Synchronous Node Research Articles

Controlled Mobility Time Synchronization for WSNs

One of the important aspects in wireless sensor networks is time synchronization. Many applications such as military activity monitoring, environmental monitoring and forest fire monitoring require highly accurate time synchronization. Time synchronization assures that all the sensor nodes in wireless sensor network have the same clock time. It is not only essential for aforementioned applications but it is mandatory for TDMA scheduling and proper duty cycle coordination. Time synchronization is a challenging problem due to energy constraints. Most of the existing synchronization protocols use fixed nodes for synchronization, but in the proposed synchronization, algorithm mobile nodes are used to synchronize the stationary nodes in the sensing field. In this paper, we propose a new time synchronization algorithm, named controlled mobility time synchronization (CMTS) with the objective to achieve the higher accuracy while synchronizing the nodes. The proposed approach is used in this paper to synchronize the nodes externally by using the mobile nodes. Simulation results exhibit that proposed controlled mobility time synchronization increases the synchronization precision and reduces the energy consumption as well as synchronization error by reducing the collisions and retransmissions.

The Expression of Fibroblast Activation Protein in Clear Cell Renal Cell Carcinomas Is Associated with Synchronous Lymph Node Metastases.

Clear cell renal cell carcinoma (CCRCC) is a heterogeneous and complex disease that frequently develops distant metastases. Fibroblast activation protein (FAP) is a serine peptidase the expression of which in cancer-associated fibroblasts has been associated with higher risk of metastases and poor survival. The objective of this study was to evaluate the role of FAP in metastatic CCRCC (mCCRCC). A series of 59 mCCRCC retrospectively collected was included in the study. Metastases developed either synchronous (n = 14) or metachronous to renal disease (n = 45). Tumor specimens were obtained from both primary lesion (n = 59) and metastases (n = 54) and FAP expression was immunohistochemically analyzed. FAP expression in fibroblasts from primary tumors correlated with FAP expression in the corresponding metastatic lesions. Also, primary and metastatic FAP expression was correlated with large tumor diameter (>7cm), high grade (G3/4), high stage (pT3/4), tumor necrosis and sarcomatoid transformation. The expression of FAP in primary tumors and in their metastases was associated both with synchronous metastases and also with metastases to the lymph nodes. FAP expression in the primary tumor was correlated with worse 10-year overall survival. Immunohistochemical detection of FAP in the stromal tumor fibroblasts could be a biomarker of early lymph node metastatic status and therefore could account for the poor prognosis of FAP positive CCRCC.

Sinusoidal disturbance induced topology identification of Hindmarsh-Rose neural networks

Topology identification of complex networks is an important problem. Existing research shows that the synchronization of network nodes is an obstacle in the identification of network topology. Identification of the structure of the network presents an interesting challenge during the synchronization of complex networks. We developed a new method using the sinusoidal disturbance to identify the topology when the complex network achieves synchronization. Compared with the disturbance of all the nodes, the disturbance of the key nodes alone can achieve a very good effect. Finally, numerical simulation data are provided to validate our hypothesis.

Role of CD15 expression in dysplastic and neoplastic tissue of the bile duct - a potential novel tool for differential diagnosis of indeterminate biliary stricture.

CD15 is expressed by various cancer types; among these are intrahepatic and perihilar cholangiocarcinoma (CCA). The aim of this study was to elucidate CD15 expression in distal CCA as well as in dysplastic biliary tissue and to determine its prognostic significance. Tissue samples from patients with intrahepatic (iCCA, n = 22), perihilar (pCCA, n = 7) and distal CCA (dCCA, n = 15), who underwent surgical resection in the period from 2010 to 2015 were evaluated for CD15 expression. Tissue of synchronous lymph node metastasis (n = 13), CCA-associated dysplasia (n = 20), dysplasia in intraductal biopsies (n = 10) and benign proliferations (n = 12), as well as inflammatory biliary lesions (n = 28) and non-inflammatory bile ducts (n = 23), were evaluated equally for CD15 expression. CD15 was found to be expressed highly in iCCA (81.8%), pCCA (85.7%), dCCA (73.3%), CCA-associated dysplasia (70.0%), dysplasia in intraductal biopsies (100%) and metastatic tissue (84.6%). CD15 expression was negative in 58 of 64 benign bile duct alterations resulting in an overall sensitivity and specificity of CD15 in CCA of 80.7 and 90.6% patients, respectively. CD15 expression was correlated significantly with a decreased overall survival in patients with CD15-positive CCA associated dysplasia (P = 0.003). However, CD15 expression in the invasive tumour component was not correlated with clinical outcome. CD15 is a sensitive and specific marker for intraepithelial and invasive neoplasias of the bile duct. Therefore, it can be helpful in the delineation of dysplastic and neoplastic biliary cells from non-neoplastic tissue, which frequently causes a diagnostic problem in indeterminate biliary stricture.

