Direct To Home (DTH) technology

BODIGUM AKILA
Roll no: 09311A0410

Sreenidhi Institute of Science & Technology College
Yamnampet,
Ghatkesar,
Hyderabad - 501301.

Under the esteemed guidance of
Mrs. V. Sudha Rani
Associate Professor
Department of ECE.

CERTIFICATE

This is to certify that BODIGUM AKILA is a student of IV year B. Tech ECE, bearing roll number 09311A0410 in the batch of 2009-2013 has taken active interest in preparing report on “Direct To Home technology”. This is in potential fulfillment of requirement for the Bachelor of Technology degree in Electronics and Communication Engineering at Sreenidhi Institute of Science & Technology, affiliated to Jawaharlal Nehru Technological University, Hyderabad.

This report is verified by:
V. Sudha Rani
Associate Professor
Department of ECE.

ACKNOLOWLEDGEMENT

I extend my sincere gratitude towards S. P. Venu Madhava Rao, Head of Department ECE, for giving us his invaluable knowledge and technical guidance. I express my thanks to my seminar guide Mrs. V. Sudha Rani for her kind co-operation and guidance for preparing and presenting this seminar.

I also thank the other entire faculty Members of all ECE department and my friends for their help and support.

(Bodigum Akila)
09311A0410
ECE IV year
Abstract

Direct to home (DTH) television is a wireless system for delivering television programs directly to the viewer's house. In DTH television, the broadcast signals are transmitted from satellites orbiting the Earth to the viewer's house. Each satellite is located approximately 35,700 km above the Earth in geosynchronous orbit. These satellites receive the signals from the broadcast stations located on Earth and rebroadcast them to the Earth.

The viewer's dish picks up the signal from the satellite and passes it on to the receiver located inside the viewer's house. The dish required is quite small (30 to 95 cm in diameter). The receiver processes the signal and passes it on to the television. The DTH provides more than 200 television channels with excellent quality of reception along with teleshopping, fax and internet facilities. Earlier satellite television was broadcasted in C-band radio -- radio in the 3.4-gigahertz (GHz) to 7-GHz frequency range. Digital broadcast satellite transmits programming in the Ku frequency range (12 GHz to 14 GHz ). Usually broadcasting stations use a powerful antenna to transmit radio waves to the surrounding area. Viewer's can pick up the signal with a much smaller antenna.

The main limitation of broadcast television is range. The radio signal used to broadcast television shoot out from the broadcast antenna is in a straight line. In order to receive these signals, there has to be in the direct "line of sight" of the antenna. Small obstacles like trees or small buildings aren't a problem but a big obstacle, such as Earth, will reflect these waves. If the Earth was perfectly flat, we could pickup broadcast television thousands of miles from the source. But because the planet is curved, it eventually breaks the signal's line of sight. The other problem with broadcast television is that the signal is often distorted even in the viewing area.
DTH Television solves both these problems by transmitting broadcast signals from satellites orbiting the Earth. Since satellites are high in the sky there are a lot more customers in the line of sight. Satellites television systems transmit and receive radio signals using specialized antennas called satellite dishes.
The television satellites are all in geosynchronous orbit approximately 35,700 km above the Earth. In this way you have to direct the dish at the satellite only once, and from then onwards it picks up the signal without adjustment.

CONTENTS 1. Introduction 2. Broadcast centre 3. QPSK(quadrature phase shift keying) 4. Uplink antenna 5. Transponder 6. Power amplifier 7. Satellite dish 8. Set top box 9. Future prospect of dth 10. Adavantages of dth over cable tv 11. Conclusion

LIST OF TABLES Table No: | Title | Page no: | 1. | Carrier phase shifts | 4 |

LIST OF FIGURES Figure No: | Title | Page No: | 1. | Basic block diagram of dth. | 5 | 2. | Uplink antenna. | 7 | 3. | Basic block diagram of transponder. | 8 | 4. | Slow wave structure. | 11 | 5. | Travelling wave tube amplifier. | 12 | 6. | Receiving components at the receiver side. | 16 | 7. | Block diagram of an lnb. | 18 | 8. | Block diagram of a set top box. | 19 |

1.INTRODUCTION:
DTH stands for Direct-To-Home television. DTH is defined as the reception of satellite programs with a personal dish in an individual home. DTH does away with the need for the local cable operator and puts the broadcaster directly in touch with the consumer. It mainly consists of a broadcasting centre, earth station, satellite, transponder, dish antenna, set top box as shown in Fig1.
There are five major components involved in a direct to home (DTH) satellite system: * programming source * broadcast center * satellite * satellite dish * receiver.

