bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stratospheric balloons as a testbed for optical space communications technology
Authors: Johann U. , Reiland W. 
Published: July 2007

AbstractAn experimental optical communications link between two stratospheric balloons is proposed as an intermediate step from limited ground laboratory tests to costly space operations. Such an experiment can overcome many environmental constraints encountered on the ground, and allows all measurements to be made directly in the antenna far field. Early performance demonstrations are possible which allow experimental trade‐offs between alternative technologies and the verification of concepts, critical system parameters and subfunctions under near space conditions.
Interface between an optical communications system and the host spacecraft
Authors: Barry J. D. 
Published: July 2007

AbstractThe current state of development of optical communications systems for intersatellite data transfer has reached an advanced level, with on‐orbit operations planned for the early 1990s. The technology and engineering aspects of the development of the optical system have been evaluated in some detail and are widely known, but the interfaces between the optical system and the host spacecraft are not as well understood. Many aspects of the optical interfaces have been identified, are currently under investigation and are discussed here. These include the interface support needed from the host spacecraft, such as thermal, electrical, mechanical, optical, radiation protection and contamination control; spacecraft attitude and vibrational stability; spacecraft level interface testing, such as EMI/EMC, vibration and thermal vacuum tests; and lifetime and reliability testing.
Alternatives for on‐board digital multicarrier demodulation
Authors: Re Enrico Del , Fantacci Romano 
Published: July 2007

AbstractIn this paper alternatives for digital multicarrier demodulators (MCD) suitable for advanced digital satellite communications systems are presented. The MCD permits the direct on‐board interfacing of FDMA and TDM communication links by digital signal processing techniques. Two main functions are implemented by a MCD: demultiplexing (DEMUX) and demodulation (DEMOD). We focus here only on a digital implementation of the MCD, looking at its advantages, flexibility, better performance and VLSI integrability.The DEMUX may be implemented in a number of ways: the analytic signal method, fast Fourier transform with polyphase network technique, or multistage methods. For all the implementation methods considered it is shown that a certain degree of integration of DEMUX and DEMOD functions is possible. To this end, in the proposed MCD schemes the receiver pulse‐shaping filter has been integrated in the DEMUX structure, reducing the overall implementation complexity. It is shown that, for the per‐channel structure based on the analytic signal method, a highly modular and flexible implementation can also be achieved.Coherent demodulation is used to reduce the signal‐to‐noise ratio required to achieve a specified bit error rate. The coherent demodulation is carried out by using the maximum likelihood (ML) estimation method. Two different approaches to receiver synchronization have been studied. For the first, the carrier phase and symbol timing estimates are independently derived by suitable techniques. The second approach makes use of the maximum a posteriori probability method to estimate both the carrier phase and symbol timing of the receivied signal. In particular, for this technique it is shown that, by a suitable choice of the architecture of the digital coherent receiver, the ML demodulator can be integrated in the joint carrier and clock recovery circuit, with no increase in the overall system complexity.The digital architecture of the proposed MCD can be adapted to different digital modulation techniques. However, here we consider only the application for QPSK signals, as this modulation scheme is the most promising for digital satellite communications.A theoretical analysis and computer simulation have been used to evaluate the performance degradation of the proposed MCD, including finite‐arithmetic implementation effects.
On‐board digital signal processing technologies for present and future SCPC systems
Authors: Kato Huzo , Ohtani Kohichi , Kohri Takehru , Morikura Masahiro , Umehira Masahiro , Kubota Shuji 
Published: July 2007

AbstractDevices and architectures for on‐board SCPC (single channel per carrier) multi‐carrier demodulators suitable for use in satellites to be launched between the present and the year 2000 are discussed in the light of trends in the development of device technology towards lower on‐board weight and power consumption. It is shown that at the present time (equivalent to about 1990 for on‐board use).The choice of demodulation scheme depends on the number of channels available for regeneration on board the satellite. The total weight and power consumption for several suitable on‐board multicarrier demodulation schemes are predicted for 1990, 1995 and 2000, as functions of the number of channels to be regenerated.
A technique for estimating the throughput of adaptive TDMA fade countermeasure systems
Authors: Barton S. K. , Dinwiddy S. E. 
Published: July 2007

