This document discusses satellite communications and provides an overview of key concepts:
- Satellite communications systems have two main components - the satellite in orbit which receives and transmits signals, and ground stations that send signals to and receive signals from the satellite.
- Satellites are used for various applications including telecommunications, cellular networks, television broadcasting, maritime communications, land mobile communications, aircraft messaging, and global positioning.
- Technological aspects discussed include error correction techniques like forward-error correction and automatic-repeat-request, hybrid satellite-terrestrial networks, and using protocols like TCP/IP over satellite links.
This document provides an overview of satellite communications. It discusses how satellites serve as radio relay stations in space to allow point-to-point communication even in remote locations. Some key events in the history of satellite communication are noted, such as the launch of Early Bird in 1965, which was the first commercial satellite. The basic elements of a satellite communication system, including the satellite in space and ground stations, are described. Various uses of satellite communication are then outlined, such as traditional telecommunications, cellular networks, television broadcasting, and applications for maritime, air, and land mobile communication.
Satellite communication uses satellites as wireless repeaters to provide communication links between geographically remote sites. Satellites are equipped with transponders consisting of a transceiver and antenna tuned to allocated spectrum. Most satellites simply broadcast whatever they receive. Packet data transmission via satellite is increasingly common, with satellites used as backbone links between dispersed LANs and MANs. Modern satellite networks incorporate on-board switching and processing rather than simply acting as "bent pipes."
The document describes a satellite communication system using SC-WFMT modulation.
SC-WFMT combines SC-FDMA and wavelet modulation techniques. It offers advantages over traditional QPSK modulation used in satellite communications, including programmable spectrum and compensation for distortions. SC-WFMT provides multipath immunity like OFDM with lower peak-to-average power ratio. It can support mobile satellite communication in urban areas with significant multipath delay spreads. The system uses novel wavelet-based modulation at the transmitter and equalization at the receiver to mitigate distortions from the satellite transponder and multipath propagation.
This document provides an overview of satellite communications systems and applications. It discusses the basic components of satellite communications systems, including active and passive satellites. It then summarizes several applications of satellite technology, including telephone communications, satellite television, satellite radio, amateur radio, satellite Internet, and military uses. Finally, it briefly outlines the history of satellite communications, noting that the Soviet Union launched the first artificial satellite, Sputnik, in 1957.
Satellite communications play a vital role in global telecommunications by relaying signals between locations worldwide using approximately 2,000 orbiting satellites. Key applications include telephone via satellite phones, television via direct broadcast satellites and fixed service satellites, radio via satellite radio services, internet access, and military communications. There are three main satellite systems: INTELSAT for international routes, DOMSAT for domestic services within countries, and SARSAT for search and rescue using polar orbiting satellites.
This document discusses VSAT (Very Small Aperture Terminal) technology for connecting remote sites via satellite. It provides an overview of VSAT components and configurations, as well as advantages such as availability, fast deployment, and reliability compared to other connectivity options. Different types of satellite orbits - geostationary, medium earth, and low earth - are described along with their implications for latency, coverage, and system complexity.
The document is an assignment on satellite communications for a student named Reymart Olaño. It provides an introduction to satellite telecommunications and discusses the main components of satellite systems, which include the satellite and ground stations. It then describes different utilities of satellite communication such as traditional telecommunications, cellular networks, television signals, marine communications, spaceborne land mobile services, and satellite messaging for commercial jets. The document also discusses satellite systems like INTELSAT, DOMSAT, and SARSAT. It concludes by explaining Kepler's laws of planetary motion and defining terms related to earth-orbiting satellites.
This document provides an overview of satellite communications. It discusses how satellites serve as radio relay stations in space to allow point-to-point communication even in remote locations. Some key events in the history of satellite communication are noted, such as the launch of Early Bird in 1965, which was the first commercial satellite. The basic elements of a satellite communication system, including the satellite in space and ground stations, are described. Various uses of satellite communication are then outlined, such as traditional telecommunications, cellular networks, television broadcasting, and applications for maritime, air, and land mobile communication.
Satellite communication uses satellites as wireless repeaters to provide communication links between geographically remote sites. Satellites are equipped with transponders consisting of a transceiver and antenna tuned to allocated spectrum. Most satellites simply broadcast whatever they receive. Packet data transmission via satellite is increasingly common, with satellites used as backbone links between dispersed LANs and MANs. Modern satellite networks incorporate on-board switching and processing rather than simply acting as "bent pipes."
The document describes a satellite communication system using SC-WFMT modulation.
SC-WFMT combines SC-FDMA and wavelet modulation techniques. It offers advantages over traditional QPSK modulation used in satellite communications, including programmable spectrum and compensation for distortions. SC-WFMT provides multipath immunity like OFDM with lower peak-to-average power ratio. It can support mobile satellite communication in urban areas with significant multipath delay spreads. The system uses novel wavelet-based modulation at the transmitter and equalization at the receiver to mitigate distortions from the satellite transponder and multipath propagation.
This document provides an overview of satellite communications systems and applications. It discusses the basic components of satellite communications systems, including active and passive satellites. It then summarizes several applications of satellite technology, including telephone communications, satellite television, satellite radio, amateur radio, satellite Internet, and military uses. Finally, it briefly outlines the history of satellite communications, noting that the Soviet Union launched the first artificial satellite, Sputnik, in 1957.
Satellite communications play a vital role in global telecommunications by relaying signals between locations worldwide using approximately 2,000 orbiting satellites. Key applications include telephone via satellite phones, television via direct broadcast satellites and fixed service satellites, radio via satellite radio services, internet access, and military communications. There are three main satellite systems: INTELSAT for international routes, DOMSAT for domestic services within countries, and SARSAT for search and rescue using polar orbiting satellites.
This document discusses VSAT (Very Small Aperture Terminal) technology for connecting remote sites via satellite. It provides an overview of VSAT components and configurations, as well as advantages such as availability, fast deployment, and reliability compared to other connectivity options. Different types of satellite orbits - geostationary, medium earth, and low earth - are described along with their implications for latency, coverage, and system complexity.
The document is an assignment on satellite communications for a student named Reymart Olaño. It provides an introduction to satellite telecommunications and discusses the main components of satellite systems, which include the satellite and ground stations. It then describes different utilities of satellite communication such as traditional telecommunications, cellular networks, television signals, marine communications, spaceborne land mobile services, and satellite messaging for commercial jets. The document also discusses satellite systems like INTELSAT, DOMSAT, and SARSAT. It concludes by explaining Kepler's laws of planetary motion and defining terms related to earth-orbiting satellites.
Satellite communications have revolutionized global connectivity. Modern satellites provide broadband internet, audio/video distribution, navigation services, and support military communications. Satellites transmit signals to and receive signals from earth stations via antennas. Communications satellites in geostationary orbit appear stationary from Earth. They provide widespread coverage for services like satellite television, radio, telephony, and internet access. While satellites enabled global connectivity, challenges include high infrastructure costs and signal delays. Future satellites aim to increase capabilities with more power and bandwidth to support growing data demand.
The document discusses satellite communication and the key components involved. It covers:
1) The three main segments of a satellite link - the transmitting Earth station, the satellite, and the receiving Earth station.
2) Components of Earth stations including antennas, amplifiers, modulators, and more.
