Fall 2012 Afshin Hemmatyar Sharif University of Technology International Campus – Kish Island Data Communications Introduction

Contents Background and Preview Random Process Continuous-Wave Modulation Pulse Modulation Base-band Pulse Transmission Signal-Space Analysis Pass-band Digital Transmission Spread-Spectrum Modulation 2

References Simon Haykin, “Communication Systems,” 4 th Edition, B.P. Lathi, “Modern Analog and Digital Communication Systems,” 3 rd Edition, John J. Proakis, “Digital Communications,” 3

Background and Preview Digital Communication System Communication Channels Mathematical Models for Communication Channels Primary Communication Resources Basic Modes of Communication Channel Sharing Information Capacity of Channel 4

Digital Communication System (1) 5

Digital Communication System (2) Information Source Generates message signals: Voice, Music, Picture, or Data. Source Encoder Removes redundant information from message signal and is responsible for efficient use of channel. Channel Encoder Adds controlled redundancy and produces sequence of symbols regarding channel specifications. Modulator Represents symbols in waveforms suitable for transmission over the physical media of interest. 6

Communication Channels (1) Wire-line (Twisted Pair, Coaxial Cable,... ) Fiber Optic Wireless (Electromagnetics) (Broadcast, Mobile, Satellite,... ) Underwater Acoustic Storage 7

Communication Channels (2) Linear or Nonlinear Time Invariant or Time Varying Frequency Dependent or Independent Bandwidth Limited or Power Limited 8

Communication Channels (3) 9

Mathematical Models for Communication Channels Additive Noise R(t) = C.S(t) + n(t) LTI Filter R(t) = C(t)*S(t) + n(t) LTV Filter R(t) = C(t,τ)*S(t) + n(t) 10

Primary Communication Resources Transmitter Power Average power of transmitted signal Channel Bandwidth Band of frequencies allocated for Transmission Usually one is more important: Power Limited Channel Band Limited Channel 11

Basic Modes of Communications Point-to-Point Broadcasting Unidirectional (Simplex) Bidirectional (Half and Full Duplex) 12

Channel Sharing Multiplexing FDM: Frequency-Division Multiplexing (WDM: Wavelength-Division Multiplexing) TDM: Time-Division Multiplexing CDM: Code-Division Multiplexing Multiple Access FDMA: Frequency-Division Multiple Access (WDMA: Wavelength-Division Multiple Access) TDMA: Time-Division Multiple Access CDMA: Code-Division Multiple Access 13

Information Capacity of Channel Shannon’s Theorem C = B log 2 (1+SNR) Channel Capacity in bits/Sec Signal to Noise Ratio (no units) Channel Bandwidth in Hz 14