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  1. 1. Learning OutcomesUpon completion of this chapter, students should be ableto :-•Understand the element in communication system.•Understand the information , messages and signal.•Understand the modulation process and its needs.•Learn noise, interference and distortion.•Know the frequency spectrum.•Understand various types of communication system. 1
  2. 2. INTRODUCTIONThe word TELECOMMUNICATION is a combination of two words... TELE + COMMUNICATION The word TELE in Latin means DISTANCE. Hence Telecommunication is DISTANCE COMMUNICATION 2
  3. 3. DEFINATION Telecommunication is the transmission of messages, over significant distances, for the purpose of communication. In earlier times, telecommunications involved the use of visual signals, such as smoke, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded drumbeats, lung-blown horns, or sent by loud whistles, for example.In the modern age of electricity and electronics, telecommunications has typicallyinvolved the use of electric means such as the telegraph, the telephone, and theteletype, the use of microwave communications, the use of fiber optics and theirassociated electronics, and/or the use of the Internet. 3
  4. 4. CLASSIFICATION OF COMMUNICATION SYSTEMS Radio Telephony Mobile Comm. Radio Aids to Navigations Broadcasting Radio telemetry Radar Point to point Telegraphy Computer Comm. 4
  6. 6. Answers 1.1 What is communication system System noise and interference Transmission medium TRANSMITTER OR RECEIVER Receiver Communication channel informetionInformation source( intelligence) Pysical facility(metalic or optical fiber cable) or free space( earth atmosphere) BASIC BLOCK DIAGRAM OF AN ELECTRONIC COMMUNICATION SYSTEM 6
  7. 7. Components of the Communication SystemA) INFORMATION SOURCE The message is the information source. Example : Text, voice, pictures or video signal Information can electrical and non-electrical. Non-electrical information source must be converted into electrical form before it is transmitted.B) TRANSMITTER A collection of one or more electronic devices or circuits that convert the original information source into a signal suitable for information. A complex processes ( Encoding and modulation ) must be done to the information signal before transmission. 7
  8. 8. Component of the Communication systemc) Transmission mediumA transmission medium (plural transmission media) is a material substance(solid, liquid, gas or plasma) that can propagate energy waves. Forexample, the transmission medium for sound received by the ears is usuallyair, but solids and liquids may also act as transmission media for sound.The absence of a material medium (the vacuum of empty space) can also bethought of as a transmission medium for electromagnetic waves suchas light and radio waves. While material substance is not required forelectromagnetic waves to propagate, such waves are usually affected by thetransmission media they pass through, for instance by absorption orby reflection or refraction at the interfaces between media. 8
  9. 9. Components of the Communication Systemd) Channel The path provided by a transmission medium can take the form of physical separation, such as by multipare cable or electrical separation such as by frequency or time division multiplexing. An example is the MIXFM which has its channel allocated at a frequency of 94.5 Mhz.e) Noise Noise is unwanted energy which is usually random in nature that is present in any point of a commnication system. Noise may be due to various causes such atmospheric noise, thermal agitation noise, shot noise and industrial noise. 9
  10. 10. Components of the Communication System f) Receiver A receiver is a collection of one or more electronic devices and circuits that accept the transmitter signals from the transmission medium and convert them back into their original form. -A band pass filter rejects all frequencies above or below its designed frequency. Most receivers utilize an LC resonant circuit as a band pass filter. The band pass filter is tuned to the carrier frequency signal of the transmitting station. In other words the receiver SELECTs the appropriate station. The last stage of the communication system is g) destination equipment which converts these electrical signals into its original form for the data broadcasting so that it can be easily understand by the end user or receiver and then this same sort of communication process is used for the acknowledgment of signals to sender machine. 10
