This document analyzes system parameters for low earth orbit (LEO) and intermediate circular orbit (ICO) satellite communication networks. It discusses:
1) The necessary number of satellites and orbits to provide global coverage based on minimum elevation angles and footprint sizes, estimating a minimum of 48 satellites for Iridium and 15 for LEONET.
2) Intersatellite links (ISL), which increase network autonomy but also complexity. It models example ISL topologies for LEONET and Iridium constellations.
3) Time-varying pointing angles for intersatellite links between orbit planes, which generally require antenna steering unlike intraplane links.
The document discusses the author's graduation project, which involved developing a direct broadcasting satellite system for TV reception. It provides background on uses of satellite communications, including weather forecasting, military applications, and GPS. It also discusses frequency bands used in satellite communications and how higher frequencies allow for wider bandwidth but are also more prone to attenuation and rain fade. The author's project focused on learning about satellite orbits and link calculations, studying how to draw satellite mounting arcs and calculate free space losses. It provides details on a typical transponder block diagram for a direct broadcasting satellite system.
R07-WP4B-C-0148TERMINOLOGY USED FOR NETWORKS USING BOTH SATELLITE AND TERREST...Queen's University
This document discusses different types of networks that combine satellite and terrestrial links. It defines integrated mobile satellite systems (MSS) as having common network control and spectrum usage for seamless switching between satellite and terrestrial links. Hybrid systems are classified into three types based on how satellite and terrestrial networks are managed and interconnected. Examples of network architectures are provided for each type. Key points covered include spectrum allocation, terminal implementation, and service aspects.
The document proposes a mission to provide commercial services on the lunar surface and in lunar orbit, including communication, positioning/navigation/timing, and cargo delivery. It will utilize a constellation of satellites and delivery vehicles to enable these services. Key requirements are constant Earth-Moon communication, PNT data services, and cargo delivery within 60 days of order. The design includes 24 PNT satellites in 1000km orbits and 3 communication satellites in 10000km orbits, along with delivery vehicles to transport cargo from Earth orbit to the Moon. Mass and power budgets as well as cost estimates are provided for the mission components.
An Adaptive Algorithm for MU-MIMO using Spatial Channel ModelCSCJournals
In this paper, Multi User Multiple Input Multiple Output (MU-MIMO) spatial channel model has been implemented for different outdoor environments – Urban Micro, and Urban Macro using MATLAB for finding various parameters like angle of arrival of the user, user direction and the distance between user and access point (AP).
This document discusses satellite communication, including that satellites orbit large objects like planets, communication satellites transmit radio and television signals from space, and they can be thought of as microwave repeaters in the sky. It also outlines different types of satellite orbits (GEO, LEO, etc.), modulation techniques (ASK, FSK, PSK), multiple access methods (FDMA, TDMA, CDMA, WCDMA), applications (weather, broadcasting, navigation), and was submitted by 3 students for a communication electronics course.
Challenging Issues in Inter-Satellite Optical Wireless Systems (IsOWC) and it...idescitation
Inter-satellite optical wireless communication
system (IsOWC), one of the important applications of FSO
(Free Space Optics) technology, will be deployed in space in
the near future because of providing power efficient and high
bandwidth allocation facilities unlike present microwave
satellite systems. In this paper, we have deliberated a
presentation of different challenging issues in achieving a
prolonged inter satellite link for an IsOWC system under
different situations and conditions. This work is also
emphasized on the suggested techniques to combat with the
degrading factors to put into practice of high speed IsOWC
system with minimum BER.
Satellite communication allows information exchange between two earth stations via a satellite. A satellite receives signals from an uplink earth station on one frequency band and retransmits them to a downlink earth station on another frequency band. Satellites are designed to provide communication services to a designated coverage area on Earth. Satellite communication overcomes limitations of line-of-sight terrestrial systems by allowing communication beyond 1500km. Applications include radio/TV broadcasting, internet access, military uses, and remote sensing.
Satellite communication plays a vital role in global telecommunications. Approximately 2,000 artificial satellites orbiting Earth relay analog and digital signals carrying voice, video, and data worldwide. Uplink frequencies from 5.9-6.4 GHz are used to transmit from earth stations to satellites, while downlink frequencies from 3.7-4.2 GHz are used for signals traveling from satellites to earth stations. Earth stations consist of high gain dish antennas, transmitters, and receivers. The dish antennas are necessary due to high transmission losses over long paths, and low noise amplifiers are important at receivers to boost weak signals received from satellites.
The document discusses the author's graduation project, which involved developing a direct broadcasting satellite system for TV reception. It provides background on uses of satellite communications, including weather forecasting, military applications, and GPS. It also discusses frequency bands used in satellite communications and how higher frequencies allow for wider bandwidth but are also more prone to attenuation and rain fade. The author's project focused on learning about satellite orbits and link calculations, studying how to draw satellite mounting arcs and calculate free space losses. It provides details on a typical transponder block diagram for a direct broadcasting satellite system.
R07-WP4B-C-0148TERMINOLOGY USED FOR NETWORKS USING BOTH SATELLITE AND TERREST...Queen's University
This document discusses different types of networks that combine satellite and terrestrial links. It defines integrated mobile satellite systems (MSS) as having common network control and spectrum usage for seamless switching between satellite and terrestrial links. Hybrid systems are classified into three types based on how satellite and terrestrial networks are managed and interconnected. Examples of network architectures are provided for each type. Key points covered include spectrum allocation, terminal implementation, and service aspects.
The document proposes a mission to provide commercial services on the lunar surface and in lunar orbit, including communication, positioning/navigation/timing, and cargo delivery. It will utilize a constellation of satellites and delivery vehicles to enable these services. Key requirements are constant Earth-Moon communication, PNT data services, and cargo delivery within 60 days of order. The design includes 24 PNT satellites in 1000km orbits and 3 communication satellites in 10000km orbits, along with delivery vehicles to transport cargo from Earth orbit to the Moon. Mass and power budgets as well as cost estimates are provided for the mission components.
An Adaptive Algorithm for MU-MIMO using Spatial Channel ModelCSCJournals
In this paper, Multi User Multiple Input Multiple Output (MU-MIMO) spatial channel model has been implemented for different outdoor environments – Urban Micro, and Urban Macro using MATLAB for finding various parameters like angle of arrival of the user, user direction and the distance between user and access point (AP).
This document discusses satellite communication, including that satellites orbit large objects like planets, communication satellites transmit radio and television signals from space, and they can be thought of as microwave repeaters in the sky. It also outlines different types of satellite orbits (GEO, LEO, etc.), modulation techniques (ASK, FSK, PSK), multiple access methods (FDMA, TDMA, CDMA, WCDMA), applications (weather, broadcasting, navigation), and was submitted by 3 students for a communication electronics course.
Challenging Issues in Inter-Satellite Optical Wireless Systems (IsOWC) and it...idescitation
Inter-satellite optical wireless communication
system (IsOWC), one of the important applications of FSO
(Free Space Optics) technology, will be deployed in space in
the near future because of providing power efficient and high
bandwidth allocation facilities unlike present microwave
satellite systems. In this paper, we have deliberated a
presentation of different challenging issues in achieving a
prolonged inter satellite link for an IsOWC system under
different situations and conditions. This work is also
emphasized on the suggested techniques to combat with the
degrading factors to put into practice of high speed IsOWC
system with minimum BER.
Satellite communication allows information exchange between two earth stations via a satellite. A satellite receives signals from an uplink earth station on one frequency band and retransmits them to a downlink earth station on another frequency band. Satellites are designed to provide communication services to a designated coverage area on Earth. Satellite communication overcomes limitations of line-of-sight terrestrial systems by allowing communication beyond 1500km. Applications include radio/TV broadcasting, internet access, military uses, and remote sensing.
Satellite communication plays a vital role in global telecommunications. Approximately 2,000 artificial satellites orbiting Earth relay analog and digital signals carrying voice, video, and data worldwide. Uplink frequencies from 5.9-6.4 GHz are used to transmit from earth stations to satellites, while downlink frequencies from 3.7-4.2 GHz are used for signals traveling from satellites to earth stations. Earth stations consist of high gain dish antennas, transmitters, and receivers. The dish antennas are necessary due to high transmission losses over long paths, and low noise amplifiers are important at receivers to boost weak signals received from satellites.
This document is a thesis submitted by Gagandeep Singh for his M.Tech degree in RS & GIS from NIT Warangal in 2013-2015. It discusses various topics related to digital terrain modeling including contour lines, grid DTMs, TINs, the differences between DSMs and DEMs, data acquisition methods, processing techniques, and applications of digital terrain data. It also evaluates different data sources for terrain modeling like SRTM, topographic maps, and Google Earth imagery and assesses their accuracy through statistical analysis and visual inspection.
SRTM is the Shuttle Radar Topography Mission that obtained digital elevation models on a near-global scale using radar. SRTM data is available in different formats from various sources and can be used for mapping geomorphology, structures, and revealing subsurface geological patterns when combined with Landsat data. SRTM imagery and derived hillshades can identify drainage patterns and be compared to paleochannels from aeromagnetic data to study geological processes over time.
This document proposes an adaptive modulation scheme using rain fade predictions from Kalman filtering to mitigate the effects of rain fade on geostationary satellite communications in the Ka-band. It simulates a cognitive radio-based satellite communication system with an adaptive transmitter and receiver. Prediction of the rain fade using a linear Kalman filter allows time for the transmitter and receiver to reconfigure before the predicted fade occurs, improving the bit error rate performance by two orders of magnitude compared to a non-adaptive system. The simulation shows switching between 4-QAM and 16-QAM modulation based on predicted fade levels keeps the bit error rate below a threshold while transmitting more data overall.
Satellite communications uses satellites as relay stations to transmit signals between Earth stations that are too far for direct transmission. Signals are sent to the satellite (uplink) and retransmitted to another station (downlink). Satellites provide wide coverage and transmission costs are independent of distance. Orbits include GEO, LEO, MEO and HAPs. Capacity is allocated using FDMA or TDMA, dividing available frequencies or time slots between users.
This summary provides an overview of seismic data processing steps performed on a P-Cable 3D seismic dataset from the Gulf of Mexico:
1. Wavelet deconvolution was applied to improve temporal resolution using a prediction-error filter estimated from the wavelet.
2. Surface-consistent amplitude corrections were applied using a method based on Taner and Koehler (1981) to obtain source and receiver terms.
3. Velocity analysis on supergathers was used to pick velocities ranging from 1.5-2.4 km/s, which were applied to NMO correct and stack the data.
