bluuebunny/crossref_metadata_2025 huggingface dataset:
Required protection ratios for co‐frequency pal fm tv transmissions
Authors: Harverson M. , Dutronc J. , Dobbie W. , Court B.
Published: July 2007

This paper contains the results of a measurement campaign to determine the protection ratio requirements for PAL FM TV satellite transmissions in a form suitable for direct application in satellite planning exercises.

The following cases were considered in the study:

the mutual interference between two co‐frequency PAL TV signals frequency modulated using a deviation sensitivity of either 16 MHz/V or 25 MHz/V

the interference effects created by two independent co‐frequency PAL TV carriers interfering with the same victim PAL TV carrier, with all signals frequency modulated using a deviation sensitivity of 25 MHz/V.

Protection ratios were assessed with a wide variety of different conditions assumed for the wanted and interfering signals, such as the target picture quality and the operating carrier to noise ratio. The analysis of the results indicates that the required protection ratio is dependent upon some of the study parameters such as the picture content of the wanted signal. Protection ratio guidelines are derived on the basis of this analysis for co‐frequency interference into PAL FM TV signals. The results also confirm that, for planning purposes, multiple interfering signals can be treated by addition on a power basis.
Fault tolerance of on‐board digital signal processing circuits
Authors: Raghunandan K. , Coakley F. P. , Evans B. G.
Published: July 2007

The paper is organized in four sections. The first section introduces the nature of faults as well as their causes. The methods used to identify faults and the actions necessary to correct the situation are outlined. The second section identifies the different fault tolerance approaches to conventional computational circuits and the DSP circuits. Current research work in the area of fault tolerance of FFT, signal processing and VLSI circuits involving systolic arrays is reviewed. Since some of the techniques do not involve error correction, reconfiguration of the circuit after error detection becomes necessary and a brief look at the relevant reconfiguration strategies is appropriate. Software fault tolerance is introduced and some work applicable to computations in general is reviewed. The implementation of the methods and its consequences are described in the third section. Concluding remarks form the final section.
Spread SCPC/FDMA, spread TDMA/FDMA and SSMA/FDMA transmission through A non‐linear satellite channel with an earth‐station off‐axis emission constraint
Authors: Albuquerque José Paulo A. , Sampaio‐Neto Raimundo
Published: July 2007

This paper analyses and compares possible access schemes to be used in satellite networks with a large number of small earth‐stations. Basically, frequency division (FDMA), time division (TDMA), and spread spectrum multiple access (SSMA) are considered. For TDMA, one single carrier originated in one particular earth‐station is transmitted in each sub‐band and therefore a single‐channel‐per‐carrier system results (SCPC/FDMA). For TDMA and SSMA, it is assumed that groups of earth‐stations using either of these access schemes share the full available band in FDMA. The corresponding systems are thus TDMA/FDMA and SSMA/FDMA. Moreover, for SCPC/FDMA and TDMA/FDMA individual carriers may be spread to the extent that the available bandwidth is always fully occupied. Spectral efficiencies for these three access modes (Spread SCPC/FDMA, Spread TDMA/FDMA and SSMA/FDMA) are computed and compared for transmission through a non‐linear satellite channel and optimum operating points for the non‐linear amplifier are also determined. Comparisons are also performed for the situation in which transmitting earth‐stations are bounded to obey an off‐axis emission constraint.
Diversity reservation ALOHA
Authors: Chung In‐Hang , Rappaport Stephen S.
Published: July 2007

A multiaccess protocol suitable for packet satellite broadcast channels is introduced in this paper. The proposed protocol, called diversity reservation ALOHA (DRA) combines the essential features of announced retransmission random access (ARRA). diversity ALOHA, and a reservation scheme with a slotted ALOHA reservation channel to achieve the goals of improved delay‐throughput characteristics and high channel utilization. Two versions of DRA protocols are analyzed. In scheme 1, called DRA with reservation cleared (DRA‐RC), no global queue information is required for a user to access the channel. In this version, even a successful transmission of reservation requests will be cleared from the system if it causes overflow. The second scheme, called DRA with reservation delayed (DRA‐RD), establishes a global queue distributed at users' terminals, so that users with successful transmission of reservation requests are assured of access rights although transmission may be delayed to later fames. Important system performance measures, such as activity‐factor‐throughput characteristics, for DRA‐RC and DRA‐RD are compared with those of ARRA. Examples of numerical results show that with system parameters properly chosen, substantial increases in attainable channel utilization are possible. Furthermore, the use of diversity for reservation allows a smaller packet delay especially under light traffic conditions. The analysis is validated in light of the simulation results.
The role of satellite communication in the ISDN era
Authors: Chitre D. M.
Published: July 2007

