then described. Results of modem performances are also indicated. Finally, a description of the first French earth‐station operating with TDMA, Pleumeur‐Bodou 6, is given.
The italian tdma‐dsi terminal for the intelsat system
Authors: La Rocca C. , Menciotti F. , Alletto G. , Argento D.
Published: July 2007

This paper describes the salient characteristics of the Italian TDMA‐DSI Terminal for the INTELSAT System. After an overall presentation, the major building blocks, i.e. the CLE, the modem and IF switchover, and the DSI TIM are discussed. A brief presentation of the maintenance and troubleshooting auxiliary equipment is also given.
A 120 mb/s qpsk modem designed for the intelsat tdma network
Authors: De Cristofaro R. , Mc Farthing A. L.
Published: July 2007

This paper presents the major aspects of a 120 Mb/s QPSK modem developed for use within the INTELSAT TDMA network. Particular attention is focused upon the most important elements of the modem, namely the pre‐modulation lowpass filters, the demodulator AGC, the carrier and symbol timing recoveries and the demodulator filtering strategy. In addition to the modem description, details of a burst mode bit error rate test equipment will also be given. This test equipment was especially designed to simulate a practical TDMA working environment thus enabling the modem's burst mode performance to be evaluated in laboratory conditions. Finally, the modem's measured probability of bit errors versus Eb/No, and the probability of clock and carrier cycle skips versus Eb/No are presented. Results of the modem performance both in IF and RF loop‐back are shown. The modem RF loop‐back performance was evaluated using an INTELSAT V satellite simulator.
An introduction to the pdts (pcm/dsi test set): design principles and application in the intelsat tdma/dsi system
Authors: Lai Daniel K. N.
Published: July 2007

The operational use of TDMA in the INTELSAT system brings about an exciting major milestone in satellite telecommunications. To a certain extent, the performance of the technically complex, robust, centrally controlled TDMA/DSI system depends on the effectiveness of the alignment, maintenance and testing procedures. The wide range of disciplines encountered in such an advanced system may raise difficulties for the station staffs currently familiar with the existing FDMA network.

Such problems have given rise to the birth of a conceptually new test equipment PDTS (PCM/DSI test set) to evaluate the performance of the DSI or DNI unit in a TDMA terminal. This equipment is capable of generating PCM test patterns in predetermined sequences and feeding them at the baseband channel level into the terrestrial interface of the DSI for purposes of operationally testing channel continuity, DSI assignment and cumulative BER during the test cycle. The present paper describes the general principles of PDTS as well as its operational use in the TDMA/DSI system.
MEASUREMENTS OF THE TIME STATISTICS OF FMTV SPECTRA AND TV INTERFERENCE INTO FDM/FM CARRIERS
Authors: Nguyen Nam , Mazur B. , Prasanna S.
Published: July 2007

When computing the amount of interference from FMTV signals in satellite systems, it is customary to consider that the only effective TV modulation is the energy dispersal signal (EDS). This leads to a sufficient but highly conservative system design, since for most of the time the wanted demodulated signal may experience interference levels well below that computed using this approach. If the time statistics of the interference can be determined through measurement, then a grade‐of‐service approach can be taken in which interference can be guaranteed not to exceed a certain level for more than a prescribed fraction of the time. This approach will lead to more efficient use of orbit/spectrum resources as a result of the implementation of less conservative system designs.

