Zee News Ltd has launched an 24 hour satellite news channel in Chhattisgarh called Zee 24 Ghante Chhattisgarh, which went on air on October 1. The channel officials claim that it is a one stop platform for reporting and covering issues related to the state and its people. The tagline for the channel is 'Sawal Aap Ka Hai' (It's a question about you). Zee 24 Ghante Chhattisgarh is a franchisee offering of Zee News, and has been launched in association with SB Multimedia, a media company founded and promoted by the Goel Group of Companies, a prominent business house in the state. The channel is being run on a build-operate-transfer basis, with Zee News sharing its brand name and functional expertise with SB Multimedia. The different programs offer are based on news, spritual, entertainment ,sports,crime, stocks, astrology, education, information(i.e.law based and agriculture based). Some programs are as followed bhramkumari, jai johar, sitare hamare,hamar bani hamr goth ,aap ki baat, Desh Hamara, Khabar Chhattisgarh, gunaah, tv tadka, filmy tashan, son kas bhuiya, City 36 and Nau Ki Baat,Hamar bani hamar goth..,guide Sports unlimited, Chhattisgarh dinbhar,rajdhani-nayadhani.talking stocks.
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INTRODUCTION TO SATELLITE COMMUNICATION
A satellite is something that goes around and around a larger something, like the earth or another planet. Some satellites are natural, like the moon, which is a natural satellite of the earth. Other satellites are made by scientists and technologists to go around the earth and do certain jobs.
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. Type of satellite system GEO, or Geostationary Earth Orbit A satellite in geosynchronous orbit circles the earth in 24 hours—the same time it takes the earth to rotate one time. If these satellites are positioned over the equator and travel in the same direction as the earth rotates, they appear "fixed" with respect to a given spot on earth— that is, they hang like lanterns over the same spot on the earth all the time. Satellites in GEO orbit 22,282 miles above the earth. In this high orbit, GEO satellites are always able to "see" the receiving stations below, and their signals can cover a large part of the planet. Three GEO satellites can cover the globe, except for the parts at the North and South poles.
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MEO, or Medium Earth Orbit Satellites circling 6,000 to 12,000 miles above the earth are in medium altitude orbit. In these larger orbits they stay in sight of a ground receiving station for 2 hours or more, compared to about 10 minutes for LEOs. It takes MEO satellites from 4 to 8 hours to go around the earth.
LEO, or Low Earth Orbit . A satellite in low earth orbit circles the earth 100 to 300 miles above the earth’s surface.Because it is close to the earth, it must travel very fast to avoid being pulled out of orbit by gravity and crashing into the earth. Satellites in low earth orbit travel about 17,500 miles per hour. These satellites can circle the whole earth in about an hour and a half.
Orbits of different satellites
OVERVIEW OF SATELLITE COMMUNICATION
Satellite Communication is a technology of data transmission whether one-way data broadcasting or two-way interactive using radio frequency as a medium.
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It consists of: i. Space Segment or Satellite (e.g. Measat, Intelsat and Insat) ii. Ground Segment or earth station which includes Antenna, Outdoor Unit, Inter Facility Link, Indoor Unit and Customer Premises Equipment.
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 Dialaway – VSAT SkyStar Advantage – VSAT Faraway
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VSAT (VERY SMALL APERTURE TERMINAL)
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VSAT (VERY SMALL APERTURE TERMINAL) A Very Small Aperture Terminal (VSAT), is small earth station which is a part of satellite communication. ground station or a stabilized maritime Vsat antenna with a dish antenna that is smaller than 3 meters. Data rates typically range from 56 Kbit/s up to 4 Mbit/s. VSATs access satellites in geosynchronous orbit to relay data from small remote earth stations (terminals) to other terminals (in mesh configurations) or master earth station "hubs" (in star configurations). VSATs are most commonly used to transmit narrowband data (point of sale transactions such as credit card, polling or RFID data; or SCADA), or broadband data (for the provision of Satellite Internet access to remote locations, VoIP or video). VSATs are also used for transportable, on-the-move (utilising phased array antennas) or mobile maritime communications WHY VSAT networks are used: 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. eg: 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.
