Control theory aspects of power control in UMTS

Gunnarsson, Fredrik

doi:10.1016/s0967-0661(03)00062-5

Cited by 65 publications

(53 citation statements)

References 37 publications

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“…The main reason for using power control in a conventional receiver based CDMA system is to combat the near-far problem, which occurs when an undesired user's signal overpowers the desired user's signal [2,3]. Therefore, power control helps to reduce co-channel interference, increasing the cell capacity by decreasing interference and prolonging the battery life by using a minimum transmitter power [4,5].…”

Section: Introductionmentioning

confidence: 99%

“…In a practical setting, CPC is hard to implement, so DPC is more appealing since only local information is needed and the complexity of the control algorithm is largely reduced. DPC has been approached from two different perspectives: multivariable optimization and control theory [4]. The advantage of using a control theory framework is that stability and reference tracking can be jointly studied for each mobile unit.…”

Section: Introductionmentioning

confidence: 99%

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Distributed power control algorithms for asynchronous CDMA systems in frequency-selective fading channels

Rivera

Campos-Delgado

2010

Wireless Netw

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In Code Division Multiple Access (CDMA) radio environments, the maximum number of supportable users per cell is limited by multipath fading, shadowing, multiple access interference and near-far effects which cause fluctuations of the received power at the base station. In this context, power control and signal detection are essential to provide satisfactory Quality of Service (QoS) and to combat the near-far problem in CDMA systems. In this paper, we raised the uplink power control problem for a generalize asynchronous direct-sequence (DS) CDMA system that explicitly incorporate into the analysis: (1) the propagation delays in the network (generally neglected in the literature), (2) the adverse effect of multipath fading for wireless channels, and (3) the asynchronous transmissions in the uplink channels. This framework is used to propose a distributed power control strategy enhanced with linear multiuser receivers. It is shown that through a proper selection of an error function, the nonlinear coupling among active users is transformed into individual linear loops. A Linear-Quadratic-Gaussian (LQG) power control strategy is derived and compared with other approaches from the literature. Simulation results show that the uplink channel variations do not destroy the stability of these power control structures. However, delays in the closedloop paths can severely affect the stability and performance of the resulting feedback schemes. It is also shown that the use of multiuser detection at the base station can bring significant improvements to the performance of power control.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Distributed power control algorithms for asynchronous CDMA systems in frequency-selective fading channels

Rivera

Campos-Delgado

2010

Wireless Netw

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“…However, CPC involves added infrastructure and introduces a feedback delay in the power control process, which degrades the system performance. For these reasons, CPC is inpractical and several DPC schemes have been proposed (Foschini and Miljanic, 1993;Yates, 1995;Gunnarsson et al, 1999;Alpcan et al, 2002;Alpcan and Başar, 2004;Gunnarsson and Gustafsson, 2003). In all the power control algorithms so far presented in the literature -see e.g.…”

Section: Introductionmentioning

confidence: 99%

“…In all the power control algorithms so far presented in the literature -see e.g. the survey papers of (Hanly and Tse, 1999) and (Gunnarsson and Gustafsson, 2003) -the primary control objective is expressed by the requirement that the SINR of each user does not exceed a pre-specified threshold determined by QoS specifications. In contrast to the conventional SINR-based approach, a novel queuebased approach will be pursued in the present paper.…”