3) Factors that impact satellite transmission such as frequency bands, transmission losses, polarization, and more.
The document provides an overview of High Altitude Aeronautical Platform Station (HAAPS) technology. It discusses how HAAPS uses airships or aircraft operating between 3-22km in altitude to provide wireless telecommunication services. A HAAPS can cover an area of up to 1000km in diameter. It then describes different platform options being proposed or used, including airships, high altitude long endurance aircraft, and tethered aerostats. The document outlines the system architecture, including the airborne and ground station equipment. It discusses power systems for solar-powered long endurance aircraft and how mission requirements impact aircraft sizing. Finally, it compares the performance and advantages of HAAPS to terrestrial wireless and satellite systems.
VSAT (Very Small Aperture Terminal) technology allows for wireless communication via satellite using small dish antennas. A VSAT network consists of a central hub with a large antenna that communicates with multiple remote VSAT sites. The hub controls and monitors the network, sending data to the satellite which amplifies and redirects the signals to the VSATs. VSAT offers advantages like flexibility, lower installation costs than terrestrial networks, and ability to access areas without terrestrial infrastructure. Common applications of VSAT include corporate networks, internet access, distance education, and retail/banking networks. VSAT uses multiple access techniques like TDMA to allow efficient sharing of satellite bandwidth among sites.
This document discusses Very Small Aperture Terminals (VSAT) and satellite television. It provides details on VSAT components, configurations including star and mesh topologies, multiple access techniques, characteristics, advantages, limitations and uses. It also describes the working principle of satellite television including encoding, transmission via satellite, reception and features of satellite TV systems. The document is authored by Arpan Deyasi from the Dept. of ECE at RCCIIT, Kolkata and covers VSAT and DSB-TV systems for a course.
VSAT (Very Small Aperture Terminal) is a satellite-based communication system that provides flexible and reliable connectivity solutions. It uses satellites to provide point-to-multipoint and point-to-point communication between a central hub station and multiple remote sites. VSAT networks offer benefits like reliability, flexibility, network management capabilities, and cost savings compared to terrestrial leased lines. Common VSAT access schemes discussed include TDMA, FDMA, DAMA, and CDMA.
This document discusses High Altitude Aeronautical Platforms (HAAPS) which could provide wireless communications services from airborne platforms like airships and aircraft operating at stratospheric altitudes. Specifically, it describes the HALO Network concept where aircraft would circle overhead at around 15 miles above ground carrying the hub of a wireless broadband network to provide internet access over a large metropolitan area. Key points discussed include the aircraft and communications payload, how multiple beams would create cellular-like coverage on the ground, and that a fleet of 3 aircraft would be needed to provide continuous 24/7 coverage. Subscriber units would provide broadband access through steerable antennas that point to the aircraft.
This is the slide of Satellite Broadcasting commonly useful for Satellite and Broadcasting describing different orbitals of satellite, frequency allocation, its use for broadcasting, Components of Broadcasting and many more. Feel free to comment but do add source if you are using it as a reference.
The document discusses HALO, a proposed broadband wireless network using high-altitude airships as nodes. HALO airships would operate in the stratosphere, above weather impacts, and use antenna arrays to provide cellular-like coverage over large areas. Key advantages over satellite and terrestrial networks include lower costs, larger coverage areas, and no need for complex infrastructure on the ground. The airships would be powered by photovoltaic cells and fuel cells, providing long-term stationary operation. HALO could enable new applications by providing broadband access across wide geographic regions.
VSAT systems use small aperture terminals (SATs) to provide satellite communication services directly to end users in a cost-effective way. A VSAT terminal consists of an outdoor unit with an antenna and radio frequency transceiver, and an indoor unit containing a modem and baseband processor. VSAT networks can be implemented in a star configuration, where terminals communicate through a central hub station, or a mesh configuration, where terminals can connect directly to each other.
VSAT technology allows for two-way communication via satellite using small terminals. A VSAT network consists of a central hub, satellite, and numerous user terminals. VSAT networks can support internet, data, video, voice, and private/public network solutions. They are becoming increasingly popular due to their flexibility, cost efficiency, and ability to quickly provide telecom solutions for consumers and businesses.
The document describes the HALO Network, a proposed broadband wireless metropolitan area network. The network would consist of a HALO aircraft operating as a hub at an altitude of 16 km, carrying an onboard network and antenna array. It would provide coverage over a 60 mile diameter area. Subscriber terminals on the ground would access broadband internet and other services through the HALO aircraft. The network aims to provide rapid, affordable broadband access with advantages over terrestrial and satellite networks in terms of speed, capacity, and cost.
1. MITRIS is a terrestrial satellite reception system that uses existing satellite TV reception technology to provide TV services to large areas using prefabricated components across different terrains.
2. It utilizes terrestrial transmitters that broadcast satellite frequencies to distribute content, allowing reception with standard satellite dishes pointed at the terrestrial transmitters rather than satellites.
3. ROKS further developed the MITRIS system into MITRIS-CS, which features a cellular structure using relay stations to expand coverage areas. This provides an inexpensive solution for distributing TV services to rural areas.
The document describes The Halo Network, a proposed broadband wireless metropolitan area network. The key aspects are:
- It uses a high-altitude aircraft called HAAPS operating at 16km to serve as an airborne hub/central node for a star topology network.
- The HAAPS aircraft houses an antenna array to create hundreds of virtual cells on the ground to provide service to thousands of users within a 100km radius area.
- It claims advantages over terrestrial and satellite networks like rapid deployment, high signal quality, availability and bandwidth, and lower costs.
This document provides an overview of satellite communication systems. It defines key terms like earth stations, uplinks, downlinks, and transponders. It describes how communications satellites can be categorized based on coverage area, service type, and usage. It also covers satellite orbit types including geostationary, medium earth, and low earth orbits. The document discusses factors that affect satellite link performance and describes frequency division multiple access and time division multiple access techniques.
This slide presentation introduces the Halo Network, a proposed broadband wireless network with its central node located on an airplane flying above 51,000 feet. The Halo Network aims to provide ubiquitous high-speed multimedia services to users across a metropolitan area using millimeter wave frequencies. Key features highlighted include seamless coverage, rapid deployability, bandwidth on demand, and efficient use of spectrum. The feasibility of the Halo Network is argued to be assured by the convergence of technologies across communications, with advantages over terrestrial and satellite networks.
The document summarizes VSAT technology, including its definition, history, components, uses, and future applications. Key points include:
- VSAT stands for Very Small Aperture Terminal and uses small satellite dishes less than 3.8 meters to transmit and receive data via satellite.
- The technology has been in development since the 1920s and was first used commercially in the 1960s for satellite television broadcasts.
- Modern VSAT systems use components like antennas, BUCs, LNBs, and indoor modems to transmit and receive data via geosynchronous satellites.
- Applications include broadband internet access, VoIP, and monitoring systems. The maritime VSAT market was over $400 million in 2007.
- Future
This document presents information about electronic shops and the history and mechanisms of radio. It discusses the key components of radio transmission and reception including transmitters, antennas, receivers, and different modulation techniques. It also outlines some of the early and modern uses of radio in communication, navigation, and other applications. Finally, it briefly introduces cognitive radio networks as an advanced wireless technology.
