SlideShare uma empresa Scribd logo
1 de 71
Baixar para ler offline
PRINCIPLES OF COMMUNICATION BY ROHAN XII SCI. 2010-11
[object Object]
[object Object]
Message signal Transmitter Communication channel Receiver Out put signal CUMMUNICATION SYSTEM
Transmitter:   Transmits   the message/signal over the communication channel. Quite often the original signal is not suitable for transmission over the communication channel to the receiver. It requires to be modified to a form suitable for transmission. Communication Channel:   Provides a link between the transmitter and the receiver. It can be a transmission line (telephone and telegraphy), an optical fibre (optical communication) or free space in which the signal is radiated in the form of electromagnetic waves. Receiver: Reconstructs the original message/signal after propagation through the communication channel.
[object Object]
[object Object]
Microphone Transmitter Amplifier Receiver Antenna   Antenna Amplifier Loud speaker
In its simplest form, the transmitter has following problems: 1. Size of the antenna or aerial   For transmitting a signal we need an antenna. It should have a size comparable   to the wavelength of the electromagnetic wave representing the signal  ( at least     /4)  so that the time variation of the signal is properly sensed by the antenna.    For an electromagnetic wave of frequency 20 kHz, the wavelength    is 15 km.   Obviously such a long antenna is not possible. Therefore,  direct transmission of   such a signal is not possible. If the frequency of the signal is 1MHz, the    corresponding wavelength is 300m and transmission of such a signal is    possible. Therefore, there is a need of  translating the information contained in    the original low frequency signal into high or radio-frequencies before   transmission. 2. Effective power radiated by an antenna   The power radiated from a linear antenna       For a good transmission we need high power hence there is need for high    frequency transmission.
3. Mixing up of signals from different transmitters   Direct transmission of baseband signal leads to interference from    multiple transmitters. Thus multiple user friendly communication is    not possible. A possible solution is provided by employing    communication at high frequencies and then allotting a band of   frequencies to each user.   The above arguments suggest that there is a  need for translating the   original signal ( low frequency) into a high frequency wave before    transmission such that the translated signal continues to possess the   information contained in the original signal. The high frequency wave    carrying the information is called the  carrier wave. The process of   transformation is called  Modulation . Modulation   Transformation of the signal into a form suitable for transmission    through a given communication channel
Modulator Amplifier Transmitter Receiver  Tunable Amplifier Demodu-lator Audio Amplifier Signal To Speaker Antenna Antenna
Basic constituents of a transmitter are:   1. Message signal  2. Modulation  3. Antenna  Message signal:   A single valued function of time that conveys the information.   Analog  Signals   Discrete or digital Analog Signal   Is a continuous function of time, with the amplitude (instantaneous    value of the signal) being continuous.
Simplest form of an analog signal is a sinusoidal signal having a single   frequency   g( t ) = A sin   t   Signals generated by different sources have their  own characteristics   - amplitude, frequency or nature.   Nature – Simple single frequency or a complex superposition of several   frequency components   The signals associated with music or speech are complex; can be    considered as superposition of several sinusoidal signals of varying    amplitudes and frequencies.   The range over which the frequencies in a signal vary is called the    bandwidth (B)  (the frequency range between the lowest and highest    frequency components). Bandwidth for audio signals is 20 Hz to 20 kHz.
Discrete Signals   Discrete signals are discontinuous in time; they are defined only at    discrete times.       In case of discrete signals the independent variable (time) takes only    discrete values which are usually uniformly spaced. Consequently,    discrete-time signals are described as sequences of samples whose   amplitudes may take a continuum of values.    When each sample of a discrete-time signal is  quantized   I.e. its    amplitude is only allowed to take on a finite set of values (e.g. in a    binary representation low and high signals are designated as 0 and 1)   and then  coded , the resulting signal is referred to as a  digital signal .
 
An analog signal can be converted into a digital signal –  A/D conversion.  A device performing this operation is called A/D converter. A discrete or digital signal can also be converted into an analog signal –  D/A conversion.  A device performing this operation is called a D/A converter. Advantages of transmitting information in the digital form are many. In a digital communication system, the receiver has to detect simple pulses, which have the same shape and height. It has only to recognize whether such a pulse is present or not in any prescribed time interval. The  signal to noise ratio  (S/N) is high.  In digital data communication, the rate at which the data is communicated is very important. It is expressed in  bits per second  (bps)
[object Object]
 
Forms of Modulation   Amplitude Modulation   Analog Signals  Angle/Frequency Modulation   Pulse Modulation   Amplitude shift keying (ASK) Digital Signals  Frequency shift keying (FSK)   Phase shift keying  (PSK)
ANALOG SIGNALS Amplitude & Frequency Modulation A sinusoidal wave conveys no information. To transmit information by the usual sinusoidal waveform, the characteristics  of the wave must be varied in some manner. A sinusoidal carrier wave C( t ) is defined by   C ( t ) =  A c  cos (   c   t  +   o  ) The modulation of the carrier wave can be accomplished in two ways:   (1)   The amplitude of   the carrier wave is varied about a mean value,    linearly with the baseband signal  m ( t ), the angular frequency    c     remaining constant. This mode of modulation is termed as amplitude    modulation.   (2) The phase angle     of the carrier wave   is varied   according to the    baseband signal, the amplitude of the carrier wave being kept   constant. This mode of modulation is termed as angle modulation.    There are two variations of angle modulation -  phase modulation    (PM)  and  frequency modulation (FM).
 
 
Amplitude Modulation: -  Employed   for commercial broadcasting of  voice signals.  Carrier    frequencies – 0.5 to 20 MHz. - Broadcast noisy – noise signals created by atmospheric static or man    made electric discharges also get amplitude modulated. Frequency Modulation: - TV   broadcast , VHF, UHF, SHF and EHF broadcasts. - Requires higher carrier wave frequencies. - Noise generated by atmospheric or man made electric discharges does    no harm to intelligence.  - Higher S/N ratio, quality of broadcast very good.   FM Radio – 88 to 108 MHz   VHF TV  –  47 to 230 MHz   UHF TV – 470 to 960 MHz
Pulse Modulation Modulation of a carrier wave may be accomplished by short pulses. Conventional telegraphy is the simplest example of this mode of modulation. Pulse systems are based on sampling of the information signal at periodic intervals, usually twice the maximum frequency present (2B). They transmit a very short pulse of radio-frequency carrier for each sample, with pulse characteristics varied in some manner proportional to the amplitude at the sampling instant. A general name given to these modes  of  modulation is the  pulse modulation. The   common   pulse systems employed in pulse modulation of analog signals are:   (i)   Pulse – amplitude modulation (PAM)  (ii)  Pulse – position modulation (PPM) (iii)  Pulse – duration/width modulation (PDM/PWM) (iv)  Pulse – code modulation  (PCM
 
Digital Signals / DATA Three modulation techniques are employed for transmitting digital signals / data. There is a step change in amplitude, frequency or phase.   1.  Amplitude – shift keying (ASK) – used for transmitting data over    optical fibre   2.  Frequency – shift keying (FSK) – Less susceptible to errors.   3.  Phase – shift keying  (PSK
 
[object Object]
 
[object Object]
 
[object Object]
 
[object Object]
Modem -  Digital data can also be represented by analog signals by use of a    modem  (modulator/demodulator). -  The modem coverts a series of binary pulse into an analog signal by    encoding the digital data into a carrier frequency. -  The resulting signal occupies a certain spectrum of frequency centred    about the carrier and propogated across the a medium suitable for that   carrier.  -  At the end of the line, the modem demodulates the signal to recover the    original data. FAX -  Facsimile or FAX means exact reproduction of a document at the    receiving end. -  The document to transmitted is first converted into digital data form. A    process called ‘scanning’, which normally is carried out by optical   means, does this. The device , which does scanning is called a    ‘scanner’. -  The digital data representing the document is then transmitted to the    destination by using a suitable medium. At the receiving end the digital    data is then used to reconstruct the original document.
 
