KJSCE/TE/ETRX/VSEM/2010-11
K. J. Somaiya College of Engineering, Mumbai-77
Lab Manual: TE ETRX (Semester V)
Instructions to the student
 Every student is expected to bring printout of write-up of his experiment to
be performed at the time of practical/tutorial session as per the time table
 The student must take counter signature of the concerned faculty on the
same day during lab session for the verification of outcomes of the
experiments
 The journal will content A4 size papers unless it is notified for particular
subject
 The students can use separate blank A4 size papers if necessary while
writing journal
 Cover page of every experiment should be in standard format as attached
along with lab manual
 The contents of the journal will be as per the format given
 Students are expected to follow the instructions given by concerned faculty
from time to time
KJSCE/TE/ETRX/VSEM/2010-11
K. J. Somaiya College of Engineering, Mumbai – 77
CONTENTS
Sr.
No.
Name of the Experiment
Page
No.
Date of
performance
Date of
Submission /
Correction
Remarks
This to certify that Bro. /Sis. _______________________________ ______________ Roll No.
______________Exam.No._______________Class____________________
Batch
No.__________
has
completed
the
specified
term
work
Div._________
in
subject
of
____________________________________in satisfactory manner inside the college of
Engineering as laid by the University of Mumbai during the academic year Jul. / Jan.20___ to
Nov./Apr.20___
Overall Grade: Grade: AA / AB / BB / BC / CC
Staff member In-charge
Head of the Department
Principal
KJSCE/TE/ETRX/VSEM/2010-11
Roll No._______________
Class: ________Branch:____________ Div: ________Batch_____
Subject: ___________________________Experiment No._______
Name of the Experiment: __________________________________
Date of performance: _____________________________________
Date of Submission / correction: ____________________________
Grade: AA / AB / BB / BC / CC
Signature of the Staff In-charge with date
KJSCE/TE/ETRX/VSEM/2010-11
K.J. Somaiya College of Engineering, Vidyavihar,
Mumbai-77.
Department of Electronics Engineering
Sub: Digital communication & coding techniques,
Sem. : V (Electronics),
Term: July – Nov 2010
List of Experiments
1) To generate and study Digital Modulation techniques by
Amplitude shift keying.
2) To generate and study Digital Modulation techniques by
Frequency shift keying.
3) To generate and study Digital Modulation techniques by Phase
shift keying.
4) To generate and study Digital Modulation techniques by
Quadrature Phase shift keying.
5) Write C-Program for Hamming code.
6) Study of systematic and non-systematic cyclic codes using
MATLAB.
7) To generate and study ISI and Eye pattern using MATLAB.
8) Study of Direct sequence spread spectrum modulation &
demodulation.
9) BER calculation for digital communication system.
KJSCE/TE/ETRX/VSEM/2010-11
EXPERIMENT NO -TITLE: Amplitude shift keying
Aim:
Design and implementation of Digital Modulation Technique-Amplitude
Shift Keying (ASK).
Purpose:



To understand the working of ASK.
To design and implement ASK.
To visualize the ASK output and make appropriate conclusions.
Theory:
The simplest way of achieving ASK is by switching ON the carrier
whenever data bit is ‘1’ and switching OFF whenever data bit is ‘0’.The ASK
waveform is generated by a balanced modulator circuit i.e Linear multiplier. One
of the inputs is AC coupled carrier wave and other input is information signal to
be transmitted, is DC coupled.
The methods to demodulate ASK waveform is to rectify it, pass it through
the filter and square up the resulting waveform. The output is the original data
stream.
Block
diagram:
KJSCE/TE/ETRX/VSEM/2010-11
Procedure:
1) Assemble the circuit as shown in hardware setup.
a) Using trainer kit.
b) Using breadboard.
2) Apply modulating signal: NRZ output and carrier
signal (1.44Mhz).
3) Observe the ASK output at pin TP28 inST2106 trainer kit.
4) Connect circuit as per connection diagram using connectors.
