Learning Outcomes

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Upon completion of this chapter, students should be able to :-

• Understand the element in communication system.• Understand the information , messages and signal.• Understand the modulation process and its needs.• Learn noise, interference and distortion.• Know the frequency spectrum.• Understand various types of communication system.

INTRODUCTION

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The word TELECOMMUNICATION is a combination of two words...

TELE + COMMUNICATION

The word TELE in Latin means DISTANCE.

Hence Telecommunication is DISTANCE COMMUNICATION

DEFINATION

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Telecommunication is the transmission of messages, over significant distances, for the purpose of communication.

In earlier times, telecommunications involved the use of visual signals, such as smoke, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded drumbeats, lung-blown horns, or sent by loud whistles, for example.

In the modern age of electricity and electronics, telecommunications has typically involved the use of electric means such as the telegraph, the telephone, and the teletype, the use of microwave communications, the use of fiber optics and their associated electronics, and/or the use of the Internet.

CLASSIFICATION OF COMMUNICATION SYSTEMS

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Communication Systems

Radio Aids to Navigations

Radio Telephony

Radio telemetry

Point to point

Computer Comm.

Telegraphy

Radar

Mobile Comm.

Broadcasting

INTRODUCTION TO COMMUNICATION SYSTEM

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Answers

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1.1 What is communication system

TRANSMITTER

Transmission mediumOR

Communication channelRECEIVER

System noise and

interference

BASIC BLOCK DIAGRAM OF AN ELECTRONIC COMMUNICATION SYSTEM

Pysical facility(metalic or optical fiber cable) or free space( earth atmosphere)

Information source( intelligence)

Receiver informetion

Components of the Communication System

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A) INFORMATION SOURCE

The message is the information source. Example : Text, voice, pictures or video signal Information can electrical and non-electrical. Non-electrical information

source must be converted into electrical form before it is transmitted.

B) TRANSMITTER

A collection of one or more electronic devices or circuits that convert the original information source into a signal suitable for information.

A complex processes ( Encoding and modulation ) must be done to the information signal before transmission.

c) Transmission mediumA transmission medium (plural transmission media) is a material substance (solid, liquid, gas or plasma) that can propagate energy waves. For example, the transmission medium for sound received by the ears is usually air, but solids and liquids may also act as transmission media for sound.

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Component of the Communication system

The absence of a material medium (the vacuum of empty space) can also be thought of as a transmission medium for electromagnetic waves such as light and radio waves. While material substance is not required for electromagnetic waves to propagate, such waves are usually affected by the transmission media they pass through, for instance by absorption or by reflection or refraction at the interfaces between media.

Components of the Communication System

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d) Channel

The path provided by a transmission medium can take the form of physical separation, such as by multipare cable or electrical separation such as by frequency or time division multiplexing.

An example is the MIXFM which has its channel allocated at a frequency of 94.5 Mhz.

e) Noise

Noise is unwanted energy which is usually random in nature that is present in

any point of a commnication system.

Noise may be due to various causes such atmospheric noise, thermal agitation noise, shot noise and industrial noise.

Components of the Communication System

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f) ReceiverA receiver is a collection of one or more electronic devices and circuits that accept the transmitter signals from the transmission medium and convert them back into their original form.

- A band pass filter rejects all frequencies above or below its designed frequency. Most receivers utilize an LC resonant circuit as a band pass filter. The band pass filter is tuned to the carrier frequency signal of the transmitting station.

In other words the receiver SELECTs the appropriate station.

The last stage of the communication system is

g) destination equipment which converts these electrical signals into its original form for the data broadcasting so that it can be easily understand by the end user or receiver and then this same sort of communication process is used for the acknowledgment of signals to sender machine.

What is information, messages and signal.

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InformationDefined as knowledge or inteligence that communicate between two or more points, Information in its most restricted technical sense is an ordered sequence of symbols that record or transmit a message. It can be recorded as signs, or conveyed as signals by waves

MessagesA telephone circuit is comprised of two or more facilities interconnected in tandem to provide a transmission path between a source and a destination. The interconnected facilities maybe temporary as in standard telephone call or permanent as in a dedicated private carrier system. The information is called messages.