A dynamical framework to relate perceptual variability with multisensory information processing.

Multisensory processing involves participation of individual sensory streams, e.g., vision, audition to facilitate perception of environmental stimuli. An experimental realization of the underlying complexity is captured by the “McGurk-effect”- incongruent auditory and visual vocalization stimuli eliciting perception of illusory speech sounds. Further studies have established that time-delay between onset of auditory and visual signals (AV lag) and perturbations in the unisensory streams are key variables that modulate perception. However, as of now only few quantitative theoretical frameworks have been proposed to understand the interplay among these psychophysical variables or the neural systems level interactions that govern perceptual variability. Here, we propose a dynamic systems model consisting of the basic ingredients of any multisensory processing, two unisensory and one multisensory sub-system (nodes) as reported by several researchers. The nodes are connected such that biophysically inspired coupling parameters and time delays become key parameters of this network. We observed that zero AV lag results in maximum synchronization of constituent nodes and the degree of synchronization decreases when we have non-zero lags. The attractor states of this network can thus be interpreted as the facilitator for stabilizing specific perceptual experience. Thereby, the dynamic model presents a quantitative framework for understanding multisensory information processing.

Multi Hop Time Synchronization Protocol for Wireless Ad-Hoc Sensor Networks

Flexible and robust time synchronization ensures effective collaboration of nodes in wireless sensor networks leading to accurate prediction of real world events in the vicinity of these networks. Amongst the confluence of factors that makes difficult the time synchronization in these networks, network dynamics while maintaining energy efficiency is a critical issue required to be addressed by existing protocols defined for time synchronization. This paper presents a sender-receiver based multihop time synchronization protocol that is energy efficient and ensures node synchronization in the network, in case of root or leader node failure. In hierarchical tree based time synchronization protocols, the root node starts and governs the synchronization process. These protocols construct tree only once at the time of network deployment and the root nodes are identified during this phase. Subsequently, the nodes in the entire network get synchronized by these root nodes. The synchronization of nodes is affected if any root node gets disconnected or turns off in the network. The proposed protocol mitigates this drawback of existing popular tree based hierarchical protocols. Moreover, the overall consumption of energy of the protocol proposed in this paper is also reduced as it involves a lower number of messages required for synchronizing multihop networks as compared to other energy efficient protocols.

Soft Computing Based Fine Tuning and Clock Synchronization in Wireless Sensor Networks

In this paper, we focus on the various aspects related to synchronization in wireless sensor networks, their features and how to increase the lifetime of the sensor and network nodes. The focus is about clock synchronization, delay measurement in time synchronization and fine grained network time synchronization. The recent advancements in the sensor technology has led to the miniaturization of the sensors and its related components, and similarly reduced the cost to a larger extent. This enabled an active rise in the research of large scale networks of sensors. The synchronization of sensor nodes is critical to its effective operation especially the time synchronization, for the data fusion, duty cycling and so on. Most of the algorithms for synchronization that were proposed recently do the same work. The server periodically sends a piece of information or message that contains the current value of clock to the client. This happens in case of time synchronization of the sensor nodes. The proper definition for sensor networks comes as follows. It is a special type of ad-hoc network, in which the nodes, also referred to ass wireless devices get together and the form a network without any need for underlying infrastructure spontaneously. They can cooperate only by forwarding packets to each other since there are no routers in an environment without any infrastructure. When the environment is distributed in nature, then more complex is the scenario. But time synchronization is an important component of such distributed environments. It aims to provide a common time for the local clocks in their network (Sivrikaya and Yener in IEEE Netw 18(4):45---50, 2004). For applications of networking protocols, at any particular instant, there should be a common view of the clock in the network.