  11. 11. What is information, messages and signal.InformationDefined as knowledge or inteligence that communicate between two or morepoints, Information in its most restricted technical sense is anordered sequence of symbols that record or transmit a message. It can berecorded as signs, or conveyed as signals by wavesMessagesA telephone circuit is comprised of two or more facilities interconnected intandem to provide a transmission path between a source and a destination.The interconnected facilities maybe temporary as in standard telephone call orpermanent as in a dedicated private carrier system. The information is calledmessages.. 11
  12. 12. SignalSignals can be defined as measurable quantities which may be either time-varying or spatial-varying. A signal may be expressed as a function of time andfrequency.When a signal is expressed as a function of time, it can be eitherdiscrete (discrete-time signal) or continuous (continuous-time signal).In a more practical sense, there are two basic types of signals:1)Digital signal2)Analogue signalDigital signalDigital signal can be defined as a discrete signal or discrete-time signal thatgenerates and process data in form of zeroes and ones (0s and 1s). This impliesthat digital signals can take on only a discrete set of values. Digital signal isquantized (has finite set of values). The value of a Digital signal may be described interms of voltage pulses that can be sent over data transmission medium. Asdescribed above, the signal sent is either off (o) or on (1) pluses, representing abinary digit. For example, computers use digital signals. 12
  13. 13. Analogue signalAnalogue signal (unlike digital signal) is not discrete and quantized.Analogue signal is continuous in nature and generates continuous values,leading to continuous wave pattern.Analogue signals can be used over a variety of transmission media. For example, telephone lines use analogue protocols.What Does Signals Do?•Signals carry information, in form of data, image, sound or pictures.•Computers depend on digital signals for data transmission.•The computer stores data in form of zeros and ones, which are called binarydigits.•A single binary digit is referred to a bit and a set of 8 bits is called a byte.1024 byte is equal to 1 kilobyte. 13
  14. 14. WHAT IS BAND PASS AND BASE BANDA bandpass filter is a device that passes frequencies within a certain rangeand rejects (attenuates) frequencies outside that range. An example ofan analogue electronic band-pass filter is an RLC circuit (a resistor–inductor–capacitor circuit. These filters can also be created by cobining a low-passfilter with a high-pass filter. 14
  15. 15. What is baseband In telecommunications and signal processing baseband is an adjective that describes signals and systems whose range of frequencies is measured from close to 0 hertz to a cut-off frequency a maximum bandwidth or highest signal frequency; it is sometimes used as a noun for a band of frequencies starting close to zero..Baseband can often be considered as a synonym to lowpass or non-modulated, and antonym to passband, bandpass, carrier-modulated or radio frequency (RF) s 15
  16. 16. 1.3 MODULATION AND DEMODULATION MODULATION is an important step of communication systemIn modulation, a message signal, which contains the information is used to control the parameters of a carrier signal, so as to impress the information onto the carrier. The Messages The message or modulating signal may be either: analogue – denoted by m(t) digital – denoted by d(t) – i.e. sequences of 1s and 0s The message signal could also be a multilevel signal, rather than binary; this is not considered further at this stage. OR Modulation is a process in which the characteristics of a signal circuit is caried in accordance with the information signal which is to be transmitted. The modulation signal,which is to be transmitted is known as Modulating signal. 16
  17. 17. MODULATION……In electronics modulation is the process of varying one or more properties of ahigh-frequency periodic waveform, called the carrier signal, with a modulatingsignal which typically contains information to be transmitted. At thedestination, a process of demodulation extracts the modulation signal from themodulated carrier. The three key parameters of a periodic waveform areits amplitude ("volume"), its phase ("timing") and its frequency ("pitch"). Anyof these properties can be modified in accordance with a low frequency signalto obtain the modulated signal. Typically a high-frequency sinusoid waveform isused as carrier signal, but a square wave pulse train may also be used.In telecommunications, modulation is the process of conveying a messagesignal, for example a digital bit stream or an analog audio signal, insideanother signal that can be physically transmitted. Modulation of a sinewaveform is used to transform a baseband message signal intoa passband signal, for example low-frequency audio signal into a radio-frequency signal (RF signal). 17
