UNIT:1
Communication
Definition:
The word communication aries from the laltin "communicates", which means "to share". Communication is the basic step for the exchange of information . For example, a baby in a cradle, communicates with a cry that she need her mother. Communication is the bridge to share. Communication can be defined as the process of exchange of information through means such as words, action, sign, etc, between two or more individuals.
Need of communication:
For any living being, while co-existing, there occurs the necessity of exchange of some information. Whenever a need for exchange of information aries, some means of communication should exist. While the means of communication, can be anything such as gestures, sigh , symbol, or a language, the need for communication is inevitable.
Language and gesture play an important role in human communication, while sounds and action are important for animal communication. However, when some message has to be conveyed, a communication has to be established.
Block Diagram of communication systems:
The block diagram given below represents to flow of the sognal from the source to the destination. The role of every device and arrangement discussed above os better understood.
Parts of Communication system:
Any system which provides communication, consists of the there important and basic parts as shown in figure:
•The Sender transmitter is the person who sends a message. It could be a transmitting station from
where the signal is transmitted. •The channel Medium is the medium through which the message signals travel to reach the destination.
•The Receiver is the person who receives the message. It could be a receiving station where the signal transmitted is received.
What is a signal?
Conveying an information by some means such as gestures, sounds, actions, etc. can be termed as signaling. Hence, a signal can be asource of energy which transmits some information. This signal helps to establish communication between sender and receiver..
An electrical impulse or an electromagnetic wave which travels a distance to Convey message a as a signal communication be termed Can systems.
Elements of Communication systems.
The definitions of the terms used in the communication system are discussed below:
Information:-
Message or information is the entity that is to be transmitted. It can be in the form of audio, video 1 temperature, picture, pressure, etc.
Signal:
The signal Valued Function of time that carries the information. The information is converted into an electrical form for transmission.
Transducer:-
A device or an argument that converty one form of energy to the other. An electrical transducer Converts physical variables such as pressure, force, temperature into corresponding electrical signal variations. Example: Microphone - converts audio signals into electrical signals. Photodetector - converts light signal into electrical signals.
Amplifier:-
The electronic circuit or device that increses that amplitude or the strength of the transmitted signal is called an amplifier. When the signal strength becomes less than the required value, amplification can be done anywhere in between transmitter and receiver. A DC power source will provide for the amplification..
Modulator:
As the original message signal cannot be transmitted over a large distance because of their low Frequency and amplitude, they are superimposed with high Frequency and amplitude wave called carrier wave. This phenomenon of superimposing of message signal with a carrier wave is m called modulation. And the resultant wave is a modulated wave which is to be transmitted. Again there are different types of Modulation
i) Amplitude Modulation (AM):
The process of changing the amplitude of the signal wave by impressing or superimposing it on a high- Frequency carrier wave, keeping its Frequency constant
is called modulation.
ii) Frequency Modulation (FM):
Frequency modulation is a technique in which the frequency of the message signal is varied by modulating with a camer wave. It is better than amplitude modulation because it eliminates noise From various sources.
iii) Phase Modulation (PM)
The phase of the carrier wave changes the phase of the signal wave. The phase shift after modulation is dependent on the frequency of the carrier wave as well. Phase modulated waves are immune to noise to a greater extent.
Transmitter:-
It is the arrangement that processes message signal into a suitable from for transmission and subsequently reception.
Antenna:
An antenna is a structure or a device that will radiate and receive electromagnetic waves. So, they are used in both tranmitters and receivers. An antenna is basically metallic object, often a collection of wires. The electromagnetic waves a are polarised according to the position of the antenna.
Channel:-
A channel refers to a physical medium such as wire cables, space through which the signal is passed from the transmitter to the receiver. There are many channel impairments that effect channel performance to a pronounced level. Noise, Attenuation and distortion to mention the major impairments.
Noise:
Noise is one of the channel imperfection or impairment in the received signal at the destination. There are external and internal source that cause noise. External sources include interference, i.e. interference from nearby transmitted signals (crass talk), interference generated by a natural source such as lightning Solar or casmic radiation, automobile generated radiation, etc. The external noise can be minimised and eliminated by the appropriate design of the channel, shielding of cables. Also by digital transmission external noise can be much minimised.
Internal sources include noise due to random motion and collision of electrons in the conductor. thermal noise due to diffusion and recombination Of charge carriers in other electronic devices. Internal noise can be minimised by cooling and using digital technology for transmission.
• A different cable design.
• Proper design of the channel.
• Use digital transmission.
• Using BPF or LPF at the receiver side.
