Make a comparative study and performance analysis of different modulation techniques which shows graphically and comparatively results like Bandwidth, Energy and Power Efficiency of AM, DSB-SC, SSB and SSB-SC

1. Problem:
Make a comparative study and performance analysis of different modulation
techniques which shows graphically and comparative results like Bandwidth,
Energy and Power Efficiency of AM, DSB-SC, SSB and SSB-SC.
Write a report on your analysis and justification of your results.
Abstract:
Several studies have been dedicated to the analysis of different modulation techniques. This paper
details a performance analysis of various modulation techniques like AM, DSB-SC, SSB, SSB-SC.
The aim of this study is to analyse and compare various techniques based on various parameters such
as bandwidth, power, energy, efficiency etc. AM generation involves mixing of a carrier and an
information signal. In Low level modulation, the message signal and carrier signal are modulated at
low power levels and then amplified. The advantage of this technique is small is that a small audio
amplifier is sufficient to amplify the message signal.
Keywords:
Modulation, Power, Efficiency, Bandwidth, Amplitude Modulation (AM), Double Sideband
Suppressed Carrier (DSB-SC), Single Sideband Suppressed Carrier (SSB-SC), Single Sideband SSB.
Introduction:
Communication is the process of conveying message or exchanging information. It means that
transmission of the encoded symbols transmitted in the communication channel, at the receiver
information is decoded and which recreates the original data. A message carrying a signal has to get
transmitted over a distance and for it to establish a reliable communication, it needs to take the help of
a high frequency signal which should not affect the original characteristics of the message signal.
Fig 1: Layout of Basic Analog Communication System
Modulation technique is used in communication process which increases the range of communication,
multiplexing and improves quality of reception. It is defined as the process of superimposing the
information contents of a base band signal on a carrier signal (which is of high frequency) by varying
the characteristic of carrier signal according to the message signal.
Advantages of implementing modulation in communication system are:
 Reduction of antenna size
 Increased in communication range
 Possibility of bandwidth adjustment.
 Improved reception quality

2. The types of modulations are broadly classified into continuous-wave modulation and pulse modulation.
In continuous-wave modulation, a high frequency sine wave is used as a carrier wave. This is further
divided into amplitude and angle modulation. If the amplitude of the high frequency carrier wave is
varied in accordance with the instantaneous amplitude of the modulating signal, then such a technique
is called as Amplitude Modulation. If the angle of the carrier wave is varied, in accordance with the
instantaneous value of the modulating signal, then such a technique is called as Angle Modulation.
Angle modulation is further divided into frequency modulation and phase modulation. If the frequency
of the carrier wave is varied, in accordance with the instantaneous value of the modulating signal, then
such a technique is called as Frequency Modulation. If the phase of the high frequency carrier wave is
varied in accordance with the instantaneous value of the modulating signal, then such a technique is
called as Phase Modulation.
Fig 2: Types of Modulation in Analog Communication System
As we discussed earlier modulation is a very important process in communication systems,
because the voice signal is dynamically varying signal hence need a high speed DSP processor to
process the signals accurately .The modulation schemes are broadly classified into two categories such
as analog and digital modulations .The topic for implementation is Amplitude modulation followed by
Double Sideband Suppressed Carrier (DSB-SC), Single Sideband (SSB) and Single Sideband
Suppressed Carrier (SSB-SC).

3. Methodology:
Amplitude Modulation:
According to the standard definition, “The amplitude of the carrier signal varies in accordance with the
instantaneous amplitude of the modulating signal” Which means, the amplitude of the carrier signal
containing no information varies as per the amplitude of the signal containing information, at each
instant. A continuous-wave goes on continuously without any intervals and it is the baseband message
signal, which contains the information. This wave has to be modulated. This can be well explained by
the following figures.
Fig 3: Baseband Signal Fig 4: Carrier Signal
Fig 5: Amplitude Modulated (AM) Signal
The first figure shows the modulating wave, which is the message signal. The next one is the carrier
wave, which is a high frequency signal and contains no information. While, the last one is the resultant
modulated wave. It can be observed that the positive and negative peaks of the carrier wave, are
interconnected with an imaginary line. This line helps recreating the exact shape of the modulating
signal. This imaginary line on the carrier wave is called as Envelope. It is the same as that of the
message signal.
Let the modulating signal be: m(t)=Am cos (2πfmt).
The carrier signal be: c(t)=Ac cos (2πfct).
The modulated wave be: s(t) = [Ac + Amcos (2πfmt)] cos (2πfct) s(t)………Eq. 1
Ac and Am are the amplitudes of carrier and message signal respectively.
fc and fm are frequency of carrier and message signal respectively.