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VSAT WORKS’ AT FOLLOWING RANGE OF FREQUENCIES:C-BAND The C band is a name given to certain portions of the electromagnetic spectrum, as well as a range of wavelengths of microwaves that are used for long-distance radio telecommunications. The IEEE C-band - and its slight variations - contains frequency ranges that are used for many satellite communications transmissions; by some Wi-Fi devices; by some cordless telephones; and by some weather radar systems. For satellite communications, the microwave frequencies of the C-band perform better in comparison with Ku band (11.2 GHz to 14.5 GHz) microwave frequencies, under adverse weather conditions, which are used by another large set of communication satellites. The adverse weather conditions all have to do with moisture in the air, such as during rainfalls, thunderstorms, sleet storms, and snowstorms. EXTENDED C BAND Extended C-Band Tx5.850–6.425, Rx 3.625–4.200
Ku-BAND Communications satellites send and receive electromagnetic Ku-band signals, which are in the super high-frequency range. Microwave phone signals, which are relayed between tall towers, are in this same frequency range. However, satellite Ku-band signals is usually not susceptible to interference from these towers. KA BAND (Pronounced: "Kay-A Band") covers the frequencies of 26.5-40GHz. The Ka band is part of the K band of the microwave band of the electromagnetic spectrum. This symbol refers to "K-above" — in other words, the band directly above the K-band. The so-called 30/20 GHz band is used in communications satellites, uplink in either the 27.5 GHz and 31 GHz bands, and highresolution, close-range targeting radars aboard military airplanes. Some frequencies in this radio band are used for vehicle speed detection by law enforcement BAND KU BAND S BAND EXTENDED C C BAND TX FREQUENCY GHz 14-14.5 1.7-2.5 5.850-6.425 5.9-6.4 RX FREQUENCY GHz 11.7-12.2 3-3.5 3.625-4.200 3.7-4.2
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Table 1.RANGE OF FREQUENCIES
ADVANTAGES & DISADVANTAGE OF USING C & KU BAND Advantages
Compared with C-band, Ku band is not similarly restricted in power to avoid interference with terrestrial microwave systems, and the power of its uplinks and downlinks can be increased. This higher power also translates into smaller receiving dishes and points out a generalization between a satellite’s transmission and a dish’s size. As the power increases, the dish’s size can decrease. This is because the purpose of the dish element of the antenna is to collect the incident waves over an area and focus them all onto the antenna's actual receiving element, mounted in front of the dish (and pointed back towards its face); if the waves are more intense, less of them need to be collected to achieve the same intensity at the receiving element. The Ku band also offers a user more flexibility. A smaller dish size and a Ku band system’s freedom from terrestrial operations simplifies finding a suitable dish site. For the End users Kuband is generally cheaper and enables smaller antennas (both because of the higher frequency and a more focused beam). Ku band is also less vulnerable to rain fade than the Kaband frequency spectrum. The satellite operator's Earth Station antenna do require more accurate position control when operating at Ku band than compared to C band. Position feedback accuracies are higher and the antenna may require a closed loop control system to maintain position under wind loading of the dish surface.
There are, however, some disadvantages of Ku band system. Especially at frequencies higher than 10 GHz in heavy rain fall areas, a noticeable degradation occurs, due to the problems caused by and proportional to the amount of rainfall (commonly known as "rain fade"). This problem can be mitigated, however, by deploying an appropriate link budget strategy when designing the satellite network, and allocating a higher power consumption to compensate rain fade loss. The Ku band is not only used for television transmission, which some sources imply, but also very much for digital data transmission via satellites, and for voice/audio transmissions. The higher frequency spectrum of the Ku band is particularly susceptible to signal degradation, considerably more so than C-band satellite frequency spectrum. A similar phenomenon, called "snow fade" (where snow or ice accumulation significantly alters the focal point of a dish) can also occur during winter precipitation. Also, the Kuband satellites typically require considerably more power to transmit than the Cband satellites. Under both "rain fade" and "snow fade" conditions, Ka and Ku band losses can be marginally (but significantly) reduced using super-hydrophobic Lotus effect coatings.
