bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractThis 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

AbstractA 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

AbstractSatellite 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

AbstractThis 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

AbstractOwing 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

AbstractThe 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

AbstractA 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

AbstractThis 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

AbstractVSAT 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

AbstractIn 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

AbstractThis 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

AbstractThis 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

AbstractA 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

AbstractThe 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

AbstractRecently, 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

AbstractAs 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

AbstractFrequency 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

AbstractRadio 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

AbstractSuccessful 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

AbstractLAMS‐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

AbstractThis 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

AbstractIt 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.