bluuebunny/crossref_metadata_2025 huggingface dataset:
Grafting of methacrylates and styrene on to polystyrene backbone via a “grafting from” ATRP process at ambient temperature
Authors: Vivek A. V. , Dhamodharan R.
Published: July 2007

Well defined graft copolymers are prepared by “grafting from” atom transfer radical polymerization (ATRP) at room temperature (30 °C). The experiments were aimed at grafting methacrylates and styrene at latent initiating sites of polystyrene. For this purpose, the benzylic hydrogen in polystyrene was subjected to allylic bromination with N‐bromosuccinimide and azobisisobutrylnitirle to generate tertiary bromide ATRP initiating sites (BrCPS). The use of BrCPS with lesser mol % of bromide initiating groups results in better control and successful graft copolymerization. This was used to synthesize a series of new graft copolymers such as PS‐g‐PBnMA, PS‐g‐PBMA, PS‐g‐GMA, and PS‐g‐(PMMA‐b‐PtBA) catalyzed by CuBr/PMDETA system, in bulk, at room temperature. The polymers are characterized by GPC, NMR, FTIR, TEM, and TGA. Graft copolymerization followed by block polymerization enabled the synthesis of highly branched polymer brush, in which the grafting density can be adjusted by appropriate choice of bromide concentration in the polystyrene. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3818–3832, 2007
Synthesis, characterization, and influence of synthesis parameters on particle sizes of a new microgel family
Authors: Martínez Virginia Sáez , Álvarez Leyre Pérez , Hernáez Estíbaliz , Herrero Teresa , Katime Issa
Published: July 2007

Poly(p‐nitrophenylacrylate‐co‐methacrylamide) and poly(p‐Nitrophenylacrylate‐co‐N,N′‐isopropylacrylamide) reactive microgels were synthesized by precipitation polymerization. The process was followed qualitatively by infrared spectroscopy (ATR‐FTIR) and microgels composition was determined by nuclear magnetic resonance (1H NMR). Scanning electron microscopy of obtained colloidal particles showed strictly spherical morphologies with a moderate polydispersity. The average hydrodynamic particle diameter and particle size distributions were measured by quasi‐elastic light scattering and the particle size distributions obtained ranged from 100 to 600 nm. Several synthetic parameters affect the particle size of these materials and thus, indirectly, their properties and future applications. In this article, we report the influence of different polymerization reaction conditions in the final microgel dimensions. For example, we observed that the different solvent‐comonomer affinity induced a significant change in swollen particle size of the copolymeric microgels. On the other hand, the crosslinking density limited the particle sizes, but an excess of crosslinker content in the reaction mixture resulted in the opposite effect. Finally, we also studied the influence of initiator content in the mean particle size. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3833–3842, 2007
Arborescent polymers and other dendrigraft polymers: A journey into structural diversity
Authors: Gauthier Mario
Published: July 2007

Arborescent polymers are characterized by a dendritic, multilevel branched architecture derived from successive grafting reactions. In spite of their much larger size, these materials display properties analogous to dendrimers and hyperbranched polymers, the two other dendritic polymer families. The distinguishing features of arborescent polymers are their assembly from polymeric building blocks of uniform size and their very high molecular weights attained in few synthetic steps. This article offers an overview of the historical aspects of the development of dendrigraft polymers, starting from our initial efforts on the synthesis of arborescent polystyrenes. Major subsequent developments in the synthetic techniques from our and other research groups allowing the synthesis of dendrigraft copolymers, tailoring of the structural characteristics of the molecules, and further simplifications to their synthesis are also reviewed, with emphasis over the broad range of architectures attainable in these systems. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3803–3810, 2007
Optical delineation of benthic habitat using an autonomous underwater vehicle
Authors: Moline Mark A. , Woodruff Dana L. , Evans Nathan R.
Published: July 2007

To better characterize and improve our understanding of coastal waters, there has been an increasing emphasis on autonomous systems that can sample the ocean on relevant scales. Autonomous underwater vehicles (AUVs) with active propulsion are especially well suited for studies of the coastal ocean because they are able to provide systematic and near‐synoptic spatial observations. With this capability, science users are beginning to integrate sensor suits for a broad range of specific and often novel applications. Here, the relatively mature Remote Environmental Monitoring Units (REMUS) AUV system is configured with multi‐spectral radiometers to delineate benthic habitat in Sequim Bay, WA. The vehicle was deployed in a grid pattern along 5 km of coastline in depths from 30 to less than 2 m. Similar to satellite and/or aerial remote sensing, the bandwidth ratios from the downward looking radiance sensor and upward looking irradiance sensor were used to identify beds of eelgrass on submeter scales. Strong correlations were found between the optical reflectance signals and the geo‐referenced in situ data collected with underwater video within the grid. Results demonstrate the ability of AUVs to map littoral habitats at high resolution and highlight the overall utility of the REMUS vehicle for near‐shore oceanography. © 2007 Wiley Periodicals, Inc.
Development of the DORADO mapping vehicle for multibeam, subbottom, and sidescan science missions
Authors: Kirkwood W. J.
Published: July 2007

