bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement and analysis of structural dynamics properties of robotic joint transmission system
Authors: Huang Shiuh‐Jer , Chen Chin‐Yih
Published: July 2007

The flexibility of a robotic manipulator is considered an important factor, especially the joint compliance for improving the accuracy and operating speed of a robot application. In this article, two methods are employed to identify the structural dynamic characteristics of each joint transmission system of an ITRI‐U type robot. The driving system of each joint is modeled as a mass‐spring‐damper mechanism that has a second‐order dynamic mathematical equation. Then, the response experiments of hammer impact excitation and motor driving actuation are done and the difference between them compared. Those are used to simulate two different operation situations, the robot colliding with the environment and the discontinuing dynamic operation impacts. The system's parameters of each joint axis are obtained by the system identification technique. From the experimental results, the angular error of the motor shaft can be compensated by the control gain of the motor controller. However, the small damping ratio of the robotic mechanism limits the magnitude of servo gain. If the servo gain increases, the robot arm has oscillation phenomenon during dynamic operation. In addition, the error due to joint elasticity cannot be overcome by the current industrial robotic controller. Therefore, a suitable controller should be designed to compensate the dynamic effects of joint compliance with the identified parameters.
Direct adaptive impedance control of robot manipulators
Authors: Colbaugh R. , Seraji H. , Glass K.
Published: July 2007

This article presents an adaptive scheme for controlling the end‐effector impedance of robot manipulators. The proposed control system consists of three subsystems: a simple “filter” that characterizes the desired dynamic relationship between the end‐effector position error and the end‐effector/environment contact force, an adaptive controller that produces the Cartesian‐space control input required to provide this desired dynamic relationship, and an algorithm for mapping the Cartesian‐space control input to a physically realizable joint‐space control torque. The controller does not require knowledge of either the structure or the parameter values of the robot dynamics and is implemented without calculation of the robot inverse kinematic transformation. As a result, the scheme represents a general and computationally efficient approach to controlling the impedance of both nonredundant and redundant manipulators. Furthermore, the method can be applied directly to trajectory tracking in free‐space motion by removing the impedance filter. Computer simulation results are given for a planar four degree‐of‐freedom redundant robot under adaptive impedance control. These results demonstrate that accurate end‐effector impedance control and effective redundancy utilization can be achieved simultaneously by using the proposed controller.
Experimental two‐axis vibration suppression and control of a flexible robot arm
Authors: Yim Woosoon , Zuang Jichun , Singh Sahjendra N.
Published: July 2007

This article focuses on the implementation of a dual‐mode controller for the maneuver of a two‐axis flexible robotic arm. The joint angle trajectory tracking is accomplished by proportional and derivative and feedforward controllers. Based on the pole placement technique, a linear stabilizer is designed for elastic mode stabilization in the plane perpendicular to each joint axis. The stabilizer is switched on when the trajectory reaches the vicinity of the terminal state. The effect of switching time of the stabilizer and varying payload on arm vibration are investigated. With the proposed control system, accurate joint angle tracking and elastic mode stabilization can be accomplished. © 1993 John Wiley & Sons, Inc.
An efficient method for inverse dynamics of manipulators based on the virtual work principle
Authors: Zhang Chang‐De , Song Shin‐Min
Published: July 2007

The computational efficiency of inverse dynamics of a manipulator is important to the real‐time control of the system. For serial manipulators, the recursive Newton‐Euler method has been proven to be the most efficient. However, for more general manipulators, such as serial manipulators with closed kinematic loops or parallel manipulators, it must be modified accordingly and the resultant computational efficiency is degraded. This article presents a computationally efficient scheme based on the virtual work principle for inverse dynamics of general manipulators. The present method uses a forward recursive scheme to compute velocities and accelerations, the Newton‐Euler equation to calculate inertia forces/torque, and the virtual work principle to formulate the dynamic equations of motion. This method is equally effective for serial and parallel manipulators. For serial manipulators, its computational efficiency is comparable to the recursive Newton‐Euler method. For parallel manipulators or serial manipulators with closed kinematic loops, it is more efficient than the existing methods. As an example, the computations of inverse dynamics (including inverse kinematics) of a general Stewart platform require only 842 multiplications, 511 additions, and 12 square roots.
Direct digital design of computed torque controllers
Authors: Ishihara Tadashi
Published: July 2007

Direct digital design of computed torque controllers for a robot manipulator is discussed in this article. A simple discrete‐time model of the robot manipulator obtained by Euler's method is used for the design. Taking account of computation delay in the digital processor, we propose predictor‐based designs of the PD and PID type controllers. The PID‐type controller is designed based on a modified version of the discrete‐time integral controller proposed by Mita. For both controllers, the feedback gains can be determined easily by using simple formulas. A simulation example is presented to illustrate the relevance of the proposed designs and the robustness of PID‐type controller against physical parameter variations. © 1994 John Wiley & Sons, Inc.
Definition of a kinematic metric for robot manipulators
Authors: Tchoń Krzysztof , Dulȩba Ignacy
Published: July 2007