4. Modulating Index:
A carrier wave, after being modulated, if the modulated level is calculated, then such an attempt is
called as Modulation Index or Modulation Depth. It states the level of modulation that a carrier wave
undergoes.
Rearranging the Eq. 1 as below:
s(t) = Ac [1 + (Am/Ac) cos (2πfmt)] cos (2πfct) s(t)
⇒ s(t )= Ac [1 + μ cos(2πfmt)] cos (2πfct) ………Eq. 2.
Where, μ is Modulation index and it is equal to the ratio of Am and Ac. Mathematically, we can write
it as: μ=Am/Ac.
Bandwidth of AM Wave:
It is the difference between the highest and lowest frequencies of the signal. Mathematically, we can
write it as: BW = fmax - fmin.
Consider the following equation of amplitude modulated wave:
s(t)=Ac [1 + μ cos (2πfmt)] cos (2πfct) s(t)
⇒ s(t) = Ac cos (2πfct) + Ac μ cos (2πfct) cos (2πfmt)
⇒ s(t) = Ac cos (2πfct) + Ac μ/2cos [2π (fc + fm) t] + Ac μ/2cos [2π(fc−fm) t]
Hence, the amplitude modulated wave has three frequencies. Those are carrier frequency fc, upper
sideband frequency (fc + fm) and lower sideband frequency (fc - fm).
BW = (fc + fm) − (fc - fm)
⇒BW=2fm
Power of AM Wave:
Consider the following equation of modulated wave:
s(t)=Ac cos (2πfct) + Ac μ/2cos [2π (fc + fm) t] + Ac μ/2 cos [2π (fc − fm) t]
Power of AM wave is equal to the sum of powers of carrier, upper sideband, and lower sideband
frequency components: Pt=Pc + PUSB + PLSB
We know that the standard formula for power of cos signal is: P=vrms
2
/R=(vm/√2)2
/2
Pc=(Ac/2√2)2
/R=AC
2
/2R
PUSB = (Ac μ/2√2)2
/R=Ac
2
μ2
/8R
PLSB = Ac
2
μ2
/8R.
Pt = AC
2
/2R+ Ac
2
μ2
/8R+ Ac
2
μ2
/8R=(Ac2
/2R) (1+μ2/4+μ2/4).
Pt = Pc (1+μ2/2)

5. Double Sideband Suppressed Carrier (DSBSC):
In the process of Amplitude Modulation, the modulated wave consists of the carrier wave and two
sidebands. The modulated wave has the information only in the sidebands. Sideband is nothing but a
band of frequencies, containing power, which are the lower and higher frequencies of the carrier
frequency. The transmission signals contain a carrier with two sidebands (known as Double Sideband
Full Carrier) as shown below:
Fig 6: Sidebands of Carrier Signal
However, such a transmission is inefficient. Because, two-thirds of the power is being wasted in the
carrier, which carries no information. If this carrier is suppressed and the saved power is distributed to
the two sidebands, then such a process is called as Double Sideband Suppressed Carrier system or
simply DSB-SC. It is plotted as shown in the following figure:
Fig 7: Suppressed Carrier Signal
Let the modulating signal be: m(t)=Am cos (2πfmt)
The Carrier Signal be: c(t) = Ac cos (2πfct)
Equation for DSB-SC modulated wave: s(t)=m(t)c(t)
⇒ s(t) = Am Ac cos (2πfmt) cos (2πfct)
Bandwidth of DSBSC Wave:
Bandwidth (BW): BW = fmax − fmin
Equation for DSB-SC modulated wave:
⇒ s(t) = Am Ac cos (2πfmt) cos (2πfct)
⇒ s(t) = Am Ac/2 cos [2π (fc + fm) t] + Am Ac/2cos [2π (fc−fm) t]