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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).
VSATFront View of VSAT IDU Components
Outdoor Unit (ODU)
Indoor Unit (IDU)
Front ComponentsVSAT IDU VSATFrontSub-Components IDU ODU View of VSAT VSAT View of
Reflector Feedhorn OMT LNB
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Out Door Unit The ODU, so named because the components reside outdoors, includes; the antenna (typically ranging in size from 3.8 meters down to as small as 0.6m in diameter), equipped with a feed system capable of receiving and transmitting, a microwave radio, also known as a HPA High Power Amplifier, and an LNA (low noise amplifier) used to convert the signal gathered by the feed. Frequency Bands are available for use in C, Ku, or Ka frequency bands and are sold by wattage capability. A complicated calculation called a "Link Budget" is performed by the satellite operator to determine both the size of the antenna and how much power (wattage) will be required to complete the transmission link between the ground station and the satellite. Frequency Bands are sometimes combined with the LNA's which are used as part of the receiving operation. The resulting combination is called a "transceiver" and saves some integration time during the installation process. The ODU or antenna includes the dish, or reflector, and the feed arm, which holds the active elements (transmitter and receiver). These are pictured above The Dish or Reflector The older dish, shown on the left with the TV attachment, is made of fiberglass, with an embedded wire mesh. It measures 0.74 meter in surface area (39" x 23"). The newer Raven dish is still .74 meter, but is rounder (34 1/4" x 28 1/2") and it is made of a lightweight metal. Often, when only referring to the dish, without the feed arm, the term reflector is used. The latest Prodelin dish was shown earlier. The Feed Arm Located on the fully assembled VSAT dish assembly, the Rx-Tx feed arm is normally removed and safely stored, as part of the process for moving to a new location. The feed arm consists of the feed support arm and the outdoor electronics. All of the active outdoor components connect to the support arm, which also adds strength (and weight) to the completely assembled antenna. The outdoor electronics consist of the LNB, which receives outroute (from the NOC) Ku-band signals from the satellite, and the transmitter, which transmits inbound (to the NOC) Ku-band signals to the satellite. Power is
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supplied by the Hughes Net satellite modem. For those who are interested, this is discussed in more detail, below. LNB The Low-Noise Block down-converter (LNB) is used to amplify and frequency convert out route signals received by the antenna, for input into the modem via the Sat-In cable. The antenna receives the outbound signal in the Ku-band frequency, for input to the wave guide end of the LNB. The LNB first amplifies the input Ku-band signals. It then uses a local oscillator (LO), to frequency translate input signals to L-band frequencies, which are used on the coaxial cables. The signal noise value is an electrical specification for the LNB, which is critical to out route signal (your received signal) quality performance. The lower the noise figure, the better the signal quality performance will be. The LNB is powered from the modem, via a DC power supply coupled on the coaxial RF input connector, which connects to the receive IFL cable.
