bluuebunny/crossref_metadata_2025 huggingface dataset:
Satellite communication systems for domestic/business services
Authors: Perrotta G. , Losquadro G. , Giubilei R.
Published: July 2007

This paper is composed of two parts.

The first part addresses some topics associated to the implementation of FDMA/TDM systems for ‘business’ services applications, operating at Ka band.

A modular regenerative and processing satellite repeater, each module capable of handling up to 16 up‐link carriers in the 2 Mb/s range is considered. Available coding techniques were reviewed; concatenated codes seem highly interesting because of the high coding gains achievable with two simpler co‐decoding processes in series, and also because they lead to an implementation wherein the internal coder is installed on board the satellite, while the external one is installed in the user terminals.

The problem of keeping stable the up‐link carriers in the satellite demodulators is discussed and a compensation method is proposed.

Finally, simulation results of co‐decoding and carrier extraction performance are illustrated.

The second part concerns the implementation of a multifrequency TDMA system. This is a hybrid system whereby the access for up‐links uses time and frequency slots in a time‐frequency map. The adoption of a clock synchronous network allows a frame for which no preamble and guard time are inserted between the burst.

The error contributions and the performance of the clock synchronous network are assessed. A solution to the problem of fast phase/frequency estimation is proposed.

For a clock synchronous network fast algorithms suitable for frequency demultiplexing and detecting of the FDM signal could be adopted; a modular solution to the implementation of the demultiplexer and detector is proposed based on the use of an optimized matched filter; a multistage scheme minimizes the number of multiplications.
An on‐board processing satellite payload for european mobile communications
Authors: Evans B. G. , Casewell I. E. , Craig A. D.
Published: July 2007

The paper considers the application of satellite on‐board processing (OBP) technology for land mobile applications for possible introduction in the late 1990s. Initially a system outline is presented followed by a discussion considering the merits of OBP over conventional transparent payloads. The paper then presents an overview of the work being carried out as part of an ESA study. Some details on the critical parts of the system are also included.
Test results for on‐board burst‐mode CQPSK modem
Authors: Kazekami Y. , Sawada H. , Ishizu T. , Betaharon K.
Published: July 2007

An on‐board burst‐mode modem for coherent processing of a QPSK signal at 120 Mb/s is realized with small, low mass and low power consumption. This paper presents the hardware configuration and the various measured test data including physical characteristics. The overall performance through an earth station modem is also presented.
Non‐regenerative satellite switched FDMA (SS/FDMA) payload technologies
Authors: De Santis Pietro V.
Published: July 2007

Satellite switched frequency division multiple access (SS/FDMA) satellite systems are new adaptations of the basic FDMA architecture for multiple beam spacecraft. Present multibeam satellite systems feature on‐board interbeam connections operating on a transponder channel basis, e.g. 72 MHz. SS/FDMA on board connectivity is based on much narrower channels and consequently achieves a much better utilization of spectrum resources whenever connectivity requirements are of the order of fractions of a transponder bandwidth.

This work presents a critical analysis of various non‐regenerative SS/FDMA satellite systems, identifies the technological requirements to be met in order to achieve the practical realization of SS/FDMA on‐board processors and, finally, proposes two novel variable bandwidth variable centre frequency (VBVCF) demultiplexers with continuous and discrete reconfigurability.
VSAT Networks—an overview
Authors: Maggenti Mark , Ha Tri T. , Pratt Timothy
Published: July 2007

This paper examines the technology and constraints of very small aperture terminals (VSAT) networks, a special type of wide‐area thin‐route satellite network that represents a recent innovation in the field of satellite communications. VSAT network architectures suitable for both data and voice communications are studied in this paper. Several issues concerning the frequency of operations, that is, C‐band versus Ku‐band are examined, and trade‐offs between non‐spread spectrum and spread spectrum techniques, as well as modulation and multiple access schemes, are considered in detail. Link design examples are given to illustrate the performance of various types of VSAT networks.
Dielectric space frame radomes for satellite communications
Authors: Rwabona‐Katashaya S. , Evans B. G.
Published: July 2007

