Aspects of Communication Systems

Modulation : To modify or temper in someway, in telecommunications transmitter creates and emits radio waves. It is necessary in order to ensure that the relevant information is carried by the wave.

The transmitter electronically modulate or decode sound or other information onto radio waves, by varying either Amplitude Modulation (AM) or Frequency Modulation (FM) within the established range. In phase modulation the phase of the wave form is shifted slightly at a clocked rate.

Demodulation : Demodulation involves the reverse approach. It's the process of capturing information from the carrier wave. It involve detecting the individual amplitude/frequency/phase shifts in carrier, and decoding them to digital data for further process.

Modulation can be seen as power sharing. If there is no modulation, all the power is in the carrier.

As Modulation is increased, more power is put in the data and lets in the carrier but it always adds up to the same amount of power.

Frequency Modulation (FM) and Amplitude Modulation (AM) :

1) Frequency Modulation (FM) has several advantages then Amplitude Modulation (AM). In that FM system is greater freedom from interference and static. 

2) AM signals that are received various electric disturbances caused by thunderstorms as noise by AM receivers. A well designed FM receiver is not sensitive to such disturbances when it is tuned to sufficient strength.

3) Signal-to-noise radio in FM system is much higher than that of an AM system.

4) FM broadcasting stations can be operated in very high frequency bands. at which AM interference is frequently severe. 

5) Commercial FM radio stations are assigned frequencies between 88 and 108 MHz. The range of transmission on these bands is limited so that stations operating on the same frequency can be located within a few hundred KM of one another without mutual interference.

Procedure in Digital Communications (Overview)

Telecommunication devices convert different types of information like audio, images, video and text into electronic or optical signals. These digitilised signals initially passed through a source encoder. After encoding, the digitized signal is processed in a channel encoder, here some errors are rectified.

These encoded signal is suitable for transmission by modulation onto a carrier wave and may be made a part of a larger signal in a process, known as multiplexing. And this signal is sent into a multiple access transmission channel. After transmission, the above process is reversed at the receiving end and the information is extracted. The device at the receiving end  converts the signal back into human comprehensible form. (Examples are voice and movable images on television and words and text on a computer screen).

Messages can be sent from sender to a signal receiver i.e., point-to-point transmission, is generally involved in personal communications like telephone conversations and fax messages are the best examples for point-to-point transmissions.

Messages can be sent from sender to many receivers is called as point-to-multipoint transmission, and also known as Broadcasts, these multiform transmissions are generally used in radio and television programs.

Communication Technology (or) Telecommunications

Communication Technologies allow people around the world to contact one another, to access news, data, entertainment information instantly, and to even communicate from remote rural areas. Information and Communication Technologies (ICTs) are powerful instrument, increasing productivity, generating Economic growth, job creation and employability and improving the quality of life of all. They can also promote dialogue among people, nations, and civilizations. 

Today the main form of communication is Telecommunication. It refers to the transmission of information by electromagnetic form, including a wide variety of information like voice, music, pictures, videos, computer files, applications and text data.

Historical Background : On 24 May 1844, Samuel Morse sent his first public message over a telegraph line between Washington and Baltimore in USA. Ten years later, telegraphy wa available as a service to the general public. The continuing rapid expansion of telegraph networks in a growing number of countries finally prompted European States to meet to develop a framework agreement covering international interconnection.


In May 1865, the first International Telegraph Convention was signed in Paris by the 20 founding members, and the International Telegraph Union (ITU) was established to facilitate subsequent amendments to this initial agreement.


Modern Telecommunication System : A modern telecom system includes hardware as well as software to transmit information. Information can include voice, data, images, music and video.


Main Components in this System :


1) Hardware : Computers and Modems
2) Media : Wire or wireless media (electronic signals may be transmitted)
3) Networks : between computers and other devices.
4) Protocols : In the form of rules governing information transmission
5) Software : Which controls the system and the transmission process.


The information transmitted is in the form of signals which can be analogue (in the form of waves) or digital (in the form of bits 0's and 1's).