The proliferation of big data has fueled the success of deep learning; however, its inherent ”black box” nature poses significant challenges for its adoption in safety-critical domains. Existing interpretable machine learning methods offer partial solutions but often struggle with model fidelity, inconsistent explanations, a lack of holistic model understanding, and critically, computational inefficiency, especially when applied to models trained on large-scale datasets. To overcome these hurdles, this paper introduces Parallel Explainer (PEXP), an innovative parallel tree-based interpretation framework designed for scalability and comprehensive understanding. PEXP initiates by generating a localized sample set around a target instance through data distribution-aware perturbations. It then computes similarity scores and employs a kernel function to weight these samples effectively. Leveraging concepts from Bagging and Boosting, PEXP efficiently constructs Parallel Ensemble Trees as its core interpretable model. This model provides feature importance-based explanations and aggregates insights across all samples to achieve a global understanding of the model's behavior on the entire dataset. Experimental results demonstrate PEXP's significant advantages over mainstream interpretable methods in both runtime efficiency and the quality of explanations, particularly crucial for big data analytics. Furthermore, a case study illustrates PEXP's application in enhancing the interpretability of video anomaly detection systems within smart cities, a domain characterized by large volumes of data and offers insights for improving Transformer-based architectures.

Social violence presents a compelling challenge to public safety, yet existing multimodal detection systems exhibit excessive reliance on RGB image semantics and opaque decision-making processes. Despite leveraging visual and auditory data, current models demonstrate RGB bias in feature prioritization, as evidenced by explainability analyzes, thereby limiting their generalization for behavioral understanding. Additionally, modality inconsistency and inefficient fusion mechanisms impair model transparency and training stability. To bridge these gaps, this study proposes modality-aligned preprocessing (VAJ) that structurally unifies visual-auditory features through conflict resolution and input optimization, explicitly suppressing color dominance while enhancing interpretable feature representations. Complementing this, we design DTVDS, an interpretable detection framework integrating knowledge distillation to transfer distilled behavioral insights from a cumbersome teacher network to an efficient student model. This dual strategy not only addresses computational overhead but also clarifies decision logic through simplified inference pathways. Evaluations on XD-Violence and UCF-Crime benchmarks demonstrate superior performance, with AP (89.64%) and AUC (88.35%) outperforming existing methods. Qualitative evaluations further validate interpretability, revealing modality-coherent attention maps and human-aligned rationale visualization. The proposed method advances violence detection by addressing persistent shortcomings in multimodal alignment and model explainability.

Advances in wireless charging technology give great new opportunities for extending the lifetime of a wireless sensor network (WSN) which is an important infrastructure of IoT. However, the existing greedy algorithms lacked learning from the experiences of energy dissipation trends. Unlike the existing studies, this article proposes a reinforcement learning approach, called reinforcement learning recharging (RLR), for mobile charger to learn the trends of WSNs, including the energy consumption of the sensors, the recharging cost as well as the coverage benefit, aiming to maximize the coverage contribution of the recharged WSN. The proposed RLR mainly consists of three modules, including sensor energy management (SEM), charger location update (CLP), and charger reinforcement learning (CRL) modules. In the SEM module, each sensor manages its energy and calculates its threshold for the recharging request in a distributed manner. The CLP module adopts the quorum system to ensure effective communication between sensors and the mobile charger. Meanwhile, the CRL module employs attraction rewards to reflect the coverage benefit and penalties of waiting time raised due to charger movement and recharging other sensors. As a result, the charger accumulates the learning experiences from the$Q$-Table such that it is able to execute the appropriate actions of charging or moving in a manner of state management. Performance results show that the proposed RLR outperforms the existing recharging mechanisms in terms of charging waiting time of sensors, the energy usage efficiency of the mobile charger, as well as the coverage contribution of the given sensor network.

Wireless body area networks (WBANs) support various types of medical applications with heterogeneous requirements. Therefore, we need to use an efficient medium access control (MAC) protocol to ensure reliable data transmission. In this article, we propose a dynamic superframe structure-based MAC protocol extending the principles of the IEEE 802.15.6 standard. In this work, to allocate dedicated slots for each sensor device, a prioritized dedicated slot allocation mechanism using the criteria importance through intercriteria correlation (CRITIC) is proposed. With the help of this method, the priority value of sensor devices is calculated based on different sensors’ parameters. We compared the performance of our proposed work with standard IEEE 802.15.6 MAC and a few other MAC protocols. The simulation result shows that our proposed MAC protocol performed better in terms of energy efficiency and reliability, as well as reducing the packet drop probability. Results show that the reliability of data transmission increases over the IEEE 802.15.6 MAC protocol by more than 50%.

Advances in wireless sensor networks and increasing Internet-of-Things devices give great opportunities for smart homecare of the elderly. Smart homecare has been a promising issue and received much attention recently. Irregularity detection is one of the most important issues in smart homecare for assessing the health condition of the elderly. However, most of the researches focused on the explicit irregularity detections which are usually based on the drastic changes of sensor data, such as falling. Existing mechanisms for detecting implicit irregularity rely on the subjective assessment of behaviors' importance by the elder and simply outputs the binary detection results. This article proposes a feature-based implicit irregularity detection mechanism (FIID), which extracts the regularity features using unsupervised learning and outputs the probability of implicit irregularity. The proposed FIID identifies the regular behaviors which satisfy the time-regular and happen-frequently properties as the regularity features of daily behaviors. These features then construct a multidimensional feature space to calculate the implicit irregularity probability of the daily health condition. Performance results show that the proposed FIID outperforms the existing implicit irregularity mechanism in terms of precision, recall as well as F-measure.

