Mobile Satellite Systems Research Articles

Propagation Modeling and Simulation For Land Mobile Satellite Systems

Land Mobile Satellite Systems (LMSS) provide voice and data communications to mobile users via a geosynchronouss satellite. LMSS is an advanced communications technology which combines satellite and mobile communications techniques. Propagation considerations are very important for a reliable LMSS. Trees shadowing and multipath propagation effects due to scattering from the surrounding terrain are the dominant effects. These effects cause fading at reception. For link design, fading level or excess path loss must be known. A LMSS propagation model is developed using statistical distribution functions of shadowing and multipath propagation. The model parameters are obtained from experimental data. Propagation measurements at the L band have been made to determine the model parametters. Fading distribution and fading depth are obtained using the model and simulation for different LMSS propagation environments.

PCS global mobile satellites

As the new era dawns in wireless information systems, mobile satellite services (MSS) are emerging as an integral component in what has become the turn-of-the-century global communication network. It is generally agreed that the universal personal communication paradigm is the confluence of terrestrial-based and satellite-based systems. PCS users will neither know nor care if their calls are being carried by satellite or cellular. Unlike their terrestrial-based counterparts. The MSS, with their global blanket coverage, are truly able to realize the vision of communications from anywhere at any time for people on the move. The MSS are also being used in developing countries without existing wireline networks to provide rapid, ubiquitous telephone service. This article provides an overview of mobile satellite systems and concepts. The materials presented are geared toward a broad audience with engineering or management back grounds.

Combined handover algorithm for dynamic satellite constellations

A combined handover algorithm is proposed for a dynamic mobile satellite system. Handover decisions are based on user terminal (UT) position and signal strength measurement. The handover performances considered are handover position and call termination probability.

Microstrip annular ring slot antennas for mobile applications

An annular slot on triplate feed is discussed which is suitable for use with vehicular mobile satellite systems. The slot is excited in a higher order mode and circularly polarised to give a conical radiation pattern. The slot can operate on a high dielectric base and a superstrate improves the gain.

Evaluation of handover mechanisms in shadowed low earth orbit land mobile satellite systems

AbstractThis paper presents a quantitative analysis by computer simulation of the active set update (ASU) handover algorithm for a shadowed low earth orbit (LEO) land mobile satellite (LMS) environment. As a precursor to the handover analysis, the mutual visibility statistics for a 66 satellite polar and 48 satellite rosette‐type constellation are presented. These results show the statistical nature of the levels of satellite diversity and mobile‐to‐satellite elevation angles (to the highest satellite) within each network and also indicate the influence of the channel characteristics on the handover strategy. A two‐state Markov modulated channel model is assumed in the handover analysis, and this enables the assessment of increased levels of power and time hysteresis on the quality of service and network signalling load in a shadowed land mobile satellite environment. In particular, attention is given to the different modes of ASU operation for hard handover, switch diversity and soft handover.

Multiple-access capacity in mobile user satellite systems

The channel capacity of a satellite direct sequence CDMA system is analyzed including the effects of faded user interference, overlapping antenna beams, imperfect equalization of the antenna pattern across an antenna cell, and diversity reception. Simplified models are used to describe the impact of these effects on the channel capacity of single and multiple cofrequency CDMA systems. In a comparison of the uplink and downlink paths, the uplink of the CDMA system is shown to limit the channel capacity because the downlink can utilize code-orthogonality and coherent demodulation. In a multiple system comparison between band-shared CDMA and band-segmented FDMA/TDMA technologies, FDMA/TDMA is shown to provide about the same capacity for uniformly distributed traffic conditions over many cells and dramatically better capacity when traffic is concentrated in one cell. Due to the peak nature of telephony, this result supports the use of band-segmented systems in mobile user satellite systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

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.

Analysis of LEO, MEO, and GEO global mobile satellite systems in the presence of interference and fading

Several multisatellite and multispot systems have been recently proposed for provision of mobile and personal services with global coverage, adopting GEO or non-GEO (i.e., MEO, LEO) satellite constellations. The paper addresses an in-depth analysis of these constellations, evaluating both geometrical performance measures and cochannel interference levels caused by extensive frequency reuse. The geometrical analysis yields the statistics for coverage, frequency of satellite hand-overs, and link absence periods. The interference analysis is based on a general model valid for all access techniques, which is here applied to the case of FDMA. The outage probability as a function of the specification on carrier-to-interference power ratio is evaluated for four selected constellations. Several techniques are introduced for interference reduction in non-GEO systems, in which the satellites coverage areas may intersect: spot turnoff, intraorbital plane frequency division, and interorbital plane frequency division. The effects of Rice fading have also been analyzed by means of an analytic approximated method. The overall analysis allows a fair comparison between LEO, MEO, and GEO constellations. >

Phase synchronization in a satellite‐mobile channel

AbstractThis paper studies several aspects relevant to the design of phase synchronization circuits for land mobile satellite systems (LMSS). First, the results of a propagation experiment are presented, with special focus on the effects of vehicle mobility on the signal phase. It is found that the changes of speed and direction cause frequency variations that can be modelled as linear. Bounds for the frequency derivative are given for different percentages of time. The use of third‐order PLLs is considered, as they are optimum for tracking a frequency ramp embedded in white Gaussian noise. The model of third‐order PLL employed is presented, as it is an original model, developed by the authors. Then the performances of second‐ and third‐order PLLs are compared. Theoretical, as well as simulation, results are given. It is shown that third‐order loops give better performance in the presence of frequency variations of the kind observed in this link, but they suffer from a higher sensitivity to oscillators' phase noise. Several conclusions regarding the use of third‐order loops in future systems are presented.