 
[object Object]
-  Water vapour is concentrated in the lowest layer. -  Ozone in the atmosphere is confined to the ozone layer, some 50 – 80   km above the ground. -  The ionosphere, which extends from 60 – 350 km, plays an important    role in space communication. It is subdivided into layers as C, D, E,   F1, F2 Communication in space -  In space communication, a signal is emitted  from the antenna of a    transmitter in the form of an electromagnetic wave, which travels   through the intervening space and received by another antenna at the   receiver. -  An electromagnetic wave after being radiated by the transmitting    antenna  may be divided into various parts. One part travels along the    surface of the earth and is called  surface  wave  ( ground wave ).  The   remainder part moves upwards towards the sky and is called the  sky    wave .   -  A signal after being transmitted from the antenna of a transmitter can   be received by the antenna of the receiver in two ways; (a) directly by   the surface wave or (b) by the sky wave after it bounces back from the   atmosphere
EARTH’S ATMOSPHERE Ionosphere Troposphere Stratosphere Mesosphere Ozone Layer 12 km 50 km 80 km EARTH
IONOSPHERE 60 100 200 300 Height (km) C Layer D Layer n   ~ 10 8   (m  3 ) n  ~ 10 9  (m  3 ) n  ~ 10 11  (m  3 ) n  ~ 5   10 11  (m  3 ) n  ~ 8   10 11  (m  3 ) E Layer F1 Layer F2 Layer
 
-  Surface wave propagation – used for medium wave band and TV    broadcasting which is done in the frequency rang 100 – 200 MHz. In this    transmission the reception is possible only when the receiver antenna   directly intercepts the signal. Thus, if the broadcast is made from a   tower of height  h  above the ground, due to the curvature of earth  no   reception is possible beyond certain points.   -  To get larger coverage TV broadcast are made from tall antennas.    Further, the power transmitted also decreases nearly as the inverse   square of the distance hence the signal becomes weak as the distance   increases, which limits the range of transmission by this mode.  -  The ground wave attenuation increases with frequency, so the    transmission via this mode is in practice possible only for frequencies   up to about 1500 kHz or wavelengths greater than 200m. -  Below 200m wavelength, the communication in AM band is via sky   wave. -  The diffraction of electromagnetic waves also affects their    propagation.The frequencies of the waves employed for radio and   television broadcast lie in the range 5 – 1000 MHz and the   corresponding wavelengths are in the range of 30 cm – 200 m. At these   wavelengths the diffraction effects are considerable and therefore these   waves lose their directional properties.
-  Microwaves have frequencies ~ 100 – 300 GHz and therefore    wavelengths in the range of few millimeter. Because of short    wavelength, they have directional properties and better suited for   beaming signals in particular direction. This possibility was first   employed in radar. Microwave communication is extensively employed   in telecommunication as it provides larger bandwidth.  -  The waves in HF band are reflected back by the ionosphere. Therefore,    employing sky wave does the broadcasting in this band. - The ionosphere consists of positively charged ions and electrons. Such    a system is known as  plasma.  It has a characteristic frequency called   ‘plasma frequency’ given by     where  N  is the electron density. When a radiation of frequency  fp    reaches the region of electron density  N  at normal incidence, it will be   reflected. Thus the radio waves of different frequencies sent from earth   will be reflected back the appropriate layers of the ionosphere. The   critical frequency for reflection is, therefore, given by
-  There exists a distance from the transmitter, measured along the    surface of the earth, to the point where the sky wave returns to the earth   after reflection from the ionosphere. This distance is known as ‘skip   distance’ for a single hop. Using multiple hops in which the wave is   reflected between ionosphere and earth several times or beaming at   different angles can increase the range of transmission.   Satellite Communication -  With increasing demands of information technology there has been    pressure on increasing the bandwidth and therefore the carrier   frequency. -  Beyond a certain frequency (>30 MHz) the ionosphere bends any EM    wave but does not reflect it back towards earth. -  A new concept of communication, the communication via the satellite   has revolutionized the communication technology. -  Signals from an earth station are  beamed up to a satellite in space,    which acts as a microwave link repeater. The signal is amplified and   returned to earth at a different frequency to avoid interference between   the up link and down link. -  Microwave frequencies have to be used to penetrate ionosphere    because all practical satellites orbit well above the atmosphere.
 
-  The satellite communication first started in 1962 with the satellite    Telstar. The first commercially operated satellite was launched in 1965.    Since then numerous communication satellites have been launched for    the services of point-to-point telecommunication circuits, vide area TV   coverage, direct broadcasting by satellite, navigational communications   to ships and aircrafts. -  Most of the satellites orbit at heights greater than 600 km to minimize    atmospheric drag. - The choice of orbit is of fundamental importance, as it determines the    transmission path loss and delay time, the earth coverage area and time   period the satellite is visible from a given area.  -  The orbits of communication satellites are conventionally classified as    inclined elliptical, polar circular and geo-stationary.  -  The geo-stationary orbit is the most widely used orbit for    communication satellites.
 
[object Object]
 
‘ Taking photograph’ of any object relies on the reflected wave from the    object as we use visible light in normal photography. -  Selection of the wavelength of the radiation depends on the effect of    atmosphere including ionosphere and the nature of the objects to be   scanned. -  The visible and near infrared spectral bands are chosen to amplify or   separate specific earth features such as vegetation and water.  -  Data from thermal infrared bands are of high interest, particularly due to   the fact that thermal infrared data is a measure of surface temperature   and can also be obtained at night. -  Microwave data are of particular relevance for certain hydrological   variables such as soil moisture and precipitation. They can also be   obtained at night and are not restricted to cloud free conditions.  -   The spatial resolution of remote sensing data varies with the form of    sensor employed and height of the satellite. The resolution also   depends on the wavelength of radiation used. Low altitude satellites are   capable of resolving 10 m while the resolution of geo-stationary satellite   is ~ 5 km. The temporal resolution depends on the nature of the orbit.   The temporal resolution of geo-stationary satellite can be half an hour   or less while that of polar orbits could be 15 days.   -  Some applications of remote sensing include meteorology, climatology,   oceanography and coastal studies. Archeology, geological surveys,   water resource surveys, urban land use surveys, agriculture and   forestry etc
[object Object]
Transmitter Guided Medium Repeater station Receiver Point-to-point Physical Connection LINE COMMUNICATION
Twisted Pair -  Two insulated copper wires arranged in a spiral pattern form a twisted   pair  -  Twisting of wires minimizes electromagnetic interference. -  A number of such wires are bundled together into a thick cable. -  Copper conductor wires in the twisted pair provide a very low cost    medium. -  Is used for transmitting both, analog as well as digital information.  -  In local telephone services, individual telephone sets from a house are    connected to the local telephone exchange box on the street using a   twisted pair. Each one of these boxes is connected underneath by a   thick cable, which carries several twisted pairs, to the main telephone   exchange and all around the city. -  Transmission of many signals at a time in a single twisted pair is done    by transmitting the signal as a modulated wave with a fixed carrier   frequency. An analog voice signal of bandwidth 3 kHz, requires a   bandwidth of 6 kHz, if such a signal is to be transmitted in the form of a    modulated wave. If we wish to send 100 such signals over the same wire   we would then require a bandwidth of 600 kHz.
[object Object]
-  The inner conductor is held at the centre by a solid dielectric    (insulating)  material all around. -  The outer conductor is normally connected to ground and thus provides   an electrical shield to the signals carried by the central conductor. -  Most of the power is carried by the electromagnetic waves and only a   relatively small amount in the form of conduction electrons in the    central conductor.  -  Very high frequencies can be transmitted before the attenuation   becomes too severe. -  Reduced attenuation in co-axial cables increases the repeater spacing    to about  20 km and permitting much larger bandwidths (20 MHz).   Employing digital transmission further enhances the bandwidth. -  Co-axial cables are commonly used for long distance high frequency    transmission. They can carry both analog and digital signals. They are   extensively used in local area computer network for high speed data   transmission.
Optical Communication -  Communication is through optical (light) signals. -  Communication medium employed is an optical fibre -  The schematics of the essential components of an optical    communication link are as shown. -  This mode of communication provides a very large bandwidth and    therefore carry large amount of information. -  Light is a form of electromagnetic wave with frequencies lying in the    range  10 12  to 10 16  Hz and corresponding wavelengths in the range 0.03   to 300   m. -  The light emitted from He-Ne laser has    = 0.63    m, or a frequency of    ~ 4.7  10 14  Hz. If we use this light and employ only 1% of this frequency    bandwidth I.e. 4700 GHz for an optical communication channel, it offers    tremendous capacity for transmission.   -  To telecast pictures through a TV channel we need an approximate    bandwidth of 4.7 MHz per channel. The number of TV channels which    can be accommodated in a bandwidth of 4700 GHz is ~  10 6
Transmitter Optical source Input signal   Modulation Optical fibre cable Receiver Optical detector Demodulation Output signal Optical Communication
Optical Fibre -  An optical fibre is a thin fibre of glass. Its diameter is about the same as   that of a human hair ~ 10 to 100   m. -  Light can be guided in such a fibre by launching it at one end, using an    intense and focused light source, and allowing it bounce down to the   other end by a series of reflections ( total internal reflections ) from the   sides.  -  An optical fibre essentially consists of an inner cylinder of glass known    as the  core,  having a refractive index  n 1 , and an outer cylinder of a   different glass, called the  cladding  having  a  refractive index  n 2 ,   n   =    n 1    n 2  ~ 10    3  . -  For use in a telecommunications system, many fibres are usually    incorporated into a cable structure for pulling into underground ducts.
 