Behavior identification plays an important role in supporting homecare for the elderly living alone. In literature, plenty of algorithms have been designed to identify behaviors of the elderly by learning features or extracting patterns from sensor data. However, most of them adopted probabilistic models or supervised learning to identify behaviors based on labeled sensor data. This paper proposes a behavior identification algorithm (BIA) using unsupervised learning based on unlabeled sensor data for the elderly living alone in smart home. This paper presents the observation of elder behaviors with three features: Event Order, Time Length Similarity and Time Interval Similarity features. Based on these features of behavior observations, two properties of behaviors, including the Event Shift and Histogram Shape Similarity properties, are presented. According to these properties, the proposed BIA is developed. Finally, performance results show that the proposed BIA outperforms the existing unsupervised machine learning mechanisms in terms of the behavior identification precision and recall.

The irregularity detection of daily behaviors for the elderly is an important issue in homecare. Plenty of mechanisms have been developed to detect the health condition of the elderly based on the explicit irregularity of several biomedical parameters or some specific behaviors. However, few research works focus on detecting the implicit irregularity involving the combination of diverse behaviors, which can assess the cognitive and physical wellbeing of elders but cannot be directly identified based on sensor data. This paper proposes an Implicit IRregularity Detection (IIRD) mechanism that aims to detect the implicit irregularity by developing the unsupervised learning algorithm based on daily behaviors. The proposed IIRD mechanism identifies the distance and similarity between daily behaviors, which are important features to distinguish the regular and irregular daily behaviors and detect the implicit irregularity of elderly health condition. Performance results show that the proposed IIRD outperforms the existing unsupervised machine-learning mechanisms in terms of the detection accuracy and irregularity recall.

In wireless sensor networks, sensor deployment is an important issue in which sensors are deployed in a specific monitoring region using low-cost hardware but achieving high coverage quality. In recent years, several mechanisms have been developed for the efficient robotic deployment of sensors. Their performance levels are highly dependent on unknown obstacles that can give rise to the dead-end problem. A key challenge when developing a robot deployment mechanism is to overcome the dead-end problem and deliver full coverage with a minimal number of sensors. This paper proposes an impasse-aware robot deployment (IAD) algorithm. The proposed IAD mainly consists of basic deployment rules and dead-end handling rules. The basic deployment rules are intended to achieve full coverage with a minimal number of sensors; the proposed dead-end handling rules can efficiently resolve the dead-end problem. Extensive experimental studies have demonstrated that our proposed IAD achieves superior performance to that of existing robot deployment mechanisms with respect to coverage ratio, energy efficiency, deployment path length, and required stack space.

Barrier coverage has received much attention in the last decade and has been an import issue in wireless sensor networks. In the previous study, a number of researchers have presented algorithms for coping with the barrier coverage problem. However, these studies consider that sensors are equipped with batteries and the sensing model applies Boolean Sensing Model (BSM). The sensor using battery as its energy source can lead to the battery change problem which is difficult and inconvenient. Unlike previous studies, this work aims to resolve the barrier coverage problem but considers solar-powered sensors and applies the Probabilistic Sensing Model (PSM). A barrier coverage mechanism, called MSQ (Maximizing surveillance quality algorithm), is proposed aiming to maximize boundary surveillance quality. Performance experiments show that the proposed MSQ mechanism outperforms existing studies in terms of surveillance quality.

Wireless communication link quality can be determined by the transmission protocol design, the interference level, the channel fading properties, and the mobility characteristics etc. As one of the most essential features for vehicular networks, high mobility brings in intermittent connectivity and relative short link lifetime. Therefore, an analytical model on link lifetime can be of great help for an efficient and effective vehicular communication protocol design. In this paper, the impact of mobility on link lifetime in the highway environment is modeled and analyzed by utilizing the discrete-time Markov chain (DTMC). Specifically, two link lifetime theoretical models, the first-order Markov model and the second-order Markov model, are studied and analyzed for effectively predicting the proprieties of a vehicular communication link. It is shown that our proposed models, especially the second-order Markov model, can provide more accuracy in performance prediction. Additionally, extensive simulations are carried out to verify our analytical results on link lifetime.

Target coverage problems have received much attention in recent years. In a large monitoring environment where targets are distributed over an entire monitored region, deploying static sensors leads to high hardware costs because a high number of sensors may be required to achieve network connectivity. This paper considers the target-patrol issue where a set of mobile data mules (DMs) are dispatched to efficiently patrol the given targets under a predefined time constraint. The targets are assigned weights indicating their importance, where more important targets should be visited more frequently by the DMs. Accordingly, this paper proposes a time-constrained weighted targets patrolling (TCWTP) algorithm for locally constructing efficient patrol paths, thereby ensuring globally stable intervals between visits to all target points. A performance analysis revealed that the proposed TCWTP mechanism outperforms existing works in terms of the average interval between visits, quality of monitoring satisfaction ratio, and monitoring fairness ratio.

