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Dr. M. Venu Gopala Rao, Professor, Dept. of ECE

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KL University

Analog Communications Lab

Lab Based Projects

Prepared by

Dr. M. Venu Gopala Rao

Professor

Dept. of ECE


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List of Lab Based Projects

S. No Title of the Project Page No.

1. DSB-SC modulation using balanced modulators and synchronous

demodulation in the presence of noise. 4

2. DSB-SC modulation using balanced modulators and synchronous

demodulation with phase and frequency deviations (offset errors). 6

3. DSB-SC modulation using multipliers (mixers) and synchronous


4. DSB-SC modulation using multipliers (mixers) and synchronous


5. Amplitude Modulation (AM) using multipliers (mixers) and synchronous


6. Amplitude Modulation (AM) using multipliers (mixers) and synchronous


7. Amplitude Modulation (AM) using multipliers (mixers) and Envelope

Detection in the presence of noise. 16

8. Amplitude Modulation (AM) using multipliers (mixers) and square law

demodulation. 18

9. Amplitude Modulation (AM) using multipliers (mixers) and demodulation

using PLL. 20

10. Single Side Band (SSB) modulation using filtering method and synchronous


11. Single Side Band (SSB) modulation using filtering method and synchronous


12. Single Side Band (SSB) modulation by phase shift method and synchronous


13. Single Side Band (SSB) modulation by phase shift method and synchronous



3

14. Narrow Band Frequency Modulation (NBFM) and synchronous demodulation

in the presence of noise. 30

15. Narrow Band Frequency Modulation (NBFM) and envelope detection

in the presence of noise. 32

16. Frequency Modulation (FM) and demodulation using frequency

discriminator in the presence of noise. 34

17. Frequency Modulation (FM) and demodulation using frequency

demodulation using PLL in the presence of noise. 36

18. Phase Modulation (PM) and demodulation using frequency

discriminator in the presence of noise. 38

19. Frequency Modulation (FM) with pre-emphasized modulating signal

and demodulation with de-emphasis in the presence of noise. 40

20. Pulse Amplitude Modulation (PAM) and demodulation in the

presence of noise. 42

21. Noise Simulation and Reduction in Hamming Radio Systems 44

22. Multi-Carrier SSB Transceiver using Filtering Method and

Synchronous Detection 46

23. Multi-Carrier SSB Transceiver using Phasing Method and

Synchronous Detection. 49

24. Multi-Carrier SSB Transceiver using Weaver’s Method and

Synchronous Detection 53

25. Carrier Acquisition in DSB-SC using Costas Loop 57

References 59


4

DSB-SC Modulation Using Balanced Modulators and Synchronous

Demodulation in the Presence of Noise.

Project Goals: To

Explore the practical implementation of theoretical concepts like DSB-SC modulation

techniques those are studied in the class room.

Investigate the effect of channel noise in the demodulation and reception of DSB- SC

signals.

Exposure to simulation on modulation / demodulation systems for DSB-SC using

MATLAB for synthetic & real signals (such as speech).

A base band signal ( )m t is used to generate DSB-SC modulated signal ( ) ( ) ( )DSB SC t m t c t ,

where ( )c t is a carrier signal ( ) cosc cc t A t as shown in the Fig.1. The objective is to explore

the theoretical concepts of DSB-SC signal by modeling and simulation using Matlab and

Simulink.

Fig 1. Block diagram of DSB-SC modulation and demodulation system.

Task1: Consider a single tone modulating signal ( ) cos1000m t t , and carrier signal

4( ) cos10c t t .

1. Determine the expression for DSB-SC modulated signal in both time domain and

frequency domain.

2. Sketch the modulating signal ( )m t and its spectrum.

3. Sketch the carrier signal ( )c t and its spectrum.

4. Sketch the DSB-SC modulated signal ( )DSB SC t and its spectrum.

5. Identify the USB and LSB spectra.

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5

6. Determine the maximum and minimum amplitudes of the envelope.

7. Find the powers of USB, LSB, total sideband and modulated waves.

Task 2: Assume that the demodulation process is synchronous detection as shown in Fig.1. The

objective is to study the impact of channel noise in demodulation / reception of DSB-SC

wave. Now consider a single tone case.

1. Add the noise variance such that the signal to noise ratio (SNR) of noisy DSB-SC

modulated signal is 20 dB.

2. Use noisy upper side frequency band for demodulation purpose. If necessary use band

pass filter.

3. Sketch noisy DSB-SC modulated signal ( ) ( )DSB SC t n t and its spectrum.

4. Sketch the demodulated output ˆ ( )m t and its spectrum.

5. Find the output SNR and corresponding figure of merit.

6. Repeat the above steps for SNR = 10 dB, 30dB and 40dB and compare. Comment on the

results.

Task3: Repeat the above Tasks 1-2 for a multi tone modulating signal

( ) 2cos1000 sin1500m t t t + 1.5cos 2000 t .

Task4: Generate band limited signal for the frequency range 300 to 3400 Hz. Repeat the

above Tasks1-2 for this signal.

Task5: Repeat above Tasks1-2 for real speech signals.


