New rain rate analyses to assess rain attenuation on satellite ehf communications

This paper provides estimates of the frequency of occurrence, duration and probability of satellite EHF communication outages due to attenuation by rain. These can be used to determine optimum frequencies, power levels and the need for space diversity of terminals or other alternatives to maintain reliable communications. Ten years of 1 min rain rates at each of 12 U.S. cities were used in conjunction with an attenuation model to quantify communication outages at locations representing a variety of climatic regimes. Analyses of the 1 min rain rates and outage estimates at 10, 30 and 45 GHz for elevation angles of 10°, 30°, 50° and 70° are presented.     

Mobile satellite communications

The paper presents an up-to-date overview as well as new results on mobile satellite communications. Specifically, the following subjects are addressed: worldwide activities; satellite orbits; multiple access techniques; Novstar global positioning system; economic and regulatory issues; future trends. Some of these technical and nontechnical subjects appeal disjoint, but they are unique and significant among the many facets, which effect the development and operation of mobile satellite communication systems     

Modem techniques in satellite communications

Since the mid 1980s, research and development in satellite modem techniques has been very active and has yielded promising results. In the article the author presents a summary of the current status of work in this area, and discusses the directions this work is taking     

Microscale diversity in satellite communications

Results from an investigation into a microscale diversity scheme for the purpose of mitigating attenuation due to tropospheric scintillations are presented. Data from an experiment using the 20-GHz Olympus satellite beacon were analyzed to evaluate the performance of short-baseline site-diversity systems. Results indicate that with a baseline separation of about 50 m (at an elevation angle of 14° in this experiment) the signals received by the main and diversity terminals become decorrelated. Examination of several high-scintillation events shows that such a diversity technique could substantially increase the uptime of low-power-margin VSAT systems. The performance of microscale diversity for several baseline separations is evaluated in terms of a parameter called diversity recovery. Applications and conditions under which microscale diversity performs best are addressed     

Personal communications by satellite

Personal communications (PC) refers to two-way voice (and possibly data) communications to a small hand-held unit, capable of being carried by a person and used in various locations. PC via satellite refers to the case where this hand-held unit communicates directly with a satellite to provide the duplex voice (or data) service. Both geosynchronous earth orbit (GEO) and low earth orbit (LEO) satellites have been considered to provide this service. GEO and LEO satellite systems must compete with existing mobile cellular radio systems both in meeting performance requirements and service costs, if they are to be a significant supplier of PC services. GEO and LEO systems each have unique advantages and disadvantages when used to provide a PC service. While these general characteristics are identified in Section 1 of the paper, a more quantitative comparison is needed. This quantitative comparison is made by comparing a GEO PC satellite system, operating at EHF (K_a-band) frequencies with a LEO system operating at UHF (L-band) frequencies, including service costs for both systems. The two systems used in the comparison are examples of realistic GEO and LEO system designs for PC service, and although it is not exhaustive, the comparison points out some of the key differences between GEO and LEO systems that affect service performance and cost.     

Commercial satellite communications experience

The operational Intelsat I (Early Bird) and Intelsat II satellites and associated earth stations that comprise the present commercial satellite communications system provide a capacity of close to 720 voice circuits between major earth stations. All but a limited portion of the inhabited globe is now within the line of sight of a commercial satellite relay. In addition, it is expected that by 1968, with the operation of Intelsat III, a truly global international satellite communications system will exist.     

GaAs FET satellite communications

What is claimed to be the industry’s first 90W c-band GaAs field effect transistor (GaAs FET) suitable for use in solid-state power amplifiers (SSPA) for base station or earth-station satcom and radar applications, as well as for microwave digital radios for terrestrial communications, has been released by Toshiba America Electronic Components Inc. Using TAEC’s HFET process technology, the TIM5964-90SL GaAs FET employs ion plantation technology to produce an output power of 49.5dBm at a frequency range of 5.9GHz to 6.4GHz. and is priced at around $1,500 each.This is a short news story only. Visit www.three-fives.com for the latest advanced semiconductor industry news.     

