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Lecture1

  1. 1. CTN521 Digital Communications
  2. 2. <ul><li>Course Title: Digital Communication System </li></ul><ul><li>Course Code: CTN-521 </li></ul><ul><li>Credit Hours: Three (3) </li></ul><ul><li>Semester:        2 nd </li></ul>Course Information
  3. 3. <ul><ul><ul><li>To be announced </li></ul></ul></ul>Grading Policy
  4. 4. <ul><li>Prerequisites </li></ul><ul><ul><li>Signals and Systems </li></ul></ul><ul><ul><li>Communication Systems </li></ul></ul><ul><ul><li>Probability and Stochastic Processes </li></ul></ul>Course Information
  5. 5. <ul><li>Probability and Stochastic Processes </li></ul><ul><ul><li>Probability definitions, </li></ul></ul><ul><ul><li>Probability distributions and densities </li></ul></ul><ul><ul><li>Random process definitions </li></ul></ul><ul><ul><li>Spectral density of random process </li></ul></ul><ul><ul><li>Linear filtering of random process </li></ul></ul><ul><li>Source Coding Techniques </li></ul><ul><ul><li>Coding for discrete sources </li></ul></ul><ul><ul><li>Coding for analog sources </li></ul></ul><ul><ul><li>PCM, DPCM, DM, Duobinary signaling </li></ul></ul>Topics
  6. 6. <ul><li>Bandpass Modulation and Detection </li></ul><ul><ul><li>MPSK, MPAM, MFSK, GMSK modulations, demodulation, </li></ul></ul><ul><ul><li>matched filter& correlator concepts, </li></ul></ul><ul><ul><li>Optimum detector, Maximum likelihood detector, Probability of error estimations </li></ul></ul><ul><li>Carrier and Symbol Synchronization </li></ul><ul><ul><li>ML carrier estimation </li></ul></ul><ul><ul><li>PLLs </li></ul></ul><ul><ul><li>ML timing estimation </li></ul></ul><ul><ul><li>Non-decision directed timing estimation </li></ul></ul>Topics
  7. 7. <ul><li>Channel Coding Theory </li></ul><ul><ul><li>Introduction to block codes </li></ul></ul><ul><ul><li>Convolutional codes & concatenated codes </li></ul></ul><ul><ul><li>Impact on BW and power performance of digital systems </li></ul></ul>Topics
  8. 8. <ul><li>Textbooks: </li></ul><ul><li>(1) Digital Communications, Fourth Edition, J.G. Proakis, McGraw Hill, 2000 </li></ul><ul><li>(2) Digital Communications: Fundamentals and Applications, B. Sklar, Prentice Hall, 2 nd ed, 2001. </li></ul><ul><li>Reference Books: </li></ul><ul><li>Communication Systems, 3 rd Ed., Simon Haykin, John Wiley & Sons, (Available in the book stores) </li></ul><ul><li>Communication Systems, J.G. Proakis and Masoud Salehi </li></ul><ul><li>Advanced Digital Communications: Systems and Signal Processing, Kamilo Feher, Noble Publishing Corporation; Reprint of original 1987 edition (1997). </li></ul><ul><li>Digital Communications: Satellite/Earth Station Engineering, Kamilo Feher, Noble Publishing Corporation; Reprint of original 1987 edition (1997). </li></ul><ul><li>Digital Communication, John R. Barry (et al), 2003. </li></ul><ul><li>Analog and Digital Communication Systems, Leaon W. Couch II, 6 th edition, Prentice Hall, 2001. </li></ul><ul><li>Modern Digital and Analog Communication Systems, B. P. Lathi, 3 rd Ed. Oxford Univ. Press 1998. </li></ul><ul><li>Digital Communication, Edward. A. Lee and David G. Messerschmitt, 2 nd Ed. Kluwer Acad. </li></ul>Course Information
  9. 9. Course Objective <ul><li>The course is designed to prepare students for engineering work in the industry and for advanced graduate work in the area of digital communications. </li></ul><ul><li>The course covers concepts and useful tools for design and performance analysis of transmitters and receivers in the physical layer of a communication system. </li></ul>
  10. 10. Communication <ul><li>Main purpose of communication is to transfer information from a source to a recipient via a channel or medium. </li></ul><ul><li>The basic elements of a digital communication system: </li></ul>
  11. 11. Communication <ul><li>Source are converted into a sequence of binary digits which is called information sequence . </li></ul><ul><li>Efficiently converting the source into a sequence of binary digits is a process, which is called source encoding </li></ul><ul><li>Channel encoder adds some redundancy into binary information sequence that can be used for handle noise and interference effects at the receiver </li></ul><ul><li>Digital modulator maps the binary information sequence into signal waveforms. </li></ul><ul><li>Communication channel is used to send the signal from the transmitter to the receiver. Physical channels: the atmosphere, wireless, optical, compact disk,…. </li></ul>
  12. 12. Communication <ul><li>Digital demodulator receives transmitted signal contains the information which is corrupted by noise </li></ul><ul><li>Channel decoder attempts to reconstruct the original information sequence from knowledge of the code used by channel encoder. </li></ul><ul><li>Source decoder attempts to reconstruct the original signal from the binary information sequence using the knowledge of the source encoding methods. </li></ul><ul><li>The difference between the original signal and the reconstructed signal is measure of the distortion introduced by the digital communication system </li></ul><ul><li>Estimate what was send, aiming at the minimum possible probability of making mistakes </li></ul>
