chapter 1 - digital telecommunication

BACIS OF COMMUNICATION

MK : TELEKOMUNIKASI-DIGITAL

ANANG ARIS WIDODO - SKI 2Magister 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 1MK : TELEKOMUNIKASI-DIGITAL

5 Basic ComponentEvery 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)


5 Basic Components


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

MK : TELEKOMUNIKASI-DIGITALSlide 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.


Generic communication system

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


ILUSTRATION COMMUNICATION

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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

MK : TELEKOMUNIKASI-DIGITAL Slide 8

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


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


Attenuation Distortion


Thermal noise


Thermal noise obtained from the formula

N0 = kTwhere 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)


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


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.


Impulse noiseThis 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.


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.


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


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?


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.

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chapter 1 - digital telecommunication

Engineering

telekomunikasidigital

digital communication

data communication

digital transmission

duplex communication

digital signals

bacis of communication

basic of communication