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Wireless & Network Security: Communication Basics and Transmission Fundamentals

Understand communication basics and transmission fundamentals in wireless and network security. Topics include signal effects, bandwidth, encoding techniques, digital modulation, and multiplexing. Learn about analog and digital data transmission, modulation, digitization, and multiplexing in this lecture.

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Wireless & Network Security: Communication Basics and Transmission Fundamentals

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  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 Wireless & Network Security 1

  2. Transmission Fundamentals 1 Cycle Wavelength Amplitude Analog: No breaks in the signal Digital: Signal intensity is discrete • How to relay information? • Electromagnetic Signals • TV, Radio, Internet etc. • Signal • 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 Wireless & Network Security 2

  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 Wireless & Network Security 3

  4. Signal/Bandwidth/Data Rate sin(2ft)+(1/3) sin(23ft) • 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. Bandwidth = 7f – f = 6f How much data can we communicate with a certain bandwidth? Wireless & Network Security 4

  5. Analog and Digital Data Transmission What does a Modem do? ? • 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: Wireless & Network Security 5

  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 Wireless & Network Security 6

  7. ASK, FSK and PSK Wireless & Network Security 7

  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 Wireless & Network Security 8

  9. AM and FM Example FM AM Wireless & Network Security 9

  10. Digitization 7D/2 5D/2 3D/2 D/2 -D/2 -3D/2 -5D/2 -7D/2 • 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) Original signal Sample value Approximation 3 bits / sample Rs = Bit rate = # bits/sample x # samples/second Wireless & Network Security 10

  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) Wireless & Network Security 11

  12. FDM Example 3 Channels 1 Link Transmission Multiplexer • Combining analog signals • Takes advantage of the fact that the useful bandwidth of the medium exceeds the required bandwidth of a given signal Wireless & Network Security 12

  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 Wireless & Network Security 13

  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: Wireless & Network Security 14

  15. General Frequency Ranges Electric Waves Radio Waves Visible Light Ultra Violet Gamma Rays Cosmic Rays Infra-red X-Rays Radio Spectrum “Sweetspot” 3G LMDS WiFiBluetooth DECT TETRA GSM FM Radio Medium Wave Radio Microwave Radio Links Long Wave Radio TV VLF LF MF HF VHF UHF SHF EHF 3 30 300 3 30 300 3 30 300 kHz MHz GHz • Infrared frequency range • Roughly 3x1011 to 2x1014 Hz • Useful in local point-to-point multipoint applications within confined areas • 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 Wireless & Network Security 15

  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 Wireless & Network Security 16

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