Slot Scheduling Research Articles

An Energy-Efficien Slotted Sense Multiple Access Broadcast Protocol for Reliable Command Delivery in Dynamic Wireless Sensor Networks.

In industrial monitoring and control applications, a server often has to send a command to a node or group of nodes in wireless sensor networks. Flooding achieves high reliability of message delivery by allowing nodes to take the redundancy of receiving the identical message multiple times. However, nodes consume much energy due to this redundancy and the long duty cycle. A reliable slotted broadcast protocol (RSBP) tackles this problem by allocating a distinct broadcast slot (BS) to every node using a tree topology. Not only does it remove collision, but it also minimizes energy consumption such that every node remains active only during its parent’s broadcast slot and its own broadcast slot to receive and rebroadcast a message, respectively. However, it suffers from low reliability in harsh environments due to the compete removal of redundancy and low responsiveness to the changes in network topology due to the global scheduling of slots. Our approach allocates one distinct broadcast sharable slot (BSS) to each tree level, thus making a BSS schedule topology-independent. Then, nodes at the same level compete to rebroadcast a message to nodes at one level higher within the BSS, thus allowing the redundancy. In addition, it uses a slot-scheduled transmission within BSS that can further improve reliability by reducing message collisions and also enables the precise management of energy. According to simulations and experiments, the proposed approach can achieve high reliability comparable to flooding and low-energy consumption comparable to RSBP.

Mobile data gathering and energy harvesting in rechargeable wireless sensor networks

In this paper, we study the joint data gathering and energy harvesting (JoDGE) problem in rechargeable wireless sensor networks (RWSNs) with a mobile sink. In RWSNs, the sensor nodes are equipped with RF circuit to harvest energy from a mobile sink that moves along a pre-defined path, and at the same time, transmit gathered sensor data to the sink. Given that the consumed and harvested energy at a sensor node is proportional and inversely proportional to the square of transmission distance, a far-relay approach is proposed to select the sensor nodes closer to the path to assist the data transmission of the farther sensor nodes. Under the far-relay approach, we formulate a network utility maximization problem (NUM), and propose an optimal scheduling scheme (Opt-JoDGE), which jointly considers the power allocation, relay selection and time slot scheduling policies. By employing the Lyapunov drift theory, a near optimal buffer-battery-aware adaptive scheduling (NO-BBA) scheme is further proposed, in which the run-time status of the data buffer and battery are utilized. Extensive simulation experiments validate the feasibility and performance of JoDGE and NO-BBA. The results show that the performance of NO-BBA is close to that of Opt-JoDGE, especially when a certain delay is tolerable.

Time division multiple access scheduling strategies for emerging vehicular ad hoc network medium access control protocols: a survey

Vehicular ad hoc network (VANET) is an emerging and promising technology, which allows vehicles while moving on the road to communicate and share resources. These resources are aimed at improving traffic safety and providing comfort to drivers and passengers. The resources use applications that have to meet high reliability and delay constraints. However, to implement these applications, VANET relies on medium access control (MAC) protocol. Many approaches have been proposed in the literature using time division multiple access (TDMA) scheme to enhance the efficiency of MAC protocol. Nevertheless, this technique has encountered some challenges including access and merging collisions due to inefficient time slot allocation strategy and hidden terminal problem. Despite several attempts to study this class of protocol, issues such as channel access and time slot scheduling strategy have not been given much attention. In this paper, we have relatively examined the most prominent TDMA MAC protocols which were proposed in the literature from 2010 to 2018. These protocols were classified based on scheduling strategy and the technique adopted. Also, we have comparatively analyzed them based on different parameters and performance metrics used. Finally, some open issues are presented for future deployment.

Resourceful Residual Energy Consumption in TDMA Scheduling for IoT-based Wireless Sensor Network

Recently, wireless sensor network (WSN) gets more concern due to the robustness in the latest communication technology iteration such as big data, IoT and 5G. Such daily usage of these technologies includes smart home, smart farming, smart traffic control etc. Moreover, WSN becomes the best preference for mobile objects in data accumulating in a wild range area. Routing distance, signal interference and routing computational cost give a significant impact to the WSN nodes lifetime. Unsynchronized node time allocation slot and neighbor discovery are the main factors in the energy consumption issue faced by the WSN. Higher energy consumption reduces the network lifetime and WSN nodes performance. This paper discusses the optimization of energy-topology (E-T) factors for distributed time division multiplexing algorithm (TDMA) slot scheduling for high-speed data link capacity. The E-T factor is based on the influence of residual energy and topology on the time slot allocation. Both node residual energy and topology information have shown a respectable impact on the TDMA node slot allocation. Moreover, the numbers of neighbors and the network residual energy have been proved both nodes execution time and energy utilization can be reduced in the algorithm. The algorithm performance has been evaluated based on the previous experiment parameters with new high-speed data link. The experimental results have shown a significant improvement in residual energy consumption for the proposed optimized TDMA slot allocation.