Oceanographic science is frequently hindered by a lack of spatial and temporal resolution for most parameters oceanographic science desires to measure. This paper discusses our effort to advance the current state of bathymetric mapping as part of the Monterey Bay Aquarium Research Institute (MBARI) charter. MBARI scientists and engineers, in consultation with the external community, have produced a new multibeam mapping autonomous underwater vehicle (AUV) system. The system is intended to reduce some of the impediments encountered by science trying to resolve specific portions of the oceans bottom. Starting with the established and in‐house developed Dorado AUV technology, MBARI engineering refined the AUV into a full ocean depth capable and now operational multibeam mapping system (MBAUV). The MBAUV system conducts regular multibeam bathymetry, subbottom, and sidescan surveys for oceanographic science. MBAUV is a torpedo‐shaped, 6000 m rated vehicle operating the aforementioned sonars simultaneously. The endurance of the MBAUV is approximately 8 h at 3 kn and is designed to support 16 h operations at 3 kn by adding an additional battery section. This paper describes the basics of the MBAUV and our design trades and modifications to the Dorado AUV in support of multibeam mapping missions. The paper also reviews a sampling of the results from a series of missions that demonstrate the performance of various subsystems and the science quality data available from the MBAUV. © 2007 Wiley Periodicals, Inc.
An integrated diagnostic architecture for autonomous underwater vehicles
Authors: Hamilton K. , Lane D. M. , Brown K. E. , Evans J. , Taylor N. K.
Published: July 2007

The architecture of an advanced fault detection and diagnosis (FDD) system is described and applied with an Autonomous Underwater Vehicle (AUV). The architecture aims to provide a more capable system that does not require dedicated sensors for each fault, can diagnose previously unforeseen failures and failures with cause‐effect patterns across different subsystems. It also lays the foundations for incipient fault detection and condition‐based maintenance schemes. A model of relationships is used as an ontology to describe the connected set of electrical, mechanical, hydraulic, and computing components that make up the vehicle, down to the level of least replaceable unit in the field. The architecture uses a variety of domain dependent diagnostic tools (rulebase, model‐based methods) and domain independent tools (correlator, topology analyzer, watcher) to first detect and then diagnose the location of faults. Tools nominate components, so that a rank order of most likely candidates can be generated. This modular approach allows existing proven FDD methods (e.g., vibration analysis, FMEA) to be incorporated and to add confidence to the conclusions. Illustrative performance is provided working in real time during deployments with the RAUVER hover capable AUV as an example of the class of automated system to which this approach is applicable. © 2007 Wiley Periodicals, Inc.
Satellites and the isdn
Authors: Lewis John
Published: July 2007

This paper addresses the question of integrating satellites within the ISDN, concentrating on PSTN application. After a brief look at the role satellites have played to date in international telecommunications, and the new environment that ISDN will bring, an examination is made of the work done by CCITT on the transmission aspects of ISDN. This is followed by a look at the main features of digital satellite systems at the present time, including transmission performance as defined by CCIR, and a critical comparison is made with ISDN requirements including an indication of how error performance may need improving. The paper concludes with a discussion of how satellite system operators might respond to the demands of the ISDN.
An introduction to testing techniques in the intelsat tdma/dsi system part 2: satellite system operations guide (ssog) tests
Authors: Colby R. J. , Parthasarathy R. , Stimson A. L.
Published: July 2007

This paper is the second of a four‐part series addressing the testing and alignment techniques to be used in the INTELSAT TDMA/DSI system. In the first part,1 the salient characteristics of the overall TDMA/DSI system were presented, together with a discussion of the fundamental requirements for testing and alignment. In this second part, INTELSAT's satellite system operations guide (SSOG) for TDMA is introduced and the principles of testing embodied in the SSOG tests are discussed. In particular, the impact of the unique TDMA access discipline on testing is examined. The third part will address the design of the specialized test equipment required. The fourth part will complete the series with a report on the operational experience gained in the initial stages of the TDMA implementation within the INTELSAT system.
Satellite switch state time plan control
Authors: Campanella S. J. , Inukai T.
Published: July 2007

This paper describes the basic control features of a typical satellite switch system, such as INTELSAT VI. Factors are addressed pertaining to the data format that is used to express the switch plan, the timing control of the switch states comprising the satellite switch frame, the transmission of the switch plan to the satellite, storage and execution of the switch plan on board, and the coding of switch plan data for protection from radiation‐induced bit errors. Also, the implementation used to achieve precision control of the on‐board clock is discussed, and the influence of clock control variation on all the terrestrial interfaces that participate in the system is demonstrated. Finally, the method for achieving network‐wide coordinated switch state time plan/TDMA burst time plan changes, which are essential in an operational satellite‐switched (SS)‐TDMA system, is discussed.
Application of 32 and 16 kb/s speech encoding techniques to digital satellite communications
Authors: Yatsuzuka Y. , Yato F. , Kurematsu A.
Published: July 2007