5) See the effect on the ASK modulator output by varying the bits in NRZ
data.
6) Observe the Demodulated Raw NRZ data wave at the Detector output.
7) Apply different signal word in the data generator and observe recovered
signal.
KJSCE/TE/ETRX/VSEM/2010-11
Observation:
Observe the waveforms and replicate it on the graph paper.
Roll No:
CONCLUSION:
Signature of faculty in-charge with date
1. Why ASK is known as on-off keying?
2. State the basic parameters to design a digital communication system.
KJSCE/TE/ETRX/VSEM/2010-11
EXPERIMENT NO –
TITLE:
Frequency Shift Keying
Aim:
Design and implementation of Digital Modulation Technique-Frequency
Shift Keying (FSK).
Purpose:



To understand the working of FSK.
To design and implement FSK.
To visualize the FSK output and make appropriate conclusions.
Method:

Principle of FSK
In FSK system two logic levels (1 and 0) of the data are represented
By two carrier signals which are of different frequencies.
The mathematical representation of FSK is
VFSK(t)=2P cos( t) (When logic data =1)
Theory:
In frequency shift keying the carrier frequency is shifted in steps i.e. from
One frequency to another, corresponding to modulating signal. If higher
frequency is used to represent data ‘1’,lower frequency is used to represent
Data ‘0’.On a closer look at the FSK waveform it can be that it can be
represented as the sum of two ASK waveform.
Functional blocks required in order to generate the FSK signal is shown
in the fig. The two carriers have different frequencies and the digital data is
inverted in one case.The demodulation of FSK waveform can be carried out by
phase locked loop. The phase locked loop tries to ‘lock’ the input frequency.
It achieves this by generating corresponding output voltage to be fed to the
voltage controlled oscillator, if any frequency deviation at its input is
encountered. Thus the PLL detector follows the frequency changes and
generates proportional output voltage.
The output voltage from PLL contains the carrier component. Therefore
thesignal is passed through a low pass filter to remove them. The resulting
signal is too rounded to be used for digital data processing. Also, the
amplitude level may be very low due to channel attenuation.
Since the amplitude change in FSK waveform does not matter this
modulation technique is very reliable even in noisy and fading channels.
However, the required bandwidth increases depending on the two carrier
frequencies. The bandwidth required is at least doubled than that in ASK
Modulation. This means lesser no. of communication channels for a given
band of frequencies.
KJSCE/TE/ETRX/VSEM/2010-11
Block
diagram:
Procedure:
Logically, sum of two ASK waveform is a FSK wave.
In order to generate the ASK wave the following procedure is followed:
1) Apply modulating signals as NRZ output and its inverted version, also
apply carrier signal1 (1.44Mhz) & carrier signal 2(960Khz to the modulators
2) The output of the modulator1 & modulator2 is given as input to the
summing amplifier input (TP34 & TP35).
KJSCE/TE/ETRX/VSEM/2010-11
3) Observe the ASK output1 & output 2 at pin TP28 inST2106 trainer kit.
Connect circuit as per connection diagram using connectors.
4) See the effect on the FSK modulator output by varying the bits in NRZ
data.
5) Observe the Demodulated Raw NRZ data wave at the Detector output.
6) Apply different signal word in the data generator and observe recovered
signal.
Observation:
Observe the waveforms and replicate it on the graph paper.
Roll No:
Signature of faculty in-charge with date
CONCLUSION:
1. Differentiate coherent and non-coherent systems.
2.What are applications of FSK ?
KJSCE/TE/ETRX/VSEM/2010-11
EXPERIMENT NO -TITLE: Binary Phase Shift Keying
Aim:
To Study the phase Shift Keying Modulation & Demodulation.
Apparatus: PSK Modulation Kit, PSK demodulation Kit, CRO, Connecting probes.
