Centralized Algorithm Research Articles

JSQE: Joint Surveillance Quality and Energy Conservation for Barrier Coverage in WSNs

Barrier coverage is a fundamental issue in wireless sensor networks (WSNs). Most existing works have developed centralized algorithms and applied the Boolean Sensing Model (BSM). However, the critical characteristics of sensors and environmental conditions have been neglected, which leads to the problem that the developed mechanisms are not practical, and their performance shows a large difference in real applications. On the other hand, the centralized algorithms also lack scalability and flexibility when the topologies of WSNs are dynamically changed. Based on the Elfes Sensing Model (ESM), this paper proposes a distributed Joint Surveillance Quality and Energy Conservation mechanism (JSQE), which aims to satisfy the requirements of the desired surveillance quality and minimize the number of working sensors. The proposed JSQE first evaluates the sensing probability of each sensor and identifies the location of the weakest surveillance quality. Then, the JSQE further schedules the sensor with the maximum contribution to the bottleneck location to improve the overall surveillance quality. Extensive experiment results show that our proposed JSQE outperforms the existing studies in terms of surveillance quality, the number of working sensors, and the efficiency and fairness of surveillance quality. In particular, the JSQE improves the surveillance quality by 15% and reduces the number of awake sensors by 22% compared with the relevant TOBA.

Resource Allocation in Time Slotted Channel Hopping (TSCH) Networks Based on Phasic Policy Gradient Reinforcement Learning

The concept of the Industrial Internet of Things (IIoT) is gaining prominence due to its low-cost solutions and improved productivity of manufacturing processes. To address the ultra-high reliability and ultra-low power communication requirements of IIoT networks, Time Slotted Channel Hopping (TSCH) behavioral mode has been introduced in IEEE 802.15.4e standard. Scheduling the packet transmissions in IIoT networks is a difficult task owing to the limited resources and dynamic topology. In IEEE 802.15.4e TSCH, the design of the schedule is open to implementation. In this paper, we propose a phasic policy gradient (PPG) based TSCH schedule learning algorithm. We construct the utility function that accounts for the throughput, and energy efficiency of the TSCH network. The proposed PPG based scheduling algorithm overcomes the drawbacks of totally distributed and totally centralized deep reinforcement learning-based scheduling algorithms by employing the actor–critic policy gradient method that learns the scheduling algorithm in two phases, namely policy phase and auxiliary phase. In this method, we show that the schedule converges quickly compared to any other actor–critic method and also improves the system throughput performance by 58% compared to the minimal scheduling function, a default TSCH schedule.

Joint Parallel Offloading and Load Balancing for Cooperative-MEC Systems With Delay Constraints

Mobile-edge computing (MEC) has been recognized as a promising solution to provide efficient communication and computation capabilities for mobile users (MUs). However, the problem relating to parallel offloading and load balancing with multiple cooperative MEC servers and massive delay-sensitive execution workloads remains to be investigated. In this paper, we study a joint parallel offloading and load balancing policy for such an MEC system. We formulate a long-term system average-cost (i.e., weighted sum of energy consumption and execution delays) stochastic programming problem under MU battery level stability and delay constraints. Our aims include optimizing the data sizes for uplink offloading transmissions for optimized communication and computation resource allocation among multi-users, and maximizing the computation capability utilization of cooperative MEC servers by load balancing. To solve this problem, we first design a Lyapunov-based centralized cost management algorithm (LYP-CCMA) to obtain the optimal system average-cost under the battery level stability constraints. Further, we propose two algorithms based on alternating direction method of multipliers (ADMM) to implement distributed resources allocation. Simulation results verify our analysis and demonstrate the superior performance of our proposed schemes over several baseline schemes.

On the advantage of centralized strategies in the three-pursuer single-evader game

Cooperation in multi-pursuer games is known to be useful. However, it is not easy to quantify how much it is convenient for the pursuers to play according to a centralized strategy with respect to a decentralized one. This paper provides an answer to this question, for the problem of three pursuers chasing a single evader in a planar environment. It is shown that centralized pursuit algorithms can halve the time required to capture the evader, with respect to decentralized pursuit strategies. Moreover, this limit is proven to be tight. Numerical computations of lower bounds to the ratio between the capture times of centralized and decentralized strategies, show that for several game initial conditions the benefit of playing in a centralized way may be significantly less than halving the game duration.