This paper presents a simulation approach used to ‘measure’ FMTV power spectra with and without EDS and the corresponding interference powers into the basebands of FDM/FM carriers. Time statistics in the form of FMTV spectral masks and FDM baseband interference power time distributions have been derived from the measured data of 1000 off‐air TV frames for co‐channel TV and standard FDM/FM carrier sets (12 to 1200 channels) deployed by INTELSAT. Sample results are given.
The variability of the ionospheric total electron content and its effect on satellite microwave communications
Authors: Wolff Richard S.
Published: July 2007

Rotation of linearly polarized waves (Faraday rotation) passing through the ionosphere causes depolarization in frequency reuse satellite communication systems. As the ionospheric total electron content (TEC) is not constant, dynamic compensation for this effect may be required. This paper investigates the magnitude of the TEC variations, the time scales of the variability and the predictability of the excursions. Analysis of long‐term TEC measurements shows that the variations are statistical with yearly and seasonal trends strongly coupled to long term solar and geophysical effects. Short‐term variations are difficult to predict. Data indicate that reliable Faraday rotation estimates can be made for 99·9 per cent of the time, provided that long‐term solar, seasonal and geographical factors are considered. Occasional bursts of solar activity limit the accuracy of long‐term predictions.
System implications of 14/11 GHz path depolarization. Part I: Predicting the impairments
Authors: Rogers D. V. , Allnutt J. E.
Published: July 2007

Exploitation of the international 14/11 GHz communications bands will probably follow the same pattern as that of the 6/4 GHz bands. First, the available monopolarized bandwidth will be filled. Next, multiple beams that use spatial isolation to provide frequency reuse will be developed. Finally, full dual‐polarized operation will be employed. In the 14/11 GHz bands, rain can cause appreciable attenuation and depolarization. In some instances, dual polarized links will be depolarization limited. If up‐link power control is implemented on attenuation dominated paths, depolarization can again dominate, owing to interference constraints. In both cases, a measure of depolarization compensation needs to be introduced to reduce the impact of interference. Part I of this paper quantifies this problem and establishes a set of reference statistics which can be used to assess the need for impairment restoration. Part II will discuss several ways of reducing the system impact of path depolarization.
System Implications of 14/11 GHz Path Depolarization. Part II: Reducing the impairments
Authors: Allnutt J. E. , Rogers D. V.
Published: July 2007

Dual‐polarized co‐channel operation via international communications satellites places stringent requirements on the amount of interference that can be allowed from all sources. System design must allow for the depolarization caused by rain and ice crystals, the principal source of additional interference. In the 14/11 and 14/12 GHz bands, some paths are depolarization limited, particularly at lower path elevation angles, or become so with up‐link power control. Others are attenuation limited. Therefore, a means must be found to reduce the level of path depolarization to meet the requirements for path availability. In Part I or this paper, reference joint statistics of cross‐polarization discrimination/attenuation statistics were derived for a number of paths and climates to establish the additional fade and cross‐polarization discrimination margins required. This second paper addresses methods for reducing the system effects of path depolarization.

Appropriate orientation of the polarization vectors at the spacecraft is shown to be an attractive alternative for spot‐beam applications. For all other situations, it is concluded that single‐parameter, phase‐only compensation at the earth terminal will meet all practical system requirements.
Development of a prototype, experimental single‐channel sequencing navstar gps receiver: Part II—Software description
Authors: Allison M. T. , Daly P.
Published: July 2007

Late in 1988 the Navstar GPS satellite navigation operational phase is planned to commence, offering world‐wide, continuous and precise position‐fixing and timing information to observers on land, sea, air and in space. This paper describes the development of a particular type of Navstar receiver—a single‐channel, single‐frequency, sequencing C/A code unit—and results of various tests carried out on the present phase—II satellite constellation. Part I of this paper deals with the NAVSTAR satellite system and the development of receiver hardware, whereas Part II concentrates on software development and system performance.
The TNS program: A computer simulation package for the intelsat TDMA network
Authors: Shinonaga Hideyuki , Yamasaki Norikazu , Koga Keiichiro , Muratani Takuro , Wu William W.
Published: July 2007

The TNS (TDMA Network Simulation) program is a computer simulation package developed for the evaluation, test and analysis of all the protocols in the INTELSAT TDMA network. The TNS program faithfully simulates the dynamic operation of the network, taking account of the satellite motion, and makes it even possible to simulate the network operation under some abnormal conditions, such as terminal function failure and transponder failure.

