Pre-specified Delay Research Articles

Optimal relay node placement in delay constrained wireless sensor network design

The Delay Constrained Relay Node Placement Problem (DCRNPP) frequently arises in the Wireless Sensor Network (WSN) design. In WSN, Sensor Nodes are placed across a target geographical region to detect relevant signals. These signals are communicated to a central location, known as the Base Station, for further processing. The DCRNPP aims to place the minimum number of additional Relay Nodes at a subset of Candidate Relay Node locations in such a manner that signals from various Sensor Nodes can be communicated to the Base Station within a pre-specified delay bound. In this paper, we study the structure of the projection polyhedron of the problem and develop valid inequalities in form of the node-cut inequalities. We also derive conditions under which these inequalities are facet defining for the projection polyhedron. We formulate a branch-and-cut algorithm, based upon the projection formulation, to solve DCRNPP optimally. A Lagrangian relaxation based heuristic is used to generate a good initial solution for the problem that is used as an initial incumbent solution in the branch-and-cut approach. Computational results are reported on several randomly generated instances to demonstrate the efficacy of the proposed algorithm.

Delay-Constrained Admission and Bandwidth Allocation for Long-Reach EPON

Next generation Passive Optical Network (PON) technology has been evolving to consolidate the metro and access networks in order to offer enhanced capacity, high split ratio and reduced deployment cost per subscriber. However, transmission of the signals to long distances up to 100km leads to increased propagation delay whereas high split ratio may lead to long cycle times resulting in large queue occupancies and long packet delays. In this article, we present a delay-constrained admission control mechanism and adapt this scheme to our previously proposed bandwidth allocation technique, namely Periodic GATE Optimization (PGO). We call this new scheme Delay-Constrained Periodic GATE Optimization (DC-PGO). DC-PGO is designed to run for multiple service classes as it inherits the advantages of PGO by periodically building and solving an ILP formula- tion at the OLT in order to obtain the appropriate credit values for the overloaded ONUs. At the ONU side, DC- PGO runs an admission control scheme before pushing the arriving packets in the sub-queues. The admission control scheme uses statistical information consisting of the local data at the ONU and the previously received GATE messages from the OLT. Through simulations, we show that DC-PGO enhances the performance of multi-threaded polling in long- reach Ethernet PON when packets of differentiated service classes arrive with pre-specified delay requirements. Index Terms—Dynamic bandwidth allocation, Ethernet PON, long-reach passive optical networks, multi-threaded polling

Cross-Layer Design for Proportional Delay Differentiation and Network Utility Maximization in Multi-Hop Wireless Networks

One major problem of cross-layer control algorithms in multi-hop wireless networks is that they lead to large end-to-end delays. Recently there have been many studies devoted to solving the problem to guarantee order-optimal per-flow delay. However, these approaches also bring the adverse effect of sacrificing a lot of network utility. In this paper, we solve the large-delay problem without sacrificing network utility. We take a fundamentally different approach of delay differentiation, which is based on the observation that flows in a network usually have different requirements for end-to-end delay. We propose a novel joint rate control, routing and scheduling algorithm called CLC_DD, which ensures that the flow delays are proportional to certain pre-specified delay priority parameters. By adjusting delay priority parameters, the end-to-end delays of preferential flows achieved by CLC_DD can be as small as those achieved by delay-order-optimal algorithms. In contrast to high network utility loss in previous approaches, we prove that our approach achieves maximum network utility. Furthermore, we incorporate opportunistic routing into the cross-layer design framework to improve network performance under the environment of dynamic wireless channels.

Enforcing Periodic Transition Deadlines in Time Petri Nets With Net Unfoldings

We define a method for the automatic generation of supervisory controllers that force a plant to perform a given operation by a given deadline. The operation must be executed by a prespecified delay λ with respect to the previous execution of the operation. Although our supervisor generation occurs offline with respect to plant execution, the resulting controllers automatically take into account variable task durations in an effort to increase the flexibility of operation schedules in the controlled plant. We model both the controlled plant and control supervisors as time Petri nets. In this setting, our control supervisors must force a target transition <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">td</i> to fire within λ time units since the previous firing of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">td</i> . Our supervisor generation is based on the concept of a transition latency. The latency of a Petri net transition <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> is the time interval during which <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> must be disabled in order for target transition <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">td</i> to fire by its deadline. If a transition <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> that may delay the firing of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">td</i> has latency <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</i> ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> ), then <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> must be disabled at least <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</i> ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> ) time units before the expiration of the deadline on <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">td</i> . In this paper, we discuss in detail two algorithms for generating transition latencies, and we show an application to a maintenance system.

Scheduling in multimedia cdma wireless networks

Wireless systems in the future will have to provide multimedia services where different users have different physical-layer quality of service (QoS) requirements (e.g., bit energy per interference power density, E/sub b//N/sub 0/, or bit error rate and power constraints) and network-layer QoS requirements (e.g., delay bound, delay-jitter, throughput, and loss). We investigate the use of power control, processing gain and/or multiple codes, and scheduling in CDMA systems to accommodate these diverse service requirements. We first show that the instantaneous capacity region, given in terms of the set of user bit rates that can be supported simultaneously subject to peak power and E/sub b//N/sub 0/ constraints, is nonconvex. This suggests that by time-sharing the channel, one may be able to get better system throughput. We define the capacity region as the convex hull of the instantaneous capacity region and we show that it may be obtained by time sharing between operating points, where each user either uses full power or is silent (bang-bang control). We then consider the problem of scheduling so as to meet prespecified delay bounds or minimum service curve requirements for traffic streams, which are specified in terms of a traffic profile such as a sigma-rho constraint (enforced by a leaky bucket) and a guarantee that the system is stable.

Fault-tolerant real-time communication in distributed computing systems

The delivery delay in a point-to-point packet switching network is difficult to control due to the contention among randomly-arriving packets at each node and multihops a packet must travel between its source and destination. Despite this difficulty, there are an increasing number of applications that require packets to be delivered reliably within prespecified delay bounds. This paper shows how this can be achieved by using real-time channels which make soft reservation of network resources to ensure the timely delivery of real-time packets. We first present theoretical results and detailed procedures for the establishment of real-time channels and then show how the basic real-time channels can be enhanced to be fault-tolerant using the multiple disjoint paths between a pair of communicating nodes. The contribution of the former is a tighter schedulability condition which makes more efficient use of network resources than any other existing approaches, and that of the latter is a significant improvement in fault tolerance over the basic real-time channel, which is inherently susceptible to component failures.

On the ability of establishing real-time channels in point-to-point packet-switched networks

There are numerous applications which require packets to be delivered within pre-specified delay bounds in point-to-point packet-switched networks. To meet this requirement, we define a real-time channel as a unidirectional connection between two nodes in such a network that guarantees every packet to be delivered before a user-defined, end-to-end deadline. The goal of this paper is to lay a mathematical basis for the problem of establishing real-time channels by (i) deriving a necessary and sufficient condition for the schedulability of a set of channels over a link, and (ii) developing an efficient method for calculating the minimum delay bound over a link for each channel. Given the traffic characteristics of a channel, our results can be used to check whether or not every packet will be delivered within a pre-specified delay bound. The results are also applicable to a wide variety of real-time task scheduling problems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>