Using a Riemannian metric in the special Euclidean group we define a kinematic metric on the space of kinematics of robot manipulators. Prospective applications of the metric in kinematic design and performance evaluation of robot manipulators are indicated. For exemplary kinematics, including the PUMA 600, explicit formulas are provided describing the dependence of the metric on manipulator's geometric parameters. © 1994 John Wiley & Sons, Inc.
On the velocity and acceleration snalyses of general parallel robotic manipulators
Authors: Wans Li‐Chun T. , Chen Chih Cheng
Published: July 2007

This article presents a unified method for the velocity and acceleration analyses of general parallel robotic manipulators. In this method, the governing velocity and acceleration equations of the robot are formulated in the joint space by considering it as a tree‐type mechanism subjected to Cartesian velocity and acceleration constraints. The procedures for solving the direct and the inverse analysis problems are established based on the generalized coordinate partitioning technique and the full pivoting Gaussian elimination method. These procedures take into account the overconstrained kinematic loops and redundant joints, and are applicable to either fully parallel robots or hybrid series‐parallel robots without any modifications. In addition, a set of generalized recursive formulas for computing the forward Cartesian velocity and acceleration transformations are developed. These formulas are also useful for efficient evaluating the complex nonlinear terms of the governing acceleration equations. © 1995 John Wiley & Sons, Inc.
Geometric phases and robotic locomotion
Authors: Kelly Scott D. , Murray Richard M.
Published: July 2007

Robotic locomotion is based in a variety of instances upon cyclic changes in the shape of a robot mechanism. Certain variations in shape exploit the constrained nature of a robot's interaction with its environment to generate net motion. This is true for legged robots, snakelike robots, and wheeled mobile robots undertaking maneuvers such as parallel parking. In this article we explore the use of tools from differential geometry to model and analyze this class of locomotion mechanisms in a unified way. In particular, we describe locomotion in terms of the geometric phase associated with a connection on a principal bundle, and address issues such as controllability and choice of gait. We also provide an introduction to the basic mathematical concepts that we require and apply the theory to numerous example systems. © 1995 John Wiley & Sons, Inc.
Analtical‐ form direct kinematicefor the second scheme of a 5–5 general‐geometry fully parallel manipulator
Authors: Innocenti Carlo
Published: July 2007

This article presents the direct kinematics of a 6 degrees of freedom fully parallel manipulator that features five connection points on both base and platform. The considered leg arrangement is one of the two possible, the other having been referred to in a previous paper. The base and platform have a general geometry, i.e., the connection points are not bound to lie on planes. The direct kinematics is solved in analytical form, which allows determination of every possible solution. After a suitable set of five equations in five unknowns has been laid down, and an original elimination procedure applied, a final polynomial equation of the 24th order is found whose 24 solutions correspond to as many assembly configurations for the considered fully parallel manipulator. A case study is reported. © 1995 John Wiley & Sons, Inc.
Measurement of pose repeatabilty of stewart platform
Authors: Masory Oren , Jiahua Yan
Published: July 2007

Manufacturing tolerances, installation errors, link offsets, and controller errors effect the positioning repeatability of serial and parallel manipulators. A variety of measurement methods have been proposed and used to measure the repeatability of serial manipulators. However, these methods might not be suitable for parallel manipulators due to limited instrumentation accessibility and the large structure involved. This article describes two measurement procedures by which the position of a target point in three‐dimensional space can be determined using a single theodolite that is used to collect two sets of measurements taken from two arbitrary locations. The required hardware needed for the implementation of this method is two standard measuring tapes installed vertically at two arbitrary locations, or one horizontal bar. If the target points are located on the end effector of a manipulator, its repeatability can be measured. The procedure that uses two vertical tapes was used to measure the repeatability of a Stewart Platform and experimental results are provided. © 2995 John Wiley & Sons, Inc.
State and dynamic behavior of a high stiffness stewart platform‐based force/torque sensor
Authors: Ferraresi C. , Pastorelli S. , Zhmud' M. Sorli N.
Published: July 2007

The performance of a Stewart platform‐based force/torque sensor is analyzed. The influence of sensor geometry is assessed with particular reference to the characteristic orientation angles of the arms connecting the platforms, which consist of single‐axis bidirectional force transducers. Static and dynamic performance is analyzed and compared with experimental tests, © 7993 John Wiley & Sons, Inc.
Companded single sideband (CSSB) AM/FDMA Performance
Authors: Campanella S. J.
Published: July 2007

The continuing need for increased traffic capacity for telephony over satellite links combined with the availability of low cost and accurate LSI compander chips has caused renewed interest in SSB satellite transmission using companders to reduce the impairments caused by thermal noise, interference and intermodulation encountered on the transmission link. This type of transmission is designated as CSSB/AM and may be operated in a multicarrier per transponder (FDMA) manner. The capacity achieved is a function of the average power during the occurrence of speech and because this value has decreased in modern telephone systems, the advantages to be gained from CSSB/AM are increased.