Types of Communication Systems:
Depending on signal specification or technology, the communication system is classified as follows:
1) Analog:
Analog technology communication data as electronic signals of varying Frequency or amplitude. Broadcast and telephone transmission are common examples of Analog technology.
2) Digital: In digital technology, the data are generated and precessed in two states High Crepresented as 1) and ton) (represented as a). Digital technology store, and transmits data in the form of Is and Os.
Depending on the network, the communication system is categorized as follows:
1) Computer Network. LAN MAN WAN
2)Radio Network
3) Pocket Switching Network
Depending on the communication channel, the communication system categorized as follows:
1. Wired line communication
Wired communication refer to the transmission of data over a wire-based communication technology. wired. communication is also known as wire line communication. It means the communication system consist of physical mediam can be twisted pair, co-axial cable optical fiber or any other existing materials. Examples include telephone network cable television or Internet access and fiber optic communication. Most wired networks use Ethernet conje to transfer data between connected Pcs: local telephone networks often form the bacle for wired communi.co ons and are used by both residential and busines customer in the area.
Source transmitter channels Receiver Destination
Noise.
Fig:- Block diagram of wired communication system.
Types of wired communication:
• Paroller wire communication
• Twisted wire communication
• Co-axial cable communication
• Optical Fiber communication.
1) Wireless (space communication) wireless communication involves the transmission of information over a distance without the help of wires, cable or any other forms OP electrical conductors. It means there is no physical medium or material for the communication between transmitter and receiver. Generally, EMW,Radio wave, Infrared are used for the transmission of information All the wireless device must consist of an Antenna or sensor Because of this absence of any physical Infrastructure.wireless communication has certain advantages.
-Source
Input Transduce and A to D converter
Source Encoder
Channel Encoder
Digital Modulator and to A convert
-Output signal
Output transducer and D to A converter
Source decoder
channel decoder
Channel Digital Demodulator and D to A converter
Types of Wireless communication:-
• Ground Wave communication
• skywave communication...
• space wave communication
• Satellite Communication
Some of the important wireless communication system are:-
• Television and Radio Broadcasting
• Satellite Communication.
• Radar
• Mobile Telephone System (cellular communication)
• Infrared communication.
• Global posting system (GPS)
• Infrared communication.
• WLAN (Wi-fi)
• Bluetooth
Comparison between wired & wireless communication system.
Example of communication systems.
The following are a few examples of communication system :-
i) Internet
ii) Public Switched Telephone network
iii) Intranet and Entranet
iv) Television Radio
v) VOIPC Voice Over Internet protocol).
Telecommunication System:-
It is defined as the exchange of information from transmitter to receiver through physi- cal medium that may be wired or wireless communication, Telecommunications are the meant of electronic transmission of information over distancer The information may be in the Form of voice telephone calls, data, text, image or video. A complete, Single telecommunication circuit consists of two o stations, each equipped with a harmonic transmitter and a receiver The transmitter and receiver at any station may be combined into a single device. called a trans receiver. The medium of signal transmi- ssion can be via electrical wire or cable also known as copper..optical five, electromagnetic fields or light.
Classification of tele-communication systems
i) Facsimiles :-
A form of telegraphy For the transmission of fixed images with or without half tones wealth a view to their reproduction In a permanent form.
ii) Cellular telephony:-
Mobile telephony is the provision of telephone services to phone which i may move around Freely rather than stay fixed in one location.
iii) Radio Paggings:-
A system consisting of person at pagging. receiver, radio transmitter and an encoding device designed to alert an individual or group of individuan and deliver short message.
iv) Video Telephone:
A telephone with a video screen and is capable of full duplex bi-directionall video audio transmission for communication between people in teal time.
• It was initially the form of video telephony latex followed by video conferencing, Webcams, and finally telepresences
V) Satellite phone:-
A telephone that transmits and receive From Satellite that provide coverage around the world.
A mobile phone that can send voice message. over extremely long distance using connection to Communication satellites. Forex. Iridium was the fint satellite phone company.
Transmission Method:-
Transmission media is a communication channel that carries the information from the sender to the receiver Data is transmitted through. the electromagnetic signal The main feature of a medium is it's potential transmission speed, also known as channel capacity which for data transmis ion channel capacity is bandwidth. The range of signal Frequencies that can be transmitted over the channel- sin popential media are employed to implement tele communication links.
1. Toisted pair
2) co-axial cable
3) Fiber optical cable
4) Terrestrial Microwave.
5) Satellite transmission.
"Other notes on PDF"