PRINCIPLES OF COMMUNICATION SYSTEMS. Lecture 1- Introduction Elements, Modulation, Demodulation, Frequency Spectrum

Transcription

1 PRINCIPLES OF COMMUNICATION SYSTEMS Lecture 1- Introduction Elements, Modulation, Demodulation, Frequency Spectrum

2 Topic covered Introduction to subject Elements of Communication system Modulation General term used in communication Frequency spectrum and bandwidth

3 GENERAL INFORMATION You can find this PPT, Course plan, Assignments, reference material on course website. You can even ask doubts and give feedback on this website Link :-

4 INTRODUCTION What is communication? Communication is the process of exchanging information.

5 INTRODUCTION Methods of communication Face to face Signals Written word (letters) Electrical innovations: Telegraph Telephone Radio Television Internet (computer)

6 ELEMENTS OF A COMMUNICATION SYSTEM Basic components: Transmitter Channel or medium Receiver Noise degrades or interferes with transmitted information

7 ELEMENTS OF A COMMUNICATION SYSTEM

8 COMMUNICATION SYSTEM Transmitter The transmitter is a collection of electronic components and circuits that converts the electrical signal into a signal suitable for transmission over a given medium. Transmitters are made up of oscillators, amplifiers, tuned circuits and filters, modulators, frequency mixers, frequency synthesizers, and other circuits.

9 COMMUNICATION SYSTEM Communication Channel The communication channel is the medium by which the electronic signal is sent from one place to another. Types of media include Electrical conductors Optical media Free space System-specific media (e.g., water for sonar).

10 COMMUNICATION SYSTEM Receivers A receiver is a collection of electronic components and circuits that accepts the transmitted message from the channel and converts it back into a form understandable by humans. Receivers contain amplifiers, oscillators, mixers, tuned circuits and filters, and a demodulator or detector that recovers the original intelligence signal from the modulated carrier.

11 COMMUNICATION SYSTEM 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.

12 COMMUNICATION SYSTEM Transceivers A transceiver is an electronic unit that incorporates circuits that both send and receive signals. Examples are: Telephones Fax machines Handheld CB radios Cell phones Computer modems

13 COMMUNICATION SYSTEM Noise Noise is random, undesirable electronic energy that enters the communication system via the communicating medium and interferes with the transmitted message. We will study in more detail

14 COMMUNICATION SYSTEMS Digital Analog

15 BASEBAND Baseband Transmission Baseband information can be sent directly and unmodified over the medium or can be used to modulate a carrier for transmission over the medium. In telephone or intercom systems, the voice is placed on the wires and transmitted. In some computer networks, the digital signals are applied directly to coaxial or twisted-pair cables for transmission.

16 MODULATION AND MULTIPLEXING Modulation and multiplexing are electronic techniques for transmitting information efficiently from one place to another. Modulation makes the information signal more compatible with the medium. Multiplexing allows more than one signal to be transmitted concurrently over a single medium.

17 MODULATION Broadband Transmission A carrier is a high frequency signal that is modulated by audio, video, or data. A radio-frequency (RF) wave is an electromagnetic signal that is able to travel long distances through space. Modulation It is the process of changing one or more properties of the analog carrier in proportion with the information signal.

18 Modulation at the transmitter. MODULATION

19 WHY MODULATION IS NECESSARY? It is extremely difficult to radiate low frequency signals form an antenna in the form of electromagnetic energy. Information signals often occupy the same frequency band and if signals from two or more sources are transmitted at the same time, they would interfere with each other. Reduction in noise

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21 ANALOG SIGNAL 3 Basic Parameters of analog signal 1. Amplitude 2. Frequency 3. Phase

22 TWO SIGNALS WITH THE SAME PHASE AND FREQUENCY, BUT DIFFERENT AMPLITUDES

23 FREQUENCY Frequency is the rate of change of cycle (Positive and Negative) with respect to time. Change in a short span of time means high frequency. Change over a long span of time means low frequency.

24 3 SINE WAVES WITH FREQUENCIES 0, 8 & 16

25 PHASE Phase describes the position of the waveform relative to time 0.

26 THREE SINE WAVES WITH THE SAME AMPLITUDE AND FREQUENCY, BUT DIFFERENT PHASES

27 MODULATION AND MULTIPLEXING Types of modulation. (a) Amplitude modulation. (b) Frequency modulation.

28 MULTIPLEXING 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

29 Multiplexing at the transmitter. MULTIPLEXING

30 TYPE OF COMMUNICATION Electronic communications are classified according to whether they are 1. One-way (Simplex) or two-way (Half duplex or Full duplex) transmissions. 2. Analog or digital signals.

31 SIMPLEX The simplest method of electronic communication is referred to as simplex. This type of communication is one-way. Examples are: Radio TV broadcasting

32 HALF DUPLEX The form of two-way communication in which only one party transmits at a time is known as half duplex. Examples are: Police, military, etc. radio transmissions Walky Talky HAM radio Morse Code

33 FULL DUPLEX Most electronic communication is two-way and is referred to as duplex. When people can talk and listen simultaneously, it is called full duplex. Telephone

34 ANALOG COMMUNICATION

35 DIGITAL COMMUNICATION

36 DATA Data can be analog or digital. The term analog data refers to information that is continuous. Digital data refers to information that has discrete states. Analog data take on continuous values. Digital data take on discrete values.