Local Oscillator (LO): 9.75 GHz /10, 11.30 GHz Frequency: 10.7 GHz-12.75 GHz Noise Figure (NF): 0.7 dB Polarization: Linear Standard DBS LNB example: Local Oscillator (LO): 11.25 GHz Frequency: 12.2 GHz-12.7 GHz Noise Figure (NF): 0.7 dB Polarization: Circular Typical North American C-band LNB specs: Local Oscillator (LO): 5.15 GHz
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• • • •
• • •
Frequency: 3.6-4.2 GHz Noise Figure (NF): 15 to 100 Kelvin’s (uses Kelvin ratings as opposed to dB rating) Polarization: Linear Dual and Quad LNB's are multiple LNB's contained in one package, to allow for multiple receivers (on one dish). A Dual LNB consists of 2 universal LNBs (affixed at a small offset angle in a single housing), and uses only one "F" connector and coaxial cable connection to the converter box. Though also a Dual LNB system, the Monobloc LNB has only one output and only one (satellite) transmission is viewable at a time, as compared to dish systems which have two or more separation’s, each connected to separate receivers, in which both transmissions can be simultaneously viewed or recorded. The Monobloc LNB was specifically designed to receive signals from satellites that are spaced very close together. For example, parts of Europe use a Monobloc LNB to receive the Astra 1 (19E) and Hotbird (13E) satellites, eliminating the need for an expensive rotator
Block Diagram Of Lnb
LNB - Low Noise Block (also called an LNC- Low Noise Converter), is used for communications (broadcast) satellite reception. The LNB is usually affixed either in or on the satellite dish.
The purpose of the LNB is to utilize the super heterodyne effect; and amplify and convert a wide block (band) of frequencies. This helps compensate the signal loss associated with typical coaxial cable at relatively high frequencies.
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The term 'low noise' relates to the quality of the 1st stage input amplifier transistor, measured in either called Noise Temperature units, Noise Figure units or Noise Factor units. Both Noise Factor and Noise Figure are easily converted into Noise Temperature units. A lower Noise Temperature rating is always better (i.e. an LNB with a Noise Temperature of 100K is 2x as good as one rated 200K). The term 'Block' refers to the conversion of a higher block of microwave frequencies (received from the satellite- typically in the range 4 GHz to 21 GHz) being down-converted to a lower block range of frequencies for the receiver. The "low-noise" part also indicates that amplification and mixing takes place prior to cable attenuation, in a circuit that requires no power supply or receiver. With the high frequencies that satellites operate at, it is critical that the noise is controlled prior to signal processing. An LNB helps keep the overall sound and picture of satellite TV from becoming greatly degraded, without the need of introducing a much larger dish reflector. For wide-band satellite television carrier reception (generally 27 MHz wide band), the tolerance (accuracy) of the LNB local oscillator frequency needs to be in the range of ±500kHz,. This makes low cost DRO's (dielectric oscillators) feasible. However, for reception of narrow bandwidth carriers (i.e. 16-QAM)- a highly stable, low phase noise dedicated LNB (local) oscillator is required. They typically contain an internal crystal oscillator (or 10 MHz reference from the indoor unit) and a PLL (Phase-Locked Loop) oscillator, and naturally tend to be noticeably more expensive. LNB Supply Power The DC supply (typically in the 13v. to 19v. range) is cable line-fed to the LNB, and it is often times possible to alter the polarization by changing this voltage. Alteration via the frequency band is also possible, albeit less common. Efficiently weather-proofing the outdoor connector is critical, as oxidation and corrosion occur rapidly. This, in turn, directly relates to signal degradation. Both the outer and inner conductors must make solid electrical contact.
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High resistance will cause the LNB to switch permanently into the low voltage state, over time, and lead to overall signal deterioration. If you are physically trouble-shooting your system, be aware that the electrical antenna contacts between the BUC chassis and LNB are often times difficult to navigate, and 'earth loop' currents may also propose a problem. As a matter of fact, it is entirely possible to become severely shocked in discovering 50 Hz or 60 Hz AC Mains currents on the outer conductors. Do be extremely cautious. The quality and smoothing of the DC supplies used for the LNB's is also of great importance.