Theory:
The PSK involves the phase change of the carrier sine wave between
00 to 1800 in accordance with the data steam to be transmitted. The
Phase Shift Keying can also be known as Phase Reversal Keying
(PRK).The functionality of the PSK modulator is very similar to the ASK
modulator. Both use the balanced modulator to multiply the carrier with
modulating signal. But in contrast to ASK, the digital signal applied as
modulating signal to PSK is bipolar. When the modulating I/P is positive
then O/P of the modulator is the sine wave which is in phase with the
carrier where as for the negative voltage levels the O/P of the modulator is
out of phase with the carrier I/P .
The unipolar to bipolar data converter converts the data bit stream
to bipolar stream. At the receiver the Square loop detector circuit is used
to demodulate the transmitted PSK signal.
The PLL block locks to the
frequency of the signal square O/P and produces a clean square wave
O/P of the same Frequency. To derive the square wave O/P of the same
frequency as the incoming PSK signal, the PLL‘s O/P is divided by two in
frequency domain using the divided by two circuit.
From the differential bit decoder O/P is a data ‘1’ when it
encounters a level changes and a ‘0’ when no change occurs. Thus the
O/P from differential bit decoder is NRZ (L) wave.
KJSCE/TE/ETRX/VSEM/2010-11
Block diagram:
Procedure:
i. Carrier input (TP26 & TP17).
ii. The NRZ output (TP6) to (TP20)
iii. Unipolar converter output (TP21) to MOD1 input (TP27).
iv. The modulated PSK output is available on pin (TP28).
KJSCE/TE/ETRX/VSEM/2010-11
v. MOD1 output (TP28) to PSK demodulator (TP10).
vi. PSK demodulator (TP15) to LPF (TP23).
vii. LPF (TP24) to comparator (TP46).
viii. Comparator (TP47) to decoder (TP39).
ix. Decoder (TP40) to PCM-NRZ data (TP1).
Observation:
Roll No:
Observe the waveforms and replicate it on the graph paper.
Signature of faculty in-charge with date
Conclusion:
1. Why PSK is preferred over ASK & FSK?
2. What modulation scheme is used for high speed telephone modem and
Why?
KJSCE/TE/ETRX/VSEM/2010-11
EXPERIMENT NO -TITLE: QPSK MODULATION AND DEMODULATION
AIM:
To study QPSK modulation and demodulation.
APPARATUS: QPSK trainer kit (ST2106), CRO, Connecting probes etc.
THEORY:
We have to modulate the analog signal either in freq, phase and
amplitude in accordance with the digital data. In QPSK each pair of
consecutive data bit is treated as a two-bit code, which is used to switch
the phase of carrier sine wave between one of four phases 90 degree
apart. The four possible combinations of the dibit code are 00, 01, 10
and 11. Each code represents either phase of 45, 135, 225 and 315
degrees lagging to relative to the phase of the unmodulated carrier. The
choice of these phases is arbitrary as it is convenient to produce them.
QPSK offers advantages over PSK, that each phase represents a two bit
so we can transmit the same amount of data with half of the phase
changes required to PSK systems. So there can be reduction in the
bandwidth. The four phases are produced by adding two carrier waves
of the same freq. but 90 degree out of phase. The 0 degree phase
carrier is called In phase carrier and labeled as I. The other is 90 degree
phase carrier and is termed as Quadrature carrier and is labeled as Q.
The I carrier is controlled by the MSB of the dibit code. When the MSB is
level ‘0’ then the phase is 0 degrees when the MSB become level ‘1’
then phase reverses to 180 degree. The Q carrier starts with 90 degree
out of phase wrt I carrier. This carrier is controlled by LSB of dibit code
when LSB is level ‘0’ the phase is 90 degree w.r.t. I carrier. When the
LSB goes to level ‘1’ the phase reverses to 270 degree as shown.
Assume that dibit code be 00 will give no phase change to any carrier
so they will be in quadrature
Similarly the phase shifts for the possible combinations would be as foll:
NRZ (L) Dibit code
Phase
00
45
01
315
10
135
11
225
At any instant of time, there is always a+/- 90° phase difference between
the two modulation o/ps. As a result the amplitude of resultant phasor will
always be √2 times if they are equal. The creation of 4 phases by vector
addition is as shown.