Switching and multicast schemes in asynchronous transfer mode networksEditor Jacotech
This document summarizes various switching and multicast schemes used in asynchronous transfer mode (ATM) networks. It discusses shared memory ATM switching architectures and different approaches for supporting multicast traffic in shared memory switches including replication-at-receiving, replication-at-sending, multiple write multiple read, and single write single read schemes. It also covers requirements for ATM multicast and compares these schemes in terms of advantages and disadvantages related to memory usage and switching performance.
10 Insightful Quotes On Designing A Better Customer ExperienceYuan Wang
In an ever-changing landscape of one digital disruption after another, companies and organisations are looking for new ways to understand their target markets and engage them better. Increasingly they invest in user experience (UX) and customer experience design (CX) capabilities by working with a specialist UX agency or developing their own UX lab. Some UX practitioners are touting leaner and faster ways of developing customer-centric products and services, via methodologies such as guerilla research, rapid prototyping and Agile UX. Others seek innovation and fulfilment by spending more time in research, being more inclusive, and designing for social goods.
Experience is more than just an interface. It is a relationship, as well as a series of touch points between your brand and your customer. Here are our top 10 highlights and takeaways from the recent UX Australia conference to help you transform your customer experience design.
For full article, continue reading at https://yump.com.au/10-ways-supercharge-customer-experience-design/
Satellite communications have revolutionized global connectivity. Modern satellites provide broadband internet, audio/video distribution, navigation services, and support military communications. Satellites transmit signals to and receive signals from earth stations via antennas. Communications satellites in geostationary orbit appear stationary from Earth. They provide widespread coverage for services like satellite television, radio, telephony, and internet access. While satellites enabled global connectivity, challenges include high infrastructure costs and signal delays. Future satellites aim to increase capabilities with more power and bandwidth to support growing data demand.
The document discusses satellite communication and the key components involved. It covers:
1) The three main segments of a satellite link - the transmitting Earth station, the satellite, and the receiving Earth station.
2) Components of Earth stations including antennas, amplifiers, modulators, and more.
3) Factors that impact satellite transmission such as frequency bands, transmission losses, polarization, and more.
The document provides an overview of High Altitude Aeronautical Platform Station (HAAPS) technology. It discusses how HAAPS uses airships or aircraft operating between 3-22km in altitude to provide wireless telecommunication services. A HAAPS can cover an area of up to 1000km in diameter. It then describes different platform options being proposed or used, including airships, high altitude long endurance aircraft, and tethered aerostats. The document outlines the system architecture, including the airborne and ground station equipment. It discusses power systems for solar-powered long endurance aircraft and how mission requirements impact aircraft sizing. Finally, it compares the performance and advantages of HAAPS to terrestrial wireless and satellite systems.
VSAT (Very Small Aperture Terminal) technology allows for wireless communication via satellite using small dish antennas. A VSAT network consists of a central hub with a large antenna that communicates with multiple remote VSAT sites. The hub controls and monitors the network, sending data to the satellite which amplifies and redirects the signals to the VSATs. VSAT offers advantages like flexibility, lower installation costs than terrestrial networks, and ability to access areas without terrestrial infrastructure. Common applications of VSAT include corporate networks, internet access, distance education, and retail/banking networks. VSAT uses multiple access techniques like TDMA to allow efficient sharing of satellite bandwidth among sites.
This document discusses Very Small Aperture Terminals (VSAT) and satellite television. It provides details on VSAT components, configurations including star and mesh topologies, multiple access techniques, characteristics, advantages, limitations and uses. It also describes the working principle of satellite television including encoding, transmission via satellite, reception and features of satellite TV systems. The document is authored by Arpan Deyasi from the Dept. of ECE at RCCIIT, Kolkata and covers VSAT and DSB-TV systems for a course.
VSAT (Very Small Aperture Terminal) is a satellite-based communication system that provides flexible and reliable connectivity solutions. It uses satellites to provide point-to-multipoint and point-to-point communication between a central hub station and multiple remote sites. VSAT networks offer benefits like reliability, flexibility, network management capabilities, and cost savings compared to terrestrial leased lines. Common VSAT access schemes discussed include TDMA, FDMA, DAMA, and CDMA.
This document discusses High Altitude Aeronautical Platforms (HAAPS) which could provide wireless communications services from airborne platforms like airships and aircraft operating at stratospheric altitudes. Specifically, it describes the HALO Network concept where aircraft would circle overhead at around 15 miles above ground carrying the hub of a wireless broadband network to provide internet access over a large metropolitan area. Key points discussed include the aircraft and communications payload, how multiple beams would create cellular-like coverage on the ground, and that a fleet of 3 aircraft would be needed to provide continuous 24/7 coverage. Subscriber units would provide broadband access through steerable antennas that point to the aircraft.
This is the slide of Satellite Broadcasting commonly useful for Satellite and Broadcasting describing different orbitals of satellite, frequency allocation, its use for broadcasting, Components of Broadcasting and many more. Feel free to comment but do add source if you are using it as a reference.
The document discusses HALO, a proposed broadband wireless network using high-altitude airships as nodes. HALO airships would operate in the stratosphere, above weather impacts, and use antenna arrays to provide cellular-like coverage over large areas. Key advantages over satellite and terrestrial networks include lower costs, larger coverage areas, and no need for complex infrastructure on the ground. The airships would be powered by photovoltaic cells and fuel cells, providing long-term stationary operation. HALO could enable new applications by providing broadband access across wide geographic regions.
VSAT systems use small aperture terminals (SATs) to provide satellite communication services directly to end users in a cost-effective way. A VSAT terminal consists of an outdoor unit with an antenna and radio frequency transceiver, and an indoor unit containing a modem and baseband processor. VSAT networks can be implemented in a star configuration, where terminals communicate through a central hub station, or a mesh configuration, where terminals can connect directly to each other.
VSAT technology allows for two-way communication via satellite using small terminals. A VSAT network consists of a central hub, satellite, and numerous user terminals. VSAT networks can support internet, data, video, voice, and private/public network solutions. They are becoming increasingly popular due to their flexibility, cost efficiency, and ability to quickly provide telecom solutions for consumers and businesses.
The document describes the HALO Network, a proposed broadband wireless metropolitan area network. The network would consist of a HALO aircraft operating as a hub at an altitude of 16 km, carrying an onboard network and antenna array. It would provide coverage over a 60 mile diameter area. Subscriber terminals on the ground would access broadband internet and other services through the HALO aircraft. The network aims to provide rapid, affordable broadband access with advantages over terrestrial and satellite networks in terms of speed, capacity, and cost.
1. MITRIS is a terrestrial satellite reception system that uses existing satellite TV reception technology to provide TV services to large areas using prefabricated components across different terrains.
2. It utilizes terrestrial transmitters that broadcast satellite frequencies to distribute content, allowing reception with standard satellite dishes pointed at the terrestrial transmitters rather than satellites.
3. ROKS further developed the MITRIS system into MITRIS-CS, which features a cellular structure using relay stations to expand coverage areas. This provides an inexpensive solution for distributing TV services to rural areas.
The document describes The Halo Network, a proposed broadband wireless metropolitan area network. The key aspects are:
- It uses a high-altitude aircraft called HAAPS operating at 16km to serve as an airborne hub/central node for a star topology network.
- The HAAPS aircraft houses an antenna array to create hundreds of virtual cells on the ground to provide service to thousands of users within a 100km radius area.
