EKT 431 DIGITAL COMMUNICATIONS

MEETING LECTURE : 3 HOURS LABORATORY : 2 HOURS LECTURER PUAN NORSUHAIDA AHMAD /

OBJECTIVES To understand and use various terminologies in Digital Communications. To be able to explain the differences between analog and digital communications. To describe the basic building blocks of a digital communication system and the performance objectives for good communication. To analyze the signals transmission via channel. To study the baseband data transmission, digital modulation and spread spectrum communications. To explore the basic principles of telephony system.

Textbook Bernard Sklar “Digital Communications: Fundamental & Applications, 2 nd Ed.” Prentice Hall International New Jersey, October 2005

References Pursley M.B. “Introduction to Digital Communications”, IE Pearson Prentice Hall, 2005 M.Schwartz “ Information Transmission, Modulation and Noise”, McGraw Hill, 3rd Ed, 2003 Proakis, John G. “Digital Communications”, International Ed.- New York; 1995

Assessment Final Exam = 50 % Coursework = 50 %  Assignments/Quiz = 10 %  Tests = 10 % (only 1 test)  Labs/Tutorials = 30 %

Chapter overview Purpose of Digital Communications History & Development Block Diagram & transformations Digital versus analog performance Advantages & Disadvantages

Purpose of communication system To transport an information signal from source to destination via communication channel. Analog and digital type.

Cont’d... Analog communication  Information signal is continuously varying in amplitude & time.  Modify some characteristic of a sinusoidal carrier wave (e.g. amplitude, phase, frequency) Digital communication  Information signal is processed & represented by a sequence of discrete messages.

Growth factors a. Computer impact b. Flexibility & compatibility c. Improved reliability d. Wide band channels e. Integrated solid state technology

History, present & future requirements History.doc

Functional Blocks of a Digital Communications System Functional Block Diagram.doc

Cont’d... Information source Two categories Analog information sources Microphone actuated by speech or song TV camera scanning a picturesque scene Discrete information sources Teleprinter, Morse key operator Numerical output of a computer Source encoder/decoder Encoder – converts the symbol sequence into a binary sequence of 0’s & 1’s by assigning code words. Decoder – converts the binary output of the channel decoder into a symbol sequences.

Cont’d... Modulator/ Demodulator Modulator – accepts the bit stream as its input and converts it into an electrical waveform suitable for transmission. Demodulator – reversible process of modulation (the extraction of message from the information bearing waveform). Communication channel Real life, maybe a microwave channel, fiber optics, waveguides etc Physical limitation – finite bandwidth Channel encoder/decoder Encoding – block coding method & convolution coding method Decoder – recovers the information bearing bits from the coded binary stream, error detection and correction.

Typical Block Diagram Decrypt

Cont’d... Transmitter side – denote signal transformations from source to transmitter Receiver side – denote signal transformation from receiver to sink

Transformations 1. Formatting & source coding Character coding, sampling, quantization, PCM 2. Baseband signaling PCM waveforms, PAM, PPM, PDM 3. Equalization Equalization with filter 4. Bandpass signaling Coherent ( ASK,FSK, PSK) & non-coherent (DPSK) 5. Channel coding M-ary signaling, convolution, block

Cont’d Synchronization Frequency synchronization, phase synchronization, network synchronization 2. Mux & multiple access TDM,SDM, FDM, TDMA,CDMA 3. Spreading Frequency hopping, Time Hopping 4. Encryption Data stream

Digital versus analog  Analog Draw their waveforms from a continuum, infinite number of possible wave shapes Performance : SNR, percent distortion.  Digital Signals represent digits Performance : Probability of error

Advantages of Digital Communications Increased demand for data transmission. Integration of transmission and switching Possibility of channel coding Facility to source code for data compression Ease of multiplexing and signaling Use of modern technology Performance monitor ability Ease of encryption

Disadvantages of Digital Communications increased bandwidth need for time synchronization topological restricted multiplexing incompabilities with analog facilities