Time Slot Assignment Research Articles

An Elastic Resource Allocation Algorithm Based on Dispersion Degree for Hybrid Requests in Satellite Optical Networks

The satellite-assisted Internet of Things (IoT) communication is considered a key component of the 6G network, and low Earth orbit (LEO) satellite is the leading choice of IoT-related satellites due to its minimum delay. Hybrid requests, including immediate reservation (IR) and advanced reservation (AR) services in LEO satellite netoworks cause the occurrence of resource fragments (RFrags), which adversely affect the network performance. To alleviate the degradation of network performance caused by resource fragmentation, a routing, wavelength, and time-slots assignment algorithm, which is named elastic resource allocation algorithm based on the dispersion degree (ERA-DD), is proposed in this article. Possible resource fragmentation types are analyzed and a fragmentation description named dispersion degree (DD) is designed. In the DD, the number of free resource blocks is accurately described by the state jumps (SJs) of adjacent resource slots, and the numerical relationship between SJs and free resource blocks is proposed and proved. Besides, restrictions on the selection priority of candidate schemes in the ERA-DD algorithm are analyzed. Finally, the traffic blocking rate, the wavelength utilization, the average communication delay, and the average initial delay are evaluated by simulation. The results demonstrate that RFrags are more fully utilized compared with the maximum total link spectrum consecutiveness (MTLSC) algorithm. The traffic blocking rate can be reduced by 32.5% and wavelength utilization can be increased by 1.6%.

NeSyChair: Automatic Conference Scheduling Combining Neuro-Symbolic Representations and Constrained Clustering

Creating the schedule for an academic conference is a time-consuming task. A typical conference schedule consists of sessions containing papers addressing the same research topic. To construct a schedule, conference papers must be grouped according to their research topic, and the obtained groups should fit the assigned time slots. This paper proposes an approach to automating the schedule-creation process. We use multilingual, neuro-symbolic paper representations and novel constrained clustering to group papers into clusters of predetermined size with the same topic fitting the schedule structure. In the process, we combine machine-learning, natural language processing, network analysis, and combinatorial optimization. We tested the components of the proposed approach on a newly created database of papers from six machine learning conferences, which were manually labeled by their research topics. The entire system was tested on two real-world conferences in a multilingual setting. The developed methodology is incorporated into an interactive automatic conference-scheduling system NeSyChair (Neuro-Symbolic Conference Chair), which can be used to create and improve conference schedules.

UAV-assisted data offloading for smart container in offshore maritime communications

Smart containers have been extensively applied in the maritime industry by embracing the Internet of Things to realize container status monitoring and data offloading without human intervention. However, the offloading rate and delay in the offshore region are limited by the coverage of the onshore base station (BS). In this paper, we investigate the unmanned aerial vehicle (UAV)-assisted data offloading for smart containers in offshore maritime communications where the UAV is as a relay node between smart containers and onshore BS. We first consider the mobility of container vessel in the offshore region and establish a UAV-assisted data offloading model. Based on this model, a data offloading algorithm is proposed to reduce the average offloading delay under data-size requirements and available energy constraints of smart containers. Specifically, the convex-concave procedure is used to update time-slot assignment, offloading approach selection, and power allocation in an iterative manner. Simulation results show that the proposed algorithm can efficiently reduce average offloading delay and increase offloading success ratio. Moreover, it is shown that the UAV relay cannot always bring the performance gain on offloading delay especially in the close-to-shore area, which could give an insight on the deployment of UAV relay in offshore communications.

Efficient ordering policy for secret key assignment in quantum key distribution-secured optical networks