  13. 13. <ul><li>Types of information </li></ul><ul><li>Voice, data, video, music, email etc. </li></ul><ul><li>Types of communication systems </li></ul><ul><li>Public Switched Telephone Network (voice,fax,modem) </li></ul><ul><li>Satellite systems </li></ul><ul><li>Radio,TV broadcasting </li></ul><ul><li>Cellular phones </li></ul><ul><li>Computer networks (LANs, WANs, WLANs) </li></ul><ul><li>Radars/EW (ECM, ECCM) </li></ul>Communication
  14. 14. <ul><li>Physical channel media </li></ul><ul><ul><li>magnetic-electrical signaled wire channel </li></ul></ul><ul><ul><li>modulated light beam optical (fiber) channel </li></ul></ul><ul><ul><li>antenna radiated wireless channel </li></ul></ul><ul><ul><li>acoustical signaled water channel </li></ul></ul><ul><li>Virtual channel </li></ul><ul><ul><li>magnetic storage media </li></ul></ul>Practical channels & their characteristics
  15. 15. <ul><li>Noise characteristic </li></ul><ul><ul><li>thermal noise (additive noise) </li></ul></ul><ul><ul><li>signal attenuation </li></ul></ul><ul><ul><li>phase distortion </li></ul></ul><ul><ul><li>multi-path distortion </li></ul></ul><ul><li>Limitation of channel usage </li></ul><ul><ul><li>transmitter power </li></ul></ul><ul><ul><li>receiver sensitivity </li></ul></ul><ul><ul><li>channel capacity (such as bandwidth) </li></ul></ul>Practical channels & their characteristics
  16. 16. Frequency range for wireline channel
  17. 17. Frequency range for wireless EM channels
  18. 18. Information Representation <ul><li>Communication system converts information into electrical electromagnetic/optical signals appropriate for the transmission medium. </li></ul><ul><li>Analog systems convert analog message into signals that can propagate through the channel. </li></ul><ul><li>Digital systems convert bits(digits, symbols) into signals </li></ul><ul><ul><li>Computers naturally generate information as characters/bits </li></ul></ul><ul><ul><li>Most information can be converted into bits </li></ul></ul><ul><ul><li>Analog signals converted to bits by sampling and quantizing (A/D conversion) </li></ul></ul>
  19. 19. Why digital? <ul><li>Digital receiver needs only distinguish between two waveforms it is possible to exactly recover digital information </li></ul><ul><li>Transmitted bits can be detected and regenerated, so Noise does not propagate additively </li></ul><ul><li>Efficient signal processing techniques are available for digital signals, such as </li></ul><ul><ul><li>Data compression (or source coding) </li></ul></ul><ul><ul><li>Error Correction (or channel coding) </li></ul></ul><ul><ul><li>Equalization </li></ul></ul><ul><ul><li>Security </li></ul></ul><ul><li>Easy to mix signals and data using digital techniques </li></ul>
  20. 20. Why digital? <ul><li>Digital ICs are inexpensive to manufacture. A single chip can be </li></ul><ul><li>mass produced at low cost, no mater how complex </li></ul><ul><li>Digital communications permits integration of voice, video, and </li></ul><ul><li>data on a single system (ISDN) </li></ul><ul><li>Implementation by software instead of hardware </li></ul><ul><li>Easy to mix signals and data using digital techniques </li></ul>
  21. 24. Performance Metrics <ul><li>Analog Communication Systems </li></ul><ul><ul><li>Metric is fidelity: want m(t)  m(t) </li></ul></ul><ul><ul><li>SNR typically used as performance metric </li></ul></ul><ul><li>Digital Communication Systems </li></ul><ul><ul><li>Metrics are data rate (R bps) and probability of bit error (P b =p(b  b)) </li></ul></ul><ul><ul><li>Symbols already known at the receiver </li></ul></ul><ul><ul><li>Without noise/distortion/sync. problem, we will never make bit errors </li></ul></ul>^ ^
  22. 25. Additive noise channel <ul><li>where </li></ul><ul><ul><li>α is the attenuation factor, </li></ul></ul><ul><ul><li>s ( t ) is the transmitted signal </li></ul></ul><ul><ul><li>n ( t ) is the additive random noise process </li></ul></ul><ul><li>Called Additive Gaussian noise (AGN) channel if n ( t ) is a Gaussian noise process </li></ul>
  23. 26. Linear filter channel with AGN <ul><li>where </li></ul><ul><ul><li>s ( t ) is the transmitted signal </li></ul></ul><ul><ul><li>c ( t ) is the channel impulse response </li></ul></ul><ul><ul><li>n ( t ) is the additive random noise process </li></ul></ul>
  24. 27. Linear time-variant filter channel with additive noise <ul><li>Time-variant multipath propagation. </li></ul>
  25. 28. Main Points <ul><li>Transmitters modulate analog messages or bits in case of a DCS for transmission over a channel. </li></ul><ul><li>Receivers recreate signals or bits from received signal (mitigate channel effects) </li></ul><ul><li>Performance metric for analog systems is fidelity, for digital it is the bit rate and error probability. </li></ul>
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