This paper presents the development of expressions for channel capacity of CSSB/AM links as a function of carrier‐to‐noise ratio and speech power level while active. These are used to estimate the capacity achievable in an INTELSAT IV type transponder.
Introduction of companded FDM/FM operation into the intelsat system
Authors: Pontano B. A. , Szarvas G. G.
Published: July 2007

INTELSAT has been studying the application of compandors in its existing FDM/FM system for a number of years. Laboratory and field tests have demonstrated the technical suitability of these devices for use on INTELSAT satellite links. Companded FDM/FM (CFDM) has recently been approved for use by INTELSAT signatories. The first CFDM service was inaugurated in April 1983 between the Etam Standard A earth station (U.S.A.) and the Grand Cayman Standard B earth, station (Cayman Islands).
Japanese commercial tdma system
Authors: Suzuki R. , Hayashizaki H. , Mitani T. , Saga R.
Published: July 2007

This paper reviews two TDMA systems which have been developed at NTT (Nippon Telegraph and Telephone Public Corporation) for domestic use in Japan.

The first system uses K‐Bands (30/20 GHz) and is called the TDMA‐65M system. This system constructs a variable channel capacity network between 8 major cities (regional centres).

The second system uses C‐Bands (6/4 GHz) and is called the TDMA‐100M system. This system provides remote island communication links for simultaneous transmission of voice and colour television signals.

These two TDMA systems were put into commercial operation in summer 1983 by using, respectively, the Communication Satellite‐2s, CS‐2a which was launched in February 1983 and CS‐2b which was launched in August 1983.
Design considerations for a larger inmarsat standard ship earth station
Authors: Nouri M. , Braine M. R.
Published: July 2007

A new standard of INMARSAT ship earth station for multi‐channel operation could find particular application on large passenger ships and off‐shore oil/gas platforms. This paper provides estimates of platform and ship motions and discusses general design requirements, notably of the antenna system. The discussion includes consideration of possible modulation and multiple access techniques. Single channel per carrier (SCPC) operation is advocated which permits easy integration with the present service to single channel INMARSAT Standard‐A ship earth stations. Major parameter/relative cost trade‐off curves needed in an overall ship earth station design optimization are presented.
Satellite broadcasting: System concepts and the television transmission standards for europe
Authors: Phillips G. J. , Shelswell P.
Published: July 2007

Within Western Europe several countries have indicated their intention to start DBS services in the 12 GHz band in 1985/6 or soon after. Against this background the European Broadcasting Union has recommended a common transmission standard known as C‐MAC/packet. An outline is given of the system, with a discussion of the requirements for a broadcasting satellite and receivers for individual reception.
Satellites for communications and broadcasting: The evolving european market
Authors: Morris R.
Published: July 2007

The paper traces the development of the market for communications and direct broadcasting satellites in Europe, since the original specification of the European Communications Satellite (ECS) in 1977. It reviews the experiments undertaken on the Orbital Test Satellite (OTS) and the way in which demonstrations with this satellite have influenced the way in which ECS is being developed.

It continues by considering the impact of television on the market, first cable television and its distribution requirements, then direct broadcasting by satellite, where the introduction of homes into the customer configuration will bring with it programme content as a salient feature in market development.

Finally it speculates on the possibilities for the future, both in terms of the effect of new and higher frequencies on satellite communications systems, and the possible effects that interaction from small earth‐stations could have on satellite design.
Performance of regenerative/conventional satellite systems
Authors: Maral G. , Bousquet M.
Published: July 2007

A great many papers have been devoted in the last few years to the advantages of regenerative communications satellite systems when compared to conventional ones. This paper attempts to summarize the most significant results which are scattered in the literature, and to provide a tutorial overview of this comparison. Linear and non‐linear satellite channel performances, with and without interference, are discussed. The major impacts on system design provided by on‐board regeneration are also presented.
Earth‐station size Vs. Error‐correction coding in the design of ku‐band satellite communications systems
Authors: Mangulis V.
Published: July 2007

A Ku‐band satellite transponder capacity is evaluated for a PCM/QPSK/FDMA system in which many carriers are transmitted in an SCPC mode. The capacity depends on earth‐station sizes, error‐correction coding, required signal‐to‐noise ratio and required availability in rain; for simplicity all of these parameters are assumed to be the same for all carriers in the transponder. A method of accounting for the effects of rain is developed; it is assumed that the earth‐stations do not adjust their output power when it rains. Trade‐offs between earth‐station sizes and error‐correction code rates are examined.
The intelsat spade system—ten years of demand assigned operation
Authors: Lynn S.
Published: July 2007

In this paper, the INTELSAT SPADE system is re‐examined after 10 years of operation in the Atlantic Ocean Region. A functional description of the system is provided together with its technical evolution from the early years of development to the current maturity. Network monitoring and control, together with a summary of the SPADE System's activity from its traffic statistics and billing information are also discussed. Finally, it is shown that SPADE has fully met its original purpose and, based on the continuing high usuage of the SPADE system and the availability of a new generation SPADE terminal, SPADE will continue to be an important service for many years to come.
Design architecture for a high performance intelsat tdma/dsi terminal
Authors: Gaske Paul , Thompson Steve
Published: July 2007

In recent years, communication equipment performance and reliability have become dominated by software factors. The architecture of the software, as well as the hardware, has a substantial impact on the software performance and, thus, the equipment performance.

