Land Mobile Satellite Services Research Articles

A Multistate Channel Model Composed of Line-of-Sight and Semi-Line-of-Sight Propagation Environments for Millimeter-Wave Mobile Radio Systems

For outdoor millimeter-wave mobile radio systems, the main service area is expected to be in line-of-sight (LOS) and semi-line-of-sight (SLOS) environments. The modeling of propagation in a mixed LOS/SLOS environment is thus important in system design. For modeling propagation in an SLOS environment, the application of the Loo model developed for land mobile satellite service with roadside shadowing is promising because this model reflects the physical mechanism of radio propagation. However, the model is inconvenient in practice because its calculation involves numerical integration over an infinite range. In this article, we approximate the Loo distribution using three basic distributions, namely the Nakagami-Rice distribution (or Rician distribution), Nakagami-m distribution, and lognormal distribution. Based on the evaluation results, we propose the use of the Nakagami-m distribution in place of the Loo distribution. We demonstrate the conversion of Loo distribution parameters to Nakagami-m distribution parameters. Finally, we examine a multistate model that expresses environments composed of LOS, SLOS, and non-LOS conditions.

Survey on Land Mobile Satellite System: Challenges and Future Research Trends

Mobile satellite systems can be characterized as a major solution since they offer mobile communication services to users in different environments and for several significant purposes. In numerous conditions, satellite systems have exclusive competences in terms of broad coverage, robustness, broadcast, and multicast capabilities. However, the implementation of Land Mobile Satellite (LMS) systems still faces some limitations regarding connectivity and stability, leading to unreliable communication. Therefore, the target of this paper is to offer a comprehensive overview of land mobile satellite systems and services from various perspectives. This includes the classification of LMS systems, the operating frequency bands, and the representative Mobile Satellite Services (MSS) systems. The research challenges and future research are further described. Such information will contribute to the understanding of satellite systems and the currently faced issues that must be addressed.

Study of Vehicle Vibration for High-Performance Land Mobile Satellite Tracking System for Telemedicine

The land mobile satellite service (LMSS) is a key component of telemedicine and an important technology for grasping the status of a patient in an ambulance. However, rough road surfaces can destabilize satellite tracking and disturb data communications with the ambulance carrying the patient. Nevertheless, accurate estimates of the location of the vehicle at any given time and rapid reconfiguration of the tracking antenna based on past data can allow stable and effective data communications. This study examined positions characterized by large vibration amplitudes from past data on vehicle vibrations due to rough road surfaces as feature points to provide the vehicle system in advance with reference pitch angle vibration data. Drawing on reference vibration data for convolution and a cost function, The authors synchronized past data with real-time vibration data and accurately estimated the point at which the ambulance or other vehicle passes on the road. They also discuss limits on the range of vibrations that can be used for data synchronization. This study demonstrates that the present method enables high-precision estimates of vehicle location.

Analysis of availability improvement in LMSS by means of satellite diversity based on three-state propagation channel model

Aiming at future multimedia land mobile-satellite services (LMSS) consisting of a large number of nongeostationary Earth-orbit satellites, we present an LMSS propagation channel model for assessing the effect of a satellite diversity scheme so that high service availability and high signal quality are assured. We classify general fading environments for LMSS into three states. By taking the occurrence probability of each state into account, a new fading channel model is developed. The validity of the model is identified by comparing its predicted values in terms of the cumulative distribution function (CDF) with measured data available so far. Then, based on this model, we calculate the satellite diversity effect assuming that the area is illuminated simultaneously by at least two satellites moving in low Earth orbits (LEO) over urban and suburban environments. In addition, state transition characteristics based on a Markov model are presented.

A compact circularly polarized microstrip antenna with integrated feed

A circularly polarized antenna, realized in a low-cost technology with an integrated feed, is presented for the land-mobile satellite service. This antenna presents large bandwidth, high gain, and good axial ratio in all frequency ranges. © 1996 John Wiley & Sons, Inc.

System unavailability and quality degradation during available time for mobile satellite systems in the mobile ISDN era

AbstractIt is expected that mobile‐radio systems will play an important role in realizing general personal communication networks through ISDN. In the near future, the so‐called mobile ISDN era, it is necessary to have common performance objectives between mobile radio links and fixed (or fiber) links and have a common assessment method for data transmission quality.In this paper, based on the ITU‐T definition, unavailability statistics are examined in mobile‐satellite systems which are characterized by low margin systems. the characteristics of signal degradation due to propagation impairments in maritime, aeronautical, and land mobile satellite services are examined. Through this analysis, the importance of differentiation between “unavailability” and “signal degradation in available time” is emphasized when the digital signal transmission quality is evaluated.

