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Analog and Digital Signal

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Introduction Analog and Digital Signal Advantages & Disadvantages Digital Signal Transmission Impairment Data Rate Limit Bandwidth of the human voice – PowerPoint PPT presentation

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Title: Analog and Digital Signal


1
  • Introduction
  • Analog and Digital Signal
  • Advantages Disadvantages Digital Signal
  • Transmission Impairment
  • Data Rate Limit
  • Bandwidth of the human voice
  • Telephone System Bandwidth
  • Digital Channel Capacity
  • Digital Signal Regeneration

2
  • Introduction
  • Data communications are the exchange of data
    between two devices via some form of transmission
    such as a wire cable.
  • For data communications to occur, the
    communicating devices must be part of
    communication system made up of a combination of
    hardware (physical equipment) and software
    (programs). See Figure 1.0
  • A data communications system has five components
    such as
  • 1. Message
  • The message is the information (data) to be
    communicated. Popular forms of information
    include text, numbers, pictures, audio, and
    video.
  • 2. Sender
  • The sender is the device that sends the data
    message. It can be a computer, workstation,
    telephone handset, video camera, and so on.

3
  • Introduction (continue )
  • 3. Receiver
  • The receiver is the device that receives the
    message. It can be a computer, workstation,
    telephone handset, television, and so on.
  • 4. Transmission medium
  • The transmission medium is the physical path by
    which a message travels from sender to receiver.
    Some examples of transmission media include
    twisted-pair wire, coaxial cable, fiber-optic
    cable and radio waves.
  • 5. Protocol
  • A protocol is a set of rules that govern data
    communications. It represents an agreement
    between the communicating devices. Without a
    protocol, two devices may be connected but not
    communicating, just as a person speaking French
    cannot be understood by a person speak only
    Japanese.

4
  • Introduction (continue )

Figure 1.0 Five components of data
communications
5
  • Analog Digital Signals.
  • Data can be analog or digital. Analog data are
    continuous and take continuous values. Digital
    data have discrete states and take discrete
    value.
  • Like the data they represent, signals can be
    either analog or digital.
  • An analog signal has infinitely many levels of
    intensity over a period of time. As the wave
    moves from value A to value B, it passes through
    and include an infinite number of values along
    its path.

6
Figure 1.1 (a) Analog signals. Example of Analog
signal A typical Commercial Radio system
7
  • Analog Digital Signals (continue ...)
  • A digital signal can have only a limited number
    of defined values. Although each value can be any
    number, it is often as simple as 1 and 0. See
    Figure 1.1 (b).
  • The constraint for both analog and digital
    communication is the physical capabilities of the
    communications media.

8
  • Figure 1.1 (b) Digital electrical signals.
  • Example of Digital signal Signal on a typical
    printer cable.

9
  • Advantages of Digital Signal
  • Digital circuits are subject to less distortion
    and interference
  • Error correction is possible.
  • Encryption and privacy is possible
  • Digital circuit is simple and cheap
  • The receiver can request a retransmission of bad
    information

10
  • Disadvantages of Digital Signal
  • Interface to analogue is needed.
  • A digital system requires a greater bandwidth
    than analogue to carry the same information.
  • Generally digital communication system require
    synchronization but analogue do not require.

11
  • Transmission Impairment.
  • Signals travel through transmission media, which
    are not perfect. The imperfection causes signal
    impairment.
  • Three causes of impairment are attenuation,
    distortion and noise.

12
  • Attenuation
  • Attenuation means a loss of energy.
  • When a signal, simple or composite, travels
    through a medium, it loses some of its energy in
    overcoming the resistance of the medium.
  • In simple term means a decrease in the electrical
    signal.
  • To composite for this loss, amplifiers are used
    to amplify the signal. See Figure 1.2 (a).

13
  • Attenuation

Figure 1.2 (a) Attenuation
14
  • Distortion
  • Means that the signal changes its form or shape.
  • Distortion can occur in a composite signal made
    of different frequencies.
  • Each signal component has its own propagation
    speed through a medium, its own delay in arriving
    at the final destination.
  • Differences in delay may create a difference in
    phase if the delay is not exactly the same as the
    period duration. See Figure 1.2(b)

15
  • Distortion

Figure 1.2 (b) Distortion
16
  • Noise
  • Noise is another cause of impairment. Several
    types of noise, such as thermal noise, induced
    noise, crosstalk and impulse noise, may corrupt
    the signal.
  • Thermal Noise is the random motion of electrons
    in a wire which creates an extra signal not
    originally sent by the transmitter.
  • Induced noise comes from sources such as motors
    and appliances.
  • Crosstalk is the effect of one wire on the other.
    One wire acts as a sending antenna and the other
    as the receiving antenna.
  • Impulse noise is a spike that comes from power
    lines, lightning and so on.
  • Figure 1.2(c) shows the effect of a noise on a
    signal.

