Adaptive Synchronization Algorithm Research Articles

A novel adaptive synchronization algorithm for a general class of fractional-order complex-valued systems with unknown parameters, and applications to circuit realization and color image encryption

This article proposes an adaptive synchronization (AS) algorithm to synchronize a general class of fractional-order complex-valued systems with completely unknown parameters, which may appear in physical and engineering problems. The analytical and theoretical concepts of the algorithm rely on the mathematical framework of the Mittag-Leffler global stability of fractional-order systems. A specific control system is established analytically based on the fractional-order adaptive laws of parameters, and the corresponding numerical results are executed to verify the accuracy of the AS algorithm. The proposed synchronization method is evaluated using the fractional-order complex Rabinovich system as an attractive example. The electronic circuits of the new system with different fractional orders are designed. By utilizing the Multisim electronic workbench software, various chaotic/hyperchaotic behaviors have been observed, and a good agreement is found between the numerical results and experimental simulation. In addition, the approximation of the transfer function for different fractional-order are presented. And the corresponding resistor and capacitor values in the chain ship model (CSM) are estimated, which can be utilized in designing electronic circuits for other fractional-order systems. Furthermore, two strategies for encrypting color images are proposed using the AS algorithm and fractional-order adaptive laws of parameters. In the first strategy, the color image is treated as a single package and divided into two vectors. The first vector is embedded into transmitter parameters, while the second vector is injected into the transmitter state signals. In the second strategy, the primary RGB channel components of the original color image are extracted and separated into two vectors, and the same process is followed as in the first strategy. These strategies complicate the decryption task for intruders. Different scales of white Gaussian noise are added to color images to examine the robustness of the proposed color images encryption strategies.

Алгоритм адаптивной кадровой синхронизации в системах сверхширокополосной радиосвязи

This paper introduces adaptive frame synchronization algorithm in HRP mode of IEEE 802.15.4-2020 radiocommunication system under unintentional; interference signals transmitted in HRP-CoU mode. Proposed algorithm is based on nulls adding to synchronization sequences and packet error rate control. True detection probability is estimated by MATLAB model.

High-Precision SLAM Based on the Tight Coupling of Dual Lidar Inertial Odometry for Multi-Scene Applications

Simultaneous Localization and Mapping (SLAM) is an essential feature in many applications of mobile vehicles. To solve the problem of poor positioning accuracy, single use of mapping scene, and unclear structural characteristics in indoor and outdoor SLAM, a new framework of tight coupling of dual lidar inertial odometry is proposed in this paper. Firstly, through external calibration and an adaptive timestamp synchronization algorithm, the horizontal and vertical lidar data are fused, which compensates for the narrow vertical field of view (FOV) of the lidar and makes the characteristics of vertical direction more complete in the mapping process. Secondly, the dual lidar data is tightly coupled with an Inertial Measurement Unit (IMU) to eliminate the motion distortion of the dual lidar odometry. Then, the value of the lidar odometry after correcting distortion and the pre-integrated value of IMU are used as constraints to establish a non-linear least-squares objective function. Joint optimization is then performed to obtain the best value of the IMU state values, which will be used to predict the state of IMU at the next time step. Finally, experimental results are presented to verify the effectiveness of the proposed method.

New adaptive synchronization algorithm for a general class of complex hyperchaotic systems with unknown parameters and its application to secure communication

The aim of this report is to investigate an adaptive synchronization (AS) for the general class of complex hyperchaotic models with unknown parameters and a new algorithm to achieve this type of synchronization is proposed. Owing to the intricacy behavior of hyperchaotic models that could be effective in secure communications, the special control based on adaptive laws of parameters is constructed analytically, and the corresponding simulated results are performed to validate the algorithm’s accuracy. The complex Rabinovich model is utilized as an enticing example to examine the proposed synchronization technique. A strategy for secure communication improving the overall cryptosystem is proposed; the scheme is designed to split the message and insert some bit of information signal into the modulation parameters and the other bit into the transmitter system’s states, making decryption by intruders more difficult. Meanwhile, adaptive techniques and a decryption function on the receiver side can accurately retrieve the message. Different types of encoded messages are examined for testing the robustness of the proposed scheme (e.g., text and gray images with diverse scales of white Gaussian noise).

