02-11-2012, 11:39 AM
VSAT- VERY SMALL APERTURE TERMINAL
[attachment=37856]
[attachment=37857]
VSAT
VSAT is a electronic device used to transmit and Receive information via satellite using a small Diameter dish antena (0.6m-3.8m).VSAT may be transmit data, voice, fax and video conferencing can be done with help of this.
A Very Small Aperture Terminal (VSAT) is a micro-Earth station that uses the latest innovations in the field of satellite communications to allow user's access to reliable satellite communications. VSATs provide users with services comparable to large gateways and terrestrial networks, at a fraction of the cost. A typical VSAT consists of communications equipment and a small antenna with a diameter less than 3.5 meters.
VSAT networks provide users with simple equipment that requires minimal installation and repair. They are easy to operate and simple to troubleshoot. VSAT installations do not require staff with extensive expertise.
A typical VSAT installation consists of an antenna, an outdoor unit (ODU), the inter facility link cable (IFL), and an indoor unit (IDU). The antenna and ODU provide the radio frequency conversion and amplification for the satellite uplink and downlink. The ODU is often called the transceiver because it includes the up converters (U/Cs); the Solid State Power Amplifier (SSPA); the Low Noise Amplifier (LNA), and the down converter (D/C). The IDU provides the baseband interfacing required to carry the user’s services.
The power requirement for each VSAT is low and in some cases solar cells supply the power. Because of its simplicity, a VSAT installation takes only a few hours and the terminals are ready for service.
VSAT NETWORK CONFIGURATIONS
As illustrated in Figure VSATs are connected by radio frequency (RF) links via a satellite, with a so-called uplink from the station to the satellite and a so-called downlink from the satellite to the station. The overall link from station to station, sometimes called hop, consists of an uplink and a downlink. A radio frequency link is a modulated carrier conveying information. Basically the satellite receives the uplinked carriers from the transmitting earth stations within the field of view of its receiving antenna, amplifies those carriers, translates their frequency to a lower band in order to avoid possible output/input interference, and transmits the amplified carriers to the stations located within the field of view of its transmitting antenna.
INDOOR UNIT
The indoor unit is placed inside so it can interface with the user’s communications de-vice.it can be a small desktop box that contains the receiver and transmitter boards and an interface to the user’s equipment.
OUTDOOR UNIT
Outdoor unit is placed outside for a line of sight to the satellite. It consists of small antenna and electronic equipment for signal reception and transmission.
A typical VSAT site consists of a parabolic-shaped antenna mounted on the roof of a building, connected by a cable to a chassis inside the building. Operators install these antennas at customer sites and buy transmission capacity on satellites. It contains a modem for translating satellite transmissions back into data (and vice versa) and terrestrial interfaces for connecting customer equipment. A block diagram of a complete VSAT link is shown in figure 4.
LNB
(LOW NOISE BLOCK DOWN CONVERTER)
The LNB (Low Noise Block Down-Converter) is part of the receive chain of your VSAT. Located on the feed horn, the LNB converts the satellite signal that was reflected off of the satellite antenna’s reflector from C-Band into an L-Band signal. The L-Band signal is in the frequency range of 950 to 1750 MHz and is considered more manageable. This is partially due to the fact that the transmission of the lower frequency signal can be more reliable when using a coaxial cable than is the case when higher frequency C-Band signals are transmitted of on this type of cable. Virtually all new satellite routers today use L-Band inputs.
BUC
(Block up converter)
The BUC (Block Up-Converter) is part of the transmit chain of your VSAT. It is often located on the feed horn, but if it is a large BUC, it may be located at the base of the antenna and connected with RF conduits (waveguides). The BUC converts the modem's L-Band transmit signal into higher frequency C-Band signals, then amplifies it before it is reflected off the satellite antenna towards the satellite. In order to perform both of its functions, the BUC is composed of two individual components: the Local Oscillator and the Power Amplifier. The Local Oscillator performs the frequency conversion between the L-Band and the satellite frequency, such as C-Band. The resulting satellite frequency is calculated by adding the L-Band frequency to a number known as the Local Oscillator Frequency that will be stamped onto the BUC. A Local Oscillator Frequency of 4900 MHz is used for a non inverted spectrum, and a Local Oscillator Frequency of 7375 MHz is used for an inverted spectrum. A typical system will require a 2-watt BUC or higher, depending on the application. Although BUCs are available with very powerful amplifiers, it is unlikely that a VSAT installation will require more than 10W, even in less than ideal circumstances.
Linear Cross Polarization
In order to transmit and receive in opposite polarities the linear polarization is used. In this we will need to assemble the feed so that the receive part of the OMT (which the LNB is attached to) is perpendicular to the ground and the wide face of the waveguide is parallel to the ground.