17
  • Noise

Figure 1.2 (c) Noise
18
  • Data Rate Limit
  • A very important consideration in data
    communications is how fast we can send data, in
    bits per second, over a channel. Data rate
    depends on three factors
  • The bandwidth available
  • The level of the signals we use
  • The quality of the channel (the level of noise)
  • Two theorectical formulas were developed to
    calculate the data rate
  • Nyquist bit rate for a noiseless channel
  • BitRate 2 bandwidth log2 L
  • Shannon Capacity for a noisy channel
  • Capacity bandwidth log2 (1 SNR)

19
  • Data Rate Limit
  • Channel Capacity
  • The maximum possible rate information rate that
    data can be transmitted over a given
    communication path or channel under given
    condition.
  • Bandwidth
  • One characteristics that measures network
    performance is bandwidth. However, the term can
    be used in two different measuring value
    bandwidth in hertz and bandwidth in bits per
    second.
  • Bandwidth in Hertz
  • Bandwidth in Hertz is the range of frequencies
    contained in a composite signal or the range of
    frequencies a can pass. For example We can say
    the bandwidth of a subscriber telephone line is
    4kHz.
  • Bandwidth in Bits per Seconds
  • Bandwidth in Bits per seconds refer to the speed
    of bit transmission in a channel, a link or even
    a network can transmit. For example One can say
    the bandwidth of a Fast Ethernet network is a
    maximum of 100 Mbps. This means that the network
    can send 100 Mbps.

20
  • Data Rate Limit
  • Relationship between bandwidth in Hertz and
    bandwidth in bps
  • There is an explicit relationship between the
    bandwidth in hertz and bandwidth in bits per
    seconds. Basically, an increase in bandwidth in
    hertz means an increase in bandwidth in bits per
    second. The relationship depends whether we have
    baseband transmission or broadband transmission.
  • Baseband Transmission
  • Transmission of digital or analog signal without
    modulation using a low-pass channel. Low pass
    channel is a channel with bandwith starts from
    zero. See Figure 1.3.1

21
  • Data Rate Limit
  • Baseband Transmission

Figure 1.3.1 Baseband Transmission
22
  • Data Rate Limit
  • Baseband Transmission

Figure 1.3.2 (a) and (b) Bandwidth of two
low-pass channel
23
  • Data Rate Limit
  • Broadband Transmission
  • Transmission of signals using modulation of a
    higher frequency signal. It means changing the
    digital signal to analog for transmission and
    modulation allows us to use a bandpass channel
    a channel with a bandwith that does not start
    with zero. See Figure 1.3.3 (a)

Figure 1.3.3 (a) Bandwidth of a bandpass channel
24
  • Data Rate Limit
  • Broadband Transmission

Figure 1.3.3 (b) Modulation of a digital signal
for a transmission on
a bandpass channel
25
Bandwidth of the human voice
  • Figure 1.4.1(a) shows the sound power a human
    vocal system can produce at various frequencies.
  • The power of human sounds at lower frequencies,
    or the base pitches, is much higher than the
    power at higher frequencies.
  • The human frequency range is from near zero to
    over 12,000 Hz i.e. bandwidth of over 12,000Hz.
  • Modern stereo equipment can reproduce most of
    this range

26

Figure 1.4.1(a) Bandwidth of the human voice.
27
  • Telephone System Bandwidth
  • Due to technology limitations and cost tradeoffs
    the public telephone system can handle only a
    small part of the total bandwidth of the human
    voice.
  • The system provides coverage for the portion of
    the voice bandwidth that can produce the greatest
    power.
  • The range is only from 300 to 3,300Hz which is
    sufficient to convey messages to distant
    listener.

28
  • Figure 1.4.1(b) shows frequency range vendors
    use to convey data communications through the
    telephone system

Figure 1.4.1 (b) Telephone signal amplitude
versus frequency.
29
  • Digital Channel Capacity
  • The number of digital values the channel can
    convey in one second.
  • A digital communications channel has limitations
    that determine how often the signal can change
    states over a period.
  • These limitations establish the maximum rate at
    which data can flow through the channel.

30
  • A variety of baseband signaling techniques are
    used to convey information or data.
  • Digital systems may have more than two discrete
    changes as shown in Figure 1.5.1.
  • A binary system has only two discrete energy
    levels
  • A digital system can have many discrete energy
    levels.

31
Figure 1.5.1 Digital system electrical signals.
32
Figure 1.5.2 Digital signal distortion and
attenuation with distance
33
  • Bandwidth versus length characteristics as shown
    in Figure 1.5.2 can be used to determine the
    length of channel they want to use for specific
    applications.
  • high-volume application requires a high bandwidth
    such as a direct connection between two mainframe
    computers, a vendor can limit the length of the
    communications channel to a short distance.
  • A low-volume application such as the connection
    between a personal computer and a low speed
    printer, the vendor can specify a longer channel.

34
Figure 1.5.3 Medium bandwidth versus length
35
  • Digital Signal Regeneration
  • Provide devices that regenerate a digital signal.
  • Repeaters receive the signal and rebuild it to
    its original strength and shape.
  • The repeater catches the signal before it
    degrades to the point that it is unusable.
  • Digital signal cannot be amplified to increase
    their distance range in a channel.

36
  • If you amplify a digital signal, you also amplify
    the noise that contaminated the signal.
  • The amplified noise can become a substantial part
    of the signal.
  • A repeater removes the noise from a signal while
    it is regenerating the signal.

37
Figure 1.5.4 Digital signal regeneration.
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