A Novel Reliable Adaptive Beacon Time Synchronization Algorithm for Large-Scale Vehicular Ad Hoc Networks

The time synchronization in vehicular ad hoc networks (VANETs) has gained significant attention in recent times. In this paper, we focus on the time synchronization in large-scale VANETs and propose an adaptive beacon time synchronization (ABTS) algorithm to enhance timing message synchronization. ABTS algorithm selects the best time synchronization pairs to decrease the number of timing messages transmitted. To guarantee the reliability of synchronization, the clock offset of the connected vehicles periodically readjust to provide a better degree of synchronization accuracy with minimum energy consumption. Based on two-way timing message synchronization, we derive maximum likelihood (ML) estimation and its equivalent Cramer-Rao lower bound (CRLB) for clock offset design in the generalized sender-to-receiver system by assuming a Gaussian noise model. We propose node pair selection algorithms to improve pairwise beacon message timing synchronization. The simulation results validate that our proposed ABTS algorithm performs better than other protocols in terms of synchronization accuracy, the rate of convergence and energy efficiency.

Providing streaming joins as a service at Facebook

Stream processing applications reduce the latency of batch data pipelines and enable engineers to quickly identify production issues. Many times, a service can log data to distinct streams, even if they relate to the same real-world event (e.g., a search on Facebook's search bar). Furthermore, the logging of related events can appear on the server side with different delay, causing one stream to be significantly behind the other in terms of logged event times for a given log entry. To be able to stitch this information together with low latency , we need to be able to join two different streams where each stream may have its own characteristics regarding the degree in which its data is out-of-order . Doing so in a streaming fashion is challenging as a join operator consumes lots of memory, especially with significant data volumes. This paper describes an end-to-end streaming join service that addresses the challenges above through a streaming join operator that uses an adaptive stream synchronization algorithm that is able to handle the different distributions we observe in real-world streams regarding their event times. This synchronization scheme paces the parsing of new data and reduces overall operator memory footprint while still providing high accuracy. We have integrated this into a streaming SQL system and have successfully reduced the latency of several batch pipelines using this approach.

Network Synchronization for Mobile Device-to-Device Systems

This paper studies the synchronization problem for mobile cellular device-to-device (D2D) networks. Depending on the number of devices that are in coverage of the base station, the D2D environment can be divided into three categories where the partial-coverage and out-of-coverage are challenging scenarios and thus are the focus of this paper. First, we discuss five main challenges imposed on the synchronization problem in mobile D2D networks. More specifically, there are different challenges in the two coverage scenarios, since they do not have exactly the same synchronization objectives. Second, we propose a low-complexity Adaptive distRibuted nEtwork Synchronization (ARES) algorithm to address the five challenges. The design principles and the theories behind the ARES scheme are also analyzed in detail. Finally, we provide comprehensive simulations to evaluate different synchronization schemes, where the proposed ARES mechanism shows very promising performance.

Cooperative Control of Heterogeneous Uncertain Dynamical Networks: An Adaptive Explicit Synchronization Framework.

This paper proposes an adaptive explicit synchronization framework to address the cooperative control for heterogeneous uncertain dynamical networks under switching communication topologies. The main contribution is to develop an adaptive explicit synchronization algorithm, in which the synchronization state can be completely tracked by each agent in real time rather than only be measured after the synchronization process of all agents is over. By introducing appropriate assumptions, a class of adaptive explicit synchronization protocols is designed by using a combination of the virtual leader's states, the neighboring agents' relative information, distributed feedback gain, and distributed average weighted parameters. It is proved in the sense of Lyapunov that, if the dwell time is larger than a positive threshold, the cooperative control problem for the closed-loop heterogeneous uncertain dynamical networks under switching of strongly-connected communication topologies can be solved by the proposed adaptive explicit synchronization algorithm. Furthermore, by assuming that the topology is frequently strongly-connected, it shows that intermittent adaptive explicit synchronization can be achieved with well-designed control parameters. Two examples are presented to demonstrate the effectiveness of the proposed theory.

