Asynchronous Wireless Sensor Networks Research Articles

SDORP: SDN Based Opportunistic Routing for Asynchronous Wireless Sensor Networks

In wireless sensor networks (WSNs), it is inappropriate to use conventional unicast routing due to the broadcast storm problem and spatial diversity of communication-links. Opportunistic-Routing (OR) benefits the low duty-cycled WSNs by prioritizing the multiple candidates for each node instead of selecting one node as in conventional unicast-routing. OR reduces the sender waiting time, but it also suffers from the duplicate packets problem due to multiple candidates waking up simultaneously. The number of candidates should be restricted to counterbalance between the sender waiting time and duplicate packets. In this paper, software-defined networking (SDN) is adapted for the flexible management of WSNs by allowing decoupling of the control plane from the sensor nodes. This study presents SDN-based load-balanced opportunistic-routing for duty-cycled WSNs that addresses two parts. First, the candidates are computed and controlled in the control plane. Second, the metric used to prioritize the candidates considers the average of three distributions, transmission distance distribution, expected number of hops distribution and residual energy distribution so that more traffic is guided through the nodes with higher priority. Simulation results show that our proposed protocol significantly improve network lifetime, routing efficiency, energy consumption, sender waiting time, and duplicate packets as compared with the benchmarks.

Consensus-Based Distributed Batch Estimation in Asynchronous Wireless Sensor Networks

In this paper, to address the distributed estimation problem over an asynchronous wireless sensor network (aWSN), an average consensus-based distributed batch estimation (DBE) method is proposed. The DBE seeks to update the global posterior with a predefined global update period (GUP) and is implemented with a local filter (LF) and a fusion filter (FF). For LF, we develop two different asynchronous batch estimation approaches to align and compute the asynchronous local posteriors of multiple nodes in an aWSN. At FF, an average consensus filter is adopted to compute the global posterior via a proposed DBE fusion rule. Numerical results show that the proposed DBE method has high target-tracking accuracy and is robust to strong asynchronism. Besides, the optimality of DBE fusion can be approximately achieved with a sufficiently large number of particles and consensus iterations.

Optimal Bibd Extended Design Based Neighbour Discovery in Asynchronous Wsn

For asynchronous Wireless Sensor Networks (WSNs), this research suggests an ideal Balanced Incomplete Block Design (BIBD) extended design based neighbour finding technique. The algorithm takes use of the characteristics of BIBD extended designs to build a series of transmission plans that guarantee effective neighbour detection with little energy consumption and delay. Simulations are used to test the proposed algorithm, and the results show that it significantly outperforms previous approaches in terms of energy usage, latency, and scalability.
 The value of this study is in the innovative neighbour finding algorithm that it proposes, which overcomes the drawbacks of existing approaches and provides a scalable and energy-efficient solution for large-scale WSNs. The suggested technique may be used in a variety of settings, including environmental monitoring, industrial automation, and healthcare, where accurate and timely data gathering and processing depend on efficient neighbour detection.
 The suggested algorithm is implemented step by step in the technique section along with the relevant equations and tables. The simulation results for sample input data are shown in the results section along with pertinent tables and graphs. The results are outlined in the conclusion section, which also emphasises the importance of the suggested method.
 Overall, the suggested technique provides a viable option for rapid neighbour detection in WSNs, potentially having repercussions for a broad variety of applications.

Energy adaptive block design based neighbor discovery for asynchronous wireless sensor networks

Background: The need for an efficient neighbor discovery model is tremendously essential with the development of Wireless Sensor Networks (WSNs).The neighbor discovery model has growingly been significant in enhancing the performance of WSNs. Methods: In this study, adaptive energy duty-cycle, energy-efficient Balanced Incomplete Block Design (BIBD) hybrid scheme is proposed for WSNs that controls collisions, and overhearing obstacle by maintaining energy over WSNs. Energy adaptive BIBD leverages the features of symmetric BIBD. Evaluation of the proposed model is demonstrated using the TOSSIM tool, and the performance parameters are compared with other wellknown neighbor discovery process, including Disco, U-Connect, and Searchlight, Hedis, and Todis algorithms. Findings: The outputs of our simulation study illustrates that the proposed model significantly outperforms other neighbor discovery algorithms with reference to energy-efficiency and discovery latency.Keywords: Wireless sensor networks; energy efficiency; neighbor discovery; block design; collisions

