Access Scheduling Research Articles

Structural properties, LQG control and scheduling of a networked control system with bandwidth limitations and transmission delays

The problem of simultaneous LQG control and scheduling of a Networked Control System (NCS) with constant network induced delays at input and output and bandwidth limitations is investigated. Delays are considered at plant as well as controller side. Sufficient conditions for controllability, stabilizability, reconstructibility and detectability of the underlying networked control system are drawn. The proposed conditions extend previous works on structural properties of NCS by capturing both plant and controller side delays together with bandwidth limitations. A framework for computing the optimal LQG controller for the NCS with a fixed scheduling is provided. The proposed modeling approach facilitates use of LQG as well as other control methods for NCSs with delays and bandwidth limitations. In order to optimize performance, a semi-online scheduling procedure is proposed based on an offline look up table. The look up table assigns an optimal schedule with associated optimal LQG controller to initial conditions. The proposed scheme improves previous results by online deployment of schedule and LQG control with stability guarantees and very low computational overhead. A simulation example with communication delays, packet losses and bandwidth limitations in both sensor and actuator sides is included. Static optimal periodic communication sequence, Optimal Pointer Placement (OPP) approach proposed in previous works, a random access scheduling method representing contention based access policies and the proposed method are simulated and compared.

Clustering-based enhanced safety message dissemination medium access control protocol for vehicular ad hoc network

Wireless access in vehicular environment employs the IEEE 802.11p/1609.4 standard wherein a multichannel architecture is envisioned to concurrently support both time-sensitive safety-related applications and value-added entertainment services. Although a standard now, the IEEE 802.11p protocol has known shortcomings of not being capable of providing reliable broadcast services. To address this issue, clustering-based enhanced safety message dissemination MAC protocol (CESD-MAC) is proposed in this paper which is an enhancement over the existing IEEE 802.11p/1609.4 protocol. CESD-MAC adopts mobility aware clustering and channel access scheduling. It rules out the concept of switching between the control channel and the service channel as implemented in the legacy standard. Simulation results are presented to verify the effectiveness of the proposed protocol and comparisons are made with the existing IEEE 802.11p MAC. The results demonstrate the superiority of CESD-MAC in terms of reduction of end-to-end delay, and increased throughput, channel utilisation and packet delivery ratio (PDR).

Cross-Layer Design and Performance Analysis of Quality of Service Control Scheme for Wireless Body Area Networks

We analyze and optimize the performance of a quality of service (QoS) control scheme in a cross-layer design for wireless body area networks (WBANs). Smart health monitoring systems that incorporate WBANs and multimedia services have recently been studied and developed. In a WBAN system, wearable and implantable vital sensor nodes can include various types of sensors. Thus, QoS control is a key technique to ensure that different kinds of data are communicated in such a system. In previous work, we proposed an optimal QoS control scheme that employs a multiplexing layer for priority scheduling and a decomposable error control coding scheme for WBANs. However, a cross-layer approach, which is an important technique to optimize the QoS requirements of various kinds of data, has not been considered. In this paper, we utilize a cross-layer design between physical and medium access control layers and analyze and compare the performance of our QoS control scheme and a standard scheme. Numerical results demonstrate that the proposed scheme outperforms the standard scheme. The proposed system achieves a more than 5 dB gain compared with the standard scheme relative to the probability of unsuccessful transmission. We also show that a scheduled access protocol outperforms a random access protocol, except for delay time. In addition, we optimize some factors of the proposed system and the standard scheme in a cross-layer design.

A Customized Many-Core Hardware Acceleration Platform for Short Read Mapping Problems Using Distributed Memory Interface with 3D\u2013Stacked Architecture

Rapidly developing Next Generation Sequencing technologies produce huge amounts of short reads that consisting randomly fragmented DNA base pair strings. Assembling of those short reads poses a challenge on the mapping of reads to a reference genome in terms of both sensitivity and execution time. In this paper, we propose a customized many-core hardware acceleration platform for short read mapping problems based on hash-index method. The processing core is highly customized to suite both 2-hit string matching and banded Smith-Waterman sequence alignment operations, while distributed memory interface with 3D–stacked architecture provides high bandwidth and low access latency for highly customized dataset partitioning and memory access scheduling. Conformal with original BFAST program, our design provides an amazingly 45,012 times speedup over software approach for single-end short reads and 21,102 times for paired-end short reads, while also beats similar single FPGA solution for 1466 times in case of single end reads. Optimized seed generation gives much better sensitivity while the performance boost is still impressive.

