Communication   theory :

This subject deals with how  signals are  transmitted   and received  with suitable  modulation and demodulation , for effective  transmission and reception without loss.

Different types of modulation

·      Amplitude modulation   and 

·      Angle  modulation

a)  Frequency  modulation

b) Phase modulation

And  at the reception end  demodulation is done to obtain the original  signal.

AMPLITUDE  MODULATION:

Wireless communication  is done in the air medium and for distant communication microwaves  are used  as  carriers.  This Carrier wave will always  be in higher frequency than the message that we send( data).

Definition : it’s the way of modulation  in which the amplitude of the carrier is changed to the instantaneous value of the  message  signal.

To  add more advantages like power saving,  cost  and bandwidth AM signal is transmitted as  DSB-SC signal i.e double side band suppressed carrier signal , SSB-SC signal i.e single side band suppressed carrier signal , VSB-SC signal i.e  vestigial side band suppressed carrier signal. Various techniques are used for the modulation and demodulation of the  above  three types of signals ….

Frequency division  multiplexing :  various signals are multiplexed and sychronised to  same frequency and sent  in a channel. This technique is used in radio stations.

ANGLE   MODULATION :

There  are two typs in angle modulation

Frequency modulation and

Phase modulation

Frequency modulation : if the frequency of the carrier wave is changed to the instantaneous value of the message signal then its called as frequency modulated signal.

Phase modulation :  if the phase of the carrier wave is changed to the instantaneous value of the message signal then its  called as  phase modulated signal.

NOISE  THEORY :

 While sending the  message signals  various  unwanted signals interrupt  and  cause  noise which is not desirable.

Various types of noises

External noises

·       Atmospheric noise

a)  Solar noise

b) Cosmis noise

·      Man made noises

a)  Industrial noises

b) And other noises made by man

  Internal noises

·       Which are caused internally in the components due to  resistors  ,capacitors,  transistors etc….

a)  White noise

b) Shot noise

c)  Partition noise.

 PERFORMANCE  AND  CW.

INFORMATION  THEORY :

To  read the message  and  for its  analysis  various coding techniques  are used

·      Shanon  coding

·      Hufmann coding and

·      Limpez  coding…

This chapter deals with analysis part……

thank you  

kousiviji.....