It ascertains that the RF equipment would cater to the requirements of the network topology and satellite modems in use. The link Budget estimates the ground station and satellite EIRP required. Equivalent isotropically radiated power (EIRP) is the power transmitted from a transmitting object. Satellite ERP can be defined as the sum of output power from the satellite’s amplifier, satellite antenna gain and losses. Calculations of signal levels through the system (from origination earth station to satellite to receiving earth station) to ensure the quality of service should normally be done prior to the establishment of a satellite link. This calculation of the link budget highlights the various aspects. Apart from the known losses due to various cables and inter-connecting devices, it is advisable to keep sufficient link margin for various extraneous noise which may affect the performance. It is also a safeguard to meet eventualities of signal attenuation due to rain/snow. As mentioned earlier a satellite provides two resources, bandwidth and amplification power. In most VSAT networks, the limiting resource in satellite trans-ponder is power rather than bandwidth .
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VSAT technology
Under this, a central network monitoring system allocates a unique code to each of the VSATs enabling multiple VSATs to transmit simultaneously and share a common frequency band. The data signal is combined with a high bit rate code signal which is independent of the data. Reception at the end of the link is accomplished by mixing the incoming composite data/code signal with a locally generated and correctly synchronized replica of the code . Since this network requires that the central network management system co-ordinates code management and clock synchronization of all remote VSATs, star topology is, by default, the best one. Although this is best applicable for very large networks with low data requirements, there are practical restrictions in the use of spread spectrum. It is employed mainly for interference rejection or for security reasons in military systems .
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VSAT technology
The network uses a pool of satellite channels, which are available for use by any station in that network. On demand, a pair of available channels is assigned so that a call can be established. Once the call is completed, the channels are returned to the pool for an assignment to another call. Since the satellite resource is used only in pro-portion to the active circuits and their holding times, this is ideally suited for voice traffic and data traffic in batch mode.
DAMA offers point-to-point voice, fax, and data requirements and supports video-conferencing. The ability to use on-board signal processing and multiple spot beams will enable future satellites to reuse the frequencies many times more than today’s’ system. In general, channel allocation may be static or dynamic, with the latter becoming. DE – 5 increasingly popular. DAMA systems allow the number of channels at any time be less than the number of potential users. Satellite connections are established and dropped only when traffic demands them .
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VSAT technology
DAMA offers point-to-point voice, fax, and data requirements and supports video-conferencing. The ability to use on-board signal processing and multiple spot beams will enable future satellites to reuse the frequencies many times more than today’s’ system. In general, channel allocation may be static or dynamic, with the latter becoming. DE – 5 increasingly popular. DAMA systems allow the number of channels at any time be less than the number of potential users. Satellite connections are established and dropped only when traffic demands them .
It implies that the VSATs are pre-allocated a designated frequency. Equivalent of the terrestrial leased line solutions, PAMA solutions use the satellite resources constantly. Consequently, there is no call-up delay what makes them most suited for interactive data applications or high traffic volumes. As such, PAMA connects high data traffic sites within an organization .
SCPC (Single Channel Per Carrier) refers to the usage of a single satellite carrier for carrying a single channel of user traffic. The frequency is allocated on a pre-assigned basis in case of SCPC VSAT which is also synonymously known as PAMA VSAT.
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VSAT technology
SCPC (Single Channel Per Carrier) refers to the usage of a single satellite carrier for carrying a single channel of user traffic. The frequency is allocated on a pre-assigned basis in case of SCPC VSAT which is also synonymously known as PAMA VSAT.