It can be appreciated from the above phasor diag that each switches its
phase depending on the data level in the same way as PSK modulation
does.The only difference is that QPSK is the sum of two PSK modulators.
KJSCE/TE/ETRX/VSEM/2010-11
Each modulator performs phase shift keying on its respective carrier input
in Accordance with respect data i/p such that
A. The o/p of the modulator 1 is a PSK sig with phase shift of 0° and 180°
respectively, relative to the I carrier.
B. The o/p of the modulator 2 is PSK signal with phase shift of 90° & 270°
respectively, relative to the I carrier.
The o/p of the two modulator is summed up by a summing amplifier.
As it is clear from the earlier phasor diagram, the phase of summing
amplifier’s o/p signal relative to I carrier at any instant of time takes 1 of
the 4 phases 45°,135°,225°&315° depending on the applied dibit code.
When these dibit codes alter, the phase of the QPSK output
changes by 0°,90°,180°&270° from its previous phase positions. Thus the
o/p of the summing amplifier is a QPSK waveform. The demodulation of
QPSK signal is performed by the 4th power loop detector. The
demodulator is quite similar to the one used in PSK system.
The incoming QPSK sig is first squared in the signal squarer 1.The
function of the signal squarer has already been discussed in the PSK
modulator section. The output of this is a signal at twice the original
frequency with the phase changes reduced to 0° & 180°. This is because
all the phase changes are also doubled. The 0° &180° becomes as 0° &
360° because the phase changes are also doubled. The output of the
signal squarer 1 is fed to signal squarer 2 which is exactly similar to the
signal squarer 1, so the output of this circuit is a sine wave of frequency at
four times the frequency of the original QPSK carrier signal with no phase
changes. The output of signal squarer 2 is fed to the PLL which locks the
incoming signal & produces a code.
NRZ (L) Code
Phase
Phase Change
00
45
No change
01
315
90
10
135
180
11
225
270
At the receiver, once again there are four possibilities the two o/ps
may be interchanged or inverted as mentioned above. To derive NRZ (L)
waveform the encoded pair a DIFFERENTIAL dibit Decoder is used at
receiver. Its o/p is serially transmitted.
KJSCE/TE/ETRX/VSEM/2010-11
Block diagram & Phasor diagram:
PROCEDURE:
1) Differentially encoded dibit MSB(TP10) to unipolar bipolar converter 1
input (TP20)
2) Unipolar – bipolar converter 1 output (TP21) to modulator 1 input
(TP27)
3) Differentially encoded dibit LSB (TP11) to unipolar – bipolar 2 input
(TP23)
KJSCE/TE/ETRX/VSEM/2010-11
4) Unipolar – bipolar converter 2 output (TP24) to modulator 2 input
(TP30)
5) 960 Khz (I) output (TP17) to modulator 1 carrier input(TP26)
6) 960 Khz (Q) output (TP18) to modulate 2 carrier input (TP29)
7) Modulator 1 output(TP28) to summing amplifiers input A (TP34)
8) Modulator 2 output (Tp31) to summing amplifiers input B (TP35)
9) Summing amplifiers output (TP36) to QPSK demodulator input (TP1)
10) QPSK demodulator output I (TP8) to low pass filter 1 input (TP23)
11) QPSK demodulator Q output (TP9) to low pass filter 2 input (TP23)
12) Low pass filter 1 output (TP24) to comparator 1 input (TP46)
13) Low pass filter 2 output (TP28) to comparator 2 input (TP49)
14) Data squaring circuit comparator 1 output (TP47) to differential
decoder MSB input (TP42)
15) Data squaring circuit comparator 2 output (TP50) to differential decoder
LSB input (TP43).
Observation:
Roll No:
Observe the waveforms and replicate it on the graph paper.
