Vu Van Yem

A Chaos-Based Secure Direct-Sequence/Spread-Spectrum Communication System

This paper proposes a chaos-based secure direct-sequence/spread-spectrum (DS/SS) communication system which is based on a novel combination of the conventional DS/SS and chaos techniques. In the proposed system, bit duration is varied according to a chaotic behavior but is always equal to a multiple of the fixed chip duration in the communication process. Data bits with variable duration are spectrum-spread by multiplying directly with a pseudonoise (PN) sequence and then modulated onto a sinusoidal carrier by means of binary phase-shift keying (BPSK). To recover exactly the data bits, the receiver needs an identical regeneration of not only the PN sequence but also the chaotic behavior, and hence data security is improved significantly. Structure and operation of the proposed system are analyzed in detail. Theoretical evaluation of bit-error rate (BER) performance in presence of additive white Gaussian noise (AWGN) is provided. Parameter choice for different cases of simulation is also considered. Simulation and theoretical results are shown to verify the reliability and feasibility of the proposed system. Security of the proposed system is also discussed.

Design and analysis of a spread-spectrum communication system with chaos-based variation of both phase-coded carrier and spreading factor

This study designs and analyses a new phase-coded spread-spectrum communication system where both phase-coded carrier and spreading factor are varied based on a chaotic behaviour in the communication process. This design aims to reduce the probability of interception of the considered system. Discrete values generated by a chaotic map are exploited to create a non-return-to-zero (NRZ)-chaos sequence and simultaneously make bit duration variable. The NRZ-chaos sequence is then modulated by binary phase-shift keying technique to produce the phased-coded carrier. Owing to chip duration being constant, the variation of bit duration also leads to the variation of spreading factor. Spectrum spreading in the transmitter is performed by multiplying directly the variable-duration bits with the phase-coded carrier. A coherent receiver relying on a direct correlator is used for recovering the data. Design of the transmitter and receiver as well as analysis of bit error probability for the proposed system in cases of single-user and multi-user under additive white Gaussian noise channel is presented. Simulation results are shown to confirm the operation of the designed structures and the obtained analytical performance.

Dynamics, Synchronization and SPICE Implementation of a Memristive System with Hidden Hyperchaotic Attractor

The realization of memristor in nanoscale size has received considerate attention recently because memristor can be applied in different potential areas such as spiking neural network, high-speed computing, synapses of biological systems, flexible circuits, nonvolatile memory, artificial intelligence, modeling of complex systems or low power devices and sensing. Interestingly, memristor has been used as a nonlinear element to generate chaos in memristive system. In this chapter, a new memristive system is proposed. The fundamental dynamics properties of such memristive system are discovered through equilibria, Lyapunov exponents, and Kaplan–York dimension. Especially, hidden attractor and hyperchaos can be observed in this new system. Moreover, synchronization for such system is studied and simulation results are presented showing the accuracy of the introduced synchronization scheme. An electronic circuit modelling such hyperchaotic memristive system is also reported to verify its feasibility.

An OFDM-based chaotic DSSS communication system with M-PSK modulation

This paper investigates a Chaotic Direct-Sequence Spread-Spectrum (CDSSS) communication system based on Orthogonal Frequency-Division Multiplexing (OFDM) technique in combination with M-ary Phase Shift Keying (M-PSK) modulation. In the combination system, depending on the quality of transmission channel, the data rate can be adjusted flexibly by using M-PSK. Error rate performances through noise- and fading-affected channels are improved by means of CDSSS and OFDM, respectively. By replacing the conventional Pseudo-random Noise (PN) sequence with a NRZ-chaos sequence in CDSSS, data security of the combination system is enhanced significantly. A detailed description of the proposed system is first given. Numerical simulation and results are then shown in order to verify operation of the system and characterize the dependence of Bit Error Rate (BER) performance on the number of symbols, spreading factor and different chaotic sequences in both Additive White Gaussian Noise (AWGN) and Rayleigh Fading channels. Notable features on security of the system are also presented.

A Three-Dimensional No-Equilibrium Chaotic System: Analysis, Synchronization and Its Fractional Order Form

Recently, a new classification of nonlinear dynamics has been introduced by Leonov and Kuznetsov, in which two kinds of attractors are concentrated, i.e. self-excited and hidden ones. Self-excited attractor has a basin of attraction excited from unstable equilibria. So, from that point of view, most known systems, like Lorenz’s system, Rossler’s system, Chen’s system, or Sprott’s system, belong to chaotic systems with self-excited attractors. In contrast, a few unusual systems such as those with a line equilibrium, with stable equilibria, or without equilibrium, are classified into chaotic systems with hidden attractor. Studying chaotic system with hidden attractors has become an attractive research direction because hidden attractors play an important role in theoretical problems and engineering applications. This chapter presents a three-dimensional autonomous system without any equilibrium point which can generate hidden chaotic attractor. The fundamental dynamics properties of such no-equilibrium system are discovered by using phase portraits, Lyapunov exponents, bifurcation diagram, and Kaplan–Yorke dimension. Chaos synchronization of proposed systems is achieved and confirmed by numerical simulation. In addition, an electronic circuit is implemented to evaluate the theoretical model. Finally, fractional-order form of the system with no equilibrium is also investigated.

