CSK Modulation for Secure Wireless Communication Networks

Chaos-shift-keying (CSK) and differential CSK (DCSK) are the two popular coherent and non-coherent modulation schemes for ultra wide-band (UWB) communications. However, security of these schemes has never been studied formally from the information-theoretic perspective. In this paper, we investigate the physical layer security of CSK and DCSK modulation schemes over AWGN and Rayleigh fading channels from the information-theoretic manner. For this aim, the average secrecy capacity and outage probability are computed and analyzed by considering the variation of bit energy Eb coming from the use of chaotic signal to convey information. Our results show that CSK has better or close secrecy capacity and outage probability compared with DCSK and the conventional spread-spectrum modulation. Additionally, these metrics favor Rayleigh fading channels over AWGN channels. Finally, we conclude that the non-constant bit energy is useful to enhance the physical layer security.

2 - Chaos-based digital communication systems

In chaos-based communication systems, parameter variation in the chaos generator and additive channel noise represent two practical problems that are hard to solve. For chaos-based digital communication, non-coherent detection has the advantage that the receiver does not need to reproduce the same chaos basis function that has been generated in the transmitter. Such reproduction typically requires a fragile operation of chaos synchronisation between the transmitter and the receiver. In this paper, we consider non-coherent detection under the practical condition of the transmitted signal being contaminated by noise and its generating function being subject to strong parameter variation. A novel tracker is proposed for reconstructing the transmitted chaotic signal. This tracker uses a modified radial-basis-function (RBF) neural network which incorporates a learning algorithm for tracking the noisy chaotic signal under parameter variation. Using this tracker, a non-coherent detector is designed for demodulating chaos-shift-keying (CSK) signals in a CSK digital communication system. Computer simulations, in which the Chua's circuit is used as the chaos generator, are presented to demonstrate the tracking ability and CSK demodulation of the proposed method.

Based on multi-carrier transmission and multi-level chaos shift keying modulation, a novel multi-carrier chaos shift keying (MC-CSK) modulation system is proposed and designed in this paper. The new system adopts multiple subcarriers, on which all chaotic basis signals along with multiple data-bearing signals are transmitted simultaneously. The data-bearing signals and their references, though sharing the same subcarriers, are separated by I/Q channels. As a consequence, the MC-CSK system can achieve higher bit rate and better spectral efficiency compared with the MC-DCSK system. It can also dispense with chaos synchronization and threshold shifting that are required in conventional CSK systems, and achieve a delay-line-free design in both transmitters and receivers. Also, the performance of the proposed system is further improved by normalizing all chaotic basis signals and making them strictly orthogonal using the Gram-Schmidt algorithm. Moreover, the bit error rates (BERs) of the MC-CSK system over additive white Gaussian noise and multipath Rayleigh fading channels are derived. Finally, simulations are performed under different channel conditions and the effects of system parameters on the BER performance are evaluated. Both analytical and simulation results confirm that the MC-CSK system outperforms differential CSK (DCSK) and MC-DCSK systems in BER performance, except a rare case when the number of subcarriers is very small.

This paper brings forward a Deep Learning (DL)-based Chaos Shift Keying (DLCSK) demodulation scheme to promote the capabilities of existing chaos-based wireless communication systems. In coherent Chaos Shift Keying (CSK) schemes, we need synchronization of chaotic sequences, which is still practically impossible in a disturbing environment. Moreover, the conventional Differential Chaos Shift Keying (DCSK) scheme has a drawback, that for each bit, half of the bit duration is spent sending non-information bearing reference samples. To deal with this drawback, a Long Short-Term Memory (LSTM)-based receiver is trained offline, using chaotic maps through a finite number of channel realizations, and then used for classifying online modulated signals. We presented that the proposed receiver can learn different chaotic maps and estimate channels implicitly, and then retrieves the transmitted messages without any need for chaos synchronization or reference signal transmissions. Simulation results for both the AWGN and Rayleigh fading channels show a remarkable BER performance improvement compared to the conventional DCSK scheme. The proposed DLCSK system will provide opportunities for a new class of receivers by leveraging the advantages of DL, such as effective serial and parallel connectivity. A Single Input Multiple Output (SIMO) architecture of the DLCSK receiver with excellent reliability is introduced to show its capabilities. The SIMO DLCSK benefits from a DL-based channel estimation approach, which makes this architecture simpler and more efficient for applications where channel estimation is problematic, such as massive MIMO, mmWave, and cloud-based communication systems.