PulseSS: A Pulse-Coupled Synchronization and Scheduling Protocol for Clustered Wireless Sensor Networks

The pulse-coupled synchronization and scheduling (PulseSS) protocol is proposed in this paper for simultaneous synchronization and scheduling of communication activities in clustered wireless sensor networks (WSNs), by emulating the emergent behavior of pulse-coupled oscillator (PCO) networks in mathematical biology. Different from existing works that address synchronization and scheduling (i.e., desynchronization) separately, PulseSS provides a coordination signaling mechanism that achieves decentralized network synchronization and time division multiple access scheduling simultaneously at different time scales for clustered WSNs. Here, we assume that the nodes are connected only locally via their respective cluster heads. Moreover, PulseSS addresses the issue of propagation delays, that may plague the accuracy of PCO synchronization in practice, by providing ways to estimate and precompensate for these values locally at the sensors (i.e., PCOs). At the same time the protocol retains the adaptivity and light-weight nature of PCO protocols both in terms of signaling and computations. Simulations of both physical and medium access control layers show a synchronization accuracy of factions of microseconds above 15 dB of signal to interference and noise ratio for a five cluster network. A hardware implementation of PulseSS using TinyOS is also provided to corroborate the real world applicability of our protocol.

Optimal CSMA Scheduling With Look Ahead Mechanism for Wireless Networks

Optimal carrier sense multiple access (CSMA) scheduling algorithms such as Q-CSMA suffer from large delay, mainly due to the strong correlations residing in consecutive link schedules. Some previous works have remedied this issue with multiple instances of the scheduler, but the baseline scheduler (Q-CSMA) itself remains untouched. By noticing the inherent inefficiency in the contention mechanism of Q-CSMA, we propose looks ahead (LA)-CSMA algorithm in which each link LA its state update in advance and utilizes this free information during the contention stage. We show that our algorithm achieves optimal throughput with reduced correlation in the service process, thereby leading to significantly smaller delay without any additional overhead.

BLISS: Balancing Performance, Fairness and Complexity in Memory Access Scheduling

In a multicore system, applications running on different cores interfere at main memory. This inter-application interference degrades overall system performance and unfairly slows down applications. Prior works have developed application-aware memory request schedulers to tackle this problem. State-of-the-art application-aware memory request schedulers prioritize memory requests of applications that are vulnerable to interference, by ranking individual applications based on their memory access characteristics and enforcing a total rank order. In this paper, we observe that state-of-the-art application-aware memory schedulers have two major shortcomings. First, such schedulers trade off hardware complexity in order to achieve high performance or fairness, since ranking applications individually with a total order based on memory access characteristics leads to high hardware cost and complexity. Such complexity could prevent the scheduler from meeting the stringent timing requirements of state-of-the-art DDR protocols. Second, ranking can unfairly slow down applications that are at the bottom of the ranking stack, thereby sometimes leading to high slowdowns and low overall system performance. To overcome these shortcomings, we propose the Blacklisting Memory Scheduler (BLISS) , which achieves high system performance and fairness while incurring low hardware cost and complexity. BLISS design is based on two new observations. First, we find that, to mitigate interference, it is sufficient to separate applications into only two groups, one containing applications that are vulnerable to interference and another containing applications that cause interference, instead of ranking individual applications with a total order. Vulnerable-to-interference group is prioritized over the interference-causing group. Second, we show that this grouping can be efficiently performed by simply counting the number of consecutive requests served from each application. We evaluate BLISS across a wide variety of workloads and system configurations and compare its performance and hardware complexity (via RTL implementations), with five state-of-the-art memory schedulers. Our evaluations show that BLISS achieves 5 percent better system performance and 25 percent better fairness than the best-performing previous memory scheduler while greatly reducing critical path latency and hardware area cost of the memory scheduler (by 79 and 43 percent, respectively), thereby achieving a good trade-off between performance, fairness and hardware complexity.