Superposition network coded cooperation for wireless networks

AbstractCooperative diversity is an innovative approach to improve the reliability of communication. Although this technique is considered in the next‐generation mobile communication standards, it has its own challenges in practice. For example, in simultaneous transmission‐based cooperative protocols, perfect synchronisation of nodes is very hard to realise. The traditional time division multiple access method can simplify the synchronisation problems but leads to long transmission delays. In this paper, a low‐delay cooperative strategy is proposed for a network with multiple sources and a single destination, which requires only a simple type of synchronisation. In this technique, we use a combination of superposition coding and network coding; hence the name superposition network coded cooperation. For this strategy, good bounds are obtained for the probability of correct detection for general M‐PSK and M‐QAM modulation and are compared with simulation results. The results demonstrate improvement in error performance compared with other transmission schemes requiring the same transmission time as superposition network coded cooperation. Copyright © 2016 John Wiley & Sons, Ltd.

Emergence and coherence of oscillations in star networks of stochastic excitable elements.

We study the emergence and coherence of stochastic oscillations in star networks of excitable elements in which peripheral nodes receive independent random inputs. A biophysical model of a distal branch of sensory neuron in which peripheral nodes of Ranvier are coupled to a central node by myelinated cable segments is used along with a generic model of networked stochastic active rotators. We show that coherent oscillations can emerge due to stochastic synchronization of peripheral nodes and that the degree of coherence can be maximized by tuning the coupling strength and the size of the network. Analytical results are obtained for the strong-coupling regime of the active rotator network. In particular, we show that in the strong-coupling regime, the network dynamics can be described by an effective single active rotator with rescaled parameters and noise.

Adaptive finite-time synchronization of a class of pinned and adjustable complex networks

This paper is concerned with the finite-time asymptotic synchronization problem of a class of dynamical complex networks with adjustable couplings. Pinning controllers are developed to guarantee that synchronization errors of pinned nodes converge to zero within finite-time. The effects of couplings in networks are further studied, and adaptive schemes for adjusting coupled strength are provided to ensure the finite-time synchronization of unpinned nodes. Through the Lyapunov function and adaptive schemes, some results indicating that control strategies and coupling adjustment laws can guarantee the asymptotic synchronization of pinned and unpinned nodes within finite-time respectively, are obtained. Simulation results are given to verify the effectiveness of the proposed method.

Underwater Acoustic Modems (S2CR Series) for Synchronization of Underwater Acoustic Network Clocks During Payload Data Exchange

Modern underwater acoustic modems, in addition to receiving and transmitting data, can measure signal propagation time and evaluate the distance between the transmitter and the receiver. These capabilities can be exploited to support the synchronization of underwater acoustic sensor networks, where sensing and actuation must be coordinated across multiple nodes. However, the problem of accurate propagation time measurement, especially in highly reverberant environments, and the evaluation of clock skew on acoustically interacting modems have been investigated rather poorly. In this paper, therefore, we conduct an experimental evaluation of stability/precision of propagation time measurements considering underwater acoustic modems communicating in reverberant environments. We also show how modem built-in tools can provide opportunities for precise estimation of the modems clock skews. Additionally, we demonstrate that payload data exchange can be used as a “comfortable” way for clock synchronization of underwater acoustic networks nodes. At-sea experiments have been carried out considering several modem pairs and node positions in conditions of reverberant underwater acoustic channels. These experiments have been conducted in collaboration with the NATO Centre for Maritime Research and Experimentation (CMRE, La Spezia, Italy) that we gratefully acknowledge.