6

DSB-SC Modulation using Balanced Modulators and Asynchronous

Demodulation

Project Goals: To



Investigate the phase and frequency deviations (offset errors) in the demodulation of

DSB- SC signals.

Exposure to simulation on modulation/demodulation systems for DSB-SC using


Fig 1. Block diagram of DSB-SC modulation and noise free demodulation system.




Simulink.

Task1: Consider a single tone modulating signal ( ) cos1000m t t , and carrier

signal 4( ) cos10c t t .


frequency domain.


3. Sketch the carrier wave ( )c t and its spectrum.


2


7




Task 2: Assume that the demodulation process is shown in Fig.1. The objective is to study the

effect of phase and frequency offset errors in demodulation of DSB-SC wave. Now

consider a single tone case.

1. The phase angle , denoting the phase difference between ( )c t and ( )m t at time t = 0, is

variable. Derive the expression for the demodulated wave and sketch for the following

values of o o o0 , 45 ,90 and o135 . Comment on the results.

2. Assume that the local oscillator frequency cf generated in the demodulation process is

not synchronized with the carrier frequency generated at transmitter. Let f is an offset

frequency deviated from the local oscillator and is variable. Derive the expression for

the demodulated wave and sketch for the following values of f = 50 Hz, 100 Hz, 300

Hz and 500 Hz. Comment on the results.


( ) 2cos1000 sin1500m t t t + 1.5cos 2000 t .





8

DSB-SC Modulation using Multipliers (Mixers) and Synchronous


Project Goals: To




signals.







Simulink.




frequency domain.






3


9



objective is to study the impact of channel noise in demodulation / reception of DSB-SC wave.

Now consider a single tone case.




pass filter.

3. Sketch the noisy DSB-SC modulated signal ( ) ( )DSB SC t n t and its spectrum.




results.

Task 3: Repeat the above Tasks1-2 for multi tone signal

( ) 2cos1000 sin1500 1.5cos2000m t t t t

Task4: Generate bandlimited signal for the frequency range 300 to 3400 Hz. Repeat the above

Tasks for this signal.

Task5: Repeat above tasks for real speech signals.


10

DSB-SC Modulation using Multipliers (mixers) and Asynchronous

Demodulation

Project Goals: To




DSB- SC signals.



Fig 1. Block diagram of DSB-SC modulation and noise free demodulation system.




Simulink.


4( ) cos10c t t .


frequency domain.



4


11






effect of phase and frequency offset errors in demodulation of DSB-SC wave. Now consider a

single tone case.






frequency deviated from the local oscillator and is variable. Derive the expression for

the demodulated wave and sketch for the following values of f = 50 Hz, 100 Hz, 300

Hz and 500 Hz. Comment on the results.


( ) 2cos1000 sin1500 1.5cos2000m t t t t





12

Amplitude Modulation using Multipliers (mixers) and Synchronous


Project Goals: To

Explore the practical implementation of theoretical concepts like Amplitude Modulation


Investigate the effect of channel noise in the demodulation and reception of Amplitude

Modulation signals.

Exposure to simulation on modulation/demodulation systems for Amplitude Modulation

using MATLAB for synthetic & real signals (such as speech).

A base band signal ( )m t is used to generate Amplitude Modulated signal

( ) [1 ( )] cos( )c cAMt A m t t , where ( )c t is a carrier signal ( ) cosc cc t A t as shown in

the Fig.1. The objective is to explore the theoretical concepts of AM signal by modeling and

simulation using Matlab and Simulink.

Fig 1. Block diagram of Amplitude Modulation and demodulation system.


4( ) cos10c t t .

1. Determine the expression for Amplitude Modulated signal in both time domain and

frequency domain.



4. Sketch the Amplitude Modulated signal ( )AM

t and its spectrum.

5. Identify the USB, LSB and carrier spectra.


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7. Find the powers of USB, LSB, total sideband, carrier and modulated signals.


objective is to study the impact of channel noise in demodulation / reception of

Amplitude Modulated wave. Now consider a single tone case.

1. Add the noise variance such that the signal to noise ratio (SNR) of noisy Amplitude

Modulated signal is 20 dB.


pass filter.

3. Sketch noisy Amplitude Modulated signal ( ) ( )AM

t n t and its spectrum.




results.


( ) 2cos1000 sin1500 1.5cos2000m t t t t





14

Amplitude Modulation using multipliers (mixers) and Asynchronous

Demodulation

Project Goals:

To explore the practical implementation of theoretical concepts like Amplitude

Modulation techniques those are studied in the class room.

To investigate the phase and frequency deviations (offset errors) in the demodulation of

DSB- SC signals.



Fig 1. Block diagram of AM modulation and noise free demodulation system.

A base band signal ( )m t is used to generate Amplitude Modulation modulated

signal ( ) [1 ( )] cos( )c cAMt A m t t , where ( )c t is a carrier signal ( ) cosc cc t A t as shown in





1. Determine the expression for AM modulated signal in both time domain and frequency

domain.



4. Sketch the AM modulated signal ( )AM

t and its spectrum.