  19. 19. DEMODULATIONIs the reverse process (to modulation) to recover the message signal m(t) ord(t) at the receiver.DEMODULATION is the act of extracting the original information-bearing signalfrom a modulated carrier wave. A demodulator is an electroniccircuit (or computer program in a software defined radio) that is used torecover the information content from the modulated carrier wave.[1]These terms are traditionally used in connection with radio receivers, but manyother systems use many kinds of demodulators. Another common one is inamodem, which is a contraction of the terms modulator/demodulator . 19
  20. 20. THE NEEDS OF MODULATION AND NEEDS OF MODULATON DEMODULATIONTo transfer the message signal from one site another site without any loss forthat we are using modulation. Modulation classified in two types.1.Analog modulation.2.DigitalModulation.Modulation is need basically to: i)To increase the bandwidth of the signalii)To multiplex more number of signal 20
  21. 21. iii)To reduce the interference( noise and distortion) made when we transmitthe signals with nearly same frequency in the audio frequency range (20-20k)Hz. iv) To reduce the antenna height. For efficient transmission the transmitting antennas should have length atleast equal to a quarter of the wavelength of the signal to be transmitted.For an electromagnetic wave of frequency 15 kHz, the wavelength λ is 20 kmand one-quarter of this will be equal to 5 km. Obviously, a vertical antenna ofthis size is impractible. On the other hand, for a frequency of 1 MHz, thisheight is reduced to 75m. 21
  22. 22. Also, the power radiated by an antenna of length l is proportional to (l/λ)2.This shows that for the same antenna length, power radiated is large forshorter wavelength. Thus, our signal which is of low frequency must betranslated to the high frequency spectrum of the electromagnetic wave. Thisis achieved by the process of modulation.v) To narrow banding system.vi) To reduce equipment complexity.vii)To favors the complexity of the transmission system Audio frequencies are within the range of 20 Hz to 20 kHz. Withoutmodulation all signals at same frequencies from different transmitters wouldbe mixed up. There by giving impossible situation to tune to any one of them.In order to separate the various signals, radio stations must broadcast atdifferent frequencies. 22
  23. 23. 1.4 NOISE, INTERFERENCE AND DISTORTIONElectrical noise is defined as any undesirable electrical energythat’s falls within the passband of the signal.It can be divided into two general categoriesi) correlated- its implies a relationship between the signal andthe noise.ii) uncorrelated-exists only when a signal is present on theotherhand is present at the time wheather there is a signal ornot. 23
  24. 24. Uncorrelated noiseUncorrelated noise is present regardless of wheather there is asignal or not. Devide into two categories: external and internal. External NoiseNoise that generated outside the device or circuit. The three primarysources of external noise are atmospheric, extraterrestrial and man-made. Refer to notes to explain …( italic)Internal noiseIs electrical interference generated within a device or circuit. There arethree kinds of internally generated noise shot, transit time andthermal.Refer to notes to explain..(italic) 24
  25. 25. Interference is a form of external noise and as the nameimplies. Means to disturb or detract from. Electrical interference is when information signals from one source produce frequencies that fall outside their allocated bandwidth and interfere with information signals from another source. Distortion A distortion is the alteration of the original shape (or other characteristic) of an object, image, sound, waveform or other form of information or representation. Distortion is usuallyunwanted, and often many methods are employed to minimize itin practice. In some fields, however, distortion may be desirable; such is the case with electric guitar distortion . 25
  26. 26. Continue distortion…………….. This diagram below shows the behaviour of a signal (made up of a square wave followed by a sine wave) as it is passed through various distorting functions. 1.The first trace (in black) shows the input. It also shows the output from a non- distorting transfer function (straight line).2. A high-pass filter (green trace) will distort the shape of a square wave byreducing its low frequency components. This is the cause of the "droop" seenon the top of the pulses. This "pulse distortion" can be very significant when atrain of pulses must pass through an AC-coupled (high-pass filtered) amplifier.As the sine wave contains only one frequency, its shape is unaltered. 26