A Type of Energy Hole Avoiding Method Based on Synchronization of Nodes in Adjacent Annuluses for Sensor Network

For the purpose of balancing energy consumption of nodes in Wireless Sensor Networks (WSNs for short), a type of energy hole avoiding method based on synchronization of nodes in adjacent annuluses (SNAA for short) is proposed in this paper. The circular network is divided into virtual annuluses with the same width. Nodes are deployed nonuniformly and their number increases in geometric progression from the outer annuluses to the inner ones which could effectively reduce the work load on nodes near the center. Moreover, each node could find its optimal parent by considering the residual energy of each candidate as well as the distance between the two nodes in adjacent annuluses. And on the basis of synchronization of nodes between adjacent annuluses during their transmitting and receiving phases, a sleep scheduling strategy is also proposed to further reduce the energy consumption of nodes in idle listening mode. Simulation results show that SNAA has a superior performance on energy consumption balance compared to the algorithm proposed (Liu et al., 2013; Wu et al., 2008) and it could also mitigate the energy hole problem in WSNs.

Energy-Efficient Hybrid CCC-Based MAC Protocol for Cognitive Radio Ad Hoc Networks

Transmitter power consumption and application throughput in cognitive radio-medium access control (CR-MAC) protocol has direct impact on control message overhead and common control channel (CCC). Hence, the design of CCC in CR-MAC plays a pivotal role in selecting an energy-efficient channel path for enhanced throughput. State-of-the-art CR-MAC protocols design CCC in in-band or out-of-band overlay spectrum bands. With in-band, imperfect node synchronization due to per-hop and group CCC coverage leads to multichannel hidden terminal and longer network access delays. Global coverage with dedicated out-of-band CCC is subject to saturation and intruder attacks, which results in single point of network failure and increased power consumption. To overcome existing problems, an energy-efficient hybrid CCC based CR-MAC protocol with omnidirectional control and directional data transmission is proposed to reduce power consumption due to link access overhead, multichannel hidden terminal, deafness, and spectrum mobility. In this paper, antenna index numbers through Global Positioning System and angle-of-arrival estimation are used for directional data transmission, whereas hybrid CCC is used to avoid interference due to multichannel hidden terminals. Experimental results reveal that the proposed hybrid CCC-MAC with directional antennas has increased network throughput and reduced transmit power consumption when compared with existing in/out-of-band omnidirectional CCC-based CR-MAC protocols.

Macroscopic morphology for estimation of malignant potential in pancreatic neuroendocrine neoplasm

Pancreatic neuroendocrine neoplasm (Pan-NEN) representing approximately 1.3% of pancreatic malignancy cases in incidence has been a so rare disease that it remains major problem to analyze the malignant potential. The aim of this study was to verify whether the macroscopic morphology of Pan-NEN, a novel pathological classification, contributes to malignant potential. From a total of 86 patients with Pan-NEN, 41 surgical sections obtained from the primary site were classified by their morphology into a simple nodular (SN) group and a non-SN group. The non-SN group was further divided into three subtypes: simple nodular with extranodular growth (SNEG), confluent multinodular (CM), and infiltrative (IF). The clinicopathological features of the SN and the non-SN groups were retrospectively compared. Overall 5-year survival rates with and without surgical resection were 94 and 48%, respectively. SN and non-SN types were identified in 21 and 20 patients, respectively. The non-SN group comprised 14 SNEG type, 2 CM type, and 4 IF type. Synchronous lymph node metastases (p=0.009), synchronous liver metastases (p=0.048), microinvasion to an adjacent organ (p<0.001), vascular invasion (p=0.023), and neural invasion (p=0.019) were more significant in the non-SN group than in the SN group. As judged by WHO 2004 classification and TNM stages (AJCC and ENETS), non-SN type showed malignant trend (p<0.05). Moreover, overall 5-year survival rates of SN and non-SN groups were 100 and 84.4%, respectively (p=0.048). Non-SN tumors may have higher malignant potential than SN tumors.

Abstract P2-12-15: The role of neck dissection in breast cancer patients with synchronous and metachronous ipsilateral supraclavicular lymph node metastasis

