Empty Time Slots Research Articles

VDIU: VLC-Based Debugging Information Upload Method for Self-Powered Sensor Nodes

Currently, more and more self-powered sensor nodes have been deployed in remote and inaccessible areas, and thus online debugging of sensor nodes becomes more necessary and important. However, the existing sensor online debugging approaches mainly rely on original network infrastructure (such as Zigbee or NB-IoT). Once the communication infrastructure is invalid, it is almost impossible to retrieve debugging information and repair the lost self-powered sensor nodes. To this end, in our previous study, we employed the onboard optical modules of the self-powered sensor node to realize a Visible Light Communication(VLC)-based hybrid communication debugging system(VHCDS). In this paper, to improve the efficiency of uploading debugging information, we propose VDIU to optimize the digital pulse interval modulation applied in the uplink of VHCDS. This method reasonably groups and sorts the origin data to reduce the number of empty time slots (unused time slots) and complete data compression in source coding for saving energy. To improve the reliability of the uplink, we also design two frame synchronization mechanisms suitable for the receiver-side optical cameras of the uplink. One mechanism considers lightweight synchronization design via restricting the position of the frame header; the other one focuses on reducing the occupation of the downlink of VHCDS via predicting the position of the frame header using a temporal convolutional network (TCN). Experiments results illustrate that the upload efficiency using VDIU is higher 78% and 28% than DPIM and DH-PIM. Both synchronization mechanisms can arrive the similar performance, but the predicting mechanism reduces the 93% occupation on the downlink.

Job Scheduling on Grid Computing Using First Fit, Best Fit, and Worst Fit

Grid computing can be considered large-scale distributed cluster computing and parallel distributed network processing. The two most important issues in managing user work are resource allocation and scheduling of required resources. When user jobs are submitted, they are managed by resource intermediaries who find and allocate the right resources. After the resource allocation stage, work scheduled on the existing resources according to the user's required resources. In most grid systems with traditional scheduling, jobs are submitted and placed in waiting room queues to wait for the required resources to become available. Each grid system can use a different scheduling algorithm to execute jobs based on other parameters, such as resources, delivery time, and execution duration. There is no guarantee that these traditional scheduling algorithms will get the job done. The First Come First Serve Left Right Hole Scheduling (FCFS-LRH) reservation strategy improves resource utilization in a grid system by using a local scheduler. Compared to traditional strategies. There are two objectives of this research. First, compare the first fit, best fit, and worst fit algorithms to find empty timeslots and place them in a virtual view. Second, reduce the idle time value. The results showed that the FCFS-LRH method could reduce the idle time value of the FCFS-EDF and FCFS methods. The overall execution time of the first fit with the FCFS-LRH strategy is better than the FCFS-EDF

Packet Squeezing of Random Access with 5G Real-Time Services for Internet of Things

Random Access techniques are many, most of which are designed for a limited number of mobile nodes. However, in a 5G Internet of Things environment, the design of random access must accommodate a very large number of devices which are heterogeneous in nature, and packets are in general short and come in a variety of lengths. Variable lengths of short packets may waste bandwidth if each packet transmits at the beginning of a time slot. In this paper, packet squeezing allows for a packet to make a selection between aligning to the beginning and aligning to the ending of a time slot. Two or more nodes transmitting at the same time slot may not result in a collision if two conditions are met simultaneously. First, one node selects an alignment mode different from that of the remaining nodes. Secondly, the sum of the time durations of two “representative” packets is shorter than the duration of a time slot. The performance analysis demonstrates that the throughput gain due to the packet squeezing is significant. The gain of packet squeezing can be enhanced by time slot management, where a transmitting node randomly selects a set of points of Finite Projective Plane and transmits at the time slots corresponding to the points of the chosen set. Due to the rather uniform distribution of the transmitting nodes and fewer empty time slots, the gain of packet squeezing is further improved for the entire frame. Based on the simulation results and analysis, we have observed that the time slot management extends the range of packet arrival rate of peak throughput for packet squeezing. Lastly, we compare and contrast the combining of packet squeezing and time slot management with well-known random access protocols of IoT such as slotted ALOHA and NOMA, and simulate real systems to verify the results of performance analysis.

