16343_communication basic block diagram _ modulation

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					       II: Communication Systems



                          Name of the Faculty: Pankaj
                          Bactor
                          UID: 16343
                          E-mail
In case you disagree with certain content of the reading material, kindly mail to the concerned faculty
                                     c. c to golp.lpu@gmail.com
  Issues to be addressed in the
               unit
• To know ,understand , analyse the basic
  concept of Communication process
• Modulation and its important




                   Mechanical Engineering   2
               Communication
• It is the process of establishing connection or say link between two points
  for exchanging the information
• It is a process of conveying the message at a distance.
• e.g telephony, radio broadcasting , point to point broadcasting , satellite
  broadcasting
• This should be done
                 - as efficiently as possible
                 - with as much fidelity/reliability as possible as
                     securely as possible
• Communication System: Components/subsystems act together to
  accomplish information transfer/exchange
• The branch of engineering deals with communication system is called as
  Telecommunication engineering

                              Mechanical Engineering                        3
          Elements of Communication
                    system

                                                 Noise


                                                                                           Output
Input message      Input                                                       Output     message
                Transducer   Transmitter        Channel           Receiver   Transducer




                                  Name of Discipline eg. Mechanical
                                                                                                    4
                                            Engineering
Input Transducer:                The message produced by a source must be
converted by a transducer to a form suitable for the particular type of
communication system.
Example: In electrical communications, speech waves are converted by a
microphone to voltage variation.




Transmitter:             The transmitter processes the input signal to produce a
signal suits to the characteristics of the transmission channel.
Signal processing for transmission almost always involves modulation and may
also include coding. In addition to modulation, other functions performed by the
transmitter are amplification, filtering and coupling the modulated signal to the
channel.
Channel:        The channel can have different forms: The atmosphere (or free
space), coaxial cable, fiber optic, waveguide, etc.
The signal undergoes some amount of degradation from noise, interference and
distortion

Receiver: The receiver’s function is to extract the desired signal from the
received signal at the channel output and to convert it to a form suitable for the
output transducer.
Other functions performed by the receiver: amplification (the received signal may
be extremely weak), demodulation and filtering.


Output Transducer: Converts the electric signal at its input into the
form desired by the system user.
Example: Loudspeaker, personal computer (PC), tape recorders.
                               Contd.
The two primary communication resources to be employed in
communication system:
     • Transmitted power:- average power of the transmitted signal
     • Channel bandwidth band of frequencies allocated for the
       transmission of messase signal.




                         Name of Discipline eg. Mechanical
                                                                     7
                                   Engineering
   Classification of Communication
• According to the mode of propagation, communication is classified into
  two categories
   o Line communication/ wired communication:-the medium in this is the
     pair of conductors between transmitter and receiver. But it has some
     disadvantages i.e
       • Installation and maintenance is costly as well as complex
       • Its message transmission capability is also limited

    o Wireless communication: a message is transmitted through open space
      by means of electromagnetic waves called as radio waves through
      antenna.The advantages of this communication is
       • cost effective
       • simplicity

                           Name of Discipline eg. Mechanical
                                                                            8
                                     Engineering
                        Modulation
•    The process by which some characteristics of a carrier signal
    (i.e. modulated signal) is varied in accordance with message
    signal (i.e. modulating signal)
       x(t): message signal (low frequency signal)
       c(t): the carrier signal, independent of f(t) (high frequency
    signal)

              :Carrier amplitude
              :Carrier frequency, (radian frequency)
              :Carrier phase
• f(t) modulates c(t) in either amplitude, frequency or phase. In
    effect,
     modulation converts f(t) to a bandpass form (modulated
    signal), in the neighborhood of the center frequency fc.
                          Name of Discipline eg. Mechanical
                                                                       9
                                    Engineering
                 Types of Modulation
•   It is basically of two types:-
•   Continuous Wave Modulation/ Analog modulation :-When the carrier wave
    is continuous in nature then modulation is said to be CW modulation.
      o Amplitude modulation
      o Angle modulation
            • frequency modulation
            • phase modulation
•   Pulse Modulation- When the carrier wave is in form of pulses( periodic
    sequence of rectangular pulses) then modulation is said to be CW modulation
    .it is of two types
      o Analog Pulse Modulation
            • Pulse- amplitude modulation (PAM)
            • Pulse- duration modulation (PDM)
            • Pulse- position modulation (PPM)
      o Digital Pulse modulation (PAM) / Pulse- code modulation (PCM)
                             Name of Discipline eg. Mechanical
                                                                              10
                                       Engineering
     Why is Modulation Required?
• To achieve easy radiation: If the communication channel consists of
  free space, antennas are required to radiate and receive the
  signal.Dimension of the antennas is limited by the corresponding
  wavelength.
• Example: Voice signal bandwidth f=3kHz




• If we modulate a carrier wave @ fc = 100MHz with the voice signal




                          Name of Discipline eg. Mechanical
                                                                        11
                                    Engineering
                                  Contd.
• To accommodate for simultaneous transmission of several signals/to
  remove interference:-The frequency range of audio signal is from 20 Hz
  to 20KHz. There are several radio station .if we don’t have modulation in
  any case, all the stations transmits radio signals in range of 20Hz to 20KHz.
  Due to this transmission over same range ,the signals of different stations
  get mixed up.
  In order to keep these signals separate ,it is required to shift them to
  different portions of electromagnetic spectrum. Thus each station is
  allocated a band of frequency. This also overcomes the drawback of poor
  radiations efficiency at low frequency.A Tuned circuit used at the receiver
  end selects the desired station and rejects all other stations.




                             Name of Discipline eg. Mechanical
                                                                             12
                                       Engineering
             Contd.




Example :Radio/ TV Broadcasting


         Name of Discipline eg. Mechanical
                                             13
                   Engineering
                                Contd.
• Reduction of Noise:-
  Noise is major limitation of any communication. Although it can not be
  completely eliminated but the effect of noise can be minimized with help
  of modulation.




                            Name of Discipline eg. Mechanical
                                                                             14
                                      Engineering
              Relevant references
• Website links:-
   o http://www.answerbag.com/q_view/969005
   o http://en.wikipedia.org/wiki/commuination system
   o http://en.wikipedia.org/wiki/modulation
• Books
   o Simon Haykin,Michael Moher,Communication Systems,Fifth
     edition,Wiley India Edition,2009
   o Sanjay Sharma, Communication System,S.K Katria &Sons,2009




                           Mechanical Engineering                15
Conclusion/Application/future scope




             Mechanical Engineering   16

				
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posted:7/13/2012
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