The cross‐polarization, signal attenuation and boresight shift for a number of dielectric space frame (DSF) radomes have been investigated using the induced field ratio method. It is shown that DSF radomes produce substantially less cross‐polarization than their metal counterparts. It is concluded that in view of INTELSAT's specification of 30.7 dB cross‐polar discrimination within an antenna's tracking beamwidth for frequency re‐use communication system antennas, DSF radomes, in particular those considered, would not yield appreciable system degradation. The general method presented is extendable to other radomes structures provided that connectivity information is available.
Ku‐Band satellite data networks using very small aperture terminals—part II: System design
Authors: Raychaudhuri D.
Published: July 2007

In this part of the paper on Ku‐band VSAT networks, the issue of overall system design is considered. After discussing possible system architectures, primary attention is given to the star network configuration in which customer‐premise VSATs communicate with a central hub station, co‐located with, or terrestrially connected to a host computer. The component elements of a Ku‐band star network for interactive data applications are discussed and the critical items from the point‐of‐view of performance, capacity and cost are identified. An analytical model for the network, which combines delay‐throughput characterization of the multi‐access inbound and TDM outbound channels with satellite link analysis is described. The analytical model is exercised over a range of typical system component, traffic model and performance objective scenarios to provide a set of general design guidelines. These guidelines are useful for evaluating the trade‐offs between key system elements (channel access unit, modem, VSAT antenna and satellite), VSAT traffic message length parameters and the performance objectives (average and peak network response time and availability). The results are used to address the issue of multi‐access protocol selection over a range of scenarios typical of 1.2 or 1.8m VSAT‐based interactive networks using current commercial Ku‐band satellites. The results show that interactive star networks are often limited by satellite power rather than bandwidth, so that the use of simple contention access for VSATs may not imply a significant system capacity penalty.
Effects of baseband predistortion at the transmitter on the performance of a DEQPSK satellite modem
Authors: Cheung S. W. , Clark A. P.
Published: July 2007

The paper presents the results of an extensive series of computer‐simulation tests to determine the effects of bandlimiting, nonlinear distortion with and without predistortion, and adjacent channel interference (ACI), on the tolerance to additive white Gaussian noise of a digital satellite modem. The modem transmits a differentially encoded quaternary phase‐shift keyed (DEQPSK) signal over a satellite link, where the high‐power amplifier (HPA) at the earth‐station transmitter may introduce AM—AM and AM—PM conversion effects into the DEQPSK signal, but the satellite transponder is linear. Four different bandwidths of the transmitted signal are tested, together with three different levels of output back‐off in the HPA at the transmitter. The predistorter operates on the baseband signal at the input to the modulator in the transmitter and assumes a prior knowledge of the HPA characteristics. ACI can be introduced into the transmitted DEQPSK signal by the corresponding DEQPSK signals, which occupy the two immediately adjacent frequency bands. The latter signals are assumed to have the same transmission rate and bandwidths as the first signal.

Various combinations of the different distortion and interference effects are studied, using an equivalent baseband model of the transmission system, and the arrangements selected are those achieving the most efficient use of bandwidth together with the best tolerance to additive white Gaussian noise. A surprisingly good performance is achieved.
Solid‐state laser cross‐link systems and technology
Authors: Begley D. L. , Kobylinski R. A. , Ross M.
Published: July 2007

Laser communications offer a viable alternative to r.f. communications for intersatellite links. High data rate, small antenna size, narrow beam divergence and narrow field of view are characteristics of laser communications that offer a number of potential advantages for system design. This paper presents an overview of solid‐state laser cross‐link systems and technologies.
An experimental optical link between an earth remote sensing satellite, spot 4, and a European data relay satellite
Authors: Arnaud M. , Barumchercyk A. , Sein E.
Published: July 2007

The implementation of an experimental optical link between a low earth orbit spacecraft (SPOT 4, of the French Earth Remote Sensing Programme) and a geostationary satellite (for which the European Space Agency is responsible) is described. This optical link is to be used for transmitting the SPOT 4 payload data stream at a rate of 50 Mb/s. These data will be relayed to a ground station through a feeder link in the Ka or Ku band.

This first model, on SPOT 4, will demonstrate the feasibility and performance of optical communications and will be used on a pre‐operational basis to relay image data. The second model, on SPOT 5, could be used on an operational basis in connection with the European Data Relay satellite.