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15



7. Find the powers of USB, LSB, total sideband, carrier and modulated waves.


effect of phase and frequency offset errors in demodulation of AM wave. Now consider a single

tone case.






frequency deviated from the local oscillator and is variable. Derive the expression for the

demodulated wave and sketch for the following values of f = 50 Hz, 100 Hz, 300 Hz

and 500 Hz. Comment on the results.


( ) 2cos1000 sin1500 1.5cos2000m t t t t





16

Amplitude Modulation (AM) using multipliers (mixers) and Envelope

Detection in the presence of noise.

Project Goals: To



Design an envelope detection for given modulating signal or speech signal

Investigate the effect of channel noise in the Envelope Detection and reception of

Amplitude Modulation signals.



A base band signal ( )m t is used to generate Amplitude Modulated signal

( ) [1 ( )] cos( )c cAMt A m t t , where ( )c t is a carrier signal ( ) cosc cc t A t as shown in



Fig 1. Block diagram of Amplitude Modulation and Envelope Detection system.


4( ) cos10c t t .


frequency domain.




t and its spectrum.



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Task 3: Assume that the demodulation process is envelope detection as shown in Fig.1. The

objectives are (a) to design an envelope detector, and (b) to study the impact of channel noise in

demodulation / reception of Amplitude Modulated wave. Now consider a single tone case.





3. Design an envelope detector for the given modulating signal




results.

Task 3: Repeat the above task3 for multi tone signal

( ) 2cos1000 sin1500 1.5cos2000m t t t t





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Amplitude Modulation (AM) using Multipliers (mixers) and Square Law

Demodulation

Project Goals: To




Modulation signals.









4( ) cos10c t t .


frequency domain.




t and its spectrum.



8


19


Task 2: Assume that the demodulation process is square law detector as shown in Fig.1. The

objective is to study the impact of channel noise in demodulation / reception of

Amplitude Modulated signal using PLL. Now consider a single tone case.









results.


( ) 2cos1000 sin1500 1.5cos2000m t t t t





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Amplitude Modulation using multipliers (mixers) and demodulation using

PLL.

Project Goals: To




Modulation signals.









4( ) cos10c t t .


frequency domain.




t and its spectrum.



9


21



objective is to study the impact of channel noise in demodulation / reception of Amplitude

Modulated signal using PLL. Now consider a single tone case.









results.


( ) 2cos1000 sin1500 1.5cos2000m t t t t





22

Single Side Band Modulation using Filtering Method and Synchronous


Project Goals: To

Explore the practical implementation of theoretical concepts like Single Side Band (SSB)


Investigate the effect of channel noise in the demodulation and reception of SSB

Modulation signals.

Exposure to simulation on modulation/demodulation systems for SSB using MATLAB

for synthetic & real signals (such as speech).

A base band signal ( )m t is used to generate SSB Modulated signal ( )SSB

t by generating

DSB-SC modulated signal and then band pass filtering either LSB or USB frequencies, as shown

in the Fig.1. The objective is to explore the theoretical concepts of SSB signal by modeling and


Fig 1. Block diagram of Amplitude Modulation and demodulation system.


4( ) cos10c t t .

1. Determine the expression for SSB Modulated signal in both time domain and

frequency domain.



3. Sketch the SSB Modulated signal (USB/(LSB) ( )SSB

t and their spectra.

4. Identify the USB / LSB) spectrum.


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6. Find the powers of USB, LSB and modulated signals.


objective is to study the impact of channel noise in demodulation / reception of SSB Modulated

signal. Now consider a single tone case.

1. Add the noise variance such that the signal to noise ratio (SNR) of noisy SSB modulated

signal is 20 dB.

2. Use noisy upper side frequency band and lower side frequency bands separately for

demodulation purpose. If necessary use band pass filter.

3. Sketch noisy SSB modulated signal ( ) ( )SSB





results.


( ) 2cos1000 sin1500 1.5cos2000m t t t t





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SSB Modulation using Filtering Method and Asynchronous demodulation

Project Goals: To




DSB- SC signals.




t by generating DSB-

SC modulated signal and then band pass filtering either LSB or USB frequencies, as shown in

the Fig.1. The objective is to explore the theoretical concepts of SSB signal by modeling and




4( ) cos10c t t .

1. Determine the expression for Single Side Band (SSB) modulated signal in both time

domain and frequency domain.





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5. Identify the USB / LSB spectrum.


7. Find the powers of USB / LSB modulated waves.


effect of phase and frequency offset errors in demodulation of SSB wave. Now consider a single

tone case.










( ) 2cos1000 sin1500m t t t + 1.5cos 2000 t .





26

SSB Modulation by phasing Method and Synchronous Demodulation in the

presence of Noise.

Project Goals:

To explore the practical implementation of theoretical concepts like Single Side Band

(SSB) Modulation techniques those are studied in the class room.

To investigate the effect of channel noise in the demodulation and reception of SSB

Modulation signals.

Exposure to simulation on modulation/demodulation systems for SSB using MATLAB



t by phase shift

method as shown in the Fig.1. The objective is to explore the theoretical concepts of SSB signal

by modeling and simulation using Matlab and Simulink.

Fig 1. Block diagram of SSB-AM and demodulation system.


