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Published on March 24, 2008

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Communication Principles (BEE 3216):  Communication Principles (BEE 3216) BEng (Hons) Electronics and Instrumentation System Batch : Penang (Sri Malaysia) 16th and 17th February 2008 Noorazlina Mohamid Salih liena_226@yahoo.com, noorazlina.feit@iuctt.edu.my (016-2903780) Faculty of Engineering and Industrial Technology International University College of Technology Twintech (IUCTT) Milestones of the module:  Milestones of the module MIP Learning Outcomes Grading – achieve ALL learning outcomes Assessment; 50% coursework & 50% final exam Coursework – tutorials, quizes, assignments and tests. Final Exam – 4 Questions. Answer ALL questions. Class Agenda :  Class Agenda Slide4:  Module Aim Manage to educate students on communication systems, communication channels, modulation techniques and information theory and coding. Synopsis This module covers the analogue and digital transmission, the concepts of communication channel, modulation techniques, noises, data transmission, optimum receiver and coding. Introduction:  Introduction Definition of COMMUNICATION? Why do we need to communicate? Definition of COMMUNICATION SYSTEM (Electronic Communication System)? Why do we need to communicate electronically? How to communicate? Interference in communications? How to overcome? Introduction to Communication Systems:  Introduction to Communication Systems Communication – Basic process of exchanging information from one location (source) to destination (receiving end). Refers – process of sending, receiving and processing of information/signal/input from one point to another point. Source Destination Flow of information Figure 1 : A simple communication system Slide7:  Electronic Communication System – defined as the whole mechanism of sending and receiving as well as processing of information electronically from source to destination. Example – Radiotelephony, broadcasting, point-to-point, mobile communications, computer communications, radar and satellite systems. Objectives:  Objectives Communication System – to produce an accurate replica of the transmitted information that is to transfer information between two or more points (destinations) through a communication channel, with minimum error. Besides – interactive purposes, business and social NEED FOR COMMUNICATION:  NEED FOR COMMUNICATION Interaction purposes – enables people to interact in a timely fashion on a global level in social, political, economic and scientific areas, through telephones, electronic-mail and video conference. Transfer Information – Tx in the form of audio, video, texts, computer data and picture through facsimile, telegraph or telex and internet. Broadcasting – Broadcast information to masses, through radio, television or teletext. Terms Related To Communications:  Terms Related To Communications Message – physical manifestation produced by the information source and then converted to electrical signal before transmission by the transducer in the transmitter. Transducer – Device that converts one form of energy into another form. Input Transducer – placed at the transmitter which convert an input message into an electrical signal. Example – Microphone which converts sound energy to electrical energy. Message Input Transducer Electrical Signal Slide11:  Output Transducer – placed at the receiver which converts the electrical signal into the original message. Example – Loudspeaker which converts electrical energy into sound energy. Signal – electrical voltage or current which varies with time and is used to carry message or information from one point to another. Electrical Signal Output Transducer Message Slide12:  Information – defined as what is being conveyed by the telecommunication environment or as knowledge or facts. It can be in analogue form (voice, video, music) or digital form ( binary-coded numbers, graphics symbols or database information). Do readings : Brief History/ Evolution of human communications (1840 – 2008). Basic Requirements of Communication Systems.:  Basic Requirements of Communication Systems. Rate of Information Transfer – defined as the amount of info that must be communicated from source to destination in a certain period of time. It determines the physical form and the techniques used to transmit and receive information. The rate of information transfer must be reasonable and acceptable rate for each communication system. Slide14:  Purity of Received Signal – the received signal must be the same as the transmitted signal Simplicity of the system – must be convenience in order to be effective and efficient/easy to use. Reliability – User must be able to depend on a communication system. It must work when needed and transmit/receive information without errors or with an acceptable errors. Elements of a Communication System:  Elements of a Communication System The basic elements are : Source, Transmitter, Channel, Receiver and Destination. Information Source Transmitter Channel Transmission Medium Receiver Destination Noise Figure : Basic Block Diagram of a Communication System Function of each Element.:  Function of each Element. Information