This paper describes the performance of various voice encoding techniques at 32 and 16 kb/s for applying to digital satellite communication systems. The subjective performances of adaptive differential PCM (ADPCM), adaptive predictive coding (APC), subband coding (SBC) and adaptive delta modulation (ADM) are compared under various satellite channel environments, that is, random and burst channel errors in satellite link and an ambient noise in the ship‐to‐shore direction in a maritime satellite channel. The performance of the voiceband data at 4·8 and 2·4 kb/s is also evaluated for these coders. ADPCM encoding at 32 kb/s is very attractive for conventional fixed satellite systems, keeping the equivalent quality to 64 kb/s PCM. On the other hand, APC encoding at 16 kb/s is also most suitable for maritime satellite communication systems at the sacrifice of a small degradation of speech quality.
The system implications of 6/4 ghz satellite‐to‐ground signal depolarization results from the intelsat propagation measurement programme
Authors: Allnutt J. E.
Published: July 2007

The results of six experiments to measure 6/4 GHz signal depolarization are presented. The measurement sites varied from the tropics to 57°N latitude and elevation angles between 12° and 38° were employed. In two of the experiments, simultaneous measurements at 6 GHz and 4 GHz were made along the same path to measure the correlation between the depolarizations occurring at the two frequencies.

It was found that, in all cases, rain was the dominant depolarizing mechanism. Where the occurrence of ice depolarization was significant the magnitude of the ice depolarization occurring was not system limiting on a statistical basis. The correlation between up‐link and down‐link depolarization occurring along the same path was found to be very good both on an instantaneous basis and a statistical basis. The use of open‐loop up‐link depolarization compensation mechanisms should therefore be feasible. An examination of the depolarization fluctuation spectra obtained in some severe depolarizing events during one of the experiments would indicate that the settling time for such a mechanism should be on the order of 1 s. The use of simple, ‘non‐perfect’, depolarization compensation mechanisms allied to a low‐cost, spectrally efficient FEC system may prove to be the best compromise in some locations that experience severe depolarization.
Investigation of 9.6 kb/s data transmission via a pcm link at 64 kb/s with and without link errors
Authors: Suyderhoud H. , Corcoran F. L. , Arnstein D. S. , Lewis H.
Published: July 2007

The problem of pulse code modulation (PCM) bit errors causing voice frequency (VF) modem errors has been studied in detail. The error mechanism consists of the addition of an impulse response type error signal added to the reconstructed VF data signal waveform at the digital‐to‐analogue (D/A) output of the PCM decoder. This error signal may cause a burst of errors registering in the VF modem receiver, depending on which PCM bit is in error.

Numerous data have been collected in a laboratory experiment and analysed in various ways. The average bit error rate (BER) enhancement factor of VF data over PCM is between 10 and 20. For each PCM bit in error, an average of two VF data bits are in error. The analysis leads to suggestions for possible solutions to the problem.
Estimating the mass and power of communications satellites
Authors: Pritchard Wilbur L.
Published: July 2007

The importance of weight and power estimates and methods for obtaining them are discussed. A method sufficiently accurate for system and launch vehicle planning is developed. It starts from operational requirements such as numbers of transponders, lifetime, eclipse service, radio frequency powers and certain general technology factors such as the performance of batteries and solar cells, and calculates the array power and the masses of the payload and primary power systems. Using these results, and differentiating between spinning and body stabilized satellites, the results of regression analyses on many communication satellites are then used to ascertain the weights of the other subsystems. Simple orbital mechanics are used to determine the weights of propellants, apogee motor, etc., to arrive at a final mass estimate. This estimate should be accurate to between 5 and 10 per cent if reliable input data are available.
Equalization of tdma links using in‐service impulse response measurement
Authors: Mazur B. , Lyons R.
Published: July 2007

This paper describes a method of measuring the frequency response of a digital radio link given the received (modulated) message signal, suitable for the incremental commissioning and in‐service monitoring of links in a QPSK/TDMA system. The method applies least squares estimation techniques to samples of the I and Q baseband components in order to derive a linear equivalent model for the channel. Results obtained by computer simulation of an INTELSAT V channel demonstrate that the method can provide a better basis for linear equalization of a non‐linear channel than the frequency response measurements provided by conventional techniques. A mathematical formulation and an implementation overview are also given.
CPM—the effect of filtering and hard limiting
Authors: Aulin Tor , Sundberg Carl‐Erik
Published: July 2007

The attractive properties of the digital constant amplitude modulation scheme CPM (continuous phase modulation) have been demonstrated in a previous paper in this journal.1 This concerned both the power and spectral efficiency of the large family of CPM schemes over the Gaussian channel.

In this paper the considered channel can be both bandlimited or band‐ and amplitude‐limited at the same time. Analytical results as well as simulations are presented for a number of selected CPM schemes.