4. FFT filtering and median filtering were tested but found to negatively impact the high frequency content of the
This document discusses digital elevation models (DEMs), including how they are generated from remote sensing data like satellite imagery and LiDAR, their typical accuracies, and common uses. DEMs can be created from aerial or satellite stereo images, radar interferometry, or terrestrial land surveying. They are used to produce topographic maps and orthophotos, model flooding, perform visibility analysis, and create 3D terrain representations. The quality and resolution of DEMs varies depending on the source data and techniques used.
Broadband Communications and Applications from High Altitude PlatformsIDES Editor
This document provides an overview of using high altitude platforms (HAPs) for wireless telecommunications and broadband services. It discusses three architectures for HAP systems: 1) stand-alone HAP systems for rural areas, 2) integrated HAP-terrestrial systems to provide coverage where deploying terrestrial networks is expensive, and 3) terrestrial-HAP-satellite systems for fault tolerance and high quality of service. The document also evaluates the performance of delivering WiMAX services from HAPs and discusses applications like wireless sensor networks and disaster response.
Implementation of Digital Beamforming Technique for Linear Antenna Arraysijsrd.com
A digital Beamforming technique used for increased channel capacity and also increased signal to noise and interference ratio. In smart antenna, different type of radiation pattern of an antenna can be changed either by selecting appropriate weights or by changing the array geometry. This paper presented based on auxiliary phase algorithm by using this algorithm in linear antenna array determine the array pattern approximating the auxiliary function in both amplitude and phase. Cost function involving auxiliary function and array pattern is minimized by modifying the pattern.
This document proposes several methods to optimize floor plans for integrated optic photonic switching architectures. It discusses removing waveguide crossovers to create planar layouts, placing switches on annular optical substrates for more freedom in input-output placement, and achieving acute bends in light-paths. Specifically, it proposes replacing waveguide crossovers with directional couplers to planarize graphs and illustrates this on fundamental non-planar graphs and the Beneš network. It also discusses advantages of annular architectures for certain switch placements.
This document summarizes applications of remote sensing for digital elevation models. It discusses how remote sensing uses electromagnetic rays to acquire data without physical contact. Digital elevation models are created using remote sensing techniques to represent terrain and are built systematically or randomly. Methods for creating DEMs include interpolation of contours or using radar data from two passes of a satellite or a single pass with two antennas. The quality depends on factors like terrain roughness and pixel size. Common software used includes TacitView, Socet GXP, and IDRISI.
This document summarizes a research paper on a new phase unwrapping algorithm called PUMF (Phase Unwrapping Max-Flow) that frames phase unwrapping as an energy minimization problem. PUMF solves the problem exactly using a binary optimization approach inspired by the ZπM algorithm and graph cuts techniques. It competes with state-of-the-art phase unwrapping algorithms on benchmark problems. The algorithm generalizes the classical minimum Lp norm formulation for phase unwrapping and can handle phase discontinuities through its flexibility to model any 2π-periodically convex potentials. Experimental results demonstrate the effectiveness and competitiveness of the proposed PUMF algorithm.
The document provides an overview and status update of the Earth Observing System Data and Information System (EOSDIS). It discusses that EOSDIS supports EOS missions by ingesting, processing, archiving, and distributing their data. It notes that the volume of archived data has grown to over 4.9 petabytes containing over 2700 datasets. It also outlines plans to transition to new systems and complete updates to the EOSDIS code by 2009.
A novel area efficient vlsi architecture for recursion computation in lte tur...I3E Technologies
This document proposes a novel area-efficient VLSI architecture for recursion computation in LTE turbo decoders. It introduces a new relation between the alpha and beta metrics that leads to an improved add-compare-select architecture. This architecture reduces the area of recursion units in MAP decoder cores by up to 18.1% compared to previous designs while maintaining the same throughput. It can benefit the decoding throughput of LTE by enabling more parallel MAP cores to fit in a smaller area.
Particle Swarm Optimization for the Path Loss Reduction in Suburban and Rural...IJECEIAES
In the present work, a precise optimization method is proposed for tuning the parameters of the COST231 model to improve its accuracy in the path loss propagation prediction. The Particle Swarm Optimization is used to tune the model parameters. The predictions of the tuned model are compared with the most popular models. The performance criteria selected for the comparison of various empirical path loss models is the Root Mean Square Error (RMSE). The RMSE between the actual and predicted data are calculated for various path loss models. It turned out that the tuned COST 231 model outperforms the other studied models.
This document provides an overview of satellite systems, including their history, characteristics, types, and advantages/disadvantages. It discusses the first satellites launched in the 1950s-60s and the development of geostationary satellites in the 1960s-70s. The types of satellite orbits covered are GEO, LEO, MEO, and HEO, outlining the basic characteristics and uses of each. GEO satellites remain fixed over one spot but have limitations at high/low latitudes. LEO satellites have smaller footprints but require more satellites for global coverage. MEO satellites move slower than LEO but have longer delays. HEO satellites have elliptical orbits and provide medium delays with some long dwell times.
A self deployed multi-channel wireless communications system for subterranean...TanBengSoon2
This document presents a dual-channel wireless communication system for subterranean robots. It describes a system using both 5.8GHz WiFi radios for high-bandwidth communication and 915MHz telemetry modules for low-bandwidth communication. It also details small, lightweight "communication breadcrumbs" that can be dropped by aerial robots to extend the communication range underground. Experimental results from underground exploration missions are presented to evaluate the system.
International Journal of Modern Engineering Research (IJMER) is Peer reviewed, online Journal. It serves as an international archival forum of scholarly research related to engineering and science education.
International Journal of Modern Engineering Research (IJMER) covers all the fields of engineering and science: Electrical Engineering, Mechanical Engineering, Civil Engineering, Chemical Engineering, Computer Engineering, Agricultural Engineering, Aerospace Engineering, Thermodynamics, Structural Engineering, Control Engineering, Robotics, Mechatronics, Fluid Mechanics, Nanotechnology, Simulators, Web-based Learning, Remote Laboratories, Engineering Design Methods, Education Research, Students' Satisfaction and Motivation, Global Projects, and Assessment…. And many more.
This document provides an overview of optical satellite communications, including intersatellite links (ISLs) and global achievements. It discusses how ISLs allow for increased capacity and coverage by connecting satellites in different orbits, such as GEO-LEO and GEO-GEO links. Optical communications provide advantages over radio links, including higher antenna gains due to shorter wavelengths, but require more accurate pointing and tracking. The document outlines examples of optical ISL applications and global satellite networks using interconnected satellites.
RT (Ray Tracing) models are widely used in RAN for channel modelling. Another possible application in
processing chain of base station with multiple purposes: positioning, channel estimation/prediction, radio
resources scheduling and others. In this paper RT positioning technique is addressed for Urban Outdoor
scenario. Proposed robust approach achieves several meters accuracy even in NLOS and multipath
conditions. Developed RT tracking was used for multiuser (MU) precoder prediction and demonstrated
significant capacity gain. Also, this paper discloses practical aspects for achieving high accuracy.
This document is a thesis submitted by Gagandeep Singh for his M.Tech degree in RS & GIS from NIT Warangal in 2013-2015. It discusses various topics related to digital terrain modeling including contour lines, grid DTMs, TINs, the differences between DSMs and DEMs, data acquisition methods, processing techniques, and applications of digital terrain data. It also evaluates different data sources for terrain modeling like SRTM, topographic maps, and Google Earth imagery and assesses their accuracy through statistical analysis and visual inspection.
SRTM is the Shuttle Radar Topography Mission that obtained digital elevation models on a near-global scale using radar. SRTM data is available in different formats from various sources and can be used for mapping geomorphology, structures, and revealing subsurface geological patterns when combined with Landsat data. SRTM imagery and derived hillshades can identify drainage patterns and be compared to paleochannels from aeromagnetic data to study geological processes over time.
This document proposes an adaptive modulation scheme using rain fade predictions from Kalman filtering to mitigate the effects of rain fade on geostationary satellite communications in the Ka-band. It simulates a cognitive radio-based satellite communication system with an adaptive transmitter and receiver. Prediction of the rain fade using a linear Kalman filter allows time for the transmitter and receiver to reconfigure before the predicted fade occurs, improving the bit error rate performance by two orders of magnitude compared to a non-adaptive system. The simulation shows switching between 4-QAM and 16-QAM modulation based on predicted fade levels keeps the bit error rate below a threshold while transmitting more data overall.
Satellite communications uses satellites as relay stations to transmit signals between Earth stations that are too far for direct transmission. Signals are sent to the satellite (uplink) and retransmitted to another station (downlink). Satellites provide wide coverage and transmission costs are independent of distance. Orbits include GEO, LEO, MEO and HAPs. Capacity is allocated using FDMA or TDMA, dividing available frequencies or time slots between users.
This summary provides an overview of seismic data processing steps performed on a P-Cable 3D seismic dataset from the Gulf of Mexico:
1. Wavelet deconvolution was applied to improve temporal resolution using a prediction-error filter estimated from the wavelet.
2. Surface-consistent amplitude corrections were applied using a method based on Taner and Koehler (1981) to obtain source and receiver terms.
3. Velocity analysis on supergathers was used to pick velocities ranging from 1.5-2.4 km/s, which were applied to NMO correct and stack the data.
4. FFT filtering and median filtering were tested but found to negatively impact the high frequency content of the
This document discusses digital elevation models (DEMs), including how they are generated from remote sensing data like satellite imagery and LiDAR, their typical accuracies, and common uses. DEMs can be created from aerial or satellite stereo images, radar interferometry, or terrestrial land surveying. They are used to produce topographic maps and orthophotos, model flooding, perform visibility analysis, and create 3D terrain representations. The quality and resolution of DEMs varies depending on the source data and techniques used.
Broadband Communications and Applications from High Altitude PlatformsIDES Editor
This document provides an overview of using high altitude platforms (HAPs) for wireless telecommunications and broadband services. It discusses three architectures for HAP systems: 1) stand-alone HAP systems for rural areas, 2) integrated HAP-terrestrial systems to provide coverage where deploying terrestrial networks is expensive, and 3) terrestrial-HAP-satellite systems for fault tolerance and high quality of service. The document also evaluates the performance of delivering WiMAX services from HAPs and discusses applications like wireless sensor networks and disaster response.
Implementation of Digital Beamforming Technique for Linear Antenna Arraysijsrd.com
A digital Beamforming technique used for increased channel capacity and also increased signal to noise and interference ratio. In smart antenna, different type of radiation pattern of an antenna can be changed either by selecting appropriate weights or by changing the array geometry. This paper presented based on auxiliary phase algorithm by using this algorithm in linear antenna array determine the array pattern approximating the auxiliary function in both amplitude and phase. Cost function involving auxiliary function and array pattern is minimized by modifying the pattern.
