Dynamic Priority Assignment Research Articles

Task reconstruction method for real-time singularity avoidance for robotic manipulators

The kinematic (KS) and algorithmic singularities (AS) in controlling robotic manipulators have been investigated intensively because they are not predictable or difficult to avoid. The problem with handling these singularities is an unnecessary performance reduction in the non-singular region and the difficulty in performance tuning. In this paper, we propose a method of avoiding KS and AS by applying a task reconstruction approach while maximizing the task performance by calculating singularity measures. The proposed method is implemented by removing the component approaching the singularity calculated by using a singularity measure in real-time. The outstanding feature of the proposed task reconstruction (TR) method is that it is based on a local TR as opposed to the local joint reconstruction of many other approaches. This method has a dynamic task priority assignment feature which ensures system stability under singular regions due to the change of task priority. The TR method enables us to increase the task controller gain to improve the task performance, whereas this increase can destabilize the system for conventional algorithms in real experiments. In addition, the physical meaning of tuning parameters is very straightforward. Hence, we can maximize task performance even near the singular region while simultaneously obtaining the singularity-free motion. The advantage of the proposed method is experimentally tested by using a 7-d. o. f. spatial manipulator and the result shows that the new method improves the performance several times over the existing algorithms.

Meeting Real-Time Constraints in CAN

This paper deals with the problem of information flow scheduling in a communication system based on CAN ISO IS-11898 physical medium access mechanism. It mainly features a bus access arbitration protocol based on a priority assigned to each message to be transmitted; if two or more messages are transmitted at the same time by different communication nodes, only the message with the highest priority continues to be transmitted, the other being stopped. In real-time applications, messages are relevant to process variables which must be transmitted within strict time constraints; according to the CAN ISO IS-11898 bus arbitration protocol, respect of real-time constraints depends on the priority assigned to each variable. The aim of the paper is to propose a procedure for dynamic assignment of priorities to variables to be transmitted, in such a way the relevant real-time requirements are fulfilled. Although many other approaches can be found in literature, the proposal is original as it is based on standard full CAN communication stacks.

Proposal and evaluation of dynamic assignment of priorities in CAN

The paper deals with the scheduling of information flow in a CAN ISO IS-11898 communication system. It mainly features a bus access arbitration protocol based on a priority assigned to each message to be transmitted; if two or more messages are transmitted at the same time by different communication nodes, only the message with the highest priority continues to be transmitted, the other being stopped. In real-time applications, messages contain information which must be transmitted within strict time constraints; according to the CAN ISO IS-11898 bus arbitration protocol, respect of real-time constraints of time critical information depends on the priority assigned to the message conveying it. The aim of the paper is to propose a procedure for dynamic assignment of priorities to messages to be transmitted, in such a way the real-time requirements of the information conveyed are fulfillled. Although many other approaches can be found in literature, the proposal is original as It is based on standard full CAN communication stacks.

Hop counting based lightweight quality of service model for sensor devices

For mobile ad hoc network (MANET) applications with sensor devices such as disaster recovery, it is necessary to provide streaming services for surveillance activities. For such uses, we propose a Spatial Resource Allocation (SRA) based Quality of Service (QoS) model for MANET integrated with sensors. Borrowing ideas from differentiated services (DiffServ), our protocol adapts to variations in terms of spatial properties such as bandwidth, interference and capacity. SRA model selects a single or multiple resource allocating (allocator) nodes to perform resource allocation in the forwarding path. The promising behaviour exhibited by SRA is its simplicity and lightweight nature. This makes it suitable for sensor networks. It differs from existing schemes, through dynamic priority assignment by nodes, in forwarding path rather than source node, reflecting network behaviour in the forwarding path. The priority assignment is done based on hop count. Extensive simulation using ns-2 is performed to evaluate the performance of the model. It has been found that the energy saving introduced is about 20% and the reduction in number of retransmissions is about 30%. This scheme works over the existing routing protocol, requiring no modification to it.

Analysis of Workflow Protocol Adaptability in TestLAN Production Systems

Abstract The testing local area network, TestLAN, is an approach to the design of integrated testing systems. Its objective is to link a network of testers such that distributed clients (jobs) requiring testing services can be served efficiently with minimum delays through the use of dynamic priority assignment, time-out, and resource allocation protocols. Previous research has shown this approach to improve performance, but assumed that the protocols are static. Events such as demand fluctuation and design changes, however, can affect the usefulness of the protocol logic, thereby adversely affecting the performance of the system. This paper investigates the thresholds of change and the time at which protocols should be re-evaluated for possible changes. The results of the analysis show that significant improvement can be gained by protocol adaptation, with certain cases realizing improvement in the flow time by as much as 32%, compared to the non-adaptable TestLAN. However, differences among adaptation methods are more difficult to generalize, as they depend on the particular cases. In many cases, adapting protocol logic when thresholds are in the range 0.2 ≤ Δ ≤ 0.4, the percentage change of the parameters of the system in either direction, reduces flow time significantly, yet these thresholds are not general. The importance of this analysis is that the experiments cover a large space of general conditions, and general design recommendations for protocol adaptation are developed.