Quantum key distribution (QKD) is a promising solution to protect data transmission in optical networks against security breaches. Hence, several studies have paid attention on integration of QKD with the existing optical networks. Meanwhile, blocking is a challenging issue for QKD lightpath requests (QLRs) due to limited number of network resources (wavelengths and time-slots) in existing optical networks. In QKD-secured optical networks, the blocking increases with increase in the number of QLRs as well as with the modifications of secret keys for enhancing the security level of QLRs. Hence, the blocking affects the QLRs of different security levels, especially the QLRs of high and moderate security levels. Thus, the prioritization of QLRs based on the security level is essential for reducing the impact of blocking in such networks. In this paper, we propose a secret key assignment priority ordering policy (SKA-POP) for routing, wavelength and time-slot assignment (RWTA) to improve the success probability of QLRs. In the proposed SKA-POP, the resources during assignment and re-assignment are allocated based on the proposed priority criteria. The performance of the proposed SKA-POP is analyzed in terms of the success probability and the probability of secret key update failure (PSKUF). Simulations performed on two different network topologies, namely, NSFNET and UBN24, indicate that the proposed SKA-POP performs better than the non-priority based RWTA (NP-RWTA), priority order-based RWTA (POB-RWTA), partial-priority based RWTA (PP-RWTA), and a version of SKA-POP, i.e., SKA-POP with the longest route first (SKA-POP-LRF) schemes, when the number of QLRs (traffic load) increase in the network. .

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).

Neighbourhood oriented TDMA scheme for the internet of things-enabled remote sensing

ABSTRACT Throughout the world, Internet of Things (IoT) have been used in different application areas to assist human beings in numerous activities such as smart buildings and cities via remote sensing-enabled techniques. However, simultaneous transmission of packet(s) by multiple devices Ci, which are interested to start a communication session with a common receiver device, is one of the challenging issues associated with these networks. In the literature, various mechanisms have been presented to resolve the aforementioned issue without changing the technological infrastructures; however, neighbourhood information of sensor nodes is not considered yet. In IoT-enabled remote sensing, neighbourhood information of various devices plays a vital role in developing a reliable communication mechanism specifically for scenarios where multiple devices Ci are interested to start communication with a common destination module. In this paper, a neighbourhood-enabled TDMA scheme is presented for the IoT to ensure the concurrent communication of multiple devices Ci with a common destination device Sj preferably with a minimum possible packet collision ratio (if avoidance is not possible). The proposed scheme bounds each and every member device Ci to assign a dedicated time slot to its neighbouring devices in the operational IoT network. Furthermore, neighbouring devices Ci are forced to communicate within the assigned time slot. Simulation results have verified that the proposed scheme is ideal solution compared to the existing schemes for the IoT and other resource-limited networks particularly in scenarios where the deployment process is random.

Challenges in current nursing home care in rural Germany and how they can be reduced by telehealth - an exploratory qualitative pre-post study

BackgroundTelemedical care of nursing home residents in Germany, especially in rural areas, is limited to a few pilot projects and is rarely implemented as part of standard care. The possible merits of implementing video consultations in longer-term nursing care currently lack supporting evidence. In particular, there is little documentation of experiences and knowledge about the effects and potential benefits of the implementation in presently existing structures. The goal was to assess the effect of implementing medical video consultations into nursing home care addressing the following research questions:How is medical care currently provided to nursing home residents, and where do problems in its implementation arise?How can video consultations be used to reduce difficulties arising in everyday care?How does implementation of video consultations impact day-to-day nursing home care delivery?MethodsTwenty-one guided interviews (pre-implementation n = 13; post-implementation n = 8) were conducted with a total of 13 participants (physicians, nurses and medical technical assistants). Narratives were analysed using qualitative content analysis. The results were contrasted in a pre-post analysis.ResultsChallenges described by the participants before implementation included a requirement for additional organisational and administrative efforts, interruptions in the daily care routine or delayed treatments, and risk for loss of patient-relevant information due to process diversity. After implementation, communication was facilitated upon introduction of assigned time slots for video consultations. Clinical information was less likely to be lost, additional work was spared, and medication and therapeutic and assistive devices were provided more quickly.ConclusionsTelehealth cannot replace physical, in-person visits, but does offer an alternative form of service delivery when properly integrated into existing structures. Our results suggest that the use of video consultations in nursing homes can reduce the burden and additional workload, and increase the efficiency of care provision for nursing home residents. Video consultations can complement in-person visits to nursing homes, especially to address the shortage of medical specialists in rural areas in Germany. To promote implementation and acceptance of video consultation in nursing homes, we need to increase awareness of its benefits and undertake further evaluation of video consultations in nursing home care.

