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A Stability of High Order Distributed Power Control Algorithms in Cellular Networks
KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
Ericsson Research.
Ericsson Research.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

In radio resource management for cellular networks a trade-off has to be made between the congestion level, related to the cell coverage and the intercell interference, and the Quality of Service (QoS), or data rates of the users. This is implemented by using a fast inner power control algorithm and an outer rate control algorithm, working on a slower time scale.

Due to the distributed nature of the network, both the information and the control are distributed. Measurements of the congestion and the QoS are used in the control algorithms and this introduces a nonlinear feedback. Another complicating factor is that filtering, computations and information exchange in the network introduce time delays.

In this paper we propose a general high order model as a cascade system with an outer and inner control loop. The control algorithms use distributed information available in the network. The full system model includes the nonlinear feedback from congestion and QoS measurements, time delays and time-scale modeling. We provide sufficient conditions for stability and convergence of the system. Our primary analysis tool is input output theory.

National Category
Computational Mathematics
Identifiers
URN: urn:nbn:se:kth:diva-93268OAI: oai:DiVA.org:kth-93268DiVA: diva2:515491
Note

Parts of the material is previously published in Proceedings of the 50th IEEE Conference on Decision and Control 2011 and Proceedings of IEEE Global Communications Conference 2011. QC 20120413

Available from: 2012-04-13 Created: 2012-04-13 Last updated: 2012-04-13Bibliographically approved
In thesis
1. Modeling and Stability Analysis of Rate and Power Control Systems in Wireless Communication Networks
Open this publication in new window or tab >>Modeling and Stability Analysis of Rate and Power Control Systems in Wireless Communication Networks
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Wireless data traffic in cellular networks is currently undergoing a strong global expansion and the demand for high and reliable data throughput increases. Capacity is, however, a limited resource, and in radio resource management a trade-off has to be made between the congestion level, related to cell coverage and interference levels, and the Quality of Service (QoS) or data rates of the users.

 

The radio channel conditions vary on a fast time scale and the measurements of the received signals are subject to disturbances and uncertainties. This motivates the use of control strategies to update the transmission powers. In fact, in implementations of uplink in cellular networks, the performance of the network is ensured by using a fast inner power control algorithm to track a QoS-target and a slower outer control algorithm to limit congestion.

 

Several theoretical challenges arise in this problem setting. Due to the nature of the network, both information and control are distributed. Furthermore, measurements of the congestion and the QoS are used in the control loops, which introduces nonlinear feedback. Another complicating factor is that filtering, computations and information exchange in the network cause time-delays and dynamics.

 

In this thesis we address these challenges by using modeling and analysis tools in systems and control. The objective is to provide systematic methods to quantify the fundamental limitations of the system and to point out the trade-offs for a given system design. We perform stability analysis on a high mathematical level that provides results that are simple to compute and that reveal the system structure.

In Paper A we extend existing power control models and stability frameworks to include dynamics. For this we use a general definition of the interference. Moreover, stability is addressed by a monotonicity approach and by proposing a Lyapunov function. Paper B provides less conservative stability results using input-output analysis for the same system model. Stability of a linearization of the system model is studied in Paper C with the multivariate Nyquist criterion. Moreover, we use discrete multivariate describing functions to analyze the equilibrium oscillations that arise due to binary feedback. In Paper D we extend the model with an outer control loop, which dynamically sets the reference value to the control algorithm studied in Papers A to C. The main analysis tool for stability is input-output theory.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xiv, 34 p.
Series
Trita-MAT. OS, ISSN 1401-2294 ; 2012:01
National Category
Mathematics
Identifiers
urn:nbn:se:kth:diva-93222 (URN)987-91-7501-302-2 (ISBN)
Public defence
2012-05-04, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
ICT - The Next Generation
Note

QC 201204013

Available from: 2012-04-13 Created: 2012-04-12 Last updated: 2013-04-15Bibliographically approved

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