Time Slot Assignment Research Articles

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.

Fine-Grained TDMA MAC Design toward Ultra-Reliable Broadcast for Autonomous Driving

In the autonomous driving era, V2X communication is essential since it enables rapid message dissemination via periodical beacon exchange (broadcast communication), which contributes to better situation awareness and maneuvering cooperation. However, designing a MAC protocol for reliable V2X broadcasting is challenging, as minimal beacon delivery delay and collision avoidance should be achieved simultaneously. In this article, we design a fine-grained TDMA-based MAC protocol to support ultra-reliable broadcast for autonomous vehicles. Specifically, three critical issues are first identified: mobility-caused time slot collision, time slot shortage, and stiff beacon rate limitation. Accordingly, three fine-grained solutions are provided to tackle those issues: mobility-aware time slot assignment, beacon rate adaption with safety awareness, and flexible beacon rates support. Moreover, a case study on mobility-aware time slot assignment based on road topology and lane distribution is presented, with simulation results' verification. Finally, we elaborate the steps to implement the fine-grained MAC protocol in autonomous driving environments.

Simulations for Resource-Allocation Protocol Optimization for MIL-STD-188-186 over a UHF SATCOM Network

A simple simulation tool was previously developed to simulate the operation and performance of demand-assigned communication networks having time-varying data traffic patterns. Such networks use protocols to increase or decrease the resources allocated to a network node as the resource needs at that node change. These resource-allocation protocols have parameters such as numerical thresholds for requesting or releasing resources. The additional simulator development and execution described herein allows a comparison of performance metrics that result when using the existing MIL-STD-188-186 protocol versus using a proposed alternative protocol. The network behavior revealed by the simulation results also allows examining network performance trade-offs as values for the protocol parameters are adjusted. Although commercially available simulation tools could be used for these simulations, such tools are often expensive and sometimes complicated to adapt to new and not yet standardized protocols. The simple simulation tool that was previously developed is described in an earlier paper and is programmed as an Excel spreadsheet. It has now been adapted to allow comparing an existing resource-allocation protocol versus a proposed protocol for MIL-STD-188-186. The simulator allows examination of performance metrics such as the average number of assigned time slots per frame assigned to a transmitting node that has a specified message generation rate, the percentage of generated messages that are discarded prior to transmission due to being queued for an excessive time, and a histogram showing the percentage of messages transmitted with each possible message delivery time.

Fuzzy-Based Dynamic Time Slot Allocation forWireless Body Area Networks.

With the advancement in networking, information and communication technologies, wireless body area networks (WBANs) are becoming more popular in the field of medical and non-medical applications. Real-time patient monitoring applications generate periodic data in a short time period. In the case of life-critical applications, the data may be bursty. Hence the system needs a reliable energy efficient communication technique which has a limited delay. In such cases the fixed time slot assignment in medium access control standards results in low system performance. This paper deals with a dynamic time slot allocation scheme in a fog-assisted network for a real-time remote patient monitoring system. Fog computing is an extended version of the cloud computing paradigm, which is suitable for reliable, delay-sensitive life-critical applications. In addition, to enhance the performance of the network, an energy-efficient minimum cost parent selection algorithm has been proposed for routing data packets. The dynamic time slot allocation uses fuzzy logic with input variables as energy ratio, buffer ratio, and packet arrival rate. Dynamic slot allocation eliminates the time slot wastage, excess delay in the network and attributes a high level of reliability to the network with maximum channel utilization. The efficacy of the proposed scheme is proved in terms of packet delivery ratio, average end to end delay, and average energy consumption when compared with the conventional IEEE 802.15.4 standard and the tele-medicine protocol.