In today's increasing demand for bandwidth, CPM is an attractive candidate for future satellite applications because of its spectral efficiency. In addition to this comes the fact that the transmitted signal has a constant amplitude and good detection performance when optimal coherent detection is performed.
Comsat's tdma traffic terminal
Authors: Benjamin Melvin C. , Bogaert Winston M.
Published: July 2007

COMSAT has installed two traffic terminals in the Etam earth‐station and is currently installing a third in the new Roaring Creek earth‐station to access the INTELSAT TDMA network. This paper describes the COMSAT TDMA traffic terminal equipment from the supergroup interface to the antenna. COMSAT's 1: N redundancy approach for terrestrial interface equipment and DSI unit back‐up is described as well as electrical path length, amplitude and group delay equalization techniques, special on‐line RF monitoring and failure reporting facilities and the operation and maintenance centre which can operate and perform diagnostic testing on up to four traffic terminals from a central location.
Reference terminal equipment for the intelsat tdma system
Authors: Saburi A. , Mitani T. , Ishi Y. , Takai H. , Takatsukasa N.
Published: July 2007

One of the distinctive features of the INTELSAT TDMA system is that the role of the reference station is completely separated from the ordinary station. For this reason, the reference station (called a TDMA reference and monitor station (TRMS)) needs special facilities: reference terminal equipment (RTE) and a TDMA system monitor (TSM). NEC corporation has developed and produced the RTE/TSM facilities necessary for the INTELSAT TDMA/DSI system.

In November 1984, the first RTE/TSM equipments were installed at the first two TRMS sites for the major path 2 in the Atlantic Ocean region. Since that time, several field tests have been successfully conducted.

In this paper, the signal processing equipment (SPE) of the RTE is described in detail.
Intelsat operations center tdma facility
Authors: Hodge G. , Johnson R. , Cook W. , Saralkar K.
Published: July 2007

The INTELSAT Operations Center TDMA facility (IOCTF) was built by COMSAT Laboratories to monitor and control the operation of the INTELSAT time‐division multiple‐access (TDMA) system. This paper describes the overall monitoring and control requirements, and the role played by the IOCTF in satisfying those requirements. The IOCTF architecture and hardware configuration are described, and key technical design and implementation issues are discussed.
Nec's traffic terminal equipment for the intelsat tdma system
Authors: Saburi A. , Oshima G. , Saga R. , Atobe M. , Shigaki S. , Yoshida K.
Published: July 2007

The traffic terminal equipment (TTE) for the INTELSAT TDMA System handles the actual traffic of the network and operates under control of the reference terminal equipment (RTE) installed at the reference station.

The required function and performance for the TTE are specified in detail by the INTELSAT TDMA/DSI specification, but there may be many approaches to actual equipment design. NEC's TTE has been designed based on NEC's extensive experience and field‐proven circuit techniques. In addition, the TTE design has been affected by the fact that NEC has been engaged in the development and production of the RTE for INTELSAT.

NEC's TTEs have been delivered to customers since the summer in 1984, with the first test with the RTE through the satellite having been successfully performed at COMSAT's Etam station at the end of 1984.

This paper describes the capabilities of the traffic terminal equipment, developed and manufactured by NEC Corporation, together with the design approach used in its fabrication.
Alignment, testing and maintenance principles in the intelsat tdma/dsi network
Authors: Oei A S. , Colby R. J. , Parthasarathy R. , Stimson A. L.
Published: July 2007

This paper discusses the principles underlying the alignment, testing and maintenance procedures (A,T & M) in the INTELSAT TDMA/DSI network. These principles are used in order to define the A, T & M functional groupings necessary to fully and systematically evaluate and maintain the network. It is shown that, as in the testing of any complex system, the overall test programme can be broken‐down into a series of individual test elements. Test elements naturally fall into logical associations called functional groups and, for practical reasons, some functional groups must be evaluated before others. Since the various users of the TDMA system will employ a variety of different manufacturers' equipment, a universal method of organizing the test programme had to be devised. To provide a set of test procedures which are independent of specific equipment design, a reference configuration approach has been taken which reflects the involvement, time‐ordering and hierarchy of the functional groups.

The objective behind the use of this reference configuration approach is to assist the development and conduct of the alignment, testing and maintenance procedures so as to ensure minimal interruption to an operational TDMA network. In addition, the use of this technique will facilitate the planning of A, T & M test schedules. Finally, it is shown how the reference configuration approach encompasses the INTELSAT TDMA traffic terminal Satellite Systems Operations Guide (SSOG) and the TDMA Reference Terminal Operations Guide (TROG).
Pointing losses in single‐axis and fixed‐mount earth‐station antennas due to satellite movement
Authors: Buchsbaum L. M.
Published: July 2007