The k-Barrier Coverage is known as the problem of detecting the intruders by at least k sensors when the intruders moving along the crossing paths from one boundary to another. This paper proposes a barrier coverage mechanism for Wireless Mobile Sensor Networks (WMSNs). At the network initialization phase, all mobile sensors move in a distributed manner for constructing the k-Barrier Coverage. The paper aims at prolonging the barrier lifetime while achieving k-barrier coverage. Experimental study reveals that our proposed k-barrier coverage approach outperforms existing related schemes in terms of the energy consumption of mobile sensors participating in the k-barrier defense curve.

Point-based approach is a well-known localization approach in Wireless Sensor Networks (WSNs). However, by applying the point-based approach, the communication disk (communication range) of each sensor has to be passed through by the mobile anchor twice at least. To address this problem, this paper presents a Rapid Localization (RL) scheme which aims at reducing the time duration required for each node to determine its location. Experimental results show that the proposed RL scheme has better performance than existing localization scheme in terms of the average location error, time required of localization, and energy conservation.

In this paper, the target patrolling problem was considered, in which a set of mobile data collectors, known as data mules (DMs), must efficiently patrol a given set of targets. Because the time interval (or visiting interval) between consecutive visits to each target reflects the degree to which that target is monitored, the goal of this paper was to balance the visiting interval of each target. This paper first presents the basic target points patrolling algorithm, which enables an efficient patrolling route to be constructed for numerous DMs, such that the visiting intervals of all target points are stable. For scenarios containing weighted target points, a weighted target points patrolling (W-TPP) algorithm is presented, which ensures that targets with higher weights have higher data collection frequencies. The energy constraint of each DM was also considered, and this paper presents a W-TPP with recharge (RW-TPP) algorithm, which treats the energy recharge station as a weighted target and arranges for DMs to visit the recharge station before running out of energy. The performance results demonstrated that the proposed algorithms outperformed existing approaches in average visiting frequency, DM movement distance, average quality of monitoring satisfaction rate, and efficiency index.

Cognitive Radio (CR) is a novel and promising spectrum management technique which aims to cope with the spectrum scarcity problem occurred in unlicensed bands and alleviate the inefficient spectrum utilization of licensed bands. To ensure that the operation of licensed users will not be adversely affected but the licensed bands can be fully utilized by the unlicensed users, this paper proposes a cognitive radio MAC protocol, called SMC-CR-MAC. When any Primary User (PU) is detected, the proposed SMC-CR-MAC applies Contiguous Channel Switching and Sender-Receiver Channel Swap approaches to cope with the rendezvous, packet collision, and channel congestion problems. Simulation results show that the proposed SMC-CR-MAC can significantly improve the network performance in terms of the utilization of licensed bands and network throughput.

ABSTRACT In wireless sensor networks (WSNs), coverage of the monitoring area represents the surveillance quality. Since sensor nodes are battery powered and placed outdoor, there will be failures due to energy exhaustion or environmental influence, resulting in coverage‐loss. In literature, a number of studies developed robot repairing algorithms that aim at maintaining full coverage. However, they did not consider the time constraint for network maintenance. Furthermore, they did not consider the existence of obstacles and the constraint of limited energy of the robot. This paper presents a novel tracking mechanism and robot repairing algorithm for maintaining the coverage quality of the given WSN. Without support of location information, the tracking mechanism leaves robot's footmark on sensors so that they can learn better routes for sending repairing requests to the robot. Upon receiving several repairing request messages, the robot applies the proposed repairing algorithm to establish an efficient route that passes through all failure regions with low overhead in terms of the required time and the power consumption. In addition, the proposed repairing algorithm also considers the remaining energy of the robot so that the robot can move back to home for recharging energy and overcome the unpredicted obstacles. Performance results reveal that the developed protocol can efficiently maintain the coverage quality while the required time and energy consumption are significantly reduced. Copyright © 2011 John Wiley & Sons, Ltd.

Wireless Visual Sensor Networks (WVSNs) consist of a set of camera sensor nodes each of which equips with a camera and is capable of communicating with the other camera sensors within a specific distance range. As an extension of wireless sensor networks (WSNs), the WVSNs can provide richer information such as image and picture during executing targets monitoring and tracking tasks. Since the sensing area of each camera sensor is fan-shaped, existing barrier-coverage algorithms developed for WSNs cannot be applied to the WVSNs. This paper is considering to address the k-barrier coverage problems in WVSNs and to propose a barrier-coverage approach aiming at finding a maximal number of distinct defense curves with each of which consists of as few camera sensors as possible but still guarantees k-barrier coverage. Compared with the related work, experimental study reveals that the proposed k-barrier coverage mechanism constructs more defense curves than the k-barrier coverage and the number of camera sensors participating in each defense curve is smaller.

Abstract Coverage is one of the most important issues in Wireless Sensor Networks (WSNs). However, full coverage only can be achieved when surplus mobile sensors contribute a coverage area larger than the hole size. When there is no surplus mobile sensor to cover a big hole, previous studies have utilized mobile sensors by moving the hole from one location to another, therefore achieving temporal full‐coverage, where each location on the monitoring region has been ever covered by mobile sensors during a fixed time interval. However, with only some mobile sensors participating in the hole‐movement task, this results in an energy‐imbalance WSN. This paper considers a mobile WSN that contains a big hole where there exists no redundant mobile sensor to heal the hole. Three distributed algorithms, called Basic, Forward‐Only, and Any‐Direction movement mechanisms, are proposed to achieve the purpose of temporal full‐coverage in a way that the total energy consumption is minimized or that the energy consumption of all mobile sensors that participate in the hole‐movement task are balanced. Simulation results reveal that the proposed hole‐movement mechanisms enhance the coverage of WSNs and balance the energy consumption of mobile sensor nodes. Copyright © 2010 John Wiley & Sons, Ltd.