During the last decade, an intense research into the chaotic communication systems have resulted into invention of several chaos based communication systems, which offer numerous advantages over the conventional communication systems. However, future of the communication systems are all about the Multiple Input Multiple Output (MIMO) systems. So, in this paper, we have tried to implement the chaos based communication in MIMO systems. We have used the Chaos Shift Keying (CSK) modified using surrogate data. We have analysed the BER of the proposed system with the conventional techniques.

In this chapter we begin our formal study of chaos-based digital communication systems. The areas of investigation to be described here include the operation, analysis and performance evaluation of communication systems that employ chaotic signals for carrying digital information. As surveyed in the previous chapter, the most widely studied chaos-based digital communication systems are the so-called chaos-shift-keying (CSK) system [Dedieu et al. (1993)] and the differential chaos-shift-keying (DCSK) system [Kolumbán et al. (1996)]. In this chapter we focus our attention on the CSK system, in which digital symbols are encoded with different chaotic signals. In the binary case, the CSK transmitter essentially transmits two chaotic signals which are derived from two chaos generating sources, one at a time, according to the binary signal being sent. Clearly, the receiver is able to demodulate the transmitted signal if it can distinguish between the chaotic signal segments generated from the two chaos generators. Alternatively, the transmitted signal may be generated from one chaos generator in which a parameter is modulated according to the binary signal being sent. In this case, the receiver’s job is to work out the parametric change by observing the transmitted signal.KeywordsChaotic SequenceChaotic SignalChaos GeneratorBinary SymbolPerformance Analysis MethodThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Chaotic optical communication at high bit rates has attracted great attention because of its potential application in secure communications. In a chaotic optical communication system, a message can participate in the dynamics of the nonlinear system and further affect the characteristics of the chaotic carrier waveform. Message encoding can also change the synchronization quality if an encoding scheme breaks the symmetry between a transmitter and a receiver. In this presentation, we experimentally investigate the influence of message encoding on the characteristics of chaotic dynamics, chaos synchronization, and chaotic communication, using three encoding schemes, namely chaos shift keying, chaos masking, and chaos modulation, with the setup of a chaotic optical communication system with optoelectronic feedback. The chaos shift keying and chaos modulation schemes are found to be able to increase the complexity of the chaotic carrier waveform due to the random nature of the encoded message. Meanwhile, the chaos shift keying and chaos masking schemes are found to deteriorate the synchronization quality when the amplitude of the message is increased. Consequently, only the chaos modulation scheme has the desired feature in increasing the complexity of the chaotic carrier waveform while maintaining the quality of chaos synchronization, which is an important feature in secure communication.

Chaos is characterized by aperiodic, wideband, random-like, and ergodicity. Chaotic secure communication has become one of the hot topics in nonlinear dynamics since the early 1990s exploiting the technique of chaos synchronization. As distinguished by the type of information being carried, chaos-based communication systems can be categorized into analogy and digital, including four popular techniques such as Chaos Masking, Chaos Shift Keying, Chaos Modulation, and Chaos Spreading Spectrum. In this chapter, the principles of these schemes and their modifications are analyzed by theoretical analysis as well as dynamic simulation. In addition, chaos-based cryptography is a new approach to encrypt information. After analyzing the performances of chaotic sequence and designing an effective chaotic sequence generator, the authors briefly presented the principle of two classes of chaotic encryption schemes, chaotic sequence encryption and chaotic data stream encryption.

By generalizing the waveform communications concept, this paper develops exact expressions, verified by computer simulations, for the noise performance of the coherent antipodal Chaos Shift Keying (CSK), coherent Differential Chaos Shift Keying (DCSK) and differentially coherent DCSK modulation schemes. We show that the properties of the basis functions have no effect on the noise performance of a modulation scheme, provided that the energy per bit is constant and the basis functions are orthogonal.

