Hierarchical Synchronization Research Articles

A Global Clock Skew Estimation Scheme for Hierarchical Wireless Sensor Networks

Time synchronization is extremely important for wireless sensor networks (WSNs). For large-scale WSNs, hierarchical clock synchronization, which can effectively save energy by reducing communication overhead, has become an attractive approach in practical networks. Based on the hierarchical network, in this paper, we present a global clock skew estimation scheme with immediate clock adjustment. The maximum likelihood estimator and corresponding Cramer–Rao lower bound of the clock skew are derived under the Gaussian delay model, and the simulation results verify that the proposed method is efficient.

Dissipative and Autonomous Square‐Wave Self‐Oscillation of a Macroscopic Hybrid Self‐Assembly under Continuous Light Irradiation

AbstractBuilding a bottom‐up supramolecular system to perform continuously autonomous motions will pave the way for the next generation of biomimetic mechanical systems. In biological systems, hierarchical molecular synchronization underlies the generation of spatio‐temporal patterns with dissipative structures. However, it remains difficult to build such self‐organized working objects via artificial techniques. Herein, we show the first example of a square‐wave limit‐cycle self‐oscillatory motion of a noncovalent assembly of oleic acid and an azobenzene derivative. The assembly steadily flips under continuous blue‐light irradiation. Mechanical self‐oscillation is established by successively alternating photoisomerization processes and multi‐stable phase transitions. These results offer a fundamental strategy for creating a supramolecular motor that works progressively under the operation of molecule‐based machines.

Dissipative and Autonomous Square-Wave Self-Oscillation of a Macroscopic Hybrid Self-Assembly under Continuous Light Irradiation.

Building a bottom-up supramolecular system to perform continuously autonomous motions will pave the way for the next generation of biomimetic mechanical systems. In biological systems, hierarchical molecular synchronization underlies the generation of spatio-temporal patterns with dissipative structures. However, it remains difficult to build such self-organized working objects via artificial techniques. Herein, we show the first example of a square-wave limit-cycle self-oscillatory motion of a noncovalent assembly of oleic acid and an azobenzene derivative. The assembly steadily flips under continuous blue-light irradiation. Mechanical self-oscillation is established by successively alternating photoisomerization processes and multi-stable phase transitions. These results offer a fundamental strategy for creating a supramolecular motor that works progressively under the operation of molecule-based machines.

Frustrated hierarchical synchronization and emergent complexity in the human connectome network.

The spontaneous emergence of coherent behavior through synchronization plays a key role in neural function, and its anomalies often lie at the basis of pathologies. Here we employ a parsimonious (mesoscopic) approach to study analytically and computationally the synchronization (Kuramoto) dynamics on the actual human-brain connectome network. We elucidate the existence of a so-far-uncovered intermediate phase, placed between the standard synchronous and asynchronous phases, i.e. between order and disorder. This novel phase stems from the hierarchical modular organization of the connectome. Where one would expect a hierarchical synchronization process, we show that the interplay between structural bottlenecks and quenched intrinsic frequency heterogeneities at many different scales, gives rise to frustrated synchronization, metastability, and chimera-like states, resulting in a very rich and complex phenomenology. We uncover the origin of the dynamic freezing behind these features by using spectral graph theory and discuss how the emerging complex synchronization patterns relate to the need for the brain to access –in a robust though flexible way– a large variety of functional attractors and dynamical repertoires without ad hoc fine-tuning to a critical point.

STAR 망 TDMA시스템의 계층적 망동기 방식

In this paper, we propose the hierarchical network synchronization scheme that is backward compatible for the existing commercial system, efficient for total system performance, and whose hardware modification is minimized. This system performance is, the relationship among bandwidth efficiency, complexity and MODEM performance, and superiority of network system applicability. The proposed structure can remedy the high hardware complexity and the lower ∙제1저자 : 윤주현 ∙투고일 : 2013. 10. 30, 심사일 : 2013. 11. 19, 게재확정일 : 2013. 12. 24. * 인하대학교 전자공학과(Dept. of Electronics Engineering, Inha University) * 과학기술연합대학원대학교 디지털방송공학부(Digital Broadcast Engineering, University of Science and Technology) * 삼성탈레스(주)(Samsung Thales) 78 Journal of The Korea Society of Computer and Information January 2014 accuracy of network sychronization that the existing satellite communication terminal system in the star network based on TDM/MF-TDMA of DVB-S2/RCS standards has. Besides, It has high efficiency in view of cost and system performance if the system designed for satellite broadcast requires system upgrade. In the body section, its hardware complexity and system performance of the proposed algorithm is analysed theoretically and treated with the related parameters(symbol rate, spreading factor, etc.) and the BER performance of control channel through the computer simulation for its verification that it can be applied for communications system. ▸

Cluster-based and energy-efficient hierarchical time synchronization algorithm for multi-hop wireless sensor network

Concerning the problem that typical time synchronous algorithms used in multi-hop Wireless Sensor Network(WSN) mainly focus on increasing the network synchronization precision,but ignore such issues as the network energy,path hop and error accumulation,a cluster-based and energy-efficient hierarchical time synchronization algorithm was proposed based on a cluster hierarchical network structure.In this algorithm,a cluster node was selected to take a two-way synchronization with the cluster head,and its neighbor nodes achieved bidirectional synchronization indirectly through the passive monitoring mode.In such a way,the number of the packet's transmission was reduced while the digital signature pattern ensured the safety of transmission.In addition,the cycle update coefficient of synchronous group delay was quoted to further reduce the consumption of synchronization packets.The simulation results show that the algorithm reduces the energy consumption and prolongs the network life time,therefore this algorithm has certain practicability.