Satellite communications can play an important role in provisioning the next‐generation telecommunications services and networks, provided that the protocols specifying these services and networks are satellite‐compatible. After a brief discussion of narrowband circuit and packet mode integrated service digital network (ISDN) services, the paper focuses on emerging standards in frame relay, broadband ISDN (BISDN) and universal personal telecommunications (UPT). The specific parameters and procedures of frame relay and BISDN protocols which are affected by a satellite delay are identified, and congestion and resource management functions for frame relay and BISDN are discussed in detail. Specific ground functions and possible on‐board functions are identified as potential candidates for implementation via neural network technology. Finally, the implication of UPT standards on satellite networks is discussed.
International fixed satellite systems in synchronous digital hierarchy transport networks
Authors: Oei W. S. , Tamboli S.
Published: July 2007

This paper discusses functional and architectural aspects and suitable networks scenarios for the integration of international fixed satellite systems, such as the INTELSAT system, in and between digital networks implementing the new CCITT synchronous digital hierarchy (SDH). The paper presents SDH transmission network functional requirements, and combines them with current and anticipated future FSS operational requirements. It is shown that integration permits the use of SDH functions and features for enhanced network service provisioning by FSS in the international network fabric, and leads to new FSS system design criteria.
Multilayer phase correcting fresnel zone plate reflector antennas
Authors: Guo Y. J. , Barton S. K.
Published: July 2007

Owing to its flat nature and light weight etc., the Fresnel zone plate antenna is becoming very attractive for such applications as DBS reception and receive‐only VSAT. The disadvantages of low efficiency and high sidelobes of the simple and the phase reversing zone plates can be improved by using phase correcting techniques. In this paper, a systematic investigation on the efficiency and sidelobe performance of subzone phase correcting zone plate antennas is presented. The design of a form of multilayer phase correcting zone plate reflector is described. A quarter‐wave zone plate reflector constructed with three dielectric layers and metallized rings is reported, with measured peak efficiency of 55 per cent.
Increasing the up‐link CW interference immunity of non‐coherent direct sequence pseudonoise (DSPN) reception with on‐board processing
Authors: Amoroso Frank , Bricker Jacob L.
Published: July 2007

The adaptive threshold A/D converter is by now a familiar technique for increasing the CW interference immunity of coherently detected direct sequence pseudonoise (DSPN) spread‐spectrum signals, especially where the frequency of the CW interferer may be changing so rapidly and over such a large portion of the signalling bandwidth that well known spectrum excision techniques prove ineffective. The present paper extends the theory to the case of non‐coherent reception of direct sequence pseudonoise (DSPN) signals. The A/D converter is found to perform well in both CW and Gaussian interference. Conversion gain is seen to persist even if the interference is intentionally pulsed at an optimally reduced duty factor (from the interferer's point of view) in the attempt to confuse the adaptive threshold. The specific case of 32‐chip data symbols is treated, wherein the adaptation is applied strictly to individual symbols. In some cases these restrictions will actually improve performance.
Analytical calculation of bistatic radar cross‐sections for rain scatter problems
Authors: Sadeghzadeh R. A. , Glover I. A. , McEwan N. J.
Published: July 2007

A formula is derived for the effective bistatic radar cross‐section of a rain cell with Gaussian reflectivity profile assuming antennas with Gaussian radiation patterns. The size and location of the rain cell are arbitrary, as is the bistatic scattering geometry. The expression is analytical, avoiding the need for numerical integration, and general, allowing treatment of cases with only partial beam intersection. Using a recently proposed model, sidelobe contributions and multiple cells embedded within widespread rain debris can be incorporated.
VSAT standards, status and applications in europe
Authors: Salomon J. , Bull S.
Published: July 2007

This paper is an attempt to present the current status of VSAT systems in Europe, based on two aspects.

1. The first part describes the actions conducted by the European Telecommunications Standards Institute (ETSI) for issuing proper technical standards. It is also explained how these standards are included in the general framework of the European legislation, the purpose of which is to create the conditions for a really open telecommunications market all over Europe, and more particularly to favour the implementation of independent (private) satellite communications networks, mainly for corporate services on a free competition basis, both as concerns operators and manufacturers.

2. The second part gives an overview of the actual implementation of VSAT networks in Europe and of the expected market trends.
A canadian perspective on vsats: Regulatory, technical and operational methodologies
Authors: Ghandeharian Hossein , Sahay Vishnu
Published: July 2007

VSAT systems have undergone a spurt of growth in recent years in Canada, particularly at Ku band using the star topology. This paper describes the regulatory, technical and networking issues in Canada. It starts out by describing the regulatory framework which has evolved in Canada to promote and foster the development and growth of such systems. It then provides a technical overview of the existing systems and possible evolution paths towards further enhanced capabilities. These include mesh networking and ISDN compatibility/capability. Finally, it discusses some end‐to‐end VSAT networking issues, including the interconnection of VSAT systems with the public switched network.
Trellis coded modulations with improved non‐coherent detection for personal and mobile satellite communications
Authors: Makrakis D.
Published: July 2007

