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CHAPTER 1

CHAPTER 1. Introduction to Communication System. CO1: Ability to analyze mathematical function of communication system model. Topics Covered in Chapter 1. Definitions Importance of Communication System Define and explain information, message, and signal

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CHAPTER 1

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  1. CHAPTER 1 Introduction to Communication System CO1: Ability to analyze mathematical function of communication system model.

  2. Topics Covered in Chapter 1 Definitions Importance of Communication System Define and explain information, message, and signal Basic components and requirements of Communication System Modulation, Multiplexing, Electromagnetic spectrum, & Bandwidth

  3. Definitions • Communications: • Transfer of Information from one place to another. • Should be efficient, reliable, and secured. • Communication system: • components/subsystems act together to accomplish information transfer/exchange

  4. Definitions (Cont’d) • Electronic communication system: • transmission, reception and processing of information between two or more locations using electronic circuits. • Information source: • analog/digital form

  5. Need For Communication • Importance of communication: exchange of information between two parties separated in distances in a more faster and reliable way.

  6. Information, message and signals • Information: • The commodity produced by the source for transfer to some user at the destination. • Message: • The physical manifestation of information as produced by the information source. • Signals: • A physical embodiment of information – voltage signal or current signal

  7. Brief History in Communication YearEvents 1844 Telegraph 1876 Telephone 1904 AM Radio 1923 Television 1936 FM Radio 1962 Satellite 1966 Optical links using laser and fiber optics 1972 Cellular Telephone 1989 Internet

  8. Methods of Communication • Face to face (verbal) • Gestures (non-verbal) • Signals • Written word (letters) • Electrical innovations: • Telegraph • Telephone • Radio • Television • Internet (computer)

  9. Analog Signals • Analog: • Continuous Variation in voltage or current • Assume the total range of frequencies/time • All information is transmitted • Examples: Sine & Cosine (TV, Radio, Voice) Figure 1: Analog signals (a) Sine wave “tone.” (b) Voice. (c) Video (TV) signal.

  10. Digital Signals • Digital: • Digital signals change in steps or in discrete increments. • Translates to 1’s and 0’s (binary) • Examples: Telegraph (Morse code); Continuous wave (CW) code ; Serial binary code (used in computers) Figure 2: Digital signals (a) Telegraph (Morse code). (b) Continuous-wave (CW) code. (c) Serial binary code.

  11. Digital CS Advantages: -Inexpensive -Privacy preserved(data encrypted) -Can merge different data -error correction Disadvantages: -Larger bandwidth -synchronization problem is relatively difficult Analog CS Disadvantages: -expensive -No privacy preserved -Cannot merge different data -No error correction capability Advantages: -smaller bandwidth -synchronization problem is relatively easier. Analog vs. Digital

  12. Basic Requirements of Communication System • Rate of information transfer: • how fast the information can be transferred • Purity of signal received: • whether the signal received is the same as the signal being transmit • Simplicity of the system: • the simpler the system, the better • Reliability

  13. Elements of Communication System(CS) Figure 3: A general model of all communication systems

  14. Elements of CS(cont’d) • Information • The communication system exists to convey a message. • Message comes from information source • Information forms - audio, video, text or data • Source of information: Analog [voice, telephone, video, audio] or Digital or often described in range of frequency range that they occupy

  15. cont’d… • Transmitter: • Processes input signal to produce a transmitted signal that suited the characteristic of transmission channel. • E.g. modulation, coding, mixing, translate • Other functions performed - Amplification, filtering, antenna • Message converted to into electrical signals by transducers • E.g. speech waves are converted to voltage variation by a microphone • Transmitters are made up of oscillators, amplifiers, tuned circuits and filters, modulators, frequency mixers, frequency synthesizers, and other circuits.

  16. Elements of CS(cont’d) • Channel (transmission media): • The communication channelis the medium by which the electronic signal is sent from one place to another. • Eg: Atmosphere (free space), coaxial cable, fiber optics, waveguide, Electrical conductors, Optical media, System-specific media (e.g., water is the medium for sonar). • signals undergoes degradation from noise , interference and distortion

  17. Elements of CS(cont’d) • Receiver: • to recover the message signal contained in the received signal from the output of the channel, and convert it to a form suitable for the output transducer. • E.g. mixing, demodulation, decoding • Other functions performed: Amplification, filtering. • Transducer converts the electrical signal at its input into a form desired by the system used • Receivers contain amplifiers, oscillators, mixers, tuned circuits and filters, and a demodulator or detector that recovers the original intelligence signal from the modulated carrier.