This document proposes several methods to optimize floor plans for integrated optic photonic switching architectures. It discusses removing waveguide crossovers to create planar layouts, placing switches on annular optical substrates for more freedom in input-output placement, and achieving acute bends in light-paths. Specifically, it proposes replacing waveguide crossovers with directional couplers to planarize graphs and illustrates this on fundamental non-planar graphs and the Beneš network. It also discusses advantages of annular architectures for certain switch placements.
This document summarizes applications of remote sensing for digital elevation models. It discusses how remote sensing uses electromagnetic rays to acquire data without physical contact. Digital elevation models are created using remote sensing techniques to represent terrain and are built systematically or randomly. Methods for creating DEMs include interpolation of contours or using radar data from two passes of a satellite or a single pass with two antennas. The quality depends on factors like terrain roughness and pixel size. Common software used includes TacitView, Socet GXP, and IDRISI.
This document summarizes a research paper on a new phase unwrapping algorithm called PUMF (Phase Unwrapping Max-Flow) that frames phase unwrapping as an energy minimization problem. PUMF solves the problem exactly using a binary optimization approach inspired by the ZπM algorithm and graph cuts techniques. It competes with state-of-the-art phase unwrapping algorithms on benchmark problems. The algorithm generalizes the classical minimum Lp norm formulation for phase unwrapping and can handle phase discontinuities through its flexibility to model any 2π-periodically convex potentials. Experimental results demonstrate the effectiveness and competitiveness of the proposed PUMF algorithm.
The document provides an overview and status update of the Earth Observing System Data and Information System (EOSDIS). It discusses that EOSDIS supports EOS missions by ingesting, processing, archiving, and distributing their data. It notes that the volume of archived data has grown to over 4.9 petabytes containing over 2700 datasets. It also outlines plans to transition to new systems and complete updates to the EOSDIS code by 2009.
A novel area efficient vlsi architecture for recursion computation in lte tur...I3E Technologies
This document proposes a novel area-efficient VLSI architecture for recursion computation in LTE turbo decoders. It introduces a new relation between the alpha and beta metrics that leads to an improved add-compare-select architecture. This architecture reduces the area of recursion units in MAP decoder cores by up to 18.1% compared to previous designs while maintaining the same throughput. It can benefit the decoding throughput of LTE by enabling more parallel MAP cores to fit in a smaller area.
Particle Swarm Optimization for the Path Loss Reduction in Suburban and Rural...IJECEIAES
In the present work, a precise optimization method is proposed for tuning the parameters of the COST231 model to improve its accuracy in the path loss propagation prediction. The Particle Swarm Optimization is used to tune the model parameters. The predictions of the tuned model are compared with the most popular models. The performance criteria selected for the comparison of various empirical path loss models is the Root Mean Square Error (RMSE). The RMSE between the actual and predicted data are calculated for various path loss models. It turned out that the tuned COST 231 model outperforms the other studied models.
This document provides an overview of satellite systems, including their history, characteristics, types, and advantages/disadvantages. It discusses the first satellites launched in the 1950s-60s and the development of geostationary satellites in the 1960s-70s. The types of satellite orbits covered are GEO, LEO, MEO, and HEO, outlining the basic characteristics and uses of each. GEO satellites remain fixed over one spot but have limitations at high/low latitudes. LEO satellites have smaller footprints but require more satellites for global coverage. MEO satellites move slower than LEO but have longer delays. HEO satellites have elliptical orbits and provide medium delays with some long dwell times.
A self deployed multi-channel wireless communications system for subterranean...TanBengSoon2
This document presents a dual-channel wireless communication system for subterranean robots. It describes a system using both 5.8GHz WiFi radios for high-bandwidth communication and 915MHz telemetry modules for low-bandwidth communication. It also details small, lightweight "communication breadcrumbs" that can be dropped by aerial robots to extend the communication range underground. Experimental results from underground exploration missions are presented to evaluate the system.
International Journal of Modern Engineering Research (IJMER) is Peer reviewed, online Journal. It serves as an international archival forum of scholarly research related to engineering and science education.
International Journal of Modern Engineering Research (IJMER) covers all the fields of engineering and science: Electrical Engineering, Mechanical Engineering, Civil Engineering, Chemical Engineering, Computer Engineering, Agricultural Engineering, Aerospace Engineering, Thermodynamics, Structural Engineering, Control Engineering, Robotics, Mechatronics, Fluid Mechanics, Nanotechnology, Simulators, Web-based Learning, Remote Laboratories, Engineering Design Methods, Education Research, Students' Satisfaction and Motivation, Global Projects, and Assessment…. And many more.
This document provides an overview of optical satellite communications, including intersatellite links (ISLs) and global achievements. It discusses how ISLs allow for increased capacity and coverage by connecting satellites in different orbits, such as GEO-LEO and GEO-GEO links. Optical communications provide advantages over radio links, including higher antenna gains due to shorter wavelengths, but require more accurate pointing and tracking. The document outlines examples of optical ISL applications and global satellite networks using interconnected satellites.
RT (Ray Tracing) models are widely used in RAN for channel modelling. Another possible application in
processing chain of base station with multiple purposes: positioning, channel estimation/prediction, radio
resources scheduling and others. In this paper RT positioning technique is addressed for Urban Outdoor
scenario. Proposed robust approach achieves several meters accuracy even in NLOS and multipath
conditions. Developed RT tracking was used for multiuser (MU) precoder prediction and demonstrated
significant capacity gain. Also, this paper discloses practical aspects for achieving high accuracy.
This document summarizes a paper that proposes using ray tracing for 5G positioning, channel estimation, and multi-user precoding. It describes using ray tracing to estimate the angles of arrival of uplink signals from user equipment at distributed base stations. The estimated angles are then used in a joint positioning technique run in the cloud to determine the user's location. Simulation results show meter-level accuracy can be achieved even in non-line-of-sight conditions. Ray tracing tracking is also used for channel prediction and improves spectral efficiency. Practical considerations for achieving high positioning accuracy with this approach are also discussed.
This document discusses channel modeling for 5G NR non-terrestrial networks (NTN). It covers the system model, which includes topology, large-scale pathloss modeling, and antenna patterns. For topology, it describes using Earth-centered Earth-fixed coordinates and UV mapping to represent satellite positions and layout beams and user equipment. It then discusses components of the pathloss model for NTN including free space pathloss, clutter loss, shadow fading, and atmospheric, ionospheric, and tropospheric attenuations. The document concludes with describing the use of directional reflector antennas and providing example antenna patterns for geostationary and low Earth orbit satellite configurations.
1) The IRIDIUM system uses 66 low Earth orbit satellites arranged in six orbital planes to provide global voice and data coverage.
2) Each satellite has inter-satellite links that allow calls to be routed through multiple satellites and downlinked to regional gateways rather than individual satellites.
3) This architecture provides worldwide connectivity with small handheld terminals, addressing a limitation of traditional geostationary satellite systems.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
The document discusses satellite communication links, including:
- Design of satellite links, which follow free-space propagation and are affected by factors like rain attenuation.
- Link budgets and their interpretation, which use decibel calculations to account for gains and losses across transmitting, receiving, and atmospheric elements.
- Multiple access systems and frequency band trade-offs that satellite communication must consider.
The document discusses satellite communication links, including:
1) The design of satellite links, which involves line-of-sight transmission between earth stations and satellites governed by free-space propagation and atmospheric effects.
2) Link budgets and their interpretation, which quantify gains and losses across transmitter, receiver, and propagation to determine overall carrier-to-noise ratio and performance.
3) Multiple access systems and frequency band trade-offs used for satellite communication.
Design and software implementation of radio frequency satellite link based on...TELKOMNIKA JOURNAL
The satellite communication providea utilization of radio frequency links. Specific frequencies are dedicated for satellite correspondences through global administrative and coordination procedures which keeps impedance amongframeworks. Over typical work, the satellite receives uplinked indicator fromearth. Progressions its frequency marginally will keep away from self-intervention then re-transmits signal ahead the downlink on the land. Pathloss depicts characteristic Propagate outside the sending signal front as it goes bythe space. A software defined radio (SDR) is a flexible technology that aimsto replace all hardware by software to enables the design of adaptive communications systems such as changing frequencies, modulation schemes and data rates. Applied to small satellites, some of the implications areincreased data through put when down-linking or up-linking by varying communications parameters and making use of one hardware design and implementation for communicating for many missions, just by updating the software. Therefore, development time for small satellite communication systems can be reduced in the future. This paper analyzes, design and software implementation of radio frequency satellite communications links under noisy channels such as phase/frequency offsets and noise temperature. Modulation schemes such as 64QAM system is used based on Matlab tools to implement the results. Obtained results shows a good response that get the goal from the paper.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
Section based hex cell routing algorithm (sbhcr)IJCNCJournal
A Hex-Cell network topology can be constructed using units of hexagon cells. It has been introduced in the literature as interconnection network suitable for large parallel computers, which can connect large number of nodes with three links per node. Although this topology exhibits attractive characteristics such as embeddability, symmetry, regularity, strong resilience, and simple routing, the previously suggested routing algorithms suffer from the high number of logical operations and the need for readdressing of nodes every time a new level is add to the network. This negatively impacts the performance of the network as it increases the execution time of these algorithms. In this paper we propose an improved optimal point to point routing algorithm for Hex-Cell network. The algorithm is based on dividing the Hex-Cell topology into six divisions, hence the name Section Based Hex-Cell Routing (SBHCR). The SBHCR algorithm is simple and preserves the advantage of the addressing scheme proposed for the Hex-Cell network. It does not depend on the depth of the network topology which leads to overcome the issue of readdressing of nodes every time a new level is added. Evaluation against two previously suggested routing algorithms has shown the superiority of SBHCR in term of less logical operations.