In this work, the performance of trellis coded modulations with improved non‐coherent receivers is examined for application to personal and mobile satellite communications. The schemes are analysed and evaluated in additive white Gaussian noise, Rayleigh, Rician and shadowed faded channels. Evaluations have shown that the improved non‐coherent receivers are capable of providing considerable gains in performance as compared to the conventional differential receivers.
A comparison of fully digital quadrature modulation for modem systems
Authors: Acha V. , Carrasco R. A.
Published: July 2007

This paper presents and evaluates the results obtained by computer simulations of different current modulation techniques by the use of DSP‐based systems and computer simulations. The modulation‐demodulation methods evaluated herein are QPSK, OQPSK, MSK, λ/4‐QPSK and Q2PSK. The constant envelope property and the relatively high power efficiency of the above‐mentioned modulation techniques makes them very suitable for digital satellite and mobile radio communications. Digital algorithms for data‐decision, carrier phase offset and timing delay estimation for each of the modems are given. Maximum likelihood carrier phase recovery performances for the different quadrature phase modulations are compared and evaluated. Results in terms of BER performances and statistical properties of the synchronization procedures are shown for the AWGN channels. Computational loads of the different modem systems evaluated are also given.
Integrated global networks, tomorrow' communications today
Authors: Castro Jonathan P.
Published: July 2007

This article presents an overview of the concept of a multiple purpose global satellite network. It identifies some of the main needs of telecommunication services today, and projects the potential of future demands. It also describes the great possibilities of economic expansion and mass participation in the growth and prosperity of a nation, if basic telecommunication services are accessible on a global scale. The study suggests that the rapid recovery of capital investments on universal satellite networks lies in developing regions through cost‐effective service diversification.
The optical crossbar switch for signal routeing on board communication satellites
Authors: Baister G. C. , Gatenby P. V. , Aldridge N. , Stace C. , White H.
Published: July 2007

A switch matrix operating on baseband or microwave signals is a critical element of communications satellites employing multiple beam antennas and on‐board switching. Optical switching by spatial light modulators (SLMs) offers a means of implementing large and highly flexible switch arrays capable of routeing signals at baseband or microwave frequencies. This approach offers potential mass, power and size advantages compared to alternative technologies. The paper reviews the essential features of optical crossbar switch architectures based on SLMs and discusses options for the lasers, SLMs, interface optics and photodetectors. Proof‐of‐concept demonstrators for optical crossbar switches operating on both baseband and microwave signals are described. Finally, an outline design for a compact switch module is described and the critical component developments needed to realize this are identified.
Broadband Island interconnection via satellite—performance analysis for the race II—catalyst project
Authors: Hadjitheodosiou M. H. , Komisarczuk P. , Coakley F. , Evans B. G. , Smythe C.
Published: July 2007

The use of communication satellites as a possible way of offering broadband island interconnectivity appears to be a very attractive option, as it will enable the provision of an all‐digital, transparent service to a number of ATM islands spanning a wide area, accommodating efficiently a variety of traffic demands. The CATALYST Project (RACE II/R2074) is an attempt to demonstrate the applicability and compatibility of satellite technology with the terrestrial BISDN. In this paper we present an overview of the project and focus on an initial study of the expected user performance through the CATALYST network. Our analysis is based upon mathematical and simulation models and describes the end‐system to end‐system transfer delay for given message lengths. The protocol profiles assume a mix of Novell NetWare and Network File System client/server architectures, which are supported by either the IEEE 802.3/Ethernet or fibre distributed data interface LANs, which are themselves linked via LAN/ATM/satellite interface units. Areas of further investigation, and the implication of our analysis on the actual network architecture, are discussed.
Voice transmission quality of mobile satellite communications systems
Authors: Dimolitsas S. , Corcoran F. L. , Ravishankar C.
Published: July 2007

Recently, a number of commercial digital mobile satellite communications systems have become operational, and the introduction of more systems is imminent. The voice transmission quality of the Inmarsat‐aeronautical, Inmarsat‐M and Inmarsat‐B systems was evaluated and compared with the quality of the Inmarsat‐A analogue communication system on the basis of subjective listener opinion assessments. From this evaluation it can be concluded that, under nominal operating conditions, the current generation of digital mobile systems may offer a perceived performance that surpasses that of the older Inmarsat‐A analogue system, at least when measured in terms of transmission quality.
Broadcasting by satellites
Authors: Drury G. M.
Published: July 2007

As a result of recent advances in signal processing technology and standards for video compression systems there has been a dramatic increase in interest in commercial applications. This paper reviews the current broadcasting situation from a number of viewpoints relevant to the future development of the available technologies.

After a review of the context, which includes alternative new broadcasting technologies as well as alternative media capable of competing with satellite, digital technology is given a wide ranging assessment with particular attention paid to the direct broadcasting to the home by satellite application currently receiving considerable attention world‐wide. The possible system architectures and subsystem design features are highlighted with the European Baseline Satellite Broadcasting specification developed by the European Digital Video Broadcasting Project gaining special attention. For completeness a brief review of the digital audio broadcasting system (DAB) is also given.

