1. CHAPTER 5 5.1 Noise 5.2 Transmission Media & EM Propagations EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

2. Introduction Define as undesired random variations that interface with the desired signal and inhibit communication. Where does noise originate in a communication system? Channel @ transmission medium Devices @ Equipments EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

3. Cont’d... Noise Effect One of the main limiting factor in obtaining high performance of a communication system. Decrease the quality of the receiving signal. EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

4. Block Diagram of Communication System With the Existence of Noise EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

5. Cont’d... Noise, interference and distortion Noise, interference and distortion Noise Refers to random and unpredictable electrical signals produced by natural process. Superimposed on information bearing signal, the message partially corrupted or totally erased. reduced Can be reduced by filtering but can’t totally eliminated. EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

6. Cont’d... Interference A contamination by extraneous signals from human sources (e.g. from other Tx, power lines, machineries) Often occurred in radio system whose Rx antenna intercept several signals at the same time. EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

7. Cont’d... Distortion Distortion The signal perturbation caused by imperfect response of the system to the desired signal. Disappear when the signal us turned- off. Can be corrected by the equalizers. EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

8. Noise Remedies? REDUCE BANDWIDTH INCREASE TRANSMITTER’S POWER LOW NOISE AMPLIFIERS EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

9. Types of NOISE EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

10. External Noise Cont’d... External Noise Noise generated outside the electronic equipment used. Source can be terrestrial or extraterrestrial (E.g. the earth, the moon, the sun, the galaxies). Do not effect the entire communication frequency spectrum but affect certain frequencies at certain times and locations. Types: Man made noise, space noise, atmospheric noise. EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

11. Cont’d... a) Man made noise o Produced by mankind o Source : Spark-producing mechanisms o Impulsive in nature & contains a wide range of frequencies propagated through space. o Sometimes called industrial noise (metropolitan & industrial area). EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

12. Cont’d... b)Space noise o The sun is a powerful source of radiation. o Stars also radiate noise called cosmic, stellar or sky noise. o Important at higher frequencies (VHF and above) because atmospheric noise dominates at lower frequencies. EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

13. Cont’d... c. Atmospheric noise o The principle source is lightning ( a static electricity discharge. o Can propagate for a long distances through space. o The lightning energy relatively low frequency (up to several MHz). EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

14. Internal Noise Cont’d... Internal Noise Electronic noise generated by the passive and active components incorporated in the designs of communications equipment. - Types : Shot noise, flicker noise, thermal noise. EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

15. Cont’d... Shot Noise Shot Noise o Caused by a random arrival of carriers (holes and electrons) at the output of an electronic devices. o Randomly varying & superimposed onto any signal present. o Sometimes called transistor noise. EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

16. Cont’d... Flicker noise Flicker noise o Excess noise that related to dc current flow through imperfect conductors. o The real nature of flicker noise not yet fully understood. EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

17. Thermal Noise This type of noise arise due to the random motion of free electrons in the conducting medium such as resistor. Each free electron inside a resistor is in motion due to its thermal energy. The path of electron motion is random and zig-zag due to collision with the lattice structure. EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

18. Cont’d... The net effect of the motion of all electrons constitutes an electric current flowing through the resistor. It causes the rate of arrival of electron at either end of a resistor to vary randomly and thereby varies the resistor’s potential difference. That is the direction of current flow is random and has a zero mean value. EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

19. Cont’d... Resistors and the resistance within all electronic devices are constantly producing noise voltage V n (t). Since it is dependent on temperature, it is also referred to as thermal noise. EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

20. Thermal noise also known as Johnson noise or white noise. In 1928, J.B. Johnson founded that Noise Power is direct proportionally with temperature and bandwidth. Noise spectrum density is constant for all value of frequency to 10 12 Hz. Watt Where P n = noise power ( Watt ) k = Boltzman constant (1.38 x 10 -23 joules per kelvin ) T = conductor temperature ( K ) [Add 273 to C] B = Bandwidth of the system ( Hz ) P n = k T B EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

21. From the study of circuit theory, the relationship between source resistor and matched load under maximum power transfer is when R n = R L. The total of noise source power is P n. EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