Odyssey, an optimized personal communications satellite system

Personal communications places severe demands on service providers and transmission facilities. Customers are not satisfied with the current levels of service and want improvements. Among the characteristics that users seek are: lower service rates, hand held convenience, acceptable time delays, ubiquitous service, high availability, reliability, and high quality. The space industry is developing commercial space systems for providing mobile communications to personal telephones. Provision of land mobile satellite service is fundamentally different from the fixed satellite service provided by geostationary satellites. In fixed service, the earth based antennas can depend on a clear path from user to satellite. Mobile users in a terrestrial environment commonly encounter blockage due to vegetation, terrain or buildings. Consequently, high elevation angles are of premium value. TRW studied the issues and concluded that a Medium Earth Orbit constellation is the best solution for Personal Communications Satellite Service. TRW has developed Odyssey, which uses twelve satellites in medium altitude orbit to provide personal communications satellite service. The Odyssey communications system projects a multibeam antenna pattern to the Earth. The attitude control system orients the satellites to ensure constant coverage of land mass and coastal areas. Pointing can be reprogrammed by ground control to ensure optimized coverage of the desired service areas. The payload architecture features non-processing, “bent pipe” transponders and matrix amplifiers to ensure dynamic power delivery to high demand areas. Circuit capacity is 3000 circuits per satellite. Each satellite weighs 1917 kg (4226 pounds) at launch and the solar arrays provide 3126 Watts of power. Satellites are launched in pairs on Ariane, Atlas, or other vehicles. Each satellite is placed in a circular orbit at an altitude of 10,354 km. There are three orbit planes inclined at 55° to the equatorial plane. Deployment of the satellites permits phased introduction of service. After only three launches, in which two satellites are launched into each plane, continuous service can be provided to most of the world. After three more launches for a total of 12 satellites, service can be expanded to all populated regions of the Earth with path diversity to most regions. The Odyssey system is superior to both geostationary satellites and low earth orbiting satellites. Odyssey provides many benefits to the end user which are described in the paper. These include: low cost, convenience, high availability, reliability, and acceptable time delay. Odyssey exhibits benefits for telecommunications operators: simple operations, incremental, phased startup, long space segment life-time, high profitability, dynamic flexibility for adjustment and short time to market. Since submission of an FCC application in 1991, TRW has continued to explore ways to further improve the Odyssey approach by expanding coverage to the entire world and reducing the initial investment while maintaining high quality service.

A systems approach to the commercialization of space communications technology: The NASA/JPL Mobile Satellite Program

This paper discusses the systems approach taken by NASA and the Jet Propulsion Laboratory in the commercialization of land-mobile satellite services (LMSS) in the United States. As the lead center for NASA's Mobile Satellite Program, JPL was involved in identifying and addressing many of the key barriers to commercialization of mobile satellite communications, including technical, economic, regulatory and institutional risks, or uncertainties. The systems engineering approach described here was used to mitigate these risks. The result was the development and implementation of the JPL Mobile Satellite Experiment Project. This Project included not only technology development, but also studies to support NASA in the definition of the regulatory, market, and investment environments within which LMSS would evolve and eventually operate, as well as initiatives to mitigate their associated commercialization risks. The end result of these government-led endeavors was the acceleration of the introduction of commercial mobile satellite services, both nationally and internationally.

Performance evaluation of channel-sensitive, stabilized multiple access schemes for land-mobile satellite services using a hybrid simulation tool

A hybrid simulation tool for real-time performance measurements of complete networks is presented. The simulation tool combines the advantages of software and hardware modules. Recorded channel data are included. They allow the reproduction of realistic situations in the laboratory. Synchronization problems and noise are considered. As an example, stabilized slotted ALOHA access protocols were implemented and investigated in land-mobile satellite environments. A slotted ALOHA-based modified channel access strategy for highly unreliable channels is proposed requiring all mobile stations to estimate the link quality before starting a transmission. The different strategies are analyzed by simulation as well as the analytical methods. Transmission parameters are determined and optimized using a combination of analysis and simulation. The results show the power of the simulation tool and the better performance of stabilized slotted ALOHA with link-quality estimation in city channels.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Land mobile satellite communication system using the geostationary platform