Photonic Devices Photonics is a subject that deals with the generation and detection of photons. The devices which generate and detect photons are called photonic devices. Such devices are extensively employed in optical communication.  To understand the functioning of these devices we need to know the different interaction mechanisms between photons and electrons in a solid. There are three important processes; (a) Absorption (b) Spontaneous emission (c) Stimulated emission
 
Optical Light Source and Optical Detector Light Source -  In optical communication light source plays a pivotal role. -  It generates a beam of light. This light wave can be modulated directly   to produce light pulses, by applying an appropriate electrical signal to   the optical source. Another alternative is to modulate the light beam   externally using an electro-optic modulator.  -  The light source to be used in optical communication is required to    have some special characteristics. -  Its physical size should be small so that it can be coupled to the thin   optical fibre. -  Monochromatic light sources which can produce light of desired   wavelength (0.85, 1.3 and 1.55   m) are preferred. -  Rapid switching. Some of these fundamental requirements are met by light emitting devices such as solid state semiconductor LASER diodes.
Light   emitting diode A light emitting diode (LED) works by the process of spontaneous emission, when a p-n junction is forward biased. In forward bias, electrons from the  n  – region migrate to the  p  – region and the holes from  the  p  – region move towards the  n  – region. Holes injected into the  n  – region quickly encounter free electrons and recombine. Electrons injected into the  p  – region encounter holes and recombine. When each electron – hole pair recombines a single photon is released which carries with it the energy required to liberate an electron from the valency bond. The wavelength and frequency of light emitted are determined by the band gap energy. The intensity of light produced is proportional to the forward current conducted by the junction that controls the number of holes and electrons crossing the junction to be recombined..
n n p Light h   =  E g Visible – Phos. Doped GaAs Infrared – Al doped  GaAs  LED Operated in  forward bias
Laser - LASER is an acronym and stands for  l ight  a mplification by  s timulated    e mission of  r adiation. -  An   important optical and electronic device. - The laser is a source of highly directional , monochromatic and coherent    light. - Laser action has been obtained using different materials, including    gases, such as neon, helium, carbon dioxide, and solids such as ruby   and semiconductors. - The action of a laser is based on the principle of stimulated emission.
When light is absorbed, electrons from the ground state  E 1  are excited to the band of level designated as E 3 . These excited levels are highly unstable, and the electrons decay rapidly to level E 2 . The energy difference E 3     E 2  is given up in the form of heat. The level E 2  is very important for the stimulated emission because this level is metastable having a mean life of few mili-seconds. If the electrons are excited from E 1  to E 3  at a rate faster than the rate E 2  back to E 1 , the population of the metastable state E 2  becomes larger than the ground state E 1 . Such a situation is called  population inversion . The population inversion is very crucial for laser action. Now if a photon of energy E 2     E 1  enters this system and interacts with one of the inverted population atoms. This photon can now actually stimulate the electron to fall from state E 2  to state E 1  and emit a photon of energy E 2     E 1 . Thus the first photon has the emission of another photon of same energy and multiplying the number of photons by a factor of two. We thus have light amplification by stimulated emission of radiation or LASER E 2     E 1 .
The construction of a semiconductor laser diode is achieved by polishing the sides of the  p-n  junction. A highly polished surface acts as a  partially reflecting surface  and also enables a back reflection process. Stimulated photons assist in the process of combining the electrons and holes by stimulating the electrons to fall quickly .
The structure of a modern semiconductor LASER designed for optical communication is very complex as shown below. The lasing material is gallium arsenide, an alloy of gallium and arsenic. It has the advantage that the material can be made  n-  type or  p -type by varying the relative proportion of the two elements. It has also the band gap whose corresponding wavelength lies in the first low loss window at 0.86   m.
Optical Detectors -  Light pulses that propagate in the fibre and reach the receiver end    become weak, due to some unavoidable losses along the way.  -  The optical detector should highly sensitive. -  The optical detector should have a quick time response. It should   respond quickly to the changing light pulses that are switching ON   and OFF. -  The physical size of the detector should be very small, so that it    can be properly coupled to the thin optical fibre.  Several kinds of photosensitive devices that generate an electrical signal  when light falls on them are used as optical detectors. These include silicon photo-diodes, avalanche photo-diodes (APD), photo-transistors, and photo-resistors .
Light p n p – n  operated in reverse bias I V    A

Mais conteúdo relacionado

Mais procurados

Introduction to communication system lecture1
Introduction to communication system lecture1Introduction to communication system lecture1
Introduction to communication system lecture1Jumaan Ally Mohamed
 
Introduction to communication systems
Introduction to communication systemsIntroduction to communication systems
Introduction to communication systemsMohsen Sarakbi
 
A Level Physics - Telecommunications
A Level Physics - TelecommunicationsA Level Physics - Telecommunications
A Level Physics - TelecommunicationsJonathan D'Cruz
 
Analog communication
Analog communicationAnalog communication
Analog communicationA. Shamel
 
Analog communication System Basic Introduction by A Sravan Kumar
Analog communication System Basic Introduction  by A Sravan KumarAnalog communication System Basic Introduction  by A Sravan Kumar
Analog communication System Basic Introduction by A Sravan KumarAPPALASRAVANKUMAR
 
Communication systems v1
Communication systems v1Communication systems v1
Communication systems v1babak danyal
 
Introduction to Communication Systems
Introduction to Communication SystemsIntroduction to Communication Systems
Introduction to Communication SystemsDr. Ghanshyam Singh
 
Wireless communication
Wireless communicationWireless communication
Wireless communicationMukesh Chinta
 
Wireless Communication and Networking by WilliamStallings Chap2
Wireless Communication and Networking  by WilliamStallings Chap2Wireless Communication and Networking  by WilliamStallings Chap2
Wireless Communication and Networking by WilliamStallings Chap2Senthil Kanth
 
Analog vs digital communication
Analog vs digital communicationAnalog vs digital communication
Analog vs digital communicationSahil Rana
 
Unit-1_Analog Communication_PPT (1).pptx
Unit-1_Analog Communication_PPT (1).pptxUnit-1_Analog Communication_PPT (1).pptx
Unit-1_Analog Communication_PPT (1).pptxVairaPrakash2
 
Electronics and Communication Engineering : Communications, THE GATE ACADEMY
Electronics and Communication Engineering : Communications, THE GATE ACADEMYElectronics and Communication Engineering : Communications, THE GATE ACADEMY
Electronics and Communication Engineering : Communications, THE GATE ACADEMYklirantga
 
Introduction to Communication Systems 3
Introduction to Communication Systems 3Introduction to Communication Systems 3
Introduction to Communication Systems 3slmnsvn
 
Networking notes part2 final
Networking notes part2 finalNetworking notes part2 final
Networking notes part2 finalSHARVAN PRAJAPATI
 
komdat3
komdat3komdat3
komdat3pasca
 

Mais procurados (20)

Introduction to communication system lecture1
Introduction to communication system lecture1Introduction to communication system lecture1
Introduction to communication system lecture1
 