Medium access scheduling for input reconstruction under deception attacks

This article presents a novel approach of state filtering scheme and the sensor scheduling co-design for cyber-physical systems subject to random deception attacks. Such cyber attacks are switching disturbances that affect the input information transmitted from the controller to the plant through a constrained communication network. The cyber-physical system dynamics can be modelled as an augmented state model, while the unknown input reconstruction is obtained from a modified Kalman filter recursions under communication constraints. To deal with limited bandwidth constraint, a periodic sensor scheduling strategy is proposed in order to ensure the minimization of disturbances and cyber-attack effects.

Joint Routing and Links Scheduling in Two-Tier Multi-Hop RF-Energy Harvesting Networks

This letter considers a two-tiered multi-hop RF-harvesting network comprising of wireless routers and so called eh-nodes that harvest energy from RF emitted by the said routers. Our aim is to derive the shortest possible superframe or time division multiple access schedule for use by routers, which are responsible for meeting flow and energy demands. We present a linear program to derive the optimal schedule whilst satisfying the said demands. We also outline a heuristic algorithm called Algo-TS to generate transmission sets. Our results show Algo-TS produces superframes that are at most 2% longer than the optimal solution in all tested scenarios.

WhiteFi Infostation: Engineering Vehicular Media Streaming With Geolocation Database

The TV white spaces (TVWS) enabled infostation has received significant attention due to its wide area coverage for cost-effective and media-rich content dissemination. In this paper, we engineer WhiteFi infostation, which is dedicated for Internet-based vehicular media streaming by leveraging geolocation database. After demonstrating the empirical observations of unique TVWS features and analyzing the real-world TVWS data collected from geolocation database, we first propose an optimal TVWS network planning to deploy WhiteFi infostation with the objective of maximizing network-wide throughput. The proposed TVWS network planning jointly considers the multi-radio configuration and the channel-power tradeoff, which can be realized by decentralized Markov approximation. Furthermore, we introduce a location-aware contention-free multi-polling access scheduling scheme for vehicular media streaming, which considered both the realistic vehicular applications and dynamics of wireless channel conditions. Through extensive simulations with real-world empirical TVWS data and urban vehicular traces, we demonstrate that our WhiteFi infostation solution can well support both the delay-sensitive and delay-tolerant vehicular media streaming services.

Intermittent access to a sucrose solution for rats causes long-term increases in consumption

Intermittent access to palatable food can elevate consumption beyond an animal's immediate needs. If adult male rats (with ad lib access to food and water) are provided with a 4% sucrose solution, daily sucrose consumption is determined by the sucrose access schedule: access that is intermittent leads to high levels of consumption. In Experiment 1, sucrose solutions were first provided continuously or every second, third, or fourth day for 23.5h over 49days. Continuous-access sucrose consumption averaged 102g per day, while that for access every fourth day averaged 294g. Daily consumption averages for access every second and third day fell between these two extremes. When all rats were then given alternate-day access to sucrose for 24days in Phase II, the previously established consumption differences were maintained. Body weight was unaffected by sucrose access; rats adjusted their food consumption so that total calorie intake remained constant. In Experiment 2, compared to continuous 4% sucrose solution access, access every third day markedly elevated daily sucrose consumption after only four sucrose exposures. With this shorter Phase I, sucrose intake in the continuous group increased markedly when in Phase II all rats were given alternate day access. In Experiment 3, a lick-by-lick analysis of the difference in sucrose consumption between access every third day and continuous access revealed that all rats were consuming a similar number of sucrose meals; however, the meals were larger both in the first hour and over the whole 24h with intermittent access. This suggests a change in satiety as a mechanism underlying sucrose consumption difference.

Patient-Centered Medical Home Adoption: Lessons Learned and Implications for Health Care System Reform.

Case studies of 8 primary care medical homes participating in a Massachusetts-based initiative were conducted to understand the approaches they used to operationalize medical home standards and associated barriers. All sites received their National Committee on Quality Assurance recognition as medical homes, yet varied considerably in how components were implemented. Despite this variation, they faced similar challenges to implementing and sustaining medical home standards. Variations and challenges strongly emerged in 4 areas: team-based care, scheduling and online access, identifying and managing high-risk patients, and organizing follow-up care. Our study offers insight into various pathways to medical home success, and notes areas for further study.

