CHAPTER Noise 5.2 Transmission Media & EM Propagations

Announcement Test #1 set 2 4 April 2008 (Friday) Test #2 set #2 9 April 2008 (Wednesday) 8.30 p.m

Introduction Define as undesired random variations that interface with the desired signal and inhibit communication. Where does noise originate in a communication system? transmission medium Equipments

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.

Block Diagram of Communication System With the Existence of Noise

Cont’d... 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.

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.

Cont’d... 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.

Noise Remedies? REDUCE BANDWIDTH INCREASE TRANSMITTER’S POWER LOW NOISE AMPLIFIERS

Types of NOISE

Cont’d... 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.

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).

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.

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).

Cont’d... - Electronic noise generated by the passive and active components incorporated in the designs of communications equipment. - Types : Shot noise, flicker noise, thermal noise.

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.

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.

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.

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.

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.

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 Hz. Watt Where P n = noise power ( Watt ) k = Boltzman constant (1.38 x J / K ) T = conductor temperature ( K ) [Add 273 to C] B = Bandwidth of system ( Hz ) P n = k T B

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.

Known as R n = R L = R, Therefore voltage at R L is

Example 1 An electronic device operating at a temperature of 17 degree Celsius with a bandwidth of 10 kHz, determine the following: i) Thermal noise power in watts and dBm. ii) rms noise voltage for a 100 ohms load resistance. Ans: N=KTB = (1.38x J/K)(290)(1x10 4 )=4x W, N(dBm)=10 log[(4x W)/(1mW)] = -134dBm. rms noise voltage, V N =(4RKTB) 1/2 = µV.

How to Quantify 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).

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

Terms and definition Noise factor, F is the ratio of the noise produced by a real resistor to the simple thermal noise of an ideal resistor. Noise figure, NF (noise factor in dB) is a frequently used measure of an amplifier's goodness, or its departure from the ideal. Noise temperature, T e is a means for specifying noise in terms of an equivalent temperature. Thermal noise – In any object with electrical resistance the thermal fluctuations of the electrons in the object will generate noise

Noise Calculation SNR is ratio of signal power, S to noise power, N. Noise Factor, F Noise Figure, NF

Noise Calculation In Amplifier o Two types of model - Noise amplifier Model. - Noiseless amplifier model.

Analysis of Noise Amplifier Model N a - Noise inside the amplifier

Analysis of Noiseless Amplifier Model N ai - Noise at the input of the amplifier

SNR 0 <<< SNR i    noiseless amplifier model As known, noise power (sometimes referred as P n ) Noise Factor, Noise Temperature, Noise Factor, F

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

Stage 1

Stage 2

Stage 3

Noise Factor, F

Known as the overall noise factor, F TOTAL

And we can calculate noise temperature, T e From F=[1+T e /T i ]=[1+Te/T o ]

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: General equation for F and T e

Transmission Loss, Attenuator Every transmission medium will produce power loss. P out < P in. (ideally P out = P in )  Power loss or attenuated is given by the following equation:

Cont’d...  We also can calculate by using this following equation; Where ℓ = transmission medium length α = attenuated constant

Example 2 For an amplifier with an output signal voltage of 4V, an output noise voltage of V, and input and output resistance of 50 ohms, determine the signal to noise power ratio. Ans : [S/N](dB)=20 log [V s /V n ]=20 log [4/0.005]=58.06dB.

Example 3 For a non-ideal amplifier and the following parameters, determine a) Input S/N ratio (dB) b) Output S/N ratio (dB) c) Noise Factor and Noise Figure, given: input signal power = 2 x W. input noise power = 2 x W. Ans : [S/N] i= 100,000,000 [S/N] o =25,000,000 F=[100,000,000/25,000,000]=4 NF = 10 log 4 = 6dB.

Example 5 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.

Example 6 For three cascaded amplifier stages, each with noise figure of 3dB and power gain of 10 dB, determine the total noise figure.

Example 7 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.

