CHAPTER 5 NOISE IN COMMUNICATION SYSTEM Noise PLT

CHAPTER 5: NOISE IN COMMUNICATION SYSTEM -Noise- PLT 208 – COMMUNICATION SYSTEMS

INTRODUCTION What is noise? • undesired random variations that interface with the desired signal and inhibit communication. • Electrical noise – undesirable electrical energy that falls within the pass-band of the signal Where does noise originate in a communication system? • Channel @ transmission medium • Devices @ Equipment PLT 208 – COMMUNICATION SYSTEMS

INTRODUCTION PLT 208 – COMMUNICATION SYSTEMS

INTRODUCTION Noise Effect • One of the main limiting factor in obtaining high performance of a communication system. • Decrease the quality of the receiving signal. PLT 208 – COMMUNICATION SYSTEMS

Block Diagram of Communication System With the Existence of Noise PLT 208 – COMMUNICATION SYSTEMS

INTRODUCTION • 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. �Can be reduced by filtering but can’t totally eliminated. PLT 208 – COMMUNICATION SYSTEMS

INTRODUCTION ▫ 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. PLT 208 – COMMUNICATION SYSTEMS

INTRODUCTION ▫ Distortion �The signal perturbation caused by imperfect response of the system to the desired signal. �Disappear when the signal is turned-off. �Can be corrected by the equalizers. PLT 208 – COMMUNICATION SYSTEMS

Noise Remedies? REDUCE BANDWIDTH INCREASE TRANSMITTER’S POWER LOW NOISE AMPLIFIERS PLT 208 – COMMUNICATION SYSTEMS

Noise Categories Correlation implies a relationship between the signal and the noise. CORRELATED NOISE exists only when a signal is present. PLT 208 – COMMUNICATION SYSTEMS UNCORRELATED NOISE present all the time whethere is signal or not.

Correlated Noise • Exists only when a signal is present. • Is a form of internal noise that is correlated to the signal. • Produced by nonlinear amplification and includes harmonic and intermodulation distortion (both of which are forms of nonlinear distortion/amplitude distortion). • Nonlinear distortion creates unwanted frequencies that interfere with the signal and degrade performance. PLT 208 – COMMUNICATION SYSTEMS

Types of Uncorrelated Noise PLT 208 – COMMUNICATION SYSTEMS

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. PLT 208 – COMMUNICATION SYSTEMS

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). PLT 208 – COMMUNICATION SYSTEMS

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. PLT 208 – COMMUNICATION SYSTEMS

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). PLT 208 – COMMUNICATION SYSTEMS

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. PLT 208 – COMMUNICATION SYSTEMS

Cont’d. . . • 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. PLT 208 – COMMUNICATION SYSTEMS

Cont’d. . . • 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. PLT 208 – COMMUNICATION SYSTEMS

Cont’d. . . • 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 zigzag due to collision with the lattice structure. PLT 208 – COMMUNICATION SYSTEMS

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. ▫ Resistors and the resistance within all electronic devices are constantly producing noise voltage Vn(t). ▫ Since it is dependent on temperature, it is also referred to as thermal noise. PLT 208 – COMMUNICATION SYSTEMS

Cont’d. . . • 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. Np = k T B Where Np = noise power (Watt) k = Boltzman constant (1. 38 x 10 -23 J/K) T = conductor temperature (K) [Add 273 to C] B = Bandwidth of system (Hz) • Noise spectrum density is constant for all value of frequency to 1012 Hz. PLT 208 – COMMUNICATION SYSTEMS

Cont’d. . . • From the study of circuit theory, the relationship between source resistor and matched load under maximum power transfer is when Rn = RL. • The total of noise source power is Pn. PLT 208 – COMMUNICATION SYSTEMS

Cont’d. . . • Known as Rn = RL = R, • Therefore voltage at RL is PLT 208 – COMMUNICATION SYSTEMS

Example 1 • A receiver has a BW of 10 k. Hz 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. PLT 208 – COMMUNICATION SYSTEMS

Example 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. PLT 208 – COMMUNICATION SYSTEMS

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). PLT 208 – COMMUNICATION SYSTEMS

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, Te. and noise figure, NF PLT 208 – COMMUNICATION SYSTEMS

Noise Calculation • SNR is ratio of signal power, S to noise power, N. • Noise Factor, F • Noise Figure, NF PLT 208 – COMMUNICATION SYSTEMS

Noise Calculation In Amplifier • Two types of model - Noise amplifier Model. - Noiseless amplifier model. PLT 208 – COMMUNICATION SYSTEMS

Analysis of Noise Amplifier Model PLT 208 – COMMUNICATION SYSTEMS

Analysis of Noiseless Amplifier Model PLT 208 – COMMUNICATION SYSTEMS

SNR 0 <<< SNRi As known as Noise Factor, Noise Temperature, PLT 208 – COMMUNICATION SYSTEMS

Analysis of Cascade Stages • Consider three two ports in cascade antenna Si Ni Ti F 3, Te 3 F 1, Te 1 G 1 Nai 1 pre-amplifier Stage 1 PLT 208 – COMMUNICATION SYSTEMS Nai 2 F 2, G 2, Te 2 demodulator Stage 2 G 3 Nai 3 amplifier Stage 3 So No

Stage 1 PLT 208 – COMMUNICATION SYSTEMS

Stage 2 PLT 208 – COMMUNICATION SYSTEMS

Stage 3 PLT 208 – COMMUNICATION SYSTEMS

Noise Factor, F PLT 208 – COMMUNICATION SYSTEMS

Known as the overall noise factor, FTOTAL PLT 208 – COMMUNICATION SYSTEMS

And we can calculate noise temperature, Te PLT 208 – COMMUNICATION SYSTEMS

It can also be shown that the overall noise figure, F and the effective noise temperature, Te of n networks in cascade is given by: PLT 208 – COMMUNICATION SYSTEMS

Transmission Loss, Attenuator • Every transmission medium will produce power loss. Pout < Pin. § Power loss or attenuated is given by the following equation: PLT 208 – COMMUNICATION SYSTEMS

Cont’d. . . • We also can calculate by using this following equation; Where ℓ = transmission medium length α = attenuated constant PLT 208 – COMMUNICATION SYSTEMS

Example 3 Determine: a. Noise Figure for an equivalent noise temperature of 75 K (use 290 K for the reference temperature). b. Equivalent noise temperature for a Noise Figure of 6 d. B. PLT 208 – COMMUNICATION SYSTEMS

Example 4 • For three cascaded amplifier stages, each with noise figure of 3 d. B and power gain of 10 d. B, determine the total noise figure. PLT 208 – COMMUNICATION SYSTEMS

Example 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 d. B when correctly matched and the noise figure is 6 d. B. Calculate the overall power gain and noise figure of the amplifier. PLT 208 – COMMUNICATION SYSTEMS