In addition to the applications for direct broadcasting, applications in the professional domain for distributing television signals from studios to terrestrial transmitters, satellite up‐link sites or cable heads or for satellite news gathering (SNG) are examined. Features of existing commercially available hardware to support these services are described briefly.
Effect of broadcast and precise ephemerides on estimates of the frequency stability of GPS Navstar clocks
Authors: McCaskill Thomas B. , Reid Wilson G. , Buisson James A. , Warren Hugh E.
Published: July 2007

Frequency stability analysis of on‐orbit Navstar clocks is performed by the Naval Research Laboratory using both the broadcast and the precise post‐processed ephemerides. The phase offset between the Navstar clock and the reference clock is computed from pseudorange measurements obtained by dual‐frequency GPS receivers at the five GPS monitor sites and at the U.S. Naval Observatory precise‐time site. The broadcast ephemerides are generated at the GPS master control station by a Kalman filter using data collected from the five GPS monitor stations. The precise post‐processed ephemerides are generated by the Defense Mapping Agency (DMA) using data collected from the GPS monitor sites and from five additional DMA monitor sites. In this paper the frequency stability is estimated for two Navstar caesium clocks–a Block I caesium clock (Navstar 9) and a Block II caesium clock (Navstar 23)–using both the broadcast and the precise ephemerides. A significant improvement in the estimate of the frequency stability of the Block II clocks has been achieved using the precise ephemeris.
Accuracies of atmospheric profiles obtained from GPS occultations
Authors: Hardy Kenneth R. , Hajj George A. , Kursinski E. Robert
Published: July 2007

Radio occultation studies of the terrestrial atmosphere are possible through the use of signals transmitted by satellites of the Global Positioning System (GPS) and received by one or more other satellites in low earth orbit (LEO). The perturbed phase of the occulted signal gives direct information on the refractivity profile in the region of occultation, from which vertical profiles of density, pressure and temperature can be retrieved. The technique requires the use of the dual GPS frequencies in order to isolate and remove most of the ionospheric effect. Analysis of the effect of the ionosphere and methods of removing it will be presented. For the recovery of atmospheric profiles, two major issues are addressed. The first is how accurately can refractivity be retrieved for a region in which there is a large horizontal refractivity gradient; the second considers the separation of temperature and moisture in the lower troposphere. Based on model simulations, the capability of GPS to provide atmospheric profiles is assessed.
On‐the‐fly carrier phase ambiguity resolution for precise aircraft landing
Authors: Blomenhofer Helmut , Hein Günter W. , Walsh David
Published: July 2007

Successful GPS on‐the‐fly (OTF) carrier phase ambiguity resolution for precise positioning at the centimetre level has already been demonstrated. This has usually been in good observation conditions, e.g. over short distances, lots of satellites, P‐code pseudoranges available, and small unmodelled errors. In order for GPS to fulfil the rigorous ICAO Cat. III precise landing navigation requirements centimetre‐level accuracy must also be obtained in more realistic conditions, e.g. A‐S on, high‐unmodelled errors and less than six satellites. Integrating GPS with other sensors, e.g. INS, is likely to aid ambiguity resolution in such conditions, but there are limitations. After discussing critically the OTF methods, approaches are examined which will provide the precise accuracy, reliability and integrity required. Combining GPS with one, or more, pseudolites to provide an extra geometrical constraint to aid ambiguity resolution is described. Flight tests using different configurations of pseudolites are carried out and analysed.
Performance of LAMS‐DLC: A protocol for low altitude satellite networks
Authors: Ward Christopher , Choi Cheong H. , Hain Thomas F.
Published: July 2007

LAMS‐DLC, a data link control protocol for low altitude satellite networks, was developed to overcome throughput limitations inherent in event‐based positive acknowledgment (POS‐ACK) automatic repeat request (ARQ) class protocols by relaxing certain reliability constraints, in particular the in‐sequence delivery constraint. This relaxation results in a new class of link layer service, that of reliable datagram, and permits a fresh approach to link layer protocol design. In this paper we discuss the motivation for such a protocol, describe one such protocol, LAMS‐DLC, and compare throughput efficiency with results obtained from a simulation model. Results suggest that LAMS‐DLC provides near optimal throughput efficiencies in the target environment, while using significantly less buffer space than is required for conventional POS‐ACK protocols.
Key payload technologies for future satellite personal communications: A European perspective
Authors: Ventura‐Traveset J. , Stojkovic I. , Coromina F. , Benedicto J. , Petz F.
Published: July 2007