A new strategy for packets scheduling in cognitive radio internet of things

The usage of Cognitive Radio Networks (CRNs) to establish Internet of Things (IoT) smart Networks is an effective and economical solution to the IoT spectrum scarcity problem. CRNs is merged with the IoT technology to be named Cognitive Radio Internet of Things (CRIoT). Spectrum sharing/scheduling in CRIoT has not attracted a lot of attention as it should do. This paper proposes a new packets' scheduling strategy for CRIoT. It is a centralized time slotted algorithm that uses discrete permutation particle swarm optimization for scheduling packets among predicted primary network empty time slots. An objective function is formulated to maximize the fairness index among fog nodes, minimize the packets' queuing delay and minimize the number of dropped packetsat each time interval. In order to evaluate the proposed protocol, it is implemented along with another protocol named spectrum auction. Using the fairness index, the average queuing delay and the number of dropped packets as evaluation metrics, simulation results proved that the proposed protocol outperforms the spectrum auction protocol. It also has a lower time and space complexity.

A New Intra-Cluster Scheduling Scheme for Real-Time Flows in Wireless Sensor Networks

Real-time flows using time division multiple access (TDMA) scheduling in cluster-based wireless sensor networks try to schedule more flows per time frame to minimize the schedule length to meet the deadline. The problem with the previously used cluster-based scheduling algorithm is that intra-cluster scheduling does not consider that the clusters may have internal or outgoing flows. Thus, intra-cluster scheduling algorithms do not utilize their empty time-slots and thus increase schedule length. In this paper, we propose a new intra-cluster scheduling algorithm by considering that clusters may have having internal or outgoing flows. Thus, intra-cluster scheduling algorithms do not differentiate the intra-cluster time slots and utilize their empty time slots. The objective is to schedule more flows per time frame, to reduce schedule length and improve the acceptance rate of flows. Simulation results show that the acceptance rate of the proposed scheme has a higher performance than the previous scheme.

A self-organizing network coordination framework enabling collision-free and congestion-less wireless sensor networks

In recent years, wireless sensor networks (WSNs) have been widely used for controlling remote devices and also for gathering sensor data of distributed WSN devices. The WSNs support current Internet of Things (IoT) technologies in the background. However, it is becoming a salient issue that frequent packet delivery losses occur during data gathering on WSNs along with the increasing number of nodes. Two fundamental difficulties exist for MAC and upper layers on IEEE 802.15.4 standard: transmission collisions among two-hop away nodes, known as the “Hidden node problem,” and traffic congestion during data transfer that engenders buffer overflow at nodes. To resolve these difficulties, we propose a self-organizing network coordination framework for WSNs that realizes an adaptive time-division transmission by nodes and also traffic congestion handling in a decentralized manner. Specifically, the framework is based on a decentralized time division technique using a simplified pulse-coupled oscillator model. By coordinating the transmission timing adaptively, each node sends messages without collisions. “Hidden node problems” as well as “Exposed node problems” will be prevented, in principle, when using our method. Additionally, to reduce traffic congestion in a decentralized manner, time slots in the transmission cycle on each node are used efficiently by additional algorithms: an “empty time slots utilization algorithm” and a “takeover algorithm of neighboring nodes’ transmission slots”. These are introduced for efficient large data gathering applications. We simulated a 60-node data gathering application and evaluated its superiority to a conventional WSN method using CSMA/CA on IEEE 802.15.4 standard. We also conducted hardware experiments using nine developed WSN nodes and confirmed our framework’s feasibility in real situations targeted at real-time landslide detection with distributed WSN nodes.