Source – the communication system exists to send messages. Messages come from voice, data, video and other types of information. Transmitter – Transmit the input message into electrical signals such as voltage or current into electromagnetic waves such as radio waves, microwaves that is suitable for transmission and compatible with the channel. Besides, the transmitter also do the modulation and encoding (for digital signal). Block Diagram of a Transmitter:  Block Diagram of a Transmitter 5 minutes exercise; Describe the sequence of events that happen at the radio waves station during news broadcast? Modulating Signal Audio Amplifier Modulator RF Amplifier Carrier Signal Transmitting Antenna Slide18:  Channel/Medium – is the link or path over which information flows from the source to destination. Many links combined will establish a communication networks. There are 5 criteria of a transmission system; Capacity, Performance, Distance, Security and Cost which includes the installation, operation and maintenance. 2 main categories of channel that commonly used are; line (guided media) and free space (unguided media) Slide19:  Receiver – Receives the electrical signals or electromagnetic waves that are sent by the transmitter through the channel. It is also separate the information from the received signal and sent the information to the destination. Basically, a receiver consists of several stages of amplification, frequency conversion and filtering. Block Diagram of a Receiver:  Block Diagram of a Receiver Destination – is where the user receives the information, such as loud speaker, visual display, computer monitor, plotter and printer. RF Amplifier Mixer Local Oscillator Intermediate Frequency Amplifier Demodulator Audio Amplifier Destination Receiving Antenna 2 Types of Electronic Communication:  2 Types of Electronic Communication Radio Communication System The information is being carried by the electromagnetic waves, which is propagated in free space (wireless communication). Electromagnetic waves are waves that travel at the speed of light (3x108m/s) and made up of an electric field and magnetic field at the right angles to one another and to the direction of propagation. The 3 wave propagation methods are; Ground wave propagation, Sky wave propagation and Space wave propagation. Radio Wave Propagation Methods:  Radio Wave Propagation Methods Ground wave propagation – wave that progress along the surface of the earth. It follows the curvature of the earth. The wave induces current in the ground over which it passes and thus losses some energy by absorption. If the distance between the transmitter and the receiver is too far, the signal strength will be reduced due to surface absorption. Surface of good conductor helps the propagation of the signal, for example sea water. Slide23:  Sky wave propagation – waves radiated towards ionosphere. By a process of refraction and reflection, the receiver on the earth will receive the signal. Various layers of the ionosphere have specific effects on the propagation of radio waves. Space wave propagation – the wave is propagated in a straight line. Space wave is limited to their propagation by the curvature of the earth (LOS). Line of Sight Propagation (LOS):  Line of Sight Propagation (LOS) The radio horizon of the antenna is the distance between the transmitter and the receiver. It is denoted by d, where d is approximate the sum of dt and dr in kilometer (km). Therefore, dt = 4√ht and dr = 4√hr dt = radio horizon of the transmitting antenna (km) ht = height of transmitting antenna (m) dr = radio horizon of the receiving antenna (km) hr = height of receiving antenna (m) Illustration of Radio wave propagation methods:  Illustration of Radio wave propagation methods Earth Transmitter Receiver Space Wave Propagation (LOS) Ground Wave propagation Sky Wave propagation Quality Time……take 5!:  Quality Time……take 5! Q1) Determine the wavelength for the signal of the following frequencies. f1 = 100 kHz f2 = 100.9 MHz f3 = 3 GHz Hint: Electromagnetic waves relationship, c = fλ where C = speed of light f = frequency λ = wavelength of the signal Question 2……during quality time:  Question 2……during quality time Radio 3 Pulau Pinang is transmitting frequency modulated signal using line of sight (LOS) wave propagation method. Calculate the height of the transmitting antenna, if the height of the receiving antenna is 6 meters and the distance between the transmitter and the receiver is 150km. Answer: ht = 1.23km Another type of electronic communication:  Another type of electronic communication Line Communication Uses metallic conductor to connect between the transmitter and the receiver. Two types of transmission line; two-wire and coaxial cable. Two-wire is for transmission of low frequency signal such as in transmitting telephone signal or low data rate transmission. Coaxial cable carries radio frequency signal. Suitable for higher frequency applications (more speech channels at one time). Slide29:  Media Guided Media Unguided Media Coax Cable Twisted Pair Fiber Optics Radio Frequency Infrared Laser Satellite Twisted Pair:  Twisted Pair least expensive, most widely deployed two wires (AWG 18-26) twisted together low noise