Adaptive Power Control Module in Cellular Radio SystemJianhua GanAbstract Adaptive power control scheme based on the optimization of transmitter powerand receiver filter coefficients is shown. The scheme is mapped to control logic, digitalfilter and adaptive amplifier.Accurate power control can reduce the interference in both Global System Mobile(GSM) and CDMA system. When the mobile is close to the base station, it can use lowerpower since the signal loss is smaller. For GSM, interference to other cells using thesame frequency is reduced when the power control is accurate. For CDMA, accuratepower control is more important because all CDMA signals interfere with each other.Lack of accurate power control reduces the capacity for CDMA. Moreover, powercontrol can reduce battery drain and increase possible talk time. The major objective ofpower control is to alleviate the co-channel and cross-channel interference [1]. Due to theeffects of fast fading, shadowing and distance loss, an adaptive power control (APC)scheme is needed. In order to get a better estimation of the received power, the receivedpower at the mobile can be estimated by using RAKE receiver [2] as shown in Figure 1.The outputs of the taps of the RAKE receiver are correlated with the de-spreadingsequence c(t) over one bit time, then squared and summed to generate X(k) at time kT.X(k) is averaged over m bits to form an estimate of the received power. These processesare typical DSP processes. By adaptively adjust the transmitter power level and receiverfilter, we can minimize the interference that users create to each other while maintainingthe desired signal to interference ratio (SIR) [3, 4].Figure 1. Power estimation diagram using RAKE [2]The simple power control approach was concerned with assigning the transmitterpowers to the users optimally with the assumption that the receiver filters of the userswere fixed to single user detector [3]. Multi-user detection was concerned with designingreceiver filters to suppress the interference seen by each user with the assumption that thereceived powers of the users were fixed. If the transmitter powers and receiver filters ofthe users are optimized jointly, the performance of a CDMA system can be improvedgreatly. This can be implemented in a distributed manner using local measurement. Eachmobile can adapt its receiver filter coefficients to interference and perform iterativetransmitter power level adjustment for fixed filter coefficients. The block diagram of theadaptive power control scheme is shown in Figure 2. This scheme can be mapped tocontrol logic, digital filter and adaptive amplifier. The power control algorithm will bereflected in control logic block.ReceiverfilterControlblockTransmitteramplifierPowermeasurementFigure 2. Block diagram of the adaptive power control schemeReferences[1] Z. Rosberg and J. Zander, “Towards a framework for power control in cellularsystems,” Wireless Networks, vol. 4, no. 3, pp. 215-222, Apr. 1998.[2] A. Chockalingam, L. B. Milstein, “Open-loop power control performance in DS-CDMA networks with frequency selective fading and non-stationary base stations”,Wireless Networks, vol. 4, no. 3, pp. 249-261, Apr. 1998.[3] S. Ulukus and R. D. Yates, “Adaptive power control and MMSE interferencesuppression”, Wireless Networks, vol. 4, no. 6, pp. 489-496, Nov. 1998.[4] P. -R. Chang, B. -C. Wang, “Adaptive fuzzy power control for CDMA mobile radiosystems”, IEEE Transactions on Vehicular Technology, vol. 45, no. 2, pp. 225- 236,
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