Analysis of workflow protocol adaptability in TestLAN production systems

The testing local area network, TestLAN, is an approach to the design of integrated testing systems. Its objective is to link a network of testers such that distributed clients (jobs) requiring testing services can be served efficiently with minimum delays through the use of dynamic priority assignment, time-out, and resource allocation protocols. Previous research has shown this approach to improve performance, but assumed that the protocols are static. Events such as demand fluctuation and design changes, however, can affect the usefulness of the protocol logic, thereby adversely affecting the performance of the system. This paper investigates the thresholds of change and the time at which protocols should be re-evaluated for possible changes. The results of the analysis show that significant improvement can be gained by protocol adaptation, with certain cases realizing improvement in the flow time by as much as 32%, compared to the non-adaptable TestLAN. However, differences among adaptation methods are more difficult to generalize, as they depend on the particular cases. In many cases, adapting protocol logic when thresholds are in the range 0.2 ≤ Δ ≤ 0.4, the percentage change of the parameters of the system in either direction, reduces flow time significantly, yet these thresholds are not general. The importance of this analysis is that the experiments cover a large space of general conditions, and general design recommendations for protocol adaptation are developed.

A CANopen-based protocol for dynamic assignment of priorities

The author deals with the problem of information flow management in a CANOpen network. CAN ISO IS-11898 physical medium access mechanism. adopted in CANOpen, features an arbitration protocol based on an identifier assigned to each message to be transmitted. The lack of a centralised scheduling for the identifier assignments in CANOpen does not allow achieving any guarantee to meet the deadlines of time-critical messages. The aim of the paper is to propose a protocol for dynamic and centralised assignment of identifiers to each message to be transmitted, in such a way that its transmission requirements are fulfilled. The main features of the protocol proposed are the operational flexibility it offers and full compatibility with the CANOpen standard.

Distributed surveillance and reconnaissance using multiple autonomous ATVs: CyberScout

The objective of the CyberScout project is to develop an autonomous surveillance and reconnaissance system using a network of all-terrain vehicles. We focus on two facets of this system: 1) vision for surveillance and 2) autonomous navigation and dynamic path planning. In the area of vision-based surveillance, we have developed robust, efficient algorithms to detect, classify, and track moving objects of interest (person, people, or vehicle) with a static camera. Adaptation through feedback from the classifier and tracker allow the detector to use grayscale imagery, but perform as well as prior color-based detectors. We have extended the detector using scene mosaicing to detect and index moving objects when the camera is panning or tilting. The classification algorithm performs well with coarse inputs, has unparalleled rejection capabilities, and can flag novel moving objects. The tracking algorithm achieves highly accurate (96%) frame-to-frame correspondence for multiple moving objects in cluttered scenes by determining the discriminant relevance of object features. We have also developed a novel mission coordination architecture, CPAD (Checkpoint/Priority/Action Database), which performs path planning via checkpoint and dynamic priority assignment, using statistical estimates of the environment's motion structure. The motion structure is used to make both preplanning and reactive behaviors more efficient by applying global context. This approach is more computationally efficient than centralized approaches and exploits robot cooperation in dynamic environments better than decoupled approaches.

Multi-Robot Path Planning by Predicting Structure in a Dynamic Environment

Path planning for multiple mobile robots is complicated by the presence of a dynamic environment, in which obstacles and other robots are moving. Centralized approaches are too computationally intensive for real-time response. Decoupled approaches which perform individual preplanning, conflict resolution, and reactive obstacle avoidance for each robot, can be globally inefficient. We propose a novel mission coordination architecture, CP AD (Checkpoint/Priority/Action Database), which performs path planning via checkpoint and dynamic priority assignment, using statistical estimates of the environment’s motion structure in order to make both preplanning and reactive behaviors more efficient. Simulation is used to validate and illustrate the approach

A fair protocol for fast resource assignment in wireless PCS networks

Efficient sharing of communication resources is essential to PCS networks since the wireless bandwidth is limited. The Resource Auction Multiple Access (RAMA) protocol was recently proposed for fast resource assignment and handover in wireless PCS networks. The RAMA protocol assigns available communication resources (e.g., TDMA time slots or frequency channels) to subscribers one at a time using a collision resolution protocol based on subscriber ID's. However, the RAMA protocol encounters an unfairness problem; furthermore, performance results also indicate that it is inefficient at transmitting fixed-length subscriber ID's. Moreover, the emerging services such as teleconferencing have been presenting new challenges to dynamic-priority resource assignment. In this paper, we propose a modification to the RAMA protocol to improve its performance and resolve the unfairness problem. The proposed protocol also adopts dynamic priority assignment to improve the QOS for subscribers in overload environments.