AbstractAdaptive TDMA is a member of the ‘Shared Resource’ branch of the Fade Countermeasures family. It attempts to maximize the throughput of a satellite channel by varying the data‐rate used by a number of transmitters according to the signal‐to‐noise ratio at the receivers. The highest possible transmission rate is used on un‐faded links so that the traffic is passed in the shortest possible bursts. This leaves the maximum fraction of the TDMA frame free for faded links to use a lower transmission rate giving rise to longer bursts. This process is transparent to the end‐user equipment, which operates at a fixed data‐rate.A new model of rainfall distribution in both area and time, based on data collected by a weather radar in Northern Italy, has been generated to analyse the performance of A‐TDMA. Taking account of all the signalling overhead and dynamic effects needed to reconfigure the system under rapidly varying rain distribution, capacity enhancement factors of 7 to 14 compared to the conventional design approach were calculated.
Computer‐aided evaluation of propagation impairment restoration techniques
Authors: Harverson M. , Brunt T. R. 
Published: July 2007

AbstractWith the increasing need for efficient exploitation of the 14/11 and 14/12 GHz frequency bands, the satellite link designer is faced with the problem of designing communication links in an environment where propagation impairment can be severe. In order to provide a communication service which will meet the desired quality and availability objectives, the designer may choose to employ any of the numerous propagation impairment restoration techniques which have been implemented or proposed in the literature. To determine the optimum technique for a given purpose requires a detailed technical and economic comparison of the candidate restoration schemes with specific reference to the defined service objectives. This paper details a computer program, IMPRES, which has been designed to provide a consistent and reproducible basis for evaluating impairment restoration techniques. The program draws on a knowledge‐base containing a profile of each restoration scheme which includes information such as the cost of implementation, the impact on the network operators and users, and the technological and economic risk associated with each scheme. The software design is such that this knowledge‐base may be easily updated and extended to accommodate advances in technology and changing costs, thus ensuring that the unified approach to the restoration technique selection problem provided by IMPRES remains valid in the rapidly changing satellite communication environment.
Implementation of intelsat IDR operation
Authors: Brown G. A. , Smith C. A. M. 
Published: July 2007

AbstractOver the next few years INTELSAT IDR carriers are expected to replace analogue FDM/FM carriers carrying trunk public switched telephony traffic. This paper describes the activities necessary to implement INTELSAT IDR operation into an existing or new earth‐station. The operational planning aspects discussed include the initial traffic and marketing forecasts to determine the IDR carrier requirements, use of DCME, the type of signalling system to be used and the interfaces with the terrestrial network, including synchronization. Typical earth‐station equipment configurations for IDR operation are described, and the design options that should be considered for the DCME, IDR modem, frequency converters, HPA and control and monitor systems are discussed.
Transmission of intermediate data rates: The mercury experience
Authors: Harman M. W. 
Published: July 2007

AbstractMercury Communications Limited was granted a telecommunications licence at a time when INTELSAT was beginning to introduce transmission methods using intermediate data rates. As a new operator with no existing earth‐stations, Mercury took the opportunity to procure equipment which would comply with the latest specifications for digital services. This paper describes the various operational needs and engineering design considerations that were necessary in order for earth‐station equipment to meet the requirements.
Digital modulation/demodulation equipment for the intelsat intermediate data rate (IDR) service
Authors: Robinson P. F. 
Published: July 2007

AbstractThis paper describes the design of a completely new satellite modulation/demodulation equipment, the Marconi P3801, aimed specifically at the INTELSAT IDR service.The major requirements for the design and the factors influencing the implementation approach are discussed, and an equipment description is presented. The equipment described includes not only the modulator and demodulator, but also the associated redundancy switching and remote control equipment.
An analytic expression for the magnitudes of the signal and intermodulation outputs of an ideal hard limiter, assuming n input signals plus gaussian noise
Authors: Comparetto G. M. , Ayers D. R. 
Published: July 2007

AbstractAn expression is derived that gives the output fundamental and intermodulation product magnitudes for an ideal hard limiter, for the case of n input signals plus Gaussian noise. The expression is derived by building upon previous work by Shimbo4 to account for the Gaussian noise input. The expression is implemented in a computational tool. Results are generated and are compared with data generated by Jain5 for three‐signal suppression, and by Blachman11 for the functional relationship between the output and input SNR for a bandpass limiter. In all cases, the data generated agree extremely well with published results.
On the definition of compandor advantage and its analytical calculation
Authors: Albuquerque José Paulo A. 
Published: July 2007

AbstractThis paper reviews several objective definitions of compandor advantage, and singles out one which is directly related to subjective measurements available in the literature. An analytical expression for compandor advantage under this definition is derived, taking into account the presence of noise at the compressor input. Values of compandor advantage computed from this expression are compared with subjective measurements.
SS/TDMA time‐slot assignment with knowledge‐base and prolog implementation
Authors: Pomalaza‐Ráez Carlos A. 
Published: July 2007