  27. 27. 3. A low-pass filter (blue trace) will round the pulses by removing the highfrequency components. All systems are low pass to some extent. Note thatthe phase of the sine wave is different for the lowpass and the highpasscases, due to the phase distortion of the filters. 4) A slightly non-linear transfer function (purple), this one is gentlycompressing as may be typical of a tube audio amplifier, will compress thepeaks of the sine wave. This will cause small amounts of low order harmonicsto be generated.5)A hard-clipping transfer function (red) will generate high order harmonics.Parts of the transfer function are flat, which indicates that all informationabout the input signal has been lost in this region. 27
  28. 28. Signal to noise(S/N) power ratioRefer to notes…..1. Formula2. Solve S/N power ratio3. Distinguish between noise factor and noise figure. 28
  29. 29. 1.5 Electromagnetic and Radio WavesThe transmission of energy through free space (vacuum) is done byelectromagnetic waves.Electromagnetic waves are caused by oscillations of electric and magneticfields. These waves moves at a constant velocity of 3 x 10 8 m/s.Electromagnetic waves are used to transmit :a)Long or short wave radio signalsb)FM wavelength radio signalsc)Wireless communication signalsThey are also responsible for transmitting energy in the form of :a)Microwave, infrared radiation (IR)b)Ultraviolet light (UV), X-rays, Gamma rays λ=c/f 29
  30. 30. Electromagnetic SpectrumThe electromagnetic spectrum extends from below frequencies used for modern radioto gamma radiation at the short-wavelength end, covering wavelengths from thousands ofkilometers down to a fraction of the size of an atom. 30
  31. 31. Radio Frequency (RF) SpectrumAudio Frequency (AF) is any frequency that human can hear, ( 20 Hz – 20 Khz)Radio Frequency (RF) is any frequency above the range of human perceptionwhich is greater than 20 Khz. Frequency Band Frequency  Application Very Low 3 - 30 KHz > 10000m Telegraphy, human range frequency Frequency (VLF) Low Frequency 30-300 KHz 10000-1000m Point to point, navigation (LF) Medium 300K-3 MHz 1000-100m AM radio broadcast, Frequency (MF) maritime/aeronautical mobile High 3 - 30 MHz 100 - 10 m Shortwave Broadcast Radio Frequency(HF) Very high 30 - 300 10 - 1 m Low band: TV Band1- Channel 2-6, Mid Frequency(VHF) MHz band: FM radio, High Band: TV Band 2- Channel 7-13 Ultra High 300M - 1 m - 10 cm Mobile phone, Channel 14 - 70 frequency (UHF) 1GHz Super high 3-30 GHz 0.01-0.001 m satellite communucation, C-band, x- frequency (SHF) band,Ku-band, Ka-band. Extremely High 30 - 300 GHz  0.01m Satellite, radar system, IR, UV, X-rays, Frekuensi (EHF) Gamma Rays. 31
  32. 32. Analog or Digital CommunicationCommunications signals can be either by analog signals or digital signals. Theseare analog communication systems and digital communication systems.• For an analog signal, the signal is varied continuously with respect to the information.• In a digital signal, the information is encoded as a set of discrete values (for example, a set of ones and zeros). Fact – Optical Fiber provides cheaper bandwidth for long distance communication 32
  33. 33. Frequency(f),wavelength(λ) and velocity(V) V = f λ, F = 1/ T From the graph : Ampl/V. Time = 10s Amplitude = 10V frequency = 1/T = 1/10 = 0.1Hz 10 0 5 10 time/s ONE CYCLE WAVE AMPLITUDE vs TIME 33
  34. 34. Frequency(f),wavelength(λ) and velocity(V) Ampl/V . 1 0 0 5 10 distance/ m wavelength,  WAVE AMPLITUDE vs DISTANCEExample : Given f = 300Mhz and V = 3 x 108 m/s, find the wavelength.Answer : wavelength, λ = v / f = 3 x 108/ 300 x 106 = 1 meter 34
  35. 35. Frequency(f),wavelength(λ) and velocity(V) Ampl/V. 10 0 360 Angle(o) 180 WAVE AMPLITUDE vs ANGLE 35
  36. 36. Frequency(f),wavelength(λ) and speed(V) Ampl/V.  10 0 180 360 sudut (o) From the graph,  = 180o - 90o = 90o Method to calculate angle from analog wave Two oscillators that have the same frequency and different phases have a phase difference, and the oscillators are said to be out of phase with each other. The amount by which such oscillators are out of step with each other can be expressed in degrees from 0° to 360°, or in radians from 0 to 2π. 36
  37. 37. 1.5.3 BandwidthThe two most significant limitations on the performance of a communicationssystem are noise and bandwidth. The bandwidth of an information signal issimply the difference between the highest and the lowest frequenciescontained the information, and the bandwidth of a communication channel isthe difference between the highest and lowest frequencies that the channel willallow to pass through itBandwidth has several related meanings:Bandwidth (signal processing) or analog bandwidth, frequencybandwidth or radio bandwidth: a measure of the width of a range offrequencies, measured in hertzBandwidth (computing) or digital bandwidth: a rate of data transfer, bit rate orthroughput, measured in bits per second (bps)Spectral linewidth: the width of an atomic or molecular spectral line, measuredin hertz 37