Frame-based synchronization adaptive method for systems based on DVB-S2 standard on FPGA

Introduction. With the development of digital technology, increasingly greater attention is paid to building radio-receiving paths based on SDR technology (Software Defined Radio). This technology involves the construction of SoC system on FPGA. Synchronization system is an important part of any radio system. This article analyzes the frame synchronization algorithms used today in terms of their efficiency and practical implementation on FPGA. Problem Statement. There are many frame synchronization algorithms for communication systems. Algorithms based on differential correlation method are extensively used these days because they are insensitive to phase and frequency distortions. The main disadvantage of the existing methods is their sensitivity to changes in the level of the input signal. Therefore, the development of the algorithm with an adaptive threshold for implementation on FPGA is an important task. Frame synchronization algorithm for DVB-S2 standard. This section shows analysis of modern frame synchronization algorithms, which are used in DVB-S2 receivers, and shows characteristics of MDP. Frame synchronization algorithm with adaptive threshold. Algorithm with adaptive threshold [P2], which is resistant to changes in the level of the input signal, is suggested. Also a comparative analysis of this method and methods listed above is made. Modification of the algorithm [P2] for implementation on FPGA. This section shows practical ways to implement the adaptive algorithm on FPGA hardware platform. In particular, the approximating method was used to find the location of the complex number modulus, the implementation of which is easily performed on the FPGA chip logic elements without loss of performance of the algorithm as a whole. Conclusions. Suggested adaptive frame synchronization algorithm eliminates Automatic Gain Control (AGC) system from signal processing phase. This approach of using an adaptive threshold can be used for more sophisticated algorithms, in particular for DPDI. In future works, these tasks will be addressed.

Adaptive Correction Algorithm for OFDM-IDMA Systems With Carrier Frequency OFFSET in A Fast Fading Multipath Channel

The Orthogonal Frequency Division Multiplexing-Interleave Division Multiple Access (OFDM-IDMA) scheme, which offers significant improvement on the performance of the conventional IDMA technique, has been in the forefront of recent mobile communication researches as it is expected to deliver a high quality, flexible and efficient high data-rate mobile transmission. Most papers on OFDM-IDMA scheme assume a system free of carrier frequency offset. However, the scheme is susceptible to synchronization errors and performance degradation because of the presence of OFDM, which is highly sensitive to carrier frequency offset (CFO) especially at the uplink. The effect of CFO on the performance of the scheme, in a slow fading multipath channel scenario, is therefore investigated, and analyzed. Also, the effect of CFO on the performance of the OFDM-IDMA scheme, in a fast fading multipath channel, which has not been hitherto reported in literature, is investigated and analyzed. An LMS-based adaptive synchronization algorithm is therefore employed to mitigate the degrading impact of carrier frequency offset errors on the OFDM-IDMA scheme. Simulation results clearly show that the presence of CFO degrades the performance of the system and that performance degradation due to CFO, increases in a fast fading multipath channel in comparison with slow fading channel scenario. Furthermore, results show substantial improvement in the overall output of the system upon the application of the adaptive synchronization algorithm, which is implemented in both slow, and fast fading Rayleigh multipath channel scenarios.

A novel adaptive synchronization algorithm for intermediate frequency architecture CO-OFDM system

An adaptive algorithm of fine synchronization for intermediate frequency architecture coherent optical orthogonal frequency division multiplexing (CO-OFDM) transmission system is proposed. The whole synchronization procedure is separated into two steps. In the first step, we use an auto-correlation-style algorithm to achieve the coarse symbol synchronization. In the second step, the proposed algorithm is used to achieve the adaptive fine synchronization. The merit of the proposed algorithm is that it can realize fine synchronization under different environments without adjusting the detect-threshold of timing metric in a dynamically reconfiguration network. And also the algorithm can implement in field-programmable gate array (FPGA) or other digital signal processing (DSP) chips easily. In this paper, the CO-OFDM model is analyzed in theory firstly. Secondly, an analysis on the performance of coarse synchronization algorithm used in this paper is made. Finally, the proposed fine synchronization algorithm is introduced in detail. The simulation experiment result demonstrates that the proposed algorithm achieves fine synchronization under different signal noise ratio (SNR) conditions after 6 fiber-spans transmission.