Transmission Media / Channels

Introduction Provides the connection between the transmitter and receiver. 1. Pair of wires – carry electric signal. 2. Optical fiber – carries the information on a modulated light beam. 3. Free space – information-bearing signal is radiated by antenna EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : TRANSMISSION MEDIA / CHANNEL

Cont’d... Signal transmission problem  additive noise – generated internally by components used to implement the communication system.  Interference from other users of the channel. EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : TRANSMISSION MEDIA / CHANNEL

Cont’d... Minimizing noise effects Increasing the power of transmitted signal. Constraint Limited power level Channel bandwidth availability EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : TRANSMISSION MEDIA / CHANNEL

Cont’d... Channels Wire lines Wireless electromagnetic Fiber optics Underwater acoustic EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : TRANSMISSION MEDIA / CHANNEL

Cont’d... Wire Lines Channel Signals transmitted are distorted in both amplitude and phase. – corrupted by noise. Carry a large percentage of daily communication around the world. EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : TRANSMISSION MEDIA / CHANNEL

Cont’d... Twisted pair Coaxial cable EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : TRANSMISSION MEDIA / CHANNEL

Cont’d... Fiber Optics Channel Low signal attenuation Highly reliable photonic devices Large bandwidth available Services : voice, data facsimile and video Tx – light source (e.g. LED, laser) Rx – photodiode Noise source : photodiodes & amplifiers EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : TRANSMISSION MEDIA / CHANNEL

Cont’d... EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : TRANSMISSION MEDIA / CHANNEL

Cont’d... Wireless Electromagnetic Channels Electromagnetic energy is coupled to the propagation medium by antenna (radiator) Antenna size & configuration – Frequency of operation Efficient radiation – antenna longer than 1/10 λ EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : TRANSMISSION MEDIA / CHANNEL

Cont’d... Example A radio station transmitting in AM frequency band, f c = 1MHz, λ = 300 m, requires antenna at least 30 m. EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : TRANSMISSION MEDIA / CHANNEL

Cont’d... Various frequency bands of the electromagnetic spectrum EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : TRANSMISSION MEDIA / CHANNEL

Cont’d... Mode of propagation of EM waves i. Ground-wave propagation ii. Sky-wave propagation iii. Line-of-sight (LOS) EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : TRANSMISSION MEDIA / CHANNEL

GROUND-WAVE PROPAGATION Surface-wave propagation Dominant mode of propagation Frequency band: 0.3 – 3 MHz Applications: AM broadcasting, maritime radio broadcasting Disturbances for signal transmission: atmospheric noise, man-made noise, thermal noise. EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : TRANSMISSION MEDIA / CHANNEL

Cont’d... EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : TRANSMISSION MEDIA / CHANNEL

SKY-WAVE PROPAGATION Transmitted signals being reflected from ionosphere Frequency : above 30 MHz Little loss Problem : Signal Multipath Application : Satellite communications EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : TRANSMISSION MEDIA / CHANNEL

Cont’d... Antenna at different angles > f c EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : TRANSMISSION MEDIA / CHANNEL

LINE-OF-SIGHT (LOS) PROPAGATION VHF band and higher Limited by curvature of earth Problem : Thermal noise (Rx front end) Cosmic noise (pick-up by antenna) Application: A TV antenna mounted on a tower of 300 m height to provide a broad coverage area (67km) EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : TRANSMISSION MEDIA / CHANNEL

Cont’d... EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : TRANSMISSION MEDIA / CHANNEL

Cont’d... Underwater acoustic channels EM waves do not propagate over long distances under water except at extremely low frequencies Expensive – because of the large and powerful transmitters required Problem : Attenuation – skin depth EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : TRANSMISSION MEDIA / CHANNEL

Cont’d... Multipath channel – signals reflections from the surface and the bottom of the sea. Noise : ambient ocean acoustic noise, man-made acoustic noise EKT 231 : COMMUNICATION SYSTEM CHAPTER 5 : TRANSMISSION MEDIA / CHANNEL

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