It is the oldest and still one of the most common methods for channel allocation. In this scheme, the available satellite channel bandwidth is broken into frequency bands for different earth stations. This means that guard bands are needed to provide separation between the bands. Also, the earth stations must be carefully power-controlled to prevent the microwave power spilling into the bands for the other channels. Here, all VSATs share the satellite resource on the frequency domain only. Typically implemented in a mesh or single satellite hop topology, FDMA has the following variants:
Labels: VSAT technologyWith TDMA networks, numerous remote sites communicate with one central hub – a design that is similar to packet-switched networks. As a leased-line equivalent, SCPC can deliver dedicated bandwidth of up to 2 Mbit/s. Remote sites in a TDMA network compete with one another for access to the central hub, restricting the maximum band-.4 – DE width in most cases to 19.2 kbit/s. Almost all international VSAT services in Asia-Pacific are based on SCPC. Most domestic offerings are based on TDMA, although some domestic operators offer point-to-point SCPC links as well. Here, we will discuss briefly TDMA, pre-assigned or demand-assigned FDMA, CDMA and other accessing techniques featuring merits and demerits of these schemes.
From the above figure the followings are noted:Switch - routing control between host & modulator/demodulator. Basically on the packets header
Modulator- modulate the outbound carriers (TDM)
Bank of Demodulators- receive inbound carriers, extract data packets.
Radio Frequency Terminal (RFT) - transmits subsystem (up converters, high power amplifier), receive subsystem (low noise amplifier, down converter)
Network Control Center (NCC) - controls and monitors hub and IDUs
Primary Power Subsystem
In a TDMA network, all VSATs share satellite resource on a time-slot basis. Remote VSATs use TDMA channels or in routes for communicating with the hub. There could be several in routes associated with one out route. Several VSATs share one in route hence sharing the bandwidth. Typical in routes operate at 64 or 128 Kbit/s. Generally systems with star topology use a TDMA transmission technique. Most common configuration of TDMA star network use one single high performance hub, many low cost VSAT terminals, centralized management, lower price, optimized use of satellite capacity .
Critical to all TDMA schemes is the function of clock synchronization what is performed by the TDMA hub or master earth station. The VSATs may also access the in route on a fixed assigned TDMA mode, wherein each VSAT is allocated a specific time slot or slots.
Broadcast Networks are used to transmit data, audio and video files to a number of users. The data is broadcast from central site for end user sites. This is a one-way system. The central site broadcasts the data. The remote site only receives data. The channel can provide an uplink speed of 36 to 40 depends on transponder’s BW .
• The main objective of 'Receive only VSAT' services is sharing and spread of information. Thus it is of benefit to society as a whole rather than few users as in the case of normal VSAT.
• The applications of this technology are mainly in areas of information, social services, education and medicine. The broadband multicast capability can provide innovative applications like Tele-Medicine, online newspapers, market rates and Tele-education. It can ensure that these applications are accessible to even the remotest parts of the country.
• This technology is predicted to play a crucial role in facilitating the government efforts to bridge the Digital Divide. Thus the success of Receive Only VSAT is in the favour of the government.
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VSAT technology
• The main objective of 'Receive only VSAT' services is sharing and spread of information. Thus it is of benefit to society as a whole rather than few users as in the case of normal VSAT.
• The applications of this technology are mainly in areas of information, social services, education and medicine. The broadband multicast capability can provide innovative applications like Tele-Medicine, online newspapers, market rates and Tele-education. It can ensure that these applications are accessible to even the remotest parts of the country.
• This technology is predicted to play a crucial role in facilitating the government efforts to bridge the Digital Divide. Thus the success of Receive Only VSAT is in the favour of the government.
i. The size of a VSAT antenna varies. The feedhorne directs the transmitted power towards the antenna dish or collects the received power from it.
ii. It consists of an array of microwave passive components. Antenna size is used to describe the ability of the antenna to amplify the signal strength.
iii. The Radio Frequency Terminal (RFT) is mounted on the antenna frame and interconnected to the feed-horn (outdoor electronics) includes Low Noise Amplifiers (LNA) and down-converters for amplification and down conversion of the received signal respectively .