6. The DSBSC modulated wave has only two frequencies. So, the maximum and minimum frequencies
are (fc + fm) and (fc − fm) respectively.
fmax = (fc + fm) and fmin = (fc−fm)
BW = (fc + fm) − (fc−fm)
⇒ BW = 2fm.
Power of DSBSC Wave:
Equation for DSB-SC modulated wave:
s(t) = Am Ac/2cos [2π (fc + fm) t] + Am Ac/2cos [2π (fc−fm) t]
Power of DSBSC wave is equal to the sum of powers of upper sideband and lower sideband frequency
components.
Pt = PUSB + PLSB
P = vrms
2
/R=(vm√2)2
/R
PUSB = (Am Ac/2√2)2/R = Am
2
Ac
2
/8R
Similarly, we will get the lower sideband same power as that of upper sideband:
PLSB = Am
2
Ac
2
/8R
Now, let these two sideband powers are added in order to get the power of DSBSC wave:
Pt = Am
2
Ac
2
/8R+ Am
2
Ac
2
/8R
⇒ Pt = Am
2
Ac
2
/4R

7. Single Sideband Modulation (SSB):
The single-sideband modulation definition is a modulation which is used for transmitting information
like an audio signal through radio waves. This modulation is used in radio communications by using
transmitter power & more bandwidth efficiently for an alteration of AM (Amplitude Modulation).
There are many radio communication devices available in the market which use single sideband radio
like SSB Tx, SSB Rx, and SSB transceiver.
There are several variations are used for SSB modulation like lower sideband (LSB), upper sideband
(USB), double sideband (DSB), Single Sideband Suppressed Carrier (SSB SC), Vestigial Sideband
(VSB), and SSB reduced carrier.
Fig 8: Single Sideband Modulation (SSB)
Power of SSB Wave:
It is often necessary to define the output power of a single sideband transmitter or single sideband
transmission. Power measurement for an SSB signal is not as easy as it is for many other types of
transmission because the actual output power is dependent upon the level of the modulating signal. To
overcome this a measure known as the peak envelope power (PEP) is used. This takes the power of the
RF envelope of the transmission and uses the peak level of the signal at any instant and it includes any
components that may be present. Obviously, this includes the sideband being used, but it also includes
any residual carrier that may be transmitted. The level of the peak envelope power may be stated in
Watts, or figures quoted in dBW or dBm may be used. These are simply the power levels relative to 1
Watt or 1 milliwatt respectively.

8. Single Sideband Suppressed Carrier (SSBSC):
The DSBSC modulated signal has two sidebands. Since, the two sidebands carry the same information,
there is no need to transmit both sidebands. We can eliminate one sideband. The process of suppressing
one of the sidebands along with the carrier and transmitting a single sideband is called as Single
Sideband Suppressed Carrier system or simply SSBSC.
It is plotted as shown below:
Fig 9: Single Sideband Suppressed Carrier (SSBSC)
In the above figure, the carrier and the lower sideband are suppressed. Hence, the upper sideband is
used for transmission. Similarly, we can suppress the carrier and the upper sideband while transmitting
the lower sideband. This SSBSC system, which transmits a single sideband has high power, as the
power allotted for both the carrier and the other sideband is utilized in transmitting this Single
Sideband.
Let the modulating signal be: m(t) = Am cos (2πfmt)
The Carrier Signal be: c(t)=Ac cos (2πfct)
The equation for SSBSC is:
s(t) = Am Ac/2 cos [2π (fm + fm) t]; for the upper sideband
s(t) = Am Ac/2 cos [2π (f c− fm) t] s(t); for the lower sideband
Bandwidth of SSBSC Wave:
Since the SSBSC modulated wave contains only one sideband, its bandwidth is half of the bandwidth
of DSBSC modulated wave. i.e., Bandwidth of SSBSC modulated wave = 2fm/2 = fm
Therefore, the bandwidth of SSBSC modulated wave is fm and it is equal to the frequency of the
modulating signal.
Power of SSBSC Wave:
Let the SSBSC modulated wave be:
s(t) = Am Ac/2 cos [2π (fm + fm) t]; for the upper sideband
s(t) = Am Ac/2 cos [2π (f c− fm) t] s(t); for the lower sideband
Power of SSBSC wave is equal to the power of any one sideband frequency components.
Pt = PUSB = PLSB
The power of the upper sideband is: PUSB = (Am Ac/2√2)2
/R = Am
2
Ac
2
/8R
The power of the lower sideband is: PLSB = Am
2
Ac
2
/8R