  38. 38. Bandwidth…..The bandwidth of a communications channel must be large enough to passall significant information frequencies.In other words the bandwidth of thecommunications channel must be equal to or greater than the bandwidth ofthe information. Bandwidth(BW) = f2- f1 Give some example from the formula ……. 38
  39. 39. 1.6 Types of communication system 39
  40. 40. 1.Broadcast communication systemBroadcasting is the distribution of audio and video content to a dispersedaudience via radio, television, or other. Receiving parties may include the general public or a relatively largesubset of thereof.Historically, there have been several different types of electronicbroadcasting media:Example….. Block diagram of broadcast receiver using AGC 40
  41. 41. 1. Telephone broadcasting (1881–1932): the earliest form of electronicbroadcasting (not counting data services offered by stock telegraphcompanies from 1867, if ticker-tapes are excluded from the definition).Telephone broadcasting began with the advent of Théâtrophone ("TheatrePhone") systems, which were telephone-based distribution systems allowingsubscribers to listen to live operaand theatre performances over telephonelines, created by French inventor Clément Ader in 1881. Telephonebroadcasting also grew to include telephone newspaper services for newsand entertainment programming which were introduced in the1890s, primarily located in large European cities. These telephone-based subscription services were the first examples of electrical/electronicbroadcasting and offered a wide variety of programming . 2. Radio broadcasting (experimentally from 1906, commercially from 1920): radio broadcasting is an audio (sound) broadcasting service, broadcast through the air as radio waves from a transmitter to an antenna and, thus, to a receiving device. Stations can be linked in radio networks to broadcast common programming, either in syndication or simulcast or both. 41
  42. 42. Continue….3.Television broadcasting (telecast), experimentally from 1925, commerciallyfrom the 1930s: this video-programming medium was long-awaited by thegeneral public and rapidly rose to compete with its older radio-broadcastingsibling.4.Cable radio (also called "cable FM", from 1928) and cable television (from1932): both via coaxial cable, serving principally as transmission mediums forprogramming produced at either radio or television stations, with limitedproduction of cable-dedicated programming.5.Satellite television (from circa 1974) and satellite radio (from circa 1990): meantfor direct-to-home broadcast programming (as opposed to studio networkuplinks and downlinks), provides a mix of traditional radio or television broadcastprogramming, or both, with satellite-dedicated programming.6.Webcasting of video/television (from circa 1993) and audio/radio (from circa1994) streams: offers a mix of traditional radio and television station broadcastprogramming with internet-dedicated webcast programming. 42
  43. 43. 2. Mobile communication systemA mobile phone, cell phone or hand phone is an electronic device used tomake mobile telephone calls across a wide geographic area, served by manypublic cells, allowing the user to be mobile. By contrast, a cordlesstelephone is used only within the range of a single, private base station, forexample within a home or an office.A mobile phone can make and receivetelephone calls to and from the public telephone network which includesother mobiles and fixed-line phones across the world. It does this byconnecting to a cellular network provided by a mobile network operator.Inaddition to telephony, modern mobile phones also support a wide variety ofother services such as text messaging, MMS, email, Internet access, short-range wireless communications (infrared, Bluetooth), businessapplications, gaming and photography. Mobile phones that offer these moregeneral computing capabilities are referred to as smartphones. 43
  44. 44. GSM (Global System for Mobile Communications, originally Groupe SpécialMobile), is a standard set developed by the European TelecommunicationsStandards Institute (ETSI) to describe technologies for second generation (or"2G") digital cellular networks. Developed as a replacement for first generationanalog cellular networks, the GSM standard originally described a digital, circuitswitched network optimized for full duplex voice telephony. The standard was expanded over time to include first circuit switched data transport, then packet data transport via GPRS. Packet data transmission speeds were later increased via EDGE. The GSM standard is succeeded by the third generation (or 3G") UMTS standard developed by the 3GPP. GSM networks will evolve further as they begin to incorporate fourth generation (or "4G") LTE Advanced standards. "GSM" is a trademark owned by the GSM Association. 44