Section: Introductionmentioning

confidence: 99%

Power Control in Wcdma Networks: A Queue-Based Approach

Chisci

Fantacci

Mucchi

et al. 2005

IFAC Proceedings Volumes

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In modern cellular communication systems, power control plays a fundamental role for efficient resource utilization. In such systems, in fact, many users transmit over the same radio channel using the same frequency band and time slots so that the signal of an individual user becomes interference for the other users. Hence the transmission power levels need to be smartly manipulated so as to achieve an adequate quality of service for as many users as possible and, thus, an efficient network utilization. Conventional power control algorithms adopt the Signal-to-Interference-plus-Noise Ratio (SINR) as controlled variable and neglect the important effects of the manipulated control variables (transmission powers) and of the retransmission mechanism on the queueing dynamics. In this paper, we pursue a different queue-based approach which takes into account the queuing dynamics and adopts the queue size as controlled variable. In this framework, the power control problem is formulated as an optimal control problem with a criterion trading off high performance (low queue sizes) vs. low costs (low transmision powers). In particular, a novel queue-based power control algorithm with low on-line computational burden is proposed and its performance is evaluated via simulation experiments. The simulation results exhibit an improved behavior of the proposed queue-based algorithm compared to conventional SINR-based algorithms.

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“…An outer loop adjusts γ t in terms of Frame Error Rate (FER) [15], but since the update rate for target SIR is generally much slower than the update rate for the corresponding power signal, it is considered as fixed for the purposes of this work as per [4], [8], [10]- [12], [14]. Since the channel knowledge is generally unpredictable and imperfect, any APC algorithm should contain a certain level of performance robustness against any or all of the aforementioned exogenous uncertain factors.…”

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confidence: 99%

Robust power control for CDMA cellular communication networks using quantitative feedback theory

Alavi

Hayes

2007

2007 46th IEEE Conference on Decision and Control

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Abstract-In this work, a new transmission power control algorithm based on the use of Quantitative Feedback Theory (QFT) is proposed for CDMA wireless cellular networks. The QFT based loop-shaping framework that is considered fully compensates the effect of link round-trip time delay within the network. The design supports predefined levels of performance robustness in the presence of channel uncertainty and signal interference. A novel stability boundary is introduced based on the use of the Jury Array that informs the necessary trade-off between disturbance attenuation and system stability. Extensive simulation results are provided that illustrate the effectiveness of the proposed methodology.Index Terms-Power control, Wireless cellular network, Quantitative feedback theory (QFT). I. IWith the rapid growth of wireless networks, there is an increasing demand for Quality of Service (QoS). In codedivision-multiple-access (CDMA) system many users share the same channel. In such a case, the power receiver from users close to the base station is much higher than that received from users further away. Therefore, a user close to the base will constantly create a lot of interference for users far from the base station, making their reception impossible. This near-far effect can be solved by applying an appropriate power control (PC) algorithms so that all users are received by the base station with the same average power. As wireless radio channels are typically affected by exogenous, uncertain factors that have an adverse impact on system performance such as path loss, shadowing and fading effects as well as noise and time delay; PC is clearly a challenging objective.In this work, a new Active Power Control (APC) algorithm is presented based on quantitative feedback theory. The basis for the work relies on the following assumptions that: (i) it is feasible to adjust the transmission power in an appropriate fashion in each base-mobile, (ii) the received signal quality at a receiver can be reliably measured using a signal-tointerference-noise ratio (SINR) type metric. It is also noted that the focus of the is on uplink system (communication from mobile users to the base station).Consider a wireless cellular system consisting of N user and M fixed base stations. The SINR for i-th user in the desired cell is given by, [17]: where g i j represents the channel gain between i-th base staion and j-th subscriber. p j also denotes the power that j−th user consumes for packet transmission. σ 2 i is the power of the white noise at the base station i. I i represents both inter and intracell interferences. SINR represented in (1), contains sufficient information on channel gain and interference so that an APC algorithm based on SINR feedback control can address the existing issues.In practice, an APC algorithm should have the properties of simplicity, the ability to adjust the power levels of each transmitted signal using only local measurements, in a reasonable time, and to maintain a desired signal-to-interference rati...

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Control theory aspects of power control in UMTS

Cited by 65 publications

References 37 publications

Distributed power control algorithms for asynchronous CDMA systems in frequency-selective fading channels

Distributed power control algorithms for asynchronous CDMA systems in frequency-selective fading channels

Power Control in Wcdma Networks: A Queue-Based Approach

Robust power control for CDMA cellular communication networks using quantitative feedback theory

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