Showing papers by "Barry G. Evans published in 1998"
TL;DR: A time-series propagation model in mobile-satellite channels which considers 3D path profiles based on the Fresnel-Kirchhoff theory leads to time- series which have both first- and second-order statistics similar to real outdoor measurements.
Abstract: The authors describe a time-series propagation model in mobile-satellite channels which considers 3D path profiles. Based on the Fresnel-Kirchhoff theory, the prediction is produced by considering statistical distributions for the building profile, leading to time-series which have both first- and second-order statistics similar to real outdoor measurements.
30 citations
TL;DR: In this article, the spectra of the two beacon signals were compared and scintillation amplitudes were extracted from the raw beacon data using a high-pass filter set at 14 different cutoff frequencies f/sub c/ ranging between 2-400 mHz.
Abstract: Beacon measurements on a moderate elevation satellite link at 20 and 30 GHz during concurrent scintillation and rain attenuation are analyzed. The spectra of the two beacon signals are compared and scintillation amplitudes are extracted from the raw beacon data using a high-pass filter set at 14 different cutoff frequencies f/sub c/ ranging between 2-400 mHz. The effect on scintillation statistics of the choice of f/sub c/ and the dependence of this choice on path elevation angle are discussed.
24 citations
TL;DR: An efficient hardware structure is reported for the Walsh-Hadamard transform based on the radix-2 algorithm, which can be implemented with shift registers and controllable adder/subtracters for high processing throughput.
Abstract: An efficient hardware structure is reported for the Walsh-Hadamard transform. Based on the radix-2 algorithm, the structure can be implemented with shift registers and controllable adder/subtracters for high processing throughput. Such an implementation is particularly suited to applications that require real-time operations and interface directly with sequential input data.
20 citations
18 May 1998
TL;DR: In this article, the authors analyzed the availability of service of two first generation satellite systems in urban environments and compared the shadowing characteristics of two different types of urban/city environments over the entire latitude range.
Abstract: We analyse the availability of service of two proposed 1st generation satellite systems in urban environments. We present results of the projected availability of service of each of these systems in two different types of urban/city environments over the entire latitude range. These two types of urban environment are a typical American city (e.g. LA) and typical European city (e.g. London). The shadowing and satellite channel correlation information was extracted from photographs taken with a fish-eye camera lens in the aforementioned urban areas. The shadowing characteristics of the two different types of urban/city environment are compared.
15 citations
01 Jan 1998
TL;DR: This study focuses on parameter optimisation of the multiple access schemes for ATM over a GEO satellite with on-board processing capabilities, considering various traffic mixes of Constant Bit Rate (CBR), real-time VBR (rt-VBR), non-real-timeVBR (nrt- VBR) and Unspecified Bit Rate(UBR).
Abstract: In this paper we analyse the performance of an Adaptive Random-Reservation Medium Access Control (MAC) protocol which can support all ATM service classes while providing the required Quality of Service (QoS). Our study focuses on parameter optimisation of the multiple access schemes for ATM over a GEO satellite with on-board processing capabilities, considering various traffic mixes of Constant Bit Rate (CBR), real-time VBR (rt-VBR), non-real-time VBR (nrt-VBR) and Unspecified Bit Rate (UBR). It is shown that a TDMA access protocol combining both Random Access and Demand Assignment Multiple Access (DAMA) can achieve a high throughput and is particularly suited for a scenario with a high number of terminals with very bursty UBR traffic (e.g. web browsing). The adaptive MAC protocol was designed to allow statistical multiplexing of ATM traffic over the air interface, especially for the independent and spatially distributed terminals. It is shown that the potential user population which can be served is considerably increased by statistically multiplexing bursty traffic over the air interface.
14 citations
TL;DR: The architecture and performance studies of demonstrations of broadband network interconnection using ATM over satellite developed in the RACE II CATALYST project are presented and techniques to improve the performance of the system are explained and information on progress is provided.
11 citations
18 May 1998
TL;DR: A physical-statistical model of satellite diversity, for particular application to non-geostationary satellite PCN systems operated in built-up areas, is proposed and found to be in excellent agreement with analysis of real buildings.
Abstract: This paper proposes a physical-statistical model of satellite diversity, for particular application to non-geostationary satellite PCN systems operated in built-up areas. The output of the model is an explicit formulation for the correlation between shadowing states associated with pairs of satellites, which can be used as input for Markov models of the satellite channel. Results are presented for a number of practical cases and are found to be in excellent agreement with analysis of real buildings.
11 citations
18 May 1998
TL;DR: It is shown that maximum throughput can be achieved by using this access scheme and a TDMA access protocol combining both random access and demand assignment multiple access (DAMA) is particularly suited for a scenario with a high number of terminals with very bursty UBR traffic.