Controlador difuso para compensar cargas de comunicación en sistemas en tiempo real

Se presenta un administrador de recursos (RM) difuso para compensar las cargas de comunicación en sistemas en tiempo real. El diseño del RM se basa en un nuevo modelo de Servidor de Ancho de Banda Constante (CBS) que se encarga, a través de una plataforma virtual, de asignar tiempo de proceso a las tareas de mayor prioridad cuando existe capacidad disponible. Si se asume que cada aplicación puede ser ejecutada con diferentes niveles de servicio sin que este esté por debajo de un límite mínimo, se propone una aproximación difusa que permite actualizar de manera gradual los tiempos de proceso asignados a cada tarea. Esta aproximación permite compensar el comportamiento no lineal en las solicitudes de tiempo de proceso. El RM aumenta o disminuye la plataforma virtual para cada aplicación y le asigna un presupuesto máximo de tiempo de proceso, mismo que la aplicación usa gradualmente y que se reasigna al agotarse, sin por ello afectar el desempeño del resto de las aplicaciones. El esquema se auto-ajusta cuando ocurren a cambios repentinos en los requerimientos de tiempo de proceso de las aplicaciones.

Enhancement of Data Collection Performance in Wireless Sensor Networks Based on Path-Constrained Mobile Sink

Due to the energy limitation in Wireless Sensor Networks (WSNs), most researches related to data collection in WSNs focus on how to collect the maximum amount of data from the network with minimizing the energy consumption as much as possible. Many types of research that are related to data collection are proposed to overcome this issue by using mobility with path constrained as Maximum Amount Shortest Path routing Protocol (MASP) and zone-based algorithms. Recently, Zone-based Energy-Aware Data Collection Protocol (ZEAL) and Enhanced ZEAL have been presented to reduce energy consumption and provide an acceptable data delivery rate. However, the time spent on data collection operations should be taken into account, especially concerning real-time systems, as time is the most critical factor for these systems' performance. In this paper, a routing protocol is proposed to improve the time needed for the data collection process considering less energy consumption. The presented protocol uses a novel path with a communication time-slot assignment algorithm to reduce the count of cycles that are needed for the data collection process with reduction of 50% of the number of cycles needed for other protocols. Therefore, the time and energy needed for data collection are reduced by approximately 25%and 6% respectively, which prolongs the network lifetime. The proposed protocol is called Energy-Time Aware Data Collection Protocol (ETCL).

Temperature aware variable time-slot assignment priority-based routing algorithm for WBANs in IoT based eHealthcare systems

The wireless body area networks are an integral part of the Internet of Things for eHealthcare applications. These networks suffer from two major problems such as energy consumption and lifetime of the overall network. To address these problems, a temperature aware priority-based routing algorithm for WBANs is proposed. This algorithm employs temperature aware routing, priority-based routing, and variable time-slot assignment. The temperature-aware routing enhances the stability of the overall network by providing an alternate route. The priority-based routing facilitates reliable data transmission among the sink and the sensor nodes which will enhance the lifetime of the overall network. The variable time-slot assignment in the scheduling phase prevents the collisions by employing a new synchronization schem e which will minimize overall network energy consumption. The performance proposed algorithm was analyzed with three network parameters and the results showed improved performance as compared with the traditional routing protocols.

Trading airport time slots: Market design with complex constraints

Due to the lasting growth in air traffic, many international airports have reached their capacity limits. Access to major airports is granted through the assignment of airport time slots. Current practices of allocating these time slots via grandfathering are widely regarded as inefficient by experts. New market mechanisms need to take into account synergistic valuations of airlines for departure and arrival time slots, as well as financial constraints of the participating airlines for the many time slots available. Unfortunately, computing core-stable outcomes in such environments is Σ2p-hard. Such problems are typically considered intractable. We introduce bilevel integer optimization models for airport time slot trading and compute core-stable outcomes, i.e. allocations and prices such that no coalition can beneficially deviate. Interestingly, despite the computational hardness of the underlying problem numerical experiments show that instances of practically relevant size can be solved in due time. The proposed market design provides a solution that addresses the specific constraints of airport time slot markets, a precondition for adoption in the field.