Introduction to communication systems
Introduction to communication systemsIntroduction to communication systems
Introduction to communication systems
 
A Level Physics - Telecommunications
A Level Physics - TelecommunicationsA Level Physics - Telecommunications
A Level Physics - Telecommunications
 
Analog communication
Analog communicationAnalog communication
Analog communication
 
Analog communication System Basic Introduction by A Sravan Kumar
Analog communication System Basic Introduction  by A Sravan KumarAnalog communication System Basic Introduction  by A Sravan Kumar
Analog communication System Basic Introduction by A Sravan Kumar
 
Communication systems v1
Communication systems v1Communication systems v1
Communication systems v1
 
Introduction to Communication Systems
Introduction to Communication SystemsIntroduction to Communication Systems
Introduction to Communication Systems
 
Ripple Control Receiver
Ripple Control ReceiverRipple Control Receiver
Ripple Control Receiver
 
Wireless communication
Wireless communicationWireless communication
Wireless communication
 
Communication
CommunicationCommunication
Communication
 
Wireless Communication and Networking by WilliamStallings Chap2
Wireless Communication and Networking  by WilliamStallings Chap2Wireless Communication and Networking  by WilliamStallings Chap2
Wireless Communication and Networking by WilliamStallings Chap2
 
Analog vs digital communication
Analog vs digital communicationAnalog vs digital communication
Analog vs digital communication
 
Unit-1_Analog Communication_PPT (1).pptx
Unit-1_Analog Communication_PPT (1).pptxUnit-1_Analog Communication_PPT (1).pptx
Unit-1_Analog Communication_PPT (1).pptx
 
Communication system
Communication systemCommunication system
Communication system
 
Ep301
Ep301Ep301
Ep301
 
Electronics and Communication Engineering : Communications, THE GATE ACADEMY
Electronics and Communication Engineering : Communications, THE GATE ACADEMYElectronics and Communication Engineering : Communications, THE GATE ACADEMY
Electronics and Communication Engineering : Communications, THE GATE ACADEMY
 
Introduction to Communication Systems 3
Introduction to Communication Systems 3Introduction to Communication Systems 3
Introduction to Communication Systems 3
 
Networking notes part2 final
Networking notes part2 finalNetworking notes part2 final
Networking notes part2 final
 
Chapter#2
Chapter#2Chapter#2
Chapter#2
 
komdat3
komdat3komdat3
komdat3
 

Semelhante a Communications

Wireless communication
Wireless communicationWireless communication
Wireless communicationMukesh Chinta
 
Communication theory
Communication theoryCommunication theory
Communication theoryVijay Balaji
 
Communication system 1 chapter 1 ppt
Communication system 1 chapter  1 pptCommunication system 1 chapter  1 ppt
Communication system 1 chapter 1 pptBetelihemMesfin1
 
ELEKTRONIKA_KOMUNIKASI_and_GELOMBANG_MIK (2).pptx
ELEKTRONIKA_KOMUNIKASI_and_GELOMBANG_MIK (2).pptxELEKTRONIKA_KOMUNIKASI_and_GELOMBANG_MIK (2).pptx
ELEKTRONIKA_KOMUNIKASI_and_GELOMBANG_MIK (2).pptxzainal968005
 
Comms 1.docx
Comms 1.docxComms 1.docx
Comms 1.docx03211830
 
Modulation seminar report
Modulation seminar reportModulation seminar report
Modulation seminar reportAmit Sahu
 
Modulation seminar report
Modulation seminar reportModulation seminar report
Modulation seminar reportAmit Sahu
 
Wmcn ch.2
Wmcn ch.2Wmcn ch.2
Wmcn ch.2Alaa2
 
Physics Class 12 Communication Powerpoint presentation
Physics Class 12 Communication Powerpoint presentationPhysics Class 12 Communication Powerpoint presentation
Physics Class 12 Communication Powerpoint presentationBibin Vincent
 
Telecommunications basics
Telecommunications basicsTelecommunications basics
Telecommunications basicsAarón Candia
 
Introduction & Wireless Transmission
Introduction & Wireless TransmissionIntroduction & Wireless Transmission
Introduction & Wireless TransmissionJoe Christensen
 
Module 1 PCS notes.pptx
Module 1 PCS notes.pptxModule 1 PCS notes.pptx
Module 1 PCS notes.pptxSaralaT3
 

Semelhante a Communications (20)

Rf fundamentals
Rf fundamentalsRf fundamentals
Rf fundamentals
 
Wireless communication
Wireless communicationWireless communication
Wireless communication
 
Communication theory
Communication theoryCommunication theory
Communication theory
 
Communication system 1 chapter 1 ppt
Communication system 1 chapter  1 pptCommunication system 1 chapter  1 ppt
Communication system 1 chapter 1 ppt
 
ELEKTRONIKA_KOMUNIKASI_and_GELOMBANG_MIK (2).pptx
ELEKTRONIKA_KOMUNIKASI_and_GELOMBANG_MIK (2).pptxELEKTRONIKA_KOMUNIKASI_and_GELOMBANG_MIK (2).pptx
ELEKTRONIKA_KOMUNIKASI_and_GELOMBANG_MIK (2).pptx
 
Comms 1.docx
Comms 1.docxComms 1.docx
Comms 1.docx
 
Modulation seminar report
Modulation seminar reportModulation seminar report
Modulation seminar report
 
Modulation seminar report
Modulation seminar reportModulation seminar report
Modulation seminar report
 
Unit 5.doc
Unit 5.docUnit 5.doc
Unit 5.doc
 
Unit 5.doc
Unit 5.docUnit 5.doc
Unit 5.doc
 
dspppt.pptx
dspppt.pptxdspppt.pptx
dspppt.pptx
 
Wmcn ch.2
Wmcn ch.2Wmcn ch.2
Wmcn ch.2
 
Introduction.pdf
Introduction.pdfIntroduction.pdf
Introduction.pdf
 
Physics Class 12 Communication Powerpoint presentation
Physics Class 12 Communication Powerpoint presentationPhysics Class 12 Communication Powerpoint presentation
Physics Class 12 Communication Powerpoint presentation
 
Telecommunications basics
Telecommunications basicsTelecommunications basics
Telecommunications basics
 
Introduction & Wireless Transmission
Introduction & Wireless TransmissionIntroduction & Wireless Transmission
Introduction & Wireless Transmission
 
ADC Unit 1.pdf
ADC Unit 1.pdfADC Unit 1.pdf
ADC Unit 1.pdf
 
Module 1 PCS notes.pptx
Module 1 PCS notes.pptxModule 1 PCS notes.pptx
Module 1 PCS notes.pptx
 
lecture15.ppt
lecture15.pptlecture15.ppt
lecture15.ppt
 
lecture15.ppt
lecture15.pptlecture15.ppt
lecture15.ppt
 

Mais de KANNAN

Faith Academy
Faith Academy Faith Academy
Faith Academy KANNAN
 
Possibility thinking
Possibility thinkingPossibility thinking
Possibility thinkingKANNAN
 
Thermal energy
Thermal energyThermal energy
Thermal energyKANNAN
 
Electromagnetic waves
Electromagnetic wavesElectromagnetic waves
Electromagnetic wavesKANNAN
 
Talent plus
Talent plusTalent plus
Talent plusKANNAN
 
QUALITIES OF A GOOD TEACHER
QUALITIES OF A GOOD TEACHERQUALITIES OF A GOOD TEACHER
QUALITIES OF A GOOD TEACHERKANNAN
 
Electricity and magnetism
Electricity and magnetismElectricity and magnetism
Electricity and magnetismKANNAN
 
Nanotechnology
NanotechnologyNanotechnology
NanotechnologyKANNAN
 
Nursery parents orientation programme
Nursery parents orientation programmeNursery parents orientation programme
Nursery parents orientation programmeKANNAN
 
A Leader
A LeaderA Leader
A LeaderKANNAN
 
Instructions
InstructionsInstructions
InstructionsKANNAN
 
Chrysantenfeestin lahr duitsland
Chrysantenfeestin lahr duitslandChrysantenfeestin lahr duitsland
Chrysantenfeestin lahr duitslandKANNAN
 
Winning with people
Winning with people Winning with people
Winning with people KANNAN
 
