# © Kemal AkkayaWireless & Network Security 1 Department of Computer Science Southern Illinois University Carbondale CS591 – Wireless & Network Security.

## Presentation on theme: "© Kemal AkkayaWireless & Network Security 1 Department of Computer Science Southern Illinois University Carbondale CS591 – Wireless & Network Security."— Presentation transcript:

© Kemal AkkayaWireless & Network Security 1 Department of Computer Science Southern Illinois University Carbondale CS591 – Wireless & Network Security Lecture 1: Communication Basics Dr. Kemal Akkaya E-mail: kemal@cs.siu.edu

© Kemal AkkayaWireless & Network Security 2 Transmission Fundamentals  How to relay information?  Electromagnetic Signals  TV, Radio, Internet etc. qSignal  A function of time  Has 3 components: Amplitude (A) : Signal strength Frequency (f) : # of cycles Phase (  ) : Relative position  Sine wave for the signal s(t) = A sin(2  f t +  )  Either analog or digital  Wavelength (λ): Distance occupied by 1 cycle λ = c*T = c / f Analog: No breaks in the signal Digital: Signal intensity is discrete 1 Cycle Wavelength Amplitude

© Kemal AkkayaWireless & Network Security 3 Effects on Signal  Attenuation:  Decrease in amplitude of signal along transmission  Distortion:  Interference of different frequency components of a signal  Noise:  In the absence of signal, there is random mixture of frequencies on the channel called channel noise  Error:  When digital signals are combined with noise, some bits can be received in error

© Kemal AkkayaWireless & Network Security 4 Signal/Bandwidth/Data Rate  Signal may include many frequencies  Combination of sinusoids  Spectrum:  Range of frequencies a signal contains  The signal in the figure contains frequencies between f and 3f  Bandwidth:  Width of the spectrum is called bandwidth  Bandwidth for the figure : 3f – f = 2f  Increasing the bandwidth makes the wave look like more square (i.e. digital signal)  Hence, increasing the bandwidth helps to reduce the distortion at the receiver side. sin(2  ft)+(1/3) sin(2  3ft) Bandwidth = 7f – f = 6f How much data can we communicate with a certain bandwidth?

© Kemal AkkayaWireless & Network Security 5 Analog and Digital Data Transmission  How analog and digital signals are transmitted?  Analog signals (continuous) can be propagated through Wire, twisted pair, coaxial cable, fiber optic cable and atmosphere  Digital signals (discrete) can only propagated through Wired medium – No wireless since it requires infinite frequencies How to propagate digital signals then?  Digital data can be represented as analog signals: What does a Modem do? ?

© Kemal AkkayaWireless & Network Security 6 How to do that encoding?  Modulation is the solution:  Modulate digital data so that an analog signal is generated  Modem would be the classical example  Motivation: When only analog transmission facilities are available, modulation is required to convert digital data into analog signals  How to do digital modulation?  Operation in on or more of the 3 characteristics of a signal  These are amplitude, frequency and phase  Three main techniques  ASK: Amplitude Shift Keying – digital data over optical fiber  FSK: Frequency Shift Keying – on LANs that use coaxial cable  PSK: Phase Shift Keying – 802.11 Networks

© Kemal AkkayaWireless & Network Security 8 Other digital modulation techniques  Binary Frequency Shift Keying (BFSK)  Uses two different frequencies  Multiple Frequency Shift Keying (MFSK)  More than two frequencies are used  Gaussian Frequency Shift Keying (GFSK)  Two level shift from base frequency : Bluetooth uses this  Binary Phase Shift Keying (BPSK)  Two phrases used to represent bits : In Satellite Systems  Differential Phase Shift Keying (DPSK)  Phase shift with reference to previous bit  Four-level (QPSK) and Multilevel Phase Shift Keying  Each element represents more than 1 bit  Differential QPSK (DQPSK) is used in 802.11b networks  Quadrature Amplitude Modulation (QAM)  Combination of ASK and PSK  Two different signals sent simultaneously on the same carrier frequency  Started to be used in Wireless Sensor Networks

© Kemal AkkayaWireless & Network Security 9 AM and FM Example AM FM

© Kemal AkkayaWireless & Network Security 10 Digitization  Converting analog data into digital signals  Digital data can then be transmitted using NRZ-L NRZ-L a way to transmit digital signals  Digital data can then be transmitted using code other than NRZ-L  Digital data can then be converted to analog signal  Analog to digital conversion done using a codec  Pulse Code Modulation (PCM)  Delta Modulation (DM) R s = Bit rate = # bits/sample x # samples/second         Original signal Sample value Approximation 3 bits / sample

© Kemal AkkayaWireless & Network Security 11 Multiplexing  Carrying multiple signals on a single medium  Capacity of transmission medium usually exceeds capacity required for transmission of a single signal  More efficient use of transmission medium: Combine multiple signals  Increased data rate provides cost efficiency  Transmission and reception equipment  Analog multiplexing  Frequency Division Multiplexing (FDM)  Digital Multiplexing  Time Division Multiplexing (TDM)

© Kemal AkkayaWireless & Network Security 12 FDM Example  Combining analog signals  Takes advantage of the fact that the useful bandwidth of the medium exceeds the required bandwidth of a given signal Transmission 3 Channels 1 Link Multiplexer

© Kemal AkkayaWireless & Network Security 13 TDM Example  Digital technique to combine data  Takes advantage of the fact that the achievable bit rate of the medium exceeds the required data rate of a digital signal

© Kemal AkkayaWireless & Network Security 14 Transmission Media for Signals  It is the physical path between transmitter and receiver  Guided media: Solid media such as copper, optical fiber etc.  Unguided media: Atmosphere or outer space: Wireless Transmission  Here is the electromagnetic spectrum for telecommunications:

© Kemal AkkayaWireless & Network Security 15 General Frequency Ranges  Microwave frequency range  1 GHz to 40 GHz  Used for satellite communications  Radio frequency range  3 KHz to 300 GHz  Can be analog : TV, Radio  Or digital: Cell phones, wireless networks Medium Wave Radio Electric Waves Radio Waves Infra-red Visible Light Ultra Violet X-Rays Gamma Rays Cosmic Rays 303 300 Long Wave Radio FM Radio GSM 3G Microwave Radio Links TV VLFLFMFHFVHFUHFSHFEHF Radio Spectrum kHzMHzGHz 330300 DECT WiFi Bluetooth TETRA LMDS 3 “Sweetspot”  Infrared frequency range  Roughly 3x1011 to 2x1014 Hz  Useful in local point-to-point multipoint applications within confined areas

© Kemal AkkayaWireless & Network Security 16 Frequency Regulations  Federal Communications Commission (FCC)  Charged with regulating interstate and international communications by radio, television, wire, satellite and cable  Prevent interferences between different devices Current Allocation of the Radio Spectrum by frequency

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