Date post: | 05-Apr-2018 |
Category: |
Documents |
Upload: | shahzad-khalid-ch |
View: | 218 times |
Download: | 0 times |
of 33
8/2/2019 Advance Communication System Lectures Part 5
1/33
Noise in CommunicationSystems
1
8/2/2019 Advance Communication System Lectures Part 5
2/33
Noise in Communication Systems
2
Outline :
Introduction
Thermal NoiseShot Noise
Signal - toNoise
Noise FactorNoise Figure Noise Temperature
BER
8/2/2019 Advance Communication System Lectures Part 5
3/33
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
3
Learning Outcomes
8/2/2019 Advance Communication System Lectures Part 5
4/33
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.
8/2/2019 Advance Communication System Lectures Part 5
5/33
Introduction
5
Noise is a general term which is used to describe an unwantedsignal which affects a wanted signal.
Noise is a random signal that exists in a communicationsystem.
Random signal cannot be represented with a simpleequation.
8/2/2019 Advance Communication System Lectures Part 5
6/33
Sources of noise
6
Noise
Internal Noise External Noise
Due to random movement ofelectrons in electronic circuit.
Electronic components in areceiver such as resistors,
diodes, and transistors aremajor sources of internal noise
Thermal (agitation) noise Shot noise
Transit time noise
Man-made noise and naturalresources
External noise comes fromsources over which we have littleor no control
Industrial sourcesmotors, generators,manufactured equipment
Atmospheric sources / staticelectricity
speaker when there is nosignal present
8/2/2019 Advance Communication System Lectures Part 5
7/33
Introduction (Contd)
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.
7
8/2/2019 Advance Communication System Lectures Part 5
8/33
Noise Effect
Degrade system performance for both analog and digitalsystems.
The receiver cannot understand the original signal.
The receiver cannot function as it should be.
Reduce the efficiency of communication system.
8
8/2/2019 Advance Communication System Lectures Part 5
9/33
Noise - Type of Noise
The are several types of noise, among them are:
1. Atmospheric
2. Extraterrestrial (Cosmic & Solar)
3. Thermal Noise
4. White Noise
5. Shot Noise
6. Quantization Noise
9
8/2/2019 Advance Communication System Lectures Part 5
10/33
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
10
8/2/2019 Advance Communication System Lectures Part 5
11/33
Extraterrestrial
Solar
Due to radiation from sun
Cosmic
Due to radiations from other heavenly bodies
11
8/2/2019 Advance Communication System Lectures Part 5
12/33
Industrial
Created by man due to several reasons
Line passing near by a transformer
Interference by other coexisting equipment
(TV remotes and IR equipments)
12
8/2/2019 Advance Communication System Lectures Part 5
13/33
Thermal Noise (Johnson Noise /white noise)
13
Thermal noise is the result of the random motion of charged particles
(usually electrons) in a conducting medium such as a resistor.
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).
When the temperature increases the movement of free electrons willincreases and the current flows through the conductor.
Movement of the electronswill forms kinetic energy in
the conductor related to the
temperature of the
conductor.
8/2/2019 Advance Communication System Lectures Part 5
14/33
Thermal Noise (Johnson Noise) (Contd)
14
Experimental results (by Johnson) and theoretical studies (by Nyquist) give
the mean square noisevoltage as
)(4 2
2_
voltTBRkV
Where k = Boltzmanns constant = 1.38 x 10-23 Joules per KT = absolute temperature (Kelvin)
B = bandwidth noise measured in (Hz)R = resistance (ohms)
8/2/2019 Advance Communication System Lectures Part 5
15/33
Thermal Noise (Johnson Noise)
15
For example :
50 k resistor at a temperature of 290 K, 3 kHz bandwidth. Find Vrmsvalue of noise:
from Kelvin to Kelvin
Celsius [C] = [K] 273.15 [K] = [C] + 273.15
Fahrenheit [F] = [K] 95 459.67 [K] = ([F] + 459.67) 59
Vn = 4 x 1.38 x 10-23 x 290 x 3000 x 50
= 49 nV
http://en.wikipedia.org/wiki/Celsiushttp://en.wikipedia.org/wiki/Fahrenheithttp://en.wikipedia.org/wiki/Fahrenheithttp://en.wikipedia.org/wiki/Celsius8/2/2019 Advance Communication System Lectures Part 5
16/33
16
Example 1.4
One operational amplifier with a frequency range of (18-20) MHz hasinput resistance 10 k. Calculate noise voltage at the input if theamplifier 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
8/2/2019 Advance Communication System Lectures Part 5
17/33
Analysis of Noise In Communication Systems
17
Thermal Noise (Johnson noise)
This thermal noise may be represented by an equivalent circuit as shown below
)(4 2____
2voltTBRkV
____
2V nVkTBR 2
(mean square value , power)
then VRMS =
i.e. Vn is the RMS noise voltage.