This paper considers the target patrolling problem which asks a set of mobile data mules to efficiently patrol a set of given targets. Since the time interval (also referred to visiting interval) for consecutively visiting to each target reflects the monitoring quality of this target, the goal of this research is to minimize the maximal visiting interval. This paper firstly proposes a basic algorithm, called Basic (B-TCTP), which aims at constructing an efficient patrolling route for a number of given data mules such that the visiting intervals of all target points can be minimized. For the scenario containing weighted target points, a Weighted-TCTP (W-TCTP) algorithm is further proposed to satisfy the demand that targets with higher weights have higher data collection frequencies. By considering the energy constraint of each data mule, this paper additionally proposes a RW-TCTP algorithm which treats energy recharge station as a weighted target and arranges the data mules visiting the recharge station before exhausting their energies. Performance study demonstrates that the proposed algorithms outperform existing approaches in terms of visiting intervals of the given targets and length of patrolling path.

Abstract A Wireless Mesh Network (WMN) consists of fixed wireless routers, each of which provides service for mobile clients within its coverage area and inter‐connects mesh routers to form a connected mesh backbone. Wireless mesh routers are assigned with a channel or a code to prevent collisions in transmission. With a power control mechanism, each router could be assigned with a power level to control connectivity, interference, spectrum spatial reuse, and topology. Assigning high transmitting power level to a router can enhance the network connectivity but may increase the number of neighbors and worsen the collision problem. How to assign an appropriate power level to each router to improve the network connectivity with a constraint of limited channels is one of the most important issues in WMNs. Given a network topology and a set of channels that has been assigned to mesh routers, the proposed channel‐switching mechanism further reassigns each router with a power level and switches channels of routers to optimize both power efficiency and connectivity. A matrix‐based presentation and operations are proposed to respectively identify and resolve the channel switching problems. Simulation study reveals that the proposed mechanisms increase network throughput and provides a variety of route selection, and thus improves the performance of a given WMN. Copyright © 2009 John Wiley & Sons, Ltd.

Smart antenna (or Multi-beam antenna) systems can support simultaneous transmissions (or receptions) of multiple packets on different beams using the same channel. However, the network performance highly depends on the transmission scheduling. Based on the cluster topology, this paper aims at developing transmission scheduling approaches with smart antenna systems for maximizing the network throughput and minimizing the transmission delays. Initially, a set of parallel groups are constructed with consideration of the constraints for multi-beam smart antenna systems. Then two scheduling approaches, called MaxPTran and DAS, are proposed for scheduling multiple transmissions on different beams. Performance study reveals that the proposed approaches outperform existing work in terms of network throughput and transmission delay.

Bounding-box mechanism is a well known low-cost localization approach for wireless sensor networks. However, the bounding-box location information can not distinguish the relative locations of neighboring sensors, hence leading to a poor performance for some applications such as location-aware routing. This paper proposes a Distinguishing Relative Locations (DRL) mechanism which uses a mobile anchor to broadcast tones and beacons aiming at distinguishing the relative locations of any two neighboring nodes. Experimental study reveals that the proposed DRL mechanism effectively distinguishes relative locations of any two neighboring nodes and hence significantly improves the performance of location-aware routing in wireless sensor networks (WSNs).

In wireless sensor networks (WSNs), the performance of robot deployment is highly determined by the obstacle-resistance capability which refers to how well the robot can overcome the Dead-End problem and deploy minimal number of sensors for achieving full coverage even though the environment contains multiple obstacles. This paper presents a Dead-End free robot deployment algorithm, called DFD, that efficiently deploys minimal number of sensors for achieving full coverage while the Dead-End problem raised by obstacles can be overcome. Performance results reveal that the proposed DFD outperforms existing robot deployment mechanisms in terms of coverage ratio, energy consumption as well as deployment time.

In wireless mobile sensor networks, spatial full-coverage only can be achieved when the surplus mobile sensors contribute a larger coverage area than the hole size. The temporal full coverage problem asks to monitor every point of a given monitoring region within a specific time interval. This paper considers a mobile WSN that contains holes but exists no redundant mobile sensor to heal the hole. To achieve the temporal full-coverage purpose, a distributed hole-movement mechanism is proposed to balance the energy consumptions of mobile sensors. Simulation study reveals that the proposed hole-movement mechanism enhances the coverage ratio of WSN and balance the energy consumption of mobile sensor nodes.

Vehicular Ad-Hoc Networks (VANETs) technologies can improve traffic safety for drivers and provide comfort services for passengers through copious amounts of Internet resources. Since the hardware of Road Side Unit (RSU) is costly, in most previous researches, vehicles exchange their data with RSU in a multi-hop manner. However, the vehicle with a larger number of hops to the RSU has fewer opportunities and longer time to communicate with RSU since the contentions and collisions increase with the number of hops. This paper proposes a Joint Throughput Enhancement and Fairness (JTEF) MAC protocol aiming to increase bandwidth utilization, maintain fairness, and avoid collision in a VANET environment. Performance study reveals that the proposed JTEF protocol outperforms existing CVIA protocol in terms of end-to-end throughput and fairness.

