Optimal Distributed Power Control in Cellular Wireless Systems

To appear in
Dynamics of Continuous, Discrete and Impulsive Systems
http:monotone.uwaterloo.ca/?journal
Optimal Distributed Power Control in Cellular Wireless
Systems
Lijun Qian
1
and Zoran Gajic
1
1
Department of Electrical and Computer Engineering
Rutgers—The State University of New Jersey
94 Brett Road, Piscataway, NJ 08854-8058
Abstract. In this paper, an optimal fast closed-loop SIR-based power control scheme
is proposed for CDMA systems. The essence of this power control algorithm is that the
power evolution is directly driven by the error between the actual SIR and the desired
SIR. The amount of power change is proportional to the SIR error, and the optimal gain
is chosen to achieve the minimum SIR error at the next time instant. Assuming perfect
estimation and prediction of the channel quality, the SIR error goes to zero in one step. In
practical situations, where the estimator need several steps to make accurate estimation
and prediction, the SIR error goes to zero in less than ten steps. The proposed controller
is an estimator based controller. An H∞ ?lter is applied in the proposed scheme instead
of a Kalman ?lter to facilitate the system ?ltering regardless of the nature of the system
and measurement disturbances. The simulation results of a multi-cell CDMA system in
all cases ?t the theoretical analysis very well. These results indicate that the proposed
optimal power control scheme is a very promissing solution to the distributed power control
problem in wireless systems, both theoretically and practically.
Keywords. Power Control, CDMA, H∞ ?lter, SIR, estimator.
AMS (MOS) subject classi?cation: control application.
1 Review of SIR based Power Control in Cel-
lular Wireless Systems
In a cellular wireless network, certain quality-of-service (QoS) should be
maintained for all active users in the network. A quantity that measures
user’s provided QoS is the signal-to-interference ratio (SIR). A general idea
to achieve the desired SIR for all the active users is to allocate the network
resources in the most e?cient way. Resource allocation in a cellular wire-
less network includes channel allocation, power control, etc. The transmitter
power is the most valuable resource in the network. By proper control of each
transmitter power, the interference can be minimized. At the same time, it
extends the battery life in the handset.