Linear Co Polarization
In order to transmit and receive in same polarities the linear co-polarization is used. In this we will need to assemble the feed so that the receive part of the OMT (which the LNB is attached to) is perpendicular to the ground and the narrow face of the waveguide is parallel to the ground.
Linear Cross Polarization
In order to transmit and receive in opposite circular polarities we will need to add the circular tube between the feed horn and the OMT. Assemble the feed so that the receive part of the OMT (which the LNB is attached to) is perpendicular to the ground and the wide face of the waveguide is parallel to the ground. Make sure that the receive part of the OMT is aligned to the desired reception polarity, either LHCP or RHCP which is displayed on the mouth of the circular tube.
C-band variations
Slight variations in the assignments of C-band frequencies have been approved for use in various parts of the world, depending on their locations in the three International Telecommunications Union radio regions. Note that one region includes all of the Americas; a second includes all of Europe and Africa, plus all of Russia, and the third region includes all of Asia outside of Russia, plus Australia and New Zealand. This latter region is the most populous one, since it includes the People's Republic of China, India, Pakistan, Japan, and Southeast Asia
Ku band
The Ku band is a portion of the electromagnetic spectrum in the microwave range of frequencies. This symbol refers to "K-under" (originally German: Kurz-unten) in other words, the band directly below the K-band. In radar applications, it ranges from 10.95-14.5 GHz according to the formal definition of radar frequency band nomenclature in IEEE Standard.
Ku band is primarily used for satellite communications, most notably for fixed and broadcast services, and for specific applications such as NASA's Tracking Data Relay Satellite used for both space shuttle and ISS communications. Ku band satellites are also used for backhauls and particularly for satellite from remote locations back to a television network's studio for editing and broadcasting. The band is split into multiple segments that vary by geographical region by the International Telecommunication Union (ITU). NBC was the first television network to uplink a majority of its affiliate feeds via Ku band in 1983.
Some frequencies in this radio band are used for vehicle speed detection by law enforcement, especially in Europe
CONCLUSION
VSAT networks have had a lot of success for specific, mainly data, services but the demand is there for a wider range of service provision and multimedia communications. We have focused on recent work on the development of adaptive, dynamic protocols that will result in the most efficient allocation of the space segment.
VSAT networks remain competitive and more effective than terrestrial solutions.
[attachment=37856]
[attachment=37857]
VSAT
VSAT is a electronic device used to transmit and Receive information via satellite using a small Diameter dish antena (0.6m-3.8m).VSAT may be transmit data, voice, fax and video conferencing can be done with help of this.
A Very Small Aperture Terminal (VSAT) is a micro-Earth station that uses the latest innovations in the field of satellite communications to allow user's access to reliable satellite communications. VSATs provide users with services comparable to large gateways and terrestrial networks, at a fraction of the cost. A typical VSAT consists of communications equipment and a small antenna with a diameter less than 3.5 meters.
VSAT networks provide users with simple equipment that requires minimal installation and repair. They are easy to operate and simple to troubleshoot. VSAT installations do not require staff with extensive expertise.
A typical VSAT installation consists of an antenna, an outdoor unit (ODU), the inter facility link cable (IFL), and an indoor unit (IDU). The antenna and ODU provide the radio frequency conversion and amplification for the satellite uplink and downlink. The ODU is often called the transceiver because it includes the up converters (U/Cs); the Solid State Power Amplifier (SSPA); the Low Noise Amplifier (LNA), and the down converter (D/C). The IDU provides the baseband interfacing required to carry the user’s services.
The power requirement for each VSAT is low and in some cases solar cells supply the power. Because of its simplicity, a VSAT installation takes only a few hours and the terminals are ready for service.
VSAT NETWORK CONFIGURATIONS
As illustrated in Figure VSATs are connected by radio frequency (RF) links via a satellite, with a so-called uplink from the station to the satellite and a so-called downlink from the satellite to the station. The overall link from station to station, sometimes called hop, consists of an uplink and a downlink. A radio frequency link is a modulated carrier conveying information. Basically the satellite receives the uplinked carriers from the transmitting earth stations within the field of view of its receiving antenna, amplifies those carriers, translates their frequency to a lower band in order to avoid possible output/input interference, and transmits the amplified carriers to the stations located within the field of view of its transmitting antenna.
INDOOR UNIT
The indoor unit is placed inside so it can interface with the user’s communications de-vice.it can be a small desktop box that contains the receiver and transmitter boards and an interface to the user’s equipment.
OUTDOOR UNIT
Outdoor unit is placed outside for a line of sight to the satellite. It consists of small antenna and electronic equipment for signal reception and transmission.