Signature of faculty in-charge with date
CONCLUSION:
1. What is the importance of in-phase and quadrature carriers in QPSK
systems?
2. Define Eucledian distance and state its significance.
KJSCE/TE/ETRX/VSEM/2010-11
EXPERIMENT NO -TITLE: Write ‘C Program for Hamming Codes
AIM:
Algorithm:
1] To generate 11 bit Hamming Code using 7 bit message bit.
2] To detect 1 bit error and correct it.
Generation:
1) Start
2) Take the 7 bit message bit (input)
3) Generate the 4 bit (parity) bits by using the message bit [Even
Parity]
a] R0= D2+D4+D6+D8+D10
b] R1= D2+D5+D6+D9+D10
c] R2= D4+D5+D6
d] R3= D8+D9+D10
4) Place this 4 bit in the position of power of 2
ie: R0 at 2 = 1st
R1 at 2 = 2nd
R2 at 2 = 4th
R3 at 2 = 8th
5) Hence the 11 bit Hamming Code is generated.
ie: D10 D9 D8 R3 D6 D5 D4 R2 D2 R1 R0
Correction:
6) Input the received 11 bit Hamming code
7) Check for the Parity bits. ie: R0, R1, R2, R3 [Even Parity]
ie: R0= R0+D2+D4+D6+D8+D10
R1= R1+D2+D5+D6+D9+D10
R2= R2+D4+D5+D6
R3= R3+D8+D9+D10
8) Calculate the position of error bit by the formula;
h= 8 x R5 + 4 x R2 + 2 x R2 + 1 x R0
9) Invert the bit at the hth position
10) Display the corrected 11 bit Hamming Code
11) Stop.
KJSCE/TE/ETRX/VSEM/2010-11
Calculation:
1)Enter the 7 bit message bits: 1 1 1 1 __ 1 1 __ 1 __ __
Even Parity
D10 D9 D8 D7 R3 D5 D4 R2 D2 R1 R0
R0: D2+D4+D6+D8+D10 :
1+1+1+1+1
: R0 = 1
R1: D2+D5+D6+D9+D10 :
1+1+1+1+1
: R1 = 1
R2: D4+D5+D6
:
1+1+1
: R2 = 1
R3: D8+D9+D10
:
1+1+1
: R3 = 1
2):. Generated 11 bits Hamming Code is :
1 1 1 1 1 1 1 1 1 1 1
3)Enter the received code:
D10 D9 D8 D7 R3 D5 D4 R2 D2 R1 R0
Even Parity:
1 0 1 1 1 1 1 1 1 1 1
R0= R0+D2+D4+D6+D8+D10: 1+1+1+1+1+1
: R0 = 0
R1= R1+D2+D5+D6+D9+D10: 1+1+1+1+0+1
: R1 = 1
R2= R2+D4+D5+D6
: 1+1+1+1
: R2 = 0
R3= R3+D8+D9+D10
: 1+1+0+1
: R3 = 1
:. h = 8 x R3 + 4 x R2 + 2 x R1 + 1 x R0
=8x1+4x0+2x1+1x0
= 10
:. Error is at position 10 from R.H.S
ie: D9 = 0 should be 1
:. Corrected Hamming Code: 1 1 1 1 1 1 1 1 1 1 1
SIMULATION: Attach the C simulation results of the same.
Roll No:
Signature of faculty in-charge with date
CONCLUSION:
1. Classify the source coding techniques into character oriented and bit
oriented protocol. Among this which one is effective technique for data
compression and why?