Distributed Triangle Approximately Counting Algorithms in Simple Graph Stream

Recently, the counting algorithm of local topology structures, such as triangles, has been widely used in social network analysis, recommendation systems, user portraits and other fields. At present, the problem of counting global and local triangles in a graph stream has been widely studied, and numerous triangle counting steaming algorithms have emerged. To improve the throughput and scalability of streaming algorithms, many researches of distributed streaming algorithms on multiple machines are studied. In this article, we first propose a framework of distributed streaming algorithm based on the Master-Worker-Aggregator architecture. The two core parts of this framework are an edge distribution strategy, which plays a key role to affect the performance, including the communication overhead and workload balance, and aggregation method, which is critical to obtain the unbiased estimations of the global and local triangle counts in a graph stream. Then, we extend the state-of-the-art centralized algorithm TRIÈST into four distributed algorithms under our framework. Compared to their competitors, experimental results show that DVHT-i is excellent in accuracy and speed, performing better than the best existing distributed streaming algorithm. DEHT-b is the fastest algorithm and has the least communication overhead. What’s more, it almost achieves absolute workload balance.

Data Reconstruction Coverage Based on Graph Signal Processing for Wireless Sensor Networks

Sensing coverage is a crucial metric for the quality of service of Wireless Sensor Networks (WSNs). Coverage models have a great impact on sensing coverage of WSNs. However, existing coverage models are simple but inefficient, like the most frequently used disk coverage model, in which a covered point is within the fixed sensing radius of at least one sensor node. Thus, how to develop an efficient coverage model is an essential problem. To this end, in this letter, we propose a novel coverage model without the limitation of the sensor’s sensing radius, namely, Data Reconstruction Coverage (DRC). Based on the theory of graph signal processing, the model can jointly reconstruct missing data at unsampled points (which are not covered by any sensors) by using our proposed centralized data reconstruction coverage algorithm which fully exploits the smoothness of temporal difference signals and the graph Laplacian matrix, without increasing the number of sensors. Simulation results based on real-world datasets show that the proposed DRC model has better coverage performance of WSNs compared with the disk coverage model and confident information coverage model typically used in WSNs.

Distributed multi-user QoS-aware service selection

Previous research on service selection in cloud environments often assumes a centralised broker that keeps track of all candidate services and selects the appropriate candidate for each user request based on quality of service (QoS). As the number of users and services increases, the centralised service selection algorithm becomes a bottleneck. We propose a distributed, multi-broker selection algorithm that enables real-time processing of a large number of user requests. Each broker keeps track of a subset of users and a subset of service candidates, and rebalancing is performed to ensure that no broker is overloaded. The selection procedure considers the user QoS requirements, service QoS values and their processing capacities. Simulations demonstrate a clear advantage of the proposed approach over a single-broker approach by up to 96% in terms of QoS satisfaction when using 100 brokers, and especially in terms of response time satisfaction, showing positive impact of user and service balancing, and analysing various selection algorithms run by the brokers.

Load-Aware Dynamic Mode Selection for Network-Assisted Full-Duplex Cell-Free Large-Scale Distributed MIMO Systems

The network-assisted full-duplex (NAFD) system realizes flexible duplex in the spatial domain within the same time-frequency resource. With the explosive growth of the number of users and remote antenna units (RAUs) under 6G scenario, the resource utilization of the system is lower. When the resource of users is selected by the RAUs to send or receive, collisions or congestion may occur due to mechanisms such as grant-free. Aiming at making better use of system resources, a load-aware dynamic mode selection scheme with NAFD scheme is proposed to improve the access efficiency and resource utility of the system. This paper first propose a centralized Q-learning algorithm which determines a clever strategy to approach the ultimate goal by itself and excels in environment dynamics. However, the size of the Q-table used in the centralized Q-learning algorithm for storage is huge. Further, a distributed multi-agent Q-learning algorithm is proposed which has a smaller size of Q-table and lower complexity to suit for actual scenarios. The simulation results showed that the proposed load-aware dynamic mode selection scheme can significantly improve resource utility and throughput performance than other traditional schemes.