A typical VSAT site consists of a parabolic-shaped antenna mounted on the roof of a building, connected by a cable to a chassis inside the building. Operators install these antennas at customer sites and buy transmission capacity on satellites. It contains a modem for translating satellite transmissions back into data (and vice versa) and terrestrial interfaces for connecting customer equipment. A block diagram of a complete VSAT link is shown in figure 4.
LNB
(LOW NOISE BLOCK DOWN CONVERTER)
The LNB (Low Noise Block Down-Converter) is part of the receive chain of your VSAT. Located on the feed horn, the LNB converts the satellite signal that was reflected off of the satellite antenna’s reflector from C-Band into an L-Band signal. The L-Band signal is in the frequency range of 950 to 1750 MHz and is considered more manageable. This is partially due to the fact that the transmission of the lower frequency signal can be more reliable when using a coaxial cable than is the case when higher frequency C-Band signals are transmitted of on this type of cable. Virtually all new satellite routers today use L-Band inputs.
BUC
(Block up converter)
The BUC (Block Up-Converter) is part of the transmit chain of your VSAT. It is often located on the feed horn, but if it is a large BUC, it may be located at the base of the antenna and connected with RF conduits (waveguides). The BUC converts the modem's L-Band transmit signal into higher frequency C-Band signals, then amplifies it before it is reflected off the satellite antenna towards the satellite. In order to perform both of its functions, the BUC is composed of two individual components: the Local Oscillator and the Power Amplifier. The Local Oscillator performs the frequency conversion between the L-Band and the satellite frequency, such as C-Band. The resulting satellite frequency is calculated by adding the L-Band frequency to a number known as the Local Oscillator Frequency that will be stamped onto the BUC. A Local Oscillator Frequency of 4900 MHz is used for a non inverted spectrum, and a Local Oscillator Frequency of 7375 MHz is used for an inverted spectrum. A typical system will require a 2-watt BUC or higher, depending on the application. Although BUCs are available with very powerful amplifiers, it is unlikely that a VSAT installation will require more than 10W, even in less than ideal circumstances.
Linear Cross Polarization
In order to transmit and receive in opposite polarities the linear polarization is used. In this we will need to assemble the feed so that the receive part of the OMT (which the LNB is attached to) is perpendicular to the ground and the wide face of the waveguide is parallel to the ground.
Linear Co Polarization
In order to transmit and receive in same polarities the linear co-polarization is used. In this we will need to assemble the feed so that the receive part of the OMT (which the LNB is attached to) is perpendicular to the ground and the narrow face of the waveguide is parallel to the ground.
Linear Cross Polarization
In order to transmit and receive in opposite circular polarities we will need to add the circular tube between the feed horn and the OMT. Assemble the feed so that the receive part of the OMT (which the LNB is attached to) is perpendicular to the ground and the wide face of the waveguide is parallel to the ground. Make sure that the receive part of the OMT is aligned to the desired reception polarity, either LHCP or RHCP which is displayed on the mouth of the circular tube.
C-band variations
Slight variations in the assignments of C-band frequencies have been approved for use in various parts of the world, depending on their locations in the three International Telecommunications Union radio regions. Note that one region includes all of the Americas; a second includes all of Europe and Africa, plus all of Russia, and the third region includes all of Asia outside of Russia, plus Australia and New Zealand. This latter region is the most populous one, since it includes the People's Republic of China, India, Pakistan, Japan, and Southeast Asia
Ku band
The Ku band is a portion of the electromagnetic spectrum in the microwave range of frequencies. This symbol refers to "K-under" (originally German: Kurz-unten) in other words, the band directly below the K-band. In radar applications, it ranges from 10.95-14.5 GHz according to the formal definition of radar frequency band nomenclature in IEEE Standard.
Ku band is primarily used for satellite communications, most notably for fixed and broadcast services, and for specific applications such as NASA's Tracking Data Relay Satellite used for both space shuttle and ISS communications. Ku band satellites are also used for backhauls and particularly for satellite from remote locations back to a television network's studio for editing and broadcasting. The band is split into multiple segments that vary by geographical region by the International Telecommunication Union (ITU). NBC was the first television network to uplink a majority of its affiliate feeds via Ku band in 1983.
Some frequencies in this radio band are used for vehicle speed detection by law enforcement, especially in Europe
CONCLUSION
VSAT networks have had a lot of success for specific, mainly data, services but the demand is there for a wider range of service provision and multimedia communications. We have focused on recent work on the development of adaptive, dynamic protocols that will result in the most efficient allocation of the space segment.
VSAT networks remain competitive and more effective than terrestrial solutions.