Matti Rintamäki

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.

Two-mode fast power control for WCDMA systems

Power control is needed in WCDMA systems to mitigate a so-called near-far effect, which is caused by the large variations of signal strength due to the Rayleigh fading radio propagation channel. This paper proposes an improved fast power control scheme for WCDMA systems, suitable for real implementation. Realistic constraints for the power control command length and step size are taken into account. The scheme consists of an adaptive generalized minimum-variance self-tuning controller and a simple bang-bang controller, which is used as a backup for the adaptive controller. The adaptive controller takes advantage of both the current and previous signal-to-interference ratio (SIR) measurements and power control commands. The proposed algorithm (called STGMV-PC for self-tuning generalized minimum-variance power control) is used in the uplink, while only a bang-bang controller is used in the downlink. Computer simulations indicated that better performance can be achieved with the proposed algorithm in comparison with either bang-bang or pure minimum variance controller.

Dynamic step-size power control in UMTS

We propose a novel dynamic stepsize power control method to improve the performance of UMTS/WCDMA cellular systems. The proposed method utilizes dynamic step-size power control commands, received SIR/power, and mobile handset location assistance data. Furthermore, dynamic inter-operation between the power control, admission control, and handoff control is evolved to improve the convergence of the proposed power control mechanism. Based on the output of this interoperability, a multi-step transmit power edge setting is proposed. Finally, the performance of the proposed method has been evaluated by extensive simulations.

Adaptive robust power control for WCDMA systems

Large variations of signal strength due to Rayleigh fading radio channel are observed in cellular radio communication systems. Power control (PC) is needed to mitigate this effect. It is essential in WCDMA, where many users share the same transmission medium simultaneously. Difficulties arise in power control because the conditions of radio channels change very rapidly. In this paper we propose a new adaptive robust algorithm for closed-loop power control for WCDMA systems, suitable for real implementation. The scheme relies on the generalized predictive controller (GPC), which is known to be able to control very difficult processes, and an adaptive self-tuning control strategy to automatically adjust the controller parameters. The approach was shown in simulations to outperform the conventional bang-bang controller.

Enhanced fast power control for WCDMA systems

The continuous increase of cellular phones shapes up the appearance of new communication systems and new technologies. In real life the radio signals are subjected to Rayleigh fading (fast fading) and interference. These result in large variations in signal strength. Power control (PC) is needed to compensate for these effects. Power control is one of the critical radio resource control functions in a WCDMA-based system. This paper describes a contribution of applying an adaptive (self-tuning) controller in the fast power control loop of WCDMA systems. Replacing the conventional controller with a controller that decides the PC command based on the history of the PC commands and errors improves the quality of the transmission significantly.

Fully distributed power control algorithm with one bit signaling and nonlinear error estimation [mobile radio systems]

In this paper, we suggest a method to estimate the carrier to interference ratio (CIR) information of the uplink using the power control ON-OFF commands at the mobile station (MS). The estimated CIR information is used to adjust the transmitted power from the mobile terminal using the distributed constrained power control (DCPC) algorithm. The main advantage of our algorithm is that it can improve the performance of power control without any increase in power control signaling. The suggested algorithm is compared with the conventional fixed step power control (FSPC) algorithm by computer simulations. Considerable improvements in system performance are observed when using the suggested algorithm in comparison with the FSPC algorithm.