.

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Signal

Signals can be defined as measurable quantities which may be either time-varying or spatial-varying. A signal may be expressed as a function of time and frequency.When a signal is expressed as a function of time, it can be either discrete (discrete-time signal) or continuous (continuous-time signal).In a more practical sense, there are two basic types of signals: 1)Digital signal2)Analogue signal

Digital signalDigital signal can be defined as a discrete signal or discrete-time signal that generates and process data in form of zeroes and ones (0s and 1s). This implies that digital signals can take on only a discrete set of values. Digital signal is quantized (has finite set of values). The value of a Digital signal may be described in terms of voltage pulses that can be sent over data transmission medium. As described above, the signal sent is either off (o) or on (1) pluses, representing a binary digit. For example, computers use digital signals.

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Analogue signalAnalogue signal (unlike digital signal) is not discrete and quantized. Analogue signal is continuous in nature and generates continuous values, leading to continuous wave pattern.Analogue signals can be used over a variety of transmission media. For example, telephone lines use analogue protocols.

 What Does Signals Do?•Signals carry information, in form of data, image, sound or pictures.•Computers depend on digital signals for data transmission.•The computer stores data in form of zeros and ones, which are called binary digits.•A single binary digit is referred to a bit and a set of 8 bits is called a byte. 1024 byte is equal to 1 kilobyte.

A bandpass filter is a device that passes frequencies within a certain range and rejects (attenuates) frequencies outside that range. An example of an analogue electronic band-pass filter is an RLC circuit (a resistor–inductor–capacitor circuit. These filters can also be created by cobining a low-pass filter with a high-pass filter.

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WHAT IS BAND PASS AND BASE BAND

In telecommunications and signal processing baseband is an adjective that describes signals and systems whose range of frequencies is measured from close to 0 hertz to a cut-off frequency a maximum bandwidth or highest signal frequency; it is sometimes used as a noun for a band of frequencies starting close to zero..

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What is baseband

Baseband can often be considered as a synonym to lowpass or non-modulated, and antonym to passband, bandpass, carrier-modulated or radio frequency (RF) s

MODULATION is an important step of communication system In modulation, a message signal, which contains the information is used to control the

parameters of a carrier signal, so as to impress the information onto the carrier.The Messages

The message or modulating signal may be either:analogue – denoted by m(t)

digital – denoted by d(t) – i.e. sequences of 1's and 0'sThe message signal could also be a multilevel signal, rather than binary; this is not

considered further at this stage.OR

Modulation is a process in which the characteristics of a signal circuit is caried in accordance with the information

signal which is to be transmitted. The modulation signal,which is to be transmitted is known

as Modulating signal.

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1.3 MODULATION AND DEMODULATION

MODULATION……

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In electronics modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted. At the destination, a process of demodulation extracts the modulation signal from the modulated carrier. The three key parameters of a periodic waveform are its amplitude ("volume"), its phase ("timing") and its frequency ("pitch"). Any of these properties can be modified in accordance with a low frequency signal to obtain the modulated signal. Typically a high-frequency sinusoid waveform is used as carrier signal, but a square wave pulse train may also be used.

In telecommunications, modulation is the process of conveying a message signal, for example a digital bit stream or an analog audio signal, inside another signal that can be physically transmitted. Modulation of a sine waveform is used to transform a baseband message signal into a passband signal, for example low-frequency audio signal into a radio-frequency signal (RF signal).

MODULATION…..

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BLOCK DIAGRAM THE PROCESS OF MODULATION

DEMODULATION

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DEMODULATION is the act of extracting the original information-bearing signal from a modulated carrier wave. A demodulator is an electronic circuit (or computer program in a software defined radio) that is used to recover the information content from the modulated carrier wave.[1]

These terms are traditionally used in connection with radio receivers, but many other systems use many kinds of demodulators. Another common one is in amodem, which is a contraction of the terms modulator/demodulator .