PTES: A New Packet Transmission Technique in Bufferless Slotted OPS Networks

Optical packet contention is the major problem in optical packet switching (OPS) networks. In this paper, a software-based contention reduction scheme is proposed for all-optical multi-fiber slotted OPS networks, called packet transmission based on the scheduling of empty time-slots (PTES), suitable for overlaid star topology used in a metropolitan area with heterogeneous distances. In the scheduling procedure (performed in a distributed manner by each edge node of a star network) within a frame interval, some time-slots are scheduled as empty time-slots and the remaining time-slots are scheduled as non-empty. Then, an edge node must avoid sending its traffic in empty time-slots. Instead, non-empty time-slots can be used for traffic transmission. With respect to this scheduling, the variance of the number of non-empty time-slots that carry traffic from all edge nodes is minimized in the core node at each time-slot, thus reducing the traffic loss. Mathematical formulas are also provided to compute the traffic loss and delay under PTES. Performance evaluation results illustrate that PTES can reduce the number of collision events and traffic loss, especially at light and moderate traffic loads.

An improved algorithm for online rectangle filling

We consider the problem of scheduling resource allocation where a change in allocation results in a changeover penalty of one time slot. We assume that we are sending packets over a wireless channel of uncertain and varying capacity. In each time slot, a bandwidth of at most the current capacity can be allocated, but changing the capacity has a cost, which is modeled as an empty time slot. Only the current bandwidth and the bandwidth of the immediately following slot are known. We give an online algorithm with competitive ratio 1.753 for this problem, improving over the previous upper bound of 1.848. The main new idea of our algorithm is that it attempts to avoid cases where a single time slot with a nonzero allocation is immediately followed by an empty time slot. Additionally, we improve the lower bound for this problem to 1.6959, and give a better randomized lower bound. Our results significantly narrow the gap between the best known upper and lower bounds.

An efficient tag collection algorithm utilizing empty time slots in active RFID systems

We propose an efficient tag collection algorithm utilizing empty time slots in active RFID systems. In the proposed tag collection algorithm, the reader recognizes the existence of empty time slots via carrier sensing, and utilizes the redundant empty time slots to transmit sleep commands to the tags collected, resulting in performance improvement for tag collection. The simulation results show that the proposed tag collection algorithm can reduce the average tag collection time by 12.28%, 12.30%, and 13.31%, for the framed slotted aloha with the fixed 128 time slots and 256 time slots, and the dynamic framed slotted aloha anticollision protocols, respectively.

A model for managing patient booking in a radiotherapy department with differentiated waiting times

Background. In Denmark, the waiting time from the ready-to-treat date to the first radiotherapy fraction is by national legislation guaranteed not to exceed 4 weeks. This guarantee has now been tightened for some specific diagnoses as it is required that e.g. intestinal and head and neck cancer patients have to be treated without unnecessary delays. Thus, patients with these tumour sites have to start radiotherapy treatment immediately after diagnosis, if it is their primary treatment modality. Previously, patients have been booked at the first empty time slot after their ready-to-treat date. Now, booking has to take the differentiated waiting times into account. To facilitate this, a model has been developed. It is used to manage the booking of patients, reserve accelerator capacity for patients with no waiting time and establish the waiting times for other patients. Methods. The patients are divided into categories according to their waiting time guarantee and for each category a maximum waiting time is defined. The required daily accelerator capacity and average new starts rate for each waiting time category has been determined from the actual patient case-mix in the department. To account for variations in treatment capacity, a prospective daily accelerator capacity is set. Based on the prospective capacity, preparation times, maximum waiting times, and new starts rates, a maximum booking curve (MBC) and a lower limit curve (LLC) are derived. They show the daily maximum and minimum limits, respectively, for booking at future dates. Results. The method is evaluated by a retrospective analysis of actual number of appointments booked compared to the MBC and LLC in situations of both excessive workload and ineffective use of capacity. Conclusion. The model represents a tool for effectively managing the capacity in a radiotherapy department with differentiated waiting times. It improves the transparency of the booking process and prospective waiting times can easily be derived on a daily basis.

