How Chaotic Direct Sequence can be used for secured communication.

1. 12/4/2016
Guided by
Dr. Saugata Sinha
Department of Electronics Engineering
VNIT, Nagpur
Visvesvaraya National Institute Of Technology, Nagpur
Presentation on
A Chaotic Direct-Sequence Spread-
Spectrum Communication System
Presented By:
LOKESH GAHANE (MT15CMN007)
MOHIT CHIMANKAR (MT15CMN008)
ARUNJITH SAHADEVAN (MT15CMN004)
MOHIT GARADE (MT15CMN009)
1

2. • Introduction
• Chaotic System
• Spread Spectrum
• Spread Spectrum Techniques
• Chaotic Sequences
• CSK Modulation
• Advantages
• Carrier Regeneration Detectors
• Code Clock Extraction Detectors
• Conclusion
• References
Contents
12/4/2016 2

3. • The introduction of chaos into communication
systems offers several opportunities for
improvement.
• What is spread spectrum?
• What is DSSS?
• What are Discrete Time Dynamical System?
Introduction
12/4/2016 3

4. • is a deterministic system
• random-like behaviour
• Hence can disguise the modulation as noise.
• Can produce large number of such signals
which can be reconstructed.
12/4/2016 4
Chaotic Systems

5. • It is a technique in which the frequency of the
transmitted signal is deliberately varied, this
results in a much greater bandwidth than the
signal would have had if its frequencies
weren’t varied.
12/4/2016 5
What is spread spectrum?

6. 1. Constant frequency signal is subject to
catastrophic interference
2. Easy to intercept.
• These vulnerabilities are overcome by
spread spectrum technique.
12/4/2016 6
Problems with conventional wireless
communication.

7. • Hence the frequency of the transmitted signal
is deliberately varied.
• Varied according to a specific but complicated
mathematical function.
• Only source and receiver know the frequency
variation. Hence can’t be intercepted.
12/4/2016 7
Spread Spectrum

8. • Direct Sequence Spread Spectrum.
• Message signal is used to modulate a bit
sequence known as the Pseudo Noise(PN)
code.
• Smaller the chip duration, the larger the
bandwidth and more immune the resultant
signal is to interference.
What is DSSS?
12/4/2016 8

9. • This paper is only concerned with discrete-
time dynamical systems.
• It is defined by the state equation
• Starting with an initial condition xo, repeated
applications of the map f give rise to the
sequence of points {x; k =0, 1, 2, ...} called an
orbit of the discrete-time system.
12/4/2016 9
Discrete-time Dynamical system

10. • Example
where, 1 < r <4, and r is called the bifurcation
parameter
Depending on ‘r’ it can exhibit periodicity or chaos.
• For 3.57.. . < r 5 4, the sequence is, for all
practical purposes, non-periodic and non-
converging.
12/4/2016 10
Continued..

11. SPREAD SPECTRUM TECHNIQUES
• Frequency Hopping Spread Spectrum(FH-SS)
-The message is transmitted in seemingly random part of the
pre-assigned band width.
-This can be visualized as the transmitted signal hopping in
frequency domain.
• Direct Sequence Spread Spectrum(DS-SS)
-The message is directly spread in to larger band-width.
-It will be difficult for a narrow band jammer to interfere
destructively with the signal because the signal power is
spread across the larger band-width and jamming a wide band
is not practical in terms of power.
12/4/2016 11

12. Cont’d
12/4/2016 12

13. Characteristic of ideal code that can be
used for DS-SS
• Zero or near zero cross-correlation and impulse like Auto-
correlation
• The codes need to be wide band to spread the signal energy over a
wide section of the spectrum
• The codes need to be easy to generate
The examples of spreading codes are
• Pseudo Noise codes
• Walsh Sequence
• Gold codes
• M-sequences
These codes belongs to the binary category so that it can take only two
Values +1&-1.ie the degree of freedom is very less.
12/4/2016 13

14. chaotic sequences
• High degree of freedom.
• The future state of the process have to be deterministic if the initial
condition is exactly known.
• The future state of the process have to be un-predictable if the initial
condition is not known.
Example : Lorenz Attractor
• The initial condition of the equation change by small number ,the
oscillation trajectory will be completely different.
12/4/2016 14