AbstractA software production system for the generation of time slot assignment plans for SS/TDMA systems is proposed and implemented. The approach used in this system conveniently combines algorithms derived for ideal configurations with heuristic procedures that are needed to account for conditions present in real systems. Algorithms that produce plans with a minimum number of switchings and minimum traffic transmission duration can now be easily implemented. The assignment plans obtained are as efficient as those previously reported when the assumptions are the same. The proposed production system, however is capable of handling a much larger variety of constraints and heuristic procedures for which no efficient solutions have been reported.
The development of a coded 8 PSK modem using digital signal processors
Authors: Heron R. , Marston P. , Garrett P. , Reece I. , Stevens R. 
Published: July 2007

AbstractA prototype 64 kb/s coded eight phase shift key (C8PSK) modem has been successfully developed using a combination of conventional analogue circuitry and software‐based digital signal processing. The C8PSK scheme is fully compatible regarding interference criteria with existing satellite FDMA access requirements and offers more efficient use of the satellite resource than conventional quaternary PSK (QPSK) systems. The C8PSK unit may either maintain channel performance with a lower satellite power requirement or improve the user bit error rate (BER) without the need for extra satellite power or bandwidth. The prototype modem was developed in a general way so that other PSK modulation schemes could be accommodated by replacing PROM units. Software processing also allows adaptive operation which adjusts the processing technique to optimize operation for a degraded signal‐to‐noise environment.
Saw chirp filter technology for satellite on‐board processing applications
Authors: Shaw M. D. , Miller N. D. J. , Malarky A. P. , Warne D. H. 
Published: July 2007

AbstractMarket growth in the area of thin route satellite communications services has led to consideration of non‐traditional system architectures requiring sophisticated on‐board processing functions. Surface acoustic wave (SAW) technology exists today which can provide implementation of key on‐board processing subsystems by using multicarrier demodulators. This paper presents a review of this signal processing technology, along with a brief review of dispersive SAW device technology as applied to the implementation of multicarrier demodulators for on‐board signal processing.
Saw and digital technologies in mutlicarrier demodulators
Authors: Saggese Enrico , Chiassarini Giuseppe 
Published: July 2007

AbstractOne key technology, for the implementation of future on‐board processing payloads, is the multicarrier demodulator (MCD). The MCD is instrumental in allowing FDMA/TDM access schemes which optimize the use of on‐board and ground resources in VSAT networks. This paper deals with the analogue and digital implementations of MCD, trying to assess the fields of application of each of the two technologies.
Saw filter technology in support of mobile communications at ESA
Authors: Coirault R. , Benedicto J. 
Published: July 2007

AbstractSevere RF spectrum limitations imposed by international regulations make filtering, and principally channel filtering, a key parameter of the mobile satellite service. About 30 MHz is available at L‐band for maritime, aeronautical and land mobile users, and must be shared between all potential service providers! Furthermore, this band must also accommodate signals with characteristics as dissimilar as: data at low and high bit rates, digital and analogue voice. Even worse, the transmissions are to be done with different categories of users, having terminals with G/T in the range of −4 to −24 dB/K.If the satellite payload provides a global earth coverage the RF spectrum will have to be channelized so that the various types of signals can be efficiently handled. This is what happens in the return transponder of the INMARSAT second‐generation satellite.If, as anticipated for future mobile satellite systems, spot beams are implemented, further channelization becomes necessary to provide the maximum of flexibility in the channel to beam allocation.In either case, a minimum of bandwidth can be wasted in the guardbands, while at the same time hardly any distortion is to be tolerated in the useful passband.The present article will illustrate, with two examples, how these drastic filtering requirements can be best fulfilled with surface acoustic wave technology.
The use of saw oscillators to suppress fm noise in local oscillators for on‐board satellite applications
Authors: Farr A. N. 
Published: July 2007

AbstractSAW oscillators can provide fundamental frequency operation to above 1·5 GHz, with stability and FM noise performance approaching that offered by bulk crystal oscillator technology. Their high fundamental frequency, small size and rugged construction gives SAW technology a unique capability at UHF and microwave frequencies.The low FM thermal noise floor associated with fundamental frequency operation can be combined with the stability and low close‐to‐carrier noise of multiplied bulk crystal oscillators by locking a high frequency SAW oscillator to a bulk crystal reference. SAW oscillator stability is compatible with conventional phase‐locked‐loop techniques and also with injection lock stabilization, and their own low close‐to‐carrier FM noise ensures that such locked sources exhibit minimum phase noise. Furthermore, locked oscillator phase noise is not significantly degraded when extreme operating conditions, such as those experienced in space applications, demand a reduced SAW device Q for reliable locking using either technique.Use of a PLL avoids any need for reference frequency multiplication, and provides additional design flexibility with respect to reference frequency selection and phase noise optimization. Injection locking offers design simplicity and uses fewer frequency control components, which can contribute additional noise in PLL sources.
A technique for the fine longitude control of a geostationary satellite as demonstrated on insat‐1B
Authors: Kale Pramod , Rangarajan S. 
Published: July 2007