Effects of frequency-degree correlation on synchronization transition in scale-free networks

Explosive synchronization in the scale-free network with a positive frequency-degree correlation has been reported recently (Gomez G. J. et al., Phys. Rev. Lett., 106 (2011) 128701). In this article, we generalize this study and find that the explosive synchronization is replaced by a kind of hierarchical synchronization if the microscopic correlation between the frequency and the interacting topology of the network becomes negative. A star network model is set to prove this novel behavior. We also find that the degree assortativity has significant influence on the explosive synchronization but slight impact on the hierarchical synchronization. These findings are meaningful for revealing unusual effects of correlations between dynamics and structure of complex networks.

Time synchronization algorithm of wireless sensor networks based on data aggregation tree

Time synchronization is a critical technique of wireless sensor networks (WSNs). Aimed at the disadvantages of hierarchical time synchronization algorithm, this paper proposes an improved algorithm used for WSNs based on data aggregation tree. Based on collection and selection principles of multiple time data point tuples, the relative time drift and phase offset of the node are calculated through linear programming method, and time synchronization is achieved eventually during the establishment of data aggregation tree. Performance analysis and simulation results prove that, compared with the existing time synchronization algorithms, the proposed algorithm can reduce the energy cost of nodes and shorten the time of synchronization effectively.

Cell Search Time Comparison Using Hierarchical and Non-hierarchical Synchronization Channels in OFDM Based Evolved UTRA Downlink

This paper presents a comparison of hierarchical and non-hierarchical synchronization channel (SCH) structures in terms of the initial cell search time and neighboring cell search time in order to establish the optimum SCH structure in the Evolved UTRA downlink. Computer simulation results show that in a 19-cell configuration, the cell search time at 90% in the cumulative distribution function (CDF) using the hierarchical SCH structure is less than half that using the non-hierarchical SCH structure in a neighboring cell search under low signal-to-interference plus noise power ratio (SINR) conditions, although both structures achieve almost the same cell search time in the initial cell search. This is due to the cross-correlation based SCH symbol timing detection in the hierarchical SCH structure, which is affected less by noise than the auto-correlation based detection in the non-hierarchical SCH structure. Thus, we conclude that the hierarchical SCH structure is superior to the non-hierarchical SCH structure based on the cell search time performance especially in the neighboring cell search.

Multi-cell communications for OFDM-based asynchronous networks over multi-cell environments

This paper investigates a multi-cell communication technique for OFDM (Orthogonal Frequency Division Multiplexing)-based asynchronous networks without the use of a GPS (Global Positioning System). First, a downlink macro-diversity technique using bandwidth division allocation is presented, where each MS (Mobile Station) simultaneously receives control information from surrounding BSs (Base Stations) using an FFT (Fast Fourier Transform) module. Second, a hierarchical master-slave synchronization technique is introduced for plug & access network synchronization. Finally, an adaptive guard carrier allocation scheme is proposed to reduce the effect of MAI (Multiple Access Interference) for users receiving multiple transmission signals from surrounding BSs. In a simulation, the proposed technique is well designed to achieve SSDT (Site Selection Diversity Transmission) and adaptive synchronization for OFDM-based networks. It is particularly noteworthy that this adaptive sub-carrier allocation is very effective in reducing MAI for plug and access network synchronization.

AADL modeling and analysis of hierarchical schedulers

A system based on a hierarchical scheduler is a system in which the processor is shared between several collaborative schedulers. Such schedulers exist since 1960 and they are becoming more and more investigated and proposed in real-life applications. For example, the ARINC 653 international standard which defines an Ada interface for avionic real time operating systems provides such a kind of collaborative schedulers. This article focuses on the modeling and the performance analysis of hierarchical schedulers. We investigate the modeling of hierarchical schedulers with AADL. Hierarchical scheduler timing and synchronization relationships are expressed with a domain specific language based on timed automata: the Cheddar language. With the meta CASE tool Platypus, we generate Ada packages implementing the Cheddar language. These Ada packages are part of Cheddar, a real time scheduling simulator. With these Ada packages, Cheddar is able to perform analysis by scheduling simulation of AADL systems composed of hierarchical schedulers. An AADL model of the ARINC 653 hierarchical scheduling is described as an illustration.