This paper focuses on the software and hardware architectures of a time division multiple access (TDMA) terminal and a digital speech interpolation (DSI) unit, which have been specifically designed to optimize software performance. This equipment is designed to operate in the INTELSAT and EUTELSAT TDMA networks.
120 Mb/s tdma traffic terminal for use in the intelsat system
Authors: Nakanishi M. , Itoh H.
Published: July 2007

This paper presents the design concept, the design features, and the configuration of the 120 Mb/s TDMA traffic terminal for use in the INTELSAT or EUTELSAT Systems. The description covers the redundancy concept, the control and supervisory system, the BTP processing method, internal interfaces between subsystems, expandability and capacity of the system, and the overall operation and maintenance concepts.

The detailed design of each subsystem is discussed, from the IF interface with the earth‐station transmit and receive equipment down to the terrestrial interface equipment. Special emphasis is given to design features associated with redundancy of the terminal equipment yielding the required operation availability, and on the scheme for supervisory data handling across the international trunk circuit through the TDMA network. As a part of the discussion, the equipment mechanical sizes and anticipated heat dissipation are presented.
16 Kb/s high quality voice encoding for satellite communication networks
Authors: Yatsuzuka Yohtaro , Yamazaki Tomohiro , Hzuka Shigeru
Published: July 2007

This paper describes applications of adaptive predictive coding (APC) with maximum likelihood quantization (MLQ) which can cover a wide range of coding rates from 4.8 to 16 kb/s for low C/N satellite communication systems, such as maritime, aeronautical mobile and thin‐route satellite communication systems, and also for speech and data integration, including digital circuit multiplication equipment (DCME) in business communication systems, such as INTELSAT business services (IBS). A 16 kb/s APC–MLQ hardware codec has been implemented by NEC–7720 DSP chips and the performance has been confirmed in subjective quality of speech through conversational tests. The objective performance has also been evaluated for non‐voice signals, such as single and multi‐frequency tones, and 1200 and 2400 b/s voiceband data signals. The APC‐MLQ codec can transmit the voice‐band data at 1200 b/s over two asynchronous tandem links and at 2400 b/s over one link. It was noted that the APC‐MLQ codec is superior in speech performance at 16 kb/s to a narrow‐band companded FM and meets requirements for low C/N satellite communication systems. For voice and data integration into 16 kb/s for 64 kb/s links, we propose a multi‐media multiplexing for low C/N digital satellite communication systems and also a small‐scale circuit multiplication system for business use. In these systems, a variable rate coding of APC‐MLQ from 4.8 to 16 kb/s can be effectively introduced for voice and data integration.
Universal digital TV codec—unicodec
Authors: Kinuhata K. , Nuspl P. , Kwan A. , Yamamoto H. , Murakami H. , Matsumoto S.
Published: July 2007

The UNICODEC, developed under the INTELSAT R & D Program, is a TV codec which can transmit and receive any standard signal of NTSC, PAL, or SECAM, by using 15 Mb/s or 30 Mb/s transmission rates (switchable) with two high quality sound channels and one voice circuit. These rates include rate 239/255 BCH FEC for video information. The codec uses the 4:2:2 digital interface for component coding based on CCIR Recommendation 601.

The UNICODEC can provide the flexibility to deal with the composite coding now needed in mixed analogue/digital networks, but can also handle either composite NTSC, PAL, SECAM or MAC (multiplexed analogue components), or digital component signals (Y, R‐Y, B‐Y) in the future.

The key technique used here is called MAP (median adaptive prediction) coding, which is one of the adaptive DPCM methods for accurate and simple control in high quality TV transmission; one prediction out of three (interframe, intrafield or interfield) is transmitted without the need for many control bits. There is also a refresh mode for burst error or synchronization recovery. The UNICODEC is expected to provide double capacity with higher quality pictures compared to conventional analogue transmission (FM in 18 MHz). Alternatively, smaller size antennas may be used.

This paper describes the objectives of the development of the UNICODEC, its main features and results of field tests.
Selection of gold and kasami code sets for spread spectrum CDMA systems of limited number of users
Authors: El‐khamy Said E. , Balamesh Ahmed S.
Published: July 2007

Spread spectrum code‐division multiple‐access (CDMA) systems are currently considered as very attractive alternatives to the more familiar FDMA and TDMA systems, especially in the presence of multipath fading and external interference. The problem of code selection in a CDMA system with a finite number of users is addressed in this paper. A simple and efficient method for the selection of finite code sets with relatively high processing gain from Gold and Kasami code families of relatively large sizes is described in detail. Selected code sets of period 63 are presented along with their overall average performance parameters for different number of users.
In‐orbit testing of digital regenerative satellite: The italsat planned test procedures
Authors: Saggese E. , Speziale V.
Published: July 2007

ITALSAT is the Italian pre‐operational satellite, funded by the National Council of Research, to be launched in late 1989. It will carry three payloads, the most innovative and challenging being a multi‐spot regenerative package providing the interconnection among six spots at 147Mb/s with SS TDMA access scheme.