In wireless local area networks and indoor communications, multipath propagation limits the performance of data communications systems. To overcome the multipath propagation problem, a spread spectrum system has to be used. The chaotic communications technique, where inherently wideband chaotic basis functions are used, offers a cheap alternative to conventional spread spectrum communications. Unfortunately, analytic expressions for the noise performance of chaotic modulation schemes are not available in the literature. This has so far prevented a full exploitation of the features of chaotic modulation schemes. By generalizing the waveform communications concept, this paper develops exact expressions for the noise performance of the coherent antipodal chaos shift keying (CSK), coherent differential chaos shift keying (DCSK), and differentially coherent DCSK modulation schemes. We show that the properties of the basis functions have no effect on the noise performance of a modulation scheme, provided that the energy per bit is constant. In this sense, the concept of waveform communications is generalized. Finally, our theoretical results are verified by computer simulations.

In recent years, chaotic communication is a hot research topic and it suits better for the emerging wireless networks because of its excellent features. Different chaos based modulation schemes have evolved, of which the CS-DCSK modulation technique provides better BER performance and bandwidth efficiency, due to its code domain approach. The QCSK modulation technique provides double benefit: higher data rate with similar BER performance and same bandwidth occupation as DCSK. By combining the advantage of code shifted differential chaos shift keying (CS-DCSK) and Quadrature chaos shift keying (QCSK) scheme, a novel modulation scheme called code shifted Quadrature chaos shift keying (CS-QCSK) is proposed and its suitability in a multiuser scenario is tested in this paper. The analytical expressions for the bit-error rate for Multi-user CS-QCSK scheme (MU-CS-QCSK) under Rayleigh multipath fading channel is derived. The simulation result shows that, in multiuser scenario the proposed method outperforms classical chaotic modulation schemes in terms of bit error rate (BER).

A novel non-coherent multi-level differential chaos shift keying (DCSK) modulation scheme is proposed in this paper. This new scheme is based on both the transmitted-reference technique and $M$ -ary orthogonal modulation, where each data-bearing signal is chosen from a set of orthogonal chaotic wavelets constructed by a reference signal. Thanks to this signaling design, the new scheme can achieve a higher attainable data rate, lower energy loss in reference transmission, increased bandwidth efficiency, better data security and better bit error rate (BER) performance as compared to the conventional DCSK. Unlike other DCSK-based systems that separate the reference and data-bearing signals using the TDMA scheme, this new system employs I/Q channels to send these two signals in a parallel and simultaneous manner, making the system easily extendable to multi-carriers. This transmission mechanism not only can further increase data rate but also can remove all radio frequency delay lines from detectors. Analytical BER expressions of the proposed system are derived for both additive white Gaussian noise (AWGN) and multipath Rayleigh fading channels. Relevant simulation results are given and compared to non-coherent binary/ $M$ -ary DCSK systems. In addition, the impacts of various system parameters on noise performance are discussed. Both theoretical analysis and simulation results confirm the promising benefits of the new design.

In this paper, a novel multi-user carrier index differential chaos shift keying (MU CI-DCSK) modulation scheme is proposed. For a better utilization of spectrum resources, each user is allocated a private subcarrier for reference signal transmission, while the remaining subcarriers are public and shared by all users to transmit their own data-bearing signals. To avoid user interferences in this design, users are distinguished in a code division multiple access (CDMA) way based on Walsh codes. By exploiting the redundancies in the transmitted signals, repeated segments of received signals are averaged, leading to greatly reduced noises and a noticeable improvement in bit error rate (BER) performance. BER expressions of this new system are derived over the additive white Gaussian noise (AWGN) and multi-path Rayleigh fading channels. Simulation results and comparisons are performed to verify the feasibility and advantages of this new scheme.

The advances in the development of chaos based communication system suggests that chaos shift keying (CSK) and its variant Differential CSK (DCSK) are one of the most promising candidates for practical implementation. In this paper a DCSK communication system incorporating a non coherent approach of demodulation based on a correlation detector is considered over a multipath fading channel. Specifically, it can be anticipated that the channel will introduce attenuation and cause distortion in the transmitted sequence due to fading and multipath. This distortion will cause Intersymbol interference (ISI) and will also add noise. Channel equalizers are capable of removing ISI from the transmitted sequence and also noise. In this paper the performance of a linear MMSE channel equalizer is analysed for a DCSK communication system over a multipath fading channel with additive white Gaussian noise.