History of communication systems

History of communication systems

Communication is one of the most important parts of electronics. When the question comes on “staying connected”, we often coin the term “communication”. From telephone,fax machine,internet,ATMs,GPS, radars,rockets to radio,antenna,missiles and satellite everything is interconnected in the field of communication.

Only a few hundred years ago when communication was totally dependent on physical means i.e one has to carry the message from one place to another. The carrier was mostly man, animals like pigeons or special form of sounds. But everything has changed after the advancement of modern electronics and communication.

Imagine yourself sitting in front of the television and getting the world's news from a broadcasting satellite, situated 35,000km away in the geostationary orbit. With a few click of the mouse, you are accessing the whole world's information and by pressing some buttons you are connecting with the person who is hundred miles away.Today all these are everyday reality and we perhaps cannot live without it.

Communication is the process of establishing connection between two points. These points are basically information sources that are set up to exchange information” The earliest communication system started with telegraph in eighteen century (1840). From then wired telephony became very much popular which further gave birth to the era of radio communication (electronics and World War II).
Brief History of Communication Engineering

1840s-Telegraph

1870s-telephony

1900s-Communication Electronics

1920s-Television

1930s-Teletypewriter

1940s-Radar and Microwave

1960s-Laser Technology

1965s-Solid State electronics

1970-ICs and Microprocessor

so far we have gone through the introduction and the development stages of communication. In my next post you will see "how does communication takes place from one point to another".

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How does a wirless device communicate?

How does wireless communication takes place?

In my last post I have given you a brief description of the history of communication. In this post we will see the basic communication system

SOURCE

A source in communication is a signal that carries information . Consider your speech when you talk or the music that you hear or pictures that you see are basically sources of information. Now our main objective is to send this source of information from one point to another.

INPUT TRANSDUCER

Now as you know that the source may or may not emit electrical signal. For e.g.: the speech when you speak is a sound signal and we cannot send a sound signal in an electrical channel. For this we convert that sound signal into electrical signal. This conversion of one form of signal to another form is done by transducer.

TRANSMITTER

The function of a transmitter is to process the signal . For e.g. in telephone communication the voice band is 3100 Hz, so signals above it are either eliminated or band restricted. Thus in order to make the information suitable for transmission over channel the signal is modulated, amplified and band restricted.

CHANNEL AND NOISE

The channel is the medium through which information travels from transmitter to receiver . So far we have seen how sound signal is converted to electrical signal and modulated inside the transmitter. This modulated signal is send to the receiver end and this could be done by sending the signal through the medium called channel. The media can anything, say telephone wires, coaxial cables, optic fibers, wireless or via microwave. When the information travels though a channel it is affected by noise. Noise is nothing but distortion or interference generated by the channel.

I am later going to discuss about various types of noises and channels used in communication.

RECEIVER

The receiver receives the signal from the channel. After receiving the signal its tries to extract the original message/information signal known as demodulation. It’s also checks if there is any error or noise present in the signal.

OUTPUT TRANSDUCER

The person at the transmitter has sent a message signal in the form of speech. After processing the signal it changed to electrical form. So our desired output should be in the form of sound signal and not electrical signal. So in order to bring back the original sound signal we use a transducer.

DESTINATION

The place where we want to send the signal. It can be loudspeaker, T.V, computer etc

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Mobile communication in spectrum

How does mobiles communicate in a spectrum?

You must have seen the term “3G spectrum or 3G auctions” in any leading newspaper or TV channel. To understand the basics, you must know a little bit of Electro Magnetic Spectrum. In mobile phones our speech signal i.e. voice is first converted to electrical pulses for processing. Since electrical signals cannot travel through air, so after processing they are converted into Radio waves (a part of EM spectrum).

What are Electromagnetic waves?

Electro-Magnetic waves are invisible waves that can pass through any solid medium. They have longer range and can travel long distance (kilometers) with the help of antennas and repeaters. These radio waves are not only used for mobile communication but are also used in wide range of applications like radio broadcasting, satellite and military communication, radars, navigators like GPS etc.

Need of spectrum management

In today’s digital world most wireless activities occurs simultaneously, so there must be a monitoring body present to look after these frequency bands and check whether these bands are overlapping with each other or not. “So several non-colliding frequency bands make up a spectrum.” For example if we do not have separate frequency bands for radio broadcasting and mobile communication then there will be overlapping of frequencies resulting in a distorted output. In order to prevent this, radio and mobiles are given different frequency bands. In India we have frequency band of radio is 87 MHz to 108 MHz and 900/1800 MHz for mobile. Similarly, for satellite communication we have 30 to 300 GHz of high frequency range.

Auction Body and role of TRAI

In India spectrum auction is done by TRAI (Telecom Regularity Authority of India). It is a part of government’s body that spends considerable amount of time allocating particular services so that they do not interfere with each other. These services are bounded by rules which are agreed and accepted internationally. Thus in order to buy any particular frequency band telecom operators has to provide a certain sum of money to the government. Some of the Telco’s that participated in the recent 3g auction were Vodafone, Bharti Airtel, Reliance, Tata etc.

Therefore the main purpose of splitting the spectrum is to provide different services with different non colliding frequency bands.

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