Point-to-Point Real-Time Communication Over a Backplane Bus

This paper suggests two scheduling methods for a real-time point-topoint communication over a backplane bus which has limited priorities for the bus mastership. Fixed priority assignment(FPA) algorithm based on the rate monotonic scheduling is suggested for the periodic hard real-time applications. Dynamic priority assignment(DPA) algorithm based on the earliest deadline first scheduling is suggested for the sporadic soft real-time applications. The worst communication latency for the proposed methods is analyzed and then the schedulability is evaluated using computer simulation.

Link-sharing method for ABR/UBR services in ATM networks

This paper presents an efficient link-sharing method for available bit rate and unspecified bit rate services in ATM networks. The method comprises an algorithm that performs cell multiplexing and scheduling such that the outgoing link is fairly shared by multiple traffic flows. The proposed algorithm adopts a dynamic priority assignment to each ATM cell, and schedules those cells having the same priority level into repeating cycles in a round-robin fashion. The algorithm also guarantees each ABR connection a specified minimum cell rate and a satisfied cell loss rate. The performance is evaluated through simulations and is also compared with another fixed method called weighted round robin. Finally, a corresponding hardware design that uses a two-stage leaky bucket circuit is presented.

Automatic synthesis of easily scalable bus arbiters with dynamic priority assignment strategies

With the advent of sophisticated multi-processor computing systems, the design of bus arbitration circuits has become a critical issue; in fact, the performance of the system do not only depend on how efficiently accesses to the bus are regulated by the bus contention resolution mechanism, but also on the way the arbitration logic is realized on silicon. In this work, we present experimental data on the automatic implementation of an easily scalable arbitration circuit realizing different dynamic priority assignment schemes. The focus of the paper is on the way the arbitration mechanisms are implemented on silicon as a digital circuit, rather than on how the selected arbitration policies affect the performace of a multi-processor system. The experimental data thus refer to the quality of the VLSI designs, in terms of area, speed, and power consumption, while they do not include a comparison to other arbitration strategies, being such a comparison out of the scope of this paper.

Analysis of dynamic priority cell discarding

A cell discarding mechanism with dynamic priority assignment is proposed and analysed. Cell streams of each connection are monitored periodically. The priority of each connection is adjusted dynamically according to its past behaviour. When congestion occurs, cells from low-priority connections shall be rejected. The rejection is done through a gating device for each connection. Using this approach, the connections which cause congestion will be enforced first and fairness is guaranteed. With this design, the quality of service of a well-behaved connection is protected and the link utilisation is improved simultaneously.

Real-Time Transaction Scheduling: A Framework for SynthesizingStatic and Dynamic Factors

Real-time databases are poised to be an important component of complex embedded real-time systems. In real-time databases (as opposed to real-time systems), transactions must satisfy the ACID properties in addition to satisfying the timing constraints specified for each transaction (or task). Although several approaches have been proposed to combine real-time scheduling and database concurrency control methods, to the best of our knowledge, none of them provide a framework for taking into account the dynamic cost associated with aborts, rollbacks, and restarts of transactions. In this paper, we propose a framework in which both static and dynamic costs of transactions can be taken into account. Specifically, we present: i) a method for pre-analyzing transactions based on the notion of branch-points for data accessed up to a branch point and predicting expected data access to be incurred for completing the transaction, ii) a formulation of cost that includes static and dynamic factors for prioritizing transactions, iii) a scheduling algorithm which uses the above two, and iv) simulation of the algorithm for several operating conditions and workload. Our dynamic priority assignment policy (termed the cost conscious approach or CCA) adapts well to fluctuations in the system load without causing excessive numbers of transaction restarts. Our simulations indicate that i) CCA performs better than the EDF-HP algorithm for both soft and firm deadlines, ii) CCA is more fair than EDF-HP, iii) CCA is better than EDF-CR for soft deadline, even though CCA requires and uses less information, and iv) CCA is especially good for disk-resident data.