1‐800‐Skype‐Me

It is increasingly common that children of divorce are geographically separated from one of their parents. This article considers the challenges that arise from that reality by exploring this problem from a variety of perspectives and by providing practical tips to minimize the impact of the distance. A review of the Ontario caselaw and Arizona Guidelines reveal that certain factors are important in the resolution of these disputes, including: the age of the child, mode of transportation between homes, distance, prior contact, and feasibility of virtual access. Court‐ordered access may include remedies that, absent the distance issue, may be considered extreme, including moving to overnight/extended access periods for young children, permitting children to travel unaccompanied, favoring the nonresident parent for holidays and vacation time, allowing children to decrease contact with the nonresident parent, and decreasing or terminating child support. Where distance dictates the in‐person and virtual access schedules, creative solutions are critical to the successful resolution of these cases. Forward thinking family law professionals can meaningfully help parents to achieve better outcomes for children.

Exploiting Core Criticality for Enhanced GPU Performance

Modern memory access schedulers employed in GPUs typically optimize for memory throughput. They implicitly assume that all requests from different cores are equally important. However, we show that during the execution of a subset of CUDA applications, different cores can have different amounts of tolerance to latency. In particular, cores with a larger fraction of warps waiting for data to come back from DRAM are less likely to tolerate the latency of an outstanding memory request. Requests from such cores are more critical than requests from others. Based on this observation, this paper introduces a new memory scheduler, called (C)ritica(L)ity (A)ware (M)emory (S)cheduler (CLAMS), which takes into account the latency-tolerance of the cores that generate memory requests. The key idea is to use the fraction of critical requests in the memory request buffer to switch between scheduling policies optimized for criticality and locality. If this fraction is below a threshold, CLAMS prioritizes critical requests to ensure cores that cannot tolerate latency are serviced faster. Otherwise, CLAMS optimizes for locality, anticipating that there are too many critical requests and prioritizing one over another would not significantly benefit performance. We first present a core-criticality estimation mechanism for determining critical cores and requests, and then discuss issues related to finding a balance between criticality and locality in the memory scheduler. We progressively devise three variants of CLAMS, and show that the Dynamic CLAMS provides significantly higher performance, across a variety of workloads, than the commonly-employed GPU memory schedulers optimized solely for locality. The results indicate that a GPU memory system that considers both core criticality and DRAM access locality can provide significant improvement in performance.

Study on using design patterns to implement a simulation system for WiMAX network

A network simulator always is an important tool to observe and evaluate the study concept for wireless networks. Considering the restriction of the limited budget, the non-commercial open-source simulation software often becomes the top choice of academia. Since the natures of academic study are innovation and excellence, a simulator frequently encounters that the existing modular functions are inadequate and need to be appended or modified. If a selected simulator inherently has poor architecture, the maintenance, recondition, and expansion of functions will become more difficult and more time-consuming in the future, while it is difficult to understand and reuse by the successors. Therefore, how to select a most suitable simulator is an important issue. In order to make a simulator have flexible architecture and believable results, design patterns are proposed as the norms to design system architecture. To realize this idea, we surveyed six most used simulators, i.e., J-Sim, NS-2, NS-3, OMNet++, OPNET, and QualNet, to ponder their system architectures and design concepts from the source codes and the related literatures of the modular function expansion. We propose a network simulator architecture, named as CCGns, which is a discrete-event virtual network simulator and follows the IEEE 802.16-2009 standard. CCGns obeys the object-oriented design principles and is coded by the Java language. CCGns comprises eight packages for physical layer, medium access control layer, network layer, devices, topologies, events, scheduler, and reports, respectively. The main contribution includes three aspects which propose a scalable MAC messages management and the corresponding architecture, an applicable for multi-hop relay network topology architecture, and a two-stage minimum variance bandwidth allocation algorithm. To the best of our knowledge, this article is not the first one to apply the design patterns for the simulator architectures of wireless network, but we use more design patterns and types than the others and also provide the unified modeling language figures to explain the system architectures. We particularly focus on how the management procedure of control messages influences the time-related performance evaluation metrics, e.g., how the amount and processing time of different control messages affect throughput, packet delay, and packet drop ratio. By using mathematic calculation to verify the simulation results, the proposed system architecture has been proven to possess excellent fidelity.

The Use of Enhanced Appointment Access Strategies by Medical Practices.

