Basics of Communication Systems

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  • Lecture 1


  • Introduction

    Electronic Communication

    The transmission, reception, and processing of information with the use of electronic circuits


    Knowledge or intelligence that is communicated (i.e., transmitted or received) between two or more points

  • Introduction

    Digital Modulation

    The transmittal of digitally modulated analog signals (carriers) between two or more points in a communications systems

    Sometimes referred to as digital radio because digitally modulated signals can be propagated through Earths atmosphere and used in wireless communications systems

  • Introduction

    Digital Communications

    Include systems where relatively high-frequency analog carriers are modulated by relatively low-frequency digital signals (digital radio) and systems involving the transmission of digital pulses (digital transmission)

  • Introduction



  • Applications

    1 Relatively low-speed voice-band data communications

    modems such as those found in most personal computers

    2 High-speed data transmission systems, such as broadband

    digital subscriber lines (DSL)

    3 Digital microwave and satellite communications systems

    4 Cellular telephone Personal Communications Systems (PCS)

  • Basic Telecommunication System

    Source Transducer Transducer Sink

    Transmission Medium


    In an electrical communication system, at the transmitting side, a transducer converts the real life information into an electrical signal. At the receiving side, a transducer converts the electrical signal back into real-life information

  • Basic Telecommunication System

    Source Transducer Transducer Sink


    Transmission Medium

    Note: As the electrical signal passes through the transmission medium, the signal gets attenuated. In addition, the transmission medium introduces noise and, as a result, the signal gets distorted.

  • Basic Telecommunication System

    The objective of designing a communication system is to reproduce the electrical signal at the receiving end with minimal distortion.

  • Basic Telecommunication System


    RS 232 Port RS 232 Port

    Note: The serial ports of two computers can be connected directly using a copper cable. However, due to the signal attenuation, the distance cannot be more than 100 meters.

  • Basic Telecommunication System

    Two computers can communicate with each other through the telephone network, using a modem at each end. The modem converts the digital signals generated by the computer into analog form for transmission over the medium at the transmitting end and the reverse at the receiving end.

  • Basic Telecommunication System

    Source Baseband

    Signal Processing

    Medium Access

    Processing Transmitter

    Receiver Decoding of


    Baseband Signal

    Processing Sink


    (a) Transmitting Side

    (a) Receiving Side

  • Basic Telecommunication System

    In the case of a radio communication system for broadcasting audio programs, the electrical signal is transformed into a high-frequency signal and sent through the air (free space). A radio transmitter is used to do this. A reverse of this transformation converting the high-frequency signal into an audio signal is performed at the receiving station. Since it is a broadcasting system, many receivers receive the information.

  • Basic Telecommunication System

    In a mobile communication system, a radio channel has to be shared by a number of users. Each user has to use the radio channel for a short time during which he has to transmit his data and then wait for his next turn. This mechanism of sharing the channel is known as multiple access.

  • Basic Telecommunication System

    1 Multiplexer

    2 Multiple access

    3 Error detection and correction

    4 Source coding

    5 Signaling

    Depending on the type of communication, the distance to be covered, etc., a communication system will consist of a number of elements, each element carrying out a specific function. Some important elements are:

  • Basic Telecommunication System Note:

    Two voice signals cannot be mixed directly because it will not be possible to separate them at the receiving end. The two voice signals can be transformed into different frequencies to combine them and send over the medium.

  • Types of Communication 1 Point-to-point communication

    2 Point-to-multipoint communication

    3 Broadcasting

    4 Simplex communication

    5 Half-duplex communication

    6 Full-duplex communication

  • Transmission Impairments



    The amplitude of the signal wave decreases as the signal travels through the medium.


    Delay distortion

    Occurs as a result of different frequency components arriving at different times in the guided media such as copper wire or coaxial cable

    3 Noise

    Thermal noise, intermodulation, crosstalk, impulse noise

  • Transmission Impairments Thermal Noise occurs due to the thermal

    agitation of electrons in a conductor. (white noise), N = kTB

    Intermodulation Noise When two signals of different frequencies are sent through the medium, due to nonlinearity of the transmitters, frequency components such as f1 + f2 and f1 f2 are produced, which are unwanted components and need to be filtered out.

  • Transmission Impairments

    Crosstalk Unwanted coupling between signal paths

    Impulse Noise occurs due to external electromagnetic disturbances such as lightning. This also causes burst of errors.

  • Analog Versus Digital Transmission

    Analog Communication

    The signal, whose amplitude varies continuously, is transmitted over

    the medium.

    Reproducing the analog signal at the receiving end is very difficult due to transmission impairments

    Digital Communication

    1s and 0s are transmitted as voltage pulses. So, even if the pulse s distorted due to noise, it is not very difficult to

    detect the pulses at the receiving end.

    Much more immune to noise

  • Advantages of Digital Transmission

    More reliable transmission

    Because only discrimination between ones and zeros is required

    Less costly implementation

    Because of the advances in digital logic chips

    Ease of combining various types of signals (voice, video, etc.,)

    Ease of developing secure communication systems

  • Questions:

    1. What are the advantages of digital communication over analog communication?

    2. Explain the different types of communication systems.

    3. What are the different types of transmission impairments?

    4. What is multiplexing?

    5. What is signaling?

  • Lecture 2


  • Claude Shannon

    -Laid the foundation of information theory in 1948. His paper A Mathematical Theory of Communication published in Bell System Technical Journal is the basis for the entire telecommunications developments that have taken place during the last five decades. A good understanding of the concepts proposed by Shannon is a must for every budding telecommunication professional.

  • Requirements of a Communication System

    The requirement of a communication system is to transmit the information from the source to the sink without errors, in spite of the fact that noise is always introduced in the communication medium.

  • The Communication System

    Information Source

    Transmitter Receiver Information


    Noise Source


    Generic Communication System

  • Symbols Produced A B B A A A B A B A

    Bit stream produced 1 0 0 1 1 1 0 1 0 1

    Bit stream received 1 0 0 1 1 1 1 1 0 1

    In a digital communication system, due to the effect of noise, errors are introduced. As a result, 1 may become a 0 and 0 may become a 1.

  • Generic Communication System as proposed by Shannon

    Information Source

    Source Encoder

    Modulator Channel Encoder

    Information Sink

    Source Decoder

    Demodulator Channel Decoder

    Modulating Signal

    Demodulating Signal

    Modulated Signal

  • Explanation of Each Block

    Information Source: Produces the symbols

    Source encoder: converts the signal produced by the information source into a data stream

    Channel Encoder: add bits in the source-encoded data

    Modulation: process of transforming the signal

    Demodulator: performs the inverse operation of the modulator

  • Explanation of Each Block

    Channel Decoder: analyzes the received bit stream and detects and corrects the error

    Source Decoder: converts the bit stream into the actual information

    Information Sink: absorbs the information

  • Types of Source Encoding

    Source encoding is done to reduce the redundancy in the signal.

    1. Lossless coding

    2. Lossy coding

    The compression utilities we use to compress data files use lossless encoding techniques. JPEG image compression is a lossy technique because some information is lost.

  • Channel Encoding

    Redundancy is introduced so that at the receiving end, the redundant bits can be used for error detection or error correction

  • Entropy of an Information Source

    What is information?