9. Code for Output Waveforms of AM, DSBSC, SSB, SSBSC:
Amplitude Modulation (AM):
m = input(‘Modulation index = ‘);
t = linespace(0,0.2,1000);
Am = 5; % amplitude of message signal
fm = 10; % frequency of message signal
M = Am*cos(2*pi*fm*t); % message signal
figure;
subplot(4,1,1);
plot(t,M);
title(‘Message Signal’);
xlabel(‘time(t)’);
ylabel(‘Amplitude’);
%% Carrier Signal :
Ac = Am/m; % amplitude of carrier signal
fc = 20; % frequency of carrier signal
C = Ac*cos(2*pi*fc*t); % carrier signal
subplot(4,1,2);
plot(t, C);
title(‘Carrier Signal’);
xlabel(‘time(t)’);
ylabel(‘Amplitude’);
y = ammod(M, fc, 100, 0, Ac); % modulated signal
% ammod(M,fc,fs,INI_PHASE,CARRAMP)
subplot(4,1,3),plot(t, y);
title(‘Modulated Signal’);
xlabel(‘time(t)’);
ylabel(‘Amplitude’);
ylim([-20, 20]);

10. Double Sideband Suppressed Carrier (DSBSC):
function amplitude = dsbsc
fm = input(‘Enter the value of message signal frequency:’);
fc = input(‘Enter the value of carrier signal frequency: ‘);
Am = input(‘Enter the value of message signal amplitude:’);
Ac = input(‘Enter the value of carrier signal amplitude:’);
Tm = 1/fm;
Tc = 1/fc;
t1 = 0:Tm/999:6*Tm;
message_signal = Am*sin(2*pi*fm*t1);
subplot(3,1,1)
plot(t1, message_signal, ‘r’);
grid();
title(‘Message signal’);
carrier_signal = Ac*sin(2*pi*fc*t1);
subplot(3,1,2)
plot(t1, carrier_signal,’b’ );
grid();
title(‘Carrier Signal’);
amplitude = message_signal.*carrier_signal;
subplot(3,1,3)
plot(t1,amplitude,’g);
grid();
title(‘DSBSC’);
end

11. Single Sideband Modulation (SSB):
function SSBAM
td = input(‘n Enter the total Signal Durationnn ->’);
ts = input(‘n Enter the sampling time for this signal and it should be less than
1nn ->’);
fc = input(‘ n Enter the carrier frequency of the cosine wave nn ->’);
k = input(‘n Enter the constant diminishing factor nn->’ );
%fs = 1/ts ;
t = 0:ts:td;
t2 = int64( (t/ts) +1 );
m(t2) = input(‘ n Enter the msg signal as a function of time “t”; nn ->’);
w(t2) = hilbert(m(t2));
c = cos((2*pi*fc*t));
cp = sin((2*pi*fc*t));
s(t2) = (c.*(1+k*m(t2))+cp.*(1+k*w(t2)));
u(t2) = (1+k*m(t2)).*c;
subplot(2,1,1),plot(t,s(t2));
grid minor
title(‘Single SideBand Modulation’)
subplot(2,1,2),plot(t,u(t2));
title(‘DSB Signal’)
grid minor
d = input(‘ n IF FUNCTION OF FOURIER TRANSFORM IS NEEDED PRESS “1” nn ->’);
if d==1
syms t;
M = input(‘ n REENTER THE MESSAGE SIGNAL AS A FUNCTION OF TIME BUT FOR THE
INFINITE TIME PERIODnn ->’);
U = (1+k*M)*(1/2)*(cos(2*pi*fc*t) + abs(cos(2*pi*fc*t)));
FourierTransform = fourier(U)
end