  45. 45. Mobile phone subscribers worldwide 700000 600000subscribers (x 1000) 500000 Analog total GSM total 400000 CDMA total 300000 TDMA total PDC/PHS total 200000 total 100000 0 1996 1997 1998 1999 2000 2001 Mobile Communications: Wireless 4.1.1 Telecommunication Systems
  46. 46. Block diagram of Mobile communication systemA wireless communication link includes a transmitter, a receiver, and achannel,as shown in Figure. Most links are full duplex and include atransmitter and a receiver or a transceiver at each end of the link 46
  47. 47. in Fig. 2-2 (a). In peer-to-peer systems, mobile units communicate directlywith each other. Mobile units sharing a frequency channel can communicatewith one another, and independent conversations can take place on differentchannels. Many amateur, and most CB radio contacts fit into this peer-to-peermodel, as shown in Fig. 2-2 (b). In peer-to-peer systems, a mobile cansometimes hear only one of two other mobiles that are using a channel, whena total of three users are active. 47
  48. 48. 3. Fixed communication systemTechnology basically gives us a lot of advantages to really connecton what we are up to and one of the most important and most commonly usedto us is “Communication”, whereas we basically exchange information from oneanother sometimes by the way of Fixed Communication Systems. I think moresurprisingly is that the evolution of this systems that allows us to communicateeven in the hardest possibilities.With the help of Fixed Communication Systems, we are able to have bettercommunication through any means of communications there is. One of the most common means of technology in our world is the telephone, and with it it’s pretty much a basic point to have access on a telephone wherever you may be. In every phone servers there is Fixed Communication System in which basically becomes the root in order for a simple communication by the use of telephone or hand held phones to another. 48
  49. 49. 4. Data communication systemData Communications is the transfer of data or information between a sourceand a receiver. The source transmits the data and the receiver receives it. Theactual generation of the information is not part of Data Communications nor isthe resulting action of the information at the receiver. Data Communication isinterested in the transfer of data, the method of transfer and the preservation ofthe data during the transfer process.In Local Area Networks, we are interested in "connectivity", connectingcomputers together to share resources. Even though the computers can havedifferent disk operating systems, languages, cabling and locations, they still cancommunicate to one another and share resources.The purpose of Data Communications is to provide the rules and regulations thatallow computers with different disk operating systems, languages, cabling andlocations to share resources. The rules and regulations are called protocols andstandards in Data Communications. 49
  51. 51. Refer to the block diagram of data communicationThere is a source of digital information ( primary station), transmissionmedium ( facility) and a destination (secondary station) .The primary source is usually a main frame computer wth its own set oflocal terminals and peripherals equipment.The digital information is then transferred by using the transmissionmedium such as free- space radio transmission ( terrestrial and satellitemicrowave), metallic cable facilities ( both digital and analog systems) andfiber-potic cable( light propogation).DTE (Data Terminal Equipment) refers to the interface equipment used at the station between the host andmodem to adapt the digital signals from the computer and terminals tosuitable form for transmission. 51
  52. 52. DCE ( data communication Equipment)Means the equipment that converts digital signal to analog signalsand interfaces the data terminal equipment to the analogtransmission medium.DCE is nothing but a modem (modulator/demodulator). It converts binary digital signals toanalog signals such as PSK.FSK and QAM and vice versa. 52
  53. 53. ASSIGNMENT1. Compare between Broadcast and mobile communication system.2. Compare between Fixed communication and data communication system. 53
  54. 54. THANK YOU 54
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