Multi-Objective Faculty Course Timeslot Assignment Problem for Tutorial and Laboratory Courses

Multi-Objective Faculty Course Timeslot Assignment Problem for Tutorial and Laboratory Courses

Energy-Efficient Cooperative Communication and Computation for Wireless Powered Mobile-Edge Computing

In this article, we present a wireless powered mobile-edge computing system consisting of a hybrid access point and multiple cooperative fogs, where the users in each cooperative fog can share communication and computation resources to improve their computation performance. Based on the classic time-division-multiple-access protocol, we propose a harvest-and-offload protocol to jointly schedule wireless energy transfer and cooperative computation offloading. We minimize the total energy consumption of the system by jointly considering energy beamforming, time-slot assignment, computation-task allocation, and the optimization of central processing unit (CPU) frequencies for computing. We transform the original nonconvex problem to a convex model via utilizing the variable substitution and the semidefinite relaxation methods, and then derive the optimal solution in a semiclosed form via exploiting the Lagrangian method. The extensive numerical results show that the proposed joint communication and computation cooperation scheme can reduce the total energy consumption considerably compared to the state of the art. Moreover, we demonstrate that the dynamic CPU frequency has a positive impact on energy saving compared with the case of fixed CPU frequency.

Priority-based Variable Time-slot Assignment Routing Algorithm in WBANs for Ehealthcare Systems

Priority-based Variable Time-slot Assignment Routing Algorithm in WBANs for Ehealthcare Systems

Slot‐hitting ratio‐based TDMA schedule for hybrid energy‐harvesting wireless sensor networks

In the energy-harvesting wireless sensor networks (EH-WSNs) with Time division multiple access (TDMA), it is challenging to assign time slots to the nodes because energy shortage causes some nodes unable to transmit in their time slots, resulting in the inefficiency in slot usage and the increase of the data packet delay. To overcome this problem, the slot assignment in TDMA is required to consider energy packet arrivals, where an energy packet is defined as the amount of energy that suffices for one transmission. In this study, the authors investigate the EH-WSN with hybrid energy sources, in which the nodes harvest energy from the fixed inter-arrival time (FIAT) and the random inter-arrival time (RIAT) energy sources. After deriving the slot-hitting ratios (SHRs) of energy packet arrivals for both FIAT and RIAT energy sources, they propose the SHR-based TDMA (SHR-TDMA) scheme. Then, they derive the delay arising from the awaiting slot (DAFAS) and formulate the DAFAS minimisation problem for the SHR-TDMA. Solution to the DAFAS minimisation problem makes the slots optimally assigned according to the characteristics of the energy packet arrivals at the nodes. The simulation results show that the SHR-TDMA outperforms the existing TDMA schemes in terms of DAFAS.

Joint resource allocation algorithm based on multi-objective optimization for wireless sensor networks

With the limitations of the network resources and battery energy of wireless sensors, the competition of resources in the process of communication will increase the network energy consumption and reduce the Quality of Service (QoS), resulting in that the application of Multi-Radio Multi-Channel (MRMC) Wireless Sensor Networks (WSNs) face many challenges. In this paper, we concentrate on the resource allocation of joint time slot assignment, channel allocation and power control for MRMC WSNs. Due to the diversity of research objectives and the computational complexity of the non-convex problem, this paper develops a two-stage resource allocation optimization algorithm by analyzing the interdependence of various resources. Specifically, to exchange information with conflict-free transmission among all sensors, a graph coloring algorithm for time slot assignment is designed firstly. Then based on the first stage of this algorithm, the problem of joint power control and channel allocation is studied and formulated as a multi-objective optimization problem to achieve the trade-off between energy efficiency and network capacity maximization under the constraints of link interference and load balance. Multi-objective hybrid particle swarm optimization is introduced to obtain the Pareto optimal solutions. The simulation results show that the proposed algorithm significantly performs better in terms of achieving the trade-off of multi-performance.

Auxiliary graph based routing, wavelength, and time-slot assignment in metro quantum optical networks with a novel node structure.

