Mini Project- USB Temperature LogMini Project- USB Temperature Loggingging

Mini Project – Communication Link Simulation

Channels, Signals and NoiseChannels, Signals and Noise Author: University of HertfordshireDate created:Date revised: 2009

AbstractThe following resources come from the 2009/10 BEng (Hons) in Digital Communications & Electronics (course number 2ELE0064) from the University of Hertfordshire. All the mini projects are designed as level two modules of the undergraduate programmes. The objective of this module is to have built communication links using existing AM modulation, PSK modulation and demodulation blocks, constructed AM modulators and constructed PSK modulators using operational function blocks based on their mathematical expressions, and conducted simulations of the links and modulators, all in Simulink®.

Use Matlab®/ Simulink® to design a communication link for AM audio broadcasting. The message signal is a mono audio signal although you may not be able to transmit the full audio frequency range that is normally required for high quality sound.

In addition to the resources found below there are supporting documents which should be used in combination with this resource. Please see:Mini Projects - Introductory presentation. Mini Projects - E-Log.Mini Projects - Staff & Student Guide.Mini Projects - Standard Grading Criteria.Mini Projects - Reflection.

You will also need the ‘Mini Project- Communication Link Simulation’ text file and the lecture presentation on ‘Digital Modulation’.

© University of Hertfordshire 2009 This work is licensed under a Creative Commons Attribution 2.0 License.

22

ContentsContents OutlineOutline Communication SystemCommunication System ChannelChannel Sources of noiseSources of noise Measures of system performanceMeasures of system performance Error performance degradationError performance degradation Thermal or Johnson NoiseThermal or Johnson Noise Additive White Gaussian NoiseAdditive White Gaussian Noise Fading and Delay of ChannelsFading and Delay of Channels CreditsCredits

33

OutlineOutline

Channels Channels Channel characteristicsChannel characteristics Noise-generalNoise-general System performance measuresSystem performance measures Error performance degradationError performance degradation Thermal noise and AWGN Thermal noise and AWGN

44

Communication SystemCommunication System

TransmitterTransmitter ChannelChannel ReceiverReceiver

Formatting

Source Encoding

Encryption

Channel Encoding

Multiplexing

Modulation

Frequency Spreading

Copper Wires

Coaxial cables Twisted pairs

Optical fibres

Atmosphere/Ionosphere

Medium over which propagation takes

place

Formatting

Source Decoding

Decryption

Channel Decoding

Demultiplexing

Demodulation

Frequency despreading

Information source

Information sink

55

ChannelChannel

Medium over which propagation Medium over which propagation takes placetakes place

Connection between the transmitter Connection between the transmitter and the receiverand the receiver

e.g.: wires, coaxial cables, fibre optics, e.g.: wires, coaxial cables, fibre optics, radio frequency (RF) links, channel radio frequency (RF) links, channel space (occupied by atmosphere & space (occupied by atmosphere & bounded by the earth’s surface)bounded by the earth’s surface)

66

Characteristics of a channelCharacteristics of a channel

NoiseNoise• Any unwanted signals that are always Any unwanted signals that are always

presentpresent• Superimposed on signalSuperimposed on signal• Tends to obscure or mask the signalTends to obscure or mask the signal

Interference amongst others Interference amongst others depending on the mediumdepending on the medium

77

Sources of noiseSources of noise NaturalNatural

• Most fundamental: Most fundamental: thermalthermal or or JohnsonJohnson noise noise Caused by thermal motion of electrons in electronic Caused by thermal motion of electrons in electronic

componentscomponents Present on Present on allall channels channels

• Atmosphere, the sun, galactic sources, Atmosphere, the sun, galactic sources, lightning, etc…lightning, etc…

Man madeMan made• Switching transients, spark-plug ignition noise, Switching transients, spark-plug ignition noise,

etc…etc…

88

Measures of system performanceMeasures of system performance

Signal-to-noise ratio (SNR)Signal-to-noise ratio (SNR)

power noise average

power signal averageSNR

Bit energy per noise power spectral density (EBit energy per noise power spectral density (Ebb/N/N00))