- It claims advantages over terrestrial and satellite networks like rapid deployment, high signal quality, availability and bandwidth, and lower costs.
This document provides an overview of satellite communication systems. It defines key terms like earth stations, uplinks, downlinks, and transponders. It describes how communications satellites can be categorized based on coverage area, service type, and usage. It also covers satellite orbit types including geostationary, medium earth, and low earth orbits. The document discusses factors that affect satellite link performance and describes frequency division multiple access and time division multiple access techniques.
This slide presentation introduces the Halo Network, a proposed broadband wireless network with its central node located on an airplane flying above 51,000 feet. The Halo Network aims to provide ubiquitous high-speed multimedia services to users across a metropolitan area using millimeter wave frequencies. Key features highlighted include seamless coverage, rapid deployability, bandwidth on demand, and efficient use of spectrum. The feasibility of the Halo Network is argued to be assured by the convergence of technologies across communications, with advantages over terrestrial and satellite networks.
The document summarizes VSAT technology, including its definition, history, components, uses, and future applications. Key points include:
- VSAT stands for Very Small Aperture Terminal and uses small satellite dishes less than 3.8 meters to transmit and receive data via satellite.
- The technology has been in development since the 1920s and was first used commercially in the 1960s for satellite television broadcasts.
- Modern VSAT systems use components like antennas, BUCs, LNBs, and indoor modems to transmit and receive data via geosynchronous satellites.
- Applications include broadband internet access, VoIP, and monitoring systems. The maritime VSAT market was over $400 million in 2007.
- Future
This document presents information about electronic shops and the history and mechanisms of radio. It discusses the key components of radio transmission and reception including transmitters, antennas, receivers, and different modulation techniques. It also outlines some of the early and modern uses of radio in communication, navigation, and other applications. Finally, it briefly introduces cognitive radio networks as an advanced wireless technology.
Switching and multicast schemes in asynchronous transfer mode networksEditor Jacotech
This document summarizes various switching and multicast schemes used in asynchronous transfer mode (ATM) networks. It discusses shared memory ATM switching architectures and different approaches for supporting multicast traffic in shared memory switches including replication-at-receiving, replication-at-sending, multiple write multiple read, and single write single read schemes. It also covers requirements for ATM multicast and compares these schemes in terms of advantages and disadvantages related to memory usage and switching performance.
10 Insightful Quotes On Designing A Better Customer ExperienceYuan Wang
In an ever-changing landscape of one digital disruption after another, companies and organisations are looking for new ways to understand their target markets and engage them better. Increasingly they invest in user experience (UX) and customer experience design (CX) capabilities by working with a specialist UX agency or developing their own UX lab. Some UX practitioners are touting leaner and faster ways of developing customer-centric products and services, via methodologies such as guerilla research, rapid prototyping and Agile UX. Others seek innovation and fulfilment by spending more time in research, being more inclusive, and designing for social goods.
Experience is more than just an interface. It is a relationship, as well as a series of touch points between your brand and your customer. Here are our top 10 highlights and takeaways from the recent UX Australia conference to help you transform your customer experience design.
For full article, continue reading at https://yump.com.au/10-ways-supercharge-customer-experience-design/
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Learn BEM fundamentals as fast as possible. What is BEM (Block, element, modifier), BEM syntax, how it works with a real example, etc.
How to Build a Dynamic Social Media PlanPost Planner
Stop guessing and wasting your time on networks and strategies that don’t work!
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The document discusses how personalization and dynamic content are becoming increasingly important on websites. It notes that 52% of marketers see content personalization as critical and 75% of consumers like it when brands personalize their content. However, personalization can create issues for search engine optimization as dynamic URLs and content are more difficult for search engines to index than static pages. The document provides tips for SEOs to help address these personalization and SEO challenges, such as using static URLs when possible and submitting accurate sitemaps.
32 Ways a Digital Marketing Consultant Can Help Grow Your BusinessBarry Feldman
How can a digital marketing consultant help your business? In this resource we'll count the ways. 24 additional marketing resources are bundled for free.
The document summarizes satellite communications and its components. It discusses how satellites are placed in geosynchronous orbit to appear stationary over a location on Earth. It describes the uplink and downlink systems, and how multiple satellites can provide global coverage through cross-linking. The key components of a satellite are also outlined, including the transponder and antenna system, power package, and control/information and thruster systems. Common uses of satellite communications discussed include traditional telecommunications, cellular networks, and television broadcasting.
This document provides an overview of satellite communications. It discusses the history of satellite communication, the main components which include the satellite and ground stations, and various utilities such as telecommunications, cellular networks, television signals, marine communications, spaceborne land mobile, and global positioning services. It also covers technological perspectives regarding the data characteristics of latency, poor bandwidth, and noise that satellite systems must address. Error correction techniques like forward-error-correction are used to mitigate the effects of noise on satellite links.
This document provides an overview of VSAT (Very Small Aperture Terminal) network technology. It describes the key components of a VSAT network including the outdoor and indoor units, hub station, and satellite. The outdoor unit includes the antenna, transceivers, and amplifiers while the indoor unit includes the multiplexer/demultiplexer, modem, and interfaces. VSAT networks can be configured in a star topology with all traffic routed through the central hub or in a mesh topology allowing direct terminal-to-terminal communication. Common applications of VSAT networks include corporate networks, broadcasting, and interactive data services between distributed sites.
This document provides an overview of VSAT (Very Small Aperture Terminal) network technology. It describes the key components of a VSAT network including the outdoor and indoor units, hub station, and satellite. The outdoor unit includes the antenna, transceivers, and amplifiers while the indoor unit includes the multiplexer/demultiplexer, modem, and interfaces. VSAT networks can be configured in a star topology with all traffic routed through the central hub or in a mesh topology allowing direct terminal-to-terminal communication. Common applications of VSAT networks include corporate networks, broadcasting, and interactive data services between distributed sites.
Satellite communication has become an integral part of global communication infrastructure. Satellites relay radio signals between Earth stations to enable services like television broadcasting, telephone calls, and internet access across long distances. There are different types of communication satellites depending on their use - fixed satellites provide point-to-point communication, broadcast satellites deliver television and radio signals directly to receivers, and mobile satellites facilitate services like satellite phones. While satellites provide advantages like universal coverage and independence from terrestrial infrastructure, they also have disadvantages like high initial costs and potential signal interference issues.
Internet of Space - Communication Systems for Future Space-bases Internet Ser...Paulo Milheiro Mendes
1) The document discusses the potential for satellite constellations in low Earth orbit (LEO) to enable a space-based internet through providing global connectivity with lower latency than traditional geostationary satellites.
2) Emerging LEO constellations from companies like SpaceX, OneWeb, and Telesat promise speeds close to fiber with nearly full global coverage and latency around 25ms.
3) For the space internet to be realized, challenges around developing low-cost user terminals, multi-tenant cooperation between constellations, and addressing different traffic needs across orbital regimes must be overcome.
The document discusses the evolution of telephony from 1876 to the present, including the development of mobile telephony. It describes the public switched telephone network and how it connects to subscribers. It also covers multiple access procedures used in mobile networks, including FDMA, TDMA, CDMA, and SDMA. Finally, it discusses technologies that enabled mobile computing through telephony networks, such as computer telephony interface, intelligent networks, and interactive voice response systems.