The optical terminal uses a 20 cm diameter telescope with Ritchey Chrétien optics, a 30 mW GaAlAs laser diode and a silicon avalanche photodiode, the total weight being around 80 kg and the power consumption 120 W.
Optical ISL tracking considerations in meeting ISDN requirements
Authors: Peters Robert A.
Published: July 2007

Burst errors in an optical intersatellite link (ISL) are short term (of the order of a millisecond) degradations of the link due to antenna mistracking. These errors degrade the average bit error rate (BER), decrease coding gain, complicate calculations of tracking accuracy, and give rise to concern about the quality of the link for carrying digital signals. After reviewing previous work on these topics, the digital performance of the link is examined in terms of how these considerations affect the ability of an optical ISL to meet ISDN (Integrated Services Digital Network) criteria for an ISL. A link with on‐board regeneration is assumed. Since no allocation has yet been made for an ISL, an allocation of 25 per cent of the degradation permitted for the satellite link by CCITT Rec. G.821 and CCIR Rec. 614 is assumed here. It is found (1) that if the requirement derived from Rec. 614 is met, the requirements derived from Rec. G.821 are also met and (2) that an optical ISL should have little difficulty in meeting these requirements.
Optical intersatellite link with direct detection: The laser diode‐pumped Nd laser option
Authors: Arrigoni M. , Maddè R.
Published: July 2007

Following a brief introduction reviewing various laser systems suitable for ISL, a typical link budget for an optical ISL with a Nd laser is calculated. Laser diode pumped Nd lasers are described, and several host materials are considered. Modulation formats and typical receiver performances for direct detection are examined in order to compute the minimum transmitted power required for the proposed link. Results show that laser diode pumped Nd laser systems are competitive for optical ISL.
Stratospheric balloons as a testbed for optical space communications technology
Authors: Johann U. , Reiland W.
Published: July 2007

An 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

The 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

In 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

Devices 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

Adaptive 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

With 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

Over 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

Mercury 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.
Intermediate data rate (IDR) implementation examples
Authors: Robusto Michael J.
Published: July 2007

Various example earth‐station equipment configurations for IDR implementation are provided. These include FDM/FM to IDR conversion, single destination IDR operation and multi‐destination IDR operation.
A modem for IDR/IBS applications
Authors: Werth Andrew M.
Published: July 2007

This paper describes the features of the Hughes Network Systems' (HNS) Model 4100 digital modem and associated switch‐over equipment developed in response to the latest IDR performance specifications.
Digital modulation/demodulation equipment for the intelsat intermediate data rate (IDR) service
Authors: Robinson P. F.
Published: July 2007

This 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

An 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

This 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

A 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

A 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

Market 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

One 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

Severe 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

SAW 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.
GHz‐range surface acoustic wave interdigital transducers and applications
Authors: Yamanouchi Kazuhiko
Published: July 2007

GHz‐range SAW interdigital transducers, unidirectional transducers and SAW filters are described. Also, new fabrication technologies which can achieve higher operating frequencies are presented.
A technique for the fine longitude control of a geostationary satellite as demonstrated on insat‐1B
Authors: Kale Pramod , Rangarajan S.
Published: July 2007

The 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

This 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

The 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

The 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

Measured 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.
11·6 GHz rain attenuation measurements in Peru
Authors: Dissanayake A. W. , McCarthy D. K. , Allnutt J. E. , Shepherd R. , Arbesser‐Rastburg B.
Published: July 2007

This paper presents the results of a Ku‐band propagation experiment conducted in a high‐rainfall‐rate region in Peru. Sky noise measurements were made with an 11·6 GHz radiometer over a period of 18 months. Simultaneous rainfall was also recorded with a tipping bucket rain‐gauge. The paper describes the experimental equipment, the characteristics of the measurement site, and the results obtained from the experiment in the form of long‐term distributions of rain rate and path attenuation. Duration statistics of attenuation are also presented.