iv. LNAs are designed to minimize the noise added to the signal during this first stage of the converter as the noise performance of this stage determines the overall noise performance of the converter unit. The noise temperature is the parameter used to describe the performance of an LNA.
v. Up- converters and High Powered Amplifiers (HPA) are also part of the RFT and are used for up converting and amplifying the signal before transmitting to the feed-horn. The Up/Down converters convert frequencies between intermediate frequency (IF level 70 MHz) and radio frequency.
vi. Extended C band, the down converter receives the signal at 4.500 to 4.800 GHz and the up converter converts it to 6.725 to 7.025 GHz. The HPA ratings for VSATs range between 1 to 40 watts.
vii. The Outdoor Unit (ODU) is connected through a low-loss coaxial cable to the indoor unit (IDU). The typical limit of an (Inter Facility Link) IFL cable is about 500 feet. The IDU consists of modulators that superimpose the user traffic signal on a carrier signal. This is then sent to the RFT for up conversion, amplification and transmission.
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VSAT technology
ii. It consists of an array of microwave passive components. Antenna size is used to describe the ability of the antenna to amplify the signal strength.
iii. The Radio Frequency Terminal (RFT) is mounted on the antenna frame and interconnected to the feed-horn (outdoor electronics) includes Low Noise Amplifiers (LNA) and down-converters for amplification and down conversion of the received signal respectively .
iv. LNAs are designed to minimize the noise added to the signal during this first stage of the converter as the noise performance of this stage determines the overall noise performance of the converter unit. The noise temperature is the parameter used to describe the performance of an LNA.
v. Up- converters and High Powered Amplifiers (HPA) are also part of the RFT and are used for up converting and amplifying the signal before transmitting to the feed-horn. The Up/Down converters convert frequencies between intermediate frequency (IF level 70 MHz) and radio frequency.
vi. Extended C band, the down converter receives the signal at 4.500 to 4.800 GHz and the up converter converts it to 6.725 to 7.025 GHz. The HPA ratings for VSATs range between 1 to 40 watts.
vii. The Outdoor Unit (ODU) is connected through a low-loss coaxial cable to the indoor unit (IDU). The typical limit of an (Inter Facility Link) IFL cable is about 500 feet. The IDU consists of modulators that superimpose the user traffic signal on a carrier signal. This is then sent to the RFT for up conversion, amplification and transmission.
Star
The hub station controls and monitors can communicate with a large number of dispersed VSATs. Generally, the Data Terminal Equipment and 3 hub antenna is in the range of 6-13m in diameter. Since all VSATs communicate with the central hub station only, this network is more suitable for centralized data applications .
Mesh
A group of VSATs communicate directly with any other VSAT in the network without going through a central hub. A hub station in a mesh network performs only the monitoring and control functions. These networks are more suitable for telephony applications.
i. Interactive real time application
• Point of Sale/retail/Banking (beg. ATM)
• Corporate data
ii. Telephony
• Rural: individual subscribers
• Corporate Telephony
iii. Intranet, Internet and IP infrastructure
• Multimedia delivery (ex. video streaming)
• Interactive distance learning/ training .
iv. Direct-to-home
• Broadband Internet access for consumers and businesses
VSAT is a term widely used in the satellite industry to describe an earth station that is installed on the ground to receive communications from a satellite or to communicate with other ground stations by transmitting to and receiving from satellite spacecraft. The ground station may be used only for reception, but is typically capable of both receiving and transmitting. Major components of a VSAT are generally grouped in two categories, ODU (Outdoor Unit) and IDU (Indoor Unit) .
Labels: VSAT technologyo computer communications
o reservation systems
o database enquiries
o billing systems
o file transfers
o electronic mail
o video conferencing
o point of sale transactions
o credit checks and credit card verification
o stock control and management
• Antenna base construction.
• Antenna installation.
• Antenna pointing.
• Cross pole test.
• Equipment configuration.
• BER test.
• Router configuration.
• Data port connects.