Win win relationship
Win win relationshipWin win relationship
Win win relationshipKANNAN
 
Beautiful creation of LORD JESUS CHRIST
Beautiful creation of LORD JESUS CHRISTBeautiful creation of LORD JESUS CHRIST
Beautiful creation of LORD JESUS CHRISTKANNAN
 
FAITH ACADEMY
FAITH ACADEMYFAITH ACADEMY
FAITH ACADEMYKANNAN
 
BETTER FINANCIAL MANAGEMENT
BETTER FINANCIAL MANAGEMENTBETTER FINANCIAL MANAGEMENT
BETTER FINANCIAL MANAGEMENTKANNAN
 
Electric Current and Building Analogy
Electric Current and Building AnalogyElectric Current and Building Analogy
Electric Current and Building AnalogyKANNAN
 
APPLICATIONS OF SHM
APPLICATIONS OF SHMAPPLICATIONS OF SHM
APPLICATIONS OF SHMKANNAN
 

Mais de KANNAN (20)

Faith Academy
Faith Academy Faith Academy
Faith Academy
 
Possibility thinking
Possibility thinkingPossibility thinking
Possibility thinking
 
Thermal energy
Thermal energyThermal energy
Thermal energy
 
Electromagnetic waves
Electromagnetic wavesElectromagnetic waves
Electromagnetic waves
 
Talent plus
Talent plusTalent plus
Talent plus
 
QUALITIES OF A GOOD TEACHER
QUALITIES OF A GOOD TEACHERQUALITIES OF A GOOD TEACHER
QUALITIES OF A GOOD TEACHER
 
Light
LightLight
Light
 
Electricity and magnetism
Electricity and magnetismElectricity and magnetism
Electricity and magnetism
 
Nanotechnology
NanotechnologyNanotechnology
Nanotechnology
 
Nursery parents orientation programme
Nursery parents orientation programmeNursery parents orientation programme
Nursery parents orientation programme
 
A Leader
A LeaderA Leader
A Leader
 
Instructions
InstructionsInstructions
Instructions
 
Chrysantenfeestin lahr duitsland
Chrysantenfeestin lahr duitslandChrysantenfeestin lahr duitsland
Chrysantenfeestin lahr duitsland
 
Winning with people
Winning with people Winning with people
Winning with people
 
Win win relationship
Win win relationshipWin win relationship
Win win relationship
 
Beautiful creation of LORD JESUS CHRIST
Beautiful creation of LORD JESUS CHRISTBeautiful creation of LORD JESUS CHRIST
Beautiful creation of LORD JESUS CHRIST
 
FAITH ACADEMY
FAITH ACADEMYFAITH ACADEMY
FAITH ACADEMY
 
BETTER FINANCIAL MANAGEMENT
BETTER FINANCIAL MANAGEMENTBETTER FINANCIAL MANAGEMENT
BETTER FINANCIAL MANAGEMENT
 
Electric Current and Building Analogy
Electric Current and Building AnalogyElectric Current and Building Analogy
Electric Current and Building Analogy
 
APPLICATIONS OF SHM
APPLICATIONS OF SHMAPPLICATIONS OF SHM
APPLICATIONS OF SHM
 

Último

What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?TechSoup
 
Quality Assurance_GOOD LABORATORY PRACTICE
Quality Assurance_GOOD LABORATORY PRACTICEQuality Assurance_GOOD LABORATORY PRACTICE
Quality Assurance_GOOD LABORATORY PRACTICESayali Powar
 
Drug Information Services- DIC and Sources.
Drug Information Services- DIC and Sources.Drug Information Services- DIC and Sources.
Drug Information Services- DIC and Sources.raviapr7
 
How to Use api.constrains ( ) in Odoo 17
How to Use api.constrains ( ) in Odoo 17How to Use api.constrains ( ) in Odoo 17
How to Use api.constrains ( ) in Odoo 17Celine George
 
Education and training program in the hospital APR.pptx
Education and training program in the hospital APR.pptxEducation and training program in the hospital APR.pptx
Education and training program in the hospital APR.pptxraviapr7
 
Presentation on the Basics of Writing. Writing a Paragraph
Presentation on the Basics of Writing. Writing a ParagraphPresentation on the Basics of Writing. Writing a Paragraph
Presentation on the Basics of Writing. Writing a ParagraphNetziValdelomar1
 
Practical Research 1: Lesson 8 Writing the Thesis Statement.pptx
Practical Research 1: Lesson 8 Writing the Thesis Statement.pptxPractical Research 1: Lesson 8 Writing the Thesis Statement.pptx
Practical Research 1: Lesson 8 Writing the Thesis Statement.pptxKatherine Villaluna
 
CAULIFLOWER BREEDING 1 Parmar pptx
CAULIFLOWER BREEDING 1 Parmar pptxCAULIFLOWER BREEDING 1 Parmar pptx
CAULIFLOWER BREEDING 1 Parmar pptxSaurabhParmar42
 
Maximizing Impact_ Nonprofit Website Planning, Budgeting, and Design.pdf
Maximizing Impact_ Nonprofit Website Planning, Budgeting, and Design.pdfMaximizing Impact_ Nonprofit Website Planning, Budgeting, and Design.pdf
Maximizing Impact_ Nonprofit Website Planning, Budgeting, and Design.pdfTechSoup
 
3.21.24 The Origins of Black Power.pptx
3.21.24  The Origins of Black Power.pptx3.21.24  The Origins of Black Power.pptx
3.21.24 The Origins of Black Power.pptxmary850239
 
How to Add a New Field in Existing Kanban View in Odoo 17
How to Add a New Field in Existing Kanban View in Odoo 17How to Add a New Field in Existing Kanban View in Odoo 17
How to Add a New Field in Existing Kanban View in Odoo 17Celine George
 
The Singapore Teaching Practice document
The Singapore Teaching Practice documentThe Singapore Teaching Practice document
The Singapore Teaching Practice documentXsasf Sfdfasd
 
Patterns of Written Texts Across Disciplines.pptx
Patterns of Written Texts Across Disciplines.pptxPatterns of Written Texts Across Disciplines.pptx
Patterns of Written Texts Across Disciplines.pptxMYDA ANGELICA SUAN
 
M-2- General Reactions of amino acids.pptx
M-2- General Reactions of amino acids.pptxM-2- General Reactions of amino acids.pptx
M-2- General Reactions of amino acids.pptxDr. Santhosh Kumar. N
 
How to Make a Field read-only in Odoo 17
How to Make a Field read-only in Odoo 17How to Make a Field read-only in Odoo 17
How to Make a Field read-only in Odoo 17Celine George
 
How to Show Error_Warning Messages in Odoo 17
How to Show Error_Warning Messages in Odoo 17How to Show Error_Warning Messages in Odoo 17
How to Show Error_Warning Messages in Odoo 17Celine George
 
Prescribed medication order and communication skills.pptx
Prescribed medication order and communication skills.pptxPrescribed medication order and communication skills.pptx
Prescribed medication order and communication skills.pptxraviapr7
 

Último (20)

What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?
 
Quality Assurance_GOOD LABORATORY PRACTICE
Quality Assurance_GOOD LABORATORY PRACTICEQuality Assurance_GOOD LABORATORY PRACTICE
Quality Assurance_GOOD LABORATORY PRACTICE
 
Drug Information Services- DIC and Sources.
Drug Information Services- DIC and Sources.Drug Information Services- DIC and Sources.
Drug Information Services- DIC and Sources.
 