Joint Transmission Power Control and Relay Cooperation for WBAN Systems.

Improving transmission reliability is a crucial challenge for Wireless Body Area Networks (WBANs) because of the instability of channel conditions and the stringent Packet Loss Ratio (PLR) requirement for many WBANs applications. On the other hand, limited by the size of WBAN nodes, the energy consumption of WBAN nodes should be minimized. In this paper, we jointly consider transmission power control, dynamic slot scheduling and two-hop cooperative mechanism and propose an Autocorrelation-based Adaptive Transmission (AAT) scheme that achieves a better trade-off between transmission reliability and energy consumption for WBAN systems. The new scheme is designed to be compatible with IEEE 802.15.6. We evaluated the performance of the newly proposed scheme by importing the real channel datasets into our simulation model. Simulation results demonstrate that the AAT method can effectively improve the transmission reliability while reducing the energy consumption. We also provide the performance evaluation from three perspectives, namely packet error ratio, energy consumption and energy efficiency, and provide recommendations on the application of the two-hop cooperative mechanism associated with the proposed AAT in the contexts of WBANs.

Channel autocorrelation-based dynamic slot scheduling for body area networks

As a promising technology in the context of m-health and e-medical, wireless body area networks (WBANs) have a stringent requirement in terms of transmission reliability. Meanwhile, the wireless channel in WBANs is prone to deep fading due to multiple reasons, such as shadowing by the body, reflection, diffraction, and interference. To meet the challenge in transmission reliability, the dynamic slot scheduling (DSS) methods have attracted considerable interest in recent years. DSS method does not require extra hardware or software overhead on the sensor side. Instead, the hub optimizes the time-division multiple access slots by selecting the best permutation at the beginning of each superframe to improve the transmission reliability. However, most existing DSS works optimize the time slot scheduling based on a two-state (“good” or “bad”) Markov channel model, which is insufficient for human daily life scenarios with a variety of irregular activities. In this paper, we first collect the channel gain data in the real human daily scenarios and analyze the autocorrelation of wireless channels based on this real database. Motivated by the significant temporal autocorrelation, we then propose a new DSS method, which applies a temporal autocorrelation model to predict the channel condition for future time slots. The new method is designed to be compatible with IEEE 802.15.6 standard. Compared to the classical Markov model-based methods, simulation results show that the newly proposed DSS method achieves up to 12.9% reduction in terms of packet loss ratios.

A new DBA algorithm for reducing delay and solving the over-granting problem of long reach PON

The main problem of the deployment of long reach passive optical network (LR-PON) is that it suffers from larger propagation delay. Multi-thread polling (MTP) based dynamic bandwidth allocation (DBA) algorithm is one of the solutions to mitigate the larger propagation delay in the LR-PON system. However, in the conventional online MTP based DBA scheme, over-granting problem is severe. In this paper, we propose a new online MTP based DBA algorithm namely slotted MTP (S-MTP) scheme, where each time cycle is divided into multiple grant scheduling slots and, in each slot, multiple request and grant messages are processed simultaneously including the use of frame by frame information in both the request and grant messages. The proposed S-MTP scheme effectively reduces the end-to-end packet delay and over-granting problem in the LR-PON system with lower computational complexity. We have evaluated the performances of the proposed scheme by numerical simulations. The simulation results show that the proposed scheme provides 45% and 20% lower end-to-end packet delay with 38% and 10% lower over-granting rate than the conventional online MTP and enhanced interleaved polling with adaptive cycle time schemes, respectively. The S-MTP scheme also provides higher throughput and bandwidth utilization than those of the existing schemes.