12. Single Sideband Suppressed Carrier (SSBSC):
function am = ssbsc
Am = input(‘Enter the value of message signal Amplitude:’);
Ac = input(‘Enter the value of carrier signal Amplitude:’);
fm = input(‘Enter the value of message signal frequency:’);
fc = input(‘Enter the value of carrier signal frequency:’);
m = Am/Ac;
A = (m*Ac);
Tm = 1/fm;
Tc = 1/fc;
t = 0:Tm/999:6*Tm;
message_signal = Am*sin(2*pi*fm*t);
carrier_signal = Ac*sin(2*pi*fc*t);
x1 = cos(2*pi*fc*t).*cos(2*pi*fm*t);
x2 = sin(2*pi*fc*t).*sin(2*pi*fm*t);
x3 = x1+x2;
x4 = x1-x2;
SSBSC_lsb = A*(x3);
SSBSC_usb = A*(x4);
subplot(4,1,1)
plot(t, message_signal, ‘r’);
grid();
title(‘message signal’);
subplot(4,1,2)
plot(t, carrier_signal , ’g’);
grid();
title(‘Carrier signal’);
subplot(4,1,3)
plot(t, SSBSC_lsb,’b’);
grid();
title(‘LSB of SSBSC wave cutting off USB’);
subplot(4,1,4)
plot(t, SSBSC_usb, ‘r’);
grid();
title(‘USB of SSBSC wave cutting off LSB’);
end

13. Results:
The basic research work carried out in the field of communication lead to the development of new
modulation techniques, error performances analysis, having immunity to noise but the ever-increasing
demand of the faster communication system with large bandwidth requirements and transmitted power
has again generated a new requirement towards the development of newer techniques.
The comparison table for various parameters for AM, DSBSC, SSB, and SSBSC is shown below:
Parameters AM DSBSC SSB SSBSC
Variable
Characteristics
Amplitude Amplitude Amplitude Amplitude
Sideband
Suppression
No No
One Sideband
Completely
One Sideband
Completely
Carrier
Suppression
No Complete
Any One
Sideband
Complete
Modulating
Input
1 1 1 1
Bandwidth 2fm 2fm fm fm
Transmission
Efficiency
Low Moderate Maximum Maximum
Power High Medium Low Low
Complexity Simple Simple Complex Highly Complex
Performance
in presence of
noise
Low Average Average
Merits Easy detection
Low power
consumption,
simple
modulation
system
Bandwidth
efficiency,
reduction in
distortion
Low power
consumption,
Better frequency
use
Demerits
Poor reception
quality,
Complex
detection
Complex
detection
Complex
detection
Table 1: Comparison of various parameters of AM, DSBSC, SSB and SSBSC
Conclusion:
An analysis of the modulation techniques carried out in this article reveals that the selection of a analog
modulation technique is solely dependent on the type of application. This is because of the fact that
some of the technique provide lesser complexities in the design of the modulation and demodulation
system and prove to be economic. Single sideband modulation, (SSB) is the main modulation format
used for analogue voice transmission for two-way radio communication on the HF portion of the radio
spectrum. Its efficiency in terms of spectrum and power when compared to other modes means that for
many years it has been the most effective option to use. Now some forms of digital voice transmission
are being used, but it is unlikely that single sideband will be ousted for many years as the main format
used on these bands.

14. References:
1) Lathi, B.P., “Modern Digital and Analog Communication,” Oxford University Press, New York,
1998.
2) ANALOG AND DIGITAL COMMUNICATION LABORATORY by Prof Shaik Aqeel,
Electronics and Telecommunication Engineering, Sreyas Institute of Engineering and Technology,
February 24, 2021.
3) John G. Proakis and Masoud Salehi, “communication systems engineering”, 2nd Ed, prentice hall,
2001.
4) Chapter 5, Traditional Analog Modulation Techniques, Mikael Olofsson, 2002-2007.
5) K. Sharma, A. Mishra & Rajiv Saxena, „Analog & Digital Modulation Techniques: An overview‟,
international Journal of Computing Science and Communication Technologies, VOL. 3, NO. 1, July
2010.
6) Schwartz, M.: Information Transmission, Modulation and Noise, McGraw-Hill, New York, 1990.