There are substantial cost advantages in the use of single‐axis or fixed‐mount earth‐station antennas, thus reducing or eliminating the need for autotracking in earth‐stations operating with quasi‐stationary satellites. Such cost advantages are more relevant in small antennas where the tracking system represents a larger percentage of the overall cost. In addition, small antennas are particularly suitable to be operated without autotracking, owing to their wider half‐power beamwidth. This paper describes a model for calculating the antenna pointing loss as a function of the antenna diameter, operating frequency band, satellite station‐keeping tolerances, and the relative geometry between the earth‐station and the satellite. The model has been extensively used in the development of INTELSAT's IBS and VISTA services as well as in domestic leases. Although the model has been developed based on orbital mechanics equations, its emphasis is towards earth‐station and systems engineering applications. Some example calculations and results obtained through an HP‐41 CV programmable calculator are also provided.
Field test results of multi‐channel digital tv transmission at 15 and 30 Mb/s through an intelsat satellite using a PSK/FDMA system
Authors: Murakami Hitomi , Sato Gunkichi , Matsumoto Shuichi , Hirabayashi Tatsuhiko , Yamamoto Hideo , Donald Wallance W. , Bachmann Erik
Published: July 2007

This paper describes field test results of multi‐channel digital TV transmission using a PSK/FDMA system and the related subjective test results of received TV pictures. The picture quality of the multi‐channel 15 or 30 Mb/s transmission for both NTSC and PAL systems through the INTELSAT POR satellite are subjectively evaluated for various bit‐error rates. In addition, subjective evaluations were made at various values of earth‐station e.i.r.p. to compare the picture quality of digital transmissions with that of current half‐transponder FM transmission.
Efficient adaptive forward error control schemes for Ka‐band satellite systems
Authors: Khan M. H. , Le‐Ngoc T. , Bhargava V. K.
Published: July 2007

Adaptive fade margin is required to counter the severe but varying rain attenuation in Ka‐band satellite communications. In a search for a suitable rain countermeasure, the effectiveness of adaptive forward error control (AFEC) schemes is studied. Two AFEC schemes using convolution codes and concatenated codes are proposed and their performances analysed. The schemes can provide progressively adaptive fade margins of 10‐1 and 10‐4 dB, respectively, in excess of the system's fixed fade margin.

To improve the efficient use of shared resources of the system, an AFEC scheme using double coding is introduced and its performance analysed. In this scheme a single codec is used repeatedly, resulting in reduced hardware cost and increased use. By using convolutional code and Golay code the above scheme can provide adaptive fade margins of 10°8 dB and 8°1 dB, respectively. Although concatenated codes have slightly better performance than double codes, the hardware implementation and decoding complexity of the latter are significantly less.

Implementation complexity of AFEC resource sharing in the light of code complexity, time frame expansion, link condition monitoring and signalling is discussed in detail.
Satellite networks in the isdn era
Authors: Amadesi P. , Haines P. , Patacchini A.
Published: July 2007

The concept of an integrated service digital network (ISDN) is becoming topical for the evolution of world‐wide telecommunications. In fact the consultative committees (CCITT and CCIR) have worked actively on the definition of the ISDN and its functions, and many PTTs and other operating companies are engaged in programmes aimed at introducing digital transmission and switching in the public switched telephone network (PSTN) with a view to establishing the first versions of an ISDN.

Satellites are well prepared to operate in an ISDN environment.

The present competition with fibre optics and other terrestrial carriers may perhaps limit the initial contribution of satellites to the establishment of trunk routes in the first ISDNs, but in the medium term the particular characteristics of flexible distribution of information over very large areas may become of fundamental importance, and many satellite‐based networks developed independently may give concrete support to the ISDN. In the long term satellites may experience an even deeper degree of integration, by providing part of the switching facilities of the ISDN on board.
Economics of multiple beam satellites
Authors: Campanella S. J. , Pontano B. A. , Kao T.
Published: July 2007

This paper describes an advanced multibeam communications satellite system using on‐board processing and hopping beams in conjunction with low‐cost earth‐stations to derive a significant advantage over fibre optic submarine cable. It serves thousands of small earth‐stations located near the origins of traffic. An economic analysis is presented for both this satellite system and competitive fibre optic cable for the 1995 to 2007 epoch. Results indicate the satellite service to be significantly lower in cost, and in addition it delivers the service near to the origin of the traffic, providing additional savings in terrestrial connections.
Access protocol performance for on‐board processing business satellite systems
Authors: El Amin M. H. M. , Chung L. N. , Evans B. G.
Published: July 2007

This paper presents protocols for use in efficient accessing of multi‐service business satellite systems. A new reservation TDMA scheme with free slots contention is proposed as being particularly suitable. The new access protocol is simulated using a numerical Petri‐net model and results are given for variations in numbers of earth‐stations, traffic mixes, balanced‐to‐unbalanced traffic, reservation scheme and free slots contention. Finally an analytical derivation is presented for the protocol performance which agrees well with simulation.
SS‐TDMA switch matrices using optical technology
Authors: Peters Robert A.
Published: July 2007

The principles and potential advantages of an optical switch matrix for use in an SS‐TDMA microwave switching matrix subsystem are reviewed, and the relative merits of three optical switching techniques are compared. An INTELSAT sponsored programme is described that has demonstrated the feasibility and the problems of developing a compact, monolithic, optical switch matrix. RF performance generally exceeded that of switch matrices built using discrete microwave components. However, the switch matrix has a high insertion loss and requires temperature stabilization or compensation. To be practical, 1‐3 micron of longer wavelength technology must be used.
Synchronization of remote digital clusters via satellite for ISDN
Authors: Johannsen Klaus G.
Published: July 2007

Presently, there are several countries in the process of converting their national communication system to an integrated digital communication system and eventually, to an integrated services digital network (ISDN). In some developing nations, where a satellite is used for long‐haul transmission to remote and isolated areas, and where there is no terrestrial connection to those areas, the question has been raised whether the satellite can remain a part of such a network, and if so, can it be used to synchronize the remote digital clusters.