How to Use api.constrains ( ) in Odoo 17
How to Use api.constrains ( ) in Odoo 17How to Use api.constrains ( ) in Odoo 17
How to Use api.constrains ( ) in Odoo 17
 
Personal Resilience in Project Management 2 - TV Edit 1a.pdf
Personal Resilience in Project Management 2 - TV Edit 1a.pdfPersonal Resilience in Project Management 2 - TV Edit 1a.pdf
Personal Resilience in Project Management 2 - TV Edit 1a.pdf
 
Education and training program in the hospital APR.pptx
Education and training program in the hospital APR.pptxEducation and training program in the hospital APR.pptx
Education and training program in the hospital APR.pptx
 
Prelims of Kant get Marx 2.0: a general politics quiz
Prelims of Kant get Marx 2.0: a general politics quizPrelims of Kant get Marx 2.0: a general politics quiz
Prelims of Kant get Marx 2.0: a general politics quiz
 
Presentation on the Basics of Writing. Writing a Paragraph
Presentation on the Basics of Writing. Writing a ParagraphPresentation on the Basics of Writing. Writing a Paragraph
Presentation on the Basics of Writing. Writing a Paragraph
 
Finals of Kant get Marx 2.0 : a general politics quiz
Finals of Kant get Marx 2.0 : a general politics quizFinals of Kant get Marx 2.0 : a general politics quiz
Finals of Kant get Marx 2.0 : a general politics quiz
 
Practical Research 1: Lesson 8 Writing the Thesis Statement.pptx
Practical Research 1: Lesson 8 Writing the Thesis Statement.pptxPractical Research 1: Lesson 8 Writing the Thesis Statement.pptx
Practical Research 1: Lesson 8 Writing the Thesis Statement.pptx
 
CAULIFLOWER BREEDING 1 Parmar pptx
CAULIFLOWER BREEDING 1 Parmar pptxCAULIFLOWER BREEDING 1 Parmar pptx
CAULIFLOWER BREEDING 1 Parmar pptx
 
Maximizing Impact_ Nonprofit Website Planning, Budgeting, and Design.pdf
Maximizing Impact_ Nonprofit Website Planning, Budgeting, and Design.pdfMaximizing Impact_ Nonprofit Website Planning, Budgeting, and Design.pdf
Maximizing Impact_ Nonprofit Website Planning, Budgeting, and Design.pdf
 
3.21.24 The Origins of Black Power.pptx
3.21.24  The Origins of Black Power.pptx3.21.24  The Origins of Black Power.pptx
3.21.24 The Origins of Black Power.pptx
 
How to Add a New Field in Existing Kanban View in Odoo 17
How to Add a New Field in Existing Kanban View in Odoo 17How to Add a New Field in Existing Kanban View in Odoo 17
How to Add a New Field in Existing Kanban View in Odoo 17
 
The Singapore Teaching Practice document
The Singapore Teaching Practice documentThe Singapore Teaching Practice document
The Singapore Teaching Practice document
 
Patterns of Written Texts Across Disciplines.pptx
Patterns of Written Texts Across Disciplines.pptxPatterns of Written Texts Across Disciplines.pptx
Patterns of Written Texts Across Disciplines.pptx
 
M-2- General Reactions of amino acids.pptx
M-2- General Reactions of amino acids.pptxM-2- General Reactions of amino acids.pptx
M-2- General Reactions of amino acids.pptx
 
How to Make a Field read-only in Odoo 17
How to Make a Field read-only in Odoo 17How to Make a Field read-only in Odoo 17
How to Make a Field read-only in Odoo 17
 
How to Show Error_Warning Messages in Odoo 17
How to Show Error_Warning Messages in Odoo 17How to Show Error_Warning Messages in Odoo 17
How to Show Error_Warning Messages in Odoo 17
 
Prescribed medication order and communication skills.pptx
Prescribed medication order and communication skills.pptxPrescribed medication order and communication skills.pptx
Prescribed medication order and communication skills.pptx
 