In the absence of an absolute calibration of the radiometer in terms of the path attenuation, selection of the best medium temperature to be used poses a problem. For comparison, sky noise to path attenuation conversion was done with two medium temperatures, 280 and 290 K. When compared with model predictions, 290 K seems to be more appropriate for the climate concerned. Both the attenuation and fade duration statistics are found to follow a lognormal distribution fairly closely.
Doppler‐shift correction for a UQPSK satellite modem
Authors: Clark A. P. , Aftelak A.
Published: July 2007

The paper describes a novel development of a previously described technique for the measurement and correction of the Doppler shift (frequency offset) in a received UQPSK signal that has been transmitted over a satellite link. The satellite is here assumed to be in a non‐geostationary orbit, so that it introduces a large and time‐varying Doppler shift into the transmitted data signal. Correction of the Doppler shift must be achieved as soon as the satellite rises above the horizon and with no prior knowledge at the receiver of the transmitted data. Furthermore, under the given conditions, the signal/noise ratio can be very low and the Doppler shift very high. A non‐data‐aided technique has therefore been selected, capable of operating under seriously adverse conditions. Results of computer‐simulation tests are presented to measure the time taken to correct an initial Doppler shift of 5 kHz in the received UQPSK signal, at low signal/noise ratios.
Performance of a circular signal set in a regenerative satellite system employing TWTA or SSPA
Authors: Cheung S. W.
Published: July 2007

This paper presents the results of a computer‐simulation study of a (4,12) circular signal set for use over regenerative satellite links. The signal has a 16‐ary symbol alphabet. The satellite transponders and each of the earth‐stations use either travelling‐wave‐tube amplifiers (TWTAs) or solid‐state power amplifiers (SSPAs) for high‐power amplification. Several different earth‐stations are assumed to have simultaneous access to a given regenerative satellite, in an arrangement of frequency division mulitple access (FDMA). Thus, adjacent‐channel‐interference (ACI) can be introduced into the wanted signal by the immediately adjacent channels. The performances of the signal are compared to those of a 16‐ary differentially encoded‐quadrature‐amplitude‐modulated (16‐ary DEQAM) signal with a rectangular signal set and the results are used to determine the preferred signal set for spectrally efficient transmission over satellite links. It has been shown that, with TWTAs used for high‐power amplification and in the absence of ACI, the circular signal set has an advantage of about 3 dB over the rectangular signal set, at the bit error rate of 10−4. While in the presence of the ACI, the advantage is 2 dB. With SSPAs, the respective advantages become 0·7 and 0·5 dB.
The DTX‐240D digital circuit multiplication system
Authors: Murphy Ron
Published: July 2007

This paper describes the DTX‐240D digital circuit multiplication system (DCMS) offered by ECI Telecom. It will accept up to 240 × 64 kb/s trunks carrying either 64 kb/s voice, voice band analogue non‐speech signals, or digital data for transmission over a 2·048 Mb/s digital link. Over 1000 are currently ‘on‐line’ and carrying traffic.

The system comprises a pair of terminals, one on each side of the interterminal digital link (bearer). It will normally operate in the network at a concentration ratio of 5:1, in which case 150 × 64 kb/s trunks, carrying voice, voice band data or digital data can be concentrated into one 2·048 Mb/s bearer. The users are able to increase the number of trunks up to 240 per 2·048 Mb/s bearer, when time zone differences cause a spread of busy‐hour traffic carried on a single system. Each terminal will normally be located at an international switching centre (ISC) but may also be located at an earth‐station.

The system uses a DSI (digital speech interpolation) stage providing a 2·5:1 multiplication, followed by an additional 2:1 multiplication by means of ADPCM (adaptive differential pulse code modulation). In addition, the VBR (variable bit rate) technique is used to prevent clipping, due to overload congestion.

The system can also be used with 1·544 Mb/s digital bit streams (trunk side or bearer).
An efficient protocol for providing integrated voice/data services to mobiles over power‐limited satellite channels
Authors: Bose Sanjay K.
Published: July 2007

Various mobile satellite communication systems are being developed for providing integrated voice/data services over a shared satellite transponder which is power‐limited in nature. A common strategy is to use slotted ALOHA request channels to request channel assignments for voice/data calls from a network management station. To maximize efficiency in a system with a power‐limited satellite transponder, it is proposed that the bursty nature of voice sources be exploited by the NMS to ‘over‐assign’ channels. This may cause problems of inefficiency, potential instability as well as a degradation in the quality of service offered to the customers. Augmenting this with the introduction of simple state‐dependent control procedures provides systems which exhibit more desirable operational features. This approach is proposed and examined in this paper.
Frequency and time stability of GPS and glonass clocks
Authors: Daly Peter , Kitching Ian D. , Allan David W. , Peppler Trudi K.
Published: July 2007

The frequency stability and reliability of the clocks are critical to the success of the GPS and GLONASS programs. We will show some of the similarities and differences between the clocks involved in these two systems. Because both systems plan to be operational in the next few years, the data leading up to this operational stage is of significant interest. On‐board clocks and the stability of the master control clocks for these systems are analysed.