Abstract Purpose: To evaluate the effect of neck dissection in breast cancer patients who present with ipsilateral supraclavicular lymphnode metastasis (ISLM) without distant metastasis and to reveal the outcomes of neck dissection in different molecular subtypes. Methods: A total of 90 patients with synchronous ISLM and 36 patients with metachronous ISLM without distant metastasis between 2000 and 2009 were retrospectively analyzed. Combined-modality treatments were performed, and patients were respectively divided into two parts according to whether they received neck dissection or not. Results: In the synchronous ISLM group, there was no significant difference between the neck dissection and non-dissection group with respect to age, menstrual status, tumour size, and histological type, PR and HER2 status. Patients with negative ER status and a higher number of positive axillary nodes were more common in the neck dissection group. The five-year locoregional relapse free survival (LRFS) was 63.6% in the neck dissection group VS. 48.9% in the non-dissection group, respectively (P=0.359). The 5-year distant metastasis free survival (DMFS) was 37.3% in the neck dissection group VS. 38.5% in the non-dissection group, respectively (P=0.882). Further analyses were performed by the site of metastases. Results showed that the incidence of bone metastasis was lower in neck dissection patients (14.7% vs. 28.6%, P=0.132). Due to the limited amount of patients, subgroup analysis was just performed in the subtypes with negative ER status, negative PR status and negative HER2 status, respectively. The five-year LRFS of patients receiving neck dissection in the subtypes with negative ER status, negative PR status and negative HER2 status was 63.7%, 59.8%and 61.2%, which was much better than their matched non-dissection group, respectively. However, the difference was not statistically significant. The 5-year overall survival (OS) was similar between the neck dissection and non-dissection group in the subtypes of negative ER status and negative PR status, respectively. However, the 5-year OS of HER2 negative subtype significantly decreased in the neck dissection group (37.2% vs. 65.4%, P=0.032). Besides, it's worth mentioning that in the HER2 positive subtype, the mean time to relapse, metastasis and death was shorter in the neck dissection subgroup compared with the non-dissection subgroup. In the metachronous ISLM group, a trend of better regional control, with similar PFS and OS, was achieved in the neck dissection group. Discussion: Neck dissection is an effective approach to improve the regional control for the patients with ISLM, especially for the subtypes with negative ER status, negative PR status and probably positive HER2 status in the synchronous ISLM. But, it might not be comfortable for the patients with negative HER2 status, because of the unfavorable effect on its overall survival. In addition, neck dissection, with better regional control, might be helpful for the control of bone metastasis, which is beneficial for long term survival. Citation Format: Xiao C, Qi X, Chen A, Zhang W, Zhang P, Cao X. The role of neck dissection in breast cancer patients with synchronous and metachronous ipsilateral supraclavicular lymph node metastasis. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-12-15.

Linear Estimation of Clock Frequency Offset for Time Synchronization Based on Overhearing in Wireless Sensor Networks

The overhearing mechanism in time synchronization has been an active research area for wireless sensor networks (WSNs), for it can save a significant amount of energy by exploiting the wireless medium broadcast property. Recently, based on acknowledgment (ACK) mechanism, a synchronization scheme has been proposed for practical WSNs that the timestamps can be directly inserted into the data frame and the corresponding ACK, instead of dedicated synchronization packet. Consequently, the overhead of time synchronization could be further reduced. Motivated by this, in this letter, we analyze the synchronization of inactive nodes overhearing the pairwise synchronization on the basis of ACK mechanism, and present a linear estimation algorithm of clock frequency offset with the nodes’ clock adjusted at every synchronization. Furthermore, assuming Gaussian delays, the linear estimation for frequency offset and the corresponding Cramer–Rao lower bound are derived. Simulation results verify that the estimator is efficient.

An Efficient TDMA MAC Protocol for Multi-hop WiFi-Based Long Distance Networks

Multi-hop WiFi-based long distance (WiLD) network is considered to be a cost-effective solution for extending Internet to rural underserved areas. In such gateway-based mesh architecture, interference-free scheduling of transmission is critical in optimizing overall network performance. In this paper, we propose an efficient TDMA-based MAC protocol for gateway-based multi-hop WiLD networks for enhancing end-to-end throughput and delay performances. The possibility of collision which exists in token-based MAC protocols has been reduced significantly by employing inherent node synchronization mechanism. The proposed protocol enhances network performance by utilizing the available bandwidth through maximization of TDMA slots overlapping. It shows clear improvement over relevant MAC protocols in terms of saturation throughput as well as average end-to-end packet delay over multiple hops.

