Direct satellite broadcast receiver using mpeg 2

Submitted by Arpit shukla 1312231039Srmcem lucknow

• Direct-broadcast satellite (DBS) is a type of artificial satellite which usually sends satellite television signals for home reception.

• All in all we can say that it is a method of receiving satellite television by means of signals transmitted from direct-broadcast satellites.

Introduction

Overview of working

Mainly five components are there –

the programming source

the broadcast center

the satellite

the satellite dish the receiver.

The working bands of DSB : the c and ku band

•C-Band

• DIRECTV (Ku-Band + Ka-Band)

• DISH (Ku-Band)

•Globe Cast World TV (Ku-Band)

At present time, there are 4 commercially available satellite television technologies

DIGITAL DSB TV (receiver)

ERROR CONTROL IN DSB

Interleaving and de-interleaving -

Interleaving is frequently used in digital communication and storage systems to improve the performance of forward error correcting codes.

13-17 Error correction 23-27 For digital data

interleaving is widely used for burst error-correction.

Transmission without interleaving

Error-free message: aaaabbbbccccddddeeeeffffgggg

Transmission with a burst error: aaaabbbbccc____deeeeffffgggg

With interleaving:

Error-free code words: aaaabbbbccccddddeeeeffffgggg

Interleaved: abcdefgabcdefgabcdefgabcdefg

Transmission with a burst error: abcdefgabcd____bcdefgabcdefg

Received code words after deinterleaving: aa_abbbbccccdddde_eef_ffg_gg

In each of the codewords aaaa, eeee, ffff, gggg, only one bit is altered, so one-bit error-correcting code will decode everything correctly

Disadvantages of interleaving

Use of interleaving techniques increases total delay. This is because the entire interleaved block must be received before the packets can be decoded.

The Moving Picture Experts Group (MPEG) is a working group of authorities that was formed by ISO and IEC to set standards for audio and video compression and transmission

MPEG has standardized the following compression formats and ancillary standards:

•MPEG 1

•MPEG 2

•MPEG 3

•MPEG 4

MPEG

MPEG 2

MPEG-2 is widely used as the format of digital television signals that are broadcast by terrestrial (over-the-air), cable, and direct broadcast satellite TV systems. It also specifies the format of movies and other programs that are distributed on DVD and similar discs. MPEG-2 removes both the temporal redundancy and spatial redundancy which are present in motion video.

Temporal redundancy arises when successive frames of video display images of the same scene. It is common for the content of the scene to remain fixed or to change only slightly between successive frames.

Spatial redundancy occurs because pats of the picture (called pels) are often replicated (with minor changes) within a single frame of video.

BASIC OPERATION OF ENCODER

MPEG-2 includes a wide range of compression mechanisms. An encoder must therefore which compression mechanisms are best suited to a particular scene / sequence of scenes. In general, the more sophisticated the encoder, the better it is at selecting the most appropriate compression mechanism, and therefore the higher the picture quality for a given transmission bit rate. MPEG-2 decoders also come in various types and have varying capabilities (including ability to handle high quality video, ability to cope with errors) and connection options.

Encoder and decoder of mpeg

Motion vectors are parsed from the data stream and fed to the motion compensator. Quantized DCT coefficients are fed to the inverse quantizer and then to an IDCT circuit that transforms them back to the spatial domain. For P and B pictures, motion vector data is translated to a memory address by the motion compensator to read a particular macroblock (predicted macroblock) out of a previously stored reference picture. The adder adds this prediction to the residual to form reconstructed picture data. For I pictures, there are no motion vectors and no reference picture, so the prediction is forced to zero. For I and P pictures, the adder output it is fed back to be stored as a reference picture for future predictions.

ADVNTAGES

•allows storage and transmission of movies using currently available storage media and transmission bandwidth•better coding quality at higher data rates in comparison with MPEG 1•often used to create movies to be distributed over the internet•offers resolutions of 720x480 and 1280x720 at 60 fps, full CD-quality audio•significant requirements for computer encoding

DISADVANTAGE

The error correcting procedure is long

Video compression is not highly efficient for high definition

The trends

Conclusion •DBS seems most appealing to persons who either are disenchanted with cable television or who live in areas that are not served by cable.

•DBS-TV systems operate with small antennas and low cost receiving systems, and offer a very large number of video and audio channels, making them attractive to customers.

•Delivery of bit stream through a direct broadcast satellite can be adapted to serve Internet users who require the download of large blocks of data.

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