Statement of Research
Topic: Chaos-Based Secure Communication
THANG MANH HOANG
A. Overview
Over the last few decades, communication systems have been developed rapidly to
meet the increasing human needs. Those are not only in the variety of services, but also
in quality of services. Hence, the conventional fundamentals of communication
techniques have been faced with strict challenges such as the increase in transmission
rate and in privacy. For a band wide requirement, optical systems offer a transmission
about terabits per seconds in the distance of hundreds of kilometers, and wireless
systems can support the services required the rate of hundreds megabits per second. It
can be regarded that the most of available services can be run reliably. However, such
transmission rates have not reached natural ones yet, and will be exhausted by some
future services such as multimedia and others. Moreover, conventional modulation
techniques are mostly based on periodic signals. As a result, the system security can not
be deployed on the physical layer due that periodic signals are easily detected by
eavesdroppers. For that reason, mathematic algorithms such as RAS, DES and so on
are developed to maintain the systems secure. With the hope of improving bit rate as
well as security, applications of nonlinear dynamics in communication have received
much interest and become an active area of research.
Recent years, researchers working on the nonlinear field have developed some novel
modulation methods [1]-[5] which utilize non-periodic signals. More specifically, a group
of logical bits can be represented by a piece of a non-periodic signal or by a sequence of
real values which are generated by dynamical systems [6]. The advantage offering by
such methods is that non-periodic signals are produced easily by some nonlinear
circuits. In addition, security of communication systems [7] can be assured if
highly-dimensional chaotic systems as well as appropriate modulation schemes are
employed.
My research concentrates on (i) investigation on synchronous regimes of dynamical
systems which present potential applications in communications, (ii) application of
synchronization of chaotic systems in communications including chaotic modulation
techniques and security, and (iii) implement chaotic communication systems on VLSI.
B. Background
Since Pecora and Caroll introduced the model of synchronization of dynamical
systems [8], there has been several synchronization models proposed and pursued
[9]-[13]. Roughly speaking, one chaotic system (plays a role of master) sends a driving
signal to other system(s) (plays a role of slave(s)) to establish the synchronous regime.
As a result, their chaotic trajectories remain in step with each other during temporal
evolution. In practical, models of synchronization of dynamical systems has been
utilized in many fields, i.e. lasers [14][15], biological [16][17], control [18], etc. Recently,
one of applications of synchronization has been investigated actively is in
communications [6][19][20]. More specifically, synchronization of chaotic systems is
applied to design chaotic secure communication systems and to propose new
transmission methods.
For the application of synchronization of dynamical systems in transmission, there
are several models proposed to modulate the information signal on chaotic signal, i.e.
multiplicative [1] and parametric [2][3] modulations, additive masking [2], chaos shift
keying (CSK) [4], synchronization-manifold shift keying [5]. For a short period of
development, chaotic communications has shown a potential alternative for
conventional one. However, one of disadvantages of chaotic communication is the
robustness. A chaotic signal is easy to be distorted by noise when it is sent via a noise
channel. As a result, BER of proposed models is slightly low in compared with that of
conventional ones. Recently, some new improvement in BER has been reported [21]
with orthogonal-CSK. For the security application of synchronization of dynamical
systems, there are many models proposed [22] in different ways but they has been
broken thereafter. Anyway, a secure system must be based on existing modulation
methods, and some schemes are used to hide the information in chaotic signals. So far,
there are two categories of methods used to unmask message signal in chaotic secure
communication systems, i.e. characteristic-based [23]-[26] and identification-based
[27][28]. Characteristic-based methods are analyzed different features of transmitted
signals to extract message signal without knowing the detail of chaotic system at the
transmitter. In contrast to Characteristic-based methods, identification-based ones
require knowing the structure of chaotic dynamics of master system at the transmitter.
Full detail about structure of master can be found by some reconstruct methods by
observing transmitted signals. Therefore, security of chaotic communication is
considered by two main points in a secure communication system. First of all, chaotic
system playing as master at the transmitter should exhibit complex dynamics (high
dimension).
Typically,
one
of
choices
is
delay
systems
which
create
very
highly-dimensional dynamics [29]. For second point, it is that the transmitter should
produce and send a complex signal. Complexly transmitted signal sent on the channel
make eavesdroppers difficult in reconstructing processes. In practical, observer-based
synchronization schemes [30] allow to produce complex signals for modulation process.
In conclusion, chaos synchronization has been applied in communication, but in fact
there are numerous issues which have not been addressed yet, i.e. improving for the
performance of proposed systems and making them suitable for various transmission
environments of radar, ultra wide band, and CDMA systems, etc.
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