In‐orbit tests (IOT) will be performed on this payload in order to verify, to the maximum possible extent, the radioelectric characteristics and the behaviour of the modems and baseband switching equipment. The importance of these measurements is two‐fold: incentive payment schemes can be applied for better‐than‐specified characteristics and the information obtained by the tests will permit gathering the information needed for the establishment to a domestic operational system.

The non‐transparent structure limits applicability of many classical RF measurements: the opportunity of adding some on‐board hardware to permit the testing of the most important parameters has been suggested. The design objectives have been to minimize the on‐board additional hardware complexity and to concentrate the test equipments on ground, in the IOT earth‐station. This paper illustrates the planned additional satellite hardware and the test procedures to be implemented for the in orbit testing.
Performance of fully variable demand assignment SS/TDMA satellite systems
Authors: Maral Gérard , Bousquet Michel
Published: July 2007

Fully variable demand assignment in a SS/TDMA satellite system requires frequent burst time plan changes with reconfiguration of the on‐board switch matrix state sequence. The burst managment presented in this paper assumes that bursts are not reconfigurated into new bursts during such burst time plan changes but merely shifted in time. The performance of this burst management procedure as obtained from simulations over three different networks is reported in terms of throughput gains, required signalling capacity and time required to change burst time plan.
The TDMA burst‐mode link analyser with least‐squares algorithm
Authors: Liu Yi‐Song , Feng Shi‐Qin
Published: July 2007

The burst‐mode link analyser with the decompositional least‐squares algorithm (BMLA/LS) is an attractive and novel computational approach for impulse response measurement and equalization of a QPSK/TDMA satellite communication channel. Analysis and simulation confirms it to be superior to the current BMLA/radar approach. This paper presents a brief and systematic introduction to the methodology of the subject, and to software simulation, system design and hardware implementation.
A comparison of the implementation and annual operating costs of IDR and TDMA in the intelsat system
Authors: Colby R. J. , Kwan A. K.
Published: July 2007

The outcome of a preliminary systems cost study which compares the cost of operating INTELSAT intermediate data rate (IDR) and time division multiple access (TDMA) stations under various conditions is reported. The differences in the annual cost of operating the two candidate methods over the range of 1 to 1000 terrestrial channels are derived under the conditions of no CME, DSI only and the use of DCME. For DCME the effect of one, two, three and four destinations per DCME is considered. The results show that while the initial cost of the TDMA equipment is higher than with IDR, the annual cost of operating the systems is dominated by the space segment costs. For this reason the greater bandwidth efficiency, inherent multidestinational capability and ease of capacity expansion of the TDMA system give it a lower annual operating cost, even at fairly moderate earthstation capacities (e.g. for DCME with two destinations TDMA becomes cheaper than IDR for capacities in excess of about 300 channels). There are attributes of both systems which will also influence the network planners' decision. The IDR system is modular in that costs associated with implementation are incurred more gradually than with the TDMA system. Furthermore, IDR is to a great extent an extrapolation of the current FDM/FM/FDMA practice. However, since the equipment costs are small compared to the space segment charges, it may prove advantageous to adopt the lowercost system as soon as possible. In addition, the TDMA system offers significant long‐term advantages of low‐cost expansion and the ability to reconfigure the system with minimal or no loss of traffic.
Principles and design of bidirectional optical isl using GaAlAs laser at λ = O·85 μm and direct detection PPM
Authors: Zhu Zhini
Published: July 2007

This paper gives a general introduction to bidirectional optical intersatellite links. The design, principles and link budget are presented, and the four subsystems—transmitter, receiver, optical channel and acquisition/tracking system—are described. GaAlAs semiconductor laser and a silicon avalanche photodiode are used as the optical transmitter and receiver. Pulse polarization position modulation is used to obtain a higher sensitivity. The acquisition/tracking signal is extracted from the top‐modulation data stream. The effect of background noise is analysed, and direct detection and heterodyne detection are compared.
Error correction, interleaving and differential pulse position modulation
Authors: Peile R. E.
Published: July 2007

This paper discusses the interaction of error, correction, interleaving and modulation format in relation to intersatellite communication by optical technologies, concentrating on the performance and design of pulse position modulation and a variant, differential pulse position modulation with Reed—Solomon codes, helical interleaving and various forecast strategies.
Functional specifications and evaluation of commercially available laser diodes for optical space links
Authors: Roux Michel , Chauve Denis , Keil‐Simon Geneviève
Published: July 2007

