This document discusses satellite communication methods, focusing on video compression techniques such as MPEG standards and various frame encoding methods to enhance transmission efficiency. It also details encryption processes, transmission systems, and the implementation of turbo codes, which provide efficient error correction for low signal-to-noise ratio channels. The document addresses the balance between coding complexity and efficiency, emphasizing the design of turbo codes for reliable communication in noisy environments.

1. SATELLITE COMMUNICATION
UNIT IV – SATELLITE ACCESS AND CODING
METHODS
KARPAGAM INSTITUTE OF TECHNOLOGY
COIMBATORE - 105.
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

2. • Broadcast Center – High quality video to MPEG-4
• Analyze each frame in Video and eliminate redundant or irrelevant data and extrapolate
information from other frame.
• Frame Encoding – Three Ways
• Intraframe - Complete image data for that frame and provide least compression.
• Predicted frame – Display the frame with enough information – Medium Compression
• Bidirectional frame – Display information from surrounding frame – Maximum compression.
• Encryption and Transmission
• Video compression, Scrambles the data and use correct decryption algorithm and security keys.
• Broadcast center beams it directly to one of its satellites and picks up the signal with an
onboard dish.
• Amplifies the signal and back to earth.
Compression - Encryption

3. • Video and Audio files have large bursts.
• Compression
• Temporal – Correlation between neighbouring pixels among
set of frame
• Spatial - Correlation between neighbouring pixels in single
frame.
• Spectral – Correlation between color or luminance
components
• Psycho Visual – Exploit perceptual properties of human visual
system
• Compression – Lossless and Lossy
• Lossless – Compressed data can be reconstructed without
loss of information
• Lossy - Minimize the bit rate to achieve fidelity measure.
Video and Audio Compression

4. • Promote system interoperability
among audio and video devices.
• MPEG-1 : Encoding and Decoding
Streaming Video and Audio files
• MPEG-2: Digital television; Compress
files for high quality video
transmission.
• MPEG-4: Standard for compression
high definition video into smaller scale
files to computers cell phone and
PDA’s
• MPEG-2I: Referred to as multimedia
framework. Interprets what digital
content to which individual use.
MPEG Video Coding Standards

5. • Encryption
• Plain text, Cipher text
• Symmetric Key encryption – Common keys
• Public key encryption – Public key, Private key
Encryption

6. • Signal transmitted via transponder is affected by many factors.
• Satellite links are usually designed with low margin of link budget
• Low Eb/N0 is preferred to provide reliable message decoding. Turbo codes represent an optimal
technique due to unique properties.
• Turbo Codes
• Introduced in 1993. Implemented in modern communication systems due to high efficiency
and code gain.
• Low BER and Low Eb/N0.
• Does not have marked limit for BER reduction – Iteration decoding to reduce BER.
• Disadvantages : Complicate implementation
• High latency due to iteration decoding and complicated decoding algorithm.
• No mathematical tool for turbo code design
Coding Schemes

7. • Compromise between turbo code complexity and efficiency is the basic task of turbo code
designing.
• For offline systems, error free detection of message can be reached for channel with strong
noise and jamming.
• SMS – Low Noise ration and error free detection
• Decoding of Turbo Codes
• Code gain with maximum channel capacity and high encoder complexity.
• Classical algorithms cannot be used for decoding.
• Two SISO (Soft Input Soft Output) decoders connected with iteration loop.
• Posteriori probability estimation
• Log likelihood Ratio (LLR)
Turbo Codes

8. Architecture of Turbo Code

9. • Telemetry turbo code – SMS.
• It is determined for short data blocks transmission with low noise ratio.
• Modification : Optimum interleaver with appropriate data block and code ratio
• Generation of sequences with the smallest mutual correlations.
• Shannon limit and efficiency of turbo code based on interleaver quality.
• Three types of interleavers
• Telemetry, Pseudorandom and Edge effect elimination interleavers; Code ratio R = ½, R=1/3,
R=1/4 & R=1/6.
• Block lengths : 1024,1784,3568,4096,7136,8464,9216
• Code ratio = ½ and block length = 4096.
• Modified turbo codes attains smallest BER. BER = 1.9 x 10-4
d Eb/N0=0.8 dB.
Modifications of Turbo Code