• • • •
Testing an LNB Check the ammeter drawing the DC current from the power supply (approx. number of mA's provided by the manufacturer). Poor quality (or corroded) F type connections are the most typical cause of concern. The center pin (of the F connector plug) should stick out ~ 2mm, away from the hreaded surrounding ring. A satellite finder power meter is also helpful. By pointing the LNB up at outer space (clear sky), the noise temperature contribution from the surroundings becomes negligible. The meter reading will directly correspond to the noise temperature of the LNB. If, for example, pointing the meter to outer space reads 100K (K is short for Kelvin, which measures absolute temperature), then you point the LNB towards the ground (say at a temperature of approximately 300K), the noise power meter reading should go up accordingly, to roughly 400K (100K +300K). LNBs that fail on a particular polarization (or particular frequency band), may only do so at certain temperatures.
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BLOCK UP CONVERTER (BUC)
A block up converter is used in the transmission of satellite signals.it converts a band or block of frequencies from a lower frequency to a higher frequency. Modern buc converts from l-band to ku-band and c band and ka band. Buc’s are generally used in conjuction with the lnb’s. The buc being an up converting device The buc is assembled with lnb in associated with omt i.e. orthogonal mode transducer to the feed horn that faces the the parabolic dish reflector. The transmitter is used to frequency translate and power amplify inroute signals from the modem and output them to the antenna, for transmission to the satellite. The modem sends the inroute signal at an L-band frequency to the transmitter, using Sat-Out and the transmit coaxial cable. This signal is input to the
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transmitter, where it is frequency converted to the transmit Ku-band frequency, using a nominally fixed local oscillator (LO). This Ku-band signal is then power amplified to operate the transmitter at a nominal one-watt output power (at saturation). The fixed output power is input to the antenna, for transmission to the satellite. The transmitter is powered from the modem, via a DC power supply coupled on the coaxial RF output connector, which connects to the transmit IFL cable
Buc mounted at antenna
Functional block diagram of BUC
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Internal protection Internal protection against high temperature and short or open circuit RF output is standard. As well, input voltage detection ensures reliable shutdown and restart under brownout or blackout conditions. External protection The VSAT transceiver is completely protected from the elements without external user controls. The VSAT BUC modules are fully sealed and pressure tested to 34 kPa (5 psi). Particle and moisture penetration is rated to IP68. High quality powder coat paint is used to protect the modules from corrosion. IDU Indoor Unit
The indoor unit is typically composed of a single unit called a modem. A satellite modem is different than a telephone modem, and is used to convert the data, video, or voice generated by the customer application for transmission over satellite. The modem takes the signals from your computer, phone or other device and changes them so they can be sent to the ODU which transmits them out to the satellite and eventually to other ground stations.
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INTEGRATED RECEIVER DECODER (IRD) An integrated receiver/decoder (IRD) is an electronic device used to pick-up a radio-frequency signal and convert digital information transmitted in it Consumer IRDs Consumer IRDs commonly called a set-top box are used by end users and are much cheaper compared to professional IRDs. To curb content piracy, they also lack many features and interfaces found in professional IRDs such as outputting uncompressed SDI video or ASI transport stream dumps. They are also designed to be more aesthetically pleasing. Professional IRDs Commonly found in radio, television, Cable and satellite broadcasting facilities, the IRD is generally used for the reception of contribution feeds that are intended for re-broadcasting. The IRD is the interface between a receiving satellite dish or Telco networks and a broadcasting facility video/audio infrastructure. Professional IRDs have various features that consumer IRDs lack such as:
• • • • • • • • • • • • •
SDI outputs. ASI inputs / outputs. AES/EBU Audio decoding. VBI reinsertion. WSS data and pass through. Transport stream demultiplexing. Genlock input. Frame synchronization of digital video output to analogue input. Closed captions and VITS/ITS/VITC Insertion. Video test pattern generator. Remote management over LAN/WAN. GPI interface - For sending external alarm triggers. Rack mountable.
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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 6-11m in diameter. Since all VSATs communicate with the central hub station only, this network is more suitable for centralized data applications.