Commercially available GaAlAs laser diodes have been tested to predict their behaviour in intersatellite communications. Three types of device with various structures have been investigated: Sharp lasers, Hitachi lasers (single longitudinal mode emission in c.w. operation) and Ortel lasers (multi‐longitudinal modes). Two modulation schemes were applied to devices (NRZ and 4‐PPM), corresponding to the two possible modulation formats selected for ISL experiments. Each laser had an average power output of 30 mW, whatever the modulation mode. The output signal, emission spectrum and beam divergence were measured. A reduction in peak power was found with some devices. Multimode spectra were detected under 4‐PPM modulation.
Multi‐carrier demodulators for on‐board processing satellites
Authors: Yim W. H. , Kwan C. C. D. , Coakley F. P. , Evans B. G.
Published: July 2007

A study of the digital transmultiplexor element of an on‐board multi‐carrier demodulator (MCD) results in design data for various architectures (FFT, tree etc.) which can be applied to a wide range of applications. A detailed design based on the latter for a 4 × 16 kb/s MCD for the U.K. T‐SAT mobile OBP payload is presented. Implementation of the MCD using TMS320C25 signal processor technology has been performed and early test results are presented.
A modular multistage approach to digital fdm demultiplexing for mobile SCPC satellite communications
Authors: Göckler Heinz
Published: July 2007

A hierarchical multistage method (HMM) for digital demultiplexing of an FDM signal composed of L adjacent SCPC signals is described; L is preferably a power of two, here L=32. This HMM approach to FDM demultiplexing applies bandpass sampling and is based on the processing of complex‐valued signals by linear‐phase FIR filters, where at any stage of processing the respective signals are always oversampled by two. The simulation results fully confirm the predicted system performance. An electrical demonstration model constructed by cascading six identical specially designed signal processors is being built.
The development of intermediate data rate (IDR) digital transmission performance characteristics
Authors: Robusto Michael J.
Published: July 2007

The evolution of IDR digital carrier performance requirements, a summary of their characteristics, and some of the trade‐offs made in the selection of various IDR parameters are described in this paper.
Development of FEC and ESC performance characteristics for IDR carriers greater than 10 Mb/s
Authors: Loureiro Francisco , Koga Keiichiro
Published: July 2007

The requirement for restoration of high capacity fibre optic cables and the new tariffs approved for INTELSAT digital services has created a requirement to develop performance characteristics for IDR carriers greater than 10 Mb/s. This paper presents the trade‐offs used in this development, and estimates the coding gains needed to meet these requirements. A number of FEC schemes are evaluated and a rate 3/4 convolutional code with soft decision Viterbi decoding is selected. Engineering service circuits (ESC) performance characteristics for IDR carriers greater than 10 Mb/s are also presented.
The role of intermediate data rate (IDR) carriers in the intelsat system and their impact upon operational planning
Authors: Roach Peter W.
Published: July 2007

IDR carriers will provide a significant proportion of the services in the INTELSAT system within the next few years. A number of factors have been identified which must be considered when developing satellite operational plans, in order to ensure satisfactory operation of an integrated environment consisting of a number of different access techniques and modulation methods.
Some practical issues in the design and application of a VLSI FEC chip
Authors: Wang Qiang , Nicholson Robert D. , Onotera Larry Y.
Published: July 2007

Forward error correction (FEC) has become a general requirement for digital satellite communications. The dominant technology is the use of convolutional codes with Viterbi decoding. At MPR (Microtel Pacific Research), a single‐chip VLSI implementation of a convolutional encoder and Viterbi decoder for constraint length 7 has been completed recently. In the design and application of the FEC chip, several practical issues had to be addressed. These include the determination of the maximum variation in path metric, generation of a convolutional encoded sequence with maximum number of transitions for symbol timing recovery, use of a unique word to detect the phase ambiguity, use of a sliding window data quality monitor to resolve an ambiguous state, etc. This paper presents our solutions to these problems. Although specific results are given for the standard constraint‐length 7 code, the methods used to obtain these results are general and can be applied to other codes. Features and implementation of the VLSI FEC chip are also discussed.
Efficient ARQ schemes for error control of satellite channels
Authors: Fantacci Romano
Published: July 2007

In this paper, the performance of some efficient ARQ schemes which make use of repeated transmissions of the same data block and compound detection are analysed. The repeated transmission of the same data block involves repeated transmission of each symbol of the data block. At the receiving end, compound detection formed of a soft detection jointly with a classical hard detection is performed by using all the received copies of the same symbol. The throughput efficiencies for the proposed ARQ schemes are analytically derived in closed form and optimized with respect to the number of copies to be transmitted for each data block. It will be shown that the optimized ARQ schemes proposed in this paper achieve better performance than classical ARQ schemes, in particular under high error rate conditions.
Design of saw filters in SS‐FDMA routers for mobile satellite systems
Authors: Ananasso Fulvio , Deacon John M.
Published: July 2007

