EENG 444 / ENAS 944 Digital Communication Systems

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1 EENG 444 / ENAS 944 Digital Communication Systems Introduction!! Wenjun Hu

2 Communication Systems What s the first thing that comes to your mind?

3 Communication Systems What s the first thing that comes to your mind? All figures from the Internet

4 The (Old) Telephone Network POTS: Plain old Telephone Service PSTN: Public Switched Telephone Network Figure from

5 Telephone Networks Nowadays POTS: Plain old Telephone Service PSTN: Public Switched Telephone Network Figure from

6 Analog TV

7 Digital TV (and its adoption)

8 A few more examples Wireless communication

9 A few more examples Spot the differences! Quantization, image compression/resampling

10 A few more examples Modulation, error correction

11 A few more examples Chu et al, Halftone QR Codes, ACM SIGGRAPH ASIA 2013 Detection, coding, and decoding

12 A few more examples Sampling

13 Anatomy of Digital Communication Systems

14 Basic system

15 Basic system (abstractions) Source Destination Source encoder Channel encoder Channel Channel decoder Source decoder Binary interface Binary interface

16 Basic system (abstractions) Source Destination Source encoder Channel encoder Channel decoder Source decoder Network - logical Channel

17 Fundamental ideas All sources representable by binary sequences Steps of communication flow Source output -> binary sequence The binary sequence -> a form suitable for transmission over particular physical media Digital sequence as interface between source and channel Digital: finite, ~ binary

18 Why digital? Why CDs, not tapes? Why digital TV? Why voice over IP?

19 Why digital? Digital hardware has become cheap, reliable, and miniaturized Standardized binary interfaces simplify understanding and implementation Source-channel separation theorem Information can be transmitted over a binary interface, if it can be transmitted at all Corner stone of information theory

20 Interfaces and layering Peering relation Input 1 Output 1 Encapsulation Input 2 Output 2 Input 3 Output 3 Input n Channel Output n

21 Communication sources Discrete symbols E.g., letters from the English alphabet Analog waveforms E.g., Videos, images, voice signals

22 Communication channels The physical communication media + related modules like amplifiers and antennas Outside the control of the source encoder Often unreliable due to various distortions Noise, interference, etc.

23 Main topics

24 Source coding Discrete source coding Just represent each symbol with a binary digit sequence How long should the sequence be? Analog source coding Discretize - Sample (fast enough) and quantize Then follow discrete source coding

25 Channel coding Encoding: Mapping binary sequences to waveforms The elementary waveform Using amplitude, phase; absolute value vs differentials; Decoding: Find the most likely binary sequence Received signal is noisy, always somewhat different from the transmitted signal

26 Error correction Simple modulation/demodulation techniques incur errors Add error correction to simple modulator (in what order?) Can achieve arbitrarily low error rate within channel capacity Many well-known error correction codes

27 Digital interfaces Complicating factors Unmatched rates between source and channel Think video streaming Errors: source (de)coding is usually lossless, channel (de)coding isn t From links to the network Network protocols

28 A few recurring themes Information theory Stochastic processes Probabilistic descriptions of inputs and outputs Sampling theory Detection, estimation,

29 Related courses (F 15) EENG 442 / AMTH 342 / ENAS 902 Linear Systems This course EENG 450 Applied Digital Signal Processing EENG 452 / ENAS 952 Internet Engineering

30 Related courses (S 16) EENG 451 / ENAS 951 Wireless Communications EENG 454 / AMTH 364 / ENAS 954 / STAT 364 / STAT 664 Information Theory ENAS 496 / ENAS 502 Probability & Stochastic Processes ENAS 963 Network Algorithms and Stochastic Optimization CPSC 433 / CPSC 533 Computer Networks

31 Some related courses Not offered this year ENAS 964 Communication Networks CPSC 434 / CPSC 534 Mobile Computing and Wireless Networking

32 This course Overview of digital communication systems A major branch of EE and related disciplines Focuses on signal representation Introduction to specialized topics E.g., wireless digital communication, sampling theory Useful concepts and tools beyond communication E.g., entropy in the context of security, data privacy

33 Administrative Details

34 Personnel Instructor: Wenjun Hu Room 17HLH Office hours: 4-6pm Mondays (tentative), or by appointment In general, feel free to stop by my office or any questions or suggestions

35 Goals of this course Understand the principles of digital communication Learn the basic concepts and mathematical tools Concepts as abstractions to reason about systems Helps you understand the fundamental limitations Apply the understanding to system building

36 Resources Textbook (on theoretical background) Gallager. Principles of Digital Communication Resources online Course material will be posted on the course web site See also material from MIT OpenCourseWare based on the same course This is the standard version

37 Three levels of understanding Non-EE students Know the basic concepts (qualitatively) Maybe build systems EE majors Learn the analytical foundations (quantitatively) EE PhD students (the standard version) Understand why everything works Use the mathematical tools

38 What do you need to do Tell me your background and interest Help me determine what level suits you The actual course material will adapt to your level and interest Your workload 4-5 problem sets, the last one a pseudo final Intro projects, mostly fixed Design project, flexible

39 Grading Approximate breakdown Problem sets 40%, projects 45% Oral review 10%, classroom participation 5% Please ask questions!! Subject to adjustment after I learn your background What you learn is more important than the grades!!

40 Tentative schedule Overview and introduction in the first three weeks, detailed exploration afterwards Helps you decide whether to take the course Start planning projects Homework starts after shopping period Detailed preliminary schedule linked from course site

41 Warning It will be more mathematical in future lectures I.e., you ll see formulae!

42 Any Questions?

ENGR 4323/5323 Digital and Analog Communication

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