Abstract Wireless sensor networks (WSNs) are characterized by their low bandwidth, limited energy, and largely distributed deployment. To reduce the flooding overhead raised by transmitting query and data information, several data‐centric storage (DCS) mechanisms are proposed. However, the locations of these data‐centric nodes significantly impact the power consumption and efficiency for information queries and storage capabilities, especially in a multi‐sink environment. This paper proposes a novel dissemination approach, which is namely the dynamic data‐centric routing and storage mechanism (DDCRS), to dynamically determine locations of data‐centric nodes according to sink nodes' location and data collecting rate and automatically construct shared paths from data‐centric nodes to multiple sinks. To save the power consumption, the data‐centric node is changed when new sink nodes participate when the WSNs or some queries change their frequencies. The simulation results reveal that the proposed protocol outperforms existing protocols in terms of power conservation and power balancing. Copyright © 2009 John Wiley & Sons, Ltd.

The IEEE 802.16j draft proposes a multi-hop relay network architecture that introduces the new network element of relay station aimed at increasing the network throughput or coverage. The deployment of the relay stations is one of the most important issues that determines the network throughput. Given a base station, k relay stations, and a deployed region that can be fully covered by the BS, this paper proposes a relay deployment mechanism that determines the deployed locations of RSs so that the bandwidth requirement of MSs can be satisfied while the network throughput can be significantly improved. Experimental study reveals that the proposed mechanism can efficiently determine the locations for relay deployment and improve the network throughput.

The k-barrier coverage problem is known as the problem of detecting the intruders by at least k sensors when the intruders moving along the crossing paths from one boundary to another. This paper proposes decentralized algorithms to cope with the k-barrier coverage problem. For a given value k, the proposed algorithms find out the maximum disjoint sets of sensors such that each set of sensors meets the requirement of k-barrier coverage for users. Three mechanisms, called Basic, Backtracking, and Branch, are proposed for constructing as more as possible the disjoint sets of sensors that satisfy the requirement of k-barrier coverage. Performance study reveals that the proposed algorithms achieve near-optimal performance.

WiMAX Mesh Network architecture is defined in IEEE 802.16 for increasing the network coverage and improving the communication performance. In the past few years, many greedy or heuristic approaches have been proposed to cope with the scheduling problem in WiMAX mesh networks. However, their performances highly depend on the network topology and the bandwidth requests and none of them achieves optimal for all cases. This paper proposes an efficient scheduling algorithm that exploits the opportunities of spatial reuse and maximize the network throughput based on the network topology and the uplink transmission requests of each Subscriber Station(SS). Simulation study reveals that the proposed efficient scheduling algorithm provides the WiMAX mesh network with maximal throughput and shortest transmission time.

This paper proposes a robot deployment algorithm that overcomes unpredicted obstacle, and employs a full-coverage deployment with the minimal number of sensor nodes. Without providing the location information, a spiral movement rule is proposed for robot efficiently deploying sensors to achieve power conservation and full-coverage purposes. Simulation results reveal that the proposed robot deployment algorithm outperforms most existing robot deployment mechanisms in power conservation and obstacle resistance, and therefore achieves the better deployment performance.

This paper proposes a robot-deployment algorithm that overcomes unpredicted obstacles and employs full-coverage deployment with a minimal number of sensor nodes. Without the location information, node placement and spiral movement policies are proposed for the robot to deploy sensors efficiently to achieve power conservation and full coverage, while an obstacle surrounding movement policy is proposed to reduce the impacts of an obstacle upon deployment. Simulation results reveal that the proposed robot-deployment algorithm outperforms most existing robot-deployment mechanisms in power conservation and obstacle resistance and therefore achieves a better deployment performance.

The greedy forwarding routing protocol has been widely used for constructing a route with low control overheads in wireless sensor networks. However, its performance drops significantly when obstacles exist. This paper proposes a novel mechanism, named WRGP, which removes the impact of obstacles on the greedy forwarding routing. The proposed WRGP initially applies the previous research to specify the border nodes that surround the obstacle. Then the border nodes in the concave region of the obstacle initiate the weight assigning process and establish a forbidden region to prevent the packets from entering the concave region. Finally WRGP specifies some border nodes to act as the effective border nodes for constructing the optimal routes from themselves to the sink node. Comparing with the existing obstacles-resisting protocols, the proposed WRGP avoids the ping-pong effect and guides the packets moving along the shortest path from the encountered effective border node to the sink node. In addition, the M-WRGP is further developed to cope with the multi-obstacle problem. Simulation results show that both WRGP and M-WRGP outperform the existing protocol PAGER in terms of control overheads and average route length.

Location information is of utmost importance for most applications in wireless sensor networks. Recent localization schemes have been categorized into range and range-free based techniques. Obvious inclination is towards range free algorithms since they do not rely on special hardware that would be required in range based algorithms. In the most proposed range-free algorithms, nodes estimate their location using the geometric constraints imposed by the location of a mobile anchor. However, there is no discussion on how the mobile anchor moves so that the maximal location accuracies of all sensor nodes can be obtained with the constraint of energy consumption of a mobile anchor. This paper assumes that traditional range-free algorithms have been executed for a certain time period and the deployed sensors are with different location accuracies. We propose path guiding mechanisms that sensor nodes cooperatively guide the mobile anchor moving along an efficient path which can maximize the improvement of location accuracies or minimize the accuracy differences for all sensor nodes in a given WSN. Experimental study reveals that the proposed path guiding mechanisms effectively guide the mobile anchor moving along the efficient path and thereby saves time and energy consumptions for improving or balancing the location accuracies of all sensor nodes.