Video Content Placement At the Network Edge: Centralized and Distributed Algorithms

In the traditional video streaming service provisioning paradigm, viewers typically request video content through a central Content Delivery Network (CDN) server. However, because of the uncertain wide area network delays, the (remote) viewers usually suffer from long video streaming delay, which affects the quality of experience. Multi-Access Edge Computing (MEC) offers a way to shorten the video streaming delay by building small-scale cloud infrastructures at the network edge, which are in close proximity to the viewers. In this paper, we present novel centralized and distributed algorithms for the video content placement problem in MEC. In the proposed centralized video content placement algorithm, we leverage the Lyapunov optimization technique to formulate the video content placement problem as a series of one-time-slot optimization problems and apply an Alternating Direction Method of Multipliers (ADMM)-based method to solve each of them. We further devise a distributed Multi-Agent Reinforcement Learning (MARL)-based method with value decomposition mechanism and parallelization policy update method to solve the video content placement problem. The value Decomposition mechanism deals with the credit assignment among multiple agents, which promotes the cooperative optimization of the global target and reduces the frequency of information exchange. The parallelization of policy network can speed up the convergence process. Simulation results verify the effectiveness and superiority of our proposed centralized and distributed algorithms in terms of performance.

Federated Learning for Privacy-Preserved Medical Internet of Things

Healthcare is one of the notable areas where the integration of the Internet of Things (IoT) is highly adopted, also known as the Medical IoT (MIoT). So far, MIoT is revolutionizing healthcare because it provides many advantages for the benefit of patients and healthcare personnel. The use of MIoT is becoming a booming trend, generating a large amount of IoT data, which requires proper analysis to infer meaningful information. This has led to the rise of deploying artificial intelligence (AI) technologies, such as machine learning (ML) and deep learning (DL) algorithms, to learn the meaning of this underlying medical data, where the learning process usually occurs in the cloud or telemedicine servers. Due to the exponential growth of MIoT devices and widely distributed private MIoT data sets, it is becoming a challenge to use centralized learning AI algorithms for such tasks. In this connection, federated learning (FL) is gaining traction as a possible method of learning on devices that do not need to migrate private and sensitive data to a central cloud. The terminal equipment and the central server in FL only share learning model updates to ensure that sensitive data is always kept secret. Even though this has recently become a promising research area, no other research has been conducted on this topic recently. In this paper, we synthesize recent literature and FL improvements to support FL-driven MIoT applications and services in healthcare. The findings of this research help stakeholders in academia and industry to realize the competitive advantage of the most advanced privacy preserved MIoT systems based on federal learning.

Energy Efficient Mobile Harvesting Scheme for Clustered SDWSN with Beamforming Technique

Software Defined Wireless Sensor Networks (SDWSN) provides a centralized scheduling algorithm to decrease energy consumption compared to WSN. The sensor nodes have a finite battery capacity in the SDWSN that reduces the lifetime of the nodes. To harvest energy for energy depleted nodes without interfering with the eventful data transfer in the clustered SDWSN, an energy efficient mobile harvesting scheme with the Multiple Input Single Output (MISO) beamforming technique is proposed. The mobile harvesting scheme transfer the energy to the energy starving node and the beamforming algorithm which transmits the energy in the desired direction increases the lifetime of the nodes. The Secondary Cluster Head (SCH) node in a cluster is selected based on Particle Swarm Optimization (PSO) with the distance between mobile harvester and sensor node, the energy consumption rate of a node and lifetime of a nodes constraints for harvesting energy without interrupting data transfer to sink node in clustered SDWSN. The distributed scheduling algorithm and efficient path planning decrease the energy consumption of mobile harvester in the network. The optimization problem is formulated with Signal to Noise Ratio (SNR) and transmit power constraints to increase the harvested energy for sensor nodes in the network. The simulation results show the enhanced performance of the proposed algorithm compared to the existing algorithm in terms of residual energy, end to end delay, throughput, travel distance, service time and charging delay.