This document summarizes key aspects of satellite communications technology. It describes transponders that relay signals between satellites and Earth, how satellites control their orientation, and how they are powered by solar cells. It discusses low Earth orbiting satellites and very small aperture terminals that allow communication across wide areas. The document outlines domestic, regional, and international satellite types and some advantages of satellite circuits like independent coverage over distance.
This document discusses applications of satellite communication. It begins by providing background on satellites and noting that over 6,600 satellites have been launched, with around 1,000 currently operational. It then discusses key applications such as fixed satellite services for voice, data and video transmission globally, mobile satellite systems for remote connectivity, and scientific research satellites. The document focuses on communication satellites and their uses for television, radio, internet access and more. It also describes very small aperture terminals (VSAT) systems and how they transmit data in real-time to satellites and between locations via satellites. The document outlines advantages of VSAT like easy deployment and independence from local networks, as well as disadvantages like latency. It concludes by restating how satellite systems
The Iridium satellite system allows for global mobile communications through a constellation of 66 low Earth orbit satellites. It uses a digitally switched network architecture to provide telephone service anywhere on Earth. Each satellite is crosslinked to four other satellites to relay digital information and determine the best routing path for calls through inter-satellite links and ground-based gateways. The unique feature of the Iridium system is its crosslinks that allow two-way global communications even when the destination location is unknown.
This document discusses satellite communication systems. It begins with an introduction describing satellites and their components. It then describes the principles of satellite communication, including how they function as repeater stations in space to extend the range of radio signals beyond line-of-sight limits. The key components of satellite systems are the space segment, consisting of satellites in orbit, and the ground segment, including earth stations. Various types of satellite orbits and applications are also outlined, such as global mobile communication, military uses, and navigation. The document concludes with references on satellite channel impairments and modeling.
The document provides information about Damodar Valley Corporation (DVC), a river valley project in India. It discusses that DVC was the first multipurpose river valley project of independent India established in 1948. It generates, transmits and distributes electricity and facilitates irrigation and water supply. The document also provides details about DVC's infrastructure including its power generation capacity, transmission lines, and command area covered.
INTELSAT was created in 1964 to provide international telecommunications via satellite. It has over 140 member countries and investing entities. In 2001, INTELSAT became a private company providing end-to-end solutions globally. INSAT is India's domestic satellite system launched in 1983 as the largest in Asia-Pacific. It provides transponders for television, communication, meteorology, and search and rescue. VSAT systems use small satellite dishes for networks connecting geographically dispersed locations like banks, retailers, and hotels. GSM is the global standard for digital cellular communications networks adopted worldwide that allows more network users through digital encoding.
Satellite systems provide global coverage without the need for wiring infrastructure. They can broadcast TV and radio signals and provide telecommunication services. Early systems included Syncom (1963), the first geostationary satellite, and Intelsat (1965), the first commercial geostationary system. Modern systems include Iridium (66 satellites at 780km), Globalstar (48 satellites at 1414km), and proposed systems like Teledesic (288 satellites at 700km) that provide voice and data services from low Earth orbit. Handover between satellites and ground stations allows mobility but introduces complexity in routing calls and data.
This document discusses satellite communication and its applications in military. It describes the different types of orbits such as GEO, MEO and LEO and frequency bands used for satellite communication. It explains the wideband gapfiller satellite program and advanced wideband system being developed by the military to meet future communication needs. Protected and narrowband communication systems are also summarized. The document concludes that future satellite communication will evolve along with terrestrial systems and help improve military communication.
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Satellite nets
1. Satellite Comunications
Satellite Communications
David Hart, dhart@cis.ohio-state.edu
This paper is intended to give an overview of that methods of and uses for satellite communications, in
addition to presenting recent trends and future directions in the field
Othet Reports on Recent Advances in Networking
Back to Raj Jain's Home Page
Table of Contents
q
Introduction
q
Basic Elements
q
Various Uses of Satellite Communications
r
Traditional Telecommunications
r
Cellular
r
Television Signals
s
C-Band
s
Digital
r
r
Spacebourne Land Mobile
r
Satellite Messaging for Commercial Jets
r
q
Marine Communications
Global Positioning Services
Technological Overview
r
Error Correction
s
Forward-error-correction
s
Automatic-repeat-request
s
Stop and Wait
s
Go-back-N t
s
Selective-repeat
r
Hybrid Networks
r
ATM over Satellite
r
SATIN
r
VSAT Networks
r
Orbits
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2. Satellite Comunications
s
s
r
GEO
LEO
Constellations
s
s
q
Global Voice Communications
Global Broadband Networks
References
r
Web Sites
r
Books and Papers
Introduction
In 1962, the American telecommunications giant AT&T launched the world's first true communications
satellite, called Telstar. Since then, countless communications satellites have been placed into earth orbit, and
the technology being applied to them is forever growing in sophistication.
Basic Elements
Satellite communications are comprised of 2 main components:
q The Satellite
q
The satellite itself is also known as the space segment, and is composed of three separate units, namely
the fuel system, the satellite and telemetry controls, and the transponder. The transponder includes the
receiving antenna to pick-up signals from the ground station, a broad band receiver, an input
multiplexer, and a frequency converter which is used to reroute the received signals through a high
powered amplifier for downlink. The primary role of a satellite is to reflect electronic signals. In the
case of a telecom satellite, the primary task is to receive signals from a ground station and send them
down to another ground station located a considerable distance away from the first. This relay action
can be two-way, as in the case of a long distance phone call. Another use of the satellite is when, as is
the case with television broadcasts, the ground station's uplink is then downlinked over a wide region,
so that it may be received by many different customers possessing compatible equipment. Still another
use for satellites is observation, wherein the satellite is equipped with cameras or various sensors, and
it merely downlinks any information it picks up from its vantagepoint.
The Ground Station.
This is the earth segment. The ground station's job is two-fold. In the case of an uplink, or transmitting
station, terrestrial data in the form of baseband signals, is passed through a baseband processor, an up
converter, a high powered amplifier, and through a parabolic dish antenna up to an orbiting satellite. In
the case of a downlink, or receiving station, works in the reverse fashion as the uplink, ultimately
converting signals received through the parabolic antenna to base band signal.
Back to Table of Contents
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3. Satellite Comunications
Various Uses of Satellite Communications
q
Traditional Telecommunications
Since the beginnings of the long distance telephone network, there has been a need to connect the
telecommunications networks of one country to another. This has been accomplished in several ways.
Submarine cables have been used most frequently. However, there are many occasions where a large
long distance carrier will choose to establish a satellite based link to connect to transoceanic points,
geographically remote areas or poor countries that have little communications infrastructure. Groups
like the international satellite consortium Intelsat have fulfilled much of the world's need for this type
of service.
q
Cellular
Various schemes have been devised to allow satellites to increase the bandwidth available to ground
based cellular networks. Every cell in a cellular network divides up a fixed range of channels which
consist of either frequencies, as in the case of FDMA systems, or time slots, as in the case of TDMA.