We will discuss the attributes of these two systems as time and frequency references. Their relationship to UTC will also be illustrated. More data over a longer period of time was available for the authors from GPS than from GLONASS. Even so it is obvious that both systems have matured. Though the GLONASS system was developed later, its overall clock performance has improved more rapidly. Some of the more recent GLONASS clock performance is at about the same level as that of the GPS clocks.

The analysis has yielded some very interesting contrasts, comparisons and changes in these systems that should be of great interest for time and frequency users, as well as for clock vendors and receiver vendors.
The german dfs and tv‐sat satellite control centre in usingen
Authors: Altmann Bernd , Damiano Antimo , Piani Gianguido
Published: July 2007

This paper describes the construction of the control centre for the satellites DFS Kopernikus and TVSAT of the German PTT Administration (DBP Telekom), with emphasis on the implemented technical solutions for monitoring and control. The space and ground segments of the two satellite systems are briefly described in relation to the TT&C operations carried out at the control centre.
We should not pool diagnostic likelihood ratios in systematic reviews
Authors: Zwinderman Aeilko H. , Bossuyt Patrick M.
Published: July 2007

Some authors plead for the explicit use of diagnostic likelihood ratios to describe the accuracy of diagnostic tests. Likelihood ratios are also preferentially used by some journals, and, naturally, are also used in meta‐analysis. Although likelihood ratios vary between zero and infinity, meta‐analysis is complicated by the fact that not every combination in ℜ+ is appropriate. The usual bivariate meta‐analysis with a bivariate normal distribution can sometimes lead to positive probability mass at values that are not possible. We considered, therefore, three different statistical models that do not suffer from this drawback. All three approaches are so complicated that we advise to consider meta‐analysis of sensitivity and specificity values instead of likelihood ratios. Copyright © 2007 John Wiley & Sons, Ltd.
Analysis of recurrent event data with incomplete observation gaps
Authors: Kim Yang‐Jin , Jhun Myoungshic
Published: July 2007

In analysis of recurrent event data, recurrent events are not completely experienced when the terminating event occurs before the end of a study. To make valid inference of recurrent events, several methods have been suggested for accommodating the terminating event (Statist. Med.1997;16:911–924;Biometrics2000;56:554–562). In this paper, our interest is to consider a particular situation, where intermittent dropouts result in observation gaps during which no recurrent events are observed. In this situation, risk status varies over time and the usual definition of risk variable is not applicable. In particular, we consider the case when information on the observation gap is incomplete, that is, the starting time of intermittent dropout is known but the terminating time is not available. This incomplete information is modeled in terms of an interval‐censored mechanism. Our proposed method is applied to the study of the Young Traffic Offenders Program on conviction rates, wherein a certain proportion of subjects experienced suspensions with intermittent dropouts during the study. Copyright © 2007 John Wiley & Sons, Ltd.
Countercurrent distribution studies on fat soluble plant pigments
Authors: Lancaster Catherine R. , Lancaster Earl B. , Dutton Herbert J.
Published: July 2007

Chlorophyll‐a, chlorophyll‐b, and carotene have been used to study the operation of countercurrent distribution apparatus. An incomplete separation of the chlorophylls was obtained by the use of the 25‐tube Craig apparatus, but nearly complete separation of the chlorophyll and carotene pigments resulted. Degree of separation can be estimated by the modification of the equation of Martin and Synge which follows:
urn:x-wiley:0003021X:media:aocs0386:equation:aocs0386-math-0001

Comparisons were made between the degree of separation predicted by these formulae and that calculated by the use of the binomial expansion. The utility of such predictions is illustrated by the problem of separating plant pigments. A nomographic solution of these equations is presented to facilitate their application.