  18. Transceivers • A transceiveris an electronic unit that incorporates circuits that both send and receive signals. • Examples are: • Telephones • Fax machines • Handheld CB radios • Cell phones • Computer modems

  19. Types of Communication Systems • Analog Communications System • A system in which energy is transmitted and received in analog form • Here, both information signal and carrier are analog signal • Digital Communications System • Covers digital transmission and digital radio • Digital Transmission: True digital system where digital pulses are transferred between two or more points in communication system • It requires “physical” facility b/w transmitter and receiver. • Digital Radio: transmission of digitally modulated analog carriers b/w two or more points in a communication system.

  20. Modulation • What is modulation? • Impractical to propagate information signals over standard transmission media • So, Carrier are used to modulate the source of information onto higher frequency analog signal • a process of changing one or more properties of the analog carrier in proportion to the information signal. • One of the characteristics of the carrier signal is changed according to the variations of the modulating signal. • v(t)=Vsin(2πft+θ) [v(t): time varying sine wave of voltage; V=peak voltage; f=frequency ; θ: phase shift ] • AM – amplitude, E ; FM – frequency , ω ; PM - phase , θ

  21. Modulation (cont’d) • What are the advantages of modulation? • To generate a modulated signal suited and compatible to the characteristics of the transmission channel. • For ease radiation and reduction of antenna size • Reduction of noise and interference • Channel assignment • Increase transmission speed

  22. Modulation at the transmitter Figure 4: Modulation at the transmitter

  23. Types of Modulation Figure 5: Types of modulation. (a) Amplitude modulation. (b) Frequency modulation

  24. Multiplexing • Multiplexing is the process of allowing two or more signals to share the same medium or channel. • The three basic types of multiplexing are: • Frequency division • Time division • Code division

  25. Multiplexing at the transmitter Figure 6: Multiplexing at the transmitter

  26. Noise, interference and distortion • Noise • unwanted signals that coincide with the desired signals. • Two type of noise: internal and external noise. • Internal noise • Caused by internal devices/components in the circuits. • External noise • noise that is generated outside the circuit. • E.g. atmospheric noise, solar noise, cosmic noise, man made noise.

  27. Noise, interference and distortion (Cont’d) • Interference • Contamination by extraneous signals from human sources. • E.g. from other transmitters, power lines and machineries. • Occurs most often in radio systems whose receiving antennas usually intercept several signals at the same time • One type of noise.

  28. Noise, interference and distortion (Cont’d) • Distortion • Signals or waves perturbation caused by imperfect response of the system to the desired signal itself. • May be corrected or reduced with the help of equalizers.

  29. Attenuation • Signal attenuation,or degradation, exists in all media of wireless transmission. It is proportional to the square of the distance between the transmitter and receiver.

  30. Limitations in communication system • Technological problems • Includes equipment availability, economic factors, federal regulations and interaction with existing systems. • Problem solved in theory but perfect solutions may not be practical.

  31. Limitations in communication system (cont’d) • Physicals limitations • Bandwidth limitation • Measure of speed • The system ability to follow signal variations depends on the transmission bandwidth. • Available bandwidth determines the maximum signal speed.

  32. Limitations in communication system (cont’d) • Noise limitation • Unavoidable. • The kinetic theory. • Noise relative to an information signal is measured in terms of signal to noise ratio (SNR).

  33. Frequency and Wavelength • Cycle- One complete occurrence of a repeating wave (periodic signal) such as one positive and one negative alternation of a sine wave. • Frequency- the number of cycles of a signal that occur in one second. • Period- the time distance between two similar points on a periodic wave. • Wavelength- the distance traveled by an electromagnetic (radio) wave during one period.

