Types of Communication Systems:

i)   Simplex (SX) Communication System:

        The communication system that is capable of one way transmission is called simplex transmission system.  In simplex type you have one unit equipped with one transmitter and on the other side equipped with one receiver but communication is done only one way by transmitter.

Simplex Communication System

For example, television broadcast system in which there is one transmitter and more than one receivers that only receives information sent by transmitter.

ii) Half-Duplex (HDX) Communication System :

      The communication system in which information flows in both directions but the flow is only one way at a given time is known as half-duplex (HDX).

      In this type, you have one unit equipped with transmitter as well receiver at one end and a transmitter-receiver at the other end but information can't flow simultaneously in both directions.

Half-Duplex Communication System

    An example of half-duplex system is two parties "walkie-talkie"  where both parties can transmit and receive but only one can transmit at a time.

iii) Full-Duplex (FDX) Communication System :

In full-duplex communication simultaneous communication is accomplished in both directions.

Full-Duplex

  
Full-duplex Ethernet connections work on the principles of full-duplex where data packets are received and sent simultaneously at a given time.

                                                         

                                                         ooooooooooooooooooo

   

General Block Diagram of Communication System

http://pocs1.blogspot.com/2012/03/types-of-communication-systems.htmlThe most general form of communication system consists of the following components:

Communication System Generic Block Diagram

Transmitter:

 The upper portion of the channel as a whole is called transmitter.

Information Source:

The information provided to a communication system is called baseband. One may define as " any information signal is known as baseband signal".

Processing Unit:

The baseband signal is passed through some processing unit where necessary operations are performed. These operations may include filtering, sampling etc. This is helpful in separating unwanted information from baseband.

Modulation:

 The process of modulation is required to make the baseband signal ready for transmission.  The modulator produces a varying signal at its output which is proportional in some way to the signal appearing across its input terminal (baseband signal). For example , a sinusoidal modulator may vary the amplitude, frequency or phase of a sinusoidal signal in direct proportion to the input baseband.

Antenna :

For wireless communication , antenna is used to send modulated information into the channel or medium.

Channel:

The transmission medium or channel is vital link between the system. Without it there would be no communication problem. The transmission medium may include wired transmission line, atmosphere (wireless) which may include the ionosphere, the trooposphere, free space etc.

It causes noise (unwanted addition to baseband signal) , attenuation and distortion in the form of electrical signal. This results interference with our error-free reception at receiving end.

Receiver:

The portion below the channel as whole called receiver.

Demodulation:

The demodulator performs the inverse process of modulator to recover the information signal in its original form.

RF Amplifier:

 The RF amplifier is used to tune the receive to frequency of the transmitted bandwidth.

Display Unit:

This shows us the received signal in the form by which we are familiar.

Basic Parameters of Communication System

Following are the most basic parameters of the communication system. We are going discuss all these one by one in detail.

a)   Bandwidth
b)   Transmit Power
c)   Signal to Noise Ratio

a)  Bandwidth

       Bandwidth is defined as " the range of frequencies required to represent original signal in time domain". This is the simplest definition of bandwidth.

As being engineer we'll use more technical definition of bandwidth which is :-

       " A ring of frequencies that falls in the amplitude of first and last by 3dB and 70% of energy left".

Some important points relating bandwidth are:-

i)   Rate of Transmission of data is directly proportional to bandwidth i.e wider the bandwidth ,

      more    data  will flow .

ii)  With wider bandwidth, there are less collisions and errors are minimum.

iii)  The bandwidth is chosen after detailed analysis which is enough for data to be transmitted. 

       This precaution is taken to avoid addition of noise since with the wider bandwidth thermal noise 

       increases. Hence thermal noise is directly proportional to bandwidth.

b)  Transmit Power

                 As the name suggests that it is the power required for transmission. Transmission power plays an important role due to its duality. 

        

               The increase in transmission power reduces the noise. Secondly information is transmitted more accurately and precisely.

      

      Usually binary (0,1) level transmission is done just to save transmission power. For example if we are going to transmit 4 bits of information withing 2 levels, 2 bits will be transmitted in one pulse width hence bandwidth will be two pulses.

         Suppose we transmit this in 4 levels , one pulse having one bit then transmit power will increase very fast which makes it more expensive system. Just to save transmission power and simplicity we use binary level at the expense of bandwidth.

c)  Signal to Noise Ratio :

     The performance of the system is defined by signal power to noise power ratio.

      Let S_o is the signal output power and N_ois the noise output power then 

          

                                               is known as signal to noise ratio. 

       The greater the signal power less the noise power affects and systems performance is better

        and vice versa.