This paper deals with satellite payload architectures adequate for the provision of universal mobile telecommunication services (UMTS) by medium altitude earth and geostationary orbit (MEO and GEO) satellites. The payload concept introduced is based on a transparent transponder with onboard digital signal processing (DSP) operations and digital beamforming at the traffic carrier level (narrowband beamforming). The emphasis of the paper is on key design aspects and technology considerations of the payload processor unit (PPU), which includes multiplexing/demultiplexing and digital beamforming operations, and on the antenna and RF signal handling subsystems. For completeness, a review on the European digital technology is also presented. The development of such a payload architecture is in line with present and planned activities of the European Space Agency (ESA) for MEO and GEO orbit systems, which are also implicitly discussed in the paper.
Concatenated coding with inner trellis codes for fading channels
Authors: Biyari Khaled H. , Al‐Semari Saud A.
Published: July 2007

It is known that concatenated coding can significantly enhance the performance of digital communication systems operating over fading channels when compared to uncoded or single‐coded systems. The price to be paid for such an improvement, however, is a substantial increase in the required bandwidth. In this paper, we consider the use of a concatenation scheme in which the inner code is a trellis‐coded modulation (TCM) system. The analysis is carried out for two different outer codes: a binary Golay code and a non‐binary Reed‐Solomon code. Results obtained for the Rayleigh and Rician fading channels through analytical bounds indicate that the use of this system does provide a significant reduction in the bit error probability, a fact that is also verified through computer simulation. Unlike a traditional concatenated system, the proposed method achieves the coding gain while maintaining acceptable bandwidth efficiency.
An environment for modelling and simulating communication systems: Application to a system based on a satellite backbone
Authors: Cohen Atika , Mrabet Radouane
Published: July 2007

The availability of good software tools is vital to simulation practitioners. The objective of the OSISIM project (open system integrated simulator) is to set up an environment which integrates facilities and tools to build a communication system, and to study its performance. The environment is called AMS : atelier for modelling and simulation. Using it, the network architect, i.e. the user of the atelier, can quickly construct, in a graphical environment, a concise system from models of several standard networks available in a specific library, and execute the system in an efficient manner. Starting with an outline of the components of the atelier, we describe the AMS prototype, and the internal structure of basic models to be included in it. Moreover, a concrete example of a communication system including a satellite backbone is provided to illustrate how AMS is used to simulate such a system.
Impact of transmission delay in audiovisual communications
Authors: Dimolitsas Spiros , Corcoran Franklin L. , Phipps John G.
Published: July 2007

In this paper, the design and results are presented of an experimental study which was conducted in order to assess subjectively the impact of transmission delay in audiovisual communications. This study was undertaken using two 64 kb/s videotelephones which were connected over links incorporating simulated one‐way circuit propagation delays of 0 ms, 250 ms and 500 ms. From the results obtained it was concluded that audiovisual communication is weakly affected by propagation delay. In general, performance degradation between terrestrial and single‐hop satellite connections was minimal and in most cases statistically insignificant. A subsidiary conclusion is that the presence of the visual cues appears to mitigate the impact of transmission delay in audiovisual communication.
Transmission techniques for dab by satellite
Authors: Carrere G.
Published: July 2007

This study is a comparison between the CDMA and COFDM transmission techniques for digital audio broadcasting. Since broadcasting is used to establish a mobile or fixed link, it is necessary to set up a transmission technique which allows the optimum use of fading and multipath channels, particularly in urban locations. This paper sums up a comparative case study between the two transmission techniques mentioned above. The interest of this paper is to point out the added value brought by these transmission techniques for requirements such as multiple path problems with digital broadcasting with mobiles, frequency mapping and synchronization, capacity of the system, jamming protection capability, BER specifications, signal processing complexity, power control, spectrum efficiency and error correction operations. Finally, this paper tries to bring the appropriate conclusion which leads the OFDM process in Europe.
Satellite DAB
Authors: Briskman Robert D.
Published: July 2007

Service requirements for digital audio broadcasting (DAB) from satellites are presented, and plans for implementing such systems in various countries are surveyed. Technical and economic constraints, including satellite transmitter power, frequencies of operation, transmission bandwidth, service interference and user receiver design are discussed particularly for DAB systems employing mobile receiving terminals where transmission outage from blockage and multipath fading must be addressed. Transmission performance improvement techniques such as spatial diversity, modulation, coding and interleaving are described. An illustration of a specific satellite DAB system design is presented to show the technical and economic feasibility of such new services.
The worldspace programme: The first dab satellite service for the world
Authors: Fournié Patrick , Courseille Olivier , Samara N. A. , Rothblatt M. A. , Harris G. C.
Published: July 2007

The WorldSpace satellite DAB system will provide by 1998‐1999 dozens of high quality radio channels accessible to a potential audience of 4 billion people world‐wide who currently receive with various kinds of difficulty and limitations terrestrial radio programming. The system will consist of geostationary satellites, low cost radio receivers called StarMan™, and the associated ground control networks. The system will use state‐of‐the‐art digital audio coding techniques and, on board the satellite, baseband processing technology. This paper presents the overall description, performance and industrial organiazation of the system.
Flight 2 version of in‐orbit test transponder (IOTT2) for on‐board regenerative satellites
Authors: Mott Richard C. , Fiore Livio Di
Published: July 2007

This paper presents the design and realization of regenerative satellite on‐board bypass test equipment. Furthermore, two particular examples of an in‐orbit test transponder (IOTT) are discussed in detail. The IOTT1, developed for the first 30/20 GHz ITALSAT satellite (F1), was launched in January of 1991. IOTT1 has been a useful tool during satellite assembly, integration and pre‐launch tests. IOTT1 was successfully used to fully characterize the multibeam ITALSAT satellite in orbit.

