Lecture#1, Lecture notes of Digital Communication Systems

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EEE353: Digital

Communication

Systems

Courtesy: Dr. Syed Ismail Shah

Lecture 1

Course Objective  (^) This course is designed to prepare students for engineering work in the industry and for advanced graduate work in the area of digital communications.  (^) The course covers concepts and useful tools for design and performance analysis of transmitters and receivers in the physical layer of a communication system.  (^) Fundamental Principles  (^) Essential Components  (^) Commonly used techniques of Modulation, Source Coding and Channel Coding  (^) Application of acquired knowledge to practical systems  (^) System performance Quantification and Evaluation  (^) Design trade-offs: rate, bandwidth, power & error probability

Text book: B. Sklar, and P. K. Ray ‘‘Digital Communications: Fundamentals and Applications”, Prentice Hall, 2001, 2 nd edition Additional reference books: J. G. Proakis, and M. Salehi, ‘‘Digital Communications”, Prentice Hall, 2002, 2 nd edition S. S. Hykins, ‘‘Communication Systems”, Wiley, 2001, 4th edition Recommended books

Communication  (^) Main purpose of communication is to transfer information from a source to a recipient via a channel or medium.  (^) Basic block diagram of a communication system:

Source Transmitter Receiver

Recipient

Channel

 (^) Types of information Voice, data, video, music, email etc.  (^) Types of communication systems Public Switched Telephone Network (voice,fax,modem) Satellite systems Radio,TV broadcasting Cellular phones Computer networks (LANs, WANs, WLANs)

Information Representation  (^) Communication system converts information into electrical electromagnetic/optical signals appropriate for the transmission medium.  (^) Analog systems convert analog message into signals that can propagate through the channel.  (^) Digital systems convert bits(digits, symbols) into signals  (^) Computers naturally generate information as characters/bits  (^) Most information can be converted into bits  (^) Analog signals converted to bits by sampling and quantizing (A/D conversion)

Why Digital Communication?  (^) Easy to regenerate the distorted signal  (^) Regenerative repeaters along the transmission path can detect a digital signal and retransmit a new, clean (noise free) signal  (^) These repeaters prevent accumulation of noise along the path  (^) This is not possible with analog communication systems  (^) Two-state (finite state) signal representation  (^) The input to a digital system is in the form of a sequence of bits (binary or M_ary)  (^) Immunity to distortion and interference  (^) Digital communication is rugged in the sense that it is more immune to channel noise and distortion

Why Digital Communication?  (^) The two types of communication are difficult to combine over the same medium in the analog domain.  (^) Using digital techniques, it is possible to combine both format for transmission through a common medium  (^) Can use packet switching  (^) Encryption and privacy techniques are easier to implement  Better overall performance  (^) Digital communication is inherently more efficient than analog in realizing the exchange of SNR for bandwidth  (^) Digital signals can be coded to yield extremely low rates and high fidelity as well as privacy

Disadvantages of Digital

Communication Systems

 Requires reliable “synchronization”

 Requires A/D conversions at high rate

 In general requires larger bandwidth

Main Points  (^) Transmitters modulate analog messages or bits in case of a DCS for transmission over a channel.  (^) Receivers recreate signals or bits from received signal (mitigate channel effects)  (^) Performance metric for analog systems is fidelity, for digital it is the bit rate and error probability.

Course Outline  (^) Signal and Spectra (Chapter 1)  (^) Formatting and Baseband Modulation (Chapter 2)  (^) Baseband Demodulation/Detection (Chapter 3)  (^) Bandpass Modulation and Demodulation/Detection (Chapter 4)  (^) Communication Link Analysis (Chapter 5)  (^) Channel Coding (Chapter 6, 7 and 8)  (^) Modulation and Coding Trade-Offs (Chapter 9)  (^) Miscellaneous Topics