Fig1: basic block diagram of dth.
Programming sources are the channels that provide programming for broadcast. The provider (the DTH platform) doesn’t create original programming itself; it pays other companies (HBO, for example, or ESPN or STAR TV or Sahara etc.) for the right to broadcast their content via satellite. In this way, the provider is kind of like a broker between the viewer and the actual programming sources. (Cable television networks also work on the same principle.) The broadcast center is the central hub of the system. At the broadcast center or the Playout & Uplink location, the television provider receives signals from various programming sources, compreses by using digital compression, if necessary scrambles it and beams a broadcast signal to the satellite being used by it. The satellites receive the signals from the broadcast station and rebroadcast them to the ground. The viewer’s dish picks up the signal from the satellite (or multiple satellites in the same part of the sky) and passes it on to the receiver in the viewer’s house. The receiver processes the signal and passes it on to a standard television. Lets look at each step in the process in greater detail.
THE PROGRAMMING
Satellite TV providers get programming from two major sources: International turnaround channels (such as HBO, ESPN and CNN, STAR TV, SET, B4U etc) and various local channels (SaBe TV, Sahara TV, Doordarshan, etc). Most of the turnaround channels also provide programming for cable television, so sometimes some of the DTH platforms will ad in some special channels exclusive to itself to attract more subscriptions.
Turnaround channels usually have a distribution center that beams their programming to a geostationary satellite. The broadcast center uses large satellite dishes to pick up these analog and digital signals from several sources.
2. BROADCAST CENTRE:
The broadcast center converts all of this programming into a high-quality, uncompressed digital stream. At this point, the stream contains a vast quantity of data — about 270

megabits per second (Mbps) for each channel. In order to transmit the signal from there, the broadcast center has to compress it. Otherwise, it would be too big for the satellite to handle. The providers use the MPEG-2 compressed video format — the same format used to store movies on DVDs. With MPEG-2 compression, the provider can reduce the 270-Mbps stream to about 3 or 10 Mbps (depending on the type of programming). This is the crucial step that has made DTH service a success. With digital compression, a typical satellite can transmit about 200 channels. Without digital compression, it can transmit about 30 channels. At the broadcast center, the high-quality digital stream of video goes through an MPEG-2 encoder, which converts the programming to MPEG-2 video of the correct size and format for the satellite receiver in your house.
ENCRYPTION & TRANSMISION
After the video is compressed, the provider needs to encrypt it in order to keep people from accessing it for free. Encryption scrambles the digital data in such a way that it can only be decrypted (converted back into usable data) if the receiver has the correct decoding satellite receiver with decryption algorithm and security keys. Once the signal is compressed and encrypted, the broadcast center beams it directly to one of its satellites. The satellite picks up the signal, amplifies it and beams it back to Earth, where viewers can pick it up.
3.QPSK (quadrature phase shift keying):
Satellite communication uses QPSK modulation techniques. Quadrature Phase Shift Keying (QPSK) is the digital modulation technique. Quadrature Phase Shift Keying (QPSK) is a form of Phase Shift Keying in which two bits are modulated at once, selecting one of four possible carrier phase shifts (0, Π/2, Π, and 3Π/2).QPSK is perform by changing the phase of the In-phase (I) carrier from 0° to 180° and the Quadrature-phase (Q) carrier between 90° and 270°. This is used to indicate the four states of a 2-bit binary code. Each state of these carriers is referred to as a Symbol. Quadrature Phase-shift Keying (QPSK) is a widely used method of transferring digital data by changing or modulating the phase of a carrier signal.
In M-ary Transmission it is Possible to Transmit M Possible Signal
M = 2n
Where n= no of Bits that we Combine signaling Interval T= nTb
In QPSK n=2 === > So M =4 and signaling Interval T= 2Tb
M=4 so we have possible signal are 00,01,10,11
Or In Natural Coded Form 00,10,11,01

The QPSK Formula

Table-1 Carrier phase shifts

code | Phase angle | 00 | -135deg | 01 | +135deg | 10 | -45deg | 11 | +45deg |

4. UPLINK ANTENNA:

Fig2: uplink antenna.