AbstractThe possibilities of finer longitude control of a geostationary satellite are studied with a view to providing insight into the problem of co‐location of satellites. It is shown that for a three‐axis stabilized satellite such as INSAT‐1B, placed close to an equilibrium longitude, the propellant expenditure for satellite attitude control is considerably larger than that required for longitude drift control. An experiment was conducted on INSAT‐1B in which the forces arising from the attitude control thrusters are optimally used to counteract the force due to the solar radiation pressure thereby reducing the perturbations on the orbital eccentricity vector. This is accomplished by suitably switching between the redundant attitude control thrusters located in the positive and negative roll faces of the satellite. The extent to which the effects of the solar radiation pressure are nullified is quantitatively estimated from the observed behaviour of the eccentricity vector. Without any recurrent propellant expenditure it is shown that it is possible to restrict the longitudinal excursions to nearly half of the normally allocated ±0·1° longitude band.
Propagation requirements for the performance evaluation of advanced satellite systems with shared resources
Authors: Barbaliscia F. , Paraboni A. 
Published: July 2007

AbstractThis paper concerns the subject of future satellite telecommunication systems in the 30/20 GHz bands, for which an on‐board common resource is envisaged, to be temporarily assigned to earth‐stations undergoing severe weather conditions, as a means of alleviating the effect of strong fades due to rain. The design of such systems is significantly dependent upon the spacial distribution of rain across a very wide range of distances. Of particular importance is the probability that certain thresholds of attenuation, or equivalent point rain intensity, are exceeded simultaneously at various sites. Joint probabilities of exceedance are pointed out here as a primary objective for the future propagation activity in this field. The paper shows how they can be used to determine the system performance both in terms of probability that the number of requests exceeds the satellite capability and in terms of probability that a given station is not helped because all the resources are engaged.
CCIR data for slant‐path propagation in tropical regions: A critical review
Authors: Hughes Kevin A. 
Published: July 2007

AbstractThe development of methods for predicting the effects of the troposphere and ionosphere on Earth‐space paths is a topic of major interest in the work of CCIR. A principal objective is that the methods have world‐wide applicability and, being essentially empirical in nature, their development relies on the availability and voluntary contribution of world‐wide data, as well as on a knowledge of the global behaviour of the propagation mechanisms involved.Despite some advances in recent years, CCIR propagation prediction methods continue to lack universal applicability, in particular in low latitude tropical areas. This is largely due to a shortage of measurement data for the regions concerned; hopefully, this situation is changing in view of recent efforts to establish appropriate propagation experiments.The paper reviews the current status of CCIR propagation data and information relating to the design of space telecommunication systems in tropical regions, making close reference to the studies and texts of CCIR Study Groups 5 and 6 (Propagation in non‐ionized and in ionized media, respectively). Shortcomings in the available information and the lack of general world‐wide applicability of the models, highlight the propagation effects for which further data are still required.
Modelling attenuation by rain in tropical regions
Authors: Crane Robert K. 
Published: July 2007

AbstractThe data in the CCIR data banks were employed for a statistical study of the relative performance of several rain attenuation prediction procedures in temperate and tropical regions. The results show that the models worked well, in general, when used for prediction at latitudes more than 30° from the equator, but, in the equatorial region, significant prediction errors were observed for all the models. Three sources of error were discovered. The most important is the use of too few rain climate zones to span the wide range of rain conditions present in the equatorial region. The second is an inadequate procedure for taking the naturally occurring vertical variations of specific attenuation into account. Finally, for the CCIR attenuation prediction model, the use of a universal shape for the cumulative distribution of path attenuation must be called into question.
Frequency scaling of slant‐path attenuation in tropical regions
Authors: Bowthorpe B. J. , Allen G. H. , Kikkert C. J. , Allnutt J. E. , Arlett P. L. 
Published: July 2007

AbstractMeasured slant‐path attenuation data currently available do not cover every eventuality, thus requiring the use of scaling algorithms to produce estimates of the transmission parameters at a particular site. Several multiple frequency propagation experiments have been conducted over the same path, and the resultant data have been used to derive frequency‐scaling models of path attenuation. Most of these experiments have been conducted in temperate latitudes, and there is some doubt that the scaling models will fit other latitudes, particularly those subject to severe rain climates.James Cook University of North Queensland, Australia has been operating a number of radiometers as part of an experiment conducted for INTELSAT. The radiometers used in this experiment operate at 7·5, 11·6, 19·5 and 28·5 GHz with a common azimuth and an elevation angle of 63°. This paper compares the results at the various frequencies with an existing frequency‐scaling model and comments on the comparison.