Communications

  • 1. PRINCIPLES OF COMMUNICATION BY ROHAN XII SCI. 2010-11
  • 2.
  • 3.
  • 4. Message signal Transmitter Communication channel Receiver Out put signal CUMMUNICATION SYSTEM
  • 5. Transmitter: Transmits the message/signal over the communication channel. Quite often the original signal is not suitable for transmission over the communication channel to the receiver. It requires to be modified to a form suitable for transmission. Communication Channel: Provides a link between the transmitter and the receiver. It can be a transmission line (telephone and telegraphy), an optical fibre (optical communication) or free space in which the signal is radiated in the form of electromagnetic waves. Receiver: Reconstructs the original message/signal after propagation through the communication channel.
  • 6.
  • 7.
  • 8. Microphone Transmitter Amplifier Receiver Antenna Antenna Amplifier Loud speaker
  • 9. In its simplest form, the transmitter has following problems: 1. Size of the antenna or aerial For transmitting a signal we need an antenna. It should have a size comparable to the wavelength of the electromagnetic wave representing the signal ( at least  /4) so that the time variation of the signal is properly sensed by the antenna. For an electromagnetic wave of frequency 20 kHz, the wavelength  is 15 km. Obviously such a long antenna is not possible. Therefore, direct transmission of such a signal is not possible. If the frequency of the signal is 1MHz, the corresponding wavelength is 300m and transmission of such a signal is possible. Therefore, there is a need of translating the information contained in the original low frequency signal into high or radio-frequencies before transmission. 2. Effective power radiated by an antenna The power radiated from a linear antenna  For a good transmission we need high power hence there is need for high frequency transmission.
  • 10. 3. Mixing up of signals from different transmitters Direct transmission of baseband signal leads to interference from multiple transmitters. Thus multiple user friendly communication is not possible. A possible solution is provided by employing communication at high frequencies and then allotting a band of frequencies to each user. The above arguments suggest that there is a need for translating the original signal ( low frequency) into a high frequency wave before transmission such that the translated signal continues to possess the information contained in the original signal. The high frequency wave carrying the information is called the carrier wave. The process of transformation is called Modulation . Modulation Transformation of the signal into a form suitable for transmission through a given communication channel
  • 11. Modulator Amplifier Transmitter Receiver Tunable Amplifier Demodu-lator Audio Amplifier Signal To Speaker Antenna Antenna
  • 12. Basic constituents of a transmitter are: 1. Message signal 2. Modulation 3. Antenna Message signal: A single valued function of time that conveys the information. Analog Signals Discrete or digital Analog Signal Is a continuous function of time, with the amplitude (instantaneous value of the signal) being continuous.
  • 13. Simplest form of an analog signal is a sinusoidal signal having a single frequency g( t ) = A sin  t Signals generated by different sources have their own characteristics - amplitude, frequency or nature. Nature – Simple single frequency or a complex superposition of several frequency components The signals associated with music or speech are complex; can be considered as superposition of several sinusoidal signals of varying amplitudes and frequencies. The range over which the frequencies in a signal vary is called the bandwidth (B) (the frequency range between the lowest and highest frequency components). Bandwidth for audio signals is 20 Hz to 20 kHz.
  • 14. Discrete Signals Discrete signals are discontinuous in time; they are defined only at discrete times. In case of discrete signals the independent variable (time) takes only discrete values which are usually uniformly spaced. Consequently, discrete-time signals are described as sequences of samples whose amplitudes may take a continuum of values. When each sample of a discrete-time signal is quantized I.e. its amplitude is only allowed to take on a finite set of values (e.g. in a binary representation low and high signals are designated as 0 and 1) and then coded , the resulting signal is referred to as a digital signal .
  • 15.  
  • 16. An analog signal can be converted into a digital signal – A/D conversion. A device performing this operation is called A/D converter. A discrete or digital signal can also be converted into an analog signal – D/A conversion. A device performing this operation is called a D/A converter. Advantages of transmitting information in the digital form are many. In a digital communication system, the receiver has to detect simple pulses, which have the same shape and height. It has only to recognize whether such a pulse is present or not in any prescribed time interval. The signal to noise ratio (S/N) is high. In digital data communication, the rate at which the data is communicated is very important. It is expressed in bits per second (bps)
  • 17.
  • 18.  
  • 19. Forms of Modulation Amplitude Modulation Analog Signals Angle/Frequency Modulation Pulse Modulation Amplitude shift keying (ASK) Digital Signals Frequency shift keying (FSK) Phase shift keying (PSK)
  • 20. ANALOG SIGNALS Amplitude & Frequency Modulation A sinusoidal wave conveys no information. To transmit information by the usual sinusoidal waveform, the characteristics of the wave must be varied in some manner. A sinusoidal carrier wave C( t ) is defined by C ( t ) = A c cos (   c t +  o ) The modulation of the carrier wave can be accomplished in two ways: (1) The amplitude of the carrier wave is varied about a mean value, linearly with the baseband signal m ( t ), the angular frequency   c remaining constant. This mode of modulation is termed as amplitude modulation. (2) The phase angle  of the carrier wave is varied according to the baseband signal, the amplitude of the carrier wave being kept constant. This mode of modulation is termed as angle modulation. There are two variations of angle modulation - phase modulation (PM) and frequency modulation (FM).
  • 21.  
  • 22.  
  • 23. Amplitude Modulation: - Employed for commercial broadcasting of voice signals. Carrier frequencies – 0.5 to 20 MHz. - Broadcast noisy – noise signals created by atmospheric static or man made electric discharges also get amplitude modulated. Frequency Modulation: - TV broadcast , VHF, UHF, SHF and EHF broadcasts. - Requires higher carrier wave frequencies. - Noise generated by atmospheric or man made electric discharges does no harm to intelligence. - Higher S/N ratio, quality of broadcast very good. FM Radio – 88 to 108 MHz VHF TV – 47 to 230 MHz UHF TV – 470 to 960 MHz
  • 24. Pulse Modulation Modulation of a carrier wave may be accomplished by short pulses. Conventional telegraphy is the simplest example of this mode of modulation. Pulse systems are based on sampling of the information signal at periodic intervals, usually twice the maximum frequency present (2B). They transmit a very short pulse of radio-frequency carrier for each sample, with pulse characteristics varied in some manner proportional to the amplitude at the sampling instant. A general name given to these modes of modulation is the pulse modulation. The common pulse systems employed in pulse modulation of analog signals are: (i) Pulse – amplitude modulation (PAM) (ii) Pulse – position modulation (PPM) (iii) Pulse – duration/width modulation (PDM/PWM) (iv) Pulse – code modulation (PCM
  • 25.  
  • 26. Digital Signals / DATA Three modulation techniques are employed for transmitting digital signals / data. There is a step change in amplitude, frequency or phase. 1. Amplitude – shift keying (ASK) – used for transmitting data over optical fibre 2. Frequency – shift keying (FSK) – Less susceptible to errors. 3. Phase – shift keying (PSK
  • 27.  
  • 28.
  • 29.  
  • 30.
  • 31.  
  • 32.
  • 33.  
  • 34.
  • 35. Modem - Digital data can also be represented by analog signals by use of a modem (modulator/demodulator). - The modem coverts a series of binary pulse into an analog signal by encoding the digital data into a carrier frequency. - The resulting signal occupies a certain spectrum of frequency centred about the carrier and propogated across the a medium suitable for that carrier. - At the end of the line, the modem demodulates the signal to recover the original data. FAX - Facsimile or FAX means exact reproduction of a document at the receiving end. - The document to transmitted is first converted into digital data form. A process called ‘scanning’, which normally is carried out by optical means, does this. The device , which does scanning is called a ‘scanner’. - The digital data representing the document is then transmitted to the destination by using a suitable medium. At the receiving end the digital data is then used to reconstruct the original document.
  • 36.  
  • 37.  
  • 38.
  • 39. - Water vapour is concentrated in the lowest layer. - Ozone in the atmosphere is confined to the ozone layer, some 50 – 80 km above the ground. - The ionosphere, which extends from 60 – 350 km, plays an important role in space communication. It is subdivided into layers as C, D, E, F1, F2 Communication in space - In space communication, a signal is emitted from the antenna of a transmitter in the form of an electromagnetic wave, which travels through the intervening space and received by another antenna at the receiver. - An electromagnetic wave after being radiated by the transmitting antenna may be divided into various parts. One part travels along the surface of the earth and is called surface wave ( ground wave ). The remainder part moves upwards towards the sky and is called the sky wave . - A signal after being transmitted from the antenna of a transmitter can be received by the antenna of the receiver in two ways; (a) directly by the surface wave or (b) by the sky wave after it bounces back from the atmosphere
  • 40. EARTH’S ATMOSPHERE Ionosphere Troposphere Stratosphere Mesosphere Ozone Layer 12 km 50 km 80 km EARTH
  • 41. IONOSPHERE 60 100 200 300 Height (km) C Layer D Layer n ~ 10 8 (m  3 ) n ~ 10 9 (m  3 ) n ~ 10 11 (m  3 ) n ~ 5  10 11 (m  3 ) n ~ 8  10 11 (m  3 ) E Layer F1 Layer F2 Layer
  • 42.  
  • 43. - Surface wave propagation – used for medium wave band and TV broadcasting which is done in the frequency rang 100 – 200 MHz. In this transmission the reception is possible only when the receiver antenna directly intercepts the signal. Thus, if the broadcast is made from a tower of height h above the ground, due to the curvature of earth no reception is possible beyond certain points. - To get larger coverage TV broadcast are made from tall antennas. Further, the power transmitted also decreases nearly as the inverse square of the distance hence the signal becomes weak as the distance increases, which limits the range of transmission by this mode. - The ground wave attenuation increases with frequency, so the transmission via this mode is in practice possible only for frequencies up to about 1500 kHz or wavelengths greater than 200m. - Below 200m wavelength, the communication in AM band is via sky wave. - The diffraction of electromagnetic waves also affects their propagation.The frequencies of the waves employed for radio and television broadcast lie in the range 5 – 1000 MHz and the corresponding wavelengths are in the range of 30 cm – 200 m. At these wavelengths the diffraction effects are considerable and therefore these waves lose their directional properties.
  • 44. - Microwaves have frequencies ~ 100 – 300 GHz and therefore wavelengths in the range of few millimeter. Because of short wavelength, they have directional properties and better suited for beaming signals in particular direction. This possibility was first employed in radar. Microwave communication is extensively employed in telecommunication as it provides larger bandwidth. - The waves in HF band are reflected back by the ionosphere. Therefore, employing sky wave does the broadcasting in this band. - The ionosphere consists of positively charged ions and electrons. Such a system is known as plasma. It has a characteristic frequency called ‘plasma frequency’ given by where N is the electron density. When a radiation of frequency fp reaches the region of electron density N at normal incidence, it will be reflected. Thus the radio waves of different frequencies sent from earth will be reflected back the appropriate layers of the ionosphere. The critical frequency for reflection is, therefore, given by