4( ) cos10c t t .


frequency domain.





5. Identify the USB / LSB) spectrum.

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objective is to study the impact of channel noise in demodulation / reception of SSB Modulated

signal. Now consider a single tone case.


signal is 20 dB.








results.

Task 3: Repeat the above Task 1-2 for multi tone signal

( ) 2cos1000 sin1500 1.5cos2000m t t t t





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Single Side Band modulation by phase shift method and Asynchronous

demodulation

Project Goals:

To explore the practical implementation of theoretical concepts like Amplitude


To investigate the phase and frequency deviations (offset errors) in the demodulation of

DSB- SC signals.




t by generating DSB-

SC modulated signal and then band pass filtering either LSB or USB frequencies, as shown in

the Fig.1. The objective is to explore the theoretical concepts of SSB signal by modeling and


Fig 1. Block diagram of SSM modulation and noise free demodulation system.



1. Determine the expression for Single Side Band (SSB) modulated signal in both time

domain and frequency domain.



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7. Find the powers of USB / LSB modulated waves.

Task 3: Assume that the demodulation process is shown in Fig.1. The objective is to study

the effect of phase and frequency offset errors in demodulation of SSB wave. Now

consider a single tone case.









Task 3: Repeat the above Task 1-2 for multi tone signal

( ) 2cos1000 sin1500 1.5cos2000m t t t t





30

Narrow Band Frequency Modulation (NBFM) and Synchronous


Project Goals: To

Explore the practical implementation of theoretical concepts like Narrow Band

Frequency Modulation techniques those are studied in the class room.

Investigate the effect of channel noise in the demodulation and reception of Narrow Band

Frequency Modulation signals.

Exposure to simulation on modulation/demodulation systems for NBFM using MATLAB


A base band signal ( )m t is used to generate Narrow Band Frequency Modulated signal

( ) cos ( ) sinc c cNBFM t A t m t t as shown in the Fig.1. The objective is to explore the

theoretical concepts of NBFM signal by modeling and simulation using Matlab and Simulink.

Fig 1. Block diagram of Narrow Band Frequency Modulation and demodulation system.


4( ) 2cos10c t t .

1. Determine the expression for NBFM signal in both time domain and frequency domain by

considering 0.2 .



4. Sketch the Narrow Band Frequency Modulated signal ( )NBFM t and their spectra.

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5. Identify the USB and LSB spectrum.

6. Compare the results with that of a tone modulated AM signal.

7. Determine the envelop of modulated signal. What is the ratio of maximum to the

minimum value of this envelope? Plot this result versus , assuming that is restricted

to 0 0.3

8. Determine the average power of the NBFM signal, expressed as a percentage of the

average power of the unmodulated carrier wave. Plot this results versus assuming that

is restricted to the interval 0 0.3 .


objective is to study the impact of channel noise in demodulation / reception of Narrow

Band Frequency Modulated signal. Now consider a single tone case.

1. Add the noise variance such that the signal to noise ratio (SNR) of noisy NBFM signal is

20 dB.

2. Sketch noisy NBFM signal ( ) ( )NBFM t n t and its spectrum.




results.

Task 3: Repeat the above Tasks 1-2 for multi tone signal

( ) 2cos1000 sin1500 1.5cos2000m t t t t





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Narrow Band Frequency Modulation (NBFM) and Envelope Detection in the

Presence Of Noise.

Project Goals: To

Explore the practical implementation of theoretical concepts like Narrow Band

Frequency Modulation techniques those are studied in the class room.

Investigate the effect of channel noise in the demodulation and reception of Narrow Band

Frequency Modulation signals.

Exposure to simulation on modulation/demodulation systems for NBFM using MATLAB



( ) cos ( ) sinc c cNBFM t A t m t t as shown in the Fig.1. The objective is to explore the

theoretical concepts of NBFM signal by modeling and simulation using Matlab and Simulink.

Fig 1. Block diagram of Narrow Band Frequency Modulation and demodulation system.


4( ) 2cos10c t t .

1. Determine the expression for NBFM signal in both time domain and frequency domain by

considering 0.2 .



4. Sketch the Narrow Band Frequency Modulated signal ( )NBFM t and their spectra.

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5. Identify the USB and LSB spectrum.

6. Compare the results with that of a tone modulated AM signal.

7. Determine the envelop of modulated signal. What is the ratio of maximum to the

minimum value of this envelope? Plot this result versus , assuming that is restricted

to 0 0.3

8. Determine the average power of the NBFM signal, expressed as a percentage of the

average power of the unmodulated carrier wave. Plot this results versus assuming that

is restricted to the interval 0 0.3 .


objective is to study the impact of channel noise in demodulation / reception of Narrow Band

Frequency Modulated signal. Now consider a single tone case.

1. Add the noise variance such that the signal to noise ratio (SNR) of noisy NBFM signal is

20 dB.

2. Sketch noisy NBFM signal ( ) ( )NBFM t n t and its spectrum.




results.


( ) 2cos1000 sin1500 1.5cos2000m t t t t





34

Frequency Modulation and Demodulation using Frequency Discriminator in

the Presence of Noise.

