Wireless sensor and actor networks: research challenges

Wireless sensor and actor networks (WSANs) refer to a group of sensors and actors linked by wireless medium to perform distributed sensing and acting tasks. The realization of wireless sensor and actor networks (WSANs) needs to satisfy the requirements introduced by the coexistence of sensors and actors. In WSANs, sensors gather information about the physical world, while actors take decisions and then perform appropriate actions upon the environment, which allows a user to effectively sense and act from a distance. In order to provide effective sensing and acting, coordination mechanisms are required among sensors and actors. Moreover, to perform right and timely actions, sensor data must be valid at the time of acting. This paper explores sensor-actor and actor-actor coordination and describes research challenges for coordination and communication problems.     

A Real-Time and Reliable Transport (RT)$^{2}$ Protocol for Wireless Sensor and Actor Networks

Wireless sensor and actor networks (WSANs) are characterized by the collective effort of heterogeneous nodes called sensors and actors. Sensor nodes collect information about the physical world, while actor nodes take action decisions and perform appropriate actions upon the environment. The collaborative operation of sensors and actors brings significant advantages over traditional sensing, including improved accuracy, larger coverage area and timely actions upon the sensed phenomena. However, to realize these potential gains, there is a need for an efficient transport layer protocol that can address the unique communication challenges introduced by the coexistence of sensors and actors. In this paper, a real-time and reliable transport (RT) protocol is presented for WSANs. The objective of the (RT) protocol is to reliably and collaboratively transport event features from the sensor field to the actor nodes with minimum energy dissipation and to timely react to sensor information with a right action. In this respect, the (RT) protocol simultaneously addresses congestion control and timely event transport reliability objectives in WSANs. To the best of our knowledge, this is the first research effort focusing on real-time and reliable transport protocol for WSANs. Performance evaluations via simulation experiments show that the (RT) protocol achieves high performance in terms of reliable event detection, communication latency and energy consumption in WSANs.     

Network Partitioning Recovery Mechanisms in WSANs: a Survey

Wireless sensor and actor networks (WSANs) are more promising and most addressing research field in the area of wireless sensor networks in recent scenario. It composed of possibly a large number of tiny, autonomous sensor devices and resources rich actor nodes equipped with wireless communication and computation capabilities. Actors collect sensors’ information and respond collaboratively to achieve an application specific mission. Since actors have to coordinate their operation, a strongly connected inter-actor network would be required at all the time in the network. Actor nodes may fail for many reasons (i.e. due of battery exhaustion or hardware failure due to hash environment etc.) and failures may convert connected network into disjoint networks. This can hinder sometimes not only the performance of network but also degrade the usefulness and effectiveness of the network. Thus, having a partitioning detection and connectivity restoration procedure at the time of failure occurs in the network is crucial for WSANs. In this paper, we review the present network partitioning recovery approaches and provide an overall view of this study by summarizing previous achievements.     

Actor-oriented directional anycast routing in wireless sensor and actor networks with smart antennas

Current routing protocols in wireless sensor and actor networks (WSANs) shows a lack of unification for different traffic patterns because the communication for sensor to actor and that for actor to actor are designed separately. Such a design poses a challenge for interoperability between sensors and actors. With the presence of rich-resource actor nodes, we argue that to improve network lifetime, the problem transforms from reducing overall network energy consumption to reducing energy consumption of constrained sensor nodes. To reduce energy consumption of sensor nodes, especially in challenging environments with coverage holes/obstacles, we propose that actor nodes should share forwarding tasks with sensor nodes. To enable such a feature, efficient interoperability between sensors and actors is required, and thus a unified routing protocol for both sensors and actors is needed. This paper explores capabilities of directional transmission with smart antennas and rich-resource actors to design a novel unified actor-oriented directional anycast routing protocol (ADA) which supports arbitrary traffic in WSANs. The proposed routing protocol exploits actors as main routing anchors as much as possible because they have better energy and computing power compared to constraint sensor nodes. In addition, a directional anycast routing approach is also proposed to further reduce total delay and energy consumption of overall network. Through extensive experiments, we show that ADA outperforms state-of-the-art protocols in terms of packet delivery latency, network lifetime, and packet reliability. In addition, by offer fault tolerant features, ADA also performs well in challenging environments where coverage holes and obstacles are of concerns.     

