Silent Node Research Articles

Timestamp-Free Clock Parameters Tracking Using Extended Kalman Filtering in Wireless Sensor Networks

Clock synchronization is crucial for applications in wireless sensor networks, such as event scheduling and data fusion. In practical wireless networks, environmental changes cause the oscillator to be imperfect. Thus, it is necessary to track the nonlinear varying clock dynamically. In this paper, we propose a timestamp-free clock skew (frequency difference) and offset (time difference) joint tracking algorithm based on extended Kalman filter (EKF), which can be embedded into the general network data flow to achieve long-term synchronization without additional communication overhead. To further improve energy efficiency of clock synchronization, this paper develops an EKF clock skew tracking algorithm for silent nodes in receiver-only synchronization. For the situation that silent node overhears synchronization information from multiple active nodes, we present multi-information timestamp-free synchronization and multi-observation clock skew fusion scheme for silent nodes. Simulation results show the effectiveness of the proposed tracking algorithms.

Receiver-Only-Based Time Synchronization Under Exponential Delays in Underwater Wireless Sensor Networks

In this article, we consider the receiver-only-based time synchronization in underwater wireless sensor networks with exponential delays emerging during the message exchanges. This article is motivated by the fact that 25% of timing messages are discarded in the existing receiver-only-synchronization (ROS)-based schemes to cope with the interaction between the discontinuity of the likelihood function and the unknown clock skews, which would result in a massive waste of energy. To account for this issue, a general ROS model under the exponential delay assumption, with clock skews taken into consideration and all timing messages utilized, is introduced. Following the proposed ROS model, we develop a three-step method to jointly estimate clock offsets and skews of both active and silent nodes, as well as other unknown parameters. Specifically, an estimation on clock offset and skew for the active node using support vector machine is followed by a joint maximum-likelihood estimation of the clock skew and clock offset for the silent node as well as clock offset for the active node, and a minimum variance unbiased estimation of the offsets for both active and silent nodes. Such method further improves the estimation accuracy of the proposed ROS model. The effectiveness and robustness of the proposed method is verified by simulations results.

Clock Skew Estimation for Timestamp-Free Synchronization in Industrial Wireless Sensor Networks

Existing packet-based synchronization approaches take extensive energy for industrial wireless sensor networks due to substantial timing message exchanges. Combined with acknowledgement (ACK), this article proposes an energy-efficient synchronization protocol without exchanging timestamps. Also, a mapping rule of ACK response time is presented for the joint estimation of skew and fixed delay without requiring a following response in each cycle, so that estimation can be implemented in parallel to data transmission. Then, the timestamp-free synchronization technique is extended to the receiver-only synchronization scenario to further reduce communication overhead. Assuming Gaussian variable delays, the maximum likelihood estimators and corresponding lower bounds for slave node and silent node are developed, as well as a low-complexity estimator for silent node. In addition, considering the dynamics of clock, a timestamp-free clock skew tracking algorithm using Kalman filtering is developed. Simulation results validate the efficiency of the proposed estimators.

Excitable Nodes on Random Graphs: Relating Dynamics to Network Structure

Rhythmic activity in complex systems is generated and sustained through interactions among the constituent units. In this paper we study the interplay between topology and dynamics of excitable nodes on random networks. The nodal dynamics are discrete, each node being in three possible states: active, refractory, or silent. Loading rules are defined whereby a subset of active nodes may be able to convert a silent node into an active one at the next time step. In the case of simple loading ($SL$) a silent node becomes active if it receives input from any neighbor. In the majority rules ($MR$) loading, a silent node fires when the majority of its neighbors are active. We address the question of whether a particular network design pattern confers dynamical advantage for the generation and sustainment of rhythmic activity. We find that the intrinsic properties of a node and the rules for interaction between them determine which structural features of the graph permit sustained activity. With $SL$ the level of...

Modeling and Performance Analysis of Automatic Meter-Reading Systems Using PLC Under Impulsive Noise Interference

This paper presents analytical models to study the performances of two schemes for automatic meter-reading (AMR) systems using power-line-communication (PLC)-access networks. These two schemes, namely, clustered simple polling and neighbor relay polling, are shown to be typically effective and efficient AMR schemes for overcoming the “silent node” problem associated with AMR systems. The analytical models also present the analysis of two different topological structures, radial and tree, of the PLC-access network assuming an automatic three-level clustering mechanism. The performances of the AMR schemes in terms of data-collection delay and throughput under impulsive noise interference are analyzed. The models are used to study the optimum packet size and data rate to mitigate the effect of impulsive noise on AMR system performance. Through comparison of the analytical results with the simulation results, it is verified that the analytical models have been accurately developed.

Solutions for the “Silent Node” Problem in an Automatic Meter Reading System Using Power-Line Communications

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper presents two algorithms, namely clustered simple polling and neighbor relay polling, for solving the typical “silent node” problem in automatic meter reading (AMR) systems using power-line communications (PLC)-access networks. These schemes are tested through computer simulations to be both effective and efficient in overcoming the “silent node” problem in AMR systems. The construction of the PLC-access network model in this paper is based on the actual structure of the PLC-access networks of Singapore public residential buildings. Also, a two-state transition Markov model is used to simulate a meter unit with such a “silent node” problem in a PLC network. The processing time model is established on a meter topology of three-level clustering. By using these models for our computer simulations, the performance of our proposed schemes can be evaluated in terms of reliability and efficiency. </para>