Distributed Combined Acoustic Echo Cancellation and Noise Reduction in Wireless Acoustic Sensor and Actuator Networks

The paper presents distributed algorithms for combined acoustic echo cancellation (AEC) and noise reduction (NR) in a wireless acoustic sensor and actuator network (WASAN) where each node may have multiple microphones and multiple loudspeakers, and where the desired signal is a speech signal. A centralized integrated AEC and NR algorithm, i.e., multichannel Wiener filter (MWF), is used as starting point where echo signals are viewed as background noise signals and loudspeaker signals are used as additional input signals to the algorithm. By including prior knowledge (PK), namely that the loudspeaker signals do not contain any desired signal component, an alternative centralized cascade algorithm (PK-MWF) is obtained with an AEC stage first followed by an MWF-based NR stage which has a lower computational complexity. Distributed algorithms can then be obtained from the MWF and PK-MWF algorithm, i.e., the generalized eigenvalue decomposition (GEVD)-based distributed adaptive node-specific signal estimation (DANSE) and PK-GEVD-DANSE algorithm, respectively. In the former, each node performs a reduced dimensional integrated AEC and NR algorithm and broadcasts only 1 fused signal (instead of all its signals) to the other nodes. In the PK-GEVD-DANSE algorithm, each node performs a reduced dimensional cascade AEC and NR algorithm and broadcasts only 2 fused signals (instead of all its signals) to the other nodes. The distributed algorithms achieve the same performance, upon convergence, as the corresponding centralized integrated (MWF) and centralized cascade (PK-MWF) algorithm. It is observed, however, that the communication cost in the PK-GEVD-DANSE algorithm can also be reduced, where each node then broadcasts only 1 fused signal (instead of 2 signals) to the other nodes. The resulting algorithm, referred to as the pruned PK-GEVD-DANSE (pPK-GEVD-DANSE) algorithm, then effectively combines the lowest possible communication cost (as low as in the GEVD-DANSE algorithm) with a lowest possible computational complexity in each node (further reduced from the PK-GEVD-DANSE computational complexity), within the class of algorithms considered in this paper.

Low-Cost Hybrid Multisensor Fusion Method and Implementation for Production Intelligent Vehicles

Faced with cost limitation and 360-degree fusion and tracking requirement of production intelligent vehicles, this paper proposes a low-cost hybrid multi-sensor fusion method, which provides flexibility and scalability for multi-level information input and different sensor configurations. By combining radar, lane detection and ego vehicle information, we design a centralized fusion algorithm for 360-degree object tracking, which provides a low-computation multi-sensor association algorithm by a scheme of local sensor to global track association, and proves an optimal centralized estimator in the condition of multi-coordinate system Doppler information. To make the sensor fusion system compatible with multi-level information input and enhance the redundancy to improve security, a distributed fusion algorithm based on covariance intersection method is also designed as a part of fusion framework for the secondary fusion of high-level information. We validate the feasibility of our fusion method in an industrial-level controller with only 10% computing power consumption and build a ground truth system to quantitatively evaluate the method, which shows that our fusion method performs well on 360-degree object tracking and guarantees stable object IDs, and greatly improves the accuracy especially for sensor boundary regions. Furthermore, we also test and evaluate the performance of our fusion method in a variety of complex open road scenarios including expressway, curved road and lane fading scenarios.

Centralized controller for the optimal operation of a cooperative cluster of connected microgrids powered multi-greenhouses

This paper aims to propose an advanced management and monitoring methodology for a cooperative cluster of interconnected networks of smart greenhouses. Each network is defined as a microgrid powered smart greenhouses. The microgrids are interconnected allowing the power exchanges to increase the usage of renewable generation. In addition, the cluster is connected to the main grid through a power link permitting power exchanges in excess/shortage cases. The developed framework integrates effective optimization approach-based management algorithm with the purpose to enhance the energy efficiency of the greenhouses. The main purpose is to optimally control of the whole cluster’ operation while considering the operational constraints with the aim of enhancing energy efficiency, as well as effectively manipulating the microclimate variables defining the optimal environment for crops development in all networks. The cooperation is secured via bidirectional communication infrastructure. Furthermore, a master centralized controller-based algorithm is in charge of securing the efficient operation of the whole cooperative cluster of networks. The effectiveness of the management-based algorithm is applied to a case study considering four cooperative networks including three greenhouses each. Results demonstrate that the energy storage systems regulate their operation responding to the dynamic references as well as enhancing the reliability of supply and balancing energy productions and electric loads. The power exchanges among microgrids take place specifically at night due to the high-power peak loads triggered by the artificial lighting. It is validated that the cluster succeed to balance the energy productions and loads locally based on cooperation and coordination among the microgrids without any interaction with the main electric grid, while satisfying the reference signals defining the optimal microclimate environments for crops development in all the greenhouses.

