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Limited By:	Subject = telecommunication channels;

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A systematic analysis of equivalence in multistage networks (2002)

Collier, Martin

A systematic analysis of equivalence in multistage networks (2002)

Collier, Martin

Abstract:

Many approaches to switching in optoelectronic and optical networks decompose the switching function across multiple stages or hops. This paper addresses the problem of determining whether two multistage or multihop networks are functionally equivalent. Various ad-hoc methods have been used in the past to establish such equivalences. A systematic method for determining equivalence is presented based on properties of the link permutations used to interconnect stages of the network. This method is useful in laying out multistage networks, in determining optimal channel assignments for multihop networks, and in establishing the routing required in such networks. A purely graphical variant of the method, requiring no mathematics or calculations, is also described.

http://doras.dcu.ie/15511/

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Channel Signal-to-Noise Ratio Constrained Feedback Control: Performance and Robustness (2009)

Rojas, A.J.; Braslavsky, J.H.; Middleton, R.H.

Channel Signal-to-Noise Ratio Constrained Feedback Control: Performance and Robustness (2009)

Rojas, A.J.; Braslavsky, J.H.; Middleton, R.H.

Abstract:

The limitations in performance and robustness imposed by explicitly considering a communication channel in a control loop have received increased attention in recent years. Previous results in the literature have stated these limitations in terms of a minimal transmission data rate necessary for stabilisation. In this paper a signal-to-noise ratio (SNR) approach is used to study two specific cases: (i) performance in terms of model matching and (ii) robustness against a multiplicative uncertainty in the plant model. The analysis performed leads to closed-form expressions that allow the quantification of the extra SNR required in both cases.

http://mural.maynoothuniversity.ie/1880/

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Feedback control performance over a noisy communication channel. (2008)

Freudenberg, J.S.; Middleton, R.H.

Feedback control performance over a noisy communication channel. (2008)

Freudenberg, J.S.; Middleton, R.H.

Abstract:

We consider the problem of minimizing the variance in the output of a plant that is driven by a Gaussian disturbance using measurements of the plant output obtained from a Gaussian channel. For the special case in which only the variance at the terminal time is penalized, we derive an optimal linear timevarying communication and control strategy, and argue that nonlinear strategies cannot achieve better performance.

http://mural.maynoothuniversity.ie/1753/

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Feedback Stabilization Over Signal-to-Noise Ratio Constrained Channels. (2007)

Braslavsky, Julio H.; Middleton, Richard H.; Freudenberg, James S.

Feedback Stabilization Over Signal-to-Noise Ratio Constrained Channels. (2007)

Braslavsky, Julio H.; Middleton, Richard H.; Freudenberg, James S.

Abstract:

There has recently been significant interest in feedback stabilization problems with communication constraints including constraints on the available data rate. Signal-to-noise ratio (SNR) constraints are one way in which data-rate limits arise, and are the focus of this paper. In both continuous and discrete-time settings, we showthat there are limitations on the ability to stabilize an unstable plant over a SNR constrained channel using finite-dimensional linear time invariant (LTI) feedback. In the case of state feedback, or output feedback with a delay-free, minimum phase plant, these limitations in fact match precisely those that might have been inferred by considering the associated ideal Shannon capacity data rate over the same channel. In the case of LTI output feedback, additional limitations are shown to apply if the plant is nonminimum phase. In this case, we show that for a continuous-time nonminimum phase plant, a periodic linear time varying feedback scheme with fast s...

http://mural.maynoothuniversity.ie/1741/

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Input Disturbance Rejection in Channel Signal-to-Noise Ratio Constrained Feedback Control (2008)

Rojas, A.J.; Middleton, R.H.; Freudenberg, J.S.; Braslavsky, J.H.

Input Disturbance Rejection in Channel Signal-to-Noise Ratio Constrained Feedback Control (2008)

Rojas, A.J.; Middleton, R.H.; Freudenberg, J.S.; Braslavsky, J.H.

Abstract:

Communication channels impose a number of obstacles to feedback control. One recent line of work considers the problem of feedback stabilisation subject to a constraint on the channel signal-to-noise ratio (SNR). It has been shown for continuous-time systems that the optimal control problem of achieving the infimal SNR can be formulated as a linear quadratic Gaussian (LQG) control problem with weights chosen as in the loop transfer recovery (LTR) technique. The present paper extends this formulation to: discretetime systems; communications over channels with memory; and input disturbance rejection. By using this formulation, we derive exact expressions for the linear time invariant (LTI) controller that achieves the infimal SNR under the effect of time-delay and additive coloured noise. We then quantify the infimal SNR required for both stabilisation and input disturbance rejection for a relative degree one, minimum phase plant and a memoryless Gaussian channel.

http://mural.maynoothuniversity.ie/2245/

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Minimum Variance Control over a Gaussian Communication Channel (2008)

Freudenberg, J.S.; Middleton, R.H.; Braslavsky, J.H.

Minimum Variance Control over a Gaussian Communication Channel (2008)

Freudenberg, J.S.; Middleton, R.H.; Braslavsky, J.H.

Abstract:

We consider the problem of minimizing the response of a plant output to a stochastic disturbance using a control law that relies on the output of a noisy communication channel. We discuss a lower bound on the performance achievable at a specified terminal time using nonlinear timevarying communication and control strategies, and show that this bound may be achieved using strategies that are linear.

http://mural.maynoothuniversity.ie/2244/

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Optimal Signal to Noise Ratio in Feedback over Communication Channels with Memory (2006)

Rojas, A.J.; Freudenberg, J.S.; Braslavsky, J.H.; Middleton, R.H.

Optimal Signal to Noise Ratio in Feedback over Communication Channels with Memory (2006)

Rojas, A.J.; Freudenberg, J.S.; Braslavsky, J.H.; Middleton, R.H.

Abstract:

Communication channels impose a number of obstacles to feedback control, such as delay, noise, and constraints in communication data-rate. One alternate line of recent work considers the problem of feedback stabilization subject to a constraint in the signal-to-noise ratio (SNR). It has been shown for continuous-time systems that the optimal control problem arising in achieving minimal SNR can be formulated as a linear quadratic Gaussian (LQG) control problem with weights chosen as in the loop transfer recovery (LTR) technique. The present paper extends such LQG/LTR formulation to discretetime systems with feedback over channels with memory. By using such formulation, we derive exact expressions for the LTI controller and loop sensitivity functions that achieve minimal SNR under the effect of time-delay, non minimum phase zeros and colored additive noise. For the minimum-phase case with white noise and no time delay, we show that the optimal feedback loop obtained after applying LTR...

http://mural.maynoothuniversity.ie/1789/

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When Is the Right Time to Transmit in Multi-hop White-Fi? (2016)

Facchi, N.; Gringoli, F.; Malone, David; Patras, Paul

When Is the Right Time to Transmit in Multi-hop White-Fi? (2016)

Facchi, N.; Gringoli, F.; Malone, David; Patras, Paul

Abstract:

While Western societies are becoming increasingly connected, many developing regions lack basic Internet connectivity, primarily due to the high costs associated with infrastructure deployment and maintenance. Potential exists for the TV white-space (TVWS) wireless technology to bridge this digital divide, though efficient channel access mechanisms suited to multi-hop networks that operate in sub-gigahertz bands are yet to be developed. Using a small test bed, we demonstrate a prototype implementation of a medium access protocol that learns appropriate transmission opportunities in such settings, achieving pseudo-scheduled behaviour ex tempore and providing substantial gains over the de facto IEEE 802.11af protocol.

http://mural.maynoothuniversity.ie/10063/