Joint Time Synchronization and Localization of Multiple Source Nodes in Wireless Sensor Networks

Time synchronisation and localisation should be jointly conducted for time-based source location estimates in an asynchronous network. In this paper semidefinite programming (SDP), complexity-reduced SDP and linear least square (LLS) estimator are proposed for time synchronisation and localisation of multiple source nodes. The proposed algorithms provide joint estimates for the source locations and clock parameters and avoid the shortcoming of maximum likelihood (ML) estimator that requires an initial solution. Then, a location refinement (LR) technique is designed to improve the accuracy performance of the estimated parameters. The simulations show that the original SDP algorithm provides better accuracy performance than the complexity-reduced SDP. However, the complexity-reduced SDP runs faster than the original SDP. Although the complexity of LLS estimator is lowest among three proposed algorithms, the convex optimisation algorithms, including the original SDP and complexity-reduced SDP, have more robust performance compared with the LLS estimator.

Memory-induced mechanism for self-sustaining activity in networks.

We study a mechanism of activity sustaining on networks inspired by a well-known model of neuronal dynamics. Our primary focus is the emergence of self-sustaining collective activity patterns, where no single node can stay active by itself, but the activity provided initially is sustained within the collective of interacting agents. In contrast to existing models of self-sustaining activity that are caused by (long) loops present in the network, here we focus on treelike structures and examine activation mechanisms that are due to temporal memory of the nodes. This approach is motivated by applications in social media, where long network loops are rare or absent. Our results suggest that under a weak behavioral noise, the nodes robustly split into several clusters, with partial synchronization of nodes within each cluster. We also study the randomly weighted version of the models where the nodes are allowed to change their connection strength (this can model attention redistribution) and show that it does facilitate the self-sustained activity.

Graph theoretical comparison of functional connectivity between cLTP treated and untreated microelectrode arrays

Analyzing graph properties of neural networks has recently gained much attention in attempts to understand how information is processed in the brain. Using in-vitro techniques to form neural networks has increased in popularity as it allows one to develop small, easy to record networks that maintain many of the graph properties of larger brain networks [1]. One widely recognized tool for studying in vitro networks is the Microelectrode Array (MEAs) on which neurons can be cultured and recorded simultaneously. MEAs can be used to grow neural networks from disassociated cells to understand how neurons spontaneously connect to create networks and how these networks then evolve over time. In addition, these cultures can be treated with pharmacological agents to study how these agents affect the networks as a whole [2,3]. To understand the network formation of MEA cultured neurons, we study the graph theoretical properties of two MEAs networks, the control MEA network and the MEA network treated with chemical Long Term Potentiation (cLTP). The data sets for each MEA network consists of recording from three days: baseline, 2 days past baseline and 5 days past baseline. Based on these data sets and the assumption that each electrode on the MEA records one neuron, we construct functional connectivity graphs of MEA networks for different days. Nodes in such a connectivity graph represent the electrodes (also neurons). To determine whether there is a connection (an edge on the graph) between two nodes, we carry out several steps of computations. We first filter the recorded spike trains with a Gaussian kernel, and perform cross-correlation analysis using the Pearson product moment correlation coefficient [4]. We set a correlation threshold by applying a shuffling method to the inter-spike intervals of a spike train. Using thresholded correlations, unweighted, undirected adjacency matrices, we create corresponding graphs for untreated (not shown) and treated MEA networks (shown baseline and 5 days past baseline in Figure 1). We find that the synchronization and average node degree increase dramatically for the cLTP treated networks while the untreated network shows no obvious change. Figure 1 Graph models. (a) cLTP treated MEA network at baseline; (b) cLTP treated MEA network at 5 days past baseline. To better understand the treated and untreated MEA network, we will evaluate the graph theoretic properties, such as degree distribution and clustering coefficient. We will determine how cLTP affects these properties. The graphical analysis will enable us to identify what type of network each is (such as a small-world or a scale free network) and determine whether cLTP has an effect on the network development or merely on the strength of connectivity. We conjecture that cLTP treated networks have more efficient and quicker communication between nodes. Therefore, the cLTP treated networks show greater clustering as well as shorter path length than the untreated networks. Information flow is another important aspect of such graph model. We intend to develop directed graphs using transfer entropy to study how information flow of the network may change during its development.