Robust adaptive synchronization for a general class of uncertain chaotic systems with application to Chua’s circuit

The synchronization problem for a general class of uncertain chaotic systems is addressed. The underlying systems may be perturbed by unknown time-varying parameters, unstructured uncertainties, and external disturbances. Meanwhile, the time-varying parameters and disturbances are neither required to be periodic nor to have known bounds. Assuming the disturbances are L(2) signals, an adaptive control incorporated with H(∞) control technique is employed to construct a robust adaptive synchronization algorithm. Then, removing such assumption, a novel adaptive-based method is developed to achieve the goal of synchronization. In order to demonstrate the effectiveness of the proposed algorithms, such methods are applied to solve the synchronization problem of uncertain chaotic Chua's circuits.

Robust synchronization of Rossler systems with mismatched time-varying parameters

This paper presents robust synchronization algorithms for the Rossler systems in the presence of unknown time-varying parameters. First, an adaptive synchronization algorithm based on the Lyapunov theory is introduced for identical Rossler systems with mismatched uncertainties. This method does not require a priori information regarding the bound of uncertainties. In addition, this technique is such that the states of the synchronization error system are uniformly ultimately bounded. Since in practice the parameters of the drive and response systems are not necessarily the same, two synchronization approaches are used for the drive and response systems with different parameters. In the first approach, a simple controller is designed for the nominal error system, as if there is no uncertainty in the system. The stability analysis is then investigated as the uncertainties are reintroduced, and it is shown that the size of the uncertainties directly affects the synchronization performance. To deal with this problem, an H∞ controller is designed in which the effects of unknown bounded uncertainties can be attenuated at an appropriate level. It is shown that, using these two approaches, the Rossler systems can be synchronized effectively and the synchronization error is uniformly ultimately bounded. Numerical simulations confirm the effectiveness of the proposed methods.

Real-Time Adaptive Content-Based Synchronization of Multimedia Streams

Traditional synchronization schemes of multimedia applications are based on temporal relationships between inter- and intrastreams. These schemes do not provide good synchronization in the presence of random delay. As a solution, this paper proposes an adaptive content-based synchronization scheme that synchronizes multimedia streams by accounting for content in addition to time. This approach to synchronization is based on the fact that having two streams sampled close in time does not always imply that these streams are close in content. The proposed scheme primary contribution is the synchronization of audio and video streams based on content. The secondary contribution is adapting the frame rate based on content decisions. Testing adaptive content-based and adaptive time-based synchronization algorithms remotely between the American University of Beirut and Michigan State University showed that the proposed method outperforms the traditional synchronization method. Objective and subjective assessment of the received video and audio quality demonstrated that the content-based scheme provides better synchronization and overall quality of multimedia streams. Although demonstrated using a video conference application, the method can be applied to any multimedia streams including nontraditional ones referred to as supermedia like control signals, haptic, and other sensory measurements. In addition, the method can be applied to synchronize more than two streams simultaneously.

Dynamic synchronization of a time-evolving optical network of chaotic oscillators

We present and experimentally demonstrate a technique for achieving and maintaining a global state of identical synchrony of an arbitrary network of chaotic oscillators even when the coupling strengths are unknown and time-varying. At each node an adaptive synchronization algorithm dynamically estimates the current strength of the net coupling signal to that node. We experimentally demonstrate this scheme in a network of three bidirectionally coupled chaotic optoelectronic feedback loops and we present numerical simulations showing its application in larger networks. The stability of the synchronous state for arbitrary coupling topologies is analyzed via a master stability function approach.