The paper proposes a self-regulatory-learning- cycle-based system to not only provide a pleasant learning environment, but also effectively enhance the performance of self-regulated learning (SRL) of learners. Learners utilizing the proposed system can repeatedly experience SRL processes and establish their patterns of SRL gradually. Experiment results show that the proposed system can help learners possess SRL skills, especially for unskillful learners.

Bluetooth is a low-cost, low-power and short range communication technology, which operates in 2.4 GHz ISM band. The important research issues in Bluetooth are scatternet formation and routing, since nodes can arrive and depart at arbitrary time. In this paper, novel route maintenance algorithms are proposed for the Bluetooth scatternet that supports mobility of the nodes. Our protocols guarantee the connectivity among nodes and reconstruct the routes dynamically by taking their location information. Besides, we propose how to reduce the number of hops and to form the shortest route between the source and the destination due to addition of nodes. Performance analysis of our work shows that it outperforms in terms of end to end transmission delay, bandwidth consumption and route maintenance as compared to similar Bluetooth routing protocols.

In wireless sensor networks (WSNs), a hole is formed due to the non-uniform deployment, nodes failure, and some natural phenomena such as animals' residence or fierce wind making sensor nodes broken. The existence of a hole reduces both the accuracy of data collection and the efficiency of communications. Recently, many studies proposed mechanisms to detach a robot that loads with static sensors to heal the hole and maintain the spatial full coverage. Some other studies utilized mobile sensors to patrol the hole, maintaining the temporal full coverage. However, an irregular hole results in the redeployment and patrolling tasks inefficiency. This protocol proposes a novel mechanism, called HONOR, to normalize an irregular hole in a mobile WSN. Mobile sensors that detect the hole cooperate with each other to regularize the irregular hole in a distributed manner. As a result, the efficiency of robot's redeployment and the mobile sensors' patrol are significantly improved. Simulation results reveal that HONOR efficiently regularizes the hole shape and therefore saves energy consumption and delay time required for the robot's redeployment and the mobile sensors' patrol.

Node deployment is an important issue in wireless sensor networks (WSNs). Sensor nodes should be efficiently deployed in a predetermined region in a low cost and high coverage quality manner. Random deployment is the simplest way for deploying sensor nodes but may cause the unbalanced deployment and therefore increase the hardware cost. This paper presents an efficient obstacle-free robot deployment algorithm, called OFRD which involves the design of node placement policy, snake-like movement policy, and obstacle handling rules. By applying the proposed OFRD, the robot rapidly deploys near-minimal number of sensor nodes to achieve full sensing coverage even though there exist unpredicted obstacles. Performance results reveal that OFRD outperforms the existing robot deployment mechanism in terms of power conservation and obstacle resistance, and, therefore achieves a better deployment performance.

This paper considers a mobile WSN that contains a big hole but there exists no redundant mobile sensor to heal the hole. To achieve the temporal full-coverage purpose or enhance the tracking quality, three distributed algorithms are proposed for moving the existing big coverage hole to a predefined location. Firstly, the sink chooses a promising direction for hole-movement. Then the basic, forward-only and any-direction movement mechanisms are proposed to move the hole along the promising direction in a manner of minimizing the total power consumption or balancing the energy consumption of the given WSN. Simulation results reveal that the proposed hole-movement mechanisms enhance the coverage of WSN and balance the energy consumption of mobile sensor nodes.

The sharable content object reference model (SCORM) is a set of specifications and guidelines for the representation and operation of asynchronous distance learning. Since it was announced in late 1990s, the reference model has been used by software developers and academics in the development of authoring tools, learning management systems, and repositories for distance learning content. To date, most e-learning systems have been based on multimedia and Web technologies on personal computers. Our project, Hard SCORM, advances the field by implementing an integrated system which allows learners to read SCORM-compliant textbooks using multimodal multimedia devices. Hard SCORM employs a pen-like optical character reader device (called Hyper Pen) as an input mechanism. A computer, a personal digital assistant, or a cellular phone can be used for user behavior supervision using the hard SCORM machine. With an authoring tool, specially designed tags are printed in textbooks and recognized by hyper pen for user navigation control. In this way, users can read hardcopy textbooks in a traditional manner while the process of reading conforms to the SCORM specification. Part of the implemented system (Pocket SCORM on PDA) received the 2005 Brandon Hall Excellence in Learning Awards. The system has also been used by an airline company for online security checking and a high school for online mobile learning

The paper proposes an RCA MAC protocol to reduce RTS collisions. The protocol utilizes a narrow band, called the tone channel, to announce the RTS transmission in advance to preclude the RTS transmissions of two-hop neighbors. To reduce the channel and hardware overhead, an improvement to the RCA protocol is also devised, which only uses a single channel and one transceiver to reduce RTS collisions. The RCA protocol provides a type of fast collision detection and decreases the probability of RTS collisions. Meanwhile, the RCA protocol can reduce the retransmission cost and has lower control overhead than that of IEEE 802.11 DCF. In addition, simulation results verify the advantages of the RCA protocol in comparison with IEEE 802.11 DCF.