The present paper reports the design of a SAW filter bank consisting of 26 linear phase filters with bandwidths ranging from 60 to 2180 kHz, 0·5/40 dB transition width narrower than 30 kHz and stopband rejection as high as possible. Passbank amplitude and phase ripple limits are 1 dB and 4° peak‐to‐peak respectively. Three candidate filters of bandwidth 60 kHz, 400 kHz and 2·180 MHz were selected for detailed design, taking into account spurious effects such as acoustic regeneration and diffraction as well as technology limits. Since the physical length of a SAW filter—as any transversal (FIR) filter—is determined by (i) the required passband amplitude ripple, (ii) the stopband rejection level and (iii) the transition width, the steepness of the required passband‐to‐stop band transitions in these filters dictates their physical size to be unusually large, resulting in an overall size for each packaged filter of 360 × 38 × 17 mm, i.e. 14·2 × 1·5 × 0·7 inches. The electrical specifications are met by all but the 2180 kHz filter, whose shape factor, for a 30 kHz transition band, would be 1·027 : 1, beyond the state of the art. The filter bank has about 27 dB insertion loss per filter, plus roughly 14 dB (1 : 26) power split loss.
Land mobile communications in Ku‐band. Results of a test campaign on eutelsat I‐F1
Authors: Dutronc J. , Colcy J. N.
Published: July 2007

This paper presents and discusses the results of technical tests on land mobile communications conducted in June and July 1989 in Europe using a EUTELSAT satellite. The land mobile communication system under test was that already operated by QUALCOMM in the U.S.A. under the registered name OmniTRACS.

The field trial was organized in conjunction with the Signatories who expressed to EUTELSAT an interest in a full‐scale technical investigation of the system. The aim of the field trial was to evaluate the technical characteristics of the system and test its performance in different operating conditions.

The results establish the relationship between transmission performance (i.e. essentially the required number of transmission attempts in order to get a message through the communication channel), and the environment of the land mobile, the satellite transponder's mode of operations and the interference conditions.
The joint African radiometric propagation measurement programme
Authors: Arbesser‐Rastburg B. , Zaks C. , McCarthy D. K. , Rogers D. V. , Allnutt J. E.
Published: July 2007

This paper summarizes the principal aspects of a major co‐operative radiowave propagation experiment that was designed to collect data for improving rain attenuation prediction models for tropical Africa. A pressing need for such data had previously been identified by Resolution 79 of the CCIR. In a unique joint arrangement with three African governments, INTELSAT, COMSAT, the U.S. Agency for International Development, the U.S. National Telecommunications and Information Administration and the U.S. Telecommunications Training Institute (USTTI) collaborated in setting up a Ku‐band radiometric measurement campaign in Cameroon, Kenya and Nigeria. A brief historical overview is given, together with the major technical parameters of the sites and the equipment installed there. The anticipated characteristics of the three locations are outlined with regard to meteorological and propagation conditions, and some preliminary indications of the results are presented based on an inspection of the early event data.
Tropical rainfall drop‐size distribution
Authors: Maciel Leandro R. , Assis Mauro S.
Published: July 2007

Based on disdrometer measurements carried out in Brazil, this paper discusses the problem of rainfall drop‐size distribution in tropical areas and its effect on radiowave propagation at frequencies above 10 GHz. A comparison between Laws and Parsons and lognormal models is made. In spite of the best fit to the experimental data shown by the lognormal distribution, in the range from 10 to 20 GHz there is no significant difference between the two models. However, as the frequency increases this difference becomes larger and may be an important source of error in the design of both terrestrial and satellite links in low‐latitude regions. Similar results from Nigeria (Africa) are also taken into account.
Preliminary plans for a propagation experiment in Mali
Authors: Haidara Fatim , Pratt Timothy , Bostian Charles W.
Published: July 2007

Measurements of propagation effects on satellite down‐links to tropical locations are rare. This paper describes two experiments that will provide new and useful data for radiowave propagation in tropical Africa. A discussion of the African tropical climate is included that shows the wide range of rainfall patterns throughout the continent. Also, the broad distribution of climate in Mali, the West African country where the experiments will be located, is described. A rain‐rate measurement programme involving autonomous terminals based on tipping bucket rain‐gauges is presented. An experiment measuring the slant‐path attenuation of the 12·5 GHz beacon of the ESA satellite OLYMPUS is described. The paper also discusses how the measured data in both experiments will be relayed daily from Mali to Virginia Tech by the low earth orbit satellite VaSTAR.
M‐ary FSK with limiter discriminator integrator detection and DPSK with differential phase detection in a Rician Fading channel
Authors: Korn I.
Published: July 2007

We derive an expression for the error probability of M‐ary differential phase shift keying with differential phase detection and of M‐ary frequency shift keying with limiter discriminator integrator detection which is valid for Rician. Rayleigh and Gaussian channels.
Radiation analysis and errors associated with the monopulse operation of a satellite direction finder
Authors: Afifi Mostafa S.
Published: July 2007