immunity (unless shielded or high turn density) limited bandwidth (maximum is MHz range for repeater spacing no longer than 6km) most subscriber loops are twisted pair (AWG24, <2 miles from CO) and all T1 trunks UTP vs STP UTP Category 3,4, and 5 based on EIA-588-A standard UTP 3 for point-to-point data (<10Mbps) and voice application wiring in office buildings UTP 5 for 100Mbps LANs (e.g. Fast Ethernet) Why the pairs are twisted?:  Why the pairs are twisted? Crosstalk Interference intelligible interference caused by the transfer of signal between adjacent pairs Near End (NEXT) - interference from same end of circuit Far End (FEXT) - interference from other end of circuit Crosstalk Mitigation: avoid mixing transmit and receive pairs in same cable (NEXT) use separate frequencies for transmit and receive signals (FEXT) twisting of paired wires or proper shielding (NEXT and FEXT) Coax Cable :  Coax Cable consists of two concentric conductors separated by a dielectric more expensive than twisted pair good noise immunity due to the outer conductor shield allows 100’s of MHz of channel bandwidth Applications 10B2 CATV distribution DS3 Fiber Optics :  Fiber Optics consists of a glass core and a glass (sometimes plastic) cladding surrounded by a protective jacket. excellent immunity to noise due to optical transmission excellent channel bandwidth (100’s of GHz) Two major types: Single mode vs multi mode (graded & stepped) Single mode superior in bandwidth and attenuation (at much higher cost) Disadvantage: cost and installation Fiber Optics:  Fiber Optics SM MM MM MM 3 types of Transmission Mode:  3 types of Transmission Mode Simplex Transmission occurs only in one direction. Some time called one-way communication, receive only or transmit only system. Example of simplex communication is television (TV). Half-Duplex Transmission occurs in both direction, but not at the same time, for example walkie-talkie. Full-Duplex Transmission can occur in both directions at the same time. Sometimes called two-way or simultaneous communication system. Example ; telephone. Limitations in a Communication System:  Limitations in a Communication System There are 2 categories of limitations:- Technological Physical Technological Constraint includes equipment availability, economy and cost factor, national and international law (ITU-T) and interaction with existing systems. Physical Constraint includes bandwidth and noise. Cont…….physical constraint:  Cont…….physical constraint Bandwidth – defined as the information carrying capacity of a system or the frequency content of a signal. BW is the difference between the upper frequency fH and the lower frequency fL of the signal. Example: The voice frequency ranges from 300 Hz to 3400 Hz. Therefore, the BW is 3.1 kHz. The limitation due to BW is applied to both signals and systems as a measure of speed. Means that the shorter transmission time will result in high-speed transmission of the signal, which require large BW and hence increasing the cost of the system Cont…….physical constraint:  Cont…….physical constraint Noise – defined as unwanted electrical energy present in the usable passband of a communication circuit. It is unavoidable. Noise is measured in terms of Signal-to-Noise ratio (SNR). Its limitation, Higher SNR…..higher transmitted power and higher cost. Noise Factor, denoted by F and defined as the ratio of SNR at the input to the SNR at the output of a network. F = (SNR)input / (SNR)output Noise Figure = 10 log F dB Noise figure or noise factor is used to compare the performance of a communication system. Higher SNR, lower F is better in a communication systems. Tutorial # 1:  Tutorial # 1 Instruction to ALL students:- 1) Submit all answers at the end of the course (10%) 2) Late submission 5% max. Quality Time……..:  Quality Time…….. To ALL students, How is it so far? Any difficulties? Repeat? Which part? Quiz # 1……..(15 minutes) Slide41:  ANALOGUE MODULATION Analogue Modulation :  Analogue Modulation Baseband Transmission Baseband signal is the information either in a digital or analogue form. Transmission of original information whether analogue or digital, directly into transmission medium is called baseband transmission. Example: intercom (figure below) Microphone Voice Audio Amplifier Audio Amplifier Speaker Voice Wire Baseband signal is not suitable for long distance communication….:  Baseband signal is not suitable for long distance communication…. Hardware limitations Requires very long antenna Baseband signal is an audio signal of low frequency. For example voice, range of frequency is 0.3 kHz to 3.4 kHz. The length of the antenna required to transmit any signal at least 1/10 of its wavelength (λ). Therefore, L = 100km (impossible!) Interference with other waves Simultaneous transmission of audio signals will cause interference with each other. This is due to audio signals having the same frequency range and receiver stations cannot distinguish the signals. Modulation:  Modulation Modulation – defined as the process of modifying a carrier wave (radio wave) systematically by the modulating signal. This process makes the signal suitable for transmission and compatible with the channel. Resultant signal – modulated signal 2 