8/2/2019 Advance Communication System Lectures Part 5
18/33
Analysis of Noise In Communication Systems (Contd)
18
22
___
21
_______
2nnn VVV
11
____2
1 4 RBTkVn
22
____2
2 4 RBTkVn
)(4 2211
____
2 RTRTBkVn
)(4 21
____2
RRBkTVn
Assume that R1 at
temperature T1 and R2 at
temperature T2, then
i.e. The resistor in series at same temperature behave as a
single resistor
Resistors in Series
8/2/2019 Advance Communication System Lectures Part 5
19/33
Shot Noise
19
Shot noise is a type ofelectronic 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 randomfluctuations 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)
8/2/2019 Advance Communication System Lectures Part 5
20/33
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,SNRi is 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 offiltering, demodulation and amplification.
20
8/2/2019 Advance Communication System Lectures Part 5
21/33
Noise Calculation
SNR is a ratio of signal power,S to noise power,N.
Noise Figure,F
Noise factor,NF
dBN
SSNR log10
21
dBNS
NS
FNF
oo
iilog10
log10
oo
ii
NS
NSF dB
8/2/2019 Advance Communication System Lectures Part 5
22/33
Signal to Noise
22
)(,
)(,
wattsPnPowerNoise
wattsPsPowerSignal
N
S
The signal to noise ratio is given by
The signal to noise in dB is expressed by
dBmdBmdBNS
N
S
for S and N measured in mW.
dBN
S
N
S10log10
8/2/2019 Advance Communication System Lectures Part 5
23/33
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
23
Signal to Noise
Solution :
To express in dB;
100001.0
10
Pn
Ps
N
S
dBN
S
N
SdB 30
01.0
10log10log10 10
8/2/2019 Advance Communication System Lectures Part 5
24/33
Example :
For an amplifier with an output signal voltage of 4V, an output noisevoltage of 0.005 V, and an input and output resistance of 50 ohm, determinethe signal to noise power ratio.
Solution :
24
Signal to Noise
dBV
V
N
S
n
sdB 06.58005.0
4
log20log20 10
8/2/2019 Advance Communication System Lectures Part 5
25/33
25
Noise Factor-Noise Figure (Contd)
Noise factor, F =
OUT
IN
NS
NS
F equals to 1 for noiseless and in general F > 1.
lower the value of F, the better the network.
Consider the network shown below,
8/2/2019 Advance Communication System Lectures Part 5
26/33
26
Noise Factor-Noise Figure (Contd)
Noise figure (NF) is the Noise factor converted to dB
Noise Figure (NF) dB = 10 log10 (F)
NF = SNRin SNRout
If every variable is a dB Noise figure;
8/2/2019 Advance Communication System Lectures Part 5
27/33
Noise Temperature
27
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)
Equivalent noise temperature Te is not the physical temperatureof the amplifier, but rather a theoretical construct that is an
equivalenttemperature that produces that amount of noise power
8/2/2019 Advance Communication System Lectures Part 5
28/33
Transmission Loss
Transmission Medium Frequency Loss dB/km
Kabel Terpiuh (Twisted-
pair Cable)10kHz
100kHz
300kHz
2
3
6
Kabel Sepaksi (CoaxialCable)
100kHz1MHz
3MHz
12
4
Pandu GelombangEmpat Segi (Rectangular
Waveguide)
10GHz 5
Kabel Fiber Optik (FiberOptic Cable)
3.6 x 1014Hz
2.4 x 1014Hz
1.8 x 1014Hz
2.5
0.5
0.2
28
8/2/2019 Advance Communication System Lectures Part 5
29/33
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.
8/2/2019 Advance Communication System Lectures Part 5
30/33
BER = The number of erroneous bits received
total number of bits transmitted
8/2/2019 Advance Communication System Lectures Part 5
31/33
8/2/2019 Advance Communication System Lectures Part 5
32/33
Noise - Bit Energy
The signal also measured in terms of the bit energy injoules (J), Eb.
The enery per bit is simply the energy of a single bitof information, E
b
.
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)
8/2/2019 Advance Communication System Lectures Part 5
33/33
Summary
33
Thermal Noise
Signal - toNoise
Noise Factor
Noise Figure
Noise Temperature
)(4 22_
voltTBRkV
)(,
)(,
wattsPnPowerNoise
wattsPsPowerSignal
N
S
OUT
IN
NS
NS
Noise Figure (NF) dB = 10 log10 (F)
Te = T(F-1)