Is the reverse process (to modulation) to recover the message signal m(t) or d(t) at the receiver.

To transfer the message signal from one site another site without any loss for that we are using modulation. Modulation classified in two types.

1.Analog modulation.2.DigitalModulation.

Modulation is need basically to:

i)To increase the bandwidth of the signal

ii)To multiplex more number of signal

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NEEDS OF MODULATONTHE NEEDS OF MODULATION AND DEMODULATION

iii)To reduce the interference( noise and distortion) made when we transmit the signals with nearly same frequency in the audio frequency range (20-20k) Hz.

iv) To reduce the antenna height. For efficient transmission the transmitting antennas should have length at least equal to a quarter of the wavelength of the signal to be transmitted.

For an electromagnetic wave of frequency 15 kHz, the wavelength λ is 20 km and one-quarter of this will be equal to 5 km. Obviously, a vertical antenna of this size is impractible. On the other hand, for a frequency of 1 MHz, this height is reduced to 75m.

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Also, the power radiated by an antenna of length l is proportional to (l/λ)2. This shows that for the same antenna length, power radiated is large for shorter wavelength. Thus, our signal which is of low frequency must be translated to the high frequency spectrum of the electromagnetic wave. This is achieved by the process of modulation.

v) To narrow banding system.

vi) To reduce equipment complexity.

vii)To favors the complexity of the transmission system

Audio frequencies are within the range of 20 Hz to 20 kHz. Without modulation all signals at same frequencies from different transmitters would be mixed up. There by giving impossible situation to tune to any one of them. In order to separate the various signals, radio stations must broadcast at different frequencies.

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Electrical noise is defined as any undesirable electrical energy that’s falls within the passband of the signal.

It can be divided into two general categories

i) correlated- its implies a relationship between the signal and the noise.

ii) uncorrelated-exists only when a signal is present on the otherhand is present at the time wheather there is a signal or not.

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1.4 NOISE, INTERFERENCE AND DISTORTION

Uncorrelated noiseUncorrelated noise is present regardless of wheather there is asignal or not. Devide into two categories: external and internal.

External NoiseNoise that generated outside the device or circuit. The three primary sources of external noise are atmospheric, extraterrestrial and man-made. Refer to notes to explain …( italic)

Internal noiseIs electrical interference generated within a device or circuit. There are three kinds of internally generated noise shot, transit time and thermal.Refer to notes to explain..(italic)

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Interference is a form of external noise and as the name implies. Means to disturb or detract from. Electrical interference

is when information signals from one source produce frequencies that fall outside their allocated bandwidth and

interfere with information signals from another source.

Distortion

A distortion is the alteration of the original shape (or other characteristic) of an object, image, sound, waveform or other

form of information or representation. Distortion is usually unwanted, and often many methods are employed to minimize it in practice. In some fields, however, distortion may be desirable;

such is the case with electric guitar distortion .

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Continue distortion……………..

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This diagram below shows the behaviour of a signal (made up of a square wave followed by a sine wave) as it is passed through various distorting functions.

1.The first trace (in black) shows the input. It also shows the output from a non-distorting transfer function (straight line).

2. A high-pass filter (green trace) will distort the shape of a square wave by reducing its low frequency components. This is the cause of the "droop" seen on the top of the pulses. This "pulse distortion" can be very significant when a train of pulses must pass through an AC-coupled (high-pass filtered) amplifier. As the sine wave contains only one frequency, its shape is unaltered.

3. A low-pass filter (blue trace) will round the pulses by removing the high frequency components. All systems are low pass to some extent. Note that the phase of the sine wave is different for the lowpass and the highpass cases, due to the phase distortion of the filters.

4) A slightly non-linear transfer function (purple), this one is gently compressing as may be typical of a tube audio amplifier, will compress the peaks of the sine wave. This will cause small amounts of low order harmonics to be generated.