In wireless sensor networks (WSNs), nodes closer to the sink node have heavier traffic load for packet forwarding. The unbalanced power consumption among sensor nodes may cause network partition. This paper proposes efficient node placement and topology control protocols to balance the power consumption of sensor nodes. Firstly, a virtual tree topology is constructed based on Grid-based WSNs. Then two node placement techniques, namely Distance-based and Density-based deployment schemes are proposed to balance the power consumption of sensor nodes. Finally, extension of the proposed protocols are made from a Grid-based WSN to a randomly deployed WSN, making the developed energy-balanced schemes can be generally applied to randomly deployed WSNs. Simulation results reveal that the developed protocols can efficiently balance each sensor node's power consumption and prolong the network lifetime in both Grid-based and randomly deployed WSNs.

In wireless sensor networks, a geographic region without functionality of sensing and communication can be generally treated as an obstacle, which significantly impacts the performance of existing location-based routing. In a WSN, an obstacle can be dynamically formed due to unbalanced deployment, failure or power exhaustion of sensors, animus interference, or physical obstacles such as mountains or buildings. This paper proposes a novel algorithm, namely RGP, to enable the existing location-based routing protocols resisting obstacles. Applying the proposed RGP, border nodes that surround the obstacles will actively establish a forbidden region for concave obstacles and make the obstacle information transparent. Then packets will be guided to overcome the obstacle and move along the shortest path from the encountered border node to the sink node. Simulation results show that RGP creates low overhead and significantly reduces the average route length and therefore improves the energy consumption and end-to-end delay for a wireless sensor network with obstacles

IEEE 802.11 provides a contention based MAC protocol for single channel wireless environment. Extending IEEE 802.11 to a multi-channel environment will not only exploit the bandwidth utilization but also reduce the degree of contentions. Involving directional antenna in designing multichannel MAC protocol additionally increases the spatial reuse, allowing more communications proceeding in parallel. This paper proposes an efficient 802.11 multi-channel MAC protocol with directional antenna (MCDA). Since each station is only equipped with a single antenna, communicating pairs that progress their communications on data channels will unable to maintain the channel usage information which is only obtained from the control channel, raising the channel collision problem. The proposed protocol adopts mechanism of channel switch sequence (CSS) to resolve the channel collision problem and reduce the overhead in message exchange for switching channel. According to the state management, MCDA then controls directional antenna transmitting data on a selected channel to exploit the opportunities of spatial reuse and maintain the fairness among communicating pairs. Simulation results show that the proposed MCDA protocol can largely improve the bandwidth utilization and throughput while the fairness could be maintained.

Scarce resources of wireless medium (e.g., bandwidth, battery power, and so on) significantly restrict the progress of wireless local area networks (WLANs). Heavy traffic load and high station density are most likely to incur collisions, and further consume bandwidth and energy. In this paper, a distributed power-saving protocol, power-efficient MAC protocol (PEM), to avoid collisions and to save energy is proposed. PEM takes advantage of power control technique to reduce the interferences among transmission pairs and increase the spatial reuse of WLANs. Based on the concept of maximum independent set (MIS), a novel heuristic scheme with the aid of interference relationship is proposed to provide as many simultaneous transmission pairs as possible. In PEM, all stations know when to wake up and when they can enter doze state. Thus, stations need not waste power to idle listen and can save much power. The network bandwidth can be efficiently utilized as well. To verify the performance of PEM, a lot of simulations are performed. The experimental results show that with the property of spatial reuse, PEM not only reduces power consumption, but also leads to higher network throughput in comparison with the existing work, such as DCF, DCS, and DPSM.

Bluetooth is a well-known wireless technology designed for wireless personal area networks (WPAN). The Bluetooth device randomly searches and connects with other devices using the inquiry/inquiry scan and the page/page scan operations, resulting an uncontrolled scatternet topology. The unpredictable scatternet topology usually raises the problem of redundant traffic and causes inefficient communications. A traffic-aware restructuring protocol (TARP) is presented for partially restructuring a piconet or neighboring piconets by applying role switch mechanism. According to the recent routes and their traffic pattern, the TARP adjusts piconet structure by selecting the proper master from devices of a piconet and switches proper devices of neighboring piconets to reduce the route length and thus improve the power and bandwidth consumptions and transmission delay. Performance results show that TARP significantly improves network performance by reducing traffic load and power consumptions.

Wireless sensor networks (WSNs) have been widely used in monitoring and collecting information. Packet flooding or broadcasting is an essential function for establishing a communication path from the sink node to a region of sensor nodes. However, flooding operation consumes power and bandwidth resources and raises the packet collision and contention problems, which reduce the success rate of packet transmissions and consume energy. This article proposes an efficient broadcasting protocol to reduce the number of sensor nodes that forward the query request, hence improving the packet delivery rate and saving bandwidth and power consumptions. The sensor node that received the query request dynamically transfers the coordinate system according to the zone-ID of the source node and determines whether it would forward the request or not in a distributed manner. Compared with a traditional flooding operation, experimental results show that the proposed zone-based broadcasting protocol decreases the bandwidth and power consumptions, reduces the packet collisions, and achieves a high success rate of packet broadcasting.

Bluetooth is a low-power, low-cost, and short-range wireless technology. A well structured scatternet, with the appropriate number of piconets and bridges for a specific traffic pattern, increases the performance of a Bluetooth network. However, the structure of a scatternet is difficult to control or predefine because the scatternet is formed using a distributed procedure, with the master and slaves of each piconet connected at random. The participation of mobile Bluetooth devices in a scatternet at different times also increases the difficulty of maintaining a good structure. A badly structured scatternet exhibits the following characteristics: too many bridges in the scatternet creates a guard slot overhead associated with bridge switching among the participating piconets, increasing the probability that a packet is lost; too many piconets in a communicative range causes packet collision and thus degrades the performance; unnecessary piconets also lengthen the routing path, delaying the transmission of packets from source to destination. The paper proposes a distributed scatternet reconstruction protocol for dynamically reorganizing the scatternet. Unnecessary bridges and piconets can be dynamically removed by applying a role switching operation, improving the packet error rate, saving guard slots, and reducing the average routing length. By experiment, it is shown that the proposed protocol improves the data transmission performance of a Bluetooth scatternet.