Time-slotted software-defined Industrial Ethernet for real-time Quality of Service in Industry 4.0

Abstract Reliable and timely data delivery, namely, real-time communication, is a key aspect for achieving the agile manufacturing goals of Industry 4.0. Moreover, reducing the maintenance, infrastructure and reconfiguration costs, and increasing the flexibility are general goals for communication systems in Industry 4.0. Although some works have extended the Ethernet standard IEEE 802.3 to satisfy the real-time requirements of industrial automation systems, the existing works have one or more of the following drawbacks: poor scalability, insufficient self-configuration capabilities, or increased costs due to their use of proprietary hardware. In this paper, we propose a Time-slotted Software-defined Industrial Ethernet (TS-SDIE) for real-time Quality of Service (QoS) in Industry 4.0. The paper addresses two key technologies of TS-SDIE, time synchronization and time slot-based packet switching. First, we develop a precision time protocol-based link delay compensation mechanism to handle the delay variance in networks. Precise synchronization is achieved at the microsecond level. Second, we design a system architecture for time slot-based industrial switches with four modules responsible for time synchronization, flow classification, time slot assignment, and packet forwarding, respectively. The experimental results show that the switch delay and its jitter can be reduced to 12 . 2 μ s and 0 . 12 μ s , respectively, for packets with a size of 100 B, which satisfies the requirements of time-sensitive networking for industrial automation systems.

Comparison Between TDMA and Random Multiple-Access Energy-Harvesting Networks Under Security Constraints

We study the maximum average energy transfer rate at a wireless charging energy-harvesting receiver when multiple transmitting nodes communicate their confidential information to a data receiver. We investigate both the time-division multiple-access (TDMA) and the random multiple-access (RMA) schemes and compare their performance. We address the question of which multiple-access scheme can maximize the average energy transfer rate under secrecy constraints. We also investigate the cases of the RMA scheme with equal access probabilities and the TDMA scheme with equal time-slot assignment probabilities.

A Quantum Access Network Suitable for Internetworking Optical Network Units

Quantum access networks allow a large number of users to access quantum networks, which can be regarded as an important part of the practical application for quantum communication. However, current quantum access networks have not considered as the peer-to-peer multimedia service between optical network units (ONUs) that have become the dominant service in the access networks. Thus, we propose a quantum access network that can support direct quantum and classical ONU-ONU communication by using an N:N splitter. In addition, we improve the efficiency of quantum key distribution (QKD) from both the physical and the data link layer. For the former, we analyze spontaneous Raman scattering (SRS) that is the main impairment source to QKD due to the co-propagation of the classical and quantum signal. Then, we propose a collision-avoiding scheme to reduce the influence of the SRS. For the latter, a dynamic time slot assignment protocol is proposed to reduce discarding secure keys greatly. The two methods are verified by simulations, and the results show that each method can effectively optimize QKD performance.

Routing, Spectrum and Modulation Level Assignment, and Scheduling in Survivable Elastic Optical Networks Supporting Multi-Class Traffic

As elastic optical networks (EONs) are expected to convey high bitrate connections, a failure in these networks causes vast data losses. Thus, addressing the problem of survivability in EONs is of great importance. In this paper, survivability of an EON with multiclass traffic is investigated, where each traffic type needs specific protection mechanism and scheduling strategy. In particular, a connection request may demand for dedicated path protection, shared backup path protection, or restoration mechanism. Besides, it can tolerate a pre-determined delay and be scheduled at future time slots, referred to as advance reservation, or must be served immediately without any delay, referred to as immediate reservation. Accordingly, we formulate an integer linear programming (ILP) to solve the routing, spectrum and modulation level assignment, and scheduling problems in both static and dynamic operation scenarios. In addition, to reduce the complexity of the ILP formulation in large scale networks, we propose a number of heuristic algorithms, in which two and three methods are considered for path selection and resource allocation, respectively. We evaluate the proposed heuristic algorithms in a small scale network by comparing their performance with the ILP formulation, then we apply them in a realistic large scale network. We compare all algorithms in terms of blocking probability, initial delay, and spectrum efficiency. Our results reveal that by using load-aware path selection and first-fit frequency-slice and time-slot assignment strategies the best compromise between blocking probability and initial delay is obtained.