Near equatorial orbit small sar constellation for developing nationseSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
Near equatorial orbit small sar constellation for developing nationseSAT Journals
Abstract The need to harness the benefits of space, to help urban growth and development, using cheaper space systems has become appealing to developing nations. The desired all weather radar satellite poses limitations on a small satellite. Several spaceborne Synthetic Aperture Radar (SAR) satellite configurations have been proposed to overcome the significant limit on earth surface revisit time for small SAR satellites, optimising a network of small SAR satellites dedicated to developing nations posed several challenges. In an effort to address some of these challenges, a new concept based on a constellation of small SAR satellite network, in an almost equatorial inclined orbit, operating in a multistatic configuration and solely dedicated to Equatorial region has been proposed. The network consists 3 receiver-only platforms (passive satellites) flying in formation with one transmit/receiver satellite (active satellite). Furthermore, five groundstation sites required for mission operation are located with the equatorial region. The system aims to provide 24 hours of near-real time data, over the equatorial region. A total of two orbital planes for 8 satellites are proposed. This report will describe the process of selecting a suitable orbit constellation configuration. It also determines the stability of the relative motion between the satellites within the formation in order to ensure the desired image product is consistent during operations. Furthermore, it also discusses the process of selecting suitable groundstation locations for the mission operations Index Terms: Near Equatorial orbit, SAR, Interferometry Pendulum, constellation
New modeling approach of laser communication in constellation and through atm...journalBEEI
Laser communication between satellites in the constellation and from the satellites to ground stations offers a gigantic data rate for the users. This principal advantage drives telecom companies to develop this technology to use it like a carrier signal, the most disadvantage of this technology is the need to very complicated pointing systems between the transmitter and the receiver due to a very small beam divergence, continually moving of satellites in orbits and the distance between the satellites (tens of thousands of kilometers). The laser beam suffers continuously from several factors like atmospheric turbulences, internal and external vibrations. All these factors lead to an increase in the bit errors rate and cause degradation in the communication quality. This paper deals with a new method of modelisation of external effects in transmission of signal light from a ground station to the satellite through atmospheric disturbances. Indeed, an in-depth investigation, of the influences of satellite vibrationsinlaser signal transmission between satellites constellation, has been conducted by studying the effect of the intensity of vibrations on the optical signal amplitude. Some solutions are proposed to improve the efficiency of optical satellites communications.
The document summarizes the history and activities of the Indian Space Research Organisation (ISRO). It discusses key ISRO missions and systems including the Indian National Satellite System (INSAT), the Indian Remote Sensing Satellite System (IRS), the Stretched Rohini Satellite Series (SROSS), the Polar Satellite Launch Vehicle (PSLV) and the Geosynchronous Satellite Launch Vehicle (GSLV). The document outlines ISRO's role in applying space technology to address national needs and its contributions to India's development.
Secure and Energy Savings Communication of Flying Ad Hoc Network for Rescue O...BRNSSPublicationHubI
This document summarizes a research article about developing a secure and energy-efficient routing protocol for Flying Ad Hoc Networks (FANETs) used in rescue operations. The protocol aims to address issues like lack of congestion control, reliability, and high energy consumption in FANETs. It proposes forming clusters of flying nodes based on distance and energy levels. It then calculates remaining energy of nodes to save resources. Finally, it establishes communication between clusters and a ground operation center using node velocity and location data. The goal is to enable secure and energy-efficient communication for coordinating rescue efforts using a rapidly deployable FANET.
This document describes a satellite tracking system that uses a microcontroller to track a satellite's position and correct its orbit if it drifts from its intended path. The system includes an orbital correction engine that calculates needed adjustments and a tracking processor that monitors the satellite's position over time to detect any deviations. It sends the satellite's location data to an earth station via an RS-232 interface. The microcontroller compares the data to an orbital database and determines corrections to guide the satellite back to its proper orbit. A visual basics program is used to model and simulate the satellite's movement and drift.
IRJET - Millisecond Rotation Pulsars as Next Generation Grid Timing SourcesIRJET Journal
This document discusses using millisecond rotation pulsars as timing sources for synchronized measurements on the electric power grid. It begins by explaining how precise time synchronization is important for measurements like phasor measurement units. It then discusses millisecond rotation pulsars as potential replacements or backups for GPS due to their high rotation precision. The document considers practical issues around receiving pulsar signals and integrating the timing information into existing grid timing distribution networks. It concludes by outlining how pulsar timing signals could be distributed to grid applications through existing protocols.
LOCALIZATION SCHEMES FOR UNDERWATER WIRELESS SENSOR NETWORKS: SURVEYIJCNCJournal
Underwater Wireless Sensor Networks (UWSNs) enable a variety of applications such as fish farming and water quality monitoring. One of the critical tasks in such networks is localization. Location information can be used in sensor networks for several purposes such as (i) data tagging in which sensed information is not useful for the application unless the location of the sensed information is known, (ii) tracking objects or (iii) multi-hop data transmission in geographic routing protocols. Since GPS does not work well underwater, several localization schemes have been developed for UWSNs. This paper surveys the state-ofthe-art of localization schemes for UWSNs. It describes the existing schemes and classifies them into different categories. Furthermore, the paper discusses some open research issues that need further investigation in this area.
A Review on Routing Algorithms for Lower Earth Orbit Satellite NetworksIRJET Journal
This document reviews and compares various routing algorithms that have been proposed for lower earth orbit (LEO) satellite networks. It first provides background on the importance and challenges of routing in LEO satellite networks due to their dynamic topology and bandwidth/latency constraints. It then summarizes 10 different routing algorithms that have been proposed in previous research, highlighting the key idea/method used by each one and their advantages. These algorithms use approaches like link reversal, dynamic clustering, ant colony optimization, software defined networking, and reinforcement learning. The document concludes by comparing the different algorithms in a table based on their approaches and benefits.
Similar to Analysis_of_System_Parameters_for_LEOICO-Satellite.pdf (20)
Applications of artificial Intelligence in Mechanical Engineering.pdfAtif Razi
Historically, mechanical engineering has relied heavily on human expertise and empirical methods to solve complex problems. With the introduction of computer-aided design (CAD) and finite element analysis (FEA), the field took its first steps towards digitization. These tools allowed engineers to simulate and analyze mechanical systems with greater accuracy and efficiency. However, the sheer volume of data generated by modern engineering systems and the increasing complexity of these systems have necessitated more advanced analytical tools, paving the way for AI.
AI offers the capability to process vast amounts of data, identify patterns, and make predictions with a level of speed and accuracy unattainable by traditional methods. This has profound implications for mechanical engineering, enabling more efficient design processes, predictive maintenance strategies, and optimized manufacturing operations. AI-driven tools can learn from historical data, adapt to new information, and continuously improve their performance, making them invaluable in tackling the multifaceted challenges of modern mechanical engineering.
Digital Twins Computer Networking Paper Presentation.pptxaryanpankaj78
A Digital Twin in computer networking is a virtual representation of a physical network, used to simulate, analyze, and optimize network performance and reliability. It leverages real-time data to enhance network management, predict issues, and improve decision-making processes.
Prediction of Electrical Energy Efficiency Using Information on Consumer's Ac...PriyankaKilaniya
Energy efficiency has been important since the latter part of the last century. The main object of this survey is to determine the energy efficiency knowledge among consumers. Two separate districts in Bangladesh are selected to conduct the survey on households and showrooms about the energy and seller also. The survey uses the data to find some regression equations from which it is easy to predict energy efficiency knowledge. The data is analyzed and calculated based on five important criteria. The initial target was to find some factors that help predict a person's energy efficiency knowledge. From the survey, it is found that the energy efficiency awareness among the people of our country is very low. Relationships between household energy use behaviors are estimated using a unique dataset of about 40 households and 20 showrooms in Bangladesh's Chapainawabganj and Bagerhat districts. Knowledge of energy consumption and energy efficiency technology options is found to be associated with household use of energy conservation practices. Household characteristics also influence household energy use behavior. Younger household cohorts are more likely to adopt energy-efficient technologies and energy conservation practices and place primary importance on energy saving for environmental reasons. Education also influences attitudes toward energy conservation in Bangladesh. Low-education households indicate they primarily save electricity for the environment while high-education households indicate they are motivated by environmental concerns.
Mechatronics is a multidisciplinary field that refers to the skill sets needed in the contemporary, advanced automated manufacturing industry. At the intersection of mechanics, electronics, and computing, mechatronics specialists create simpler, smarter systems. Mechatronics is an essential foundation for the expected growth in automation and manufacturing.
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Use PyCharm for remote debugging of WSL on a Windo cf5c162d672e4e58b4dde5d797...shadow0702a
This document serves as a comprehensive step-by-step guide on how to effectively use PyCharm for remote debugging of the Windows Subsystem for Linux (WSL) on a local Windows machine. It meticulously outlines several critical steps in the process, starting with the crucial task of enabling permissions, followed by the installation and configuration of WSL.
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Null Bangalore | Pentesters Approach to AWS IAMDivyanshu
#Abstract:
- Learn more about the real-world methods for auditing AWS IAM (Identity and Access Management) as a pentester. So let us proceed with a brief discussion of IAM as well as some typical misconfigurations and their potential exploits in order to reinforce the understanding of IAM security best practices.
- Gain actionable insights into AWS IAM policies and roles, using hands on approach.
#Prerequisites:
- Basic understanding of AWS services and architecture
- Familiarity with cloud security concepts
- Experience using the AWS Management Console or AWS CLI.
- For hands on lab create account on [killercoda.com](https://killercoda.com/cloudsecurity-scenario/)
# Scenario Covered:
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- Exploiting IAM PassRole Misconfiguration
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- Access sensitive resources.
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Try at [killercoda.com](https://killercoda.com/cloudsecurity-scenario/)
Gas agency management system project report.pdfKamal Acharya
The project entitled "Gas Agency" is done to make the manual process easier by making it a computerized system for billing and maintaining stock. The Gas Agencies get the order request through phone calls or by personal from their customers and deliver the gas cylinders to their address based on their demand and previous delivery date. This process is made computerized and the customer's name, address and stock details are stored in a database. Based on this the billing for a customer is made simple and easier, since a customer order for gas can be accepted only after completing a certain period from the previous delivery. This can be calculated and billed easily through this. There are two types of delivery like domestic purpose use delivery and commercial purpose use delivery. The bill rate and capacity differs for both. This can be easily maintained and charged accordingly.
Supermarket Management System Project Report.pdfKamal Acharya
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This project contains all the necessary required information about maintaining
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The core idea of this project to minimize the paper work and centralize the
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application the information will be stored in client itself. For further security the
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DEEP LEARNING FOR SMART GRID INTRUSION DETECTION: A HYBRID CNN-LSTM-BASED MODELijaia
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Robust Intrusion Detection Systems (IDS) are necessary for early threat detection and mitigation because
of the interconnection of these networks, which makes them vulnerable to a variety of cyberattacks. To
solve this issue, this paper develops a hybrid Deep Learning (DL) model specifically designed for intrusion
detection in smart grids. The proposed approach is a combination of the Convolutional Neural Network
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dataset (DNP3), which focuses on unauthorized commands and Denial of Service (DoS) cyberattacks, to
train and test our model. The results of our experiments show that our CNN-LSTM method is much better
at finding smart grid intrusions than other deep learning algorithms used for classification. In addition,
our proposed approach improves accuracy, precision, recall, and F1 score, achieving a high detection
accuracy rate of 99.50%.