KJSCE/TE/ETRX/VSEM/2010-11
2. Can parity be used to correct errors? Explain your answer.
KJSCE/TE/ETRX/VSEM/2010-11
START
INPUT THE
SEVEN
MESSAGE BITS
CALCULATE THE FOUC PARITY BITS BY THE
APPROPRIATE FORMULA
DISPLAY THE
ELEVEN BIT
HAMMING
CODE
INPUT THE
RECIVED 11 BIT
HAMMING
CODE
CALCULATE THE
POSITION OF
ERROR BIT
INVERT THE
BIT AT ERROR
POSITION
STORE THE
NEW BIT AT
THE ERROR
POSITION
DISPLAY THE
CORRECTED 11 BIT
HAMMING CODE
STOP
KJSCE/TE/ETRX/VSEM/2010-11
EXPERIMENT NO -TITLE: Cyclic Codes.
Aim:
To study systematic and non-systematic cyclic codes.
Purpose:
To study cyclic codes for various data bits.
Method 1:
Systematic Cyclic Codes:
● In today’s era of digital communication, various types of codes are
used.
The use of these codes has various advantages.
● Performance v/s Eb / No
 The curve represents a typical modulation scheme one without
coding
and the other with coding.
 In systematic cyclic coding, the code is calculated as:
C(x)=x^(n-k)d(x) + m(x)
where d(x)= data polynomial
m(x)= system polynomial
[data: parity] or [parity: data]
Algorithm:


●


●
●
Method 2:
Non-Systematic Cyclic Codes:
Start the program.
Enter the total length of required code.
Input the message bits as d(x)
Compute the codeword C(x)=x^(n-k)d(x) + m(x)
Compute G(x)= generator polynomial
Display generator and output.
Stop.
● In today’s era of digital communication, various types of codes are
used. The use of these codes has various advantages.
KJSCE/TE/ETRX/VSEM/2010-11
 Performance v/s Eb/No
 The curve represents a typical modulation scheme one without coding
and the other with coding.
● It also gives facility for error correction.
 In non-systematic cyclic coding, the code is calculated as:
C(x)=D(x) + G(x)
where D(x)= Data polynomial
G(x)= Generator polynomial
Algorithm:
 Start the program.
 Enter the total length of required code.
● Input the message bits as d(x)
 Compute G(x)= generator polynomial by inhibit function.
 Compute the codeword C(x)= D(x) + G(x).
● Display the code.
● Stop.
MATLAB SIMULATION: Attach the Matlab simulation results of the same.
Roll No:
Signature of faculty in-charge with date
Conclusion:
1. Note down the metrics of software techniques used in digital comm.
System.(C ,C++ ,Matlab).
KJSCE/TE/ETRX/VSEM/2010-11
EXPERIMENT NO -TITLE: EYE DIAGRAM USING MATLAB
Generation & study of eye diagram using MATLAB Software.
(1) Eye diagram for sinusoid.
(2) Eye diagram for QPSK
AIM:
APPARATUS:
THEORY:
Simulation using MATLAB toolbox.
An eye diagram is a simple and convenient tool for studying the
effects of intersymbol interference and other channel impairments
in digital transmission. When this blockset constructs an eye diagram,
it plots the received signal against time on a fixed-interval axis.
At the end of the fixed interval, it wraps around to the beginning of
the time axis. Thus the diagram consists of many overlapping curves.
One way to use an eye diagram is to look for the place where the
"eye" is most widely opened, and use that point as the decision
point when demapping a demodulated signal to recover a digital
message. The Discrete-Time Eye Diagram Scope block produces eye
diagrams. This block processes discrete-time signals. And periodically
draws a line to indicate a decision, according to a mask parameter.
1] Eye diagram for Sinusoid
The following model produces a scatter plot and an eye diagram from
a complex sinusoidal signal. Because the decision time interval is
almost, but not exactly, an integer multiple of the period of the sinusoid,
the eye diagram exhibits drift over time. More specifically, successive
traces in the eye diagram and successive points in the scatter diagram are
near each other but do not overlap.
To build the model, gather and configure these blocks:
 Sine Wave, in the Signal Processing Blockset DSP Sources library
Set frequency to .502.
Set Output complexity to Complex.
Set Sample time to 1/16.