The matter of concern is the satellite's residual motion. The residual relative motion between the satellite and a ground station produces doppler and therefore, frequency shifts which may cause loss of information, the amount of doppler or carrier frequency shift is location dependent, in general it increases with station latitude and satellite inclination. However, for a given geographic area and a given accuracy in satellite station keeping, it can be shown that satellite links can provide network synchronization to remote digital clusters within the slip rate requirements of a domestic integrated services digital network. In order to permit a less stringent orbit maintenance, or to include earth‐stations of higher geographical latitudes, it is practical to include doppler buffers as part of the satellite earth‐station equipment.
Some aspects of the analysis of experimental data for short‐term frequency scaling
Authors: Upton S. A. J. , Holt A. R. , Upton G. J. G.
Published: July 2007

Over one hundred hours of British Telecom's half‐second event data from the OTS and ATS‐6 satellites has been analysed with respect to short‐term frequency scaling of attenuation. The ratio of attenuation at two frequencies is particularly vulnerable to system effects and noise. Data analysis techniques are discussed and it is shown that a least‐squares analysis is not suitable when the time period is short. Appreciable variation occurred in the mean value of the short‐term ratio from one event to another. Only on a few occasions did significant changes occur during an event. Simultaneous data from other equipment gives confidence that these changes are due to propagation effects.
Large/small carrier performance of non‐linear devices
Authors: Stette Gunnar
Published: July 2007

The intermodulation properties of a memoryless non‐linear amplifier with two carriers having large level difference are in the limit determined by the properties of the amplitude characteristic of the amplifier at a single point, i.e. at the operating point determined by the stronger carrier. The paper derives the mathematical expression for the level of the dominating third‐order intermodulation product, and also shows how this level can be determined graphically from a given amplitude characteristic.
CDMA versus FDMA channel capacity in mobile satellite communication
Authors: Johannsen Klaus G.
Published: July 2007

At present a major effort is under way to define the most efficient modulation/multiple access system in mobile satellite communication. Where the emphasis is on digital voice modulation, the proposed multiple access methods almost always imply frequency division multiple access (FDMA). This analysis presents a comparison between FDMA and code division multiple access (CDMA), for the operation of both multiple access methods in the mobile satellite communication environment. The mobile satellites under consideration use multiple‐beam or scan‐beam antennas and employ frequency reuse of the allocated L‐band frequency spectrum. As CDMA is better at absorbing Doppler and multipath effects, and permits higher rate coding, in general (practical considerations aside) it appears to be the more capable system.
Propagation theory in adaptive cancellation of cross‐polarization
Authors: Ghorbani A. , McEwan N. J.
Published: July 2007

The application of propagation theory to the structure and control of adaptive networks designed to cancel hydrometeor‐induced cross‐polarization in microwave communication links is summarized. When adaptive cross‐coupling networks are realized at radio frequency as variable waveguide polarizers, desirable simplifications are to make them lossless devices with at most two free parameters. Performance calculations for such simplified forms are fully reviewed.

Several new approaches to the design of controllers for the cancelling networks are also made possible. New results are presented on the performance of systems which use only one pilot tone, or even dispense with cross‐polar measurement completely. It is also shown that the reciprocity of the hydrometeor medium, an apparently safe assumption, makes possible an extract precorrection of a transmitted polarization if control is based on a beacon signal of the orthogonal polarization sent back from the receiving point.
Effects of solar transit on Ku‐band VSAT systems
Authors: Mohamadi Farshad , Lyon David L. , Murrell Peter R.
Published: July 2007

A satellite earth‐station is affected by added radio noise from the Sun when the Sun passes behind the satellite as seen from the earth‐station. In the following, an exact analysis of this solar transit is derived, and an approximate method is presented for practical cases. Moreover, networks of very small aperture satellite terminals (VSATs) operating at Ku‐band microwave frequencies of 12–14 GHz behave differently during the solar transit period than the more traditional C‐ or Ku‐band satellite networks; therefore analytical and experimental results for VSATs have been presented. An explanation is given, based on these analyses, of why solar transit outages are rarer in VSATs than in conventional satellite communications systems.
Research and development activities of optical ISLS in Japan
Authors: Yasukawa Koji , Araki Ken'Ichi , Kashiki Kanshiro , Aruga Tadashi
Published: July 2007