Since a particular cell can only operate within those channels allocated to it, overloading can occur. By
using satellites which operate at a frequency outside those of the cell, we can provide extra satellite
channels on demand to an overloaded cell. These extra channels can just as easily be, once free, used
by any other overloaded cell in the network, and are not bound by bandwidth restrictions like those
used by the cell. In other words, a satellite that provides service for a network of cells can allow its
own bandwidth to be used by any cell that needs it without being bound by terrestrial bandwidth and
location restrictions.
q
Television Signals
Satellites have been used for since the 1960's to transmit broadcast television signals between the
network hubs of television companies and their network affiliates. In some cases, an entire series of
programming is transmitted at once and recorded at the affiliate, with each segment then being
broadcast at appropriate times to the local viewing populace. In the 1970's, it became possible for
private individuals to download the same signal that the networks and cable companies were
transmitting, using c-band reception dishes. This free viewing of corporate content by individuals led
to scrambling and subsequent resale of the descrambling codes to individual customers, which started
the direct-to-home industry. The direct-to-home industry has gathered even greater momentum since
the introduction of digital direct broadcast service.
r
C-band
C-Band (3.7 - 4.2 GHz) - Satellites operating in this band can be spaced as close as two degrees
apart in space, and normally carry 24 transponders operating at 10 to 17 watts each. Typical
receive antennas are 6 to 7.5 feet in diameter. More than 250 channels of video and 75 audio
services are available today from more than 20 C-Band satellites over North America. Virtually
every cable programming service is delivered via C-Band. SBCA
r
Ku-Band
s
Fixed Satellite Service (FSS)
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4. Satellite Comunications
Ku Band (11.7 - 12.2 GHz) - Satellites operating in this band can be spaced as closely as
two degrees apart in space, and carry from 12 to 24 transponders that operate at a wide
range of powers from 20 to 120 watts each. Typical receive antennas are three to six feet
in diameter. More than 20 FSS Ku-Band satellites are in operation over North America
today, including several "hybrid" satellites which carry both C-Band and Ku-Band
transponders. PrimeStar currently operates off Satcom K-2, an FSS or so-called
"medium-power" Ku-Band satellite. AlphaStar also uses an FSS-Ku Band satellite,
Telestar 402-R. SBCA
s
Broadcasting Satellite Service (BSS)
Ku-Band (12.2 - 12.7 GHz) - Satellites operating in this band are spaced nine degrees
apart in space, and normally carry 16 transponders that operate at powers in excess of 100
watts. Typical receive antennas are 18 inches in diameter. The United States has been
allocated eight BSS orbital positions, of which three (101, 110 and 119 degrees) are the
so-called prime "CONUS" slots from which a DBS provider can service the entire 48
contiguous states with one satellite. A total of 32 DBS "channels" are available at each
orbital position, which allows for delivery of some 250 video signals when digital
compression technology is employed. SBCA
r
DBS
DBS (Direct Broadcast Satellite) -The transmission of audio and video signals via satellite direct
to the end user. More than four million households in the United States enjoy C-Band DBS.
Medium-power Ku-Band DBS surfaced in the late 1990s with high power Ku-Band DBS
launched in 1994. SBCA
q
Marine Communications
In the maritime community, satellite communication systems such as Inmarsat provide good
communication links to ships at sea. These links use a VSAT type device to connect to
geosynchronous satellites, which in turn link the ship to a land based point of presence to the
respective nations telecommunications system.
q
Spacebourne Land Mobile
Along the same lines as the marine based service, there are VSAT devices which can be used to
establish communication links even from the world's most remote regions. These devices can be
hand-held, or fit into a briefcase. Digital data at 64K ISDN is available with some (Inmarsat).
q
Satellite Messaging for Commercial Jets
Another service provided by geosyncronous satellites are the ability for a passenger on an airbourne
aircraft to connect directly to a landbased telecom network.
q
Global Positioning Services
Another VSAT oriented service, in which a small apparatus containing the ability to determine
navigational coordinates by calculating a triangulating of the signals from multiple geosynchronous
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5. Satellite Comunications
satellites.
Back to Table of Contents
Technological Overview
Satellites for Data
q
Characteristics
Incorporating satellites into terrestrial networks is often hindered by three characteristics possessed by
satellite communication.
r Latency (propagation delay): Due to the high altitudes of satellite orbits, the time required for
a transmission to navigate a satellite link (more than 2/10ths of a second from earth station to
earth station) could cause a variety of problems on a high speed terrestrial network that is
waiting for the packets.
r Poor Bandwidth: Due to radio spectrum limitations, there is a fixed amount of bandwidth
allocable to satellite transmission.
r Noise: A radio signals strength is in proportion to the square of the distance traveled. Due to the
distance between ground station and satellite, the signal ultimately gets very weak. This problem
can be solved by using appropriate error correction techniques, however. SULU
q
Error Correction
Due to the high noise present on a satellite link, numerous error correction techniques have been tested
in on such links. They fall into the two categories of forward-error-correction (FEC) and
automatic-repeat-request (ARQ):
r Forward-error-correction (FEC)
r
In this method a certain number of information symbols are mapped to new information
symbols, but in such a way as to get more symbols than were original had. When these new
symbols are checked on the receiving end, the redundant symbols are used to decipher the
original symbols, as well as to check for data integrity. The more redundant symbols that are
included in the mapping, the better the reliability of the error correction. However it should be
noted that the more redundant symbols that are used to achieve better integrity, the more
bandwidth that is wasted. Since this method uses relatively a large amount redundant data, it
may not be the most efficient choice on a clear channel. However when noise levels are high,
FEC can more reliably ensure the integrity of the data.
Automatic-repeat-request (ARR)
In this method, data is broken into packets. Within each packet is included an error checking
key. This key is often of the cyclic redundancy check (CRC) sort. If the error code reflects a loss
of integrity in a packet, the receiver can request the sender to resend that packet. ARR is not
very good in a channel with high noise, since many retransmissions will be required, and the
noise levels that corrupted the initial packet will be likely to cause corruption in subsequent
packets. ARR is more suitable to relatively noise free channels.
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6. Satellite Comunications
s
Stop and Wait (SW)
s
With this form of ARR, the sender must wait for an acknowledgement of each packet
before it can send a new one. This can take upwards of 4/10ths of a second per packet
since it takes 2/10ths seconds for the receiver to get the packet an another 2/10th seconds
for the sender to receive the acknowledgement.
Go-back-N (GBN)
s
This method of ARR is an improvement over stop and wait in that it allows the sender to
keep sending packets until it gets a request for a resend. When the sender gets such a
request, it sends packets starting at the requested packet over again. It can again send
packets until it receives another retransmit request, and so on.
Selective-repeat (SR)
This ARR protocol is an improvement over GBN in that it allows the receiver to request a
retransmit of only that packet that it needs, instead of that packet and all that follows it.
The receiver, after receiving a bad packet and requesting a retransmit, can continue to
accept any good packets that are coming. This method is the most efficient method for
satellite transmissions of the three ARR methods discussed.
ARR methods can be demonstrated to provide a usable error correction scheme, but it is
also the most expensive, in terms of hardware. This is in part due to the buffering memory
that is required, but more importantly to the cost of the receiver, which needs to be able to
transmit re-requests. Systems such as the Digital Broadcast Satellites used for television
signal distribution would become inordinately expensive if they had to make use of ARR,
since the home based receiver would now need to be a transmitter, and the 18 inch dish
would be inadequate for the requirements of transmitting back to a satellite.
q
Hybrid Networks
In today's global networking landscape, there are many ways to transmit data from one place to
another. It is desirable to be able to incorporate any type of data transmission media into a network,
especially in networks that encompass large areas. A hybrid network is one that allows data to flow
across a network, using many types of media, either satellite, wireless or terrestrial, transparently.