Project Goals: To

Explore the practical implementation of theoretical concepts like Frequency Modulation


Investigate the effect of channel noise in the demodulation and reception of Frequency

Modulation signals.

Exposure to simulation on modulation/demodulation systems for FM using MATLAB for

synthetic & real signals (such as speech).


( ) cos 2 ( )t

c cFM ft A t K m d

as shown in the Fig.1. The objective is to explore

the theoretical concepts of FM signal by modeling and simulation using Matlab and Simulink.

Fig 1. Block diagram of Frequency Modulation and demodulation system.

Task1: Consider a single tone modulating signal ( ) 1.2cos500m t t , carrier signal

4( ) 2cos10c t t and frequency deviation is 1.2 KHz.

1. Determine the expression for FM signal in both time domain and frequency domain.



4. Sketch the Narrow Band Frequency Modulated signal ( )FM t and their spectra.

5. Identify the side frequencies from the spectrum.

6. Determine the approximate minimum bandwidth using Carson’s rule.

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7. Determine the minimum bandwidth from the Bessel function table.

8. Sketch the output frequency spectrum from the Bessel approximation.

9. If the modulating signal voltage is now increased to 2.4 Volts, what is the new deviation?

Find the modulation index in this case.

10. If the modulating signal voltage is increased to 4 Volts, while its frequency is decreased to

200 Hz, what is the new deviation? Find the modulation index in this case.

11. Determine the power of modulated signal in all the above cases.


objective is to study the impact of channel noise in demodulation / reception of Frequency

Modulated signal. Now consider a single tone case.

1. Add the noise variance such that the signal to noise ratio (SNR) of noisy FM signal is 20

dB.



3. Sketch noisy FM signal ( ) ( )FM t n t and its spectrum.




results.


( ) 2cos1000 sin1500 1.5cos2000m t t t t





36

Frequency Modulation (FM) and demodulation using frequency

demodulation using PLL in the presence of noise.

Project Goals:

To explore the practical implementation of theoretical concepts like Frequency


To investigate the effect of channel noise in the demodulation and reception of Frequency

Modulation signals.




( ) cos 2 ( )t

c cFM ft A t K m d

as shown in the Fig.1. The objective is to explore

the theoretical concepts of FM signal by modeling and simulation using Matlab and Simulink.




1. Determine the expression for FM signal in both time domain and frequency domain.



4. Sketch the Frequency Modulated signal ( )FM t and their spectra.

5. Identify the side band frequencies and their amplitudes from the spectrum.


17


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Task 2: Assume that the demodulation process using PLL as shown in Fig.1. The objective is to

study the impact of channel noise in demodulation / reception of Frequency Modulated signal.


1. Add the noise variance such that the signal to noise ratio (SNR) of noisy FM signal is 20

dB.

2. Sketch noisy FM signal ( ) ( )FM t n t and its spectrum.




results.

Task3: Repeat the above Tasks 1-2 for multi tone signal

( ) 2cos1000 sin1500 1.5cos2000m t t t t





38

Phase Modulation (PM) and Demodulation using Frequency Discriminator

in the Presence of Noise.

Project Goals: To

Explore the practical implementation of theoretical concepts like Phase Modulation


Investigate the effect of channel noise in the demodulation and reception of Phase

Modulation signals.



A base band signal ( )m t is used to generate Narrow Band Phase Modulated signal

( ) cos ( )c cPM Pt A t K m t as shown in the Fig.1. The objective is to explore the theoretical

concepts of PM signal by modeling and simulation using Matlab and Simulink.




1. Determine the expression for PM signal in both time domain and frequency domain.



4. Sketch the Narrow Band Frequency Modulated signal ( )PM t and their spectra.

5. Identify the side frequencies from the spectrum.


18


39









objective is to study the impact of channel noise in demodulation / reception of Phase


1. Add the noise variance such that the signal to noise ratio (SNR) of noisy PM signal is 20

dB.

2. Sketch noisy PM signal ( ) ( )PM t n t and its spectrum.




results.


( ) 2cos1000 sin1500 1.5cos2000m t t t t





40

Frequency Modulation with Pre-emphasized Modulating Signal and

Demodulation with De-emphasis in the Presence of Noise

Project Goals: To

Explore the practical implementation of theoretical concepts like Frequency Modulation

techniques with pre-emphasized modulating signal those are studied in the class room.

Investigate the effect of channel noise in the demodulation with de-emphasis and

reception of Frequency Modulation signals.

Exposure to simulation on modulation / demodulation systems for FM using MATLAB


A carrier signal cosc cA t is used to generate Frequency Modulation. The modulating signal

( )m t is pre-emphasized before modulation and denoted as ( )pm t as shown in the Fig.1. The

resultant Frequency Modulated signal is defined as

( ) cos 2 ( )t

c c pFM ft A t K m d

.

The objective is to explore the theoretical concepts of Frequency Modulation (FM) with pre-

emphasized modulating signal and demodulation with de-emphasis in the presence of noise by

modeling and simulation using Matlab and Simulink.

Fig 1. Block diagram of Frequency Modulation and demodulation system including pre-emphasis and de-

emphasis.