In general, the IOTT functions to bypass the demodulator, the baseband switchboard and the modulator of the multibeam package of the ITALSAT spacecraft payload, providing the ability to fully characterize the satellite's transponders using well‐established IOT test techniques.

This paper describes and compares the design, fabrication and test of both ITALSAT in‐orbit test RF bypass transponders (IOTT1 and IOTT2) mounted on board the ITALSAT multibeam spacecraft, (F1) and (F2), respectively. The IOTT1 contains the first MMIC circuitry ever launched into space on a communications satellite. The improved IOTT2, fabricated for the second 30/20 GHz ITALSAT satellite (F2), is schedule for launch in early 1996.

These fully space‐qualified designs incorporate COMSAT Laboratories' designed and fabricated MMIC Ku‐band amplifiers, lightweight waveguide Ku‐band channel filters and electronic power conditioner (EPC) and combined IOTT telemetry/command (T&C) circuitry.
Use of transportable test stations for measuring satellite coverage dependent parameters during IOT campaigns
Authors: Barthmann P. , De Vincenti P. , Moens C.
Published: July 2007

The in‐orbit tests of the satellite coverage dependent parameters require the rotation of the satellite around its pitch and roll axes in order to ‘bring’ the various coverage locations onto one fixed IOT station. Alternatively, several transportable test stations can be located at different sites in the coverage area in order to measure the satellite performances on site. Although the second technique does not provide enough measurement points to reconstruct the complete coverage of shaped beam antennas, it presents several advantages for which it is still used by EUTELSAT for the IOTs of its satellites in conjunction with measurements based on the satellite attitude movements.

In particular, the transportable test stations are used to test the stability of satellite EIRP and IPFD at the edges of the coverage areas, where the performances are more sensitive to the pointing errors induced by thermal deformation or satellite attitude changes.

This paper presents the common experience gained by EUTELSAT and ESA in testing the coverage dependent parameters of the first and second generation of EUTELSAT satellites. In particular, the paper deals with the use of the transportable test stations during the EUTELSAT II F1 to F3 acceptance tests and with the test campaigns performed at several sites in the eastern European countries.

In the first case, the transportable test stations were used in conjunction with satellite rotations around the pitch axis in order to measure the coverage dependent parameters along several cuts parallel to the equatorial plane at different roll angles. In the second case, the transportable test stations were used to periodically repeat the EIRP measurements of many satellite channels over several hours in order to test the EIRP stability of the EUTELSAT II satellites.

For both cases, the paper presents a synthesis of the most significant IOT results together with a comparison between these results and the values of the coverage dependent parameters predicted on the basis of the on‐ground tests.
G/T predictions of communication satellites based on a new earth brightness model
Authors: Fenech H. T. , Kasstan B. , Lindley A. , De Maagt P. J. I. , Badessi S.
Published: July 2007

The G/T predictions of communications satellites in the past usually stipulated that an antenna noise temperature of 290 K be used in the calculations. This, when compared to in‐orbit derived data, has resulted in large discrepancies (up to 3 dB). These discrepancies result directly from the use of a pessimistic value of the antenna noise temperature. The actual antenna noise temperature is lower because a portion of the spacecraft receive antenna pattern falls in deep space and because the brightness temperatures of large parts of the Earth are lower than 290 K. This discrepancy has become more apparent as technology of low noise amplifiers advances, thus making the antenna temperature the predominant factor when budgeting the system noise temperature of the spacecraft.

This paper focuses on a model to determine the antenna noise temperature and especially how this model was directly verified in orbit during the acceptance campaign of EUTELSAT II‐F6 (Hot Bird 1). The methodology used for the determination of the integrated antenna temperature is also fully discussed. Full results are also presented.
Recent advances in ‘in‐orbit testing’ of communications satellites
Authors: Kasstan B. , De Vincenti P. , Schulze H. J. , Tharaud Y.
Published: July 2007

After a successful launch of a new communications satellite, it is essential to test the communications subsystem while the spacecraft is in orbit so as to compare with prelaunch data in order to ensure that no impairment has resulted from the stress of the launch and to verify that the spacecraft payload is compliant with the specifications sought.

The thrust of in‐orbit test technology has stemmed from the fact that the spacecraft has to be operational very quickly while not sacrificing the number of tests that have to be performed and increasing their measurement accuracies.