Preemptive and non-preemptive scheduling of optical switches with configuration delay

Utilizing optical technologies for the design of packet switches and routers offers several advantages in terms of scalability, high bandwidth, power consumption, and cost. However, the configuration delays of optical crossbars are much longer than that of the electronic counterpart, which makes the conventional slot-by-slot scheduling methods no longer the feasible solution. Therefore, some tradeoff must be found between the empty time slots and configuration overhead. This paper classifies such scheduling problems into preemptive and non-preemptive scenarios, each has its own advantages and disadvantages. Although non-preemptive scheduling is inherently not good at achieving the above-mentioned tradeoff, it is shown, however, that the proposed maximum weight matching (MWM) based greedy algorithm is guaranteed to achieve an approximation 2 for arbitrary configuration delay, and with a relatively low time complexity O(N2). For preemptive scheduling, a novel 2-approximation heuristic is presented. Each time in finding a switch configuration, the 2-approximation heuristic guarantees the covering cost of the remaining traffic matrix to have 2-approximation. Simulation results demonstrate that 2-approximation heuristic (1) performs close to the optimal scheduling, and (2) outperforms ADJUST and DOUBLE in terms of traffic transmission delay and time complexity.

Channel estimation and equalisation via implicit training with zero-mean input data packets

In implicit training for channel estimation the training sequence is added to the information data, as opposed to it being placed in a separate empty time-slot, as in say, GSM. It is shown that by also removing each data packet's deterministic mean before transmission, both the channel estimate, and the BER after MMSE equalisation, can be improved.

Channel Estimation Using Implicit Training

In this paper, a new method to perform channel estimation is presented. It is shown that accurate estimation can be obtained when a training sequence is actually arithmetically added to the information data as opposed to being placed in a separate empty time slot: hence, the word implicit. A closed-form solution for the estimation variance is derived, as well as the Cramer-Rao lower bound. Conditions are derived for the training sequences that result in a channel estimation performance that is independent of the channel characteristics. In addition, estimation performance is shown to be independent of the modulation format. A procedure to synthesize optimal training sequences is presented, and the problem of synchronization is solved. The performance of the algorithm is then compared with other methods that use explicit training under GSM-like environmental conditions, and the new algorithm is shown to be competitive with these. Finally, comparisons are also carried out against blind methods over realistic bandlimited channels, and these show that the new method exhibits good performance.

A semi-dynamic time window constrained routeing strategy in an AGV system

This study addresses the issue of vehicle route planning in an AGV system. The two salient approaches to route planning static and dynamic are briefly discussed. The main thrust of the present work is development and testing of a proposed semi-dynamic time window constrained routeing strategy. Reserved time windows are placed on nodes indicating sequential crossing of nodes by the respective vehicles. Free time windows represent empty time slots available for vehicles to cross the nodes. Similarly, time windows representing the direction of traffic flow are placed on the bidirectional arcs. Based on these time windows, Dijkstra's algorithm is applied to find the least congested fastest routes for vehicles. A simulation study of a bidirectional flow path is then reported. The aim of the simulation experiment is to evaluate the system performance under the proposed routeing strategy vis-a-vis static routeing strategy. The results show that the proposed routeing strategy helps in reducing vehicle blocking time and improving the throughput potential of the system.

Dynamic Frame Length ALOHA

Adding frame structure to slotted ALOHA makes it very convenient to control the ALOHA channel and eliminate instability. The frame length is adjusted dynamically according to the number of garbled, successful, and empty timeslots in the past. Each terminal that has a packet to transmit selects at random one of the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</tex> timeslots of a frame. Dynamic frame length ALOHA achieves a throughput (expected number of successful packets per timeslot) of 0.426 which compares favorably with the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/e (\approx0.368)</tex> upper bound of ordinary slotted ALOHA.