Improvements and New Techniques for Deterministic and Stochastic SIR based Power Control for 3-G Wireless CDMA Networks

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The proposed research is about the use of optimal control theory and modern numerical linear algebratechniques to improve existing power control schemes and to formulate and solve more general and morerealistic formulations of power control problem in 3-G wireless CDMA networks. The first two parts of theproposal deal with the deterministic power control problem and its variants, and the third part is onstochastic versions of the same problem. In the first part of the proposed research, an improvement of distributed constrained power controlalgorithm (PCPC), which is presently considered in the literature as the most efficient one, is suggestedvia the use of the acceleration techniques for fixed-point iterations and via the use Krylov subspaceiterations (presently considered as the most efficient numerical method for solving systems of linearlarge scale algebraic equations). The second part of the proposal considers an optimal fast closed-loop SIR-based power controlscheme for 3-G wireless CDMA network, based on the recent research work of the author of this proposaland his doctoral student. In addition of being optimal, the scheme obtained theoretically converges in oneiteration. This scheme follows perfectly channel variations and assumes that the link gains constantlychange in time. Due to the fact that the scheme needs a scalar discrete-time estimator (predictor), itpractically converges in 4-5 iterations. Simulations on a CDMA system demonstrate the effectiveness ofthe optimal power control algorithm and its superiority over the corresponding IS-95 algorithm and thepresent version of the DCPC algorithm. As a future research topic, a comparative analysis between theoptimized power control algorithm and the improved versions of the DCPC algorithm (accelerated andKrylov subspace based) to be obtained in the first part of this proposal, is suggested first. Secondly, sinceduring optimization, the weighted sum of the transmission power and the SIR (signal-to-interference)error, are jointly optimized, the power control problem can be put in the framework of Nash dynamicgames. It is suggested to extend the optimized power control results to capture the conflict situationamong users in a wireless network, which leads to the formulation of a Nash dynamic game problem. The third part of this proposal deals with the stochastic formulation of the power control problem. Thisis a pretty much new and widely open research problem. The basic problem formulation extends thedeterministic optimized power control problem to a stochastic environment, and leads to the linear powerevolution equation with additive Gaussian white noise. This problem formulation assumes that either linkgains or background noise or both are modeled as Gaussian white noise stochastic processes. Its variantof colored background noise and colored link gains noise are also suggested for future research. Inaddition, more realistic situations of state- and control-dependent noise using optimal control theoryresults will be considered. The control variables will be the ones that regulate the convergence process ofthe state variables (transmission powers and SIR errors) to their optimal values in a noisy environment.Note that the state- and control-dependent noise optimal control problems in discrete-time domain havebeen solved recently in the optimal control literature. In the final stage of this proposal, it is suggested tostudy the power control problem assuming that the link gains change according to Poisson stochasticprocesses. The impact of the proposed research will be in the area of improvements of the capacity of 3-Gwireless CDMA networks, reliability of quality of service (QoS) and durability of user's battery life. Allthese will be achieved by controlling interference in an optimal manner.