Adaptive OFDM synchronization algorithm in frequency selective fading channels

With the development of mobile communication, adaptive algorithms are often chosen in real time process because of their high speed. However, existing adaptive algorithms are not suitable in frequency selective fading channels. In this paper, an improved adaptive synchronization algorithm is proposed for the application under frequency selective fading channels. A novel correlation function is proposed to reduce the effect of intersymbol interference, which only requires coarse channel length estimation. A gate value is also used to combine both the constant and decreasing step size methods; thus, the proposed algorithm is capable of distinguishing between tracking and convergent stages, and then choosing the right step size. Furthermore, an accelerating method is introduced to make the algorithm track faster, i.e. making the algorithm move more steps if it searches in the same direction as the last step. It is shown that the mean square errors of time and frequency offset estimates can be reduced to 0.9243 and 0.003 respectively even when the channel length estimate is not good, which totally satisfies Beek's requirement for synchronization. Simulation also shows that it takes only 10-20 symbols for the proposed algorithm to track the change of channel delay. Compared with the existing adaptive algorithm, the proposed algorithm has a higher accuracy with a higher tracking speed, and the proposed algorithm also has advantages over some nonadaptive algorithms with higher accuracy and lower computational complexity.

Envelope and phase delays correction in an EER radio architecture

This article deals with synchronization in the Envelope Elimination and Restoration (EER) type of transmitter architecture. To illustrate the performances of such solution, we choose to apply this architecture to a 64 carriers 16QAM modulated OFDM. We first introduce the problematic of the realisation of a highly linear transmitter. We then present the Envelope Elimination and Restoration solution and draw attention to its major weakness: a high sensitivity to desynchronization between the phase and envelope signal paths. To address this issue, we propose an adaptive synchronization algorithm relying on a feedback loop, a Least Mean Square formulation and involving an interpolation step. It enables the correction of delay mismatches and tracking of possible variations. We demonstrate that the quality of the interpolator has a direct impact on Error Vector Magnitude (EVM) value and output spectrum. Implementation details are provided along with an analysis of the behaviour and performances of the method. We present Agilent-ADS and Matlab simulation results and then focus on the enhancement of the transmitter performances using the proposed algorithm.

Adaptive dual-model control and synchronization of generalized Hénon chaotic systems

A kind of adaptive dual-model control and synchronization algorithm for generalized Hénon chaotic system was proposed. Chaos attractor of generalized Hénon map is much more complicated than that of Hénon chaotic systems. It is more difficult to control and synchronize. The generalized Hénon chaotic systems under consideration makes the communications system more secure. This algorithm adopts adaptive dual-model control, which realizes the tracking control and synchronization of generalized Hénon chaotic systems, and meanwhile advances the ability of restraining the parameter perturbation and stochastic disturbance. The robustness performance of controlled system is improved. Theoretical analysis and simulation results proved the effectiveness of this method.

Adaptive OFDM synchronization algorithms based on discrete stochastic approximation

This paper presents discrete stochastic approximation algorithms (DSA) for time synchronization in orthogonal frequency division multiplexing (OFDM) systems. It is shown that the discrete stochastic approximation algorithms can be effectively used to achieve a significant reduction in computational complexity compared to brute force maximum-likelihood (ML) methods for OFDM synchronization. The most important property of the proposed algorithms is their recursive self-learning capability-most of the computational effort is spent at the global or a local optimizer of the objective function. The convergence of the algorithms is analyzed. An adaptive version of the discrete stochastic approximation algorithm is also presented for tracking time-varying time delays and frequency offsets in time-selective fading channels. Detailed numerical examples illustrate the performance gains of these DSA-based synchronization algorithms.

Scene Synchronization for Real-Time Interaction in Distributed Mixed Reality and Virtual Reality Environments

Advances in computer networks and rendering systems facilitate the creation of distributed collaborative environments in which the distribution of information at remote locations allows efficient communication. One of the challenges in networked virtual environments is maintaining a consistent view of the shared state in the presence of inevitable network latency and jitter. A consistent view in a shared scene may significantly increase the sense of presence among participants and facilitate their interactivity. The dynamic shared state is directly affected by the frequency of actions applied on the objects in the scene. Mixed Reality (MR) and Virtual Reality (VR) environments contain several types of action producers including human users, a wide range of electronic motion sensors, and haptic devices. In this paper, we propose a novel criterion for categorization of distributed MR/VR systems and present an adaptive synchronization algorithm for distributed MR/VR collaborative environments. In spite of significant network latency, results show that for low levels of update frequencies the dynamic shared state can be kept consistent at multiple remotely located sites.