Optimizing Gradle Builds - Gradle DPE Tour Berlin 2024Sinan KOZAK
Sinan from the Delivery Hero mobile infrastructure engineering team shares a deep dive into performance acceleration with Gradle build cache optimizations. Sinan shares their journey into solving complex build-cache problems that affect Gradle builds. By understanding the challenges and solutions found in our journey, we aim to demonstrate the possibilities for faster builds. The case study reveals how overlapping outputs and cache misconfigurations led to significant increases in build times, especially as the project scaled up with numerous modules using Paparazzi tests. The journey from diagnosing to defeating cache issues offers invaluable lessons on maintaining cache integrity without sacrificing functionality.
Build the Next Generation of Apps with the Einstein 1 Platform.
Rejoignez Philippe Ozil pour une session de workshops qui vous guidera à travers les détails de la plateforme Einstein 1, l'importance des données pour la création d'applications d'intelligence artificielle et les différents outils et technologies que Salesforce propose pour vous apporter tous les bénéfices de l'IA.
1. IEEE JOURNAL ON SELECTEDAREAS IN COMMUNICATIONS, VOL. 13, NO. 2, FEBRUARY 1995 371
Number of
spot-beams
per satellite
Analysis of System Parameters for
48 16 37 37
LEODCO-Satellite Communication Networks
Markus Werner, Member, IEEE, Axel Jahn, Member, IEEE, Erich Lutz, Member, IEEE, and Axel Bottcher, Member, IEEE
Abstract- Currently many efforts are undertaken to develop
and install communication networks based on low earth orbit
(LEO) and intermediate circular orbit (ICO) satellites. However,
many problems are to be solved until the final operation of
such networks. This paper deals with basic design problems
of LEODCO-based networks. In the first part, the topology of
the satellite network is considered and estimates for the neces-
sary number of satellites,orbits and number of communication
channels per satellite are derived. Features and consequences
of intersatellite links are discussed. In the second part of the
paper, the number of communicationchannels per link is derived
with a more elaborate model. This includes the radio links
from the satellites to mobile users and to gateways, as well as
intersatellite links and terrestrial lines. We introduce a formal
model for LEO/ICO-based networks and propose a method for
the evaluation of link capacities,given the network topology and
the trafflc requirements. As an example, two constellations are
investigated in detail. One of these constellations is the Iridium
system proposed by Motorola, the other one is the LEONET
concept developed in an ESA study. Finally, the influence of
unequal traffic distribution is discussed.
I. INTRODUCTION
XISTING terrestrial radio networks (GSM, AMPS, etc.)
Eprovide mobile communications services within limited
regions. In order to supplement these terrestrial systems, a
number of LEOACO-satellite systems for global personal
communications have been proposed (Globalstar [11, Iridium
[2],Odyssey [3], etc.). Mobile users will be able to alterna-
tively access a terrestrial or a satellite network through dual-
mode handheld terminals, in this way achieving worldwide
roaming capability. In the future, third generation mobile
telecommunications systems (UMTS, FF'LMTS) with a fully
integrated satellite component will globally provide seamless
personal communications.
For the design of LEODCO-satellite systems many require-
ments have to be taken into account. For reasons of link
quality, global coverage must be achieved with a sufficiently
high satellite elevation. Together with the (restricted) choice
of orbit height and inclination, this requirement leads to the
necessary number of satellites and orbits. A larger number of
satellites might be chosen to increase the link availability by
means of multiple satellite visibility. The number of satellites
may be reduced by choosing high satellite orbits, but this
will increase propagation delay and required transmit power.
Usually, the footprint of a satellite is divided into a number
Manuscript received January 15, 1994; revised June 30, 1994. This work
The authors are with the German Aerospace Research Establishment (DLR),
IEEE Log Number 9407509.
was supported in part by ESAESTEC under Contract 9732/91/NL/RE.
Institute for Communications Technology, D-82230 WeSling, Germany.
TABLE I
SYSTEM PARAMETERS OF SOME PROPOSED LEOACO-SYSTEMS
Number of I 66 I 48 I 12 I 15
of cells, thus reducing power requirements and, by means of
frequency reuse, increasing bandwidth efficiency. The gain
in bandwidth efficiency may be reduced, however, when the
mobile users are unequally distributed within the satellite
footprint.
For a few examples of LEODCO systems, the main param-
eters of the respective satellite constellations are summarized
in Table I. LEONET is an IC0 concept developed in the
framework of an ESA study [8].'
In addition to the above mentioned requirements related
to the satellite constellation, several networking aspects have
to be considered. The demand for telephony and its global
distribution, together with upper limits for blocking probabil-
ity and speech delay, essentially determine the requirements
for network capacity and connectivity. These characteristics
depend on the number of satellites and gateway earth stations
and on the number of links between mobile users, satellites,
and gateways, including intersatellite links (EL'S).For a high
degree of connectivity, various routing alternatives are possible
and a good distribution of the traffic flow can be achieved.
Moreover, the flexibility of the network to cope with link or
node failures is enhanced. On the other hand, manufacturing
and positioning of a large number of satellites and gateways
means high fixed costs, and the permanent supply of large
capacities causes high recurring costs.
The discussions above show that because of the manyfold
interrelation of a large number of parameters the basic design
of a LEOACO-satellite system is an involved task and must
be tackled already in the initial state of system planning.
The subject of this paper is the analysis of basic param-
eters of the satellite constellation and the communications
'The name LEONET is historically derived from the title of this study.
0733-8716/95$04.00 0 1995 IEEE
2. 312 IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 13, NO. 2, FEBRUARY 1995
Fig. 1.
isatellite
I
Ernin
Earth'sCentre
Illustration of the geometrical considerations.
Equator
~
Fig. 2. Hexagons inscribed into the footprints
of six isosceles spherical triangles, each one with an angle of
60" at the center of the footprint and two identical angles
network. In Section 11, we derive estimates for the necessary a = arctan (s) (2)
number of satellites and orbits and discuss the features and
consequences of intersatellite links. In Section 111, we analyze
the connectivity requirements in more detail. To this end, we
introduce a formal model for the description of the system
at the periphery of the footprint. With
(3)
2
1
T
3
< = 2 a - -
structure. Based on this, we investigate different constellations
with regard to link capacity requirements. Some constellations
are compared on the basis of numerical results. Finally,
the influence of unequal traffic distribution within a satellite
denotingthe spherical
hexagon is
of the triangles, the area of the
A = 6p2[. (4)
footprint is discussed.
11. LEO~~CO-SATELLITE
NETWORK
TOPOLOGY To cover the total surface of the earth, at least
A. Number of Satellites and Orbits
In this section, we derive estimates for the number of
satellites and orbits which are necessary to achieve a global
coverage.
The service area of a single satellite, called footprint, is a
spherical segment of the earth's surface in which the satellite
can be seen under an elevation angle E, equal or greater than
a certain minimum elevation angle The extent of the
footprint is determined by €,in and orbit height h, which
therefore are the most crucial system parameters. The half-
sided center angle Q of the footprint (cf. Fig. 1) is given by
[41
7l
@ = - -
2
arcsin -
( P L
with p denoting the mean radius of the earth.
By simply considering the extent of a footprint without
resorting to a specific satellite constellation, a lower limit
for the necessary number of satellites can be derived. For a
complete coverage of the earth's surface, it is inevitable that
the footprints overlap. The largest possible effective footprint
of a single satellite is then equivalent to the largest hexagon
inscribed into the footprint (cf. Fig. 2). This hexagon consists
(5)
4lTp2 - lT
n = - - ~
A 3a-IT
satellites are necessary. This lower limit holds for any type
of satellite constellation. Fig. 3 shows the number of re-
quired satellites versus orbit height for different values of
the minimum elevation. The number of satellites for proposed
systems (Table I) are also indicated. It can be seen that for the
systems Globalstar and Odyssey in relation to their designed
minimum elevation angles (20" and 30°, respectively) the
planned number of satellites is only slightly greater than
the required minimum according to (5). On the other hand,
LEONET uses 15 satellites, which is substantially more than
the theoretically required 9 satellites. Consequently, most of
the time a LEONET user would see two or more satellites
simultaneously, which increases the link availability in built-up
areas.
Besides the number of satellites, also the number of orbits,
0, is important, because usually a dedicated launch is neces-
sary for each orbit. In order to determine the required number
of orbits, it is sufficient to consider the satellite coverage at the
equator or at any other great circle. The best case for equatorial
coverage is depicted in Fig. 2. On the condition that in every
orbit there are at least two satellites, each orbit covers 3p@ of
3. WERNER et al.: ANALYSlS OF SYSTEM PARAMETERS 313
20” elevation
30” elevation
0 Globalstar
1000 10000
orbit height (km)
Fig. 3. Least number of satellites required for global coverage.
the equator. Therefore, at least
n=
orbits are necessary to guarantee global coverage. In Fig. 4, R
is shown versus the orbit height. Again, the values of proposed
systems are included for reasons of comparison. Similar to
Fig. 3, the values for Globalstar and Odyssey correspond very
well to the estimations. For LEONET the number of orbits is
also close to the estimated value. With 6 orbit planes, Iridium
achieves a minimum elevation of 8.2”.
Starting from the required number of orbits, R, a more
realistic estimation of the required number of satellites can
be derived for satellite constellations with polar orbits. For a
continuous belt of hexagons along an orbit track (Fig. 2)
(7)
satellites are necessary, giving a total number of R . n1
satellites. For example, assuming 8.2” minimum elevation for
the Iridium system, the above estimations yield R =6 and
n/ =11, resulting in 66 satellites, as actually planned for
Iridium. A comparison with Fig. 3 reveals that constellations
with polar orbits are not very efficient with regard to the
required number of satellites. For inclined orbit constellations,
(7) is not useful, because the concept of a continuous belt of
footprints along the orbit tracks is usually not followed here.
B. Intersatellite Links
The connectivity of a LEOACO-satellite network substan-
tially depends on the presence of intersatellite links (ISL’s).
The possibility to route long-distance traffic via ISL’s adds
to the autonomy of the system, reduces uncontrollable costs
for terrestrial PSTN links, and may decrease communications
delay. Also, vast areas can be served in which a LEO-
satellite cannot see any gateway station (e.g., the Pacific
15 I I
10” elevation
- - .
