In this paper, a multiuser OFDM-based chaos shift keying (MU OFDM-DCSK) modulation is presented. In this system, the spreading operation is performed in time domain over the multicarrier frequencies. ...To allow the multiple access scenario without using excessive bandwidth, each user has NP predefined private frequencies from the N available frequencies to transmit its reference signal and share with the other users the remaining frequencies to transmit its M spread bits. In this new design, NP duplicated chaotic reference signals are used to transmit M bits instead of using M different chaotic reference signals as done in DCSK systems. Moreover, given that N P <;<; M, the MU OFDMDCSK scheme increases spectral efficiency, uses less energy and allows multiple-access scenario. Therefore, the use of OFDM technique reduces the integration complexity of the system where the parallel low pass filters are no longer needed to recover the transmitted data as in multicarrier DCSK scheme. Finally, the bit error rate performance is investigated under multipath Rayleigh fading channels, in the presence of multiuser and additive white Gaussian noise interferences. Simulation results confirm the accuracy of our analysis and show the advantages of this new hybrid design.
Since the early 1990s, a large number of chaos-based communication systems have been proposed exploiting the properties of chaotic waveforms. The motivation lies in the significant advantages ...provided by this class of non-linear signals. For this aim, many communication schemes and applications have been specially designed for chaos-based communication systems where energy, data rate, and synchronization awareness are considered in most designs. Recently, the major focus, however, has been given to the non-coherent chaos-based systems to benefit from the advantages of chaotic signals and non-coherent detection and to avoid the use of chaotic synchronization, which suffers from weak performance in the presence of additive noise. This paper presents a comprehensive survey of the entire wireless radio frequency chaos-based communication systems. First, it outlines the challenges of chaos implementations and synchronization methods, followed by comprehensive literature review and analysis of chaos-based coherent techniques and their applications. In the second part of the survey, we offer a taxonomy of the current literature by focusing on non-coherent detection methods. For each modulation class, this paper categorizes different transmission techniques by elaborating on its modulation, receiver type, data rate, complexity, energy efficiency, multiple access scheme, and performance. In addition, this survey reports on the analysis of tradeoff between different chaos-based communication systems. Finally, several concluding remarks are discussed.
In recent years, free space optical (FSO) communication has gained significant importance owing to its unique features: large bandwidth, license free spectrum, high data rate, easy and quick ...deployability, less power, and low mass requirements. FSO communication uses optical carrier in the near infrared band to establish either terrestrial links within the Earth's atmosphere or inter-satellite/deep space links or ground-to-satellite/satellite-to-ground links. It also finds its applications in remote sensing, radio astronomy, military, disaster recovery, last mile access, backhaul for wireless cellular networks, and many more. However, despite of great potential of FSO communication, its performance is limited by the adverse effects (viz., absorption, scattering, and turbulence) of the atmospheric channel. Out of these three effects, the atmospheric turbulence is a major challenge that may lead to serious degradation in the bit error rate performance of the system and make the communication link infeasible. This paper presents a comprehensive survey on various challenges faced by FSO communication system for ground-to-satellite/satellite-to-ground and inter-satellite links. It also provides details of various performance mitigation techniques in order to have high link availability and reliability. The first part of this paper will focus on various types of impairments that pose a serious challenge to the performance of optical communication system for ground-to-satellite/satellite-to-ground and inter-satellite links. The latter part of this paper will provide the reader with an exhaustive review of various techniques both at physical layer as well as at the other layers (link, network, or transport layer) to combat the adverse effects of the atmosphere. It also uniquely presents a recently developed technique using orbital angular momentum for utilizing the high capacity advantage of optical carrier in case of space-based and near-Earth optical communication links. This survey provides the reader with comprehensive details on the use of space-based optical backhaul links in order to provide high capacity and low cost backhaul solutions.