Analysis of Delay time by Adjusting of Check Interval in Asynchronous Wireless Sensor Network with Low Power

Analysis of Delay time by Adjusting of Check Interval in Asynchronous Wireless Sensor Network with Low Power

TDOA-Based Joint Synchronization and Localization Algorithm for Asynchronous Wireless Sensor Networks

This paper presents a joint synchronization and localization algorithm based on the time-difference-of-arrival (TDOA) for asynchronous Wireless Sensor Networks (WSNs), where the positions of anchors are relatively fixed but unknown. To obtain time synchronization and anchor positions, each anchor broadcasts signals periodically, while other anchors receive the broadcasting signals and stamp times-of-arrival (TOAs). Based on these TOAs, we estimate the internal clock parameters and anchor positions in three steps: least square estimation (LSE) of the relative clock skew based on TDOAs, maximum likelihood localization (MLE) of anchors using biased time of flight (TOF), and LSE estimation of relative clock offsets. Anchor pairs stamp the TDOAs when a tag (a wireless sensor node that requires localization) transmits a signal. The biased TDOAs, due to asynchronous local clocks, are compensated by relative clock offset estimation. The maximum likelihood estimation is used for the tag localization based on the Gaussian noise model. We evaluate the performance of the proposed synchronization and localization algorithm using the Cramer-Rao lower bound (CRLB). Simulations are carried out to verify the validity of the algorithm in this paper.

Shortest-Latency Opportunistic Routing in Asynchronous Wireless Sensor Networks with Independent Duty-Cycling

For opportunistic routing in independent duty-cycled wireless sensor networks (WSNs), a sender dynamically determines a relay candidate set depending on the real-time network conditions. Due to independent and varying duty cycle length, the sender may handle different waking-up orders of the potential forwarders when it tries to forward data packets at different time instants. Conventional opportunistic routing protocols overlook the time-varying property of the waking-up order of the candidate nodes. In this paper, we theoretically analyze how to obtain an optimal candidate set for each node in order to minimize the end-to-end latency. Then, considering the realistic scenarios, we propose an opportunistic routing which jointly considers global and localized optimizations. Based on the relatively stable topology and duty-cycle length information, an original candidate set is constructed. Then, by considering the real-time link and duty cycle information in the local context, a further optimization for the original candidate set can be achieved. Simulation results show that our proposed schemes can significantly improve the end-to-end latency compared with the benchmarks.

E-DTDOA Based Localization for Wireless Sensor Networks With Clock Drift Compensation

A high time resolution localization scheme, using ultra-wide band ranging signal with bandwidth of 2GHz, is proposed for a fully asynchronous wireless sensor network (WSN). The proposed scheme is specifically useful for sensor nodes which are designed to operate at very low ADC sampling rate, in the order of 2–3 MHz, but still achieves the sampling resolution in the order of sub-nanoseconds. To achieve low sampling rate, equivalent time sampling (ETS) technique is used at the sensor nodes. Reconstructed signal obtained by ETS technique, that require periodic transmission of the same signal repetitively, is severely affected by the variation in transmitter and receiver clock drift as against the real time sampling where the variations are due to receiver node clock drift only. Thus, it requires a protocol to precisely estimate the transmitter and receiver clock parameters. A scheme, which uses a novel mathematical equivalent time of arrival (E-TOA) model for ETS based system, for clock drift estimation is presented. Based on clock drift estimation parameters, receiver nodes are tuned to the same frequency. E-TOA measurements are further used to propose an equivalent differential time difference of arrival (E-DTDOA) based ranging algorithm, which relaxed the time synchronization requirement between the wireless nodes, and still achieving high time resolution. The E-DTDOA range measurements are subsequently used to obtain precise localization of the target node/s. The feasibility of the algorithm proposed is demonstrated experimentally using in house designed wireless sensor nodes.