Handling Mobility in Wireless Sensor and Actor Networks

In Wireless Sensor and Actor Networks (WSANs), the collaborative operation of sensors enables the distributed sensing of a physical phenomenon, while actors collect and process sensor data and perform appropriate actions. WSANs can be thought of as a distributed control system that needs to timely react to sensor information with an effective action. In this paper, coordination and communication problems in WSANs with mobile actors are studied. First, a new location management scheme is proposed to handle the mobility of actors with minimal energy expenditure for the sensors, based on a hybrid strategy that includes location updating and location prediction. Actors broadcast location updates limiting their scope based on Voronoi diagrams, while sensors predict the movement of actors based on Kalman filtering of previously received updates. The location management scheme enables efficient geographical routing, and based on this, an optimal energy-aware forwarding rule is derived for sensor-actor communication. Consequently, algorithms are proposed that allow controlling the delay of the data-delivery process based on power control, and deal with network congestion by forcing multiple actors to be recipients for traffic generated in the event area. Finally, a model is proposed to optimally assign tasks to actors and control their motion in a coordinated way to accomplish the tasks based on the characteristics of the events. Performance evaluation shows the effectiveness of the proposed solution.     

事件驱动的带执行器无线传感器网络分簇算法研究

带有执行器的无线传感器网络是指在传统无线传感器网络中加入执行节点,形成传感器节点、执行节点和基站共同构成的三层监控网络。根据执行器在能量、计算能力和感知能力方面的优势,提出建立应用于事件调度的双环分簇算法。算法将执行器连接成双环结构,提升网络在线扩展能力的同时,也为无线传感器网络满足事件驱动构建基础。仿真实验证明,此算法能够有效降低网络能耗,随着节点数目的增加和监控领域的扩大,表现更加凸出。     

WSANs中基于跳步数自适应的路由算法

无线传感反应网络是由大量传感节点和少量（可移动）资源丰富的反应节点构成.传感节点 负责收集外部环境信息,而反应节点对外部环境实施相应的操作.本文分析节点能量消耗模 型,求解出理想条件下单条路径上总能耗最小时的最优跳步数.在此基础上,提出了一种跳 步数自适应的路由算法HAR,用来实现数据收集的实时需求与能量消耗之间的平衡.仿真实验 表明：HAR算法在平衡能量消耗与时间延迟的性能上优于HBMECT算法,而且能较好地适用于 反应节点移动的情形.     

Scate: A Scalable Time and Energy Aware Actor Task Allocation Algorithm in Wireless Sensor and Actor Networks

In many applications of wireless sensor actor networks (WSANs) that often run in harsh environments, the reduction of completion times of tasks is highly desired. We present a new time‐aware, energy‐aware, and starvation‐free algorithm called Scate for assigning tasks to actors while satisfying the scalability and distribution requirements of WSANs with semi‐automated architecture. The proposed algorithm allows concurrent executions of any mix of small and large tasks and yet prevents probable starvation of tasks. To achieve this, it estimates the completion times of tasks on each available actor and then takes the remaining energies and the current workloads of these actors into account during task assignment to actors. The results of our experiments with a prototyped implementation of Scate show longer network lifetime, shorter makespan of resulting schedules, and more balanced loads on actors compared to when one of the three well‐known task‐scheduling algorithms, namely, the max‐min, min‐min, and opportunistic load balancing algorithms, is used.     

Lightweight routing with dynamic interests in wireless sensor and actor networks

Wireless sensor and actor networks (WSANs) have been increasingly popular for environmental monitoring applications in the last decade. While the deployment of sensor nodes enables a fine granularity of data collection, resource-rich actor nodes provide further evaluation of the information and reaction. Quality of service (QoS) and routing solutions for WSANs are challenging compared to traditional networks because of the limited node resources. WSANs also have different QoS requirements than wireless sensor networks (WSNs) since actors and sensor nodes have distinct resource constraints.In this paper, we present, LRP-QS, a lightweight routing protocol with dynamic interests and QoS support for WSANs. LRP-QS provides QoS by differentiating the rates among different types of interests with dynamic packet tagging at sensor nodes and per flow management at actor nodes. The interests, which define the types of events to observe, are distributed in the network. The weights of the interests are determined dynamically by using a nonsensitive ranking algorithm depending on the variation in the observed values of data collected in response to interests. Our simulation studies show that the proposed protocol provides a higher packet delivery ratio and a lower memory consumption than the existing state of the art protocols.     

Greedy algorithms for actor redeployment in wireless sensor–actor networks

In a wireless sensor–actor network, an actor usually has to provide services as soon as the actor receives the event signals from the sensors. Therefore, the performance of a wireless sensor–actor network depends on the actor deployment. In many circumstances, actors may fail or go out to deal with events, and thus, the sensors covered by the missing actors could be not to be reachable in time. This introduces the necessity of actor redeployment. In this paper, we study the problems of redeploying actors to maximize the number of sensors able to be covered by actors and to maximize the decrease of the residual distances of sensors, respectively. Both problems are shown to be NP-complete. Additionally, we prove that the greedy algorithm for each problem has an approximation ratio of 2. Simulations show that the greedy algorithm for each problem performs well.     