5)A hard-clipping transfer function (red) will generate high order harmonics. Parts of the transfer function are flat, which indicates that all information about the input signal has been lost in this region.

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Signal to noise(S/N) power ratio

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Refer to notes…..

1. Formula2. Solve S/N power ratio3. Distinguish between noise factor and noise figure.

1.5 Electromagnetic and Radio Waves

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The transmission of energy through free space (vacuum) is done by electromagnetic waves.

Electromagnetic waves are caused by oscillations of electric and magnetic fields. These waves moves at a constant velocity of 3 x 10 8

m/s.

Electromagnetic waves are used to transmit :

a)Long or short wave radio signalsb)FM wavelength radio signalsc)Wireless communication signals

They are also responsible for transmitting energy in the form of :

a)Microwave, infrared radiation (IR)b)Ultraviolet light (UV), X-rays, Gamma rays

λ = c / f

Electromagnetic Spectrum

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The electromagnetic spectrum extends from below frequencies used for modern radio to gamma radiation at the short-wavelength end, covering wavelengths from thousands of kilometers down to a fraction of the size of an atom.

Radio Frequency (RF) Spectrum

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Audio Frequency (AF) is any frequency that human can hear, ( 20 Hz – 20 Khz)

Radio Frequency (RF) is any frequency above the range of human perception which is greater than 20 Khz.

Frequency Band Frequency ApplicationVery Low Frequency (VLF)

3 - 30 KHz > 10000m Telegraphy, human range frequency

Low Frequency (LF)

30-300 KHz 10000-1000m Point to point, navigation

Medium Frequency (MF)

300K-3 MHz 1000-100m AM radio broadcast, maritime/aeronautical mobile

High Frequency(HF)

3 - 30 MHz 100 - 10 m Shortwave Broadcast Radio

Very high Frequency(VHF)

30 - 300 MHz

10 - 1 m Low band: TV Band1- Channel 2-6, Mid band: FM radio, High Band: TV Band 2- Channel 7-13

Ultra High frequency (UHF)

300M - 1GHz

1 m - 10 cm Mobile phone, Channel 14 - 70

Super high frequency (SHF)

3-30 GHz 0.01-0.001 m satellite communucation, C-band, x- band,Ku-band, Ka-band.

Extremely High Frekuensi (EHF)

30 - 300 GHz 0.01m Satellite, radar system, IR, UV, X-rays, Gamma Rays.

Analog or Digital Communication

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Communications signals can be either by analog signals or digital signals. These are analog communication systems and digital communication systems.

• For an analog signal, the signal is varied continuously with respect to the information.

• In a digital signal, the information is encoded as a set of discrete values (for example, a set of ones and zeros).

Fact – Optical Fiber provides cheaper bandwidth for long distance communication

Frequency(f),wavelength(λ) and velocity(V)

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V = f λ, F = 1/ T

Ampl/V.

time/s105

10

0

From the graph :

Time = 10s

Amplitude = 10V frequency = 1/T = 1/10 = 0.1Hz

WAVE AMPLITUDE vs TIME

ONE CYCLE

Frequency(f),wavelength(λ) and velocity(V)

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Ampl/V.

distance/ m

10

0105

wavelength,

WAVE AMPLITUDE vs DISTANCE

Example : Given f = 300Mhz and V = 3 x 108 m/s, find the wavelength.

Answer : wavelength, λ = v / f = 3 x 108/ 300 x 106

= 1 meter

Frequency(f),wavelength(λ) and velocity(V)

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Angle(o)

Ampl/V.

10

0

360180

WAVE AMPLITUDE vs ANGLE

Frequency(f),wavelength(λ) and speed(V)

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Ampl/V.

sudut (o)

10

0360180

From the graph, = 180o - 90o = 90o

Method to calculate angle from analog wave

Two oscillators that have the same frequency and different phases have a phase difference, and the oscillators are said to be out of phase with each other. The amount by which such oscillators are out of step with each other can be expressed in degrees from 0° to 360°, or in radians from 0 to 2π.