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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. Hybrid Network In practice usually using hybrid networks, where a part of the network operates on a star topology while some sites operate on a mesh topology, thereby accruing benefits of both topologies
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Multiple Accessing Schemes The primary objective of the VSAT networks is to maximize the use of common satellite and other resources amongst all VSAT sites. The methods by which these networks optimize the use of satellite capacity, and spectrum utilization in a flexible and cost-effective manner are referred to as satellite access schemes. Each of the above topologies is associated with an appropriate satellite access scheme. Good network efficiency depends very much on the multiple accessing schemes. There are many different access techniques tailored to match customer applications. Access techniques including stream, transaction reservation, slotted Aloha and hybrid mechanisms are used and are configurable on a per-port basis, enabling customers to run multiple applications simultaneously. Voice of 5.6 kbit/s Hughes-proprietary CELP compression as well as voice of 8/16 kbit/s ADPCM compression schemes, synchronous data of 1.2 to 64 kbit/s, asynchronous data of up to 19.2 kbit/s and G3 fax relay are some of the applications. The satellite links are often referred to as long fat pipes – they represent paths with high bandwidth-delay product. Moreover, since they typically provide a broadcast channel, media sharing methods are needed at the MAC sublayer of the data link control layer. The traditional CSMA/CD schemes typically used in LANs can not be used with satellite channels since it is not possible for earth stations to do carrier sense on the up-link due to the point-to-point nature of the link. A carrier-sense at the downlink informs the earth stations about potential collisions that may have occurred 270 ms ago (for GEO). Such delays are not practical for implementing CSMA/CD protocols. Most satellite MAC schemes usually assign dedicated channels in time and/or frequency for each user. This is due to the fact that the delay associated in detecting and resolving multiple collisions on a satellite link is usually unacceptable for most applications. The VSAT services are primarily based on one of two technologies: i. Single-carrier per channel (SCPC) and ii. Time-division multiple access (TDMA).
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SCPC (Single-Carrier Per Channel) SCPC-based design provides a point-to-point technology, making it the VSAT equivalent to conventional leased lines.
TDMA (Time-division multiple access) With 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 AsiaPacific 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. In a TDMA network, all VSATs share satellite resource on a time-slot basis. Remote VSATs use TDMA channels or inroutes for communicating with the hub. There could be several inroutes associated with one outroute. Several VSATs share one inroute hence sharing the bandwidth. Typical inroutes operate at 64 or 128 Kbit/s. Generally systems with star topology use a TDMA transmission technique. Critical to all TDMA schemes is the function of clock synchronization what is
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performed by the TDMA hub or master earth station. The VSATs may also access the inroute on a fixed assigned TDMA mode, wherein each VSAT is allocated a specific time slot or slots.
FDMA (Frequency Division Multiple Access) 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:
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i. PAMA (Pre-Assigned Multiple Acceess) 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. ii. DAMA (Demand Assigned Multiple Access) 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.
iii. CDMA (Code Division Multiple Access) 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
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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.
