Chapter4-1

Chapter4-1 - Spring 2009 ELEC001 Electronic & Information...

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P.1 Chapter 04 – Coding of Digital Information Source Coding and Channel Coding for Compression and Error Protection Spring 2009 ELEC001 Electronic & Information Technology
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P.2 Coding Coding is the conversion of digital information into different forms for the purpose of storage, transmission, or other types of processing Why do we need coding? Reasons include: - Compression - Error Protection - Secrecy
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P.3 Coding for Digital Communications x(t) x(nT s ) ADC Analog/ Digital Converter modulator x T (t) T s S/H channel coding Source coding The picture above represents a model for digital communications In Chapter 3, we discussed digitization, where the analog signal x(t) is sampled and quantized to become a digital signal Digitization: Sampling and Quantization (Chapter 3) Coding: Source and Channel (Chapter 4) Communications: (Chapter 5) Communications and Security Protocol Overheads (Not covered) x d [n]
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P.4 Coding for Digital Communications x(t) x(nT s ) ADC Analog/ Digital Converter modulator x T (t) T s S/H channel coding Source coding In this chapter we will discuss source coding and channel coding Source coding ensures that bits are used efficiently ( reduces the number of bits ) Channel coding helps the receiver to detect and possibly recover bit errors ( adds redundant bits for protection ) Digitization Coding Communications Communications and Security Protocol Overheads x d [n]
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P.5 Coding for Digital Communications x(t) x(nT s ) ADC Analog/ Digital Converter modulator x T (t) T s S/H channel coding Source coding The modulator shift the signal to a frequency and format suitable for transmission over a given medium (wireless, optical, etc.). This is known as modulation and will be discussed in Chapter 5. If you want to keep the information secret, you may need to encrypt the data before channel coding. Digitization Coding Communications x[n] Communications and Security Protocol Overheads
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P.6 Part 1: Source Coding Source coding is to encode the data so that we can represent information with a smaller number of bits – compression , so that we may store fewer bits and transmit fewer bits Compression can be lossless or lossy
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P.7 Lossless Compression Lossless compression : a class of compression techniques for which nothing about the original set of numbers or symbols is lost in the compression process. Lossless compression is reversible and the reverse process is called decompression . In this case, the exact set of the original numbers can be recovered by undoing the compression process. As we will see , Huffman Code is a type of Lossless Compression (it reduces the bits/sym by knowing the symbol frequency and use less bits for the more frequent symbols)
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P.8 Lossy Compression Lossy compression : a class of compression techniques that selectively throw away information about the sets of numbers or symbols being compressed. The goal in lossy compression is
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This note was uploaded on 01/28/2011 for the course ELEC 001 taught by Professor Albertwong during the Spring '09 term at HKUST.

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Chapter4-1 - Spring 2009 ELEC001 Electronic & Information...

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