  34. T = One period One cycle Period and Frequency compared time Frequency = f = 1/T

  35. Frequency and wavelength compared T  + 0 time f = 1/T distance

  36. Calculating Wavelengthand Frequency Frequency and Wavelength: Wavelength Wavelength (λ) = speed of light ÷ frequency Speed of light = 3 × 108 meters/second Therefore: λ = 3 × 108 / f in Meters or f=300/ λ MHz • Example: • What is the wavelength if the frequency is 4MHz? λ = 3 × 108 / 4 MHz = 75 meters (m)

  37. Wavelength Frequency THE ELECTROMAGNETIC SPECTRUM FROM 30 HZ TO 300 GHZ ( = 300/f) 10-1 m 10-2 m 10-3 m 10-4 m 106 m 105 m 104 m 103 m 107 m 102 m 10 m 1 m Millimeter waves ELF VLF LF MF HF VHF UHF SHF EHF VF 3 kHz 30 Hz 3 GHz 3 MHz 30 kHz 300 Hz 30 GHz 300 kHz 30 MHz 300 GHz 300 MHz (f = 300/)

  38. Low and Medium Frequencies • Extremely Low Frequencies - 30 to 300 Hz • Voice Frequencies - 300 Hz to 3 kHz • Very Low Frequencies - 3 kHz to 30 kHz • Human hearing range up to 20kHz • Low Frequencies - 30 kHz to 300 kHz • Medium Frequencies - 300 kHz to 3 MHz • AM radio 535–1605 kHz.

  39. High Frequencies • High Frequencies - 3 MHz to 30 MHz • short waves; VOA, BBC broadcasts; government and military two-way communication; amateur radio • Very High Frequencies - 30 MHz to 300 MHz • FM radio broadcasting (88–108 MHz), television channels 2–13 • Ultra High Frequencies - 300 MHz to 3 GHz • (1 GHz and above = microwaves) • TV channels 14–67, cellular phones, military communication • Super High Frequencies - 3 GHz to 30 GHz • Satellite communication, radar, wireless LANs, microwave ovens • Extremely High Frequencies - 30 GHz to 300 GHz • Satellite communication, computer data, radar

  40. The Electromagnetic Spectrum above 300 GHz Wavelength 0.8 x 10-6 m 0.4 x 10-6 m 10-5 m 10-3 m 10-4 m Millimeter waves Ultraviolet X-rays Infrared Gamma rays Visible Cosmic rays 300 GHz

  41. Optical Frequencies • Infrared - 0.7 to 10 micron • Visible light - 0.4 to 0.8 micron • Ultraviolet - Shorter than 0.4 micron Note: A micron is one millionth of a meter. Light waves are measured and expressed in wavelength rather than frequency.

  42. TYPES OF COMMUNICATIONS Simplex: One-way TX RX Channel Duplex: Two-way Half duplex: Alternate TX/RX Full duplex: Simultaneous TX/RX TX RX Channel(s) TX RX

  43. Simplex • Paging services • Navigation and direction-finding services • Telemetry • Radio astronomy • Surveillance • Music services • Internet radio and video • AM and FM broadcasting • Digital radio • TV broadcasting • Digital television (DTV) • Cable television • Facsimile • Wireless remote control

  44. Duplex • Family Radio service • The Internet • Wide-area networks (WANs) • Metropolitan-area networks (MANs) • Local area networks (LANs) • Telephones • Two-way radio • Radar • Sonar • Amateur radio • Citizens radio

  45. Various forms of communication system • Broadcast: radio and television • Mobile communications • Fixed communication system- land line • Data communication-internet

  46. Frequency Spectrum &Bandwidth • The frequency spectrum of a waveform consists of all frequencies contained in the waveform and their amplitudes plotted in the frequency domain. • The bandwidth of a frequency spectrum is the range of frequencies contained in the spectrum. It is calculated by subtracting the lowest frequency from the highest.

  47. Frequency Spectrum &Bandwidth(cont’d) • Bandwidth of the information signal equals to the difference between the highest and lowest frequency contained in the signal. • Similarly, bandwidth of communication channel is the difference between the highest and lowest frequency that the channel allow to pass through it

  48. Communication system design • Compromise within: • Transmission time and power • Signal to Noise Ratio (SNR) performance • Cost of equipments • Channel capacity • Bandwidth

  49. THANK YOU

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