Power Loss Minimization of Off-Grid Solar DC Nano-Grids—Part I: Centralized Control Algorithm

Peer-to-peer interconnection of households having on-site batteries, multi-port converters and solar panels to form a multi-port converter-enabled solar DC nano-grid is an emerging approach for providing affordable energy access in rural areas. Battery charge and discharge losses, distribution losses and converter losses are significant problem when operating such nano-grids. This paper presents a centralized control algorithm that can help address the power loss problem. The proposed algorithm uses a new problem formulation where the power loss problem is formulated as a two-stage convex optimization problem. The first stage of the optimization problem is an optimal battery dispatch problem for determining optimal battery charge and discharge currents. The second stage is an optimal current flow problem for determining optimal distribution voltages which corresponds to the optimal battery currents. Simulation results of the nano-grid show that the proposed algorithm can minimize the nano-grid power losses while facilitating the power exchange between the households. The proposed algorithm is suitable for small nano-grids where privacy of households is not a concern. In Part II of this paper we propose a distributed control algorithm that preserves the privacy of the households especially where the size of the nano-grid is large.

Efficient Link Scheduling Based on Estimated Number of Packets in Queue on Industrial Wireless Sensor Networks

The links of low power wireless sensor networks are error prone and the transmission on a wireless link is determined probabilistically by the packet reception rate (PRR) of the link. On the other hand, there is a very strict requirement in the end-to-end reliability and delay of sensor data in industrial wireless sensor networks (IWSNs). The existing approaches to provide the end-to-end reliability in IWSNs is retransmitting the packet when failure occurs. These approaches transmit a packet multiple times in successive time slots to provide the required reliability. These approaches, however, can increase the average delay of packets and the number of packets buffered in a queue. This paper proposes a new scheme to estimate the probabilistic amount of packets, called queue level (QL), in the buffer of each node based on the PRRs of the wireless links. This paper also proposes a QL-based centralized scheduling algorithm to assign time slots efficiently in TDMA-based IWSNs. The proposed scheduling algorithm gives higher priority to the nodes with higher QL. By assigning time slots first to the node with the highest QL, we can reduce the average end-to-end delay of packets and reduce the amount of buffered packets in the queue while satisfying the required end-to-end reliability. The performance of the proposed scheduling algorithm have been evaluated through a simulation using the Cooja simulator and compared with the existing approach. In the simulation on an sample network with the target end-to-end reliability of 99%, all of the flows were shown to guarantee the target reliability in both algorithms: on average, 99.76% in the proposed algorithm and 99.85% in the existing approach. On the other hand, the proposed algorithm showed much better performance than the existing approach in terms of the average end-to-end delay of packets (about 47% less) and the number of maximally buffered packets in the queue of each node (maximally, more than 90% less).

EEHCHR: Energy Efficient Hybrid Clustering and Hierarchical Routing for Wireless Sensor Networks

In cluster-based Wireless Sensor Network (WSN), the Cluster Heads (CHs) consume massive amount of energy due to uneven processing and routing of the information of their Cluster Members (CMs) to the Base Station (BS), and results in lower network lifetime e.g., REHR (Residual Energy based Hybrid Routing). Also, the centralized clustering algorithms introduce unnecessary consumption of energy e.g., FFTHR (Fitness Function based Two-Hop Routing) and UCRA-GSO (Uneven Clustering Routing Algorithm using Glowworm Swarm Optimization). Thus, for extending the network lifetime, we introduce a new clustering algorithm named as Energy Efficient Hybrid Clustering and Hierarchical Routing (EEHCHR) in WSN. Here, a new scheme of adaptive and hybrid clustering has been proposed for minimum usage of the node’s energy using the Euclidean distance parameter, Fuzzy C-Means (FCM) technique, location of BS, and residual energy of the nodes. Here, the clustering is performed only in a few rounds, and this results in reduction of energy consumption of the network. All the CHs are selected using the energy efficient fitness function, which works in an adaptive way with the residual energy of the nodes to improve the CH selection process. For efficient usage of the network’s energy, we have also given a hierarchical packet routing strategy by introducing the concept of DCH (Direct Cluster Head) and CCH (Central Cluster Head), which are selected by different fitness functions, and work as a relay for few other CHs. The simulation results of EEHCHR proved that it extends the network lifetime, coverage, and saves the network energy as compared to similar existing algorithms e.g., FCM, REHR, FFTHR, UCRA-GSO and CCA-GWO.