Hybrid Robust Sequential Fusion Estimation for WSN-Assisted Moving-Target Localization With Sensor-Node-Position Uncertainty

This article presents a hybrid robust sequential fusion estimation (HRSFE) method for moving-target localization in mobile asynchronous wireless sensor networks (WSNs). The estimation error or inconsistency, caused by the uncertainties of sampling, communication, and sensor-node position, is considered fully and compensated by incorporating the sensor-node position with uncertainty into the state vector as well as introducing an adaptive fading factor into the cubature Kalman filter (CKF) to maintain the estimation consistency. In addition, a QR-decomposition-based square-root form of the cubature strong localization filter (SR-CSLF) is proposed to improve the accuracy and stability of the CSLF. Moreover, an HRSFE method is designed to estimate the augment state of the WSN-assisted moving-target-localization system, and the proposed estimation method combines the merits of both the SR-CSLF and SR-CKF effectively and is able to deal with the uncertainties of sampling, communication, and sensor-node position in a unified framework. Simulations and experiments of a WSN-assisted moving-target-localization system under various uncertainty settings are employed to demonstrate the effectiveness and superiorities of the proposed method.

Oppo-Flood: An Energy-Efficient Data Dissemination Protocol for Asynchronous Duty-Cycled Wireless Sensor Networks

In this paper, we propose a data dissemination protocol for asynchronous duty-cycling wireless sensor networks. In an asynchronous duty-cycling network, each node independently selects its wake-up time. In this environment, data dissemination becomes energy consuming, because broadcasting a packet does reach all neighbors but only the neighbors that are awake at the time. A node can forward its packet to all neighbors by continuously transmitting the packet for a whole wake-up interval, but it leads to high energy consumption and high dissemination delay. The idea proposed in this paper is to use opportunistic forwarding, where each node forwards the packet to a neighbor that wakes up early and receives the packet. Each node forwards the packet, as long as there is a neighboring node that has not received the packet yet. The main benefit of this opportunistic forwarding-based dissemination is that every time a packet is disseminated, it may take a different path to reach the nodes. At the beginning of dissemination, a sender needs to transmit for a very short duration of time because there are plenty of neighboring nodes to receive the packet. As more nodes receive the packet, the transmit duration of the sender becomes longer, thus consuming more energy. Since the order of dissemination is different every time, energy consumption is naturally balanced among the nodes, without explicit measures. Through extensive simulations, we show that the proposed protocol achieves longer network lifetime and shorter dissemination delay compared to other dissemination protocols in various network environments.

Energy efficient broadcast protocols for asynchronous duty-cycled wireless sensor networks

In asynchronous duty-cycled wireless sensor networks (WSNs), each node has its own sleep schedule that is independent of the schedules of neighboring nodes. Since each node follows its own independent sleep schedule, the probability that a node’s neighbors will wake up concurrently is quite low. For this reason, each single hop broadcast must be completed through multiple unicast transmissions, and the sender node must remain awake until all of its neighboring nodes have received the broadcast packet. In this paper, we present two energy efficient broadcast protocols, namely Broadcast Progress-based Efficient Multihop Broadcast (BPEMB) protocol and Tree-based Efficient Multihop Broadcast (TEMB) protocol, for asynchronous duty-cycled WSNs. In both of the proposed protocols, the decision of whether to transmit the broadcast packet is based on the link quality information and without any forwarder’s guidance list. The redundant transmissions and collisions are avoided effectively with cooperation among the neighbors, so that the node with the best link quality to the receiver node takes responsibility to forward the packet to the receiver node. With this approach, nodes that are not involved in transmitting the broadcast packet can go to sleep and save their energy. In the BPEMB protocol, the forwarding decision of transmitting the broadcast packet is also influenced by the broadcast progress information, which is piggybacked in the broadcast packet. Through extensive simulations, we demonstrate that the proposed protocols can significantly improve the broadcast efficiency through reducing the energy consumption and minimizing the broadcast latency. The evaluation results also show that both the BPEMB and TEMB protocols can substantially reduce the collisions and redundant transmissions in asynchronous duty-cycled WSNs.