20” elevation
l
n
c
.-
n
L
0
;10
L
W
n
5
t
.
0 5
l
n
W
U
W
c
0
30” elevation
’ proposed systems: ’
- 0 Globalstar
- -
-- V I r i d i u m
v LEONET
1000 10000
orbit height (km)
Fig. 4. Least number of orbits required for global coverage.
Ocean). Generally, the requirements of satellite handover can
be loosened because the path to a certain fixed gateway can
be maintained as long as the mobile user is served by the
current satellite, whereas without ISL’s the satellite has to
“see” the gateway and the mobile user simultaneously.Finally,
the ISL network is well suited to carry signalling and network
management traffic.
On the other hand, the introductionof ISL’s entails a number
of consequences, such as additional weight, complexity, and
cost of the satellite payload. This comprises ISL antennas,
transmitters, and receivers, as well as switching capabilities
on board the satellite, which are inevitable when ISL’s are to
be used. The required ISL pointing, acquisition, and tracking
(PAT) also increases satellite complexity and demands steer-
able ISL antennas (in addition to steerable gateway antennas
on board the satellite). A serious problem for the negotiation
of national landing rights may be that PTT’s could consider
ISL’s a rival to their terrestrial networks.
Roughly speaking,LEO satellitesystems intended for global
coverage, such as Iridium or Calling [5] includeISL’s, whereas
for IC0 systems the advantages of ISL’s seem to diminish.
There are two types of ISL’s, namely intraplane ISL’s
connecting satelliteswithin the same orbit plane and interplane
ISL’s connecting satellites in adjacent orbit planes.
Two satellites on different orbit planes “see” each other un-
der time-varying pointing angles. Therefore, interplane ISL’s
generally require antenna steering, whereas intraplane EL’S
can be maintained with fixed antennas. Moreover, interplane
ISL’s may not be permanently maintained, because as the
satellites follow their orbits, their distance may vary within
a large range and the earth may interrupt the line of sight. In
this case, the interplane ISL would have to be switched off
and on again, requiring the formidable task of PAT.
Fig. 5 shows possible topologies of satellites and ISL’s for
the LEONET and Iridium constellations, respectively. The
LEONET constellation serves as an example for a typical IC0
concept, Iridium represents a well-known LEO system.
4. 314
LEONET
IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS,VOL. 13, NO. 2, FEBRUARY 1995
Iridium
8000 I 1000
'
'
1
.
0 sec
~000+70&
Distance range
Loss variation
Horizontal pointing
Vertical oointina
1 -
2000
I
3000
intraplane interplane
ISL 1 ISL
12.2 dB
-106". ..106"
-10". ..- 46'
-36"
5 -20
.E -30
intraplane interplane
ISL 1 ISL
34" ...65"
f -40
2 -50
k -60
-70
-80
I
I I
I 1
-16" I -16"
~
80
60
40
F 20
- 0
f -20
-40
-60
-80
-150 -100 -50 0 50 100 150
Longilude 8" deg
(a)
80
60
40
d 20
0 0
g -20
-40
-60
-80
-150 -100 -50 0 50 100 150
Longitude in dsg
(b)
Fig. 5. Topology of satellites and ISL's for (a) LEONET at t = 240 s and
(b) Iridium at t = 0 s. Subsatellite points -intraplane ISL's - - - - -
interplane ISL's.
For the LEONET constellation, intraplane ISL's and perma-
nently maintainable interplane ISL's are considered, Fig. 5(a).
Each satellite must be equipped with four bidirectional ISL
ports (ISL antenna, transmitter, and receiver); two of the four
ISL antennas must be steerable.
For the Iridium constellation, intraplane ISL's and three
equatorial rings of interplane ISL's are shown in Fig. 5(b).
It is assumed that for each time those interplane rings are
maintained which are closest to the equator. For the north-
bound satellites new interplane ISL's south of the equator
are switched on when the oldest interplane ISL's north of
the equator are switched off. The corresponding procedure is
followed for the south-bound satellites. For the boundaries
between north-bound and south-bound satellites we assume
appropriate interplane ISL's at any moment of time.
The above mentioned ISL topology only serves as an
example which will be used in Section 111 for the evaluation
I / I I V
6000
2 -40
z -50 l l o ~ ~
13000
I
I I I I 1
-50 0 50 100
-90 -
-100
Homonloi Poinling ~n deg
(b)
Fig. 6.
(b). Pointing from satellite 1 to satellite 12, for both constellations.
Time-varyinginterplanepointing angles for LEONET (a) and Iridium
of traffic flows. As discussed below, however, the considered
ISL topology seems to be a reasonable choice.
Fig. 6 gives an impression of the time-varying interplane
pointing angles in azimuth and in elevation,related to the flight
direction of a satellite. Fig. 6(a) shows that for the LEONET
constellation a large range of pointing angles is necessary,
causing rather challenging PAT requirements.
From Fig. 6(b) it can be seen that the PAT requirements
for Iridium are easier. The flat shape of the loop suggests to
keep the vertical antenna pointing fixed and to move the ISL
antenna only in horizontal position, as indicated in the Figure.
This approach is already mentioned in the literature [6].Here, a
vertical two-sided 2 dB-beamwidth of 5" is assumed, in which
the ISL can be maintained. With a 1:2 beam ellipticity, this
corresponds to approximately 36 dBi gain at 23 GHz. Then,
from the vertical pointing angles, Fig. 6(b), it can be concluded
that interplane ISL's can be maintained between latitudes of
approximately 60" south or north, respectively. This agrees
very well with the example ISL topology discussed above.
The remaining horizontal steering range amounts to 31O.
In Table 11, the geometric characteristics of ISL's are
compared for the LEONET (KO) and Iridium (LEO) con-
5. WERNER et al.: ANALYSIS OF SYSTEM PARAMETERS 315
stellations. The free space loss variation defined by 20 lg
max./min. distance is also included.
In the following we assume that ISL’s are used for Iridium;
for LEONET we consider ISL’s as a system option and
investigate both, the LEONET constellation with and without
ISL’s, respectively.
111. CAPACITY REQUIREMENTS
AND
TRAFFIC
ENGINEERING
ASPECTS
In this section we will first discuss the main network
elements and give an estimation of the number of channels
to mobile users. After that we develop a possible approach
to network capacity design on the basis of an elaborate
network model. The underlying capacity evaluation procedure
is discussed in detail and representative results are presented.
The main network nodes are communications satellites in
low earth or intermediate circular orbits (polar or inclined)
with periods of a few hours and a regular phasing between the
satellites within the same orbit. They have transmission and,
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1000 10000
orbit height (krn)
optionally (with onboard processing), a switching function.
The to existing public networks is guaranteed by
Fig. 7. Necessary number of channels on the mobile user link. Lines
represent estimates accordingto (8), symbols represent numerical resultsfrom
detailed analysis.
terrestrial gateway stations. Besides this interface function
their main tasks are switching and network management. The
third group of network nodes are the terminals of mobile and
fixed users, representingthe sources and destinations of traffic.
The network nodes are connected by several kinds of links:
Mobile user links (MUL’s).
Links between satellites and those mobile users within
their footprint, who communicate via the satellite.
Links between satellites and gateways in the coverage
area of the satellite.
Links through the public switched telephone net-
worWpublic data networks (PSTNPDN’s).
Totality of existing telephone and data networks,
thus providing the possibility for all fixed users to
communicate with mobile LEOACO system users via
gateway stations.
Direct connections between satellites; their use in a
LEOACO satellite system is optional. ISL’s may connect
satellites within the same orbit (intraplane) or satellites
in adjacent orbits (interplane).
For the routing of long-distance traffic (i.e., traffic between
users in different coverage areas), there exist two major
alternatives, depending on the use of ISL’s. In a system
providing ISL’s this traffic may be transported as far as
possible through the space segment. In connection with a
terrestrial backbone it is possible to significantly reduce the
number of worldwide necessary GW stations. Theoretically,
one GW could be sufficient for global connectivity. If the
system does not provide ISL’s, then the whole long-distance
traffic has to be transported through public lines. In this case
it is necessary for global connectivity that every satellite
has connection to at least one GW station at any instant of
time. A reasonable realization of a LEOnCO-satellite based
communicationssystem should of course combine the positive
Gateway links (GWL’s).
Intersatellite links (ISL’s).
features of both alternatives. To optimize configuration and
connectivity in this sense, a computer aided analysis-based
on an appropriate mathematical model-is a promising ap-
proach.
Due to the low antenna gain of the mobile terminals, the
power consumption of the MUL’s is high. Therefore, these
links are the most crucial ones with respect to the power
budget.
A. Estimation of the Number of Channels to Mobile Users
In the following we assume one million mobile users
worldwide and a traffic intensity of 5 mErl per user, resulting
in an overall traffic Tnet= 5000 Er1 to be transported within
the network. Additionally, we assume that Tnetis completely
generated on the land masses of the earth, which correspond to
a fraction of 26% of the total surface. With these assumptions
we can calculate an estimate for the number IC of required
MUL channels per satellite. In the worst-case, the footprint of
a satellite is completely over land; then
(8)
is an estimation for the number of channels needed.to carry all
the traffic generated in that footprint. This relation is plotted
versus orbit height in Fig. 7, together with results from a more
detailed analysis (Section 111-B).
k = - . -
1 Tnet
0.26 n
B. Network Capacity Design
The previous subsection gives a rough estimate for the
number of required MUL channels. Since the number of
communications channels per satellite (including GWL and
ISL’s as well as the MUL) determines the power subsystems
and thus the satellite mass and cost, this parameter will now
be discussed in more detail. Especially, a tool is presented and
6. 316 IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 13, NO. 2, FEBRUARY 1995
used to calculate the necessary number of channels per satellite
based on a given traffic intensity distribution on the earth.
Additionally, with respect to traffic routing considerations also
the number of required PSTN lines will be discussed.
The main task of this analysis is the investigation of link
capacity requirements for various constellations, under some
basic conditions like permanent global connectivity and upper
limits for blocking probability and delay. The dimensioning of
the network should be user-oriented, i.e., adapted to the world-
wide expected demand for mobile communications and its
distribution (considering a realistic market share for LEOIICO
systems).
1)Network Model: As a base for the capacity investiga-
tions we present a graph-theoretical model describing the
network configuration at a certain instant of time [7]. (Time
variance of network topology and traffic are taken into account
on the computer calculation level and will be discussed later.)
The model consists of the following components:
1) n satellites SI,.. ..sn.
