Mini Project Communication Link Simulation Channels And Noise Lecture

Mini Project – Communication Link Simulation Channels, Signals and Noise Author: University of Hertfordshire Date created : Date revised : 2009 Abstract The 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 .

Contents
Outline
Communication System
Channel
Sources of noise
Measures of system performance
Error performance degradation
Thermal or Johnson Noise
Additive White Gaussian Noise
Fading and Delay of Channels
Credits

Outline
Channels
Channel characteristics
Noise-general
System performance measures
Thermal noise and AWGN

Communication System Transmitter Channel Receiver 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

Channel
Medium over which propagation takes place
Connection between the transmitter and the receiver
e.g.: wires, coaxial cables, fibre optics, radio frequency (RF) links, channel space (occupied by atmosphere & bounded by the earth’s surface)

Characteristics of a channel
Noise
Any unwanted signals that are always present
Superimposed on signal
Tends to obscure or mask the signal
Interference amongst others depending on the medium

Sources of noise
Natural
Most fundamental: thermal or Johnson noise
Caused by thermal motion of electrons in electronic components
Present on all channels
Atmosphere, the sun, galactic sources, lightning, etc…
Man made
Switching transients, spark-plug ignition noise, etc…

Measures of system performance
Signal-to-noise ratio (SNR)
Bit energy per noise power spectral density (E b /N 0 )
Where Eb = bit energy
N 0 = noise power spectral density
Most commonly used in digital communication systems

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

Graphs of system performance BER SNR or E b /N 0 As E b /N 0 increases, a corresponding decrease in BER is expected

Task of detector is to retrieve the bit stream from the received waveform as error free as possible
Two primary causes for error performance degradation:
Effect of filtering at transmitter, channel, receiver  symbol smearing or intersymbol interference (ISI)
Electrical noise and interference from a variety of sources

Thermal or Johnson Noise
It is a noise source that cannot be eliminated
Nominal background noise
Arises due to the thermal motion of electrons in conducting media
Characteristics of Thermal Noise:
Statistical characteristic
Spectral characteristic

Thermal or Johnson Noise: Statistical characteristic
Noise amplitudes are distributed according to a normal or Gaussian distribution [probability density function (pdf) v/s ampitude]
amplitude pdf

Thermal or Johnson Noise: Spectral characteristic
Power Spectral Density (PSD) is the same for all frequencies
Often referred to as “white noise” due to the uniform PSD
f 0 N 0 /2 G n (f)

Additive White Gaussian Noise
Noise affecting the transmitted signal often termed “Additive White Gaussian Noise” (AWGN)
Additive: noise is simply superimposed or added to the transmitted signal
White: As a result of its uniform PSD
Gaussian: As a result of its statistical characteristics (uniform distribution)

Fading and Delay of Channels
Attenuation, fading
Phase shift, time delay
Multi-path effects (reflection, refraction)

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.

Mini Project Communication Link Simulation Channels And Noise Lecture

by University of Hertfordshire, School of Electronic Communications and Electrical Engineering

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