If the geostationary platform (GPF) is available in the first decade of the 21st century, the demand on a voice communication base is expected to be about 800,000 Land Mobile Satellite Service (LMSS) terminals. To improve the frequency use of an LMSS over Japan, it is important to reuse the frequencies allocated to the Tokyo metropolitan area in the Osaka-Kobe-Kyoto region. An onboard multibeam antenna with beam intervals of 0.468 deg (L band 30-m class) for each of the 11 beams covering the main Japanese islands, cluster power feeding, and dual polarization can enable the reuse of frequencies at one-beam intervals. A deployable antenna is under development that is lightweight and has a high storage efficiency for launching. This will form the basis for an antenna with an aperture diameter of 30 m. Such a large antenna will be a key factor in reducing ground terminal size. This paper estimates the weight and power requirements of the mission payloads onboard the GPF, which include an LMSS, a millimeter wave personal satellite communication system, and a high-definition television/regional television satellite broadcasting service system. The total weight of this GPF would be approximately 4-5 tons.

Development of Land Mobile Satellite Services in Europe

This paper was presented at the Institutes NAV90 Conference but was received too late for inclusion in the Proceedings. Copies of the Proceedings are available on application to the Director.

Radio Astronomy at WARC MOB-87

ABSTRACTThe World Administrative Radio Conference for the Mobile Services (WARC Mob-87), held in Geneva in September-October, 1987, took several actions that will have an impact on radio astronomy. Worldwide frequency allocations were made for the Radiodetermination Satellite Service (RDSS) in the 1610 to 1626.5 MHz band. The secondary allocation to radio astronomy in this band has received strong protection, however. The 1660 to 1660.5 MHz band, which radio astronomy shared on a primary basis with the Aeronautical Mobile Satellite Service has been reallocated to the Land Mobile Satellite Service, shared with radio astronomy on a similar basis. The impact that this reallocation will have on radio astronomy is not clear. Since the Radioastronomy Service is primary in the band, Mobile Satellite Systems that evolve will have to provide adequate protection. Perhaps most significantly, WARC Mob-87 recommended that a conference be convened to reallocate all bands in the 1 to 3 GHz range, no later than in 1992. Several other conferences dealing with particular services have been proposed. At first glance, some of these some of these proposals may not appear to have an impact on radio astronomy. They will, however, increase the pressure on the entire radio spectrum. Finally, it is highly likely that a General WARC will be proposed to be held before the end of the 1990s. The radio astronomy community will have to prepare for these conferences.

Management of transponder resources in mobile satellite systems

Allocation of L-band spectrum for land mobile satellite (MSAT) services in Mobile-WARC-87 paves the way for the introduction of such services in the early 1990s. An overview of the proposed network architecture of the Canadian MSAT network is presented. Management of transponder resources, i.e. power, bandwidth, and spot-beam antennas, which poses a set of unique and significant problems in the design and operation of MSAT networks, is addressed. The three-level hierarchical approach used by the Canadian network is described, and the technical requirements for solving the above problems are identified. The two upper levels employ reconfigurable fixed assignment for allocating transponders to antenna spot beams, and transponder power and bandwidth to different services. The lowest level employs demand assignment and packet multiple access protocols for resource sharing among different subscribers. Uncoupling the resource management problems into manageable portions reduces the complexity and enhances the robustness of the network.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Land mobile satellite services in Europe

The demand for land-mobile communications on a Europe-wide basis is an important and pressing problem. The pan-European cellular network now in the planning stage will be slow in coming and it will have its limitations. A regional satellite system for Europe to complement the cellular network is the only practical way to satisfy a specialised market that encompasses a population of several hundred thousand mobiles, including road vehicles, merchant shipping, fishing boats, and trains. The deployment of a regional system would take place in a number of phases, the first being based on a simple payload embarked on a host satellite belonging to a European organisation. Further phases will involve the development of more advanced payloads on dedicated satellites. For the long-term future, the use of satellites in highly inclined orbits is being considered as a means of improving their visibility and hence the service quality.