The current state of research and development activities of optical intersatellite links (ISLs) and related optical devices in Japan, including semiconductor laser diodes, photodiodes, CCDs and modulation/demodulation techniques, is described. Subjects for further research on optical devices and communications are summarized. An optical communication experiment which uses the communications system on board the Engineering Test Satellite‐VI to be launched in Japan in 1992, is outlined.
A PSK group modem based on digital signal processing: Algorithm, hardware design, implementation and performance
Authors: Takahata Fumio , Yasusaga Masayuki , Hirata Yasuo , Ohsawa Tomoki , Namiki Junji
Published: July 2007

A PSK group modem which modulates and demodulates multiple PSK signals en bloc will play an important role in cost‐effective satellite communications systems based on the narrow‐band multicarrier PSK/FDMA technique. This paper describes the development of a PSK group modem, including its algorithm, hardware design and implementation. In the algorithm, PSK signals are efficiently filtered by digital signal processing applied to the digital transmultiplexor. Furthermore, in order to compensate for the difference between the operation timing of the PSK group modem and the symbol timing of each input/output data signal, digital signal processing based on a table‐look‐up method using ROM and a rate‐conversion filter with adaptive weighting are proposed for the modulator and demodulator, respectively. An experimental four‐phase PSK group modem has been developed, and experiments have been conducted under various conditions. The measured performance of the developed hardware is also demonstrated.
Frequency diversity and its applications
Authors: Carassa F. , Tartara G. , Matricciani E.
Published: July 2007

Adaptive shared resource methods may be the only available effective countermeasure to rain‐induced attenuation in satellite communication systems above 20 GHz. Two of these methods, frequency diversity (FDV) and burst length control (BLC) are examined and compared by using a unified approach. The fundamental statistical relationships between unassisted and assisted conditions are derived, and optimum values are identified. It is found that BLC (which improves power margins) is easier to implement than FDV, but FDV (which improves outage probability and retains most of its advantages at higher frequencies) is more effective in reducing built‐in power margins in ‘unassisted’ conditions. From a large database at 11.6 GHz collected in the Sirio experiment, some realistic FDV results are derived for systems using 20/30 GHz bands for unassisted conditions and 12/14 GHz bands for assisted conditions. As the ESA Olympus satellite will carry both 20/30 GHz and 12/14 GHz transponders, an FDV experiment with Olympus has been proposed by CSTS; the characteristics of the three earth‐stations planned to be built in Italy for the experiment are described.
Up‐link power control of satellite earth‐stations as a fade countermeasure of 20/30 GHz communications systems
Authors: Hörle J.
Published: July 2007

All 20/30 GHz satellite communications systems suffer from atmospheric attenuation in cloudy or rainy weather, particularly if high link availabilities are required. In FDMA systems the power transfer characteristic of each carrier is linear, so any up‐link fade degrades the overall performance on a dB‐by‐dB basis. This, together with the fact that the 30 GHz up‐link attenuation is much greater than the 20 GHz down‐link attenuation, makes adaptive countermeasures of up‐link fades most important. This paper shows how the overall link performance can be improved by applying up‐link power control. It is explained how this improvement depends on the up‐link/down‐link balance, the dynamic range of the up‐link power control, and the up‐link and down‐link atmospheric attenuation.

If a small number of carriers can be allocated in an intermodulation‐free frequency plan, the satellite transponder can be operated near saturation in order to optimize the down‐link performance. Computer simulations of up‐link power control for such an FDMA scheme have been performed based on measured three‐carrier characteristics of a transponder TWT. It is shown that the overall link performance in faded conditions can be significantly improved with up‐link power control. This may be utilized to increase the availability of a satellite link or to relax the earth‐station performance in terms of G/T or EIRP if the link margin provided by an earth‐station with fixed EIRP is satisfactory.
Forward error correction applied to intelsat IDR carriers
Authors: Morley S. A.
Published: July 2007

Forward error correction (FEC) techniques are applied to INTELSAT intermediate data rate (IDR) services to reduce the transmitted power requirements relative to uncoded systems, thereby increasing the satellite transponder capacity. Properly designed FEC systems reduce data errors in the received digital stream with minimal impact to the protocols, operation and equipment involved with the communication system. This paper discusses the overall system impact of the addition of FEC to the IDR service. The appropriateness of the specific application of convolutional encoding combined with Viterbi decoding techniques is discussed. Basic concepts of convolutional encoding and Viterbi decoding are presented in order to provide understanding of the trade‐offs involved in the specification of the coding technique for the IDR service. The details of the IDR FEC specification are presented. The implementation of a system based on a VLSI Viterbi decoder device which conforms to the INTELSAT requirements is described.
New rain rate analyses to assess rain attenuation on satellite ehf communications
Authors: Tattelman Paul
Published: July 2007