A Hybrid Timer Based Single Node Failure Recovery Approach for WSANs

The inter-actor connectivity is a very crucial issue to maintain network operation in the wireless sensor and actor networks. Most of the applications have been proposed for harsh environments where the backbone actor nodes are prone to failure or get damaged due to their battery power exhaustion or get physically damaged. Such failures can partition the network due to failure of the cut-vertex node and eventually decrease the network performance or even sometimes make the network useless. Currently, a few approaches have been proposed to restore the partitioned network due to failure of the cut-vertex node but without considering the recovery node capabilities. This paper proposes a localized hybrid timer based cut-vertex node failure recovery approach called distributed prioritized connectivity restoration algorithm (DPCRA) to handle such partitions and restore connectivity with the help of a small number of nodes. The main idea is to proactively identify whether the failure of an actor node causes partition or not in the network. If partition occurs the designated failure handlers (FHs) detect that partition and repair it locally using minimum information stored in each actor node. In case first designated node is unable to start the recovery process within a permissible reaction time the next designated FH could start the recovery process. The main strength of our paper is the use of multiple backup nodes for the guaranteed partitioned recovery. The experimental simulation shows that DPCRA outperforms other existing state-of-the-art approaches in terms of the number of participated repairing nodes and their total moving distance for the recovery to restore the disconnected partitions.     

Two Fuzzy-Based Systems for Selection of Actor Nodes inWireless Sensor and Actor Networks: A Comparison Study Considering Security Parameter Effect

A group of wireless devices with the ability to sense physical events (sensors) or/and to perform relatively complicated actions (actors), is referred to as Wireless Sensor and Actor Network (WSAN). In WSANs, sensors gather information about the physical events, while actors perform appropriate actions upon the environment, based on the sensed data shared by sensors. In order to provide effective sensing and acting, a distributed local coordination mechanism is necessary among sensors and actors. In this work, we propose and implement two Fuzzy Based Actor Selection Systems (FBASS): FBASS1 and FBASS2. We focus on actor selection problem and implement two fuzzy-based system. The systems decide whether the actor will be selected for the required job or not, based on data supplied by sensors and actual actor condition. We use three input parameters for FBASS1: Type of Required Action (TRA), Distance to Event (DE) and Remaining Power (RP). In FBASS2, we add the Security (SC) parameter as additional parameter. The output parameter for both systems is Actor Selection Decision (ASD). The simulation results show that the proposed systems decide the actor selection in order to have short delays, low energy consumption and proper task assignment. Comparing FBASS1 with FBASS2, the FBASS2 is more complex than FBASS1, because it has more rules in FRB. However, FBASS2 is able to decide secure actor nodes, which makes the system more secure.     

Communication and Coordination in Wireless Sensor and Actor Networks

In this paper, coordination and communication problems in wireless sensor and actor networks (WSANs) are jointly addressed in a unifying framework. A sensor-actor coordination model is proposed based on an event-driven partitioning paradigm. Sensors are partitioned into different sets, and each set is constituted by a data-delivery tree associated with a different actor. The optimal solution for the partitioning strategy is determined by mathematical programming, and a distributed solution is proposed. In addition, a new model for the actor-actor coordination problem is introduced. The actor coordination is formulated as a task assignment optimization problem for a class of coordination problems in which the area to be acted upon needs to be optimally split among different actors. An auction-based distributed solution of the problem is also presented. Performance evaluation shows how global network objectives, such as compliance with real-time constraints and minimum energy consumption, can be achieved in the proposed framework with simple interactions between sensors and actors that are suitable for large-scale networks of energy-constrained devices.     

Connectivity-Preserved and Force-Based Deployment Scheme for Mobile Sensor Network

This paper considers the self-deployment of wireless sensor networks. Conventional deployment problem usually focuses on enhancing the coverage, while the conditions for network connectivity are largely simplified. We present a deployment scheme to enhance the coverage while keeping the network connected at each step of the deployment. Our scheme contains two parts. The coverage improvement part proposes an improved force-based mechanism. A limit is provided to determine the sensors which should attractive each other, so the wasted overlap and communication resource can be reduced. The connectivity preservation part provides constrains for the movement distance of each sensor, in order to take account of both connectivity and coverage enhancement. Some simulation results are presented to show the connectivity preservation and coverage maximization properties of our mechanism.     