Abstract: We analyse the performance of an adaptive random-reservation medium access control (MAC) protocol which can support all ATM service classes while providing the required quality of service (QoS). Our study focuses on parameter optimisation of the multiple access schemes for ATM over a GEO satellite with on-board processing capabilities, considering various traffic mixes of constant bit rate (CBR), real-time VBR (RT-VBR), non-real time VBR (NRT-VBR) and unspecified bit rate (UBR). It is shown that maximum throughput can be achieved by using this access scheme. A TDMA access protocol combining both random access and demand assignment multiple access (DAMA) is particularly suited for a scenario with a high number of terminals with very bursty UBR traffic (e.g. Web browsing). UBR sources with short burst length access the slots remaining after the reservation procedure by random access which drastically reduces the slot access delay, at the expense of lower utilisation. However for UBR sources with burst sizes consisting of several ATM cells, reservation access provides higher throughput but the access delay is considerable longer.
10 citations
TL;DR: A mutual authentication protocol between the user and the satellite network is presented using digital signature and public key systems to provide end-to-end authentication and negotiation of security options such as selecting a secret key system and the key length.
Abstract: In recent years there has been increasing interest in interconnecting satellite and ATM networks, because both share common characteristics of the ability to provide bandwidth-on-demand and flexibility of integrating voice, video and data services. There are several new satellite constellation proposals that support multimedia service and transport ATM traffic. For a successful implementation of such systems it is essential to address the security requirements of users, satellite ATM network operators and multimedia service providers. In order to minimize delay and the cost of implementing security systems for satellite ATM networks, the network operator role (in security services) can be limited to the mutual authentication with satellite users during call set-up periods. In this paper a mutual authentication protocol between the user and the satellite network is presented using digital signature and public key systems. Also, another mutual authentication protocol between the user and the service provider is presented to provide end-to-end authentication and negotiation of security options such as selecting a secret key system and the key length. Finally, a detailed hardware implementation of ATM cell payload encryption is presented using the DES/TripleDES secret key system.
9 citations
01 Nov 1998
TL;DR: In this article, a time series propagation model for three-dimensional urban path profiles where the buildings can have unequal heights, widths and spacings based on the Fresnel-Kirchhoff theory is proposed.
Abstract: The present work describes a time series propagation model which considers three-dimensional urban path profiles where the buildings can have unequal heights, widths and spacings Based on the Fresnel-Kirchhoff theory, it is mainly applicable to mobile satellite propagation channels where the final building face, just before the mobile user, is the most dominant source of diffraction phenomena Although the model is considered to adopt a deterministic type of process, the outcome of the proposed work is achieved by considering only statistical distributions for the building path profile
8 citations
TL;DR: This paper considers a configuration where uplink transmitter beam-size is controlled in real-time in response to measured turbulence parameters to maximize mean intensity and minimize fluctuations on the satellite receiver.
Abstract: Atmospheric turbulence severely degrades the performance of uplinks. Employment of adaptive optics to enhance ground-space laser communication systems has recently been considered and possible benefits have been shown. Uplink scintillation reduction by using multiple transmitters is also being considered. What appears to be currently missing in these works is the realization that transmitter beam-size is a crucial design parameter and its optimum value changes continuously according to changing turbulence conditions along the propagation path. In this paper we consider a configuration where uplink transmitter beam-size is controlled in real-time in response to measured turbulence parameters to maximize mean intensity and minimize fluctuations on the satellite receiver. Controlling the beam-size, especially by a factor of two or so, in relatively long time scales (seconds) should not be a problem. Although it is obvious that this will greatly improve the performance of especially a variable data rate communication system, we find that the current state of knowledge is fragmentary and insufficient to quantify the improvement in any general and sufficiently accurate way. Semi-analytic simulations can be useful in exploring the improvement for different scenarios and site conditions© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
TL;DR: Further evidence of the strong correlation between sky-noise temperature and scintillation intensity at 12.5 GHz is revealed in this paper, where predictions from an measurement derived linear regression fit are compared with CCIR predictions.
Abstract: Further evidence of the strong correlation between sky-noise temperature and scintillation intensity at 12.5 GHz is revealed. Predictions from an measurement derived linear regression fit are compared with CCIR predictions and show a net improvement in the accuracy of the scintillation levels. Extrapolation to 30 GHz also gives reasonably accurate intensities.
07 Jun 1998
TL;DR: The performance of a medium access control (MAC) protocol which is particularly suited for a scenario with a high number of terminals with very bursty unspecified bit rate traffic (e.g. web browsing) is analyzed.
Abstract: In this paper we analyse the performance of a medium access control (MAC) protocol which is particularly suited for a scenario with a high number of terminals with very bursty unspecified bit rate (UBR) traffic (e.g. web browsing). In order to guarantee the required quality of service (QoS) requested by the user for all ATM service classes, priorities between the service classes must be implemented. Hence prioritised queueing of requests is proposed. The adaptive MAC protocol was designed to allow statistical multiplexing of ATM traffic over the air interface, especially for independent and spatially distributed terminals. It is shown that the potential user population which can be served is considerably increased by statistically multiplexing bursty traffic over the air interface.
TL;DR: From the results it can be seen that the interbeam handover probability depends strongly on the roll-off characteristics of the beam pattern and forced termination and time availability depend on the quality of the received signal and the selected criterion.
