Chapter 1 - Digital Telecommunication

BACIS OF COMMUNICATION
MK : TELEKOMUNIKASI-DIGITAL
ANANG ARIS WIDODO - SKI 2
Magister Teknik Elektro - Universitas Brawijaya

BASIC OF COMMUNICATION
A very simple telecommunication system. The signal is sent over a transmission medium
and,at the receiving end, the transducer again converts the electrical signal into data and
is given to the destination (sink)
Slide 1

5 Basic Component
Every communication system has 5 basic requirements
• Data Source (where the data originates)
• Transmitter (device used to transmit data)
• Transmission Medium (cables or non cable)
• Receiver (device used to receive data)
• Destination (where the data will be placed)
Slide 2

5 Basic Components
Slide 3

PC-to-PC communication
A communication system used to interconnect two computers 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
Slide 4

PC-to-PC communication over
telephone network
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.
Slide 5

Generic communication system
In a radio communication system, the electrical signal is transformed into a
high-frequency signal and sent over the air
Slide 6

ILUSTRATION COMMUNICATION
Kabel logam
Sisi
pengirim
Sisi
penerima
Media udara
Sisi
pengirim
Sisi
penerima
Sisi
pengirim
Sisi
penerima
Kabel optik
Slide 7

Element Communication
• Multiplexer : Combines the signals from different sources to transmit on the
channel. At the receiving end, a demultiplexer is used to separate the signals
• Multiple access : When two or more users share the same channel, each user has
to transmit his signal only at a specified time or using a specific frequency band.
• Error detection and correction : Detection, and if possible correction, of the errors
has to be done at the receiving end. This is done through a mechanism called
channel coding
• Source Coding : the input signal has to be processed to reduce its bandwidth so
that it can be accommodated on the channel.
• Switching : If a large number of users has to be provided with communication
facilities, as in a telephone network, the users are to be connected based on the
numbers dialed. This is done through a mechanism called switching.
• Signaling : The information sent by the subscriber/switch for call setup,
disconnection, and management, such as billing
Slide 8

TYPES OF COMMUNICATION
• Point-to-point communication
• Point-to-multipoint communication
• Broadcasting
• Simplex communication
• Half-duplex communication
• Full-duplex communication
Slide 9

TRANSMISSION IMPAIRMENTS
While the electrical signal is traversing over the medium, the signal will be
impaired due to various factors. These transmission impairments can be classified
into three types :
- Atenuasi distorsi
- Delay Distorstion
- Noise
Slide 10

Attenuation Distortion
Slide 11

Thermal noise
Slide 12

Thermal noise obtained from the
formula
N0 = kT
where No is noise power density, watts per Hz
Thermal noise for a bandwidth of B Hz is given by
If N is expressed in dB (decibels)
Slide 13

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
Slide 14

Crosstalk
Unwanted coupling between signal paths is known as crosstalk. In the telephone network,
this coupling is quite common. As a result of this, we hear other conversations. Crosstalk
needs to be eliminated by using appropriate design techniques.
Slide 15

Impulse noise
This is caused by external
electromagnetic disturbances such
as lightning. This noise is
unpredictable. When the signal is
traversing the medium, impulse
noise may cause sudden bursts of
errors. This may cause a temporary
disturbance in voice
communication. For data
communication, appropriate
methods need to be devised
whereby the lost data is
retransmitted.
Slide 16

ANALOG VERSUS DIGITAL TRANSMISSION
In a digital communication system, 1s and 0s are transmitted as voltage pulses. So,
even if the pulse is distorted due to noise, it is not very difficult to detect the pulses at
the receiving end. Hence, digital communication is much more immune to noise as
compared to analog communication.
Slide 17

Due to advances in digital electronics, digital systems
have become cheaper, as well. The advantages of digital
systems are:
• 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
The advantages of digital communication are more reliable transmission, less
costly implementation, ease of multiplexing different types of signals, and secure
communication
Slide 18

Questions
• What are the advantages of digital communication over analog communication?
• Explain the different types of communication systems.
• What are the different types of transmission impairments?
• What is multiplexing?
• What is multiple access?
• What is signaling?
Slide 19

References
• G. Kennedy and B. Davis. Electronic Communication Systems. Tata McGraw-Hill
Publishing Company Limited, 1993.
• R. Horak. Communication Systems and Networks. Wiley-Dreamtech India Pvt. Ltd.,
2002.
CP : anangariswidodo@gmail.com
Slide 20

Chapter 1 - Digital Telecommunication

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