A Survey on Long Term Evolution Scheduling in Data Mining

Scheduling procedures implemented in wireless networks consists of varied workflows such as resource allocation, channel gain improvement, and reduction in packet arrival delay. Among these techniques, Long term evolution (LTE) scheduling is most preferable due to its high speed communication and low bandwidth consumption. LTE allocates resources to the workflow based on time and frequency domains. Normally, the information gathered prior to scheduling increases the processing time since each attributes of the users have to be verified. In order to solve this issue, parallel processing via data mining is analyzed in recent research studies. The label that is assigned to the user attributes contributes primarily on scheduling time slots effectively. The label assignment and parallel processing via data mining reduces the delay and increases the throughput respectively. Additionally, the matched data extraction from the library and the prediction of available channels with fewer dimensions posed major challenges in the LTE scheduling. This paper surveys about various LTE scheduling algorithms, dimensionality reduction techniques, optimal feature selection techniques, multi-level classification techniques, and data mining combined with LTE techniques. A brief survey illustrates the impact of each technique on 3G/4G networks, channel availability prediction, scheduling of time slots in detail. A brief comparison of the techniques involved in the respective LTE processes via tabular form reveals that the verification of channel and user availability are the primary functions of the LTE scheduling. The survey of this paper identifies the limitations such as computational complexity and poor scheduling performance in the existing systems and encourages researchers to develop novel algorithms for LTE scheduling.

A virtual slotframe technique for reliable multi-hop IEEE 802.15.4e time-slotted channel hopping network

Time-slotted channel hopping is one of the medium access control modes defined in IEEE 802.15.4e. Although time-slotted channel hopping provides high reliability, it cannot be achieved automatically. A time-slotted channel hopping should be configured properly according to the dynamic changes in a network. When new devices participate in the network or the data traffic is increased, link allocation may not be possible due to the fixed slotframe length. The simplest way to acquire additional links is to change the length. However, the conventional method to change this length involves significant overhead and the possibility of link failures. In this article, we evaluate the performance of the conventional IEEE 802.15.4e method and analyze the problems that can occur when changing the slotframe length. To resolve these problems, we propose a virtual slotframe technique that forms a logical slotframe by connecting multiple slotframes. A slot scheduler will then perceive the virtual slotframe as merely a long slotframe. The devices can translate the schedules made for the longer slotframe into real links using the virtual slotframe technique. These features allow the time-slotted channel hopping network to allocate additional slots without reconfiguration. The simulation results show that the proposed technique is a maximum of 18 times and an average of 10 times faster than the conventional method.

Multiaggregator Collaborative Electric Vehicle Charge Scheduling Under Variable Energy Purchase and EV Cancelation Events

With the growth of electric vehicles across the globe, it is essential to have a corresponding charging infrastructure developed. Several research works highlight the benefits of aggregator-based scheduling, where all aggregators operate in similar conditions with the same amount of purchased energy. However, there are unscheduled EVs left due to unavailability of sufficient energy and/or charging slots. This paper presents a multiaggregator-based charge scheduling scheme that incorporates collaborative charging and realistic situations with variable energy purchase (VEP) and cancelation charges. VEP reflects a practical situation where the aggregator purchases energy based on average scheduling requests per day. Similarly, customers are penalized for not arriving at the scheduled slot. The charge scheduling problem is addressed from the aggregator point of view, wherein the total profit and the number of scheduled EVs are maximized. With VEP, a greater number of EVs were scheduled through collaboration and overall profits were observed to be higher than with equal energy purchased. The implementation of cancelation charges on the customer further resulted in an increase in the profits.

Genetic Algorithm for Solving 3 Dimensional Time Table Problem Based on Traveling Salesman Problem (TSP) Method

Scheduling problems are problems that are often faced by educational institutions, especially at the university level. This is because there are several obstacles in the preparation of the schedule, namely first, there should be no duplication of space, day, and hour. Second, there should be no duplication of lecturers on the same day and time, even though in different rooms and in different subjects. Third, there should be no duplication of group classes (study groups). Therefore, the purpose of this study is to obtain a genetic algorithm as a solution in overcoming the three constraints of preparing the schedule by using the Traveling Salesman Problem (TSP) method in the crossover process. To make it easier to organize the schedule, a 3-dimensional matrix is used with the x-axis representing (space, day, hour), the y-axis representing (courses, lecturers, credits) and the z-axis representing (classes). This study simulates the scheduling of 20 courses, 50 credits, 8 lecturers, and 19 classes. Chromosomes in this study are permutations of integers 1-20. Each gene in a chromosome represents a course package. From the scheduling results, the fitness function is 0.96 for 48 schedule slots (2 rooms x 3 days x 8 hours). For schedule slots greater than 50 (3 rooms x 3 days x 8 hours, 2 rooms x 4 days x 8 hours, and 2 rooms x 3 days x 9 hours), this algorithm is successful in getting fitness function 1. ©2018 JNSMR UIN Walisongo. All rights reserved.