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The two most significant limitations on the performance of a communications system are noise and bandwidth. The bandwidth of an information signal is simply the difference between the highest and the lowest frequencies contained the information, and the bandwidth of a communication channel is the difference between the highest and lowest frequencies that the channel will allow to pass through it

Bandwidth has several related meanings:Bandwidth (signal processing) or analog bandwidth, frequency bandwidth or radio bandwidth: a measure of the width of a range of frequencies, measured in hertzBandwidth (computing) or digital bandwidth: a rate of data transfer, bit rate or throughput, measured in bits per second (bps)Spectral linewidth: the width of an atomic or molecular spectral line, measured in hertz

1.5.3 Bandwidth

Bandwidth…..

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The bandwidth of a communications channel must be large enough to pass all significant information frequencies.In other words the bandwidth of the communications channel must be equal to or greater than the bandwidth of the information.

Give some example from the formula …….

Bandwidth(BW) = f2- f1

1.6 Types of communication system

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1.Broadcast communication system

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Broadcasting is the distribution of audio and video content to a dispersed audience via radio, television, or other. Receiving parties may include the general public or a relatively large subset of thereof.Historically, there have been several different types of electronic broadcasting media:Example…..

Block diagram of broadcast receiver using AGC

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1. Telephone broadcasting (1881–1932): the earliest form of electronic broadcasting (not counting data services offered by stock telegraph companies from 1867, if ticker-tapes are excluded from the definition). Telephone broadcasting began with the advent of Théâtrophone ("Theatre Phone") systems, which were telephone-based distribution systems allowing subscribers to listen to live operaand theatre performances over telephone lines, created by French inventor Clément Ader in 1881. Telephone broadcasting also grew to include telephone newspaper services for news and entertainment programming which were introduced in the 1890s, primarily located in large European cities. These telephone-based subscription services were the first examples of electrical/electronic broadcasting and offered a wide variety of programming .2. Radio broadcasting (experimentally from 1906, commercially from 1920): radio broadcasting is an audio (sound) broadcasting service, broadcast through the air as radio waves from a transmitter to an antenna and, thus, to a receiving device. Stations can be linked in radio networks to broadcast common programming, either in syndication or simulcast or both.

Continue….

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3.Television broadcasting (telecast), experimentally from 1925, commercially from the 1930s: this video-programming medium was long-awaited by the general public and rapidly rose to compete with its older radio-broadcasting sibling.4.Cable radio (also called "cable FM", from 1928) and cable television (from 1932): both via coaxial cable, serving principally as transmission mediums for programming produced at either radio or television stations, with limited production of cable-dedicated programming.5.Satellite television (from circa 1974) and satellite radio (from circa 1990): meant for direct-to-home broadcast programming (as opposed to studio network uplinks and downlinks), provides a mix of traditional radio or television broadcast programming, or both, with satellite-dedicated programming.6.Webcasting of video/television (from circa 1993) and audio/radio (from circa 1994) streams: offers a mix of traditional radio and television station broadcast programming with internet-dedicated webcast programming.

2. Mobile communication system

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A mobile phone, cell phone or hand phone is an electronic device used to make mobile telephone calls across a wide geographic area, served by many public cells, allowing the user to be mobile. By contrast, a cordless telephone is used only within the range of a single, private base station, for example within a home or an office.A mobile phone can make and receive telephone calls to and from the public telephone network which includes other mobiles and fixed-line phones across the world. It does this by connecting to a cellular network provided by a mobile network operator.In addition to telephony, modern mobile phones also support a wide variety of other services such as text messaging, MMS, email, Internet access, short-range wireless communications (infrared, Bluetooth), business applications, gaming and photography. Mobile phones that offer these more general computing capabilities are referred to as smartphones.

