General DTH

Concept.BY ASHISH KOUL

NETWORK ENGINEER

The DTH technology enables us to directly beam the signal to your TV set through a receiver that is installed in the house.

• In India, direct-to-home (DTH) Broadcasting Service refers to the distribution of multi channel TV programmes in Ku Band by using a satellite system by providing TV signals direct to subscribers' premises. For DTH connection the broadcasting company provides a set that comprises the dish and a receiving set. The company beams an encrypted signal that only the set installed in your household can receive and enable viewing.It is a system of T.V. broadcasting services where T.V. signal are transmitted directly to the viewer side stepping the cable operators

In DTH system, the service provider branches together signals of bouquet of channels in a codified or scrambled form to be received by Ku- band transponder present in Geostationary satellite, from where these signals can be easily down linked by the viewers-by using dish antenna.These signals can be made compatible to T.V. viewing by using a smart card and decoder, the combination which helps in unscrambling the codified signals. In general, DTH service is one in which a large number of channels are digitally compressed, encrypted and beamed from very high power satellites. The programmes can be directly received at homes. However, a digital receiver is needed to receive the multiplexed signals and view them on a TV.The technology of DTH ensures highest quality of voice, video as it uses digital form of communication system. The DTH service also provides various value added services such as internet services, telemedicine, video conferencing etc. Since in DTH technology, all the encoded transmission signals are digital.

Thus, it provides higher resolution picture quality and better audio than traditional analog signals. In recent years DTH has become the buzzword in the satellite broadcasting industry because of immense opportunities it offers to broadcasters and viewers. However, the main advantages of DTH transmission are:1) It facilitates use of small dish antennas which could be easily installed in individual homes and provides a large number of services within the same transponder.2) The broadcaster would be able to introduce a number of new interactive applications such as internet access, email, VoD. It can be also used for public service messages.3) Another benefit of the DTH transmission is that it keeps out intermediaries like cable operators who could distort the subscription income.4) For public broadcaster like Prasar Bharati, free to air DTH broadcasting has emerged as viable alternative for universal coverage of population with Television programmes.

The government permitted DTH broadcasting in India on November 2000. The primary reason for the government to have permitted DTH seems to be its proven capability of serving rural areas as well as population scattered over vast distances in remote and hilly areas. The DTH policy is also in place to regulate the broadcasters and keeping interests of consumer in mind.The TRAI under unified license Regime has recommended that DTH can serve as alternative platform for broadband services. Considering this view, DTH services of Doordarshan has been launched in 2004.Apart from India DTH service is operational in US, Europe, Australia, Japan, South Korea, Thailand and other countries. It is also estimated that, soon the number of households receiving DTH will cross 100 million subscriber worldwide. Europe has got the distinction of having world's most developed DTH market. In the Asian region its penetration is not to the extent of US and Europe.

General Overview

ESSENTIAL COMPONENTS OF DTH SERVICE

Broadcasting Centre Satellites Encoders Multiplexers Modulators DTH receivers

Modulators In telecommunication, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that typically contains information to be transmitted.In telecommunications, modulation is the process of conveying a message signal, for example a digital bit stream or an analog audio signal, inside another signal that can be physically transmitted. Modulation of a sine waveform transforms a baseband message signal into a passband signal.A modulator is a device that performs modulation. A demodulator (sometimes detector or demod) is a device that performs demodulation, the inverse of modulation. A modem (from modulator–demodulator) can perform both operations.The aim of digital modulation is to transfer a digital bit stream over an analog bandpass channel, for example over the public switched telephone network (where a bandpass filter limits the frequency range to 300–3400 Hz), or over a limited radio frequency band.The aim of analog modulation is to transfer an analog baseband (or lowpass) signal, for example an audio signal or TV signal, over an analog bandpass channel at a different frequency, for example over a limited radio frequency band or a cable TV network channel.Analog and digital modulation facilitate frequency division multiplexing (FDM), where several low pass information signals are transferred simultaneously over the same shared physical medium, using separate passband channels (several different carrier frequencies).

Broadcasting Centre• The broadcast centre is the main part

of the whole system. It is from the broadcast station that the signals are sent to the satellites to be broadcasted. The broadcast station receives the signals from various program channels.

• The satellite receives the signal from the broadcast centre and compresses the signals and makes them suitable for re-transmission to the ground.

• The DTH providers give dish receivers for the viewers to receive the signal from the satellites. There may be one or multiple satellites that send the signals at the same time. The receiver receives the signal from them and is passed on to the Set Top Box [STB] receiver in the viewer’s house.

• The STB receiver changes the signal in a form suitable for our television and then passes it on to our TV.