Novel MIMO antenna using Complementary Split Ring Resonator(CSRR) for LTE applications

A small multiband-printed antenna for multi-input and multi-output (MIMO) communication system using metamaterial structure is proposed as well as the whole concepts of miniaturization are introduced. To reduce the mutual coupling between two multi-band antennas, we develop a compact stop-band filter loaded with Complementary Split Ring Resonator Transmission Line (CSRR-TL) on ground plane. A resonant frequency obtained with high isolation value is f0 = 2.33GHz. Total small patch size is 0.20λ0 × 0.11λ0 with 1.6 mm thickness. The novel MIMO antenna for Long Term Evolution (LTE) is fabricated by using low cost FR4 (εr = 4.4) substrate. Both the simulated and measured results are shown to illustrate the performances of the proposed antenna.

A Chaotic Pulse-Time Modulation Method for Digital Communication

We present and investigate a method of chaotic pulse-time modulation (PTM) named chaotic pulse-width-position modulation (CPWPM) which is the combination of pulse-position-modulation (PPM) and pulse-width modulation (PWM) with the inclusion of chaos technique for digital communications. CPWPM signal is in the pulse train format, in which binary information is modulated onto chaotically-varied intervals of position and width of pulses, and therefore two bits are encoded on a single pulse. The operation of the method is described and the theoretical evaluation of bit-error rate (BER) performance in the presence of additive white Gaussian noise (AWGN) is provided. In addition, the chaotic behavior with tent map and its effect on average parameters of the system are investigated. Theoretical estimation and numerical simulation of a CPWPM system with specific parameters are carried out in order to verify the performance of the proposed method.

M×N‐ary chaotic pulse‐width‐position modulation: An effective combination method for improving bit rate

Purpose – This paper presents and investigates a method named M×N‐ary chaotic pulse‐width‐position modulation (CPWPM) which is based on the combination of M‐ary chaotic pulse‐position modulation (CPPM) and N‐ary chaotic pulse‐width modulation (CPWM) in order to provide a better performance in noise‐affected environments as well as improve significantly bit rate.Design/methodology/approach – Analysis of schemes for modulator and demodulator are presented in detail through describing the schemes of the individual methods and their combination. Theoretical evaluation of bit‐error rate (BER) performance in presence of additive white Gaussian noise (AWGN) is provided. Chaotic behavior with tent map in variation of modulation parameters is also investigated. In order to verify the theoretical analyses, numerical simulations are carried out and their results are reported.Findings – Both evaluation and simulation results show that when the number of symbols increases, the bit rate is improved significantly but th...

Compact MIMO antenna with low mutual coupling using defected ground structure

Defected Ground Structure (DGS) is a newly introduced revolutionary technique in the field of microstrip antenna to enhance the performance of antenna parameters as bandwidth. In this paper, a design of compact MIMO antenna using DGS is proposed. The antenna operates at 3.5 GHz for WiMax/LTE tablet applications. Compare to theoretical microstrip antenna design, the suggested MIMO antenna using a simple DGS shape has achieved not only an enlarged bandwidth but also more compact size. In addition, the mutual coupling between two antenna elements with close distance is low (less than -20dB) thanks to proper position in antenna ground as well as the fed method using.

Novel high gain and broadband CPW-fed antennas with EBG for ITS applications

We propose in this paper a novel high gain coplanar waveguide-fed antenna, in which a wide bandwidth is achieved by adjusting taper numbers and slot shape. The proposed compact antenna utilizes the advantages of the CPW line to simplify the antenna structure into a single metallic level, which makes easier the integration with the microwave integrated circuits. To enhance antenna operation in term of gain and bandwidth as well as to control far-field radiation patterns, the initial CPW-fed antenna is with an array of EBG structures in three different ways. Based on this design procedure, proposed antennas are designed, optimized, compared as well as fabricated on low cost material substrate (FR-4, ε=4.4, h=1.6mm). The experimental result of these antennas at 915 MHz and 5.8 GHz band has a measured impedance bandwidth of 5% and 14.6%, a simulated gain of 5.56 dBi and 5.9 dBi, respectively. These properties make the antennas suitable for UHF RFID applications and Dedicated Short Range Communication (DSRC) in Intelligent Transport System.