TDMA Timedivision Multiple Access
VSAT TECHNOL0GY SCPC Singlecarrier per Channel FDMA Frequency Division Multiple Access
VSAT Accessing Schemes
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HOW VSAT WORK
i. The size of a VSAT antenna varies. The feed-horn 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 (Interfacility Link) IFL cable is about 300 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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Fig:-Working of VSAT ( hpa-high power amplifier, cpe-customer premises equipment, lna-low noise amplifier, pstn-public switched telephone network)
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VSAT NETWORK CHARACTERISTICS
Modern satellites are often equipped with multiple transponders. The area of the earth’s surface covered by a satellite’s transmission beam is referred to as the “footprint” of the satellite transponders. The up-link is a highly directional, point-to-point link using a high-gain dish antenna at the ground station. The down-link can have a large footprint providing coverage for a substantial area or a “spot beam” can be used to focus high power on a small region thus requiring cheaper and smaller ground stations. Moreover, some satellites can dynamically redirect their beams and thus change their coverage area. The received microwave power involved in satellite links is typically very small (of the order of 100 picowatts). This means that specially designed earth stations that keep carrier-to-noise ratio to a minimum are used to transmit/receive satellite communications. The front-end receiver is the most crucial part of a transceiver and contributes to the overall cost of the satellite earth station in a significant way. Here, we describe some of the characteristics of a VSAT network:
Flexibility The VSAT networks offer enormous expansion capabilities; it factors in changes in the business environment and traffic loads that can be easily accommodated on a technology migration path. There are limitations faced by terrestrial lines in reaching remote and other difficult locations. On the other hand, VSATs offer unrestricted and unlimited reach. Additional VSATs can be rapidly installed to support the network expansion to any site, no matter however remote. Network Management Network monitoring and control of the entire VSAT network is much simpler than a network of leased lines, involving multiple carriers at multiple locations. A much smaller number of elements need to be monitored in case of a VSAT network and also the number of vendors and carriers involved in between any two user terminals in a VSAT network is typically one. This results in a single point of contact for resolving all your VSAT networking issues. A VSAT network management system easily integrates end-to-end monitoring and configuration control for all network subsystems.
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Reliability A single-point contact for operation, maintenance, rapid fault isolation and trouble-shooting makes things very simple for a client, using VSAT services. VSATs also enjoy a low mean-time to repair (MTTR) of a few hours, which extends up to a few days in the case of leased lines. Essentially, lesser elements imply lower MTTR. Uptime of up to 99.5 percent is achievable on a VSAT network. This is significantly higher than the typical leased line uptime of approximately 80-85%. Cost A comparison of costs between a VSAT network and a leased line network shows that a VSAT network offers significant savings over 2-3 years timeframe. This does not take into account the cost of downtime, inclusion of which would result in the VSAT network being much more cost-effective. Pay-by-mile concept in case of leased line sends the cost spiraling upwards. More, so if the locations to be linked are dispersed all over the country. In case of VSATs, the service charges depend on the bandwidth which is allocated to the network in line with customer requirements. With a leased line, a dedicated circuit in multiples of 64 kbit/s is available whether the customer needs that amount of bandwidth or not.
Link Budgets 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 originatin 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 effect 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.
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APPLICATION OF VSAT
Typical customer applications of VSATs include: Supermarket shops (tills, ATM machines, stock sale updates and stock ordering). Chemist shops - Shoppers Drug Mart - Pharmaprix. Broadband direct to the home. e.g. Downloading MP3 audio to audio players. Broadband direct small business, office etc, sharing local use with many PCs. Internet access from on board ship Cruise ships with internet cafes, commercial shipping communications. Garages / vehicle sales / petrol stations / motor spares (tills, ATM machines, stock sale updates and stock ordering). Hotel chains, hotel internet cafes. Insurance offices, quotations access to head office computers, VPN. Car rental offices, ATM machines. Airlines, travel agents, booking systems. Airport air traffic control, flight data. Financial institutions - Banks, ATM machines. Lottery terminals. Manufacturers - sales offices, service divisions, plants. Job centres. Customs and tax offices / border passport control checkpoints. Internet Service Providers. POP, VoIP, Cafe. Phone booths, VoIP, SCPC. Data file and software distributors. Pipeline monitoring, well heads, oil rigs. Rural telephony, data, videophone. Schools. Military, data transfer, voice, temporary fixed and mobile VSAT. Environmental monitoring, weather stations, seismic monitoring. Mobile phone base station in remote locations or on board ship. VSAT is an expensive means of communications and should not be used if terrestrial alternatives are available. The terrestrial method (cable modem , ADSL phone line) should be much cheaper
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ZEE 24 GHANTE CHHATTISGARH STRUCTURE
S T U D I O
MCR(MASTER CONTROL ROOM) (PROMOS AND ADS’)
CAR ROOM, SERVER.