• End-to-End data flow test.
• Link test by different way.
• Ready for service
i. Rapid, reliable satellite transmission of data, voice and video and an ability to allocate resources (bandwidth and amplification power) to different users over the coverage region as needed.
ii. VSAT industry is offering fixed network solutions that can provide a full suite of services at reasonable price. e.g.: a toll quality voice channel via VSAT is available between 3-15 cents/minute today.
iii. Easy to provide point-to-multipoint (broadcast), multipoint-to-point (data collection), point-to-point communications and broadband multimedia services .
iv. VSATs are serviced not only in cases where the land areas are difficult to install, say in the case of remote locations, water areas, and large volumes of air space.
v. An ability to have direct access to users and user premises .
vi. VSAT systems can also provide a variety of services including broadband communication systems satellite-based video, audio, Internet and data distribution networks .
VSAT (Very Small Aperture Terminal) is a satellite-based communications service that offers businesses and government agencies flexible and reliable communications solutions, both nationally and internationally, on land and at sea and represents a cost effective solution for users seeking an independent communications network connecting a large number of geographically dispersed sites .
VSAT’s are small, software-based earth stations (generally 0.9 - 4.5 meters), which are used for transmission of data, voice, or video via satellite. It can be operated without additional manpower or technology. VSAT services are delivered using C or KU band GEO satellites .
Satellite communication provides services:
i. International Telephony
• using Public Switched Telephone Network (PSTN)
• Intermediate Data Rate (IDR)
• Time Division Multiple Access (TDMA)
ii. Broadcasting
• TV Uplink
• Television Receive Only (TVRO)
• Digital Satellite News Gathering (DSNG)
iii. VSAT ( Very Small Aperture Terminal)
• Personal Earth Station (PES-TDMA)
• Telephony Earth Station (TES-TDMA)
• Domestic IDR/Single Channel Per Carrier (SCPC)
• VSAT Dial away
• VSAT Sky Star Advantage
• VSAT Faraway
For satellite communications the following three types of frequencies are used which are IEEE standards .
C Band : Range between 4 GHz to 8 GHz
Ku Band : Range between 12 GHz to 18 GHz
Ka Band : Range between 20 GHz to 30 GHz
From the above figure the followings are noted:
HPA – High Power Amplifier
LNA - Low Noise Amplifier (Earth station equipment that amplifies the transmit RF signal)
CPE – Customer Premises Equipment (e.g. Telephone, PABX, Ethernet Hub, Host Server etc)
Satellite Communication is a technology of data transmission whether one-way data broadcasting or two-way interactive using radio frequency as a medium.
It consists of-
i. Space Segment or Satellite ( eg. Measat, Intelsat and Inmarsat)
ii. Ground Segment or earth station which includes Antenna, Outdoor Unit, Inter Facility Link, Indoor Unit and Customer Premises Equipment.
Satellite Communication using VSAT (Very Small Aperture Terminal) since the science fiction on radio transmission through space using geo-synchronous earth satellite, provider has progressed significantly in the field of satellite communications. The early earth stations were large and expensive. The reason for the size and complexity of the early stations was not related to inadequate performance. In fact, the antennas had very high efficiency and the noise temperatures of their receivers were low. However, the satellites at that time had a relatively poor performance providing considerably low RF (radio frequency) power per transponder and a rather high noise temperature for the on-board receivers. Additionally, satellites were then considered suitable only for very long distance communication. Gradually, satellite communications have appeared as regional systems requiring smaller coverage on the earth’s surface enabling higher gain antennas. Subsequently, increase in transponder out-put power, introduction of systems having several spot beams, development of field-effect transistor amplifier for low noise receivers as well as its availability as power amplifier have changed the satellite communication scenario. Once it was possible to envisage an all solid-state transmit and receive earth station even with a rather low power output, low price, large quantity, VSAT-based earth station design could be conceived.
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VSAT technology
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