Discrete-Time Scatter Plot Scope, in the Comm. Sinks library : The
Discrete-Time Scatter Plot Scope block displays scatter plots of a
modulated signal, to reveal the modulation characteristics, such as pulse
shaping or channel distortions of the signal.
KJSCE/TE/ETRX/VSEM/2010-11
-
On the Plotting Properties panel, set Samples per symbol
to 16.
On the Figure Properties panel, set Scope position to
Figposition([2.5 55 35 35]);.

Discrete-Time Eye Diagram Scope, in the Comm Sinks library
:The Discrete Eye Diagram Scope block displays multiple
traces of a modulated signal to produce an eye diagram. You
can use the block to reveal the modulation characteristics of the
signal, such as pulse shaping or channel distortions.
On the Plotting Properties panel, set Samples per symbol to 16.
-
On the Figure Properties panel, set Scope position to
figposition([42.5 55 35 35]);.
2] Eyediagram for Modulated Signal
This multipart example creates an eye diagram, scatter plot, and signal trajector
plot for a modulated signal. It examines the plots one by one in these sections:
 Eye Diagram of a Modulated Signal
 Scatter Plot of a Modulated Signal
 Signal Trajectory of a Modulated Signal
Eye Diagram of a Modulated Signal
The following model modulates a random signal using QPSK, filters
the signal with a raised cosine filter, and creates an eye diagram from
the filtered signal.
To build the model, gather and configure the following blocks:
 Random Integer Generator, in the Data Sources sublibrary of the
Comm Sources library
The Random Integer Generator block generates uniformly
distributed random integers in the range [0, M-1], where M
is the M-ary number defined in the dialog box.
- Set M-ary number to 4.
- Set Sample time to to 0.01.
 QPSK Modulator Baseband, in PM in the Digital Baseband sub
library of the Modulation library of the Communications Blockset,
with default parameters: The QPSK Modulator Baseband block
modulates using the quaternary phase shift keying method. The
output is a baseband representation of the modulated signal.
 AWGN Channel, in the Channels library of the Communications
Block set, with the following changes to the default parameter
settings: The AWGN Channel block adds white Gaussian noise to a
real or complex input signal. When the input signal is real, this block
adds real Gaussian noise and produces a real output signal.
- Set Mode to Signal-to-noise ratio (SNR).
KJSCE/TE/ETRX/VSEM/2010-11
- Set SNR (dB) to 15.
 Raised Cosine Transmit Filter, in the Comm. Filters library
- Set Filter type to Normal.
- Set Group delay to 3.
- Set Roll off factor to 0.5.
- Set Input sampling mode to Sample-based.
- Set Up sampling factor to 8.
MATLAB SIMULATION: Attach the Matlab simulation results of the same.
Roll No:
Signature of faculty in-charge with date
CONCLUSION:
1. What information can be obtained from an eye-diagram?
KJSCE/TE/ETRX/VSEM/2010-11
EXPERIMENT NO -TITLE: Study of Direct sequence spread spectrum modulation &
demodulation.
AIM:
Study of Direct sequence spread spectrum modulation &
demodulation.
APPARATUS: COM 1012& COM101 TRAINER KIT.
THEORY:
Direct Sequence (DS) Spread Spectrum
A direct sequence spread spectrum signal is one in which the amplitude of an
already modulated signal is amplitude modulated by a very high NRZ binary
stream of digits. Thus, if the original signal is s (t) where
S (t) = (2 Ps) d (t) cos wot
The DS spread spectrum is
V (t) =g (t) s (t) = (2 Ps) g (t) d (t) cos wot
Where g (t) is pseudo random noise PN binary sequence having values ±1
Here we merely assume that g (t) is a binary sequence as is the data d
(t). The sequence g (t) is generated in a deterministic manner and is repetitive.
However the sequence length before repetition is usually extremely long and to
all intents and purposes, and without serious errors , we can assume that the
sequence is truly random, i.e. there is no correlation at all between the values of
a particular bit and the value of any other bits.