An analytical model for wireless mesh networks with collision-free TDMA and finite queues

Wireless mesh networks are a promising technology for connecting sensors and actuators with high flexibility and low investment costs. In industrial applications, however, reliability is essential. Therefore, two time-slotted medium access methods, DSME and TSCH, were added to the IEEE 802.15.4 standard. They allow collision-free communication in multi-hop networks and provide channel hopping for mitigating external interferences. The slot schedule used in these networks is of high importance for the network performance. This paper supports the development of efficient schedules by providing an analytical model for the assessment of such schedules, focused on TSCH. A Markov chain model for the finite queue on every node is introduced that takes the slot distribution into account. The models of all nodes are interconnected to calculate network metrics such as packet delivery ratio, end-to-end delay, and throughput. An evaluation compares the model with a simulation of the Orchestra schedule. The model is applied to Orchestra as well as to two simple distributed scheduling algorithms to demonstrate the importance of traffic-awareness for achieving high throughput.

Ergodic optimization of stochastic differential systems in wireless networks

The present work is the second article in a couple of intertwined papers. They form complementary items on the same subject. They both address the problem of joint power allocation and time slot scheduling in a wireless communication system with time varying traffic. The system is handled by a single base station transmitting over time varying channels. The operating time horizon is divided into time slots, and a fixed amount of power is available at each time slot. The mobile users share each time slot and the power available at this time slot. Since many wireless network applications have stringent delay requirements, designing high-performance resource allocation algorithms to achieve minimum possible delay is of great importance, and this is the main objective of the work presented in this paper. The delay performance of a resource allocation algorithm can be characterized by the average delay experienced by the data transmitted in the network. We propose a heavy traffic analysis for the physical system on hand, i.e., appropriate re-scaling that leads to a diffusion approximation of the system in the sense of weak convergence. The approximate diffusion is constrained or bounded in the K-dimensional positive orthant. We establish the convergence result of the heavy traffic analysis, and then a closed form solution to the resource optimization problem is provided. Here the solution relies on the ergodicity of the approximate diffusion.

A Slotted Sense Multiple Access Protocol for Timely and Reliable Data Transmission in Dynamic Wireless Sensor Networks

A wireless medium access control protocol that uses a topology-dependent slot schedule is vulnerable to link failures. This becomes severer in industrial fields due to node mobility and various obstructions unfriendly to wireless communication. The proposed protocol allocates a big sharable slot (SS) to each tree level, producing a topology-independent schedule that makes the protocol highly responsive to the changes of topology. Then, the nodes at the same level use carrier sense multiple access (CSMA)/CA for data transmission and channel hopping to cope with the varying condition of a channel. The use of CSMA/CA and channel hoping makes data transmission reliable against internal and external interferences. Another feature is that every node gets its SS using a slot generation function independently of other nodes. Simulations and experiments verify that the proposed protocol achieves good performance in terms of packet delivery ratio and energy efficiency against the variation of multipath fading, various external sources of interference, and node mobility.

Self-Learning-Based Data Aggregation Scheduling Policy in Wireless Sensor Networks

The problems of reducing the transmission delay and maximizing the sensor lifetime are always hot research topics in the domain of wireless sensor networks (WSNs). By excluding the influence of routing protocol on the transmission direction of data packets, the MAC protocol which controls the time point of transmission and reception is also an important factor on the communication performance. Many existing works attempt to address these problems by using time slot scheduling policy. However, most of them exploit the global network knowledge to construct a stationary scheduling, which violates the dynamic and scalable nature of WSNs. In order to realize the distributed computation and self-learning, we propose to integrate the Q-learning into the exploring process of an adaptive slot scheduling with high efficiency. Due to the convergence nature, the scheduling quickly approaches an approximate optimal sequence along with the execution of frames. By conducting the corresponding simulations, the feasibility and the high efficiency of the proposed method can be validated.

Optimal Multicommodity Spectrum‐Efficient Routing in Multihop Wireless Networks

Finding the route with maximum end‐to‐end spectral efficiency in multihop wireless networks has been subject to interest in the recent literature. All previous studies, however, focused on finding one route from a given source to a given destination under the constraint of equal bandwidth sharing. To the best of our knowledge, for the first time, this paper provides extensions to the multicommodity flow case, i.e., the case of multiple simultaneous source‐destination (s‐d) pairs. In particular, given an arbitrary number of s‐d pairs, we address the problem of finding a route for every s‐d pair such that the minimum spectral efficiency across all routes is maximized. We provide two alternative approaches, where one is based on fixed‐sized time slots and the other is based on variable‐sized time slots. For each approach, we derive the provably optimal routing algorithm. We also shed the light on the arising tradeoff between the complexity of network‐layer route computation and the complexity of medium access control (MAC) layer scheduling of time slots, as well as the amenability to distributed implementation of our proposed algorithms. Our numerical results further illustrate the efficiency of the proposed approaches and their tradeoffs.