A multiclass priority-based slotted-ring network for LAN-ATM interworking

Interworking LANs with an ATM backbone network is considered a cost-effective and most promising solution for bringing ATM into the mainstream. To sustain delay-sensitive applications (e.g., video or voice) and loss-sensitive applications (e.g., data transfer), this paper presents a slotted-ring network (SRN) with spatial reuse. In order to provide nonpreemptive multipriority services over SRN, a simple priority-based media access protocol, called the check requested before send (CRBS), is proposed. A dynamic priority assignment technique is described to assign priorities based on their delay and loss requirements. An analytical model is presented to analyze CRBS protocol under Poisson input traffic and uniform output traffic. Extensive simulations are run to assess the performance of CRBS protocol for two classes of cells with priorities 0 and 1.

Optimization of a low-cost truly preemptive multitasking PC diagnostic workstation.

The Windows 95/NT operating systems (Microsoft Corp, Redmond, WA) currently provide the only low-cost truly preemptive multitasking environment and as such become an attractive diagnostic workstation platform. The purpose of this project is to test and optimize display station graphical user interface (GUI) actions previously designed on the pseudomultitasking Macintosh (Apple Computer, Cupertino, CA) platform, and image data transmission using time slicing/ dynamic prioritization assignment capabilities of the new Windows platform. A diagnostic workstation in the clinical environment must process two categories of events: user interaction with the GUI through keyboard/mouse input, and transmission of incoming data files. These processes contend for central processing units (CPU) time resulting in GUI "lockout" during image transmission or delay in transmission until GUI "quiet time." WinSockets and the Transmission Control Protocol/Internet Protocal (TCP/IP) communication protocol software (Microsoft) are implemented using dynamic priority timeslicing to ensure that GUI delays at the time of Digital Imaging and Communications in Medicine (DICOM) file transfer do not exceed 1/10 second. Assignment of thread priority does not translate into an absolute fixed percentage of CPU time. Therefore, the relationship between dynamic priority assignment by the processor, and the GUI and communication application threads will be more fully investigated to optimize CPU resource allocation. These issues will be tested using 10 MB/sec Ethernet and 100 MB/sec fast and wide Ethernet transmission. Preliminary results of typical clinical files (10 to 30 MB) over Ethernet show no visually perceptible interruption of the GUI, suggesting that the new Windows PC platform may be a viable diagnostic workstation option.

A decentralized approach for the conflict-free motion of multiple mobile robots

This article presents a novel approach to decentralized motion planning and conflict-resolution for multiple mobile robots. The proposed multi-robot motion planning is an on-line operation, based on cost wave propagation within a discretized configuration space-time. By use of the planning method, a framework for negotiation is developed, which permits quick decentralized and parallel decision making. The key objective of the negotiation procedure is dynamic assignment of robot motion priorities. Thus, robots involved in a local conflict situation cooperate in planning and execution of the lowest cost motion paths without application of any centralized components. The features required for individual and cooperative motion are embedded in a hybrid control architecture. Results obtained from realistic simulation of a multi-robot environment and also from experiments performed with two mobile robots demonstrate the flexibility and the efficiency of the proposed method.

A dynamic priority assignment technique for streams with (m, k)-firm deadlines

The problem of scheduling multiple streams of real-time customers, is addressed in this paper. The paper first introduces the notion of (m, k)-firm deadlines to better characterize the timing constraints of real-time streams. More specifically, a stream is said to have (m, k)-firm deadlines if at least m out of any k consecutive customers must meet their deadlines. A stream with (m, k)-firm deadlines experiences a dynamic failure if fewer than m out of any k consecutive customers meet their deadlines. The paper then proposes a priority-based policy for scheduling N such streams on a single server to reduce the probability of dynamic failure. The basic idea is to assign higher priorities to customers from streams that are closer to a dynamic failure so as to improve their chances of meeting their deadlines. The paper proposes a heuristic for assigning these priorities. The effectiveness of this approach is evaluated through simulation under various customer arrival and service patterns. The scheme is compared to a conventional scheme where all customers are serviced at the same priority level and to an imprecise computation model approach. The evaluation shows that substantial reductions in the probability of dynamic failure are achieved when the proposed policy is used.

Real-time transaction scheduling

Real-time databases are an important component of embedded real-time systems. In a real-time database context, transactions must not only maintain the consistency constraints of the database but must also satisfy the timing constraints specified for each transaction. Although several approaches have been proposed to integrate real-time scheduling and database concurrency control methods, none of them take into account the dynamic cost of scheduling a transaction. In this paper, we propose a new cost conscious real-time transaction scheduling algorithm which considers dynamic costs associated with a transaction. Our dynamic priority assignment algorithm adapts to changes in the system load without causing excessive numbers of transaction restarts. Our simulations show its superiority over EDF-HP algorithm.