Towards optimal source location privacy-aware TDMA schedules in wireless sensor networks

Source Location Privacy (SLP) is becoming important for wireless sensor networks where the source of messages is kept hidden from an attacker. In this paper, we conjecture that similar traffic perturbation to altering the routing protocol can be achieved at the link layer through assignment of time slots to nodes. This paper presents a multi-objective optimisation problem where SLP, schedule latency and final attacker distance are criteria. We employ genetic algorithms to generate Pareto-optimal schedules using two fitness criteria, examining the Pareto efficiency of selecting either and confirming the efficiency by performing simulations which show a near optimal capture ratio.

SOBM - Server Occupancy Based Migration by Optimizing Link and Storage Capacity in Check Points

Checkpoint (CP) routing requires a procedure for heavy load and dynamic routing packets over a cluster network, by monitoring network load. High traffic CP network does intense transactions by multiple applications and shares the information among the nodes in the network and delivers the same to the server. The Proposed work assigns time slots and each slot checks the path to send or migrate the data to manage the load and data accumulation between servers and if there arises any data loss it recovers from the previous node buffers. Data rate and delay is checked by each link and adjust the data flow to various servers. Based on time, network state, incoming packet rates, server load, link-based migration is applied. It increases network packets receiving rates, and minimizes the delay in checkpoints.

Study on the Optimization and Performance of TDMA Allocation Algorithm in Ships’ Ad Hoc Networks

Abstract This paper analyzes the requirements of the information transmission network of ship integrated condition monitoring system, and proposes a design scheme of ship condition monitoring system based on wireless ad hoc network. The wireless ad hoc network protocol was designed, its networking process was analyzed in detail, and the network transmission performance of the monitoring system was tested. The results proved the feasibility of the system. The above solution can be used for the transmission of ship state information that satisfies the requirements of wireless transmission, and has important theoretical and practical significance. The slot allocation algorithm has been receiving extensive attention as an important part of the TDMA system research. This paper analyzes the summarization and summarization of TDMA time slot assignment algorithms from several aspects such as slot synchronization, existing slot allocation algorithm, and slot assignment model, laying an important foundation for researchers to do further research. In the TDMA system, time is divided into non-overlapping time frames, and the time frames are divided into non-overlapping time slots. Each node in the network performs corresponding operations in each time slot.

Grant-sizing-differentiated bandwidth allocation algorithm for the coexistence of ONUs with and without wavelength tunability in WDM/TDM PONs

Adopting the pay-as-you-grow approach to upgrade passive optical network (PON) facilities by WDM technology insures the smoothness of the upgrade, and also results in the coexistence of wavelength-fixed/tunable optical network units (ONUs) in WDM/TDM PONs. Dynamic bandwidth allocation (DBA) is the key to support such coexistence of heterogeneous ONUs. Thus, DBA is also the key to support the smooth evolution of PONs. To more fairly coordinate the bandwidth allocation among the coexisting heterogeneous ONUs, a differentiated grant sizing (DGS) scheme is proposed. In DGS, not only the fairness between the wavelength-fixed/tunable ONUs but also the fairness between the lightly/heavily loaded ONUs is taken into account. To further carry out load balancing among wavelengths, a grant scheduling scheme is also proposed to cooperate with the grant sizing scheme. In the grant scheduling scheme, a measure of the ONUs’ flexibility is given, and then the least flexible job first rule (LFJF) is adopted for joint wavelength and time-slot assignment. Finally, to demonstrate the effectiveness of the proposed algorithm, a series of comparative analyses is conducted based on simulation experiments.

