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In a cellular network it is necessary to make a trade-off between congestion and Quality of Service (QoS) of the users. To ensure good system performance in uplink of a WCDMA network, control loops are used to adapt to changing radio and interference conditions. A fast inner power control loop updates the transmission powers of the mobiles based on measurements related to QoS, which are compared to a reference value. The reference value is set dynamically by a slower outer rate control loop that uses measurements of congestion. There is a time-scale difference between the loops, but joint dynamics cannot be neglected. In this paper we derive a high order system model with distributed feedback control based on locally measurable information. We model the time-scale difference between the loops and include this in the model. We give sufficient conditions for stability using control theoretic methods and validate the model and results by simulations.