Task1: Given a direct FM frequency modulator (VCO) with a deviation sensitivity

1 1kHz/VK , a PLL FM demodulator with a transfer function 1V/kHzdK , and the following

input signals:

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1 kHz at 4

2 kHz at 2

3 kHz at 1

p

p

p

V

V

V

(a) Determine the frequency deviation at the output of the VCO for the three input signals and

the demodulated voltages at the output of the PLL demodulator and sketch the frequency

spectrum at the output of the demodulator.

(b) For the following internally generated noise signals, determine the signal-to-noise ratios at

the output of the demodulator.

1 kHz at 0.1

2 kHz at 0.25

3 kHz at 0.5

p

p

p

V

V

V

(c) Determine the frequency spectrum at the output of the pre-emphasis network, the frequency

deviation at the output of the modulator, the demodulator output voltages, the frequency

spectrum at the output of the PLL demodulator and at the output of the de-emphasis

network, and the signal to noise ratios at the output of the PLL demodulator and the de-

emphasis circuit.


above Task1 for this signal.

Task3: Repeat above Task1 for real speech signals.

Reference: Electronic Communications Systems, Fundamentals through advanced, by Wayne

Tomasi, 5th edition, Page 270, Pearson education, 2011.


42

Pulse Amplitude Modulation (PAM) and Demodulation in the Presence of

Noise.

Project Goals: To

Explore the practical implementation of theoretical concepts like Pulse Amplitude


Investigate the effect of channel noise in the demodulation and reception of Pulse

Amplitude Modulation signals.

Exposure to simulation on modulation/demodulation systems for PAM using MATLAB


A base band signal ( )m t is used to generate Pulse Amplitude Modulation (PAM) signal as

shown in the Fig.1. The objective is to explore the theoretical concepts of PAM signal by

modeling and simulation using Matlab and Simulink.

Fig 1. Block diagram of :ulse Amplitude Modulation and demodulation system.

Task1: A base band signal ( ) cos2000m t t is natural sampled with a square signal with

sampling frequency of 10000 Hz and 50 % duty cycle.

1. Determine the expression for PAM signal in both time domain and frequency domain.


3. Sketch the pulse carrier signal ( )p t and its spectrum.

4. Sketch the PAM signal ( )PAM t and their spectra.

5. Compare the envelopes of PAM signal with that of the sampling signal.

6. How many samples are taken of each cycle of the message signal?

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7. A resemblance between the PAM and message signal is defined as the ratio of / msf f ,

where sf is the sampling frequency and mf is the modulating signal. The lower the ratio,

the less the resemblance. Determine the resemblance in this case.

8. Decrease the sampling rate from 10 KHz to (i) 5 KHz, (ii) 2 KHz, and (iii) 1.2 KHz. Now

determine whether the message signal is recognizable in the PAM signal as the sampling

frequency is decreased. Observe the demodulated out for each case and comment on

results. I which case will occur?

Task2: Assume that the demodulation process is used a Low Pass Filter as shown in Fig.1. The

objective is to study the impact of channel noise in demodulation / reception of PAM signal.


1. Add the noise variance such that the signal to noise ratio (SNR) of noisy PAM signal is 20

dB.

2. Sketch noisy PAM signal ( ) ( )PAM t n t and its spectrum.




results.

6. Justify the statement that PAM signals have little resistance to noise.


( ) 2cos2000 sin 2500m t t t cos3000 t





44

Noise Simulation and Reduction in Hamming Radio Systems

Project Goals:

To explore the practical implementation of theoretical concepts like SSB-AM techniques

those are studied in the class room.

To investigate the effect of channel noise in the demodulation and reception of SSB

Amplitude Modulation systems.

To recover weak or low SNR signals.

Exposure to simulation on modulation/demodulation systems for SSB-AM using

MATLAB / Labview for synthetic & real signals (such as speech).

Fig 1. Block diagram of SSB-AM and demodulation system.


4( ) cos10c t t .


frequency domain.



4. Sketch the SSB Modulated signal (USB/LSB) ( )SSB





21


45

Task 2: Assume that the demodulation process is synchronous detection as shown in Fig.1.

The objective is to study the impact of channel noise in demodulation / reception of SSB



signal is 20 dB.





Task3: Design a low pass filter with cutoff frequency equivalent to message signal bandwidth

and draw its spectrum.




results.

Task4: Design a filter using Boll Spectral Subtraction technique with cutoff frequency

equivalent to message signal bandwidth and draw its spectrum.

Repeat the steps in Task3 for this filter.

Task5: Design a Wiener filter with cutoff frequency equivalent to message signal bandwidth and

draw its spectrum.

Repeat the steps in Task3 for this filter.


( ) 2cos2000 sin 2500m t t t cos3000 t





46

Multi-Carrier SSB Transceiver using Filtering Method and Synchronous

Detection

Project Goals: To

Explore the practical implementation of theoretical concepts like SSB-AM techniques


Generate Multi-Carrier SSB-AM system using filtering method.

Implement Synchronous Detection of SSB waves.

Investigate the effect of channel noise in the demodulation and reception of SSB-AM

systems.



