Noise in Communication Systems Chapter # 2 Lecture # 3

1. Noise in Communication Systems Chapter # 2 Lecture # 3

2. Outline : • Introduction • Thermal Noise • Shot Noise • Signal - to – Noise • Noise Factor – Noise Figure • Noise Temperature • BER Noise in Communication Systems

3. Learning Outcomes Student Able to : • Define noise and describe the prominent sources of electrical noise • Explain and calculate the most common types of noise in communication system

4. Introduction Noise is the static you hear in the speaker when you tune any AM or FM receiver to any position between stations. It is also the “snow” or “confetti” that is visible on a TV screen.

5. Noise is a general term which is used to describe an “unwanted signal which affects a wanted signal.” Noise is a random signal that exists in a communication system. Random signal cannot be represented with a simple equation. Introduction

6. Sources of noise Noise Internal Noise External Noise • Man-made noise and natural resources • External noise comes from sources over which we have little or no control • Industrial sources • motors, generators, manufactured equipment • Atmospheric sources / static electricity • speaker when there is no signal present • Due to random movement of electrons in electronic circuit. • Electronic components in a receiver such as resistors, diodes, and transistors are major sources of internal noise • Thermal (agitation) noise • Shot noise • Transit time noise

7. Introduction (Cont’d) • The noise level in a system is proportional to temperature and bandwidth, the amount of current flowing in a component, the gain of the circuit, and the resistance of the circuit.

8. Noise Effect • Degrade system performance for both analog and digital systems. • The receiver cannot understand the original signal. • The receiver cannot function as it should be. • Reduce the efficiency of communication system.

9. Noise - Type of Noise • The are several types of noise, among them are: • Atmospheric • Extraterrestrial (Cosmic & Solar) • Thermal Noise • White Noise • Shot Noise • Quantization Noise

10. Atmospheric Noise (Static) • Results due to spurious radio waves inducing voltages at antenna creating spurious waveforms • Reasons • Weather conditions (moisture, lightening and thunder) • Dominant upto 30 MHz

11. Extraterrestrial • Solar • Due to radiation from sun • Cosmic • Due to radiations from other heavenly bodies

12. Industrial • Created by man due to several reasons • Line passing near by a transformer • Interference by other coexisting equipment • (TV remotes and IR equipments)

13. Thermal noise is the result of the random motion of charged particles (usually electrons) in a conducting medium such as a resistor. Thermal Noise (Johnson Noise /white noise) This type of noise is generated by all resistances (e.g. a resistor, semiconductor, the resistance of a resonant circuit, i.e. the real part of the impedance, cable etc). Movement of the electrons will forms kinetic energy in the conductor related to the temperature of the conductor. When the temperature increases the movement of free electrons will increases and the current flows through the conductor.

14. Experimental results (by Johnson) and theoretical studies (by Nyquist) give the mean square noisevoltage as Thermal Noise (Johnson Noise) (Cont’d) Where k = Boltzmann’s constant = 1.38 x 10-23 Joules per K T = absolute temperature (Kelvin) B = bandwidth noise measured in (Hz) R = resistance (ohms)

15. For example : 50 kΩ resistor at a temperature of 290 K, 3 kHz bandwidth. Find Vrms value of noise: Thermal Noise (Johnson Noise) Vn = √ 4 x 1.38 x 10-23 x 290 x 3000 x 50 x 103 = 49 nV

16. Example 1.4 One operational amplifier with a frequency range of (18-20) MHz has input resistance 10 k. Calculate noise voltage at the input if the amplifier operate at ambient temperature of 270C. Vn2 = 4KTBR = 4 x 1.38 x 10-23 x (273+ 27) x 2 x 106 x 104 Vn = 18 volt

17. Thermal Noise (Johnson noise) This thermal noise may be represented by an equivalent circuit as shown below Analysis of Noise In Communication Systems (mean square value , power) then VRMS = i.e. Vn is the RMS noise voltage.

18. Resistors in Series Assume that R1 at temperature T1 and R2 at temperature T2, then Analysis of Noise In Communication Systems (Cont’d) i.e. The resistor in series at same temperature behave as a single resistor

19. Shot noise is a type of electronic noise that occurs when the finite number of particles that carry energy, such as electrons in an electronic circuit or photons in an optical device • Shot noise was originally used to describe noise due to random fluctuations in electron emission from cathodes in vacuum tubes (called shot noise by analogy with lead shot). • Shot noise also occurs in semiconductors due to the release of charge carriers. • Shot noise is found to have a uniform spectral density as for thermal noise(White noise) Shot Noise

20. Flicker Noise • Also known as low frequency noise • Also known as pink noise • Also known as 1/f noise • It occurs due to fluctuations in current desnity of the carrier currents • RMS value is proportional to the square of the current

21. Transit Time Noise • Due to time taken by the carriers to cross the junction • Also known as high frequency noise

22. How to determine noise level in communication system? • Noise effect can be determined by measuring: - Signal to Noise Ratio, SNR for analog system - Noise Factor, F - Noise Temperature, Te . - probability of error or bit error rate, BER for digital system • To determine the quality of received signal at the receiver or an antenna, SNRiis used. • SNR o is always less than SNRi, due to the facts that the existence of noise in the receiver itself. In the receiver usually constitute a process of filtering, demodulation and amplification.

23. dB Noise Calculation • SNR is a ratio of signal power,S to noise power, N. • Noise Figure, F • Noise factor, NF

24. The signal to noise ratio is given by Signal to Noise The signal to noise in dB is expressed by for S and N measured in mW.

25. Signal to Noise • Example : For an amplifier with an output signal power of 10 W and an output noise power of 0.01 w, determine the signal to noise power ratio • Solution : • To express in dB;

26. Signal to Noise • Example : For an amplifier with an output signal voltage of 4V, an output noise voltage of 0.005 V, and an input and output resistance of 50 ohm, determine the signal to noise power ratio. Solution :

27. Noise Factor- Noise Figure (Cont’d) Consider the network shown below, Noise factor, F = lower the value of F, the better the network. • F equals to 1 for noiseless and in general F > 1.

28. Noise Factor- Noise Figure (Cont’d) • Noise figure (NF) is the Noise factor converted to dB Noise Figure (NF) dB = 10 log10 (F) If every variable is a dB Noise figure; • NF = SNRin − SNRout

29. Equivalent noise temperature Te is not the physical temperature of the amplifier, but rather a theoretical construct that is an equivalent temperature that produces that amount of noise power Noise Temperature Noise temperature (Te) is expressed as : Where; Te = equivalent noise temperature (Kelvin) T = environmental temperature (reference value of 290 K) F = Noise factor Te = T(F-1)

30. Transmission Loss

31. What is Error Rate? • The error rate is the degree of errors in the transmission of data due to bad hardware or noisy links. The higher the error rate the less reliable the connection or data transfer will be. • It occurred in digital communication.

32. BER = The number of erroneous bits received total number of bits transmitted

34. Noise - Bit Energy The signal also measured in terms of the bit energy in joules (J), Eb. The enery per bit is simply the energy of a single bit of information, Eb . It is defined as below: Eb = energy of a single bit (joules per bit) Tb = time of a single bit (seconds) C = carrier power (watts) Eb= CTb(J/bit)

35. Summary • Thermal Noise • Signal - to – Noise • Noise Factor • Noise Figure • Noise Temperature Noise Figure (NF) dB = 10 log10 (F) Te = T(F-1)