Computing non-fragile PI controllers for delay models of TCP/AQM networks

Comparing PI Controllers for Delay Models of TCP/AQM Networks

“…It was shown there that PI controllers provide good responses in achieving AQM performance requirements. Based on this and their ease of implementation in real networks, several PI AQM controller designs have been proposed following those works, see for instance, [12][13][14][15]. Note that, from the practical implementation of a controller, it is required to keep the stability of the closed-loop system under round-off errors during implementation.…”

“…To the best of the authors' knowledge, the first study was performed in [14], where a method to compute the largest available intervals for the PI controllers parameters have been developed. Recently in [15], using the complete characterization of the set of all stabilizing PI controllers and its corresponding geometric properties, a new method for tuning the parameters of PI/AQM controllers has been proposed. Such an approach allows us to design a PI controller stabilizing the network against perturbations in the network parameters.…”

“…In this paper, we compare several PI controllers designed for TCP/AQM considering some performance requirements with arising problems in practice such as fragility and robustness. Some of these PI controllers are currently available for TCP/AQM given in [11,15,14] and the other PI controllers are designed in the paper by utilizing the approaches in [19][20][21][22][23]. The designed PI controllers are based on considering the transfer function of the linearized model of TCP as an integrating system or a second order system with delay.…”

The use of a non-integer order PI controller with an active queue management mechanism

“…Based on easy implementation of PI AQM controllers in real networks, a number of PI controllers have been proposed (Michiels et al, 2006;Melchor-Aquilar and Castillo-Tores, 2007;Ustebay et al, 2007;Melchor-Aquilar and Niculescu, 2009). Unal et al (2013) compared the performance of several of them.…”

Stability crossing boundaries and fragility characterization of PID controllers for SISO systems with I/O delays

“…In this context of delay free systems, some remarks concerning the controller robustness via coprime factorization and robustness optimization tools can be found in [15], [13]. However, there exists only a few results in the delay case as, for example, [27], where only (stable) first-order systems were considered, the authors in [16] proposed a non-fragile controller design for a linearized TCP/AQM model, more recently, based on the D-composition method, the properties regarding the increase in the number of unstable poles across the boundary of the PID gain were studied in [25],whereas in [12], the lines that contain the boundary of the stabilizing gain set for the ID (integral-derivative) plane are obtained, finally, based on the extension of the Hermite-Biehler theorem, in [24] a method to compute the set of stabilizing PID gain is obtained, but it requires much computation.…”