21,015 research outputs found
Tradeoffs and limitations in Networked Control Systems
Control and communication have been increasingly studied together in the recent past. The \u27Satellite - Ground Controller\u27 is a classic example of a remote control problem. Another closely related topic of study is control over an unreliable communication network and its applications seem to grow continuously. Networked Control Systems (NCS) is a rapidly growing research topic and examples of practical significance include multiple vehicle coordination, air-traffic control, and Micro-Electro-Mechanical Systems (MEMS). The work presented consists of two problems (1) The Remote control problem and (2) The Networked control problem. The remote control problem we address is the feedback stabilization of a linear discrete-time plant in feedback with a linear controller via unreliable communication channels. The channels are modeled as analog packet-drop (erasure) channels. Erasure channel is a good model of loss of data packets, typical in large networks like the Internet. We analyze the maximum sustainable erasure on the sensor and actuator channels given a level of erasure on the feedback (Service) channel and synthesize controllers. The networked control problem we address is a special case of spatially invariant plants interconnected through a static network. We consider a circular topology of interconnection and introduce a new notion of Bode sensitivity integral for networks of spatially invariant plants in feedback with static networks and comment on the fundamental limitations of design of such feedback networks
JiTS: Just-in-Time Scheduling for Real-Time Sensor Data Dissemination
We consider the problem of real-time data dissemination in wireless sensor
networks, in which data are associated with deadlines and it is desired for
data to reach the sink(s) by their deadlines. To this end, existing real-time
data dissemination work have developed packet scheduling schemes that
prioritize packets according to their deadlines. In this paper, we first
demonstrate that not only the scheduling discipline but also the routing
protocol has a significant impact on the success of real-time sensor data
dissemination. We show that the shortest path routing using the minimum number
of hops leads to considerably better performance than Geographical Forwarding,
which has often been used in existing real-time data dissemination work. We
also observe that packet prioritization by itself is not enough for real-time
data dissemination, since many high priority packets may simultaneously contend
for network resources, deteriorating the network performance. Instead,
real-time packets could be judiciously delayed to avoid severe contention as
long as their deadlines can be met. Based on this observation, we propose a
Just-in-Time Scheduling (JiTS) algorithm for scheduling data transmissions to
alleviate the shortcomings of the existing solutions. We explore several
policies for non-uniformly delaying data at different intermediate nodes to
account for the higher expected contention as the packet gets closer to the
sink(s). By an extensive simulation study, we demonstrate that JiTS can
significantly improve the deadline miss ratio and packet drop ratio compared to
existing approaches in various situations. Notably, JiTS improves the
performance requiring neither lower layer support nor synchronization among the
sensor nodes
Kalman Filtering Over a Packet-Dropping Network: A Probabilistic Perspective
We consider the problem of state estimation of a discrete time process over a packet-dropping network. Previous work on Kalman filtering with intermittent observations is concerned with the asymptotic behavior of E[P_k], i.e., the expected value of the error covariance, for a given packet arrival rate. We consider a different performance metric, Pr[P_k ≤ M], i.e., the probability that P_k is bounded by a given M. We consider two scenarios in the paper. In the first scenario, when the sensor sends its measurement data to the remote estimator via a packet-dropping network, we derive lower and upper bounds on Pr[P_k ≤ M]. In the second scenario, when the sensor preprocesses the measurement data and sends its local state estimate to the estimator, we show that the previously derived lower and upper bounds are equal to each other, hence we are able to provide a closed form expression for Pr[P_k ≤ M]. We also recover the results in the literature when using Pr[P_k ≤ M] as a metric for scalar systems. Examples are provided to illustrate the theory developed in the paper
Kalman Filtering Over A Packet Dropping Network: A Probabilistic Approach
We consider the problem of state estimation of a discrete time process over a packet dropping network. Previous pioneering work on Kalman filtering with intermittent observations is concerned with the asymptotic behavior of E[P_k], i.e., the expected value of the error covariance, for a given packet arrival rate. We consider a different performance metric, Pr[P_k ≤ M], i.e., the probability that P_k is bounded by a given M, and we derive lower and upper bounds on Pr[P_k ≤ M]. We are also able to recover the results in the literature when using Pr[P_k ≤ M] as a metric for scalar systems. Examples are provided to illustrate the theory developed in the paper
Dynamic Queue Utilization Based MAC for multi-hop Ad Hoc networks
The end-to-end throughput in single flow multi-hop Ad Hoc networks decays rapidly with path length. Along the path, the success rate of delivering packets towards the destination decreases due to higher contention, interference, limited buffer size and limited shared bandwidth constraints. In such environments the queues fill up faster in nodes closer to the source than in the nodes nearer the destination. In order to reduce buffer overflow and improve throughput for a saturated network, this paper introduces a new MAC protocol named Dynamic Queue Utilization Based Medium Access Control (DQUB-MAC). The protocol aims to prioritise access to the channel for queues with higher utilization and helps in achieving higher throughput by rapidly draining packets towards the destination. The proposed MAC enhances the performance of an end-to-end data flow by up to 30% for a six hop transmission in a chain topology and is demonstrated to remain competitive for other network topologies and for a variety of packet sizes
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Performance modelling of a multiple threshold RED mechanism for bursty and correlated Internet traffic with MMPP arrival process
Access to the large web content hosted all over the world by users of the Internet engage
many hosts, routers/switches and faster links. They challenge the internet backbone to operate at
its capacity to assure e±cient content access. This may result in congestion and raises concerns over
various Quality of Service (QoS) issues like high delays, high packet loss and low throughput of the
system for various Internet applications. Thus, there is a need to develop effective congestion control
mechanisms in order to meet various Quality of Service (QoS) related performance parameters. In this
paper, our emphasis is on the Active Queue Management (AQM) mechanisms, particularly Random
Early Detection (RED). We propose a threshold based novel analytical model based on standard RED
mechanism. Various numerical examples are presented for Internet traffic scenarios containing both the
burstiness and correlation properties of the network traffic
Analysis and control of bifurcation and chaos in averaged queue length in TCP/RED model
This paper studies the bifurcation and chaos phenomena in averaged queue length in a
developed Transmission Control Protocol (TCP) model with Random Early Detection
(RED) mechanism. Bifurcation and chaos phenomena are nonlinear behaviour in network
systems that lead to degradation of the network performance. The TCP/RED model used
is a model validated previously. In our study, only the average queue size k q
−
is
considered, and the results are based on analytical model rather than actual measurements.
The instabilities in the model are studied numerically using the conventional nonlinear
bifurcation analysis. Extending from this bifurcation analysis, a modified RED algorithm
is derived to prevent the observed bifurcation and chaos regardless of the selected
parameters. Our modification is for the simple scenario of a single RED router carrying
only TCP traffic. The algorithm neither compromises the throughput nor the average
queuing delay of the system
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