This paper provides estimates of the frequency of occurrence, duration and probability of satellite EHF communication outages due to attenuation by rain. These can be used to determine optimum frequencies, power levels and the need for space diversity of terminals or other alternatives to maintain reliable communications. Ten years of 1 min rain rates at each of 12 U.S. cities were used in conjunction with an attenuation model to quantify communication outages at locations representing a variety of climatic regimes. Analyses of the 1 min rain rates and outage estimates at 10, 30 and 45 GHz for elevation angles of 10°, 30°, 50° and 70° are presented.
Asymptotic analysis of unslotted frequency‐hop multiple‐access without side information
Authors: Kim Sang Wu , Kim Sangmun
Published: July 2007

In a packet radio network that employs frequency‐hop transmission and error control coding, the use of side information permits identification and erasure of symbols that have been corrupted by multiple‐access interference, and thus greatly enhances multiple‐access capability. In one approach, side information is generated from an error detecting random code. We investigate the trade‐off between the reliability of side information and the rate of the code, and derive the maximum allowable code rate to achieve a certain reliability of side information. An achievable region and the channel throughput are examined for an unslotted frequency‐hop packet radio network that employs Reed‐Solomon codes and side information generated within the radio by an error detecting code.
The data station controller of the apollo system
Authors: Pahl J.
Published: July 2007

This paper describes a high speed satellite communication system called APOLLO, designed to allow the transmission of documents across Europe. Emphasis is put on the hardware and software for which Logica is responsible, and the message flow through the system. A review is given of the current position and future plans of the project.
Analytical evaluation of average bit error rate for the land mobile satellite channel
Authors: Cygan Daniel
Published: July 2007

An analytical solution is presented showing the average bit error probability for the land mobile satellite channel. The channel is modelled as Rice and Rayleigh—lognormal fading. Modulation schemes under consideration include differentially detected PSK and non‐coherently detected FSK. Results indicate that the receiver performance is highly dominated by the time share of shadowing. The ratio of the BERs in shadowed and unshadowed areas of typical measured channels and an operating point assumed to be at Es/No = 10 dB is of the order of 10−2.
On‐board non‐linear circuitry for Ku‐band active arrays
Authors: Giannini F. , Leuzzi G. , Ruggieri M.
Published: July 2007

Active phased arrays will play an important role in future satellite communications, because of the system flexibility and potential reconfigurability that they may provide.

Therefore, an investigation of the relationship existing between payload characteristics and the synthesis parameters of this kind of antenna may constitute a helpful tool.

To this end, a parametric analysis of the on‐board non‐linear circuitry of the transmitting system (power and up‐converter sections) has been carried out, establishing the dependence of the mass and DC power demand on the number of beams and feeds of the transmitting phased array.

The parametric investigation has been, in particular, applied to an active imaging phased array and an active direct radiating phased array whose suitability to provide a multibeam coverage of Western Europe at Ku band has been demonstrated within an ESA/ESTEC contract.

This paper describes the parametric approach followed in the investigation of the on‐board non‐linear subsystems of the active transmitting phased arrays.

The assumed circuitry configurations are widely commented, and the parametric curves for the case of imaging and direct radiating phased arrays are reported.
Channel coding for satellite mobile channels
Authors: Wong K. H. H. , Hanzo L. , Steele R.
Published: July 2007

The deployment of channel coding and interleaving to enhance the bit‐error performance of a satellite mobile radio channel is addressed for speech and data transmissions. Different convolutional codes (CC) using Viterbi decoding with soft decision are examined with inter‐block interleaving. Reed‐Solomon (RS) codes with Berlekamp‐Massey hard decision decoding or soft decision trellis decoding combined with block interleaving are also investigated. A concatenated arrangement employing RS and CC coding as the outer and inner coders, respectively, is used for transmissions via minimum shift keying (MSK) over Gaussian and Rayleigh fading channels. For an interblock interleaving period of 2880 bits, a concatenated arrangement of an RS(48,36). over the Galois field GF(256) and punctured PCC(3,1,7) yielding an overall coding rate of 1/2, provides a coding gain of 42dB for a BER of 10−6, and an uncorrectable error detection probability of 1–10−9.
Comparison of advanced coding and modulation schemes for multicarrier satellite communication systems
Authors: Benedetto S. , Pent M. , Zhang Z.
Published: July 2007

Digital satellite communication systems use coherent quaternary PSK (QPSK) as the preferred modulation scheme. In recent years, however, the search for bandwidth and power‐efficient digital modulation methods has become an active research area. In this paper the performances of combined coding and modulation schemes employing multilevel signal alphabets are considered, in the framework of a system model which reasonably approximates the INTELSAT SCPC system. The main goal of the research was to investigate whether the efficiency of coded modulation schemes and their savings in transmitted power could be maintained in a system environment dominated by interference more than by the additive white Gaussian noise. A second goal was to compare the performance of signals with constant envelope, such as multilevel PSK, with that of signals allowing variations in amplitude, such as multilevel PSK, with that of signals allowing variations in amplitude, such as multilevel QAM. In the paper, we propose a channel model which is reasonably close to the real system, and a method for performance evaluation leading to an estimate of the asymptotic power gain of the modulation systems. The channel model and the method are applied to the analysis of coded 16‐ and 32‐ PSK and QAM.