22. Known as R n = R L = R, Therefore voltage at R L is EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

23. Example 5.1 A receiver has a BW of 10 kHz with the 4.14 x 10 -17 W noise power. A resistor that matches the receiver input impedance is connected across its antenna terminals. Calculate the resistor’s temperature in Celsius. EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

24. Example 5.2 A 1 kΩ resistor is connected across 1 kΩ antenna input of a television receiver. The BW of the receiver is 5 MHz and the resistor at the room temperature 293 K. Calculate the noise power and noise voltage applied to the receiver input. EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

25. How to Quantifying the Noise? The presence of noise degrades the performance of analog and digital communication. The extent to which noise affects the performance of communication systems is measured by the output signal to noise power ratio or SNR (for analog communication systems) and probability of error (for digital communication systems). EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

26. Cont’d... The signal quality at the input of the receiver is characterized by the input signal to noise ratio. Because of the noise sources within the receiver, which is introduced during the filtering and amplification processes, the SNR at the output of the receiver will be lower than at the input of the receiver. This degradation in the signal quality is characterized in terms of noise equivalent bandwidth, N 0, effective noise temperature, T e. and noise figure, F EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

27. Noise Calculation SNR is ratio of signal power, S to noise power, N. Noise Factor, F Noise Figure, NF EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

28. Noise Calculation In Amplifier o Two types of model - Noise amplifier Model. - Noiseless amplifier model. EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

29. Analysis of Noise Amplifier Model EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

30. Analysis of Noiseless Amplifier Model EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

31. SNR 0 <<< SNR i As known as Noise Factor, Noise Temperature, EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

32. Analysis of Cascade Stages Consider three two ports in cascade G3G3 SoNoSoNo G1G1 F 2, G 2, T e2 antenna pre-amplifier demodulatoramplifier F 1, T e1 F 3, T e3 SiNiTiSiNiTi N ai1 N ai2 N ai3 S1N1S1N1 S2N2S2N2 Stage 1 Stage 2 Stage 3 EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

33. Stage 1 EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

34. Stage 2 EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

35. Stage 3 EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

36. Noise Factor, F EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

37. Known as the overall noise factor, F TOTAL EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

38. And we can calculate noise temperature, T e EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

39. It can also be shown that the overall noise figure, F and the effective noise temperature, T e of n networks in cascade is given by: EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

40. Transmission Loss, Attenuator Every transmission medium will produce power loss. P out < P in.  Power loss or attenuated is given by the following equation: EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

41. Cont’d...  We also can calculate by using this following equation; Where ℓ = transmission medium length α = attenuated constant EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

42. Example 5.3 Determine: a. Noise Figure for an equivalent temperature of 75 K (use 290 K for the reference temperature). b. Equivalent noise temperature for a Noise Figure of 6 dB. EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

43. Example 5.4 For three cascaded amplifier stages, each with noise figure of 3dB and power gain of 10 dB, determine the total noise figure. EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

44. Example 5.5 An amplifier consists of three identical stages in tandem. Each stage having equal input and output impedances. For each stages, the power gain is 8 dB when correctly matched and the noise figure is 6dB. Calculate the overall power gain and noise figure of the amplifier. EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

45. External Atmospheric static space noise solar flare sunspot solar flux cosmic Man made Any noise generated outside a receiver Electrical disturbances outside in the earth’s atmosphere Lightning strikes Sun and star disturbances Violent storm on sun’s surface Massive magnetic storm on sun Varies with frequency, increases when solar flares occurs From stars more distance than sun Any form of electromagnetic interference from non natural causes. Ignition and impulse noise from combustion engines and electrical appliances; high voltage lines; fluorescent lights. Summary (Noise sources and causes) EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM

46. Internal Thermal Shot Random noises from active or passive devices inside receiver Also termed thermal agitation, White or Johnson generated by rapid and random motion of atoms and electrons. Related directly to bandwidth. From shot effect, caused by random variation in arrival of majorities carriers at the output of an amplifying device. Summary (Cont’d) EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : NOISE IN COMMUNICATION SYSTEM