This work describes the radiation performance of a novel concept for direction and location finding, using stationary satellite beacons. The received signals are processed with a monopulse four‐element array. The monopulse mode is generated using the phase excitation of the radiating elements. For accurate processing the radiation phase should correspond with the bearing angle around the boresight direction. Phase deviations, however, occur in this phase pattern owing to the discrete excitation of the elements. Therefore, detailed analyses are presented for this phase pattern, its attainable gain and the depolarization effects, in order to select the kind of array elements, and their spacings, which minimize the phase pattern deviations. The dipoles and the slots, as array elements, yield better phase performance, smaller size and simpler structures than horn radiators, at the expense of worse depolarization.
Advanced techniques for circuit multiplication: Celtic 3G
Authors: Aboaf P. , Bailly R.
Published: July 2007

The Celtic 3G is Alcatel CIT's new digital circuit multiplication system designed to enhance the cost‐effectiveness of long‐haul links by increasing their capacity by a factor of between 5 and 8. The Celtic 3G offers an effective, versatile solution to congestion problems on 2048 and 1544 kb/s digital transmission links.

The paper describes the compression modes used by Celtic 3G family to transmit the various types of signals (speech, voice band data, 64 kb/s digital data), the applications and the operating principles of the equipment.

A number of telecommunication administrations and agencies have adopted and will this year deploy the Celtic 3G because of its benefits, technical qualities and the savings which it will achieve on digital links.
The use of digital circuit multiplication equipment in satellite communications
Authors: Viklund Nils‐Erik , Nycander Claes
Published: July 2007

The use, within satellite communications, of low rate encoding (LRE) techniques, based on 24, 32 and 40 kb/s ADPCM coding, coupled with digital speech interpolation (DSI) to form a digital circuit multiplication equipment (DCME), is addressed in this paper. The need for a system simulation tool, in order to plan for and correctly use the DCME concept is identified. Results obtained with this simulation tool are presented. The simulation model makes it possible to predict the behaviour of the system from a quality point of view, with external conditions simulated to be very close to actual operating conditions.
Optimum processing of qpsk signals for site diversity
Authors: Sandström Henrik
Published: July 2007

For satellite communications systems which use frequencies above 10 GHz, rain and clouds attenuate signals severely, leading to an increase in bit error rate (BER) in digital links. This may be coped with by using two or more receivers on the ground, spaced far enough apart to avoid simultaneous rain outages. In this paper, a BER‐minimizing decision processor is derived for two receivers and QPSK modulation. In particular, it is applied to a linear attenuating transmission channel adding independent white Gaussian noise. It is found that gains of nearly 3 dB compared to a switched system are possible in down‐link limited cases.
Modelling direct sequence pseudonoise(dspn) satellite reception with directional antennas in the dense scatterer mobile environment
Authors: Amoroso Frank , Jones William W.
Published: July 2007

A geometric propagation model is developed for simulating the reception of direct sequence pseudonoise (DSPN) satellite signals by a directional or omni antenna in the dense scatterer mobile environment. The model is first validated for narrowband signals by a direct comparison of both simulated cumulative signal strength statistics and simulated diffuse Doppler spectra with classical theory. The model is then used to predict fading statistics for DSPN signaling, either with omni or directional antennas. As expected, the mitigation of fading is closely related to the ratio of DSPN chip duration to delay spread of the scatterer medium for both the omni and directional antennas.
Comparison of the simulated performance of a vsat satellite link with measurements
Authors: Mwanakatwe M. , Willis M. J. , Evans B. G.
Published: July 2007

This paper combines a number of features. First the simulation of the transmission performance of a Ka‐band VSAT system (CODE) is presented. The results are used to verify the systems design that was performed for CODE and to demonstrate that the implementation margin due to intermodulation noise, adjacent channel interference, filter ISI, amplifier non‐linearities and phase noise was sufficient. In the design of VSAT systems of this type phase noise was thought to be particularly important, and a new and detailed simulation of its effects is presented in the paper. For the first time, experimental measurements of system degradations have been taken on a VSAT system which have been used to verify simulation results. This was particularly important for the new phase noise simulation results and good agreement was obtained. An overall loop‐back experiment using the Ka‐band VSAT terminal with the Olympus satellite shows good agreement with the simulation results. Finally, the availability of experimental results has enabled us to compare the accuracy of TOPSIM III and BOSS simulations for the VSAT system. The paper indicates some shortcomings in the TOPSIM III simulation of phase noise and highlights the generally good agreement obtained with experimental results by the BOSS simulations.
ISDN and the digital satellite revolution
Authors: Pelton Joseph N.
Published: July 2007

The greatly increased capacity and capabilities of terrestrial fibre networks, current and future satellites bring forth key issues relative to ISDN and other advanced communications concepts. This paper explores a brief history of the development and characteristics of both satellite and fibre, together with a description of advanced satellite concepts. Key advantages and disadvantages of satellites are described and related to future communications environments. These analyses are then discussed relative to their impact and implications on the design and operation of ISDN networks.