2) n traffic sources/destinations ml....,m,; mLrepresents
all mobile users communicating via satellite s,.
3) n network nodes fl,. ...f n in the footprints of the
corresponding satellites. The whole amount of PSTN
traffic “belonging” to the footprint of s, is assumed
to be concentrated in node f,. Furthermore, the fL are
assumed to be completely connected with each other
via the PSTN. The presence of at least one GW in the
footprint of s, results in a direct connection between fz
and s, via a GWL; therefore, such a GW can be regarded
as physically representing the fictitious node f7.
The whole traffic generated at an instant of time can be
described by a traffic matrix T of dimension 2n . 2n:
(no traffic to
In this matrix, the elements t i j describe the amount of
traffic between nodes i and j in Erlang (Erl). Traffic between
two fixed users fi and f j is assumed as pure PSTN traffic
and therefore not included in the analysis. In case only voice
communication over full duplex channels is considered, the
traffic matrix T becomes symmetric.
The totality of connections within the network is described
by a symmetric connectivity matrix C of dimension 371 . 371,
where “1” denotes an existing connection between adjacent
nodes:
n l . ... .. . ,m,,
0
0
E
f l , . . . .. .,Jn
0
I
(PSTN)
C&J,
’ I , . . . ...,S“
E
Cl,$,
cs,s,
(ISLS)
Here, E = ( e z J )denotes the unit matrix, i.e., eZJ= 1 for
i = j and eZJ= 0 for i # j. The c , , ~ ~
describe connections
with ISL’s, and the cszf,and cfZs,mark a connection between
a satellite and a GW station in its footprint, i.e.,
1,
0, for i = j and no GW present in the footprint
0, for i # j .
for i = j and a GW present in the footprint
(9)
2) Capacity Evaluation Procedure: Any LEO/ICO satellite
system is on principle highly dynamic. The movement of
network nodes-satellites and mobile users-on the one hand,
as well as the dynamic user activity due to the time zones
on the other hand, lead to time variance of network topology
(switching of ISL’s, changing GW’s in a footprint, etc.) and of
demand for link capacities. In order to take this time variance
into account, investigations are made for several successive
instants of time, in which the system is assumed as static.
By choosing the time interval small enough, it is possible
to gain reliable worst-case and average results for required
link capacities and for delay values. The generalized flow
chart of the C computer program developed for this capacity
evaluation in Fig. 8 illustrates the evaluation procedure for a
certain instant of time.
Starting point is a certain satellite constellation, which is
characterized through orbit height (respectively orbit period),
through number and inclination of orbits and throagh number
and phasing of satellites in these orbits. With a given minimum
elevation angle for the connection to the satellites the coverage
areas can now be calculated.
With respect to communications traffic, the underlying re-
quirement is to provide voice service with a blocking probabil-
ity less than 5% for 1million subscribers which are assumed to
be distributed within six regions according to Table 111. These
(land mass) regions are visualized in Fig. 9. Furthermore, it
is assumed that all users are permanently generating traffic
with 5 mErl, no matter which time zone they are actually in.
This assumption of a “permanent worldwide busy hour” seems
7. WERNER et al.: ANALYSIS OF SYSTEM PARAMETERS
Region
North America
311
Percentage Absolute #
25% 250 000
INPUT
- __ -
r i r - 7
Connectivitymatrix C
Traffic matrix T
N.America
CALCULATION I I
Europe Asia %America Africa Australia
PROCESS
- variationof routing strategies
OUTPUT
- Mean utilizationof different kinds of links
- Propagation delay statistics
- Statisticsabout lengthsof required PSTN lines
Fig. 8. Schematic description of network connectivity analysis.
to be quite legitimate if one considers that the main interest
with respect to system capacity design, and especially satellite
design, is in worst-case traffic requirements on the different
links in the network.
The traffic flow between the six regions is assumed accord-
ing to the regional traffic flow matrix in Table IV. In addition, a
distinction is made between two types of connections, mobile-
to-fixed and mobile-to-mobile. Assuming 10%of the users to
be mobile, yields a ratio of mobile-to-fixed traffic : mobile-
to-mobile traffic = 18:l.
For further network analysis the regional traffic is allocated
to the different satellites according to their percentage of
coverage of the respective land mass. This mapping of land
mass regions onto coverage areas is indicated by the hatchings
in Fig. As a result we get a traffic matrix T for the specific
configuration. Together with a given GW distribution, also the
connectivity matrix C can be determined.
Now the central aim is to transport all the generated
traffic from source to destination, considering the underlying
conditions (blocking probability, delay, etc.). That is, we
have to determine paths from source i to destination j with
t i j > 0. From connectivity matrix C it can be seen that
*This approach assumes footprints to be centered around the subsatellite
points, which does not hold for the Odyssey concept. Nevertheless, in this
mapping approach spot-beams are not taken into account, and the possible
land mass coverage of any satellite is clearly limited by the minimum elevation
angle; therefore, by applying the same approach to Odyssey with the minimum
elevation angle foreseen for this system, the comparison of the respective
numerical results with those of other systems seems to be legitimate.
TABLE I11
REGIONAL
DISTRIBUTION
OF SUBSCRIBERS
Europe 11 25% I 250000
Asia 11 20% I 200000
South America 1 N
I
: 1 :iiCMlii
Africa
Australia/NZ 10% 100000
Fig. 9.
constellation LEONET.
Traffic regions on earth; footprints and example GW distribution for
Africa 11 24 Er1 I 36 Er1 I 19 Er1 I 10 Er1 1 436 Er1 I 5 Er1
Australia 11 24 Er1 I 12 Er1 I 39 Er1 I 5 Er1 1 5 Er1 I 441 Er1
no direct connections (c;j = 0) exist between source and
destination nodes (mobile and fixed users). The basic criterion
for path search is a generalized cost function, and “cheapest”
paths are selected for the traffic transport; this is performed
with the well-known Dijkstra algorithm [9]. On the basis of
different cost functions several strategies for the routing of
long-distance traffic are possible:
ISL’s are preferred, i.e., high pseudo-costs are attached
to PSTN links and low ones to ISL’s.
PSTN links are preferred, i.e., high pseudo-costs are
attached to ISL’s and low ones to PSTN links.
If not each satellite has connection to at least one GW
station during the whole time, then a certain amount
of ISL capacity is necessary to maintain global connec-
tivity. Then it is desirable to use this ISL capacity in
the whole network as far as possible and route only the
traffic exceeding this amount through PSTN.
Paths with smallest possible propagation delay are cho-
sen.
If the cost function is 1 for each link, the algorithm
yields shortest paths in the sense of hops.
8. 37R IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 13, NO. 2, FEBRUARY 1995
80
60
40
20
0
-20
-40
-60
-80
Fig. IO. Land mass coverage and traffic mapping for constellation LEONET
In the computer program the first three routing strategies
were implemented. As output the algorithm yields the re-
quired (worst-case) link capacities in Erlang for the different
connections (MUL, GWL, ISL, PSTN). Furthermore, the av-
erage utilization is calculated for every link type, so that the
calculation of average capacity requirements is possible, too.
For network dimensioning the maximum number of required
channels on any link is of importance. Therefore, channel
numbers are calculated according to the Erlang B formula [101
(B:blocking probability; C: number of channels; A: traffic
in Erl).
In addition, from all point-to-point-connections the maxi-
mum propagation delay is extracted and an average value for
the whole network is calculated.
C. Results
First of all, we present results for the MUL. In Fig. 7,
the estimated value IC (cf. (8)) is plotted versus the orbit
height and compared with results from the more detailed
analysis. In this context it should be noted that the estimation
is based on the theoretically minimum number of required
satellites w.r.t. global coverage, whereas the exact figures are
derived from the proposed systems. Furthermore, in contrast
to the estimation, an unequal userhraffic density over land
mass is assumed for the numerical analysis, as presented
above. Especially, the region of Europe is characterized by
a high traffic density. For the LEO systems Iridium and
Globalstar, with footprint areas in the order of magnitude
of the European land mass, the calculated figures are close
to or even larger than the estimation. On the contrary, for
LEONET and Odyssey the exact figures are significantly
below the estimation. This is mainly due to the following two
reasons: First, the comparatively large footprints do in reality
not cover only land mass, but-ven in the worst-case-they
include quite a share of oceanic regions (cf. Fig. 9). Second,
bigger overlapping zones of the satellite footprints increase the
2ooo k
I
0 ‘ I I I A I
0 2 4 6 8 1 0 1 2 1 4
Number of gateway stations
Fig. 11. Required full duplex channels per ISL. ARS = Advanced routing
strategy (cost function #3). Constellarion: LEONET with 4ISL’s per satellite.
multiple satellite visibility, and thus the mobile user traffic can
advantageously be shared among satellites.
In order to evaluate the long-distance traffic requirements,
all constellations were investigated for three different routing
strategies and for several GW distributions, with ‘‘reasonable”
locations for the GW stations (e.g., preferably in most industri-
alized regions, on dry land). Figs. 11 and 12exemplarily show
worst-case channel requirements per ISL and in the PSTN,
respectively, for the LEONET constellation with 4 ISL’s per
satellite as presented in Section 11-B.
Fig. 11 shows the maximum required number of full duplex
channels per ISL. With an increasing number of GW stations,
the worst-case channel requirement for the ISL is decreasing
monotoneously to zero, if all long-distance traffic is preferably
routed via PSTN. With 7 GW stations reasonably distributed
over dry land, the LEONET system is able to guarantee global
connectivity without use of ISL’s. This is due to the fact
that every satellite has connection to at least one GW station
during the whole time, so that long-distance traffic can always
9. WERNER er al.: ANALYSIS OF SYSTEM PARAMETERS 319
I I I I I
I
E 1500
a
ln
.-
?
! loo0 t
Prefer PSTN
“ L o Prefer lSLs
I I - 6 I A I
0 2 4 6 8 1 0 1 2 1 4
Number of gateway stations
Fig. 12. Required full duplex PSTN lines for long-distance traffic in the
whole network. ARS = Advanced routing strategy (cost function #3).
Constellation: LEONET with 4 ISL’s per satellite.
be routed via PSTN. The corresponding GW distribution is
depicted in Fig. 9. If ISL’s are preferred, a roughly constant
amount of required ISL capacity remains for more than 3 GW
stations.
Fig. 12 illustrates the number of public full duplex lines that
are required to transport the long-distance traffic. If existing
public networks are preferred, then these requirements remain
relatively constant with a varying number of GW stations. On
the analogy of Fig. 11 it can be seen, that with 7 reasonably
located GW stations it is possible to avoid the use of PSTN
lines for transport of long-distance traffic.