Autonomous and traffic-aware scheduling for TSCH networks

Wireless Sensor Networks (WSNs) have been recognized as a promising communication technology for smart grid monitoring and control applications. However, the deployment of WSNs in smart grid brought new challenges that pertain to the harsh electrical grid nature, and the different and often contradicting communication requirements of smart grid monitoring applications. MAC protocols play a crucial role to meet the reliability and latency requirements of WSN-based smart grid communications. In particular, the IEEE 802.15.4 TSCH (Time Slotted Channel Hopping), the latest generation of low-power and highly reliable MAC protocols, orchestrates the medium access according to a time-frequency communication schedule. However, TSCH specification does not provide any practical solution for the establishment of the schedule. Orchestra is a recent scheduling solution for TSCH that brings significant advantages such as, the use of simple scheduling rules, the low signaling overhead, and the high delivery ratio. Despite its unique features, Orchestra has the limitation of computing the TSCH schedule at each node independently from its traffic load, which can drastically affect the communication delay. This limitation makes Orchestra not sufficiently convenient for several delay-sensitive smart grid applications. Further, the current TSCH specification does not support traffic differentiation (i.e. handle all packets equally regardless of their criticality levels). In this paper, we propose an enhanced Orchestra-based TSCH protocol, called e-TSCH-Orch, that dynamically adjusts time slots assignment according to traffic load and criticality level. The performance analysis of e-TSCH-Orch shows that it significantly reduces the communication delay compared to the original Orchestra-based TSCH, while preserving the low signaling overhead and the high packet delivery ratio.

Optimal time and channel assignment for data collection in wireless sensor networks

This paper studies the joint assignment of time slots and frequency channels in treebased wireless sensor networks (WSNs) for data collection applications. In order to approximate the optimal solution, we propose a series of algorithms that exploit the network topology and maximise concurrent communications within each time slot through dynamic programming. Unlike peer approaches established upon idealised link-layer models, our algorithms are designed to be resilient to link errors and they are evaluated with the presence of unreliable links and in various deployment scenarios. Evaluation results show that our new algorithms outperform the state of the art in terms of data collection delay performance under unreliable conditions with moderate node deployment. Finally, the impacts of assorted implementation-oriented network parameters are investigated and summarised as design guidelines.

Optimal time and channel assignment for data collection in wireless sensor networks

This paper studies the joint assignment of time slots and frequency channels in treebased wireless sensor networks (WSNs) for data collection applications. In order to approximate the optimal solut...

Simultaneous Optimization of Airspace Congestion and Flight Delay in Air Traffic Network Flow Management

Air traffic flow management (ATFM) aims to facilitate the utilization of airspace and airport resources and is critical in air transportation systems. During the past decades, several challenging problems have arisen from this domain and attracted intensive studies. This paper addresses the problem of alleviating the airspace congestion and reducing the flight delays in ATFM simultaneously. We formulate this problem as a multi-objective air traffic network flow optimization (MATNFO) problem. In this MATNFO model, comprehensive ATFM actions, for instance, ground-holding, airborne-holding, rerouting, and speed control, are considered. Meanwhile, a systematic approach, namely route and time-slot assignment (RTA) algorithm, is developed to solve the MATNFO problem. The idea of divide-and-conquer is embedded in the algorithm by sequentially applying both route searching module and time refinement module. Furthermore, for the sake of efficiency, a pre-selection operator is proposed as one heuristic strategy to identify promising solutions and reduce the search space by defining a sector equilibrium metric. Experiments on real data of the Chinese airspace show that the RTA algorithm outperforms an existing competitor and three related multi-objective evolutionary algorithms. In addition, RTA is competent for high-quality real-time air traffic network flow assignment.