In this team project you will be implementing the SSB modulator using filtering method as part

of a multicarrier transmission scheme. Coherent demodulation will be implemented for a single

carrier that lies between two adjacent carriers. Test message signals consisting of bandlimited

noise will be used to check crosstalk levels. Recorded speech waveforms will be used to provide

a final test of the complete system after it has been turned in. A block diagram of the complete

multicarrier single sideband system (SSB) is shown in Fig1.

Fig 1. Multicarrier SSB transmission system top level block diagram

22


47

Task1: Generate two types of message signals as given below:

1. Create transmitter message signals from bandlimited white noise with the following

Matlab code:

% % Design 9th order Bandpass noise noise shaping filter with 3 dB % % cutoffs at 300 and 3400 Hz relative to a 8000 Hz sampling rats. % [bn,an] = butter(9,2*[300 3400]/8000); % % Create zero mean NOISE VECTORS

N = 5000; % No. of samples (modify as needed) m1 = randn(1,N); m2 = randn(1,N); m3 = randn(1,N);

% Filter the noise vectors m1 = filter(bn,an,m1); m2 = filter(bn,an,m2); m3 = filter(bn,an,m3);

%-----------------------------------------------------------------------

2. Read the speech signal % Speech signal m1 = audioread('OSR_uk_000_0050_8k.wav',[1 N]);m1 = m1'; m2 = audioread('OSR_us_000_0018_8k.wav',[1 N]);m2 = m2'; m3 = audioread('OSR_us_000_0030_8k.wav',[1 N]);m3 = m3';

m = m1 + m2 + m3; %-----------------------------------------------------------------------

3. Draw the message signals generated as above, their spectrum and their power density

spectrum.

Task2: Generation of SSB-AM system using filtering method

1. Generate USB(SSB-AM) system using filtering method for modulating signal m1, with

carrier frequency fc1= 20 KHz and fs= 96000 sam/sec

2. Plot the modulated SSB, its spectrum and its power density spectrum (psd).

3. Similarly, repeat the above steps for message signals m2, m3 and m = m1+m2+m3 and

carrier frequencies fc2= 24 KHz and fc3= 28 KHz.

Task3: Implement a coherent SSB demodulator.

Test your modulator using just a single SSB carrier at 20kHz(turn off the other carriers in SSB

transceiver by letting m = m1), plot the PSD of the recovered message signal. Assume again that

band limited noise is used for the input message.


48

Task4: In this task all three carriers will be turned on. Choose any 4 kHz spacing you wish for

the carriers so long as they fit within the channel bandwidth. Band limited noise messages

sources will again be employed for testing.

1. Obtain a composite signal spectrum plot for your specific modulator bank

implementation.

2. Moving to the demodulator output measure the signal-to-interference ratio (SIR) in dB

via superposition of demodulated output signals. Set the demodulator to recover the

center carrier (this should be carrier number 2). With just the center carrier being

transmitted, i.e. set m = m2, find the power in the demodulator output as Psig =

var(m_rec) where m_rec is reconstructed signal. Next find the interference power by

setting the transmiiter output to be m = m1+ m3 and find the interference power to be

Pinterfere = var(m_rec).

Now form the ratio

3. Measure the SIR on one of the outside signals, e.g., fc1 or fc3 to see if there is less

iterference present than when surrounded by two signals.

4. Comment on your SIR measurement results.

Task5: Repeat the Task3, except now you are free to move the carrier frequencies to allow guard

bands. Note that the channel band pass filter must be left intact, that is you may not change it.

Comment on any observed performance improvements obtained by including guard bands

between the carriers.

Task6: Repeat the above Tasks2-5 for speech signals Listen to this demodulated signal using

the PC sound system.

1. Listen carefully for any interference heard in the background of the desired message

signal. You may want to listen to all three speech files so that you know what they are

supposed to sound like. Comment on what you hear.

2. Calculate the SIR for demodulation of the center signal using the superposition

technique of Task 4(2).


49

Multi-Carrier SSB Transceiver using Phasing Method and Synchronous

Detection

Project Goals: To



Generate Multi-Carrier SSB-AM system using phasing method.



systems.



In this team project you will be implementing the SSB modulator using phasing method as part

of a multicarrier transmission scheme. Coherent demodulation will be implemented for a single



23


50



multicarrier single sideband system (SSB) is shown in Fig1.


2. Create transmitter message signals from bandlimited white noise with the following

Matlab code:




%-----------------------------------------------------------------------

2. Read the speech signal % Speech signal m1 = audioread('OSR_uk_000_0050_8k.wav',[1 N]);m1 = m1'; m2 = audioread('OSR_us_000_0018_8k.wav',[1 N]);m2 = m2'; m3 = audioread('OSR_us_000_0030_8k.wav',[1 N]);m3 = m3';

m = m1 + m2 + m3; %-----------------------------------------------------------------------

4. Draw the message signals generated as above, their spectrum and their power density

spectrum.

Task2: Generation of SSB-AM system using phasing method

4. Generate USB(SSB-AM) system using phasing method for modulating signal m1, with







51

Test your modulator using just a single SSB carrier at 20kHz(turn off the other carriers in SSB

transceiver by letting m = m1), plot the PSD of the recovered message signal. Assume again that

band limited noise is used for the input message.


the carriers so long as they fit within the channel bandwidth. Band limited noise messages

sources will again be employed for testing.