Strategies to enhance appointment access are being adopted by medical practices as part of patient-centered medical home (PCMH) implementation, but little is known about the use of these strategies nationally. We examine practice use of open access scheduling and after-hours care. Data were analyzed from the Third National Study of Physician Organizations (NSPO3) to examine which enhanced appointment access strategies are more likely to be used by practices with more robust PCMH capabilities and with greater external incentives. Logistic regression estimated the effect of PCMH capabilities and external incentives on practice use of open access scheduling and after-hours care. Physician organizations with >20% primary care physicians (n=1106). PCMH capabilities included team-based care, health information technology capabilities, quality improvement orientation, and patient experience orientation. External incentives included public reporting, pay-for-performance (P4P), and accountable care organization participation. A low percentage of practices (19.8%) used same-day open access scheduling, while after-hours care (56.1%) was more common. In adjusted analyses, system-owned practices and practices with greater use of team-based care, health information technology capabilities, and public reporting were more likely to use open access scheduling. Accountable care organization-affiliated practices and practices with greater use of public reporting and P4P were more likely to provide after-hours care. Open access scheduling may be most effectively implemented by practices with robust PCMH capabilities. External incentives appear to influence practice adoption of after-hours care. Expanding open access scheduling and after-hours care will require distinct policies and supports.

Communication Scheduling and Control of a Platoon of Vehicles in VANETs

This paper is concerned with the problem of vehicular platoon control in vehicular ad hoc networks subject to capacity limitation and random packet dropouts. By introducing binary sequences as the basis of network access scheduling and modeling random packet dropouts as independent Bernoulli processes, we derive a closed-form methodology for vehicular platoon control. In particular, an interesting framework for network access scheduling and platoon control codesign is established based on a set of priority rules for network access control. The resulting platoon control and scheduling algorithm can resolve network access conflicts in vehicular ad hoc networks and guarantee string stability and zero steady-state spacing errors. The effectiveness of the method is demonstrated by numerical simulations and experiments with laboratory-scale Arduino cars.

Open access scheduling: Improving access to rural healthcare

Background and Purpose: Open access scheduling is a model that allows patients to choose appointments at their convenience in an effort to provide timely access to healthcare. Healthcare providers typically have overbooked schedules that make it difficult to provide access to primary care appointments for patients in need without long wait times. The purpose of this quality improvement project was to implement open access scheduling at a federally-qualified health center to evaluate the number of missed patient appointments and the amount of time it takes to receive an appointment. Methods: Patient appointments (N=1,333) were analyzed via the Allscripts™ electronic computer system. During project implementation, staff utilized a written protocol for open access that had been tested at a satellite office with successful results. Patients were placed in appointment slots daily as they were available. Conclusions: The highest no-show rate prior to implementation was 42%, which improved after open access to 27%. Average TNAA trended downward post-implementation from 8.9 days three-months pre-intervention to 4.3 days three-months post-implementation. This scheduling model was successful in decreasing no-show rates by allowing patients to be seen in a timely manner and can be utilized in primary care to improve access to healthcare.

Estimating the Transmission Probability in Wireless Networks with Configuration Models

We propose a new methodology to estimate the probability of successful transmissions for random access scheduling in wireless networks, in particular those using Carrier Sense Multiple Access (CSMA). Instead of focusing on spatial configurations of users, we model the interference between users as a random graph. Using configuration models for random graphs, we show how the properties of the medium access mechanism are captured by some deterministic differential equations when the size of the graph gets large. Performance indicators such as the probability of connection of a given node can then be efficiently computed from these equations. We also perform simulations to illustrate the results on different types of random graphs. Even on spatial structures, these estimates get very accurate as soon as the variance of the interference is not negligible.

Enhancing Reliability of IEEE 802.15.6 Wireless Body Area Networks in Scheduled Access Mode and Error Prone Channels

This paper investigates reliability of wireless body area networks based on the IEEE 802.15.6 standard, for the scheduled access mode in an error prone channel. In scheduled access mode, during a time slot that is allocated for communication between a sensor node and the hub, the frame transmission fails if the link is in the deep fade state. To improve reliability of the network, we propose an efficient scheme for packet retransmission. The proposed scheme relies on allocation of spare slots for packet retransmissions in each superframe. We then present analytical models to find the energy efficiency and reliability of the network under the proposed retransmission scheme. Through analytical and simulation results, we establish that the proposed retransmission scheme can significantly improve the reliability of the network in the scheduled access mode, without causing degradation of energy efficiency.