Covariance matrix properties and multiple symbol/soft decision detection in slow flat Rician fading

For a small number of symbols N and slow flat fading channels, it is shown that covariance matrices encountered in practice have two nonnegligible eigenvalues, the first much larger than the second, with a symmetric eigenvector associated with the first eigenvalue, and a skew symmetric eigenvector associated with the second eigenvalue. The first eigenvector is well approximated by a conditional mean, and the second eigenvector represents a small drift about the mean. The eigenvalues and eigenvectors of the slow flat fading channel covariance matrix are shown to be strongly related to those of a certain conditional covariance matrix. The maximum likelihood (ML) rules for block hard decision and symbol-by-symbol hard decision, and a rule for soft decision detection of M-DPSK, all using multiple symbol information, are obtained for the Rician channel as a function of N. The eigenvalue-eigenvector results lead to practical implementations of all rules. For small to moderate N, it is shown that a simple open-loop algorithm, of complexity N log N, attains the performance of the ML decision rules for an E/sub s//N/sub 0/ range of interest for several land mobile satellite systems. The ML decision rules are seen to give rapidly diminishing returns as N increases, showing that simple noncoherent techniques can have very effective performance for the Rician fading channel. Lastly, several conclusions are drawn about the asymptotic channel behavior, including the Rayleigh channel. The work is directly applicable to the Australian and North American land mobile satellite systems. >

Open-loop power control error in a land mobile satellite system

In order to combat large scale shadowing and distance losses in a land mobile satellite system, an adaptive power control (APC) scheme is essential. Such a scheme, implemented on the uplink ensures that all users' signals arrive at the base station with equal average power as they move within the satellite spot beam-an important requirement in a CDMA system. Because of the lengthy round-trip delay on a satellite link, closed-loop power control systems are only of marginal benefit. Therefore, an open-loop APC scheme is proposed to counteract the effects of shadowing and distance loss. A fairly general channel model, consisting of log-normal shadowing and Rician fading, is assumed. This can be applied to a specific two-state land mobile satellite channel model, involving shadowed intervals with Rayleigh fading and unshadowed intervals with Rician fading. It is found that the power control error can be approximated by a log-normally distributed random variable. To quantify the performance of the APC, the standard deviation of the power control error in decibels is analyzed as a function of the specular power-to-scatter power ratio, the measurement time and the vehicle velocity. To illustrate the usefulness of the results, we analyze the effect of the power control error on the system capacity of a CDMA mobile satellite link. >

The ITU's role in the restructuring revolution

The ITU recognizes a twofold mission: to monitor regulatory policy changes and technological developments to be in a position to advise members; and to link restructuring changes to overall basic telecommunication development needs. The fundamental goal of the international community in this sector is to achieve universal access to basic telecommunications services. In this context, restructuring is but one component, although the global challenge is to work together to ensure that the restructuring revolution paves the way to filling the development gap. It is readily admitted that new technologies such as mobile satellite systems enable developing countries to leapfrog their infrastructure problems, and that governments recognize the potential benefits of these new technologies and the need to reform regulations in order to facilitate the introduction of these services. >

Signal statistics obtained from a LMSS experiment in Europe with the MARECS satellite

A land mobile satellite system (LMSS) propagation experiment at 1.5 GHz has been carried out in Europe in the framework of ESA's PROSAT program using the MARECS satellite as the signal source. Rural, suburban and urban environments were investigated in Spain, France and Sweden in order to analyze the propagation factors responsible for degradations in LMSS. A second series of tests were performed in Spain using a locomotive as mobile platform. The results obtained show that shadowing is the main impairment in LMSS, achieving availabilities of 80-90% for the unfaded signal which decrease to 30% for the extreme cases of urban environments, dense woods, or suburban environments in low elevation angles, or railroads with a large number of tunnels. >

Facsimile transmission over digital satellite land-mobile channels

The importance of facsimile communication over public telephone networks is evidenced by the rapid growth in the number of Group 3 facsimile terminals. In this paper, the main characteristics of a real-time approach are described whereby facsimile signals are demodulated and their associated protocols are packetized and converted by a Facsimile Interface Unit (FIU) to a format suitable for transmission over digital land-mobile satellite channels. The FIU concept was developed to allow off-the-shelf facsimile terminals to be interconnected via the PSTN through satellite networks and to permit the provision of enhanced user services, such as facsimile broadcasting (point-to-multipoint) to mobile terminals, to be offered. In addition, the FIU concept is designed to mitigate for the longer access and transport link delays encountered in mobile satellite systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