5. Obtain a composite signal spectrum plot for your specific modulator bank

implementation.








Now form the ratio





bands. Note that the channel band pass filter must be left intact, that is you may not change it.

Comment on any observed performance improvements obtained by including guard bands

between the carriers.

Task6: Repeat the above Tasks2-5 for speech signals Listen to this demodulated signal using



52




4. Calculate the SIR for demodulation of the center signal using the superposition

technique of Task 4(2).


53

SSB Transceiver using Weaver’s Method and Synchronous

Detection

Project Goals: To



Generate Multi-Carrier SSB-AM system using Weaver method.



systems.



In this team project you will be implementing the Weaver SSB modulator as part of a

multicarrier transmission scheme. Coherent demodulation will be implemented for a single




multicarrier single sideband system (SSB) is shown in Fig1. The block diagram of SSB

modulation using Weaver’s method and synchronous demodulator is Illustrated in Fig 2.


(a) Create transmitter message signals from bandlimited white noise with the following

Matlab code:



24


54


%-----------------------------------------------------------------------

(b) Read the speech signal % Speech signal m1 = audioread('OSR_uk_000_0050_8k.wav',[1 N]);m1 = m1'; m2 = audioread('OSR_us_000_0018_8k.wav',[1 N]);m2 = m2'; m3 = audioread('OSR_us_000_0030_8k.wav',[1 N]);m3 = m3';

m = m1 + m2 + m3; %-----------------------------------------------------------------------

Draw the message signals generated as above, their spectrum and their power density spectrum.


Fig 2. Block diagram of SSB-AM (Weaver’s method) and Synchronous demodulation system.


55

Task2: Generation of SSB-AM system using Weaver method

1. Generate USB(SSB-AM) system using Weaver method for modulating signal m1, with






Test your modulator using just a single SSB carrier at 20kHz(turn off the other carriers

in SSB transceiver by letting m = m1), plot the PSD of the recovered message signal.

Assume again that band limited noise is used for the input message.


the carriers so long as they fit within the channel bandwidth. Band limited noise

messages sources will again be employed for testing.

1. Obtain a composite signal spectrum plot for your specific modulator bank implementa-

tion.








a. Now form the ratio

1.





56


bands. Note that the channel band pass filter must be left intact, that is you may not

change it. Comment on any observed performance improvements obtained by including

guard bands between the carriers.

Task6: Repeat the above Tasks 2-5 for speech signals, listen to this demodulated signal using





2. Calculate the SIR for demodulation of the center signal using the superposition technique

of Task 4(2).


57

Carrier Acquisition in DSB-SC using Costas Loop

Project Goals: To


and demodulation techniques those are studied in the class room.

Generate DSB-SC modulation using Multiplier modulation.

Acquisition the carrier using Costas loop in demodulation process

Performing synchronous demodulation using the carrier acquired using Costas loop.


signals using Coastas loop.


MATLAB/ Labview for synthetic & real signals (such as speech).





Simulink.


4( ) cos10c t t .


frequency domain.



25


58





Task 2: Use the Costas loop for DSB-SC demodulation as shown in Fig.1. This Costas loop

acquire the carrier signal using PLL and recover the message signal using synchronous detection

technique as shown in Fig1. Further investigate the impact of channel noise in demodulation /

reception of DSB-SC wave. Now consider a single tone case.




pass filter.

3. Sketch the noisy DSB-SC modulated signal ( ) ( )DSB SC t n t and its spectrum.




results.


( ) 2cos1000 sin1500 1.5cos2000m t t t t





59

References

1. B.P. Lathi and Zhi Ding, “Modern Digital and Analog Communication Systems”,

International 4th Edition, Oxford University Press, 2010.

2. H Taub & D.L Schilling, Gautam Saha, ”Principles of Communication Systems, TMH,

2007, 3rd Edition.

3. J. G. Proakis and M. Selehi, Contemporary Communication systems using Matlab,

Vikas Publishing House, Bookware company series.

4. Leon W. Couch, II, ‘Digital and Analog Communication Systems’, Seventh edition,

Pearson Prentice Hall, 2009.

5. Michael Fitz, ‘Fundamentals of Communications Systems’, Tata McGraw-Hill Education, 2008.

6. K. C. Ravindra Nathan, Communication systems modeling and simulation using Matlab

and Simulink, University Press (India) private limited, Hyderabad.

7. www.mathswork.com

8. Labview.

http://www.amazon.com/s/ref=dp_byline_sr_book_1?ie=UTF8&field-author=Michael+Fitz&search-alias=books&text=Michael+Fitz&sort=relevancerank

https://books.google.co.in/url?id=bbA7-SYUoc8C&pg=PR2&q=http://www.tatamcgrawhill.com&clientid=ca-print-tata_mcgraw_hill&linkid=1&usg=AFQjCNGaTLIV67KSKuULeSEnq9j9hzHoLw&source=gbs_pub_info_r

http://www.mathswork.com/

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