This paper describes the TNS program in terms of its design approach, its capabilities, its structure, its input and output data, and its operation. An example simulation for the whole system start‐up procedure assuming the Atlantic Ocean region is also presented.
Design of a selective FEC subsystem to counteract rain fading in ku‐band TDMA systems
Authors: McMillen G. R. , Mazur B. A. , Abdel‐Nabi T.
Published: July 2007

A major concern in satellite communications systems operating at frequencies above 10 GHz (e.g. Ku band) is the performance degradation caused by rain fading. In this paper, an effective method for combatting this phenomenon in TDMA systems is described. This method is based on the application of additional FEC coding protection on a dynamic basis to faded traffic terminals. Selective (adaptive) forward error correction (S‐FEC) coding permits the fixed fade margins used by the network earth‐stations to be substantially reduced, while a desired outage probability is maintained. This paper deals primarily with the implementation of the monitoring and control subsystems required in a practical S‐FEC network.
North‐south coupling study
Authors: Pardo Jeff
Published: July 2007

An empirical study of stationkeeping data on several RCA series 3000 spacecraft which was used to analyse coupling effects during inclination manoeuvres has yielded valuable data on changes in east‐west drift and eccentricity which result from these manoeuvres. The major origins of these effects are thruster alignments and plume impingement on the north solar panel. While thruster alignments for a given spacecraft will differ depending on its centre of mass, plume impingement showed a higher order seasonal influence over the basic cant angle differences between thruster pairs on opposite sides of a satellite, i.e. when the solar arrays are at a ‘near zero’ angle (array panel directly facing earth) the net radial vector bias is attenuated. Plume impingement has a primary seasonal influence in tangential coupling, however: when the solar array was ‘looking east’, eastward drift was observed, and likewise when the solar panel was west‐oriented, there was a westward drift effect. Recommendations are made as to how this information might be used to improve an operator's stationkeeping schedule.
FM/TV Interference into rate 1/2 FEC encoded SCPC/QPSK
Authors: Dutronc J. , Freixe J. M. , Prouse D. , Cooke R.
Published: July 2007

This paper presents some results obtained in laboratory measurements of interference caused by FM television signals to encoded SCPC/QPSK carriers. Certain parameters, such as the TV energy dispersal excursion, the frequency spacing between wanted and interfering carriers, the SCPC bit rate, etc., were varied during the measurements in order to study their influence on the amount of interference suffered by the SCPC channel.

Computer simulations were also carried out in order to analyse and interpret measurement results obtained in some cases.

Conclusions are drawn on the use of a possible interference criterion when rate 1/2 convolutional encoding and soft decision Viterbi decoding is used in the SCPC system as well as on the expected improvement with frequency offset.
An improved step‐track algorithm for tracking geosynchronous satellites
Authors: Richaria M.
Published: July 2007

A computer simulation of three maximum‐seeking algorithms has been performed to select the most accurate for tracking geosynchronous satellites. It is concluded that a gradient algorithm provides the highest accuracy and is well suited for practical implementation. An experiment performed by tracking the OTS satellite confirmed the validity of the simulation.
A coded 8‐PSK system for 140 Mb/s information rate transmission over 80 MHz non‐linear transponders
Authors: Fang R. J. F.
Published: July 2007

A combined 8‐PSK modulation and rate 7/9 convolutional coding technique is proposed for 140 Mb/s information rate transmission over the 80 MHz INTELSAT transponders, thus achieving a bandwidth efficiency of 1.75 b/s/Hz of allocated bandwidth. The desired power efficiency is to achieve a bit error rate of 10−6 at an Eb/N0 of 11 dB, including modem and codec implementation losses. The proposed system employs an 8‐PSK modem operating at a 60 MHz symbol rate (or 180 Mb/s bit rate), as well as a rate 7/9 convolutional encoder and a 16‐state Viterbi algorithm decoder operating at 60 MHz. The rate 7/9 code is periodically time varying and is designed to maximize the Euclidean distance between the modulated codeword sequences, thereby achieving a 3 dB asymptotic coding gain relative to the conventional QPSK system over an AWGN channel. This code is also designed to reduce decoder complexity for high‐speed operations.