V S A T
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(BHARATI AND VSNL LINK)
MUX Connected to switch via Rj45
ISP NOIDA A1 A2
ZEE NEWS CHANNEL TRANSMISSION
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A1 A2 V
Rx Raipur Tx Bilaspur
COMMUNICATION BETWEEN TWO BUREAUS’ COMMUNICATION BETWEEN TWO BUREAUS’
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DSNG(OB VAN) (DIGITAL SATELLITE NEWS GATHERING)
Eng became a catch-all term for various elements of the electronic news gathering process, including the use of point-to-point terrestrial microwave signals to backhaul the remote signal to the studio. In modern news operations, however, it also includes sng (satellite news gathering) and dsng (digital satellite news gathering). Eng field operations are usually done with a specially modified truck or van. Terrestrial microwave vehicles can usually be identified by their masts which can be extended up to 50 feet (15 m) in the air (to allow line-of-sight with the station's receiver antennas), while satellite trucks normally use a dish that points skywards towards one of the geostationary communications satellites. New phased array satellite antennas are, as of 2010, being adapted from military and aircraft applications for news gathering by networks and local stations. These systems will allow broadcast live from moving vehicles. The interior of DSNG, satellite trucks and microwave vans resemble small control rooms on wheels. With digital evolution, bulky tape editing systems are being replaced with single computers using multiple monitors or the computer's screen. An edit suite, which used to weigh over one hundred pounds, can now be replaced by a laptop computer. This is made possible by the fact that digital video is easier to transport (inside and outside an edit system), because it takes less bandwidth. There are many other qualities available through digital video that were previously unavailable or only through systems costing hundreds of thousands of dollars. In its essence, digital video allows the manipulation of video scenes more easily because all of the scene is translated into computer language, thus making it accessible to the computer instead of a fixed video frame. The DSNG system consists of programme video and two audio channels, digitally multiplexed and compressed together via the encoder.
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The vision signal from the camera is fed via an optical fibre to the vehicle, along with associated programme audio and comms. This fibre-optic “cable” can also carry return video and comms signals from the vehicle to the camera position. The video and programme audio is then fed to the coder (see Fig. 2) and sent as a serial data stream to modulator. From here, it is modulated as a 3/4 FEC QPSK signal with overhead framing information, in accordance with Insat IDR specification IESS 308 , and this signal is then fed to two stages of up conversion
DSNG Internal block diagram
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INTERNAL CABLING OF DSNG VAN OF ZEE NEWS CHHATTISGARH
MIXER VTR ADA
VTR OUTPUT CAMERA OUTPUT
E N C O D E R
A C U C O N T R O L L E R
M O N I T O R
B U C
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The network of VSATs at different locations adopts different topologies depending on the end applications traffic flow Requirements. These topologies could be star, mesh or hybrid networks. The primary objective of the VSAT networks is to maximize the use of common satellite and other resources amongst all VSAT sites. The methods by which these networks optimize the use of satellite capacity, and spectrum utilization in a flexible and cost-effective manner are referred to as satellite access schemes. Each topology in VSAT is associated with an appropriate satellite access scheme. Good network efficiency depends very much on the multiple accessing schemes. There are many different access techniques tailored to match customer applications. The evolution in satellite communication will be affected to VSAT services. Satellite technology improvements give longer life, greater flexibility, higher performance and higher reliability overall and new on-board technology implementations. While in the ground station developments for improving satellite access technologies will make lower space segment utilization and lower operational costs. The smaller and highly integrated terminals provide more opportunity for mass deployment. Volume production and lower costs will make satellite alternative for multimedia services
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References 1. http://www.marketinfo4me.com/Satellite%20Evolution%202003/ Section_1/s1_Binariang. htm, Binariang Satellite System – Measat, Satellite Evolution Asia, 2003 2. Presentation on Telekom Malaysia, Satellite Network, August 2001 3. REPORT ON E-CLASSROOM (SCOPIA), From Science College, Raipur (C.G.).