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lect1 - Kevin Buckley 2007 1 ECE 8770 Topics in Digital...

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Kevin Buckley - 2007 1 ECE 8770 Topics in Digital Communications - Sp’2007 Lecture 1 1 Digital Communications System, and Signal & Chan- nel Representation 1.1 Digital Communication System Block Diagram & Course Focus Figure 1 is a block diagram of a typical digital communication system, followed by a description of its components and accompanying comments on their relation to this course. source information encoder source channel encoder communication channel compressed information bits transmitted signal received signal a i information output decoder source channel decoder received signal a i ^ compressed information bits estimated estimated information modulator s (t) r (t) information demodulator r (t) ^ ^ j j x x C C k k estimated codeword. bits codeword bits Figure 1: Digital communication system block diagram. Source Encoder Transforms information to bits, and implements data compression for efficient repre- sentation for transmission; e.g. * Adaptive Differential Pulse Code Modulation (ADPCM) - lossy * Huffman Coding - lossless * Lempel Ziv Coding - lossless * Sampling & Quantization - lossy This is a very interesting topic from a signal processing point of view, but it is not a topic of this course. It is a primary topic of ece8771.
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Kevin Buckley - 2007 2 Channel Encoder Introduces redundancy for error management; e.g. * Block Coding * Convolutional Coding This topic is not covered in depth in this course., but it is a primary topic of ece8771. The Viterbi algorithm, which is a principal topic of the course, is often used as a convolutional code decoder. Digital Modulator Binary or M -ary data to waveform (symbol) translation; e.g. * Pulse Amplitude Modulation (PAM) * Quadrature Phase Shift Keying (QPSK) * Minimum Shift Keying (MSK) * Direct Sequence Code Division Multiple Access (DS-CDMA) We will review those listed above, and others, and use them as examples in this course. Communication Channel This is the heart of the problem addressed in this course. Examples of channels, which will be studied via examples, problems and simulation in this course, are * baseband wireline * magnetic recording * electromagnetic with multipath Such channels distort the transmitted symbols, smear them together, and superimpose random noise. The challenge addressed in this course it to mitigate these deleterious effects. Digital Demodulator This signal processor transforms the distorted, noisy received symbols into binary or M -ary data. Processors include * matched filters * nearest neighbor threshold detectors * channel equalizers * sequence estimators Design of the digital demodulator is the principal topic of this course. Channel Decoder This transforms binary or M -ary outputs of the digital demodulator to error de- tected/corrected binary data. This is not covered in this course. It is a primary topic of ece8771.
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Kevin Buckley - 2007 3 Source Decoder This reverses the source coder, as much as possible or reasonable. This is not covered in this course. It is discussed in ece8771.
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