Enhanced Predictive Up/Down Power Control for CDMA Systems (original) (raw)

Improved Predictive Power Control Algorithms to Increase CDMA System Capacity

ITB Journal of Engineering Science, 2009

In this paper capacity of CDMA system is evaluated using an improved algorithm of channel prediction-based power control in Rayleigh fading channel environments. One of the most serious problems which degrades the performance of power control algorithm is the effect of feedback delay. To overcome the effect of feedback delay, power control algorithm relies on channel prediction techniques, which utilize the correlation property of the past channel measurements. In CDMA power control, however, the correlation property of channel measurements is destroyed because the transmit power is continuously updated for each power control interval. In order to restore the correlation property of the channel, the past channel measurements are compensated for by the same factors that were given by power updating for each power control interval. The prediction algorithm in this paper is proposed using the least mean square (LMS) technique. The result shows that the capacity of CDMA systems increase significantly when the improved predictive algorithm is used. Numerical evaluation shows that CDMA capacity increases by more than 40 % for fixed step algorithm and more than 50 % for variable step algorithm when the proposed algorithm is employed.

Performance Analysis of Downlink Power Control in CDMA Systems

IEEE Sarnoff Symposium, Princeton, 2003

Three downlink power control algorithms have been studied and evaluated in this work. Additionally, an uplink power control algorithm has been modified and adapted for downlink. An enhancement has been proposed to one of the studied algorithms based on the ...

New Approach to Closed-Loop Power Control in Cellular CDMA Systems under Multipath Fading

2008 4th International Conference on Wireless Communications, Networking and Mobile Computing, 2008

This paper proposes a new approach to the closed-loop power control algorithm with decision feedback, called NAPC-DF algorithm. In this algorithm, the step size of the transmitting power by the mobile station (MS) in uplink channel is variable and adjusted by the received command from the base station (BS) and channel conditions. This algorithm is compared with fixed-step, variable step and adaptive step closed-loop power control with decision feedback (FSPC-DF, VSPC-DF and ASPC-DF, respectively). Numerical results indicate that NAPC-DF algorithm, under fading can significantly improve the radio network capacity without any increase in power control signaling. Also the speed of convergence and stability against loop delay can be increased and it decreases the outage probability and bit error rate (BER) of uplink channel in compared with the mentioned references algorithms.

A New Power Control Algorithm for Cellular CDMA Systems

2009

The conventional closed-loop power control in cellular code division multiple access systems can only achieve limited performance due to its inability to track channel variations quickly. In this paper, we present a new power control algorithm which is able to increase the speed of convergence to track the changes in radio channel efficiently. Simulation results show that it outperforms the conventional algorithms.

Modified Variable Step Size Power Control Algorithm for CDMA Systems

2012

Power control mechanism is an important issue for Code Division Multiple Access (CDMA) systems which helps in achieving higher capacity, combating against near far effect and provides high link performance. Unless a suitable power control mechanism is developed cellular systems cannot perform better. Power control allows to minimize the transmit power while keeping the system performance above the required value. In previous research [4], variable step size for closed loop power control system has been studied and results showed an increase in convergence speed and stability by properly choosing the step size. The new algorithm presented in this paper shows that it can perform better than variable step size power control algorithm and can obtain higher stability and convergence speed for step size δ at 0.1.

researchpaper Modified Variable Step Size Power Control Algorithm for CDMA Systems

Power control mechanism is an important issue for Code Division Multiple Access (CDMA) systems which helps in achieving higher capacity, combating against near far effect and provides high link performance. Unless a suitable power control mechanism is developed cellular systems cannot perform better. Power control allows to minimize the transmit power while keeping the system performance above the required value. In previous research [4], variable step size for closed loop power control system has been studied and results showed an increase in convergence speed and stability by properly choosing the step size. The new algorithm presented in this paper shows that it can perform better than variable step size power control algorithm and can obtain higher stability and convergence speed for step size δ at 0.1.

Improved Predictive Power Control of Cdma System in Rayleigh Fading Channel

MAKARA of Technology Series, 2010

In this paper an improved prediction-based power control is proposed for code division multiple access (CDMA) systems in Rayleigh fading channel environments. One of the most serious problems which degrades the performance of power control algorithm is the effect of feedback delay. To overcome the effect of feedback delay, power control needs to employ prediction algorithm which utilises the correlation property of the past channel samples measurements to predict the future sample values. In CDMA power control, however, the correlation property of channel measurements is destroyed because the transmit power is continuously updated for each power control interval. The prediction algorithm in this paper uses the recursive least square (RLS) technique and an improved predictor algorithm is proposed to compensate for the channel correlation. The result shows that the performance of improved predictive power control proposed in this paper evaluated in terms of bit error rate (BER) as a function of bit energy-tointerference power density ratio E b /I o improved significantly from that of the conventional predictor.

Unified framework for the analysis and design of linear uplink power control in CDMA systems

Wireless Networks, 2012

In this work, it is proposed a unified framework to design and analyze uplink distributed power control schemes over flat-fading channels from a control theory perspective. The effects of linear detectors and round trip delays are explicitly characterized in this study. First, the optimal solution to the power minimization problem under signal to interference-noise ratio (SINR) restrictions is reviewed, where sufficient conditions for its existence are presented that depends on the detection strategy. Four different linear detection schemes are studied in this work: Matched Filter, Decorrelator, MMSE and Projector. Specifically, two special cases are analyzed with respect to the spreading codes properties: uniform crosscorrelation and orthogonal codes, and under both conditions an explicit expression for the central solution is obtained. Nevertheless, one drawback of the central solution is its lack of robustness against channel estimation errors, transport delays and noise. Hence, it is proposed closed-loop control laws with linear power assignment which are capable of provide robustness to these channel effects. It is then presented that under certain conditions, stable feedback loops can be obtained considering SINR quantification, transmission and processing delays, and the resulting closed-loop power solutions tend to the central ones. Finally, it is illustrated that the selection of the linear detectors does not affect the resulting closed-loop dynamics, but the uplink transmission power in steady-state. An exhaustive simulation evaluation is included to validate the mathematical analysis presented for open and closed-loop solutions.

Variable Step Closed-Loop Power Control in Cellular Wireless CDMA Systems under Multipath Fading

2007 IEEE Pacific Rim Conference on Communications, Computers and Signal Processing, 2007

The Power control has been widely studied and shown to be crucial for the capacity and performance of directsequence 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 variable step closed-loop power control algorithm (VSPC) and fixed-step closed loop power control with information feedback (FSPC-IF), that are able to increase speed of convergence and alleviate the effect of the loop delay. We carried out computational experiments on a DS-CDMA network using these algorithms. Fixed-step power control with decision feedback (FSPC-DF) is reference algorithm. New algorithms are compared with it. The numerical results indicate that new algorithms can significantly improve the radio network capacity without any increase in power control signaling, also increase speed of convergence and decrease loop delay.