OLT Energy Savings via Software-Defined Dynamic Resource Provisioning in TWDM-PONs

Time and wavelength division multiplexed passive optical network (TWDM-PON) standards dramatically increase the performance of PON systems and address ever-increasing demands for bandwidth. However, these schemes increase the complexity and energy consumption of PON systems because they exploit multiple wavelengths, which requires multiple transceivers in the optical line terminal (OLT). In this paper, we propose to integrate software-defined networking (SDN) into standard PON architectures to facilitate an orchestrated energy-efficient operation in which the SDN controller dynamically provisions the number of wavelengths, link-rates, and timeslot assignments depending on the global traffic conditions. The simulation results show that the proposed architecture and mechanism improves the energy-saving performance of OLTs if the traffic load is less than 80%, while guaranteeing the quality of service requirements in terms of the mean packet delay, jitter, queue length, throughput, and packet loss ratio.

Resource Assignment Strategy in Optical Networks Integrated With Quantum Key Distribution

Data transmission with optical fiber is vulnerable to eavesdropping. Moreover, conventional key distribution technology suffers from increasing computational power and upgraded attack algorithms. To address these issues, quantum key distribution (QKD), a quantum technology that secures secret information (such as a cryptographic key) exchange between two parties, can be used to guarantee secure data transmission. Integrating QKD into existing wavelength division multiplexing optical networks has been verified through a series of experiments, which contribute to ensuring network security and saving fiber resources. This paper addresses the resource assignment problem in QKD-enabled optical networks. First, a QKD-enabled optical network architecture is introduced. A small fraction of wavelength channels are segmented into multiple time slots with optical time division multiplexing technology to construct quantum key channels (QKChs) and measuring-basis channels, and then the remaining wavelengths can construct traditional data channels. Second, a static routing, wavelength, and time-slot assignment (RWTA) strategy is proposed and verified by the integer linear programming formulation and a heuristic algorithm. In the RWTA, QKChs are assigned for service requests according to the security levels specified by relevant key-updating periods. Thus, the secret keys for data encryption can update periodically to enhance security. Simulation results indicate that there is a trade-off between security (i.e., security levels and security-level types) and resource utilization.

Coordinated lab-clinics: A tactical assignment problem in healthcare

In some medical outpatient settings, it is desirable to perform patient diagnostic testing just before the appointment with the physician, effectively linking the testing to the clinic appointment. If testing resources are shared by several physicians, it becomes difficult to assure that testing is completed in time (with some probability) due to the variation in testing requirements across patients and types of clinics held concurrently. To address this tactical-level doctor–clinic assignment problem, we develop a mixed-integer programming (MIP)-based approach for assigning time slots to the physician clinics. The approach maximizes the minimum service level across blocks of time to reduce the likelihood of a patient not completing testing in time for their clinic appointment. A branch-and-price heuristic procedure is proposed to solve practical problem instances, and numerical examples are presented to show the efficiency of this model. Two mini-cases based on clinics’ actual operations are provided. The results of the mini-cases suggest that the proposed scheduling method will bring important improvements to these systems.

Hybrid Uplink Traffic Scheduling Algorithms in FMC Networks: A Comparative Study of Performance

Todate, the integration between EPON and WiMAX to form a Hybrid ONU-BS (Optical Network Unit-Base Station) Architecture in a Fixed Mobile Convergence (FMC) network rapidly matures and represents one of the promising candidates for next generation network (NGN) broadband access networks. In this paper, first we propose a new QoS mapping policy between two types of networks to enable a dedicated transmission across wireless and optical networks; and propose a hybrid uplink scheduling algorithm which the intra-ONU-BS scheduler employs queue scheduling only on the packets that arrive before sending the REPORT message, and the inter-ONU-BS scheduler employs the transmission time slot assignment based on the REPORT message information. Lastly, the paper provides a comparative performance study to find a decent combination of hybrid uplink traffic scheduling in terms of classic well-known traffic scheduling algorithms. Simulation results show that the inter uplink scheduling has significant impacts on the overall packet delay, loss rate and jitter performance; on the other hand, the intra uplink scheduling has significant influences on the packet delay, loss rate, jitter and fairness performance. Both inter and intra uplink traffic scheduling have particular functions to enhance the QoS and Class of Service (CoS) of system performance, respectively.