Geographical routing and participant collaboration model based communication mechanism of WSAN

The communication mechanism of wireless sensor and actor network (WSAN) was studied.Firstly,a proactive location management mechanism based on the update messages sent by mobile actors to sensors and the actors’ scope limited by Voronoi diagram was proposed.Thus,sensors predicted the movement of actors using Kalman filtering of the previously received updates.Then,an optimal energy-aware forwarding rule based on geographical routing was presented for sensor-actor communication,and the delay of the data delivery process was controlled using the power control and the network congestion was dealed with by forcing multiple actors to share the traffic generated in the event area.Finally,based on the characteristics of multiple concurrent events,a model for actor-actor coordination was proposed to coordinate their movements in order to optimally accomplish the tasks.Performance simulation results show that the proposed cooperative communication mechanism for WSAN can effectively reduce end-to-end delays,energy consumption and percentage of packet drops.     

Adaptive Pull�CPush Based Event Tracking in Wireless Sensor Actor Networks

Wireless sensor networks have attracted significant interest for various scientific, military, and e-health applications. Recently a new class of sensor networks ??sensor/actor networks?? has been introducing new research challenges due to the unique coordination requirements among sensors and actors. In sensor/actor networks, actors are the nodes that have the capability to move in the field, equipped with powerful devices and can respond to the events of interest. With this capability, autonomous operation of the network is possible without a centralized controlling mechanism. This, however, requires the network to apply cooperative mechanism to decide when and how monitoring is done to track the event and how the event will be responded. In this regard, little work has been done in terms of co-existing Push and Pull data flows in the network. In this paper, we propose an Adaptive Pull?CPush (APP) based Event Tracking approach that allows sensor-to-actor communication as well as actors coordination in response to the events occurred. APP proposes two models of sensors organization: region-based organization (RAPP) and neighbor-based organization (NAPP) to alert nodes in the vicinity of reported event. APP exploits the mobility of actor nodes to form dynamic responsibility clusters, thus ensuring an event specific response to emergencies. Routing in APP is based on Routing by Adaptive Targeting (RAT), which is a delay-constrained geographical routing protocol. Simulation results reveal significant performance improvement in terms of response time and energy conservation.     

一种无线传感器网络全连通群的休眠调度算法

该文针对无线传感器网络的覆盖性和连通性问题,在假设传感器节点地理位置信息已知的条件下,设计了一种包含全连通群的建立和维护以及群内节点休眠调度的全新算法。该算法采用保证群内节点彼此一跳可达的全连通群分群方法,以及分布式节能的休眠调度策略,最大程度上减少传感器网络的能量消耗,延长了网络寿命。仿真结果表明:该算法能较好地保证无线传感器网络的覆盖性和连通性,且能耗较低。     

Timing-Based Mobile Sensor Localization in Wireless Sensor and Actor Networks

In this paper, localization problem in wireless sensor and actor networks (WSAN) is addressed. In WSAN, the performance of event detection and tracking highly depends on the exact location information of the events that must be reported along with the event features. Having precise location information of the sensor nodes, actors are able to execute actions more effectively in the region of detected events. In this context, the accurate localization of sensor nodes is essential with respect to the actors. Particularly, the problem becomes much more complicated when the sensor nodes as well as the anchor nodes (actors) are mobile. In order to localize the mobile sensor nodes relative to the actors, a novel Timing-based Mobile Sensor Localization (TMSL) algorithm is introduced. In TMSL, sensor nodes determine their distance from actors by using propagation time and speed of RF signal. In order to determine distance from the actors, actors actively broadcast reference beacons in a pattern of intervals adaptively defined according to the mobility of sensor nodes and the required level of localization accuracy. These reference beacons carry the interval numbers in which they were transmitted. The interval numbers are then used by the sensor nodes to calculate the start time of the beacons locally which is then used to determine the propagation time. TMSL does neither require nor assume any time synchronization among the sensor nodes or with the actors. Performance evaluations clearly show that TMSL is adaptive to velocity of mobile sensor and actor nodes and can be configured according to the required localization accuracy in order to avoid overhead raised due to high velocity.     

SANSync: An Accurate Time Synchronization Protocol for Wireless Sensor and Actuator Networks

Wireless Personal Communications - Wireless sensor and actuator networks (WSANs) consists of a large number of sensors and a relatively small number of actuators connected through wireless links....     

Intelligent actor mobility in wireless sensor and actor networks

In wireless sensor and actor network research, the commonly used mobility models for a mobile actor are random walk model, random waypoint mobility model, or variants thereof. For a fully connected network, the choice of mobility model for the actor is not critical because, there is at least one assured path from the sensor nodes to the actor node. But, for a sparsely connected network where information cannot propagate beyond a cluster, random movement of the actor may not be the best choice to maximize event detection and subsequent action. This paper presents static and dynamic intelligent mobility models that are based on the inherent clusters’ information of a sparsely connected network. Simulation results validate the idea behind the intelligent mobility models and provide insights into the applicability of these mobility models in different application scenarios.