Thus, in order to respond favourably to the cited criteria, microwave measurement techniques with more powerful computers and software technology have been used to automate the measurements.

The paper is geared to the history, design, implementation and operation of EUTELSAT's in‐orbit test (IOT) facilities, and mostly reflects technological advances in communications satellite payload testing. The paper will first detail the hardware/software novel concepts of the measurement environment. Then new measurements are summarized. New spacecraft antenna mapping procedures are detailed both in measurement and spacecraft attitude aspects.
ESA's in‐orbit test facilities for communications satellites
Authors: Moens César , Absolonne Francis
Published: July 2007

The facilities and in orbit test methods developed by the European Space Agency over the last two decades, in the frame of the various communications satellite programmes, are reviewed. The lessons learned and the hardware and software precautions implemented to enhance accuracy and operational flexibility are described. New facilities and methods currently under development are also addressed.
Low earth orbit satellite communications experiments using the digital signal processing payload on the PoSAT‐1 microsatellite
Authors: Sun W. , Sweeting M. N. , Hodgart M. S.
Published: July 2007

There is a growing interest in using networks of small satellites in low Earth orbit (LEO) to provide a variety of communications services in conjunction with small ground terminals. The only ’little LEO’ microsatellite digital store‐and‐forward communications network (HealthNet) in commercial operation at the time of writing uses microsatellites, communications payloads, and protocols designed and built at the University of Surrey, U.K. In order to provide an in‐orbit research test‐bed for improving communications with microsatellites in LEO by optimizing modulation and demodulation techniques, an advanced DSP payload, the digital signal processing experiment (DSPE), was included on board the latest Surrey microsatellite (PoSAT‐1). In‐orbit experiments using the PoSAT‐1 DSPE first optimized the existing non‐coherent CPFSK communication systems and then investigated the use of coherent MSK to provide a potential 3dB advantage while remaining compatible with the spacecraft systems. A novel DSP implementation of the Hodgart‐Massey coherent MSK demodulator/decoder was developed by the authors and its behaviour compared with the classical de Buda demodulator undertypical LEO conditions through a sequence of rigorous computer simulations and laboratory bench tests. The simulations and bench tests quantified a practical 2dB improvement in BER performance when compared with non‐coherent CPFSK, while also exhibiting considerable tolerance to the frequency and amplitude variations which are encountered in an LEO environment. These characteristics were subsequently confirmed by in‐orbit demonstrations using the PoSAT‐1 DSPE. The microsatellite, payload, modems and experimental results are presented in this paper and discussed with a view towards implementing an adaptable DSP‐based communications system capable of optimizing data throughput with LEO microsatellites.
Directed interesterification in glycerides. Reaction in presence of added glycerol
Authors: Eckey E. W. , Formo M. W.
Published: July 2007

Directed interesterification, in which ester‐ester interchange is carried out in triglyceride mixtures with simultaneous crystallization of solid glycerides, has been applied to glyceride mixtures containing free hydroxyl groups. Solid glycerides precipitated from cottonseed oil with added glycerol were principally saturated diglycerides or saturated monoglycerides.

The prineipal varables controlling the kind and proportion of solid precipitated during reaction from glycerides of a given original composition are the proportion of free alcohol groups, the time‐temperature schedule for the reaction, and the method of seeding, if any, used to start the crystallization. The method makes it possible to segregate the high‐melting and low‐melting fatty acids of a fat practically completely into separate ester fractions.
Non‐ionic detergents from wax
Authors: Griesinger W. K. , Nevison J. A. , Gallagher G. A.
Published: July 2007

Conclusion

Non‐ionic synthetic detergents having detergent properties similar to those of alkyl phenol polyethylene glycol ethers and alkyl mercapto polyethylene glycol ethers can be prepared by reacting the optimum quantity of ethylene oxide with the composite crude fatty acids made by the air oxidation of low melting chemical grade paraffin wax.
Studies on the detoxication of castor seed pomace
Authors: Kodras Rudolph , Whitehair C. K. , MacVicar Robert
Published: July 2007

Solvent extracted castor seed pomace has been shown to have a high acute oral toxicity for the rat and chick. This acute toxicity has been destroyed by various physical and chemical treatments designed to denature the toxic protein constituent, ricin. Of these, autoclaving for 15 minutes at 125°C. produced essentially complete destruction of ricin with minimal changes in the physical character of the pomace. Biological tests of the feeding value of the detoxified pomace as a protein source indicated that the material was not of high biological value. Microbiological analysis of the total seed protein for the principal amino acids showed that the protein contained relatively large amounts of glutamic acid and was serisously deficient in tryptophan. The methionine content was also inadequate and the lysine was marginal.
Thin lipid membranes with aqueous interfaces: Apparatus designs and methods of study
Authors: Howard Robert E. , Burton Robert M.
Published: July 2007

Thin membranes can be formed in aqueous media from amphiphilic lipids, and will spontaneously approach a limiting thickness of bimolecular dimensions (bilayers). This paper describes apparatus and methods for studying such thin lipid membranes, and illustrates their use in determining some of the basic properties of the membranes, especially bilayers.