ASSESSMENT OF A PUBLIC MOBILE SATELLITE SYSTEM COMPATIBLE WITH THE GSM CELLULAR NETWORK

AbstractThe integration between cellular networks and satellite systems is a very promising issue, since it permits the immediate provision of the radio services offered by the cellular networks to areas lacking in terrestrial facilities.In this paper the viability of a full integration between the GSM cellular network and a satellite system is dealt with. The L‐band land mobile payload has been assumed as a reference; nevertheless the presented results can be extended to other payloads.The basic requirement of full integration is that the insertion of the satellite system does not entail any modification of the already existing GSM network.The integration analysis has been carried out by examining both the link feasibility and the network architecture.As far as link feasibility is concerned, the analysis is performed by means of an ad hoc simulation tool developed at CSELT (Turin). The simulation results are displayed for GSM speech channels at both full‐rate (TCH/FS) and half‐rate (TCH/HS). Such results are used in order to compute the satellite link budgets and the satellite system capacity. The characteristics of the satellite propagation channel, of the satellite‐compatible mobile station and of the reference payload are explained as well.As far as the network architecture is concerned, the paper identifies the most promising satellite system configuration and the satellite system counterpart of the GSM functional areas (cell, location area, MSC area). Moreover, the problems and the relevant solutions related to the extension of the main GSM procedures (e.g. call set‐up, cell selection/reselection, handover) to the integrated network are dealt with.This paper is based upon the work performed by the authors in the framework of the European Space Agency (ESA) study: ‘Assessment of a public mobile satellite system compatible with the GSM cellular network’, Telespazio (Rome) is the prime contractor of this study.The opinions herewith reported are not necessarily those of ESA.

Mobile radio group communications by satellite

Mobile radio group communications enable a closed group of users to communicate among themselves using push-to-talk (PTT), half duplex transmissions, such that one's transmission is received by all. New protocol designs are presented which support group communications over mobile satellite systems. A new demand assignment multiple access (DAMA) protocol is necessitated by the inappropriateness of call-based channel assignments. Channels are assigned to individual user-groups engaged in active conversations. As members of a user-group contend for access to the assigned channel, access control by the usual manual methods is ineffective due to the very long round trip delay. A novel signaling protocol which automates access control is proposed. Carrier sensing, signal capture, and collision detection are employed to minimize access contentions. The throughput and holding time of the assigned channel are analyzed. Numerical results show that the access control protocol improves the capacity of the assigned channel by up to 65%. >

The American mobile satellite system

This paper describes the present status and plans of three programs of the American Mobile Satellite Corporation, who was authorized to construct, launch and operate satellites to provide mobile satellite services to the U.S. and Puerto Rico. The three programs concern the space segment, the ground segment and the First Service. This paper also provides an update on related business arrangements and regulatory matters.

Novel calibration technique employing a spread-spectrum tone for mobile satellite systems

A calibration technique based on a low-power spread-spectrum tone to assist demodulation is presented. The technique does not impose any requirements on signal modulation, spectral shaping, nor on channel spacing, and is highly spectrum efficient. The performance is analysed in the presence of cochannel and adjacent channel interference, diffused-multipath fading and additive white Gaussian noise, and results are presented for M-PSK. (M = 2, 4, 8).

Further results on LMSS experiment in Kyoto City

In February of 1990, land mobile satellite experiments were conducted in Kyoto City, Japan, using the Engineering Test Satellite V (ETS-V). The received signal strength was recorded, as was the speed of the mobile as it traversed various downtown streets. The setting was that of a built-up urban area with medium and high rise buildings, electric utility poles, and trees lining the streets. These caused obstruction to the satellite line of sight (LOS). The signal level fluctuation due to diffraction of radio waves by the urban structures is analyzed. The results obtained from the measurements and theoretical calculation agree. The spatial frequencies due to diffraction are found to vary between 1.8 Hz to 5.3 Hz. It is concluded that this variation of received signal level will not adversely affect the receiver performance. Based on recorded signal strength, the performance of a digital land mobile satellite system (LMSS), under the above mentioned environment, is analyzed and the results presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Transmission of group 3 facsimile over inmarsat maritime digital satellite mobile channels

AbstractThe importance of facsimile communication over public telephone networks is evidenced by the rapid growth in the number of Group 3 facsimile end‐user terminals. In this paper the main characteristics of a real‐time bit‐rate reducing approach are described whereby facsimile signals are demodulated and their associated protocols converted by a facsimile interface unit (FIU) to a format suitable for transmission over Inmarsat‐B maritime digital satellite channels. The FIU concept was developed to allow ‘off‐the‐shelf’ facsimile terminals to be interconnected via the PSTN through Inmarsat's satellite networks and to permit the provision of enhanced user services by converting Group 3 facsimile protocols to broadcast operation. In addition, the FIU concept is designed to compensate for the longer access and transport link delays encountered in mobile satellite systems, and to permit facsimile call recovery procedures to be successfully concatenated with satellite channel error detection mechanisms.