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

Rutgers University New Brunswick, New Brunswick NJ

Investigators

Abstract

The proposed research is about the use of optimal control theory and modern numerical linear algebra techniques to improve existing power control schemes and to formulate and solve more general and more realistic formulations of power control problem in 3-G wireless CDMA networks. The first two parts of the proposal deal with the deterministic power control problem and its variants, and the third part is on stochastic versions of the same problem. In the first part of the proposed research, an improvement of distributed constrained power control algorithm (PCPC), which is presently considered in the literature as the most efficient one, is suggested via the use of the acceleration techniques for fixed-point iterations and via the use Krylov subspace iterations (presently considered as the most efficient numerical method for solving systems of linear large scale algebraic equations). The second part of the proposal considers an optimal fast closed-loop SIR-based power control scheme for 3-G wireless CDMA network, based on the recent research work of the author of this proposal and his doctoral student. In addition of being optimal, the scheme obtained theoretically converges in one iteration. This scheme follows perfectly channel variations and assumes that the link gains constantly change in time. Due to the fact that the scheme needs a scalar discrete-time estimator (predictor), it practically converges in 4-5 iterations. Simulations on a CDMA system demonstrate the effectiveness of the optimal power control algorithm and its superiority over the corresponding IS-95 algorithm and the present version of the DCPC algorithm. As a future research topic, a comparative analysis between the optimized power control algorithm and the improved versions of the DCPC algorithm (accelerated and Krylov subspace based) to be obtained in the first part of this proposal, is suggested first. Secondly, since during 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 dynamic games. It is suggested to extend the optimized power control results to capture the conflict situation among 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. This is a pretty much new and widely open research problem. The basic problem formulation extends the deterministic optimized power control problem to a stochastic environment, and leads to the linear power evolution equation with additive Gaussian white noise. This problem formulation assumes that either link gains or background noise or both are modeled as Gaussian white noise stochastic processes. Its variant of colored background noise and colored link gains noise are also suggested for future research. In addition, more realistic situations of state- and control-dependent noise using optimal control theory results will be considered. The control variables will be the ones that regulate the convergence process of the 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 have been solved recently in the optimal control literature. In the final stage of this proposal, it is suggested to study the power control problem assuming that the link gains change according to Poisson stochastic processes. The impact of the proposed research will be in the area of improvements of the capacity of 3-G wireless CDMA networks, reliability of quality of service (QoS) and durability of user's battery life. All these will be achieved by controlling interference in an optimal manner.