Communications Systems

The process of transmission of information or message from one end to another is known as communication. When electromagnetic or radio waves are utilized for communication purpose, then it is called as radio communication. Electronic communication is started with wire telegraphy in the first half of nineteenth century. After a decade of years, telephony was developed, In the beginning of the twentieth century, radios come into existence. Radio communication made possible by the invention of the triode tubes. 

The modern communication system involves the process of sorting, processing and storing of information before conveying the message. During transmission, the filtering of Noise takes place. Finally there includes the processing steps like decoding, storage and interpretation. Some types of communication include radar, telecommunications, mobile, computer, radio telemetry etc. The essential requirements of any communication system are fundamentally same.

Communication System Block Diagram with Explanation

The general block diagram of a general communication system is shown in figure. Any communication system is consist of an information source, transmitter, receiver, channel and noise.

Information

The purpose of communication system is to communicate a message. This message comes from an information source. The message from an information source may be a speech from an individual or a numerical data from a computer. The total number of messages consists of individual messages which can be distinguished from one another. The amount of information contained in any given message is measured in bits depending upon the method of communication.

Transmitter

The message comes from an information source may not be an electrical Signal. Unless the message that comes from the information source is electrical in nature, it will be unsuitable for sending. So the physical quantity must be converted into an electrical signal before it is applied to the transmitter. This is done with a transducer. The transducer will convert the physical quantity (in which the information is presented) into a corresponding electrical signal. For example, a carbon microphone will convert sound into electrical signal. The output from the transducer is known as signal. The signals are of two types — analogue type or digital type. According to the type of signals used, communication systems are also classified into either analogue or digital systems. In modem communication systems, the analogue signals are converted into digital signals, and thereafter transmitted through a digital system.

Even though the message that comes from the information source is electrical in nature, it is unsuitable for immediate sending. A lot of process must be done on the message to make it suitable for transmission. The transmitter is required to process the incoming information. The main process to be done is known as modulation. Modulation is a process in which some characteristics of a high frequency sine wave (carrier) is varied in accordance with the instantaneous values of the message signals. In a transmitter, the information modulates a carrier. That is, the information is impressed on a high frequency sine wave. The method of modulation may be analog or digital, high level or low level. The system may be amplitude modulator, frequency modulator, phase modulator, or pulse code modulator or combination of these.

Channel

Channel is the medium through which the information is transmitted from the transmitter to the receiver. The channel may be free space, air, wire, or fiber optic channel. In radio communication, the medium is free space where as in line communication it is a cable or a wire. In radio communication, information is transmitted as electromagnetic waves into the free space. In line communication it is transmitted as electric signals through cable. The acoustic channel is not used for long distance communication.

Noise source

The reason for noise is

1. Some distortion in the system

2. Because of introduction of noise, which is present in a transmission system.

Noise is defined as any unwanted form of energy tending to interfere with the proper and easy reception and reproduction of wanted signals. Noise can interfere with the signal at any point in a communication system. There are many ways of classifying noise, It is most convenient here to divide noise into two broad groups — internal noise and external noise.

External noise is the noise whose sources are external to the receiver. For example, atmospheric noise and industrial noise. Internal noise is the noise created within the receiver itself. For example, thermal agitation noise.

Receiver

The transmitted signal finally reaches at the receiver. The main function of a receiver is to demodulate the modulated incoming signal so as to retrieve the original message. The signal from the channel is amplified and the information is extracted in the desired form with the help of a transducer.