Uplink satellite dishes as in Fig2 are very large, as much as 9 to 12m (30 to 40ft) in diameter.The increased diameter results in more accurate aiming and increased signal strength at the satellite. The uplink dish is pointed toward a specific satellite and the uplinked signals are transmitted within a specific frequency range, so as to be received by one of the transponders tuned to that frequency range aboard that satellite * EIRP (effective isotropically radiated power)=Pt- Lc + Ga Pt=power of transmitter (dbm) Lc=path loss(db) Ga=antenna gain (dbi)
5. TRANSPONDER: A communications satellite's transponder, is the series of interconnected units which form a communications channel between the receiving and the transmitting antennas and is housed onboard the operating satellite to amplify one or more carriers on the downlink side of a geostationary communication satellite and they use C and Ku bands.
The basic types of transponders are :
BENT PIPE

The bent pipe transponders are so called because it takes a band of signals and bents it back to the earth just like a bent pipe which changes the direction of flowing water.
An onboard oscillator and mixer are used to separate the uplink and downlink signals this is done inorder to prevent the antenna receive the same signal that is being transmitted by it. The uplink frequency is always greater than downlink frequency as the antenna size at ground terminal can have larger size while the size of antenna on the satellite is fixed as the gain is higher in upper frequencies.
The major characteristics of bent pipe architecture are * Simpler satellites * Complex ground stations * Controlled by a ground station * Longer propagation delay * Limited means of sharing resources * Fixed interconnectivity

REGENERATIVE/ON BOARD PROCESSING
In regenerative the signal is processed on the satellite and then transmitted towards the destination. In this case the destination may be a different network or any other satellite. In this type of model inter satellite links or cross links is possible.
There are three main classes of OBP
i.baseband processing and switching (routing) ii.IF or RF switching(frequency or time domains), and iii.Support processing
A transponder is typically composed of (as shown in Fig3): * An Input low-noise amplifier (LNA), designed to amplify the (normally very weak, because of the large distances involved) signals received from the earth station * A frequency translator (normally composed of an oscillator and a frequency mixer) used to convert the frequency of the received signal to the frequency required for the transmitted signal * A power amplifier (this can be a traveling-wave tube or a solid state amplifier).

Fig3: basic block diagram of transponder.

6. POWER AMPLIFIER(TWTA):
A traveling-wave tube (TWT) (as shown in Fig5) is a specialised vacuum tube that is used in electronics to amplify radio frequency (RF) signals to high powers.The bandwidth of a broadband TWT can be as high as one octave, and operating frequencies range from 300 MHz to 50 GHz. The voltage gain of the tube is on the order of 70 decibels.
Slow wave structure reduces the wave velocity in a certain direction so that the signal and electron beam interact Gain of TWTA is proportional to the length of the slow wave structure(Fig4). a. ring bar circuit
b.Contra wound circuit

Fig4: Slow wave structure.

Fig5: travelling wave tube amplifier.
1. Electron gun
2. RF input
3. Magnets
4. Attenuator
5. Helix coil
6 . RF output
7 . Vacuum tube
8. Collector.

7.SATELLITE DISH:

Fig6: receiving components at the receiver side.
A satellite dish is just a special kind of antenna designed to focus on a specific broadcast source. The standard dish consists of a parabolic (bowl-shaped) surface and a central feed horn. To transmit a signal, a controller sends it through the horn, and the dish focuses the signal into a relatively narrow beam. The dish on the receiving end can’t transmit information; it can only receive it. The receiving dish works in the exact opposite way of the transmitter. When a beam hits the curved dish, the parabola shape reflects the radio signal inward onto a particular point, just like a concave mirror focuses light onto a particular point. In this case, the point is the dish’s feed horn, which passes the signal onto the receiving equipment. In an ideal setup, there aren’t any major obstacles between the satellite and the dish, so the dish receives a clear signal. The central element in the feed horn is the low noise block down converter, or LNB. The LNB amplifies the signal bouncing off the dish and filters out the noise (signals not carrying programming). The LNB passes the amplified, filtered signal to the satellite receiver inside the viewer’s house.

Fig7 :block diagram of an lnb.