In existing parallel computing structures, hypercubes have several distinct advantages; they support parallel computing, provide disjoint path and tolerate faults. If devices with computing capabilities can be linked as a hypercube by taking advantage of Bluetooth radio's features, then a high performance computing and efficient communication environment can be established by applying currently used algorithms. This is a pilot study of applying Bluetooth wireless technology to construct a parallel computation and communication environment. A three-stage distributed construction protocol is presented for automatically constructing a hypercube computing environment from Bluetooth devices. The proposed protocol tackles the link construction, role assignment, scatternet formation and network management problems, to construct efficiently a hypercube structure. The proposed protocol enables Bluetooth devices easily to construct a routing path, tolerate faults and create disjoint paths. Parallel and distributed computing will be realized in a Bluetooth wireless environment. Experimental results show the proposed protocol will be able to set up a scatternet that is appropriate for parallel computing and communications.

Mobile ad hoc networks (MANET) comprise mobile hosts in a network bereft of base stations and characterized by a highly dynamic network topology. The MANET environment contains unpredictable obstacles, such as mountains, lakes, buildings, or regions without any hosts, impeding or blocking message relay. This study proposes geocasting protocol for sending short message from a source host to a geocasting region in ad hoc networks. The proposed protocol keeps messages away from unpredictable obstacles and creates a small flooding region. Experimental results show that a source host can send a short message to all hosts located in geographical area with a high success rate and low flooding overhead.

The paper presents an algorithm to reduce cache conflicts and improve cache localities. The proposed algorithm analyzes unique locality reference space for each reference pattern, partitions the multi-level cache into several parts with different size, and then maps array data onto the scheduled cache positions such that cache conflicts can be eliminated. To reduce the memory overhead for mapping array variables onto partitioned cache, a greedy method for rearranging array variables in declared statement is also developed. In addition, we combine loop tiling and the proposed schemes for exploiting both temporal and spatial reuse opportunities. To demonstrate that our approach is effective at reducing the number of cache conflicts and exploiting cache localities, we use Atom as a tool to develop a simulator for simulation of the behavior of direct-mapping cache. Experimental results show that applying our cache partitioning scheme can largely reduce the cache conflicts and thus save program execution time in both one-level cache and multi-level cache hierarchies.

This paper presents an efficient compilation technique to generate the local memory access sequences for block-cyclically distributed array references with affine subscripts in data-parallel programs. For the memory accesses of an array reference with affine subscript within a two-nested loop, there exist repetitive patterns both at the outer and inner loops. We use tables to record the memory accesses of repetitive patterns. According to these tables, a new start-computation algorithm is proposed to compute the starting elements on a processor for each outer loop iteration. The complexities of the table constructions are O(k+s/sub 2/), where k is the distribution block size and s/sub 2/ is the access stride for the inner loop. After tables are constructed, generating each starting element for each outer loop iteration can run in O(1) time. Moreover, we also show that the repetitive iterations for outer loop are Pk/gcd(Pk,s/sub 1/), where P is the number of processors and s/sub 1/ is the access stride for the outer loop. Therefore, the total complexity to generate the local memory access sequences for a block-cyclically distributed array with affine subscript in a two-nested loop is O(Pk/gcd/(Pk,s/sub 1/)+k+s/sub 2/).

Abstract A large class of loop programs applied in solving differential equations, Fourier transforms, image processing and neural processing can be translated or rewritten into a vector execution form with a π‐block dependence graph. In the paper we propose a multithreading strategy to partition such vectorized loops into multithread execution form. Each partitioned thread consists of instances of statements with localities in vector registers. The multithreading scheme gives a novel combination of loop unrolling, statement instances reordering, index shifting, vector register reuse exploiting and multithreading. For some cases of loop program with π‐block dependence graph, experimental results show that our scheme assists vector compilers of the Convex C38 series to reduce the number of memory accesses and synchronizations among CPUs.

In this paper, we propose a source-to-source compilation strategy to partition vectorized loop programs into multithread execution form. Each partitioned thread consists of instances of statements with localities in vector registers. The multi-threading scheme gives a novel combination of loop unrolling, statement instances reordering, index shifting, vector register reuse exploiting, and multi-threading. Experimental results show that our multithreading scheme assists vector compiler of Convex C38 series to reduce the number of memory accesses and the number of synchronizations among CPUs and usually obtains a better performance.

FOR-loops are the main source of parallelism in programs. A nonlinear transformation algorithm for parallelizing the execution of FOR-loop models is proposed. It is shown that by the mapping of nonlinear transformation, iterations of FOR-loops can be executed in a parallel form. The algorithm is useful in exploiting the parallelism of FOR-loops with one or more partitions on the innermost loop. Algorithms to partition and map the nested FOR-loops onto fixed size systolic arrays are discussed. Based on the time and space mapping schemes, all the iterations of FOR-loops can be correctly executed on the array processors in a parallel form.>