MATLAB Assignment: Communications IV

5/24/2019
MATLAB ASSIGNMENT
4035 COMMUNICATIONS IV

INTRODUCTION
Communication systems are used to convey information from one source to a given or intended
destination. These systems are used in broadcasting and developing the cellular network such as
the television, radio systems, PDA, satellite systems, and the cellphone systems. The key
components of the communication system are the input transducer, the transmitter, a working
channel, receiver systems and an output transducer. The information is mostly obtained from
analog or real world sources but in some cases it could have a digital source. The input
transducer converts the analog signals to digital signals. The transmitter couples the message and
lays it to the channel in preparation for amplification and modulation. The modulation encodes
message into amplitude, phase, or frequency of the carrier signals.
It is important to have proper modulation so as to reduce noise and interference, multiplexing,
and channel assignment. To transmit the signal, the designer must make a good choice of the
transmission channel. The channel introduces some amount of distortion, noise, and interference.
The capacity of the channel is determined based on the maximum rate at which it can transfer
information. The channel capacity determine the maximum rate at which information may pass
error free over a given channel. The Hartley-Shannon law is used to determine the appropriate
channel capacity for a given communication system,
C=
Bandwidth∗log (1+ ( S
N ) )b
s
The bandwidth and noise of a channel are the key parameters that classify the channel as
appropriate. In the communication industry, a very limited resource, the frequency spectrum, is
required by many service providers or users. The spectrum is managed for a particular physical
medium under the regulation of the International Telecommunications Union, ITU and the
federal communications commission, FCC for licensing.
Continuous time signals are analog signals while the discrete time signals are digital signals. The
periodic analog signals are set up as simple or composite. The sine wave is made up of different
segments as discussed in the system modelling. The frequency of a signal is the inverse of a
period. Sine waves in complete time domain are represented as a single spike in the frequency
domain. The frequency domain is more compact and useful when dealing with sine waves. In
1

Fourier analysis, signal composites are combinations of simple sine waves with different
frequencies, amplitudes, and phases.
AIMS OF THE PROJECT
 To generate a frequency modulated signal, add noise, filter and demodulate the signal.
 To compute the signal to noise ratio.
SYSTEM MODELLING & SIMULATION
PART I:
Message Signal is developed as a sine wave signal obtained from the surrounding. The
sinusoidal message signal is developed as,
m ( t ) =Am cos ( 2 π f m t )
m ( t ) =120cos ( 2 π ( 1500 ) t )
m (t)=120 cos ( 3000 πt )
A reference signal is generated as the carrier signal of the channel such as,
V ref (t )=Ac cos (ωc t )
V ref ( t ) =15 cos 4 00 πt
The amplitude of a carrier signal in a transmission channel from a direct current source is given
as unity but in a sinusoidal transmission it has a value greater than or less than 1. The message is
modulated using the formula,
SAM ( t )= [ Ac+ m ( t ) ] cos ( 2 π f c t )
The Matlab code snippet to generate the signal is as shown below,
2

The message signal is illustrated as shown in the x-y graph below,
PART II:
For the reference signal,
3