The Advent of Land Mobile Satellite Service Systems

The practicality of providing cellular-type communications service to underserved remote areas of the country is now possible through the use of satellites in geostationary orbit. The advent of high-power, land-mobile satellites, coupled with high-performance, low-cost ground receivers, makes it possible to provide mobile radio, mobile telephone, data communication, and other services to large numbers of rural and suburban users. A recent Federal Communications Commission (FCC) decision has allocated L-band (1.5 GHz, 1.6 GHz) spectrum to this service. Even though there is a significant amount of spectrum available at L-band, the expected demand for this service is high and spectral efficient means must be devised to maintain sufficient capacity. Expedient means used to increase capacity, in the absence of additional spectrum, are single channel per carrier, demand assignment multiple access (SCPC-DAMA) with voice, frequency reuse via multiple beams, and orbital reuse by using multiple satellites. Some of the operational, systemic, and technological considerations of the first generation land mobile satellite service (LMSS) that would provide thin-route services to large land masses of North America are considered here.

The Impact of the 1979 World Administrative Radio Conference on the Fixed-Satellite, Inter-Satellite, and Mobile-Satellite Services

The Fixed-Satellite service (FSS) is the most heavily used and still the fastest growing of the seventeen space radio communications services recognized by the International Telecommunication Union (ITU). To provide the additional spectrum needed for continued growth in both domestic and international satellite networks, the ITU's 1979 World Administrative Radio Conference (WARC-79) more than doubled the bandwidth allocated to this service in most parts of the spectrum. The Inter-Satellite service (ISS) is an "auxilliary" service whose allocations are intended to provide intersatellite links between the space stations of other services. Although not yet implemented in commercial systems, such links are expected to be used extensively in future FSS networks. To permit the introduction of the ISS earlier and at lower cost than would be possible with the existing allocations above 50 GHz, WARC-79 allocated two 1-GHz-wide bands to the ISS at 23 and 33 GHz. The Mobile-Satellite services (MSS) include land, maritime, and aeronautical components. WARC-79 left the Aeronautical-Mobile Satellite allocations essentially unchanged, created new possibilities for development in the Land-Mobile Satellite service, and essentially doubled the spectrum that will be available to the Maritime-Mobile Satellite service. WARC-79 made only minor changes to the regulatory procedures for gaining access to the various space service allocations. However, in response to the concerns of developing nations about equitable access to the spectrum and the geostationary satellite orbit for future satellite systems, WARC-79 resolved to convene another World Administrative Radio Conference in two sessions scheduled for 1984 and 1985 (WARC-84/85). This Space Conference would consider the use of the geostationary satellite orbit and the planning of the space services using it with the objective of guaranteeing in practice for all countries equitable access to the orbit. This paper provides a detailed description of the WARC-79 allocation actions affecting the FSS, ISS, and MSS and provides background on the decision to convene WARC- 84/85.

The Impact of the 1979 World Administrative Radio Conference on the Fixed-Satellite, Inter-Satellite, and Mobile-Satellite Services

The Fixed-Satellite service (FSS) is the most heavily used and still the fastest growing of the seventeen space radio communications services recognized by the International Telecommunication Union (ITU). To provide the additional spectrum needed for continued growth in both domestic and international satellite networks, the ITU's 1979 World Administrative Radio Conference (WARC-79) more than doubled the bandwidth allocated to this service in most parts of the spectrum. The Inter-Satellite service (ISS) is an auxilliary service whose allocations are intended to provide intersatellite links between the space stations of other services. Although not yet implemented in commercial systems, such links are expected to be used extensively in future FSS networks. To permit the introduction of the ISS earlier and at lower cost than would be possible with the existing allocations above 50 GHz, WARC-79 allocated two 1-GHz-wide bands to the ISS at 23 and 33 GHz. The Mobile-Satellite services (MSS) include land, maritime, and aeronautical components. WARC-79 left the Aeronautical-Mobile Satellite allocations essentially unchanged, created new possibilities for development in the Land-Mobile Satellite service, and essentially doubled the spectrum that will be available to the Maritime-Mobile Satellite service. WARC-79 made only minor changes to the regulatory procedures for gaining access to the various space service allocations. However, in response to the concerns of developing nations about equitable access to the spectrum and the geostationary satellite orbit for future satellite systems, WARC-79 resolved to convene another World Administrative Radio Conference in two sessions scheduled for 1984 and 1985 (WARC-84/85).