types of modulation; Analogue Modulation and Digital Modulation. Analogue Modulation – to transfer an analogue low pass signal over an analogue bandpass channel. Digital Modulation – to transfer a digital bit stream the carrier is a periodic train and one of the pulse parameter (amplitude, width or position) changes according to the audio signal. Purpose of Modulation Process in Communication Systems :  Purpose of Modulation Process in Communication Systems To generate modulated signal that is suitable for transmission and compatible with the channel. To allow efficient transmission – increase transmission speed and distance, eg; By using high frequency carrier signal, the information (voice) can travel and propagate through the air at greater distances and shorter transmission time Also, high frequency signal is less prone to noise and interference. Certain types of modulation have the useful property of suppressing both noise and interference For example, FM use limiter to reduce noise and keep the signal’s amplitude constant. PCM systems use repeaters to generate the signal along the transmission path. Purpose of Modulation Process in Communication Systems:  Purpose of Modulation Process in Communication Systems To overcome hardware limitations The physical size of some electronic components depend on the range of frequencies that are used in the circuit. The higher the frequencies, the physical size of the components may be reduced. Examples 1 & 2:  Examples 1 & 2 Amplitude Modulation (AM):  Amplitude Modulation (AM) Objectives:- Recognize AM signal in the time domain, frequency domain and trigonometric equation form Calculate the percentage of modulation index Calculate the upper sidebands, lower sidebands and bandwidth of an AM signal by given the carrier and modulating signal frequencies Calculate the power related in AM signal Define the terms of DSBSC, SSB and VSB Understand the modulator and demodulator operations Introduction:  Introduction Modulation The alteration of the amplitude, phase or frequency of an oscillator in accordance with another signal. Input signal is encoded in a format suitable for transmission A low frequency information signal is encoded over a higher frequency signal Carrier Signal Sinusoidal wave, Modulating Signal/Base band Information signal, Modulated Wave Higher frequency signal which is being modulated Modulation Schemes To counter the effects of multi path fading and time-delay spread Slide50:  Carrier Signal, Vc Modulating Signal, Vm Modulation Schemes Modulated Signal VAM VPM VFM Amplitude Modulation:  Amplitude Modulation Time Domain Frequency Domain AM Modulator:  AM Modulator AM Modulator:  Modulator Information Signal Carrier Signal Output AM Modulator Amplitude Modulation:  Amplitude Modulation Vc - Vc Vm - Vm Modulation Index:  Modulation Index Modulation Index, m Indicates the amount that the carrier signal is modulated. It is an expression of the amount of power in the sidebands. Modulation level ranges = 0-1 where 0 = no modulation 1 = full modulation >1 = distortion Modulation Index:  Modulation Index Modulation Index:  Modulation Index Vmin Vmin (p-p) Vmax Vmax (p-p) Modulation Index:  Modulation Index Bandwidth:  fLSB fUSB fC Bandwidth VC Bandwidth for AM signal, fc-fm fc+fm Bandwidth:  fC Bandwidth VC When fm signal in a baseband signal (f1 to f2) fc-f2 fc-f1 fc+f1 fc+f2 Exercise::  Exercise: For an AM modulator with a carrier frequency of 150 kHz and a modulating signal frequency of 10 kHz, determine the: Frequency for the upper and lower sideband Bandwidth Sketch the frequency spectrum Power Distributions:  fC Power Distributions VC Total transmitted power, PT If R= 1, Exercise::  Exercise: For an AM wave with a peak unmodulated carrier voltage, Vc = 20V, a load resistance RL= 20Ω and a modulation index, m =0.2, determine: Power contained in the carrier, the upper and the lower sidebands. Total sideband power Total power of the modulated wave Double Side Band Suppressed Carrier (DSBSC):  Double Side Band Suppressed Carrier (DSBSC) It is a technique where it is transmitting both the sidebands without the carrier (carrier is being suppressed/cut) Characteristics: Power content less Same bandwidth Disadvantages - receiver is complex and expensive. Single Side Band (SSB):  Single Side Band (SSB) Improved DSBSC and standard AM, which waste power and occupy large bandwidth SSB is a process of transmitting one of the sidebands of the standard AM by suppressing the carrier and one of the sidebands Advantages: Saving power Reduce BW by 50% Increase efficiency, increase SNR Disadvantages Complex circuits for frequency stability Vestigial Side Band (VSB):  Vestigial Side Band (VSB) VSB is mainly used in TV broadcasting for their video transmissions. TV signal consists of Audio signal – transmitted by FM Video signal – transmitted by VSB A video signal consists a range of frequency and fmax = 4.5 MHz. If it transmitted using conventional AM, the required BW is 9 MHz (BW=2fm). But according to the standard, TV signal is limited to 7 MHz only So, to reduce the BW, a part of the LSB of picture signal is not fully transmitted. Vestigial Side Band (VSB):  Vestigial Side Band (VSB) The frequency spectrum for the TV signal / VSB: Lower Video Bands Upper Video Bands Total TV signal bandwidth = 7 MHz Video Carrier Audio Carrier 4.5 MHz Upper Audio Bands Lower Audio Bands 1.25 6.75 5.75 7.0 6.25 0 f (MHz) Modulator Circuits :  Modulator Circuits Modulator Circuits :  Modulator Circuits A. Modulating Signal B. Carrier C. Sum of carrier and modulating signal D. Diode current E. AM output across tuned circuit Demodulator :  Demodulator Demodulator :  Demodulator A. AM aignal B. Current pulses through diode C. Demodulating signal D. Modulating signal Slide72:  FREQUENCY MODULATION Frequency Modulation (FM):  Frequency Modulation (FM) Objectives:- Recognize FM signal in the time domain, frequency domain and trigonometric equation form Calculate the percentage of modulation index Calculate the upper sidebands, lower sidebands and bandwidth of an FM signal by Carsons’s Rule and Bessel Function Table Calculate the power related in FM signal Understand the modulator and demodulator of FM stereo Introduction:  Introduction FM is the process of varying the frequency of a carrier wave in proportion to a modulating signal. The amplitude of the carrier is kept constant while its frequency is varied by the amplitude of the modulating signal. In all types of modulation, the carrier wave is varied by the AMPLITUDE of the modulating signal. FM signal does not have an envelope, therefore the FM receiver does not have to respond to amplitude variations  it can ignore noise to some extent. Slide75:  Frequency Modulation Frequency Modulation:  Frequency Modulation The importance features about FM waveforms are: The frequency varies The rate of change of carrier frequency changes is the same as the frequency of the information signal The amount of carrier frequency changes is proportional to the amplitude of the information signal The amplitude is constant Slide77:  Carrier Signal Sinusoidal wave Modulating Signal/Base band Information signal Modulated Wave Higher frequency signal which is being modulated Where Frequency Modulation Frequency Modulation:  Frequency Modulation Time Domain Frequency Domain FM Modulator:  FM Modulator FM Modulator:  FM Modulator Modulator Information Signal Carrier Signal Output Frequency Modulation:  Frequency Modulation Frequency:  Frequency Carrier Frequency As in FM system, carrier frequency in FM systems must be higher than the information signal frequency. Maximum Frequency Minimum Frequency Carrier Swing Modulation Index:  Modulation Index Modulation Index, m @ β Indicates the amount that the carrier signal is modulated. It is an expression of the amount of power in the sidebands. Modulation level ranges = 0 – Where Δf = fd = frequency deviation fm = modulating frequency Vm = amplitude of modulating signal Modulation Index:  Modulation Index Modulation Index:  Modulation Index Modulation Index:  Modulation Index Exercise::  Exercise: FM broadcast station is allowed to have a frequency deviation of 75 kHz. If a 4 kHz audio signal causes full deviation, calculate the modulation index. (18.75) Exercise::  Exercise: Determine the peak frequency deviation, Δf, and the modulation index, m for a FM modulator with a deviation sensitivity, k = 10 kHz/V. The modulating signal to be transmitted is (Frequency deviation = 50 kHz) (Modulation index = 10) Bandwidth:  Bandwidth Using Bessel Function, the bandwidth for FM signal, n = number of pairs of the significant sidebands fm = the frequency the modulating signal Bessel Function Table::  Bessel Function Table: Bandwidth:  Bandwidth Using Carson’s Rule, to estimate the bandwidth for an FM signal transmission. Δf = peak frequency deviation fm(max) = highest modulating signal frequency Exercise::  Exercise: An FM modulator is operating with a peak frequency deviation Δf = 20 kHz. The modulating frequency, fm is 10 kHz, and the 100 kHz carrier signal has an amplitude of 10V. Determine: The minimum bandwidth using Bessel Function Table (80 kHz) The minimum bandwidth using Carson’s Rule (60 kHz) Sketch the frequency spectrum Power Distributions:  Power Distributions FM transmitted power, PFM where FM vs AM::  FM vs AM: FM Stereo Modulator:  FM Stereo Modulator Spectrum Frequency FM Stereo :  Spectrum Frequency FM Stereo FM Stereo Demodulator :  FM Stereo Demodulator Slide98:  PULSE MODULATION Introduction:  Introduction Digital Communications – rapid technology changes A lot of information to be transmitted in pulse / digital, so sending them in the simplest technique. The advent of large-scale integration has permitted the use of complex coding systems that take the best channel capacities. Pulse Modulation is divided into 2 categories; Analogue Pulse Modulation and Digital Pulse Modulation. Pulse Modulation can be used to transmit analogue information such as continuous speech or digital speech. Sampling:  Sampling Process of taking a periodic samples of the waveform to be transmitted. Sufficient samples are sent, the waveform can be reconstructed at the receiver. More samples taken, results the most looks like the original wave. The sampling theorem, Nyquist, is used to determine the minimum sampling rate for any signal so that the signal will be correctly restored at the receiver.

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