Furthermore the bit rate is usually much greater than the bit rate fb of d (t). As a
matter of fact the rate is usually so much greater than fb, we say that
g (t) chops the bits of data into chips , and we call the rate of g(t) the chip rate fc
retaining words , bit rate to represent fb .
To see that multiplying the BPSK sequence s(t) by g(t) spreads the spectrum
we refer to sequence g(t) and the product sequence g(t) d(t). Note that the edges
are aligned that is each transition in d(t) coincides with a transition on g(t). The
product sequence would be another random sequence g (t) having same chip
rate fc as g(t). Since the bandwidth of BPSK signal s (t) is nominally 2fb the
bandwidth of the BPSK spread spectrum signal v (t) is 2fc and the spectrum has
KJSCE/TE/ETRX/VSEM/2010-11
been spread by the ratio fc fb. Since the power transmitted by s (t) and v (t) is the
same, that is Ps, the power spectral density Gs (f) is reduced by the factor fb/ fc.
To recover the DS spread spectrum signal, the receiver shown first multiples the
incoming signal with the waveform g (t) and then by the carrier
2 cos wot. The resulting waveform is then integrated for the bit duration and the
output of integrator is sampled, yielding the data d (kTb). We note that at the
receiver it is necessary to regenerate both the sinusoidal carrier frequency Wo
and also to regenerate the PN waveform g (t).
Procedure:
Procedure for CDMA-DSSS 2131 DSSS Spreading (Modulation):
1. Detect COM 1012 and COM 1011 modules via RS232C serial port/LAN using
COM block s/w provided.
2. For spreading, user needs data to be spread and PN sequence in Modulator. For
the generation of pseudo random codes from DSSS modulator, user has to
provide resistors with HEX values only.
3. For this use registers from Reg 0 to REG 12.
4. Let the other register from REG 13 to REG 17 =00 HEX
5. Register 18 Setting for Spreading.
Procedure for CDMA-DSSS 2131 Despreading (Demodulation):
1. Detect COM 1012 and COM 1011 modules via RS232C serial port/LAN using
COM block s/w provided
2. Users needs input data to be despread in Demodulator. For the generation of
pseudorandom codes for DSSS, user has to provide registers with hex values
only.
3. For this use registers from REG 0 to REG 12.
Observation:
Roll No:
CONCLUSION:
Observe the waveforms and replicate it on the graph paper.
Signature of faculty in-charge with date
KJSCE/TE/ETRX/VSEM/2010-11
1. Why do Spread spectrum techniques increase the privacy of
communication?
2. Why is it preferable for all CDMA signals using a given frequency to have
orthogonal PN codes?
3. How do Spread spectrum signals reduce the effect of multipath fading?
4. What is orthogonality of signals?
5. What is chip rate?
KJSCE/TE/ETRX/VSEM/2010-11
EXPERIMENT NO -TITLE: BER calculation.
AIM: Bit error rate calculation for digital communication systems.
APPARATUS:
COM 1012& COM101 TRAINER KIT.
THEORY:
Bit error rate calculation:
The quality of transmission is decided by parameter, signal-to-noise
ratio (SNR) in analog and by bit error rate (BER) in digital. In digital
communication we can employ different coding techniques to improve
BER and compression techniques to reduce the required bit rate which in
turn reduces bandwidth.
Procedure:
Test Point
TP1
TP2
TP3
TP4
TP5
TP6
TP7
Roll No:
Description:
Synchronization
Cycle slips
Bit error
Start of PRBS-11 Periodic test sequence detected with less than
10 bit errors.
Received data string(After QPSK ambiguity removal if needed)
Local data stream replica(To be compared with received data
stream on TP5)
Reset command was received to re-initialize the cumulative
BER counters
Signature of faculty in-charge with date
CONCLUSION:
1. Explain the difference between terms—Bit rate and Baud rate.
KJSCE/TE/ETRX/VSEM/2010-11
2.Distinguish symbol error rate and bit error rate.