A Fast and Efficient Broadcast Protocol With a Mobile Sink Node in Asynchronous Wireless Sensor Networks

We investigate a broadcast scenario that a mobile sink disseminating broadcast packets while moving in asynchronous wireless sensor networks (WSNs), to prolong the network lifetime and reduce the broadcast delay. Such a scenario may yield multiple logical sink nodes in WSNs and the moving speed and trajectory of the mobile sink have the significant impact on the speed and efficiency of the broadcast. Thus, the conventional broadcast protocols may not fit for the mobile sink scenario. We propose a fast and efficient broadcast (FEB) protocol with a mobile sink in asynchronous WSNs. We analyze the moving pattern as well as the travel speed of the mobile sink. We jointly consider the broadcast process, the node location, and the neighbor coverage information within two-hops and then propose an efficient broadcast scheme together with a heuristic moving strategy for the mobile sink. The proposed broadcast scheme needs to exchange node coverage information before the transmission begins, thus to avoid redundant packet transmissions, and the proposed moving pattern strategy decreases the network broadcast delay by moving the mobile sink to monitoring areas, where fewer nodes are covered by the broadcast process. The simulation results show that our proposed protocol significantly reduces the broadcast delay and energy consumption.

A Compensated Multi-Anchors TOF-Based Localization Algorithm for Asynchronous Wireless Sensor Networks

Tag localization for asynchronous wireless sensor networks requires the development of a scheme for clock synchronization. This remains a difficult and open problem since the performance of tag localization can be adversely affected by complications such as reply time and relative clock skew. Joint clock synchronization and a tag localization algorithm that implements a multi-anchor compensated time-of-flight (TOF) to the asynchronous wireless sensor network is a possible and viable solution. Although previous methods that leverage TOF measurements are effective and easily conducted, their performance is not always superior due to the relative clock skew. In this paper, we propose to extend the joint clock/tag synchronization/localization algorithm by introducing a compensation factor that can cancel relative clock skews from multi-tag anchor pairs. We apply a least squares estimation (LSE) algorithm to both the time of emission (TOE) and time of arrival (TOA) for the clock synchronization step. Under the assumption of a Gaussian measurement noise model, the tag localization problem is approximately solved by maximum likelihood estimation (MLE). To assess the performance of our algorithm, we derive the mean square error (MSE) of both relative clock skew and tag location and numerically evaluate the Cramer–Rao lower bound (CRLB) as a benchmark. The simulation results show that the accuracy of the relative clock skew-based estimation and tag localization are significantly improved over traditional algorithms when the appropriate reply time is selected. This is what our proposed algorithm focuses on: it is robust to tag mobility to some extent. We test the performance of proposed algorithm using a well-designed experiment. Based on the experiment results, the localization algorithm can achieve high accuracy without an additional restriction on the reply time and the clock skew.

Resilient Consensus-Based Time Synchronization in Asynchronous Sensor Networks

This paper addresses the time synchronization problem of asynchronous wireless sensor networks (WSNs) under false data injection attacks. First, we extend the fundamental metric of r-robustness with the notion of trusted links and then show that the structural robustness of networks can be significantly improved without adding additional links after setting a small subset of links to be trusted. Then, for a more practical case where the intercommunication topologies between each sensor node are time-varying, we develop a resilient consensus-based distributed algorithm where the sampling period is allowed to be chosen by each sensor independently and it is shown that the time synchronization problem for WSNs can be solved via the proposed controller. Numerical simulations are conducted to illustrate the effectiveness of our proposed method.