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GSM (Global System for Mobile Communications, originally Groupe Spécial Mobile), is a standard set developed by the European Telecommunications Standards Institute (ETSI) to describe technologies for second generation (or "2G") digital cellular networks. Developed as a replacement for first generation analog cellular networks, the GSM standard originally described a digital, circuit switched network optimized for full duplex voice telephony.

The standard was expanded over time to include first circuit switched data transport, then packet data transport via GPRS. Packet data transmission speeds were later increased via EDGE. The GSM standard is succeeded by the third generation (or 3G") UMTS standard developed by the 3GPP. GSM networks will evolve further as they begin to incorporate fourth generation (or "4G") LTE Advanced standards. "GSM" is a trademark owned by the GSM Association.

Mobile Communications: Wireless Telecommunication Systems

Mobile phone subscribers worldwide

0

100000

200000

300000

400000

500000

600000

700000

1996 1997 1998 1999 2000 2001

sub

scri

ber

s (x

100

0)

Analog total

GSM total

CDMA total

TDMA total

PDC/PHS total

total

4.1.1

Block diagram of Mobile communication system

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A wireless communication link includes a transmitter, a receiver, and a channel,as shown in Figure. Most links are full duplex and include a transmitter and a receiver or a transceiver at each end of the link

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in Fig. 2-2 (a). In peer-to-peer systems, mobile units communicate directly with each other. Mobile units sharing a frequency channel can communicate with one another, and independent conversations can take place on different channels. Many amateur, and most CB radio contacts fit into this peer-to-peer model, as shown in Fig. 2-2 (b). In peer-to-peer systems, a mobile can sometimes hear only one of two other mobiles that are using a channel, when a total of three users are active.

3. Fixed communication system

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Technology basically gives us a lot of advantages to really connect on what we are up to and one of the most important and most commonly used to us is “Communication”, whereas we basically exchange information from one another sometimes by the way of Fixed Communication Systems. I think more surprisingly is that the evolution of this systems that allows us to communicate even in the hardest possibilities. With the help of Fixed Communication Systems, we are able to have better communication through any means of communications there is.

One of the most common means of technology in our world is the telephone, and with it it’s pretty much a basic point to have access on a telephone wherever you may be. In every phone servers there is Fixed Communication System in which basically becomes the root in order for a simple communication by the use of telephone or hand held phones to another.

4. Data communication system

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 Data Communications is the transfer of data or information between a source and a receiver. The source transmits the data and the receiver receives it. The actual generation of the information is not part of Data Communications nor is the resulting action of the information at the receiver. Data Communication is interested in the transfer of data, the method of transfer and the preservation of the data during the transfer process.In Local Area Networks, we are interested in "connectivity", connecting computers together to share resources. Even though the computers can have different disk operating systems, languages, cabling and locations, they still can communicate to one another and share resources.The purpose of Data Communications is to provide the rules and regulations that allow computers with different disk operating systems, languages, cabling and locations to share resources. The rules and regulations are called protocols and standards in Data Communications.

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BASIC BLOCK DIAGRAM OF DATA COMMUNICATION

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Refer to the block diagram of data communication

There is a source of digital information ( primary station), transmission medium ( facility) and a destination (secondary station) .

The primary source is usually a main frame computer wth its own set of local terminals and peripherals equipment.

The digital information is then transferred by using the transmission medium such as free- space radio transmission ( terrestrial and satellite microwave), metallic cable facilities ( both digital and analog systems) and fiber-potic cable( light propogation).

DTE (Data Terminal Equipment) refers to the interface equipment used at the station between the host and modem to adapt the digital signals from the computer and terminals to suitable form for transmission.

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DCE ( data communication Equipment)

Means the equipment that converts digital signal to analog signals and interfaces the data terminal equipment to the analog transmission medium.DCE is nothing but a modem ( modulator/demodulator). It converts binary digital signals to analog signals such as PSK.FSK and QAM and vice versa.

ASSIGNMENT

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1. Compare between Broadcast and mobile communication system.

2. Compare between Fixed communication and data communication system.

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THANK YOU