Nowadays, critical sectors in government, finance, and military are facing increasingly high security challenges. However, traditional public-key crypto-systems based on computational complexity are likely to suffer from upgrade computational power. Quantum key distribution (QKD) is a promising technology to effectively address the challenge by providing secret keys due to the laws of quantum physics. Limited by the transmission distance of quantum communications, remote parties have to share secret keys by exchanging keys through the trusted relay nodes hop by hop. However, if relaying hop by hop is still used in metro quantum-optical networks (MQON), a large amount of key resources will be wasted since the distance between any two nodes is short. Therefore, the problem of how to distribute quantum keys with lower waste of key resources over MQON is urgent. In order to solve this problem, we design a novel quantum node structure that is able to bypass itself. Also, by extending the connectivity graph, auxiliary graphs are constructed to describe the adjacency of quantum nodes in different levels influenced by the physical distance. Based on the novel node, two routing, wavelength and time-slot assignment algorithms are proposed, in which some middle nodes can be bypassed to reduce the resource consumption as long as the distance between the two parties meets the requirement of quantum key distribution. Simulations have been conducted to verify the performance of the proposed algorithms in terms of blocking probability, resource utilization, number of bypassed nodes, and security rate per service. Numerical results illustrate that our algorithms perform better on resource utilization than a traditional scheme without bypass. Furthermore, a tradeoff between the keys saved and blocking probability is analyzed and discussed in our paper.

A Trust Framework for Centralized TDMA Scheduling Mechanism in Vehicular Ad hoc Networks

Vehicular ad hoc networks, known as VANETs, are deployed to improve passenger comfort as well as to reduce the risk of road accidents by allowing vehicles to provide a warning in real time when a critical event is detected. In such networks, communication is possible both between the vehicles themselves and between the vehicles and the infrastructure. These applications need a reliable and secure broadcast system that takes into consideration the security issues in VANETs, the high speed of nodes, and the strict QoS requirements. For these reasons, the authors propose a trust-based and centralized TDMA-based MAC protocol that avoids time slot assignment to malicious nodes and minimizes message collision. The solution is based on the design of a generic trust mechanism for VANETs based on the MAC requirements and its integration into a centralized TDMA-based MAC protocol, named trust-CTMAC. The mechanism will permit roadside units (RSUs) to manage trust level assignment via security check during free slot allotment. The experiments carried out and the results obtained prove the effectiveness of the approach.

Optimisation‐based time slot assignment and synchronisation for TDMA MAC in industrial wireless sensor network

Wireless sensor network in the industrial environment [industrial wireless sensor network (IWSN)] has data delivery time constraint. Due to the dynamic routing and transmission collision, the data delivery time is unpredictable. The authors utilised time division multiple access (TDMA) MAC to avoid data collision and to provide bounded transmission delay. Moreover, a linear programming model is proposed to construct the TDMA schedules, which is focused on spatial reuse and fixed routing in IWSN. The objective function of the model is to minimise the time slot usage to increase the overall network bandwidth. Finally, both simulated annealing algorithm and particle swarm optimisation are applied to approximate the optimal solution of time slot usage.

Prioritized Clock Synchronization for Event Critical Applications in Wireless IoT Networks

With the proliferation of the Internet of Thing (IoT) technologies in vertical industry applications, provisioning of accurate synchronization and low latency communication has become critical for dense wireless IoT networks to support distributed sensing and control. Due to the contention-based channel access, achieving accurate synchronization in most of unlicensed wireless IoT networks could be extremely challenging. Specifically, the critical challenge at medium access control (MAC) layer for dense IoT communication is how to eliminate random access delay while supporting a large number of heterogeneous nodes with diverse quality of service (QoS) requirements. In this paper, we propose an efficient MAC protocol for supporting distributed synchronization through guaranteed channel access for time-critical sensor nodes in dense wireless IoT networks. The proposed protocol assigns time slots to timestamp packets of the time-critical nodes using a prioritized channel access mechanism, and also guarantees channel access in event-based situations. In addition, the proposed protocol also provides deterministic scheduling for the scenarios where the delay bound of a certain priority traffic changes based on the circumstances of the emergency situation. Our results show that the proposed scheme significantly improves the synchronization precision of the event critical sensor nodes, and also enhances the reliability of overall IoT networks.