The performance of the proposed system over INTELSAT V and VI non‐linear transponders was evaluated by Monte Carlo computer simulation. The 180 Mb/s 8 PSK modem, including the automatic frequency control, automatic gain control, carrier recovery and clock recovery circuits, has been implemented and tested. The complete Viterbi decoder is being implemented on five boards, and the critical add‐compare‐select (ACS) circuit of the high‐speed Viterbi algorithm decoder is being implemented with hybrid technology employing 100‐K series emitter‐coupled logic dies on specially designed ceramic substrates. The ACS circuit operates at a speed exceeding 120 MHz, well over the design goal of 60 MHz. Construction of this codec is almost complete.
Low rate encoding: A means of increasing system capacity in a TDMA/DSI system
Authors: Fresia F. , Patacchini A. , Prins C.
Published: July 2007

The satellite capacity required in a TDMA/DSI system for a certain amount of traffic can be substantially reduced when using associated LRE techniques. An analysis based on the future EUTELSAT TDMA/DSI traffic forecast has been made in this respect, by using the computer program presently in use at EUTELSAT for the generation of burst time plans.

The analysis considers different operational modes (single destination, multidestination and multiclique) and presents also some considerations on the problem of transition from a 64 kb/s TDMA/DSI system to a 32 kb/s TDMA/DSI system.
Sixty Mb/s transversal equalizer
Authors: Uzunoglu Vasil
Published: July 2007

A model of a linear digital communication system is introduced and adaptive equalization in general is explained. A five‐tap transversal equalizer is designed, breadboarded and tested in a 60 Mb/s burst mode modem in a quasi‐linear and a non‐linear channel under the following configurations:

Parabolic, linear and combination of parabolic and linear delay distortions were inserted after the non‐linearity (TWTA).

Case 1 was repeated with distortions inserted before the non‐linearity.

When parabolic distortion is added before the non‐linearity improvements in the BER are significant.
Generalized satellite link model and its application to the transmission plan
Authors: Tamir Izhak , Rappaport Yigal
Published: July 2007

A generalized model for the satellite link that includes non‐linear effects is presented. The transponder is handled as a black box with nominal gain gs. At a specific operating point each signal in the transponder has its own gain, gsci, that may be different from gs. The parameter gsci depends on the operating point of the transponder, the power of the signal and the distribution of the residual transponder power among the other carriers. The intermodulation between the carriers and between them and the up‐link noise is included in the model as well. The generalized model is represented by the conventional traditional equation, modified with correction factors which account for the nonlinear effects. Application of the model to typical transmission plans is given and comparison of the results to field experiments and transponder analysis program is included. Emphasis is placed on the use of the transponder with mixed TV and SCPC operation.
On‐board processing for communications satellites: Systems and benefits
Authors: Nuspl P. P. , Peters R. , Abdel‐Nabi T. , Mathews N.
Published: July 2007

This paper discusses on‐board processing systems and associated benefits including connectivity, increased capacity, lower costs and system improvements; there are complex trade‐offs in design approaches. Several architectures are described which use a microwave switch matrix, a baseband switch matrix or baseband processor. Regeneration (an advanced form of on‐board processing) consists of demodulation followed by remodulation and provides access to baseband signals. The link advantages of this method are clearly presented for 120Mb/s TDMA and for IBS at 1/544 Mb/s. Additionally, there are discussions of five architectures using multi‐carriers per transponder, and their advantages and disadvantages. Some considerations of using on‐board decoding and baseband processing functions are also briefly presented.