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communication system Chapter 6
communication system Chapter 6
communication system Chapter 6
communication system Chapter 6
communication system Chapter 6
communication system Chapter 6
communication system Chapter 6
communication system Chapter 6
communication system Chapter 6
communication system Chapter 6
communication system Chapter 6
communication system Chapter 6
communication system Chapter 6
communication system Chapter 6
communication system Chapter 6
communication system Chapter 6
communication system Chapter 6
communication system Chapter 6
communication system Chapter 6
communication system Chapter 6
communication system Chapter 6
communication system Chapter 6
communication system Chapter 6
communication system Chapter 6
communication system Chapter 6
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communication system Chapter 6

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  • 1. Communication System Ass. Prof. Ibrar Ullah BSc (Electrical Engineering) UET Peshawar MSc (Communication & Electronics Engineering) UET Peshawar PhD (In Progress) Electronics Engineering (Specialization in Wireless Communication) MAJU Islamabad E-Mail: ibrar@cecos.edu.pk Ph: 03339051548 (0830 to 1300 hrs) 1
  • 2. Chapter-6 Sampling And Pulse Code Modulation 1. Sampling 2. Signal interpolation 3. Pulse code modulation 2
  • 3. Sampling 3
  • 4. Sampling (Cont…) 4
  • 5. Sampling (Cont…) 5
  • 6. Signal Interpolation 6
  • 7. Signal Interpolation (Cont…) 7
  • 8. Signal Interpolation (Cont…) 8
  • 9. Signal Interpolation (Cont…) 9
  • 10. Pulse Code Modulation 10
  • 11. Pulse Code Modulation (Cont…) 11
  • 12. Pulse Code Modulation (Cont…) 12
  • 13. Pulse Code Modulation (Cont…) 13
  • 14. Noise In any real physical system, when the signal voltage arise at the demodulator, it will be accompanied by a voltage waveform which varies with time in an entirely unpredictable manner. This unpredictable voltage wave form is a random process called noise. Types of Noise Most man made electro-magnetic noise occurs at frequencies below 500 MHz. The most significant of these include: • Hydro lines • Ignition systems • Fluorescent lights • Electric motors Therefore deep space networks are placed out in the desert, far from these sources of interference. 14
  • 15. Types of Noise (cont..) • There are also a wide range of natural noise sources which cannot be so easily avoided, namely: • Atmospheric noise - lighting < 20 MHz • Solar noise - sun - 11 year sunspot cycle • Cosmic noise - 8 MHz to 1.5 GHz • Thermal or Johnson noise. Due to free electrons striking vibrating ions. • White noise - white noise has a constant spectral density over a specified range of frequencies. Johnson noise is an example of white noise. • Gaussian noise - Gaussian noise is completely random in nature however, the probability of any particular amplitude value follows the normal distribution curve. Johnson noise is Gaussian in nature. • Shot noise - bipolar transistors (caused by random variations in the arrival of electrons or holes at the output electrodes of an amplifying device) • Transit time noise - occurs when the electron transit time across a junction is the same period as the signal. 15 • Of these, only Johnson noise can be readily analyzed and compensated
  • 16. Noise power • The noise power is given by: Pn = kTB • Where: • k = Boltzman's constant (1.38 x 10-23 J/K) • T = temperature in degrees Kelvin • B = bandwidth in Hz • If the two signals are completely random with respect to each other, such as Johnson noise sources, the total power is the sum of all of the individual powers: 16
  • 17. Noise power (Cont..) • A Johnson noise of power P = kTB, can be thought of as a noise voltage applied through a resistor, Thevenin equivalent. An example of such a noise source may be a cable or transmission line. The amount of noise power transferred from the source to a load, such as an amplifier input, is a function of the source and load impedances 17
  • 18. Noise power (Cont..) The rms noise voltage at maximum power transfer is: Observe what happens if the noise resistance is resolved into two components: 18
  • 19. Noise Figure • The terms used to quantify noise : • Signal to noise ratio: It is either unit-less or specified in dB. The S/N ratio may be specified anywhere within a system. Noise Factor (or Noise Ratio): (unit less) 19
  • 20. Noise Figure (cont..) • This parameter (i.e. Noise Figure ) is specified in all high performance amplifiers and is measure of how much noise the amplifier itself contributes to the total noise. In a perfect amplifier or system, NF = 0 dB. This discussion does not take into account any noise reduction techniques such as filtering or dynamic emphasis. 20
  • 21. Noise Figure (cont..) • Friiss' Formula & Amplifier Cascades • It is interesting to examine an amplifier cascade to see how noise builds up in a large communication system. Amplifier gain can be defined as: Therefore the output signal power is: 21
  • 22. Noise Figure (cont..) and the noise factor (ratio) can be rewritten as: The output noise power can now be written: From this we observe that the input noise is increased by the noise ratio and amplifier gain as it passes through the amplifier. A noiseless amplifier would have a noise ratio (factor) of 1 or noise figure of 0 dB. In this case, the input noise would only be amplified by the gain since the amplifier would not contribute noise. Friiss' Formula 22
  • 23. Model Paper Communication system CU-510 5th semester Deptt. Of Electrical Engineering, CECOS Univ. Total Time: 3 hrs Q # 1 Time: 30 minutes (1):Is frequency modulation a linear modulation? A) Yes B) No (2): Does Dirichlet’s condition require a signal to be absolutely integrable? A) Yes B) No (3): suitable measure for this signal is ----------- 23
  • 24. Q#2 (a) (b): Differentiate between Energy and power signals what is correlation. 24
  • 25. The end 25

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