Distributed Constrained Power Control Research Articles

Optimal linear and bilinear algorithms for power control in 3G wireless CDMA networks

AbstractIn this paper we present two power control algorithms that potentially can be used as efficient techniques for power updates in 3G wireless CDMA communication networks. The algorithms are obtained by optimising the signal‐to‐interference‐ratio (SIR) error. The control laws are distributed, respectively linear and bilinear, and either requires estimation of the channel interference (or the quantity inversely proportional to the signal interference, known as the channel variation) or the development of efficient numerical algorithms for solving a set of obtained algebraic equations. Simulation results show superiority of the proposed algorithm over the distributed constrained power control (DCPC) algorithm. Copyright © 2005 AEIT.

Adaptive Closed-Loop Power Control Algorithms for CDMA Cellular Communication Systems

Power control has been widely studied and shown to be crucial for the capacity and performance of direct-sequence code-division multiple-access (DS-CDMA) systems. Practical implementations typically employ fast closed-loop power control, where transmitters adjust their transmit powers according to commands received in a feedback channel. The loop delay resulting from the measurements, processing, and transmission of the power control commands can result in oscillations of the transmission powers and lead to degradation in the system performance. In this paper we present new adaptive closed-loop power control algorithms that are able to alleviate the effect of the loop delay. The algorithms are based on self-tuning controllers designed for a log-linear model of the power control process. We carried out computational experiments on a DS-CDMA network using the distributed constrained power control (DCPC) as a reference algorithm. Practical versions of the algorithms are also provided and they were compared with the fixed-step power control (FSPC) algorithm employed in the IS-95 and WCDMA systems. The numerical results indicate that our algorithms can significantly improve the radio network capacity without any increase in power control signaling.

Distributed power control and removal algorithms for multimedia CDMA wireless networks

We study in this paper both distributed power control and removal algorithms for multimedia CDMA wireless networks. In our study, users can have different data rates as well as different quality of service (QoS) requirements. We derive a necessary and sufficient condition for the fully distributed power control (FDPC) algorithm to find a feasible power set. We also prove that, if the maximal power level is used at the start, then the distributed constrained power control (DCPC) algorithm is equivalent to the FDPC algorithm. For the connection removal algorithm, we prove that the non-reinitialized removal algorithm finds a feasible power set faster and employs smaller power levels than the reinitialized one does. Performances of some connection removal criteria are also studied. Our simulation results reveal that the smallest normalized CIR (SNC) and largest CIR requirement (LCR) criteria result in smaller outage probability than the smallest CIR (SC) criterion in a multimedia environment.

Power adjustment and allocation for multimedia CDMA wireless networks

A power adjustment and allocation (PAA) algorithm to speed up the process in finding a feasible power set for multimedia CDMA wireless networks is proposed. It was found, from numerical experiments, that the PAA algorithm can find a feasible power set much faster than the distributed constrained power control (DCPC) algorithm.

Second-order power control with asymptotically fast convergence

This paper proposes a distributed power control algorithm that uses power levels of both current and previous iterations for power update. The algorithm is developed by applying the successive overrelaxation method to the power control problem. The gain from such a second-order algorithm is in faster convergence. Convergence analysis of the algorithm in case of feasible systems is provided in this paper. Using the distributed constrained power control (DCPC) as a reference algorithm, we carried out computational experiments on a DS-CDMA system. The results indicate that our algorithm significantly enhances the convergence speed of power control. A practical version of the proposed algorithm is provided and compared with the bang-bang type algorithm used in the IS-95 and the WCDMA systems. The results show that our algorithm also has a high potential for increasing the radio network capacity. Our analysis assumes that the system is feasible in the sense that we can support every active user by an optimal power control. When the system becomes infeasible because of high traffic load, it calls for other actions such as transmitter removal, which is beyond the scope of the present paper.

Soft and safe admission control in cellular networks

We study the mobile admission control problem in a cellular PCS network where transmitter powers are constrained and controlled by a distributed constrained power control (DCPC) algorithm. Receivers are subject to nonnegligible noise, and the DCPC attempts to bring each receiver's CIR (carrier-to-interference ratio) above a given quality target. Two classes of distributed admission control are considered. One is a noninteractive admission control (N-IAC), where an admission decision is instantaneously made based on the system state. The other is an interactive admission control (IAC), under which the new mobile is permitted to interact with one or more potential channels before a decision is made. The algorithms are evaluated with respect to their execution time and their decision errors. Two types of errors are examined: type I error, where a new mobile is erroneously accepted and results in outage; and type II error, where a new mobile is erroneously rejected and results in blocking. The algorithms in the N-IAC class accept a new mobile if and only if the uplink and the downlink interferences are below certain corresponding thresholds. These algorithms are subject to errors of type I and type II. In the IAC class, we derive a soft and safe (SAS) admission algorithm, which is type I and type II error free, and protects the CIR's of all active links at any moment of time. A fast-SAS version, which is only type I error-free, is proposed for practical implementation, and is evaluated in several case studies.

Resource allocation for cellular radio systems

High terminal traffic densities are expected in urban multiuser radio systems. An efficient allocation of resources is the key to high system capacity. In this paper, a distributed dynamic resource allocation (DDRA) scheme based on local signal and interference measurements is proposed for multiuser radio networks. It offers "soft capacity" for time division multiple access (TDMA) and frequency division multiple access (FDMA) systems, bounded above by N per base station, where N is the total number of channels in the system. The decisions are made local to a terminal and its base and are essentially independent of the rest of the system. A distributed dynamic channel assignment scheme is used to assign channels to new calls. This scheme assigns a channel that offers the maximum carrier to interference ratio (CIR) to a new call. A distributed constrained power control (DCPC) scheme based on CIR measurements is used for power control. The channel assignment scheme and the power control scheme are coupled to obtain an interactive resource allocation scheme. We compare the capacity of a system which uses the distributed dynamic resource allocation scheme described above with the capacity of a system which uses the channel assignment scheme alone. The system capacity is measured by simulation as the number of terminals that can be served by the system with a CIR above an acceptable minimum. In a 1D cellular system, coupling the channel assignment scheme with power control is discussed. Simulations were also used to show the effect of varying the maximum transmitter power on system capacity.

Gradual removals in cellular PCS with constrained power control and noise

In this paper we study the mobile removal problem in a cellular PCS network where transmitter powers are constrained and controlled by a Distributed Constrained Power Control (DCPC) algorithm. Receivers are subject to non-negligible noise, and the DCPC attempts to bring each receiver's CIR above a given target. To evaluate feasibility and computational complexity, we assume a paradigm where radio bandwidth is scarce and inter-base station connection is fast. We show that finding the optimal removal set is an NP-Complete problem, giving rise for heuristic algorithms. We study and compare among three classes of transmitter removal algorithms. Two classes consist of algorithms which are invoked only when reaching a stable power vector under DCPC. The third class consist of algorithms which combine transmitter removals with power control. These are One-by-one Removals, Multiple Removals, and Power Control with Removals Combined. In the class of power control with removals combined, we also consider a distributed algorithm which uses the same local information as DCPC does. All removal algorithms are compared with respect to their outage probabilities and their time to converge to a stable state. Comparisons are made in a hexagonal macro-cellular system, and in two metropolitan micro-cellular systems. The Power Control with Removals Combined algorithm emerges as practically the best approach with respect to both criteria.