Satellites

An artificial satellite is a man made object placed into orbit around the Earth for the purpose of scientific research, weather reports, or military reconnaissance. Scientific satellites are set into orbit to observe the space environment, the Earth, the Sun, stars and extra galactic objects. These satellites have retrieved a huge amount of information helpful to scientific research. Weather satellites are used every day for meteorological forecasts and in shipping. Also military satellites play a important role in today's modern military. Satellites are extremely important today. All artificial satellites have certain features in common. They all include radar systems, sensors like optical devices in observation satellites and receivers and transmitters in communication satellites. Solar cells are used to generate power for the satellites and in some cases ,nuclear power is used. All satellites need altitude-control equipment to keep the satellite in the desired orbit.

Encoders • The Digital Encoder is a combinational circuit that generates a specific

code at its outputs such as binary or BCD in response to one or more active inputs. There are two main types of digital encoder. The Binary Encoder and the Priority Encoder.

• We have seen that the Binary Encoder converts one of 2n inputs into an n-bit output. Then a binary encoder has fewer output bits than the input code. Binary encoders are useful for compressing data and can be constructed from simple AND or OR gates. One of the main disadvantages of a standard binary encoder is that it would produce an error at its outputs if more than one input were active at the same time. To overcome this problem priority encoders were developed.

• The Priority Encoder is another type of combinational circuit similar to a binary encoder, except that it generates an output code based on the highest prioritised input. Priority encoders are used extensively in digital and computer systems as microprocessor interrupt controllers where they detect the highest priority input.

• In the next tutorial about combinational logic devices, we will look at complementary function of the encoder.

Multiplexers • a multiplexer (or mux) is a device that selects one of several

analog or digital input signals and forwards the selected input into a single line. A multiplexer of 2n inputs has n select lines, which are used to select which input line to send to the output.

Multiplexers are mainly used to increase the amount of data that can be sent over the network within a certain amount of time and bandwidth. A multiplexer is also called a data selector.

• An electronic multiplexer makes it possible for several signals to share one device or resource, for example one A/D converter or one communication line, instead of having one device per input signal.

Frequency Band for Dth

In India we use Ku Band.

Ku Band• The Ku band is the 12–18 GHz portion of the electromagnetic spectrum in the

microwave range of frequencies. This symbol refers to "K-under" (originally German: Kurz-unter)—in other words, the band directly below the K-band. In radar applications, it ranges from 12-18 GHz according to the formal definition of radar frequency band nomenclature in IEEE Standard 521-2002.

• 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 International Space Station (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.

Ku Band Specification.• Frequency range• 12 – 18 GHz Wavelength range• 2.5 – 1.67 cm

MAIN FEATURES AND TECHNOLOGY OF EDUSAT

The need for simple cost effective but more powerful satellite remote terminals calls for very powerful transponders on the satellite and the large number of wide band channels indicates the need to move to the higher frequency bands such as the Ku band. Thus Edusat is a satellite constellation which carries five Ku band transponders providing spot beams, one Ku band transponder providing a national beam and six extended C band transponders providing national coverage beams.

Following are some of the major parameters of EDUSAT (GSAT-3) transponders ,2007 A total of 6 FSS C-band transponders, which will operate in upper Ext. C-band. A total of 6 FSS Ku-band transponders and A Beacon operating in Ku-Band. The coverage contours on earth’s surface are, Indian Coverage of C-band (ICC) Beam will be over Indian geographical Boundary. Ku-band National beam will be over Indian mainland region.

Overall Process flow

Broadcasting Process Flow

ROT Process Flow

DTH receivers

ROT Installation Procedure

While going for the receiving center installation we need to follow certain criteria's, mentioned as follows;

1) Material Check List.(Consumable, Non Consumable & tools).2) Line Of Sight for receiving antenna.3) Antenna pointing.4) IDU and ODU connectivity.

Material Check List.(Consumable, Non Consumable & tools).

• Here this section we will discuss about the materials & equipments required at the receiving center; broadly classified as:

1) Consumables.2) Tools.

Consumables.• Consumables are those items which are a part

of ROT systems and need to be installed i=on site.

• Dish Antenna with stand & LNB

Consumables.• RG 6 Cable • RG 6 Connectors

Consumables.• Set top Box & Remote • Audio Video Cable

Consumables.OUTPUT DEVICES.• VIDEO OUTPUT • Audio Output

Tools• For the installation and end to end

connectivity of ROT we require some tools which are mentioned as:

• Drilling Machine

Tools• Hammer • Spanners

ToolsCrimping tool Wire Stripper

CONCLUSION • DTH has made the hope of the people of rural

area to come true.• DTH service in India is in its initial stage. • We are enriching the education system with help

of DTH service.• In near future, launch of DTH internet service is

expected in India.• It provides the wide thinking of ruler people

which helps to develop the culture of society.