  • 45. - There exists a distance from the transmitter, measured along the surface of the earth, to the point where the sky wave returns to the earth after reflection from the ionosphere. This distance is known as ‘skip distance’ for a single hop. Using multiple hops in which the wave is reflected between ionosphere and earth several times or beaming at different angles can increase the range of transmission. Satellite Communication - With increasing demands of information technology there has been pressure on increasing the bandwidth and therefore the carrier frequency. - Beyond a certain frequency (>30 MHz) the ionosphere bends any EM wave but does not reflect it back towards earth. - A new concept of communication, the communication via the satellite has revolutionized the communication technology. - Signals from an earth station are beamed up to a satellite in space, which acts as a microwave link repeater. The signal is amplified and returned to earth at a different frequency to avoid interference between the up link and down link. - Microwave frequencies have to be used to penetrate ionosphere because all practical satellites orbit well above the atmosphere.
  • 46.  
  • 47. - The satellite communication first started in 1962 with the satellite Telstar. The first commercially operated satellite was launched in 1965. Since then numerous communication satellites have been launched for the services of point-to-point telecommunication circuits, vide area TV coverage, direct broadcasting by satellite, navigational communications to ships and aircrafts. - Most of the satellites orbit at heights greater than 600 km to minimize atmospheric drag. - The choice of orbit is of fundamental importance, as it determines the transmission path loss and delay time, the earth coverage area and time period the satellite is visible from a given area. - The orbits of communication satellites are conventionally classified as inclined elliptical, polar circular and geo-stationary. - The geo-stationary orbit is the most widely used orbit for communication satellites.
  • 48.  
  • 49.
  • 50.  
  • 51. ‘ Taking photograph’ of any object relies on the reflected wave from the object as we use visible light in normal photography. - Selection of the wavelength of the radiation depends on the effect of atmosphere including ionosphere and the nature of the objects to be scanned. - The visible and near infrared spectral bands are chosen to amplify or separate specific earth features such as vegetation and water. - Data from thermal infrared bands are of high interest, particularly due to the fact that thermal infrared data is a measure of surface temperature and can also be obtained at night. - Microwave data are of particular relevance for certain hydrological variables such as soil moisture and precipitation. They can also be obtained at night and are not restricted to cloud free conditions. - The spatial resolution of remote sensing data varies with the form of sensor employed and height of the satellite. The resolution also depends on the wavelength of radiation used. Low altitude satellites are capable of resolving 10 m while the resolution of geo-stationary satellite is ~ 5 km. The temporal resolution depends on the nature of the orbit. The temporal resolution of geo-stationary satellite can be half an hour or less while that of polar orbits could be 15 days. - Some applications of remote sensing include meteorology, climatology, oceanography and coastal studies. Archeology, geological surveys, water resource surveys, urban land use surveys, agriculture and forestry etc
  • 52.
  • 53. Transmitter Guided Medium Repeater station Receiver Point-to-point Physical Connection LINE COMMUNICATION
  • 54. Twisted Pair - Two insulated copper wires arranged in a spiral pattern form a twisted pair - Twisting of wires minimizes electromagnetic interference. - A number of such wires are bundled together into a thick cable. - Copper conductor wires in the twisted pair provide a very low cost medium. - Is used for transmitting both, analog as well as digital information. - In local telephone services, individual telephone sets from a house are connected to the local telephone exchange box on the street using a twisted pair. Each one of these boxes is connected underneath by a thick cable, which carries several twisted pairs, to the main telephone exchange and all around the city. - Transmission of many signals at a time in a single twisted pair is done by transmitting the signal as a modulated wave with a fixed carrier frequency. An analog voice signal of bandwidth 3 kHz, requires a bandwidth of 6 kHz, if such a signal is to be transmitted in the form of a modulated wave. If we wish to send 100 such signals over the same wire we would then require a bandwidth of 600 kHz.
  • 55.
  • 56. - The inner conductor is held at the centre by a solid dielectric (insulating) material all around. - The outer conductor is normally connected to ground and thus provides an electrical shield to the signals carried by the central conductor. - Most of the power is carried by the electromagnetic waves and only a relatively small amount in the form of conduction electrons in the central conductor. - Very high frequencies can be transmitted before the attenuation becomes too severe. - Reduced attenuation in co-axial cables increases the repeater spacing to about 20 km and permitting much larger bandwidths (20 MHz). Employing digital transmission further enhances the bandwidth. - Co-axial cables are commonly used for long distance high frequency transmission. They can carry both analog and digital signals. They are extensively used in local area computer network for high speed data transmission.
  • 57. Optical Communication - Communication is through optical (light) signals. - Communication medium employed is an optical fibre - The schematics of the essential components of an optical communication link are as shown. - This mode of communication provides a very large bandwidth and therefore carry large amount of information. - Light is a form of electromagnetic wave with frequencies lying in the range 10 12 to 10 16 Hz and corresponding wavelengths in the range 0.03 to 300  m. - The light emitted from He-Ne laser has  = 0.63  m, or a frequency of ~ 4.7  10 14 Hz. If we use this light and employ only 1% of this frequency bandwidth I.e. 4700 GHz for an optical communication channel, it offers tremendous capacity for transmission. - To telecast pictures through a TV channel we need an approximate bandwidth of 4.7 MHz per channel. The number of TV channels which can be accommodated in a bandwidth of 4700 GHz is ~ 10 6
  • 58. Transmitter Optical source Input signal Modulation Optical fibre cable Receiver Optical detector Demodulation Output signal Optical Communication
  • 59. Optical Fibre - An optical fibre is a thin fibre of glass. Its diameter is about the same as that of a human hair ~ 10 to 100  m. - Light can be guided in such a fibre by launching it at one end, using an intense and focused light source, and allowing it bounce down to the other end by a series of reflections ( total internal reflections ) from the sides. - An optical fibre essentially consists of an inner cylinder of glass known as the core, having a refractive index n 1 , and an outer cylinder of a different glass, called the cladding having a refractive index n 2 ,  n = n 1  n 2 ~ 10  3 . - For use in a telecommunications system, many fibres are usually incorporated into a cable structure for pulling into underground ducts.
  • 60.  
  • 61. Photonic Devices Photonics is a subject that deals with the generation and detection of photons. The devices which generate and detect photons are called photonic devices. Such devices are extensively employed in optical communication. To understand the functioning of these devices we need to know the different interaction mechanisms between photons and electrons in a solid. There are three important processes; (a) Absorption (b) Spontaneous emission (c) Stimulated emission
  • 62.  
  • 63. Optical Light Source and Optical Detector Light Source - In optical communication light source plays a pivotal role. - It generates a beam of light. This light wave can be modulated directly to produce light pulses, by applying an appropriate electrical signal to the optical source. Another alternative is to modulate the light beam externally using an electro-optic modulator. - The light source to be used in optical communication is required to have some special characteristics. - Its physical size should be small so that it can be coupled to the thin optical fibre. - Monochromatic light sources which can produce light of desired wavelength (0.85, 1.3 and 1.55  m) are preferred. - Rapid switching. Some of these fundamental requirements are met by light emitting devices such as solid state semiconductor LASER diodes.
  • 64. Light emitting diode A light emitting diode (LED) works by the process of spontaneous emission, when a p-n junction is forward biased. In forward bias, electrons from the n – region migrate to the p – region and the holes from the p – region move towards the n – region. Holes injected into the n – region quickly encounter free electrons and recombine. Electrons injected into the p – region encounter holes and recombine. When each electron – hole pair recombines a single photon is released which carries with it the energy required to liberate an electron from the valency bond. The wavelength and frequency of light emitted are determined by the band gap energy. The intensity of light produced is proportional to the forward current conducted by the junction that controls the number of holes and electrons crossing the junction to be recombined..
  • 65. n n p Light h  = E g Visible – Phos. Doped GaAs Infrared – Al doped GaAs LED Operated in forward bias
  • 66. Laser - LASER is an acronym and stands for l ight a mplification by s timulated e mission of r adiation. - An important optical and electronic device. - The laser is a source of highly directional , monochromatic and coherent light. - Laser action has been obtained using different materials, including gases, such as neon, helium, carbon dioxide, and solids such as ruby and semiconductors. - The action of a laser is based on the principle of stimulated emission.
  • 67. When light is absorbed, electrons from the ground state E 1 are excited to the band of level designated as E 3 . These excited levels are highly unstable, and the electrons decay rapidly to level E 2 . The energy difference E 3  E 2 is given up in the form of heat. The level E 2 is very important for the stimulated emission because this level is metastable having a mean life of few mili-seconds. If the electrons are excited from E 1 to E 3 at a rate faster than the rate E 2 back to E 1 , the population of the metastable state E 2 becomes larger than the ground state E 1 . Such a situation is called population inversion . The population inversion is very crucial for laser action. Now if a photon of energy E 2  E 1 enters this system and interacts with one of the inverted population atoms. This photon can now actually stimulate the electron to fall from state E 2 to state E 1 and emit a photon of energy E 2  E 1 . Thus the first photon has the emission of another photon of same energy and multiplying the number of photons by a factor of two. We thus have light amplification by stimulated emission of radiation or LASER E 2  E 1 .
  • 68. The construction of a semiconductor laser diode is achieved by polishing the sides of the p-n junction. A highly polished surface acts as a partially reflecting surface and also enables a back reflection process. Stimulated photons assist in the process of combining the electrons and holes by stimulating the electrons to fall quickly .
  • 69. The structure of a modern semiconductor LASER designed for optical communication is very complex as shown below. The lasing material is gallium arsenide, an alloy of gallium and arsenic. It has the advantage that the material can be made n- type or p -type by varying the relative proportion of the two elements. It has also the band gap whose corresponding wavelength lies in the first low loss window at 0.86  m.
  • 70. Optical Detectors - Light pulses that propagate in the fibre and reach the receiver end become weak, due to some unavoidable losses along the way. - The optical detector should highly sensitive. - The optical detector should have a quick time response. It should respond quickly to the changing light pulses that are switching ON and OFF. - The physical size of the detector should be very small, so that it can be properly coupled to the thin optical fibre. Several kinds of photosensitive devices that generate an electrical signal when light falls on them are used as optical detectors. These include silicon photo-diodes, avalanche photo-diodes (APD), photo-transistors, and photo-resistors .
  • 71. Light p n p – n operated in reverse bias I V  A