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.     

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.     

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.     

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.     

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.     

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.     

Detecting and connecting disjoint sub-networks in wireless sensor and actor networks

Wireless sensor and actor networks (WSANs) can be considered as a combination of a sensor network and an actor network in which powerful and mobile actor nodes can perform application specific actions based on the received data from the sensors. As most of these actions are performed collaboratively among the actors, inter-actor connectivity is one of the desirable features of WSANs. In this paper, we propose a novel distributed algorithm for establishing a connected inter-actor network topology. Considering initially disjoint sets of actors, our algorithm first initiates a search process by using the underlying sensor network in order to detect the possible sub-networks of actors in the region. After these sub-networks are detected, our algorithm pursues a coordinated actor movement in order to connect the sub-networks and thus achieve inter-actor connectivity for all the actors. This coordinated movement approach exploits the minimum connected dominating set of each sub-network when picking the appropriate actor to move so that the connectivity of each sub-network is not violated. In addition, the approach strives to minimize the total travel distance of actors and the messaging cost on both sensors and actors in order to extend the lifetime of WSAN. We analytically study the performance of our algorithm. Extensive simulation experiments validate the analytical results and confirm the effectiveness of our approach.     

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.     

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.     

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。     

Analysis and modeling of task scheduling in wireless sensor network based on divisible load theory

In this paper, we propose a novel task scheduling algorithm (Divisible Task scheduling Algorithm for Wireless sensor networks (DTAW)) based on divisible load theory in heterogeneous wireless sensor networks to complete the tasks within the shortest possible time and reduce the sensors' energy‐consuming. In DTAW, the tasks are distributed to the wireless sensor network by the (SINK) on the basis of the processing and communication capacity of each sensor. After receiving the subtasks, the intracluster sensors carry out its tasks simultaneously and send the results to cluster head sequentially. By removing communication interference between each sensor, reduced task completion time and improved network resource utilization are achieved. Each cluster head simultaneously finishes sending fused data to the SINK after fusing the data obtained from intracluster sensors. In this way, the overlap between the task performing and communication phase would be much better. Simulation results are presented to demonstrate the impacts of different network parameters on the makespan and energy consumption. The results show that the algorithm enables to reasonably distribute tasks to each sensor and then effectively reduces the time‐consuming and energy‐consuming. Copyright © 2012 John Wiley & Sons, Ltd.     

通信受限时传感器管理方法研究

在通信受限的情况下,如何进行传感器的管理以满足多目标的跟踪需求,优化完成跟踪任务.针对这一问题,对通信受限这种情形进行了描述,提出了数据获取概率的概念;利用扩展卡尔曼滤波和序贯卡尔曼滤波推出了序贯扩展卡尔曼滤波算法;结合信息论传感器管理方法和协方差控制传感器管理方法的优缺点提出了一种新的传感器分配准则.对比仿真实验表明,这种新的传感器管理方法能对传感器进行良好的管理,减小通信受限所带来的干扰;相比传统的传感器管理方法,传感器分配更为合理.     

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.     

Hierarchical Group Location Tracking for Transportation Systems in Wireless Personal Communication Networks

A hierarchical group location tracking (HGLT) based on grouplocation tracking and hierarchical location update is proposed toreduce the location management cost for terrestrialtransportation systems (TSs) in personal communication networks. A global group location update (GGLU) and a local group locationupdate (LGLU) are performed to provide an accurate position for auser. The GGLU informs a virtual visitor location register of thecurrently camped-on location area and the LGLU informs the servingmobile switching center of the currently camped-on cell. Althoughthe LGLU is done each time a TS moves into a new cell, it causessmall increment in the signaling cost due to localized updates andgroup updates compared with the previous group location trackingscheme. The proposed scheme significantly reduces the paging costbecause the scheme pages only a camped-on cell using the LGLUinformation. Compared with the previous schemes, the HGLT reducesthe location management cost, and it is more efficient as thecost for paging a cell increases.     

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.     

一种基于ID的传感器网络密钥管理方案

对偶密钥的建立是无线传感器网络的安全基础,它使得节点之间能够进行安全通信。但是由于节点资源的限制,传统的密钥管理方法在传感器网络中并不适用。在分析了现有密钥预分配协议的前提下,该文提出一种新的基于ID的密钥预分配协议。此协议用计算和比较散列值的方式替代广播方式协商密钥,减少了传感器节点大量的通信消耗。然后,分析了所提出方案的安全性、通信量和计算量,并和已有协议进行了比较。结果表明本文的方法不仅能保证安全性,而且节约了大量通信资源。     

Distributed Active Sensor Scheduling for Target Tracking in Ultrasonic Sensor Networks

Active ultrasonic sensors for target tracking application may suffer from inter-sensor-interference if these highly dense deployed sensors are not scheduled, which can degrade the tracking performance. In this paper, we propose a dynamic distributed sensor scheduling (DSS) scheme, where the tasking sensor is elected spontaneously from the sensors with pending sensing tasks via random competition based on Carrier Sense Multiple Access (CSMA). The channel will be released immediately when sensing task is completed. Both simulation results and testbed experiment demonstrate the effectiveness of DSS scheme for large scale sensor networks in terms of system scalability and high tracking performance.     

Performance evaluation of single and multi-channel actor to actor communication for wireless sensor actor networks

The paper discusses two distributed actor to actor communication schemes (a single channel one and a multi-channel one) for wireless sensor actor networks (WSANs). The performance of these two schemes is evaluated through analysis and simulation. The simulation results show that the whole analysis is fairly accurate. It is further proven that the multi-channel scheme has better performance than the single channel one. The key feature of the multi-channel scheme is the separation of the single hop from the multi-hop traffic.     

Optimal Power Allocation for Distributed Detection Over MIMO Channels in Wireless Sensor Networks

In distributed detection systems with wireless sensor networks, the communication between sensors and a fusion center is not perfect due to interference and limited transmitter power at the sensors to combat noise at the fusion center's receiver. The problem of optimizing detection performance with such imperfect communication brings a new challenge to distributed detection. In this paper, sensors are assumed to have independent but nonidentically distributed observations, and a multiple-input/multiple-output (MIMO) channel model is included to account for imperfect communication between the sensors and the fusion center. The J-divergence between the distributions of the detection statistic under different hypotheses is used as a performance criterion in order to provide a tractable analysis. Optimization of performance with individual and total transmitter power constraints on the sensors is studied, and the corresponding power allocation scheme strikes a tradeoff between two factors, the communication channel quality and the local decision quality. For the case with orthogonal channels, under certain conditions, the power allocation can be solved by a weighted water-filling algorithm. Simulations show that the proposed power allocation in certain cases only consumes as little as 25% of the total power used by an equal power allocation scheme while achieving the same performance.      

Controlling mobile robots in distributed intelligent sensor network

Mobile robots need sufficient sensors and information on the environment in order to navigate. In this paper, we propose a system of mobile robots, which is controlled in a distributed intelligent sensor network. In such a networked space, the environment is divided by distributed sensors. Each area is monitored by a distributed sensor device, which connects with other distributed sensor devices and robots throughout the network. As a result, the mobile robots are able to accomplish tasks simply by following orders from the sensor devices in the networked environment, although the mobile robots are not self-contained with information on the environment and sensors for self-positioning and control. We test several situations to verify the proposed system.