15. Cont’d
12/4/2016 15

16. Existing method of Generating chaotic
sequence for BPSK DS-SS System
• Assign different initial condition to the users
• Start the chaotic map and repeatedly generate points on the
orbit.
• Let N be the length of the spreading sequence needed for each
bit of information . So every consecutive N points generated
by the chaotic map can be taken to be a signature sequence for
a bit of information.
• Each bit gets a different sequence of chips.
Disadvantage
• Occurrence of periodicities in the generated sequence.
-cross-correlation never be zero over there , so it will deviate
from the characteristics of ideal code.
12/4/2016 16

17. CSK Modulation
• A message symbol must have a code sequence nearly
orthogonal to those of the other symbols.
• This can be accomplished by assigning different Bifurcation
parameters to each symbol.
• Once the symbol is decided, one code sequence will be
associated with it. The last chip of that sequence will be in the
initial point of the next.
• So error in detection of one symbol leads to incorrect
generation of all the code sequence that follows.
12/4/2016 17

18. Scheme proposed for the generator
12/4/2016 18

19. Cont’d
12/4/2016 19

20. Advantages
Its advantages are :
I. Chaotic Sequences are easy to generate and
store.
II. Provide Secure Communication as;
a) The transmitted signal look like noise.
b) The sequences are no longer binary.
c) A Receiver who may know its parameters
and functions involved, it is still difficult for
him to estimate it.
12/4/2016 20

21. The generation of chaotic sequences can
easily be made as complicated as desired.
For example, multi-dimensional chaotic maps
may be used instead of the one-dimensional.
Or doing cascading of several chaotic systems.
 Incorporation of the chaotic sequences into
the DS/SS system has dramatically enhanced
the LPI (low probability of intercept)
performance of these systems.
12/4/2016 21

22. • It reduces the PSD of the Transmitted Signal.
• Difficult to intercept because of Spectral
Spreading.
• However Binary DS/SS does not provide much
protection against two particular interception
methods :
I. Carrier Regeneration Detectors.
II. Code Clock Regeneration Detectors.
12/4/2016 22

23. Carrier Regeneration Detectors :
• It is used for the detection of Signals which
suppress the carriers like DS/SS systems with
BPSK, QPSK, SQPSK etc.
• It consists of squaring the received signal in
order to wipe out the modulation.
• Using the resultant double frequency term to
detect the BPSK signal and Quadrupled
frequency for QPSK and SQPSK.
12/4/2016 23

24. Block diagram of carrier regenerating detector for
Binary BPSK DS/SS
12/4/2016 24

25. Block diagram of carrier regenerating detector
for Binary QPSK DS/SS
12/4/2016 25

26. Code Clock Extraction Detector
• Rc = 1/Tc = Chip rate
• Tc = Chip duration
12/4/2016 26

27. It is technique used for extraction of chip rate
called “Delay and Mix”
Delay the spreading sequence and multiply
with undelayed sequence
This method is effective on Binary DS/SS
Chaotic DS/SS is resistant to this method of
detection
12/4/2016 27

28. CONCLUSION
Chaotic sequence for spectral spreading in
DS/SS system has several advantage over
conventional method
Same error performance
Enormous number of different sequences
Generation and regeneration of chaotic
sequences is simple
Code sequences are easily made independent
12/4/2016 28

29. Chaotic DS/SS is inherently difficult to
intercept conventional dispreading procedure
Offers increased LPI
Provides more security
12/4/2016 29

30. Reference
 G. Heidari-Bateni, C.D. McGillem, “A Novel Multiple-Address Digital
Communication System Using Chaotic Signals,” Proceedings of
International Conference on Communications, Chicago, IL, June 15-
18,1992.
 T.S. Parker and L.O. Chua, “Chaos: A Tutorial for Engineers,” Proc.
IEEE, Special h u e on Chaotic System, August 1987.
 G. Heidari-Bateni, “Chaotic Signals for Digital Communication,”
Ph.D. Dissertation, School of Electrical Engineering, Purdue
University, W. Lafayette, IN, Dec. 1992.
 D.J. Torrieri, Principles of Secure Communication Systems, Artech
House, Inc., 1985.
 D.E. Reed, “Comparison of S ymbol-Rate Detector and Radiometer
Intercept Receiver Performances in a Nonstationary Environment,”
Proceedings of 1989 IEEEMilitary Communications Conference, vol.
1, Boston, Massachusetts, October 1989, pp. 19.5.1-19.5.5.12/4/2016 30