Underwater wireless information transfer is of great interest to the military, industry, and the scientific community, as it plays an important role in tactical surveillance, pollution monitoring, ...oil control and maintenance, offshore explorations, climate change monitoring, and oceanography research. In order to facilitate all these activities, there is an increase in the number of unmanned vehicles or devices deployed underwater, which require high bandwidth and high capacity for information transfer underwater. Although tremendous progress has been made in the field of acoustic communication underwater, however, it is limited by bandwidth. All this has led to the proliferation of underwater optical wireless communication (UOWC), as it provides higher data rates than the traditional acoustic communication systems with significantly lower power consumption and simpler computational complexities for short-range wireless links. UOWC has many potential applications ranging from deep oceans to coastal waters. However, the biggest challenge for underwater wireless communication originates from the fundamental characteristics of ocean or sea water; addressing these challenges requires a thorough understanding of complex physio-chemical biological systems. In this paper, the main focus is to understand the feasibility and the reliability of high data rate underwater optical links due to various propagation phenomena that impact the performance of the system. This paper provides an exhaustive overview of recent advances in UOWC. Channel characterization, modulation schemes, coding techniques, and various sources of noise which are specific to UOWC are discussed. This paper not only provides exhaustive research in underwater optical communication but also aims to provide the development of new ideas that would help in the growth of future underwater communication. A hybrid approach to an acousto-optic communication system is presented that complements the existing acoustic system, resulting in high data rates, low latency, and an energy-efficient system.
One of the major drawbacks of the conventional differential chaos shift keying (DCSK) system is the addition of channel noise to both the reference signal and the data-bearing signal, which ...deteriorates its performance. In this brief, we propose a noise reduction DCSK system as a solution to reduce the noise variance present in the received signal in order to improve performance. For each transmitted bit, instead of generating β different chaotic samples to be used as a reference sequence, β/P chaotic samples are generated and then duplicated P times in the signal. At the receiver, P identical samples are averaged, and the resultant filtered signal is correlated to its time-delayed replica to recover the transmitted bit. This averaging operation of size P reduces the noise variance and enhances the performance of the system. Theoretical bit error rate expressions for additive white Gaussian noise and multipath fading channels are analytically studied and derived. Computer simulation results are compared to relevant theoretical findings to validate the accuracy of the proposed system and to demonstrate the performance improvement compared to the conventional DCSK, the improved DCSK, and the differential-phase-shift-keying systems.
Pressure ulcer prevention is a vital procedure for patients undergoing long-term hospitalization. A human body lying posture (HBLP) monitoring system is essential to reschedule posture change for ...patients. Video surveillance, the conventional method of HBLP monitoring, suffers from various limitations, such as subject's privacy, and field-of-view obstruction. We propose an autonomous method for classifying the four state-of-the-art HBLPs in healthy adults subjects: supine, prone, left and right lateral, with no sensors or cables attached on the body and no constraints imposed on the subject. Experiments have been conducted on 12 healthy adults (age 27.35 ± 5.39 years) using a collection of textile pressure sensors embedded in a cover placed under the bed sheet. Histogram of oriented gradients and local binary patterns were extracted and fed to a supervised artificial neural network classification model. The model was trained based on the scaled conjugate gradient backpropagation. A nested cross validation with an exhaustive outer validation loop was performed to validate the classification's generalization performance. A high testing prediction accuracy of 97.9% with a Cohen's Kappa coefficient of 97.2% has been interestingly obtained. Prone and supine postures were successfully separated in the classification, in contrast to the majority of previous similar works. We found that using the information of body weight distribution along with the shape and edges contributes to a better classification performance and the ability to separate supine and prone postures. The results are satisfactorily promising toward unobtrusively monitoring posture for ulcer prevention. The method can be used in sleep studies, post-surgical procedures, or applications requiring HBLP identification.