Since each type of media will have different characteristics, it is necessary to implement a standard
transmission protocol. One that is normally used in hybrid networks is TCP/IP. In addition, much work
is being done to use TCP/IP over ATM for the satellite segments of hybrid networks, about which
more will be discussed later.
One way to get around the need in ARR for the receiver to have to request retransmit via an expensive
and slow satellite link is to use a form of hybrid network. In one form of hybrid network, the reciever
transmits its requests back to the sender via a terrestrial link. Terrestrial link allows for quicker, more
economical and less error prone transmission from the reciever, and the costs associated with the
receivers hardware are greatly reduced when compared to the costs involved if it had to transmit back
over the satellite link. There are products on the market today that allow a home user to get intenet
access at around 400MB via digital satellite, while its retransmit signals are sent via an inexpensive
modem or ISDN line.
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7. Satellite Comunications
In fact, a product currently being marketed by Direct PC called Turbo Internet uses a form of hybrid
network. The system uses two network interfaces; one connects via a special ISA bus PC adapter to a
receive-only Very Small Aperture Terminal (VSAT), while the other is a modem attached to a serial
port. Inbound traffic comes down to the VSAT, while outbound traffic goes through the modem link.
The two interfaces are combined to appear as a single virtual interface to upper layer TCP/IP protocol
stacks by a special NDIS compliant driver. The Serial Line Internet Protocol (SLIP) is used to connect
the modem-based link with an internet service provider. Packets, which are encapsulated by the
terminal such that the desired ip address of the destination host is embedded underneath the IP address
of the Direct PC Gateway, to which all packets leaving the terminal must go. Once at the gateway, the
outer packet is stripped, and the gateway contacts the destination address within. Upon the gateway's
receiving the request from the host, it then prepares the packet for satellite transmission, which is then
used to send the packet back to the terminal.
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8. Satellite Comunications
This Picture's Source: Vivek Arora, Narin Suphasindhu, John S. Baras, Douglas Dillon
Back to Table of Contents
q
ATM Over Satellite
Two qualitites of Asynchronous Transfer Mode (ATM) made it highly desirable for the
implementation of satellite links within hybrid networks. The first is the ATM's asynchrony and the
second is its ability to use variable transfer rates. In addition, ATM fits well into existing networks
with its wide range of upper-layer services and its ability to operate in a wide range of environments.
There are problems, however. ATM's relatively large propagation delays can significantly increase the
latency of feedback mechanisms essential for congestion control. acquisition time, cell in-synch time
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9. Satellite Comunications
and cell discard probability (BARAS). Solutions to these issues are still being explored.
The group that is currently working to develop interoperability specifications that facilitate ATM
access and ATM network interconnect in both fixed and mobile satellite networks is known as The
TIA/SCD/CIS - WATM group. As of March, 1997 they have proposed the following standards:
r SATATM Type 1 - Fixed ATM Direct Access
Fixed network access via satellite that is characterized by a large number of small
inexpensive user terminals and a small number of gateway earth stations. Provides for a
radio interface of 64 kbit/s - NxE1 and a service interface of 2.4 kbit/s - NxE1 while
providing no mobility support
r
r
r
SATATM Type 2 - Fixed ATM Network Interconnect
High speed interconnections using PNNI, B-ICI, or Public UNI between earth stations
and fixed ATM networks.
Allows for a radio interface of T1 - 1.2 Gbit/s but provides no mobility support.
SATATM Type 3 - Mobile ATM Direct Access
ATM network access by mobile terminals. The radio interface provides for 64 kbit/s - E1
for moving, 64 kbit/s - NxE1 for portable terminals and the rervice interfaceallows for 75
bit/s - E1 for moving, 75 bits/s - NxE1 for portable terminals.
SATATM Type 4 - Mobile ATM Network Interconnect
High speed interconnections between mobile and fixed networks or between two mobile
networks providing fast moving land-mobile data rates < NxE1 and slow-moving airborne
data rates of < 622 Mbit/s.
The group also has established requirements for dealing with the physical layer, the media access
control layer and the data link control layer.
q
SATIN - Satellite Integrated Terrestrial Network:
The goal of SATIN is to create a fully integrated hybrid network in which the method of
communication, which can incorporate networks of local, metropolitan and wide area scope,
Broadband ISDN, Integrated Network Management, AIN (Advanced Intelligent Networks) and
PCS (Personal Communications Services), in addition to ATM (Asynchronous Transfer Mode)
over satellite, is totally transparent to the user. The difficulties inherent in this are obvious.
Differences in latency, noise, bandwidth and reliability must be equalized in all the media that
will encompass the network.
q
VSAT Networks
VSAT stands for Very Small Aperture Terminal. Although this acronym has been used amongst
telecom groups for some time now to describe small earth stations, the concepts of VSAT are being
applied to modern hand held satellite communications units, such as GPS (Global Positioning System),
portable Inmarsat phones and other types of portable satellite communication devices.
q
Orbits
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10. Satellite Comunications
r
GEO
GEO stands for Geostationary Earth Orbit. This refers to satellites that are placed in orbit such
that they remain stationary relative to a fixed spot on earth. If a satellite is placed at 35,900 km
above the earth, its angular velocity is equal to that of the earth, thereby causing it to appear to
be over the same point on earth. This allows for them to provide constant coverage of the area
and eliminate blackout periods of ordinary orbiting satellites, which is good for providing
television broadcasting. However their high altitude causes a long delay, so two way
communications, which would need to be uploaded and then downloaded over a distance of
72,000 km, are not often used with this type of orbit.
r
LEO
LEO stands for Low Earth Orbit, and it refers to satellites in orbit at less that 22300 miles above
the earth. This type of an orbit reduces transmission times as compared to GEO. A LEO orbit
can also be used to cover a polar region, which the GEO cannot accomplish. Since it does not
appear stationary to earth stations, however, earth stations need an antenna assembly that will
track the motion of the satellite.
q
Constellations
The idea behind a constellation is to use to acheive global simultaneous satellite coverage by placing
enough satellites into orbit so that (nearly) every point on earth is covered. There are currently two
main types of service being planned at the moment, global voice and global data.
r Global Voice Communications
There are currently several consortiums that are working on global voice via satellite. One
of the most prominant is the IRIDIUM constellation, which will consist of 66
interconnected satellites orbiting 420 nautical miles above the earth. The satellites will
use a LEO orbit so that very small handheld terminals can be used by ground-based
cutomers. The system will use intersatellite crosslink transmissions that will take place in
the Ka frequency band between 23.18 and 23.38 GHz. The IRIDIUM system will use a
combination of Frequency Division Multiple Access (FDMA) and Time Division
Multiple Access (TDMA) signal multiplexing to make the most efficient. The L-Band
(1616-1626.5 MHz), is used to link the satellite and IRIDIUM the subscribers equipment.