Abstract: This paper evaluates the performance of interbeam handover in LEO Satellite systems. The evaluation is based on an analytical model that is specific for interbeam handover. There are three performance parameters concerned: handover probability, forced termination probability, and time availability. From the results, it can be seen that the interbeam handover probability strongly depends on the roll-off characteristics of the beam pattern. Forced termination and time availability depend on the quality of the received signal and the selected criterion. A comparison between the use of signal level and position as handover criteria is presented.
01 Apr 1998
TL;DR: This paper analyzes the performance of an Adaptive Random-Reservation Medium Access Control (MAC) protocol which can support all ATM service classes while providing the required Quality of Service (QoS) and shows that maximum throughput can be achieved by using this access scheme.
Abstract: In this paper we analyse the performance of an Adaptive Random-Reservation Medium Access Control (MAC) protocol which can support all ATM service classes while providing the required Quality of Service (QoS). Our study focuses on parameter optimisation of the multiple access schemes for ATM over a GEO satellite with on-board processing capabilities, considering various traffic mixes of Constant Bit Rate (CBR), real-time Variable Bit Rate (rt VBR), non-real-time VBR (nrt VBR) and Unspecified Bit Rate (UBR). It is shown that maximum throughput can be achieved by using this access scheme. A TDMA access protocol combining both Random Access and Demand Assignment Multiple Access (DAMA) is particularly suited for a scenario with a high number of terminals and very bursty UBR traffic (e.g. web browsing). UBR sources with short burst length access the slots remaining after the reservation procedure by random access which drastically reduces the slot access delay, at the expense of lower utilisation.
TL;DR: In this article, experimental evidence for a negative exponential distribution of intensity in a ground-to-satellite optical link is presented, and it is shown that too large a beam size can have deleterious effects on fading performance.
Abstract: Experimental evidence for a negative exponential distribution of intensity in a ground-to-satellite optical link is presented. The asymptotic limit for the normalised variance of intensity is unity, but both theoretical and experimental results show that this limit is approached very slowly. It is apparent that too large a beam size can have deleterious effects on fading performance.
TL;DR: The performance of multilevel trellis-coded modulations for satellite mobile multimedia systems using synchronous CDMA and the impact on the transmission of synchronization errors between the different users is presented and the power control requirements are derived.
Abstract: In this paper the performance of multilevel trellis-coded modulations (MTCMs) for satellite mobile multimedia systems using synchronous CDMA is investigated. A model for the multiple-access interference arising from the non-orthogonality of the spreading waveforms is developed for different modulation and spreading schemes and transmission over the mobile satellite channel. Using this model, the performance of MTCMs for synchronous CDMA is analysed and compared with the Ungerboeck and Schegel-Costello trellis-coded modulation (TCM) designs. The impact on the transmission of synchronization errors between the different users is presented and the power control requirements are derived.
TL;DR: A mobile terminal positioning scheme in Non-Geostationary satellite constellation systems is presented and it is shown that the positioning accuracy error is minimised when dual-satellite diversity is utilised.
Abstract: A mobile terminal positioning scheme in Non-Geostationary satellite constellation systems is presented. The scheme utilises the propagation delay and Doppler shifts experienced in such dynamic constellations. The various factors that affect the accuracy of a user position have been identified and thoroughly investigated; to demonstrate the user position accuracy results, an ICO-10 like satellite constellation was used with different measurement noise conditions. The scheme does not impose any additional signalling on the air-interface and the user position can be estimated at an LES with no assistance from the mobile terminal. It will also be shown that the positioning accuracy error is minimised when dual-satellite diversity is utilised. In this paper, we also discuss the applications of this user position information and its impact on management of mobility and resources. © 1998 John Wiley & Sons, Ltd.
TL;DR: The THESEUS project as mentioned in this paper developed a terminal that enables stock brokers located in Europe to communicate not only with their national stock exchange, but also with all the other European stock exchanges.
Abstract: The objective of the THESEUS project is to develop a terminal that enables stock brokers located in Europe to communicate not only with their national stock exchange, but also with all the other European stock exchanges. Such a terminal is necessary to put into practice the EC directives concerning the opening of the European capital market. This paper presents an overview of the THESEUS terminal design strategy. It focuses on the communication protocol stack design and the implementation of broadband network access. The first European demonstration, using national host access facilities, was conducted successfully in January 1998. An overview of this demonstration is presented.
02 Sep 1998
TL;DR: It is shown that even though S- CDMA is less sensitive than A-CDMA to the near-far effect, a good accuracy of the power control technique(s) is still required.
Abstract: The aim of this paper is to analyse and compare the performance of TCMs in satellite S-CDMA channels considering both Ungerboeck (1982) and Schegel-Costello (1989) designs. The performance of the different codes are simulated in Ricean fading channel for different values of the K factor. The impact of imperfect synchronisation between the different users on the performance is assessed. Finally, it is shown that even though S-CDMA is less sensitive than A-CDMA to the near-far effect, a good accuracy of the power control technique(s) is still required.