37 FREQUENCY SPECTRUM Available range of frequencies for communication Starts from low frequency communication such as voice and progresses to high frequency communication such as satellite communication The spectrum spans the entire bandwidth of communicable frequencies

38 THE ELECTROMAGNETIC SPECTRUM The range of electromagnetic signals encompassing all frequencies is referred to as the electromagnetic spectrum.

39 THE ELECTROMAGNETIC SPECTRUM Figure 1-13: The electromagnetic spectrum.

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41 THE ELECTROMAGNETIC SPECTRUM Frequency Ranges from 30 Hz to 300 GHz The electromagnetic spectrum is divided into segments: Extremely Low Frequencies (ELF) Voice Frequencies (VF) Very Low Frequencies (VLF) Low Frequencies (LF) Hz Hz. include the higher end of the human hearing range up to about 20 khz khz. Medium Frequencies (MF) khz AM radio khz.

42 ELECTROMAGNETIC SPECTRUM Frequency Ranges from 30 Hz to 300 GHz High Frequencies (HF) (short waves; VOA, BBC broadcasts; government and military two-way communication; amateur radio, CB. Very High Frequencies (VHF) FM radio broadcasting ( MHz), television channels Ultra High Frequencies (UHF) TV channels 14 67, cellular phones, military communication MHz MHz MHz

43 ELECTROMAGNETIC SPECTRUM Frequency Ranges from 30 Hz to 300 GHz Microwaves and Super High Frequencies (SHF) Satellite communication, radar, wireless LANs, microwave ovens Extremely High Frequencies (EHF) Satellite communication, computer data, radar 1 30 GHz GHz

44 BA N D Frequen cy range Designations applications 2 30 Hz- 300 Hz KHz 3 KHz 4 3 KHz 30 KHz 5 30 KHZ 300 KHz MHz 3 MHz 7 3 MHZ 30 MHz 8 30 MHz MHz ELF ( Extremely low frequencies) VF ( Voice frequencies) VLF( Very low frequencies) LF (low frequencies) Mf( MEDIUM FREQUECNIE S) HF ( high frequencies) VHF( Very high frequency) Include AC power distribution signals (60Hz) and low telemetry signals. Include frequencies generally associated with human speech. Standard Telephone channels have a 300 Hz to 3000 Hz bandwidth and are often called Voice Frequency of Voice band frequencies. Includes upper end of the hearing range. Used for Specialized government and military systems like submarine communications Used for marine and aeronautical navigation Used for commercial AM radio broadcasting (535 KHZ to 1605 KHz) Referred as SHORT waves. Used in two way radio communications, Voice of America and Radio Free Europe broadcast within the HF band. Amateur radio and citizens band (CB) radio are also use signals in this range. Used for mobile radio, marine and aeronautical communications, commercial FM broadcasting ( 88 MHz to 108 MHz) and commercial TV broadcasting of channels 2 to 13 ( 54 MHz to 216

45 9 300 MHz 3 GHz 10 3 GHz 30 GHZ GHz 300 GHz UHF ( Ultra high frequency) SHF( Super high frequency) EHF ( Extremely high frequency) Used by commercial TV broadcasting of channels 14 to 83, land mobile communications services, cellular telephones, certain radar and navigation systems, and microwave and satellite Radio systems. Frequencies above 1 GHz are considered microwave frequencies, which include the upper end of the UHF range. Used for microwave and satellite radio communications systems. Seldom used for radio communication except in very sophisticated expensive and specialized applications THz 3 THz 13 3 THz 30 Thz THz 300 THz PHz- 3 PHZ 16 3 PHz- 30 PHz Infrared Light Infra red light Infra red light Visible light Ultraviolet light Not referred as radio waves. It refers to Electromagnetic radiation generally associated with heat. Used in heat seeking guidance systems, electronic photography, and astronomy. Includes electromagnetic frequencies that fall within the visible range of humans. Light wave communications is used with optical fiber systems. Ultraviolet rays, X rays, Gamma Rays and cosmic rays have little application to electronic communication.

46 ELECTROMAGNETIC FREQUENCY SPECTRUM PHz 300 PHz EHz- 3 EHz 19 3 EHz 30 EHz X rays Gamma rays Cosmic rays

47 WAVELENGTH It is the length that one cycle of an electromagnetic wave occupies in space i.e. the distance between similar points in a repetitive wave. It is inversely proportional to the velocity of propagation.

48 WAVELENGTH

49 BANDWIDTH Bandwidth (BW) is that portion of the electromagnetic spectrum occupied by a signal. Channel bandwidth refers to the range of frequencies required to transmit the desired information.

50 BANDWIDTH More Room at the Top Today, virtually the entire frequency spectrum between approximately 30 khz and 300 MHz has been spoken for. There is tremendous competition for these frequencies, between companies, individuals, and government services in individual carriers and between the different nations of the world. The electromagnetic spectrum is one of our most precious natural resources.

51 BANDWIDTH More Room at the Top Communication engineering is devoted to making the best use of that finite spectrum. Great effort goes into developing communication techniques that minimize the bandwidth required to transmit given information and thus conserve spectrum space. This provides more room for additional communication channels and gives other services or users an opportunity to take advantage of it.