Structure–function relationship in complex brain networks expressed by hierarchical synchronization

The brain is one of the most complex systems in nature, with a structured complex connectivity. Recently, large-scale corticocortical connectivities, both structural and functional, have received a great deal of research attention, especially using the approach of complex network analysis. Understanding the relationship between structural and functional connectivity is of crucial importance in neuroscience. Here we try to illuminate this relationship by studying synchronization dynamics in a realistic anatomical network of cat cortical connectivity. We model the nodes (cortical areas) by a neural mass model (population model) or by a subnetwork of interacting excitable neurons (multilevel model). We show that if the dynamics is characterized by well-defined oscillations (neural mass model and subnetworks with strong couplings), the synchronization patterns are mainly determined by the node intensity (total input strengths of a node) and the detailed network topology is rather irrelevant. On the other hand, the multilevel model with weak couplings displays more irregular, biologically plausible dynamics, and the synchronization patterns reveal a hierarchical cluster organization in the network structure. The relationship between structural and functional connectivity at different levels of synchronization is explored. Thus, the study of synchronization in a multilevel complex network model of cortex can provide insights into the relationship between network topology and functional organization of complex brain networks.

A Radio Synchronization Technique for Asynchronous Broadband Networks

A radio synchronization technique that dispenses with GPS (Global Positioning System) for OFDM (Orthogonal Frequency Division Multiplexing)-based broadband networks is described. UMTS (Universal Mobile Telecommunications System) employs three main mechanisms, a node, transport channel and radio interface synchronization. The RNC (Radio Network Controller) is used as a key network component for the centralized synchronization mechanism. Here, we explore a more accurate and simpler asynchronous technique for broadband networks from the perspective of a distributed manner, where MSs (Mobile Stations) play an important role in timing adjustment. Propagation delay and the hierarchical synchronization mechanism are taken into account in the mathematical analysis.

Hierarchical synchronization in complex networks with heterogeneous degrees

We study synchronization behavior in networks of coupled chaotic oscillators with heterogeneous connection degrees. Our focus is on regimes away from the complete synchronization state, when the coupling is not strong enough, when the oscillators are under the influence of noise or when the oscillators are nonidentical. We have found a hierarchical organization of the synchronization behavior with respect to the collective dynamics of the network. Oscillators with more connections (hubs) are synchronized more closely by the collective dynamics and constitute the dynamical core of the network. The numerical observation of this hierarchical synchronization is supported with an analysis based on a mean field approximation and the master stability function.

A hierarchical synchronization technique based on the EREC for robust transmission of H.263 bit stream

We propose an error-resilient transmission technique for the H.263 compatible video data stream, based on the data-partitioning technique. The proposed algorithm employs the bit rearrangement technique of the error-resilience entropy coding in each layer, providing unequal error protection against the channel errors, without requiring additional side information. In addition, we propose the recovery algorithm for the lost or erroneous motion vectors. The proposed algorithm is implemented, based on the H.263 standard, and evaluated through intensive computer simulation. The experimental results demonstrate that the proposed algorithm provides acceptable performance both subjectively and objectively at various bit error rates and burst lengths.

Human islet isolation using a new enzyme blend

In this article, a novel robust compression-encryption of images based on Set partitioning in Hierarchical Trees (SPIHT) coding-decoding algorithm and synchronization of chaotic maps with non-integer order is proposed. The essential innovation in the proposed communication system is that the source image is compressed and encrypted by several secret keys. The developed transmission scheme is designed to take profit of two advantages. The first is the use of standard SPIHT coding which is an efficient and computationally very fast technique for image compression. The second is to introduce farther complexity to the cryptosystem through the use of fractional-order chaotic maps which has many advantages such as the generation of supplementary secret keys with respect to the discrete-time chaotic systems. From the obtained simulation results, we can see that the original image has been well encoded in the cipher text and retrieved with success through the chaotic signals. Further, to verify the high confidentiality of the presented cryptosystem, cryptanalysis is studied in detail through the various tests.

A new multimedia synchronization model

The paper presents a hierarchical synchronization model for the description of the time relations and regimes necessary for the presentation of multimedia or animated data which have either natural or implied time dependencies. The model generalizes some previous multimedia synchronization models by unifying time and event based synchronization concepts and offering a consistent framework in which to handle dynamic media presentation functionality.

Hierarchical algorithms and architectures for parallel scientific computing

There has been a recent emergence of many interesting and highly efficient hierarchical (multilevel) algorithms (e.g. multigrid, domain decomposition, wavelets, multilevel preconditioning, the fast multipole algorithms, etc.) for solving numerical problems in scientific computing. These algorithms derive their efficiency from using a hierarchical approach to capture the sharing of global information which is inherent in the physical processes being modelled. In addition to being computationally efficient, these algorithms also possess relatively high degrees of parallelism. I therefore argue that the architectures of parallel computers (especially massively parallel ones) should be designed to support hierarchical communication and synchronization needs of these algorithms. Hierarchical architectures are also more universal because they go beyond supporting a particular class of algorithms to supporting the underlying physical processes being modelled. Finally, I propose that algorithm designers take a critical look at traditional kernel algorithms and re-examine their cost-effectiveness in a massively parallel computing environment.