Laser technology has observed a great advancement over the last few decades. This technology is used for a wide range of applications including medical sciences, military, industrial manufacturing, ...electronics, holography, spectroscopy, astronomy and much more. Military operations often demand a secure and timely transmission of a massive amount of information from one place to another. Until now, the military has relied on the radio spectrum for effective communication, which is vulnerable to security threats and susceptible to electromagnetic interference (EMI). Also, this spectrum is hard-pressed to meet the current bandwidth requirement for high-resolution images, on-air video conferencing and real-time data transfer. Therefore, the focus has shifted to visible and infrared spectrum using laser technology which is capable of providing secure data transfer because of its immunity to EMI. The probability of intercepting a laser signal is very low due to its narrow beam divergence and coherent optical beam, making the laser a suitable candidate for secure military tactical operations. Besides the communication aspect, the highly directive nature of a laser beam is also used as a directed energy laser weapon. These highly powerful and light weighted directed energy laser weapons are very cost-effective countermeasures for airborne threats. Furthermore, laser sensors are deployed in the battlefield or in space for tracking the path of a wide range of military vehicles like missiles, unmanned aerial vehicles, fighter aircraft, warships, submarines, and so on. Advancements in space operations and laser technology have offered synergistic possibilities of using lasers from space-based platforms during military operations. In this paper, we are providing our readers with a comprehensive study of laser applications, used by the military, to carry out tactical operations on the ground or space-based platforms. Also, an intensive investigation on the development of laser technology for sensors, range-finders and target designators that are used for intelligence, surveillance and reconnaissance is presented in the paper. The advancement of laser communication for military purposes and its current state of the art is reviewed as well as some recent scientific developments in the area of high-energy directed laser weapons are discussed, which have revolutionized military battlefields. Therefore, this manuscript highlights recent trends and engineering breakthroughs for the use of lasers in tactical operations.
The Vehicle-to-Grid (V2G) network is, where the battery-powered vehicles provide energy to the power grid, is highly emerging. A robust, scalable, and cost-optimal mechanism that can support the ...increasing number of transactions in a V2G network is required. Existing studies use traditional blockchain as to achieve this requirement. Blockchain-enabled V2G networks require a high computation power and are not suitable for micro-transactions due to the mining reward being higher than the transaction value itself. Moreover, the transaction throughput in the generic blockchain is too low to support the increasing number of frequent transactions in V2G networks. To address these challenges, in this paper, a lightweight blockchain-based protocol called Directed Acyclic Graph-based V2G network (DV2G) is proposed. Here blockchain refers to any Distributed Ledger Technology (DLT) and not just the bitcoin chain of blocks. A tangle data structure is used to record the transactions in the network in a secure and scalable manner. A game theory model is used to perform negotiation between the grid and vehicles at an optimized cost. The proposed model does not require the heavy computation associated to the addition of the transactions to the data structure and does not require any fees to post the transaction. The proposed model is shown to be highly scalable and supports the micro-transactions required in V2G networks.
The past few years have witnessed a tremendous development in power-line communications (PLCs) for the realization of smart grids. Since power lines were not originally intended for conveying ...high-frequency signals, any communication over these lines would be exposed to severe adversarial factors, such as interference, impulsive, and phase noise. This elucidates the importance of employing robust modulation techniques and motivates research in this direction. Indeed, the aim of this brief is to propose a differential chaos shift keying (DCSK) modulation scheme as a potential candidate for smart grid communication networks. This DCSK class of noncoherent modulation is very robust against linear and nonlinear channel distortions. More importantly, the demodulation process can be carried out without any channel estimator at the receiver side. In this work, we analyze the bit error rate performance of DCSK over multipath PLC channels in which phase, background, and impulsive noise are present. A simulator is developed to verify the performance of the proposed DCSK against direct sequence code division multiple access and direct sequence differential phase shift keying. The results presented in this work prove the advantages of this low-cost noncoherent modulation technique for PLC systems over its rivals.
This paper presents the design and performance analysis of an analog network coding (ANC) scheme for multi-user multi-carrier differential chaos shift keying (MC-DCSK) modulation. The incentives to ...employ the MC-DCSK system are to achieve a better spectral efficiency and more efficient energy consumption compared to that of a conventional DCSK system. The proposed scheme considers a network comprising L user nodes (L ≥ 2) and a single relay node R. In this scheme, called the ANC-based two-way relay system, all users transmit their signals to the relay in the first time slot, and the relay forwards the superposition of the received signals each of the user nodes in the second time slot. At the receiver end, each user mitigates the overall interference by subtracting its own data signal from the received combined signal and then starts the decoding process. The system design is analytically studied, and the corresponding theoretical bit error rate expression for the multipath fading channel is derived. Additionally, the conventional ANC-DCSK scheme is analyzed and compared to the proposed ANC-based MC-DCSK scheme to show the improvement in the performance of our approach. Finally, to validate the accuracy of the methodology, the simulation results are compared to the related theoretical expressions.
PDF