Where Where Eb = bit energyEb = bit energy

NN00 = noise power spectral density = noise power spectral density• Most commonly used in digital communication systemsMost commonly used in digital communication systems

99

Measures of system Measures of system performance (ctd)performance (ctd)

Most commonly in digital systems is:Most commonly in digital systems is: Probability of error or Bit Error Rate (BER)Probability of error or Bit Error Rate (BER)

ed transmittbits of no. Total

errorin bits of No.BER

1010

Graphs of system performanceGraphs of system performanceBER

SNR or Eb/N0

As Eb/N0 increases, a corresponding decrease in BER is expected

1111

Error performance degradationError performance degradation Task of detector is to retrieve the bit Task of detector is to retrieve the bit

stream from the received waveform as stream from the received waveform as error free as possibleerror free as possible

Two primary causes for error performance Two primary causes for error performance degradation:degradation:• Effect of filtering at transmitter, channel, Effect of filtering at transmitter, channel,

receiver receiver symbol smearing or intersymbol symbol smearing or intersymbol interference (ISI)interference (ISI)

• Electrical noise and interference from a Electrical noise and interference from a variety of sources variety of sources

1212

Thermal or Johnson NoiseThermal or Johnson Noise

It is a noise source that cannot be It is a noise source that cannot be eliminatedeliminated

Nominal background noiseNominal background noise Arises due to the thermal motion of Arises due to the thermal motion of

electrons in conducting mediaelectrons in conducting media Characteristics of Thermal Noise:Characteristics of Thermal Noise:

• Statistical characteristicStatistical characteristic• Spectral characteristicSpectral characteristic

1313

Thermal or Johnson Noise: Thermal or Johnson Noise: Statistical characteristicStatistical characteristic

Noise amplitudes are distributed according to a Noise amplitudes are distributed according to a normal or Gaussian distribution [probability normal or Gaussian distribution [probability density function (pdf) v/s ampitude]density function (pdf) v/s ampitude]

0

0.1

0.2

0.3

0.4

-4 -3 -2 -1 0 1 2 3 4amplitude

pdf

1414

Thermal or Johnson Noise: Thermal or Johnson Noise: Spectral characteristicSpectral characteristic

Power Spectral Density (PSD) is the same for all Power Spectral Density (PSD) is the same for all frequenciesfrequencies

Often referred to as “white noise” due to the uniform PSDOften referred to as “white noise” due to the uniform PSD

f0

N0/2

Gn(f)

1515

Additive White Gaussian NoiseAdditive White Gaussian Noise

Noise affecting the transmitted signal often Noise affecting the transmitted signal often termed “Additive White Gaussian Noise” (AWGN)termed “Additive White Gaussian Noise” (AWGN)• Additive: noise is simply superimposed or added to the Additive: noise is simply superimposed or added to the

transmitted signaltransmitted signal• White: As a result of its uniform PSDWhite: As a result of its uniform PSD• Gaussian: As a result of its statistical characteristics Gaussian: As a result of its statistical characteristics

(uniform distribution)(uniform distribution)

1616

Fading and Delay of ChannelsFading and Delay of Channels

Attenuation, fadingAttenuation, fading Phase shift, time delay Phase shift, time delay Multi-path effects (reflection, Multi-path effects (reflection,

refraction) refraction)

1717

This resource was created by the University of Hertfordshire and released as an open educational resource through the Open Engineering Resources project of the HE Academy Engineering Subject Centre. The Open Engineering Resources project was funded by HEFCE and part of the JISC/HE Academy UKOER programme.

© University of Hertfordshire 2009

This work is licensed under a Creative Commons Attribution 2.0 License.

The name of the University of Hertfordshire, UH and the UH logo are the name and registered marks of the University of Hertfordshire. To the fullest extent permitted by law the University of Hertfordshire reserves all its rights in its name and marks which may not be used except with its written permission.

The JISC logo is licensed under the terms of the Creative Commons Attribution-Non-Commercial-No Derivative Works 2.0 UK: England & Wales Licence.  All reproductions must comply with the terms of that licence.

The HEA logo is owned by the Higher Education Academy Limited may be freely distributed and copied for educational purposes only, provided that appropriate acknowledgement is given to the Higher Education Academy as the copyright holder and original publisher.