Several methods of forming thin lipid membranes are described. The early stages in apparatus development are traced, and the theoretical variables and operational parameters relating to apparatus and system design are discussed.

Designs for two basic types of apparatus are presented in detail: one is a cylindrical chamber especially constructed to permit optical investigation of the membrane; the second is a multiple chamber system designed for the study of several different membranes either simultaneously or in rapid succession. Interchangeable chamber units are held in a thermostat block, and assemblies of electrodes and provisions for perfusion or sampling of aqueous medium are placed in the chambers as required. Methods are described which enable simultaneous mechanical, electrical, optical, and chemical operations and studies to be performed on the same membrane with either type of apparatus.

Membranes were formed from several purified amphiphilic lipids and from mixed‐lipid extracts from a variety of biological membranes. The types and mechanisms of drainage of thin lipid membranes with aqueous interfaces are analogous to those previously described for aqueous soap films in air. The limiting bilayer thickness is confirmed by electrical measurements. The resistivity of the bilayers is ca. 1012 to 1014 ohm‐cm, their capacity is ca. 0.4 μfd‐cm−2 and their dielectric breakdown voltage is ca. 3×105 V‐cm−1. Other physical properties of the bilayers are described. Permeability of the bilayers to various substances was determined by diffusion flux, osmotic flux, and electrochemical potential methods using the apparatus described. Substances studied included water, small monovalent ions, glucose, acetylcholine, salicylamide and synaptic vesicles.

The chemical, physical, electrical, and permeability properties of the experimentally formed lipid bilayer membranes are similar to those of biological membranes. These similarities strongly support the Danielli‐Davson hypothesis, which proposes that a lipid bilayer is the basic structure of biological membranes. The apparatus, methods, and information presented in this paper provide tools for further investigation of lipid bilayer membrane properties and for further testing of hypotheses relating to membranes.
Properties of lipid bilayers at a water‐water interface
Authors: Haydon D. A.
Published: July 2007

This paper is essentially a review of the work on black hydrocarbon films in aqueous media which has been carried out by the author and his colleagues during the last few years.

The theory of the formation and stability of the films is discussed in terms of the structure and physical properties of the constituent molecules. Particular consideration is given to the adsorption of the stabilizing molecule and the metastable equilibrium of the resultant thin film. The various systems which have been examined experimentally are described. The interrelation of the film capacitances, thicknesses, and compositions is discussed in the light of the theoretical expectations.

The films are permeable to water although the measurement of their permeability is complicated by the difficulty of stirring the boundary layers of the aqueous solutions. There is a discussion of the progress in this problem and the interpretation of the permeability measurements in terms of the structure and composition of the films.

Finally some conditions under which films become strongly conducting are described.
Component fatty acids and composition of some oils and fats
Authors: Sreenivasan B.
Published: July 2007

Nineteen different samples of oils and fats have been examined for their component acids and composition by gas‐liquid chromatography. Under programmed‐temperature operations, the temperatures at which different components start to elute bear a straight‐line relationship with their respective carbon numbers. Chromatograms, under programmed‐temperature conditions, of methyl esters from such oils as coconut, groundnut, mustard, etc., are used for identifying the components of an unknown oil by comparing its chromatogram taken under nearly identical conditions. For confirmatory identifications, such plots as logarithm of retention times versus carbon numbers for saturated acids (14:0 to 24:0), monoenoic acids (14:1 to 24:1), and dienoic acids (18:2 to 24:2), under isothermal conditions, have also been used. Some new fatty acids, noted for the first time in traditional oils, are 15:0 in cottonseed oil, 20:1 in sesame oil, 22:0 in soybean oil, and 24:2 in mustard oil. Odd‐carbon chain acids from 11∶0 to 23:0 have been observed in such vegetable oils as peanut germ, rice bran, andMesua ferrea. Fatty acid composition by GLC for new samples like peanut lecithin, peanut germ oil,Myristica attenuata, Myristica kanarica, Myristica magnifica, Mesua ferrea, Vateria indica, Schleichera trijuga, and shark‐liver stearine are presented. Industrial utilization of these new oils and fats is discussed.
An electrophoretic study of the detergency process
Authors: Rutkowski B. J.
Published: July 2007

By using a micro‐electrophoresis technique, the electrokinetic behavior of cotton and a clay soil was studied in various surfactant, tripolyphosphate, and carboxymethylcellulose solutions. Correlative soil‐deposition studies were also made.

Data are presented which show that doublelayer forces of repulsion are not of major importance in preventing the deposition of a clay soil on fabric. However a correlation was demonstrated between soil deposition and adsorption processes which occur at soil‐solution and fabric‐solution interfaces.