Learning Communication for Cooperation in Dynamic Agent-Number Environment

The number of agents in many multiagent systems in the real world, such as storage robots and drone cluster systems, continually changes. Still, most current multiagent reinforcement learning (RL) algorithms are limited to fixed network dimensions, and prior knowledge is used to preset the number of agents in the training phase, which leads to a poor generalization of the algorithm. In addition, these algorithms use centralized training to solve the instability problem of multiagent systems. However, the centralized learning of large-scale multiagent RL algorithms will lead to an explosion of network dimensions, which in turn leads to very limited scalability of centralized learning algorithms. To solve these two difficulties, in this article propose a group centralized training and decentralized execution-unlimited dynamic agent-number network (GCTDE-UDAN). First, since we use the attention mechanism to select several leaders and establish a dynamic number of teams, and the UDAN performs a nonlinear combination of all agents' Q values when performing value decomposition, it is not affected by changes in the number of agents. Moreover, our algorithm can unite any agent to form a group and conduct centralized training within the group, avoiding network dimension explosion caused by the global centralized training of large-scale agents. Finally, we verified on the simulation and experimental platform that the algorithm can learn and perform cooperative behaviors in many dynamic multiagent environments.

Message-Aware Graph Attention Networks for Large-Scale Multi-Robot Path Planning

The domains of transport and logistics are increasingly relying on autonomous mobile robots for the handling and distribution of passengers or resources. At large system scales, finding decentralized path planning and coordination solutions is key to efficient system performance. Recently, Graph Neural Networks (GNNs) have become popular due to their ability to learn communication policies in decentralized multi-agent systems. Yet, vanilla GNNs rely on simplistic message aggregation mechanisms that prevent agents from prioritizing important information. To tackle this challenge, in this letter, we extend our previous work that utilizes GNNs in multi-agent path planning by incorporating a novel mechanism to allow for message-dependent attention. Our Message-Aware Graph Attention neTwork (MAGAT) is based on a key-query-like mechanism that determines the relative importance of features in the messages received from various neighboring robots. We show that MAGAT is able to achieve a performance close to that of a coupled centralized expert algorithm. Further, ablation studies and comparisons to several benchmark models show that our attention mechanism is very effective across different robot densities and performs stably in different constraints in communication bandwidth. Experiments demonstrate that our model is able to generalize well in previously unseen problem instances, and that it achieves a 47% improvement over the benchmark success rate, even in very large-scale instances that are ×100 larger than the training instances.

SATPAS: SINR-based adaptive transmission power assignment with scheduling in wireless sensor network

In this work, a centralized metaheuristic algorithm is proposed for assigning minimum transmission power to each sensor node for every transmission link along with a scheduling slot while satisfying the Signal to Interference plus Noise Ratio constraint in the Wireless Sensor Network. Simultaneous communication in all communication links is not possible while maintaining SINR constraints. Thus, the algorithm also tries to maximize the number of concurrent transmission links in each scheduling slot. We formulate the optimization problem with two objective functions as (i) Communication link wise adaptive and minimum transmission power assignment together with scheduling slot number and (ii) Minimization of the required number of scheduling slots. Probabilistic interference model, which is more realistic, is used for calculating the receiver interference, unlike the graph-based interference model mostly described in the literature. Genetic Algorithm with Edge-set and Edge-window-decoder chromosome representation schemes are used for optimization. Extensive simulations are carried out to demonstrate the efficiency of proposed algorithms using different benchmark data sets and special network topologies like spiral, cluster, and mesh. Our proposed algorithm outperforms the existing MST-based algorithm in terms of minimum transmission power requirement, number of scheduling slots required, and rate of convergence.