LNA(low noise amplifier)
The LNA actually consist of 2 or 3 amplifying stages that boost the signal to a reasonable level at which it can be further processed. The LNA is designed with an all out effort to keep noise down to the barest minimum.
After the C or KU band frequencies are amplified by the LNA, they need to be processed. The processing is done in the satellite receiver which is usually located 10 meters to 50 meters away from the dish antenna. Microwave signals in the S, C or KU Band would suffer very high attenuation if they were carried via coaxial cable from the LNA to the Satellite Receiver 50 meters away. To overcome this problem, the microwave signals are converted to a block of frequencies from 950 MHz to 2150 MHz. Hence, incoming signals received by the LNA at 2 GHz, 4 GHz and even 12 GHz are even block converted down to 950 MHz to 2150 MHz. This range of frequencies is referred to as Intermediate Frequencies since their range of temporary or intermediate frequencies in the chain of satellite reception which receives microwave signals and finally yields video and audio signals from the satellite receiver. This function is carried out by a “Block Converter” located within the LNB. A combination of Low Noise amplifier + Block converter is referred to as an LNB.
MIXER
The Block Converter uses the Hetrodyne principle for conversion of a block of S, C or KU Band frequencies to the IF or Intermediate Frequencies. The Hetrodyne principle mixes an external fixed frequency with the incoming frequency. The output from the mixer is a series of signals at the sum and difference of the two inputs to the mixer. Outputs are also produced at multiples of these frequencies. A simple filter is used to suppress all frequency components except those required.
LOCAL OSCILLATOR
The Local Oscillator (LO) is a section of the LNB and gets its name since it is present locally or within the LNB. The local oscillator produces a fixed output at a pre-determined frequency. The Local Oscillator (LO) frequencies have been standardized by LNB manufacturers worldwide for S, C, Ku and even Ka band frequencies. The LO frequencies have been selected to yield an output in the IF (950 MHz to 2150 MHz) range, for all types of LNBs. As a result, universal satellite receivers can be designed for reception of C and KU Band signals through the same satellite receiver.
8.SET TOP BOX(IRD):
The end component in the entire satellite TV system is the receiver. The receiver has four essential jobs: It de-scrambles the encrypted signal. In order to unlock the signal, the receiver needs the proper decoder chip for that programming package. The provider can communicate with the chip, via the satellite signal, to make necessary adjustments to its decoding programs. The provider may occasionally send signals that disrupt illegal de-scramblers, as an electronic counter measure (ECM) against illegal users.

TUNER
DEMODULATOR
DECODER
AMPLIFIER
MICROCONTROLLER
DISH ANTENNA
A
V

Fig8: block diagram of a set top box.

A set top box can demodulate the received signal and can convert these signal into audio and video signal. The basic blocks are shown in Fig8.

TUNNER
It select particular channel range from 48 Mhz to 840 Mhz
DEMODULATOR
Selected channel is demodulated and fed to decoder
DECODER
It is a D to A converter which provide audio and video signal as output.
MICROCONTROLLER
It controls all the process performed by each block.
9.FUTURE PROSPECT OF DTH:
The DTH market in INDIA is relatively incresing day by day and in next 5 years (by 2017 ) we will be able to add another 30 million subscriber. In the next 5 years we have manage to overtake JAPAN as the largest DTH market in ASIA.
10.ADVANTAGES OF DTH OVER CABLE TV:
In DTH , TV channel are directly transmitted from satellite to a small dish antenna at the subscriber home. The broadcaster directly connect to the subscriber ,the middlemen like local cable operator are not there in the picture , hence provide better picture quality directly from satellite to the user. The cable TV was limited to the urban area but the DTH followed cable TV in urban as well as in rural area. DTH technology is more resistive to the weather condition it can work in any type of environment. Since coaxial cable connection are used in DTH technology less distortion of the signal take place , which ultimately provides better picture quality and better signal.
11.CONCLUSION:
DTH has made the hopes of people of the rural area to come true. It helps to develop the economic condition of our country. It provides wide thinking of rural people which helps to develop the culture of society.

ABBREVIATIONS
DTH-Direct To Home
TWTA-Travelling Wave Tube Amplifier
LNA-Low Noise Amplifier
LNB-Low Noise Block Down Convertor
IRD-Integrated Receiver Decoder
OBP-On Board Processing

References: * http://www.scatmag.com/technical/techarticle-mar05.pdf * http://www.satsig.net/lnb/explanation-description-lnb.htm * Microwave and radar engineering –M.kulkarni * Timothy Pratt, Charles Bostian and Jeremy Allnut,”Satellite Communications", John Wiley & Sons,Inc,Second Edition,2006.