A Hybrid Localization Algorithm Based on TOF and TDOA for Asynchronous Wireless Sensor Networks

A Hybrid Localization Algorithm Based on TOF and TDOA for Asynchronous Wireless Sensor Networks

An Energy-Efficient Network-Wide Broadcast Protocol for Asynchronous Wireless Sensor Networks

It is very challenging to design an efficient network-wide broadcast protocol for asynchronous wireless sensor networks (AWSNs). Since the neighbors adopt sleep schedule independently and the probability that they wake up concurrently is very low, each single-hop broadcast has to be substituted by multiple unicast transmissions. Moreover, without the schedule knowledge of designated neighbors, a sender has to keep active until all these nodes are covered, which consumes a large amount of energy. In this letter, we propose an energy-efficient network-wide broadcast protocol (EENWB) for AWSNs. By introducing more aggressive cooperations among the neighboring senders, some senders can go to sleep much earlier, only at the cost of increasing the active periods of their cooperators slightly. Extensive simulation results show that EENWB can reduce the total energy consumption greatly.

Present State-of-the-Art of Continuous Neighbor Discovery in Asynchronous Wireless Sensor Networks

In this paper, we reviewed the literature on various techniques found in WSN for neighbor discovery. Neighbor discovery is a fundamental phenomenon in the network in the deployment phase. However, due to the dynamic nature of WSN, and there are possibilities of adding new nodes and removing nodes fr

Optimizing Opportunistic Routing in Asynchronous Wireless Sensor Networks

Asynchronous sleep schedule and geographical routing are two efficient and scalable solutions for wireless sensor networks (WSNs). However, the schedule may degrade the delay performance of the routing protocol, and the optimal combined utilization of these two solutions is still an open question. In this letter, we propose a geographical-based opportunistic routing protocol for asynchronous WSNs. Each node maintains multiple relay candidates that make geographical progresses of more than a threshold $\gamma$ , and opportunistically forwards data packet to the first candidate that wakes up. We can obtain the optimal end-to-end delay performance, by just tuning $\gamma$ . Analytical and simulation results show that the derived optimal $\gamma$ can make a good tradeoff between the single-hop delay and the hop count of forwarding path, and minimize the end-to-end delay of forwarding path.

Hybrid Sequential Fusion Estimation for Asynchronous Sensor Network-Based Target Tracking

This brief presents a sequential fusion estimation method for maneuvering target tracking in asynchronous wireless sensor networks. The modeling error caused by asynchronous sampling and communication uncertainties is considered and compensated for by introducing a time-varying fading factor into the unscented Kalman filter (UKF). A square root form of the unscented strong tracking filter (SR-USTF) based on QR decomposition is proposed to improve the stability and performance of the USTF. Moreover, a hybrid sequential fusion estimation method is presented to estimate the state of the target, and the proposed sequential fusion estimation method combines the superiorities of both the SR-USTF and the conventional UKF, and is able to deal with communication uncertainties such as time delay and packet loss in a unified framework. Both simulations and experiments of an E-puck robot tracking example are provided to demonstrate the effectiveness and superiorities of the proposed sequential fusion estimation method.

Dynamic Delegation-Based Efficient Broadcast Protocol for Asynchronous Wireless Sensor Networks

In broadcast for asynchronous wireless sensor networks (WSNs), delegation refers to a sender node delegating an uncovered node to a neighbor node already received the broadcast packet. Conventional delegation schemes make their delegation decision based on incomplete information and do not change the decision anymore, which may induce inefficient transmission or collision. We propose a dynamic delegation-based efficient broadcast (DDEB) protocol for asynchronous WSNs. DDEB dynamically delegates an uncovered node to a sender with the best link quality to it so far. It can adapt to the change of link quality and broadcast process. Moreover, it can solve the inefficient transmissions and conflicts problem in quadrilateral topologies. Simulation results show that DDEB can reduce the energy consumption, message cost, and broadcast delay.