Comparing the numerical results for LEONET in Figs. 11
and 12, the importanceof the applied routing strategy becomes
obvious: For a number of 6 GW stations (one in each region)
for example, in the case of ISL preference the maximum
required ISL capacity is high, whereas the demand for public
lines is low. If public networks are preferred, the amount of
required ISL channels can be reduced by more than 50%, but
at the same time the PSTN channel requirements enormously
increase. With the advanced routing strategy (cost function 3
in Section 111-B)
the demand for both, ISL channels and PSTN
lines can be clearly reduced at the same time.
From these results, it can be seen that a number of 6
or 7 GW stations is a clear lower limit for a reasonable
LEONET system realization; considering some other relevant
aspects as well (e.g., regulatory and political issues, multiple
visibility between satellites and GW’s, robustness w.r.t. failure
or regional traffic overload), one may regard a number of
10-20 GW stations as good choice for LEONET. However,
the 7 GW constellation is well suited to show the fundamental
trade-off between the use of ISL’s and the amount of required
public lines, in this context also stressing the importance
and prospectives of adapted strategies for the routing of
long-distance traffic. Corresponding numerical results for a
LEONET constellation without and with 4 ISL’s per satellite,
respectively, are given in Table V.
The Iridium system concept is essentially based on the
presence of an extensive ISL infrastructure;nevertheless, both
the GW distribution and the supplementaryuse of public lines
for transportof long-distancetraffic are importantmainly w.r.t.
the task of reasonably interfacingmobile and fixed users in the
global communications system. Therefore, detailed investiga-
tions for Iridium were performed similarly to LEONET. As
one expects, due to the smaller footprints the number of GW
stations should be higher than in LEONET, in order to use
the installed ISL infrastructure efficiently while reducing the
amount of required PSTN capacity. A number of 55 GW’s,
compared to GW distributions including 12-20 GW’s, yields
significantly lower worst-case channel requirements for MUL,
GWL, and PSTN; additionally, the utilization of installed
ISL links can be increased. Generally, the scope for traffic
flow optimization by means of adapted routing strategies is
quite limited for Iridium in comparison to LEONET. The
numerical results show that a preference of ISL’s for long-
distance traffic routing is the best choice. The ARS approach
is not suitable for Iridium in order to decrease ISL and PSTN
channel requirements to reasonably low values at the same
time, as can be seen in Table V.
The figures discussed so far refer to long-distance traffic
requirements. For the channel requirements on the GWL
the routing strategy’s influence is not significant. Due to a
reduction of traffic concentration, the worst-case demand for
GWL channels monotoneously decreases with an increasing
number of GW stations until all satellites have a direct
connection to at least one GW station.
Based on the worst-case channel figures for MUL (down-
link), ISL, and GWL, link budget calculations can be per-
formed to determine peak RF power requirements on board
the satellite, which is of basic importance for satellite design.
Results for LEONET and Iridium are given in Table V. The
budget was calculated with the same assumptions (e.g., link
margins, user antenna gain, satellite antenna pattern. .. ). The
average power values are calculated by considering the mean
utilization of the respective links. The figures show that the
power consumptionon board the satelliteis mainly determined
by the MUL. Consequently,the overallpower requirementsare
significantly lower for Iridium satellites.
In the last two lines of Table V, figures for maximum
and average propagation delay are denoted, showing a better
performance for Iridium due to the lower orbit altitude. As far
as voice service is concerned, an upper limit of 400 ms for the
end-to-end delay is set by CCITT, where signal processing and
switching delays are included as well as propagation delay.
Considering a typical packet length of 20 ms and current
switching technology, the sum of additional delays through
codec, assembling/disassembling processes and switch-
inghuffering operations should be in the range of 100 ms for
a typical point-to-point connection, so that the CCITT limit
for voice transmission can be guaranteed within either system.
D.Partition of Satellite Footprints into Spot-Beams
By use of multibeam antennas, the satellitefootprints can be
divided into smaller cells. Typical numbers of spot-beam cells
are NZ = 7, 19, 37, 48, or 61. An advantage is the increase
10. 380
Constellation
Gateway distribution
per satellite
ISL'S intra-orbit
inter-orbit
IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS,VOL. 13, NO. 2, FEBRUARY 1995
Iridium Iridium LEONET LEONET
55GW's 55 GW's 7 GW's 7 GW's
2/4 2/4 4 0
2 2 2 0
012 012 2 0
TABLE V
COMPARISON
OF NUMERICAL
RFSULTSFOR DIFFERENT
CONSTELLATIONS
Min. elevation angle (mob. user)
Min. elevation angle (GWs)
Results:
Required channels per MUL
(5 mErl, worst-case) per ISL
8.2" 8.2" 20" 20"
5" 5" 5" 5"
-
488 488 1047 1047
902 82 248 0
11 Pref. ISL's I ARS I ARS I Pref.PSTN
Routing strategy
Peak power MUL (1.6 GHz) 81 W
per satellite ISL (23 GHz) 7 W
(5 mErl) GWL (4 GHz) 3.9 W
Average power MUL (1.6 GHz) 13 W
per satellite ISL (23 GHz) 2 W
(5 mErl) GWL (4 GHz) 0.6 W
Max. propagation delay 171 ms
Aver. propagation delay 46 ms
Elevation parameters:
81 W 393 W 393 W
0.7 W 11.5 W 0
4.2 W 8.3 W 8.5 W
13 W 124 W 124 W
0.1 W 5.5 W 0
0.7 W 2.7 W 2.7 W
171 ms 265 ms 198 ms
32 ms 95 ms 75 ms
of bandwidth efficiency due to the reuse of frequency bands
in sufficiently separated cells. In a narrowband system, the
number of different frequency bands is typically NF = 3,4, 7 ,
or 9. For a uniform traffic distribution within the footprint, the
resulting reduction of required system bandwidth is Nz/NF.
Another advantage is the reduction of RF power for the MUL's
due to the concentration of the power within smaller areas,
equivalent to a higher satellite antenna gain. The reduction of
power is approximately Nz. The use of multi-beam antennas
requires high technical efforts, but they are planned for all
relevant LEOACO systems in order to reduce the transmission
power of the handheld terminals.
For many areas within the system coverage, we must take
into account that the mobile user traffic is unequally distributed
within a satellite footprint. Then, the advantages of spot-beams
will partially diminish.
In the extreme case, all traffic channels may have to
be concentrated in a single spot-beam, requiring sufficiently
flexible satellite onboard processing. Then, for a narrowband
system, the gain in bandwidth efficiency is completely lost, but
the reduction in necessary transmit power of the satellite and
the mobile terminals remains. For a spread spectrum system,
the interference within the heavily loaded cell approximately
rises by a factor of Nz. Since spread spectrum systems are
interference limited, this causes a link degradation of 10
lgNz dB. As a countermeasure, the processing gain could
be increased by increasing the chip rate (and the bandwidth
requirement, correspondingly) or by decreasing the service bit
rate (and voice quality).
A detailed investigation of the significant influences of
unequal traffic distribution represents a rewarding subject of
further research.
IV. CONCLUSION
Several basic system parameters of LEOACO systems have
been discussed. Estimations for the number of satellites, num-
ber of orbits and number of transmission channels have been
presented. A major part of the paper was devoted to the
discussion of the number of communication channels per satel-
lite. To this end, a formal model for mobile communications
networks based on LEOACO satellites was introduced and a
method for the analysis of network connectivity requirements
was proposed. This evaluation procedure can efficiently be
used in the initial process of planning and dimensioning
LEOACO networks. The concrete application in form of a
specially developed software tool was shown exemplarily
for a comparison between two proposed systems, Iridium
and LEONET. Numerical results of network connectivity
investigation show that the system constellation basically
11. WERNER et al.: ANALYSIS OF SYSTEM PARAMETERS 381
influences the link capacity requirements. Thus the presented
of network components and for comprehensive system cost
calculations [111.
Axel Jahn (M’90)received the Dipl.-Ing. degree in
1990 from the University of Karlsruhe, Germany.
Since September 1990, he has been a Research
Scientist with the Institute for Communications
Technology of the German Aerospace Research Eb-
tablishment (DLR) at Oberpfaffenhofen, Germany
results provide important input information for the design
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Markus Werner (M’92) received the DipL-lng.
degree in electrical engineering from the Technical
University Darmstadt, Germany, in 1991.
Since 1991,he has been a Research Scientist with
the Institute for Communications Technology of the
German Aerospace Research Establishment (DLR)
at Oberpfaffenhofen, Germany. His research inter-
ests are network aspects of communication systems.
Currently he is working on routing and congestion
control in dynamic satellite networks. He is also a
lecturer at the Carl-Cranz-Gesellschaft.
his main tields of
also a Lecturer at
From 1990-1993, he was a Scientific Assistant at
the FemUniversitat Hagen, Germany. His research
interests are simulation methods and the analysis of
communication networks. LEO satellite systems and
the influence of land-mobile channels are currently
interest. He is doing Ph.D. work on these subjects. He is
the Carl-Cranz-Gesellschaft.
Erich Lutz (M’92) was born in Augsburg, Ger-
many, in 1950 He received the Ing grad degree
from the Polytechnic Augsburg in 1972, the Dipl:
Ing degree from the Technical University Munich
in 1977, and the Dr -1ng degree from the Military
University Munich in 1983
From 1977to 1982he was a Research Assistant at
the Technical University and the Military University
Munich, working in the field of digital transmis-
sion over cables and optical fibers. Since 1982,
he has been with the Institute for Communications
Technology of the German Aerospace Research Establishment (DLR) in
Oberpfaffenhofen, Germany Since 1986, he has been head of the Digital
Networks section of this institute. His current research interests include
mobile radio channel characterization, error control techniques, multiple
access techniques, and networking aspects, in particular, for mobile satellite
communication networks
Gesellschaft fur Betrieb
at the Carl-Cranz-Gese
Axel Bottcher (M’89) received the Dipl.Math.
degree in 1987 from the Ludwig-Maximilian-
Universitat, Munich, and the Dr.1ng. degree from
the University of the Armed Forces, Munich, in
1992.
From 1988 to 1994, he worked as a Research
Scientist at the Institute for Communications
Technology of the German Aerospace Research
Establishment (DLR) at Oberpfaffenhofen, Ger-
many. Since July, 1994, he has been Head of the
radio planning group at T B&D Telekommunikation
und Dienstleistungen in Munich. He is also a Lecturer
Ilschaft.
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