The emergence of satellite systems for rural communications

Technology improvements in recent years are leading toward low-cost satellite communications systems that can be applied to rural telephony solutions worldwide. This paper will review some of the key technology and economic developments that are taking place today and further developments projected for the near future that can make this prospect a reality. Advances in signal processing and error-correction techniques have enabled more efficient use of space segment. In parallel, the trend of higher power, higher frequency satellites is causing dramatic reductions in size and cost of corresponding ground segment earth terminals. Coupled with these developments will be intelligent on-board switched satellite processors which can provide added network flexibility and further reduce overall system costs. Candidate systems, technology, and economic analyses will be discussed to demonstrate the feasibility of these services for both telephony and data, as well as a projected time schedule when they may be achieved.     

VSAT applications in Russian satellite communications

The development of satellite communications in Russia tends to their application in low-capacity voice and data systems in which earth terminals are installed directly at users premises. Low-power small terminals employed for this purpose can be classified as VSAT-type stations. This paper considers the applications of these terminals in voice and data transfer networks in Russia, their interaction with terrestrial systems, their basic technical characteristics and regulatory issues related to their use.     

Advances in multibeam communications satellite antennas

The evolution of satellite antennas over the past quarter of a century is presented. Five major areas of advances in communications satellite antenna technology are reviewed: single offset reflectors with feed arrays, shaped reflector systems, active phased arrays, phased-array-fed dual reflector systems, and lightweight feed elements. Examples are given of existing systems and of the ongoing development of new technologies     

Cost effectiveness in global satellite communications

Global satellite communications, as the INTELSAT system has demonstrated, is a commercially successful business with over ten years of operating experience. The system provides high-quality reliable communications over a large number of links in successful competition with other modes of communications. The cost effectiveness of the INTELSAT system has increased in the last decade as measured by the per-circuit-year cost of satellites in orbit, space segment charges, and earth station and total circuit costs. Economies of scale and the use of progressively more advanced technology are expected to increase the cost effectiveness of global satellite communications in the future.     

Regulatory flexibility in commercial satellite communications

MSAT, a domestic mobile satellite service (MSS) system under development in the US, is addressed. The high effective isotropic radiated power (EIRP) of each MSAT satellite, which is orders of magnitude greater than any existing L-band satellite and will allow the introduction of new services, and the economics of MSAT are discussed. The RadioSat system currently being developed, which is optimized for services that support enormous numbers of mobiles on each MSAT channel, is briefly described. The highly flexible MSS regulatory structure established by the US Federal Communications Commission (FCC) is examined     

Blockage mitigation techniques in satellite communications

This article proposes systematic approaches to minimize severe channel degradation. Detection of channel condition is performed by means of two continuous ARQ NAK counting schemes. Stop-and-wait ARQ non-NAK counting is used for timed complete blockage. A single (31,21,5) code is designed for all the ARQ systems proposed. After the blockage state of a transmission channel is determined, satellite link parameter trade-offs and other specific remedy alternatives are recommended to enhance channel performance. System performance criteria are derived with different Earth station capabilities.     

The use of digital circuit multiplication equipment in satellite communications

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

The new space race: satellite mobile communications

The how and why of LEO satellite communications are considered from technical and economic viewpoints; the market forecast for large systems of this nature is pessimistic. Particulars of six major services planned for launch within the next 10 years are tabulated     

Interactive multimedia satellite access communications

Recent advances in satellite technology are making possible the development of broadband satellite access (BSA) systems for two-way access to multimedia Internet services. This article provides an overview of BSA systems with an emphasis on resource management and interworking techniques to support IP-based multimedia services. The article draws on collaborative research performed over the past few years as part of the Broadband Satellite Communications Major Project of the Canadian Institute of Telecommunications Research. Some key innovations are described: combined free/demand assigned multiple access (CFDAMA) for dynamic satellite bandwidth allocation; an architecture for DiffServ provisioning over BSA systems; and a dynamic TCP Vegas protocol as a proxy service for split-TCP connections over BSA systems.