The Ka-Band (19.4-19.6 GHz for downlinks and 29.1-29.3 GHz for uplinks) links the
satellite and the gateways and earth terminals.
r Global Broadband Networks
There are basically two types of networks being proposed here, namely LEO based and GEO
based ones.
s LEO
LEO networks use low orbits, which allows for much less latency that do GEO based
networks. One problem that these satellites have is that since the are not geostationary
(they are contsantly orbiting around the earth) they cannot talk continuously to that same
ground station. The way this is overcome is by using intesatellite communications, so that
the sattellites function together as a blanket of coverage. A major player in this are is
Teledesic.
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11. Satellite Comunications
The Teledesic Network uses a constellation of 840 operational interlinked low-Earth orbit
satellites. The system is planned to provide "on-demand" channel rates from 16 Kbps up
to 2.048 Mbps ("E1"), and for special applications up to 1.24416 Gbps ("OC-24"). The
network uses fast packet switching technology based on the Asynchronous Transfer Mode
(ATM) using fixed-length (512) bit packets.. Each satellite in the constellation is a node
in the fast packet switch network, and has intersatellite communication links with eight
adjacent satellites. Each satellite is normally linked with four satellites within the same
plane (two in front and two behind) and with one in each of the two adjacent planes on
both sides. Each satellite keeps the same position relative to other satellites in its orbital
plane. The Teledesic Network uses a combination of multiple access methods to ensure
efficient use of the spectrum. Each cell within a supercell is assigned to one of nine equal
time slots. All communication takes place between the satellite and the terminals in that
cell during its assigned time slot . Within each cell’s time slot, the full frequency
allocation is available to support communication channels. The cells are scanned in a
regular cycle by the satellite’s transmit and receive beams, resulting in time division
multiple access (TDMA) among the cells in a supercell. Since propagation delay varies
with path length, satellite transmissions are timed to ensure that cell N (N=1, 2, 3,...9) of
all supercells receive transmissions at the same time. Terminal transmissions to a satellite
are also timed to ensure that transmissions from the same numbered cell in all supercells
in its coverage area reach that satellite at the same time. Physical separation (space
division multiple access (SDMA) and a checkerboard pattern of left and right circular
polarization eliminate interference between cells scanned at the same time in adjacent
supercells. Guard time intervals eliminate overlap between signals received from
time-consecutive cells. TELEDESIC
Photo by TELEDESIC
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12. Satellite Comunications
Within each cell’s time slot, terminals use Frequency Division Multiple Access (FDMA)
on the uplink and Asynchronous Time Division Multiple Access (ATDMA) on the
downlink. On the uplink, each active terminal is assigned one or more frequency slots for
the call’s duration and can send one packet per slot each scan period (23.111 msec). The
number of slots assigned to a terminal determines its maximum available transmission
rate. One slot corresponds to a standard terminal’s 16 Kbps basic channel with its
associated 2 Kbps signaling and control channel. A total of 1800 slots per cell scan
interval are available for standard terminals. The terminal downlink uses the packet’s
header rather than a fixed assignment of time slots to address terminals. TELEDESIC
Photo by TELEDESIC
s
GEO
GEO's high points are that it's satellites are geostationary, which means that the
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13. Satellite Comunications
difficulties of intersatellite communications are avoided. The problem arises due to the
latency delays caused by the high orbit. Applications which rely on steady bandwidth,
like multimedia, will definately be affected.
References
Web Sites
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Intelsat
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Inmarsat
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Iridium
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Teledesic
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ATM by Satellitehttp://www.telesat.ca/
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SATELLITE COMMUNICATIONS NETWORK TECHNOLOGY
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Satellite Broadcasting and Communications Association
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DBS DISH Satellite News and Informationhttp://www.dbsdish.com/
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High Bandwidth Web Page: http://www.specialty.com/hiband/satellite_index.html
The Center for Satellite and Hybrid Communication Networks:
http://www.isr.umd.edu/CSHCN/
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r
Low Earth Orbiting Satellites and Internet-Based Messaging Services:
http://www.isoc.org/isoc/whatis/conferences/inet/96/proceedings/g1/g1_1.htm
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SATELLITE COMMUNICATIONS IN THE 21ST CENTURY:
http://www.hughes.com/speeches/century21.html
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Analysis: Telecoms Virtual Library: http://www.analysys.com/vlib/satellit.htm
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Big LEO Overview: http://www.idt.unit.no/
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Centre for Satellite Engineering Research: http://www.ee.surrey.ac.uk:80/EE/CSER/
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Lloyd's satellite constellations http://www.sat-net.com/L.Wood/constellations/
Books and Papers
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Daniel E. Friedman, Masters Thesis: "Error Control for Satellite and Hybrid Communication
Networks", directed by Daniel E. Friedman, 1995
John S. Baras, ATM in Hybrid Networks, Center for Satellite and Hybrid Communication
Networks, 1996
Vivek Arora, Narin Suphasindhu, John S. Baras, Douglas Dillon, "Effective Extensions of
Internet in Hybrid Satellite-Terrestrial Networks", University of Maryland at College Park &
Hughes Network Systems, Inc., 1996
Tom Logsdon, "Mobile Communication Satellites", McGraw Hill Text, February 1995
Dennis Roddy, "Satellite Communications", McGraw Hill Text, 1995
TIA/SCD/CIS - WATM WG Meeting Overview, 3/26/97
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14. Satellite Comunications
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Deepak Ayyagari and Anthony Ephremides, "Enhancement of Cellular Service via the use of
Satellite Capacity," University of Maryland, 1995
Pelton, Joseph N., "Wireless & Satellite Telecommunications: The Technology, the Market, &
the Regulations", Prentice Hall 1995
Cochetti, Roger, "Mobile Satellite Communications Handbook", Quantum Publishing,
Incorporated 1995
Michael J. Miller (Editor),Branka Vucetic (Editor),Les Berry (Editor) , "Satellite
Communications: Mobile & Fixed Services" Kluwer Academic Publishers, 1993
Gerard Maral,Michel Bousquet, "Satellite Communication System: Systems, Techniques &
Technology", John Wiley & Sons, Incorporated, 1993
Wood, James, Satellite communications and DBS systems. Boston : Focal Press, 1992.
Elbert, Bruce R, The satellite communication applications handbook, Boston, MA : Artech
House, 1997.
Miller, Michael J., Vucetic, Branka., Satellite communications : mobile and fixed services,
Boston : Kluwer Academic Publishers, c1993
Satellite communications systems and technology--Europe, Japan, Russia / Burton I. Edelson ...
[et al.], Park Ridge, N.J., U.S.A. : Noyes Data Corp., c1995
Broadband communications : global infrastructure for the information age / proceedings of the
International IFIP-IEEE Conference on Broadband Communications, Canada, 1996 ; edited by
Lorne Mason and Augusto Casaca., London : Chapman and Hall on behalf of the International
Federation for Information Processing, 1996
Litva, J. (John), Digital beamforming in wireless communications, Boston : Artech House,
c1996.
Lindberg, Bertil C., Digital broadband networks and services, New York : McGraw-Hill, 1995
International journal of satellite communications., Chichester, Sussex : Wiley, c1983Feldman, Phillip M., An overview and comparison of demand assignment multiple access
(DAMA) concepts for satellite communications networks Santa Monica, CA : RAND, 1996
Maral, Gerard., VSAT networks, Chichester, West Sussex, England ; New York : Wiley, c1995.
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