An Efficient Retransmission Scheme for Reliable End-to-End Wireless Communication Over WSANs

A wireless sensor and actuator network is increasingly recognized as an important technology in the realization of the future Internet of Things. The ability to cater to the demands of real-time, reliable, and resource-constraint communication in industrial areas is highly dependent on efficient scheduling of communication links. Harsh industrial environments make packet retransmission inevitable, which causes the waste of link resource and deteriorates the reliability. Most of the studies that focus on real-time and reliable performance underestimate the complexity of packet retransmission. Therefore, this paper proposes an efficient retransmission scheme to guarantee deterministic communication and decrease the resource utilization. We combine deterministic communication with a novel reliable method by proposing a flow-based slot scheduling with a concession timeslot assistant. The proposed concession slot works by using the CCA and the pre-signal to avoid the contention of one channel during the communication on shared links. Furthermore, we use the theory of discrete-time Markov chain to analyze another two randomly backoff-based and flow-based shared link schedules. This paper demonstrates that the proposed retransmission scheme can significantly improve the reliability of end-to-end packet delivery and the efficiency of slot utilization, as well as decrease energy consumption. The proposed scheduling is applied in a real factory, where the efficiency of the slot is significantly improved, and a flow reliability of 95.3% under a 12% packet error rate is guaranteed.

Topology-Transparent Scheduling Based on Reinforcement Learning in Self-Organized Wireless Networks

Topology-transparent scheduling policies do not require the maintenance of accurate network topology information and therefore are suitable for highly dynamic scenarios in self-organized wireless networks. However, in topology-transparent scheduling, it is a very challenging problem to make individual nodes efficiently select their transmission slots in a distributed manner. It is desirable for individual nodes, through time slot selection, to avoid collision on the one hand and utilize as many time slots as possible (i.e., minimize the number of redundant slots) on the other. In this paper, learning-based approaches are employed to solve the time slot scheduling problem. Specifically, the proposed method uses a temporal difference learning approach to address the collision issue and use a stochastic gradient descent approach to reduce the number of redundant slots. Unlike previous works, this learning approach is trained through self-play reinforcement learning without incurring communication overhead for the exchange of reservation information, thereby improving the network throughput. Extensive simulation results validate that our proposal can achieve better efficiency than the existing approaches.

Minding the gap: Optimizing airport schedule displacement and acceptability

Serious congestion problems at slot-controlled airports worldwide call for some action. Slot scheduling related research has mainly focused on scheduling models allocating airport capacity by optimising scheduling efficiency. However, existing literature does not capture the effect of slot allocation decisions on the acceptability of slot schedules. The objective of this paper is to investigate the trade-off between scheduling efficiency and the airlines’ dis-utility of slot schedules expressed by various metrics of schedule displacement. We develop and solve two bi-objective scheduling models considering different combinations of total and maximum acceptable slot displacement objectives. The proposed models are applied to real-world scheduling data. Substantial improvements in schedule acceptability metrics are achieved without sacrificing a lot in terms of scheduling efficiency. Sacrifices in scheduling efficiency increase the capability of the airport coordinator to allocate slots that are eventually acceptable and hence more intensively used.

Priority-based scheduling using best channel in 6TiSCH networks

Many industrial wireless sensor networks deploy the IEEE 802.15.4-2015 standard with low power consumption and the Internet networking capabilities. The time-slotted channel hopping (TSCH) is an amendment to the medium access control protocol defined by the IEEE 802.15.4 standard. Furthermore, the Internet engineering task force (IETF) defines an architecture for IPv6 over the TSCH mode of IEEE 802.15.4 (6TiSCH) to provide deterministic properties on wireless sensor networks. The TSCH leverages the scheduled time slot to achieve low power operation and frequency hopping to combat external interference and multi-path fading. Although TSCH provides the channel hopping mechanism to increase transmission reliability, it is still susceptible to periodic interference for the specific frequency. In this research, we focus on the issue of random channel hopping in the error-prone wireless channel condition and the scheduling for different service requirements. We propose a priority-based scheduling using best channel (P-SBC) mechanism for periodic sensing data and emergency packets transmission in 6TiSCH networks. The simulation results show that the proposed P-SBC achieves higher reliability with significantly lower end-to-end latency for emergency packets transmission as compared to TSCH standard.