Burst error smoothing by using the outer loop power control in DS-CDMA systems

In this paper we propose an algorithm for reverse link outer loop power control in COMA systems to smooth burst errors. DS-CDMA systems require tight control of transmit power to obtain the required performance. In DS-CDMA systems, closed loop power control on the reverse link is executed the inner loop and the outer loop. The inner loop allows the mobile station to reach its current signal to interference ratio (SIR) target through using a sequence of power up/down commands. The outer loop dynamically adjusts the target SIR so that adequate performance in terms of frame error rate (FER), the truly quality measure, is achieved. The propagation conditions of different mobile stations are different. For this reason, the effectiveness of the inner loop is not the same for all users. In some cases, it always comes close to the target, while in others the variability could be quite significant. The outer loop compensates for such variability by adjusting the SIR targets so that all users obtain the same performance in terms of error rate. In this work, we propose an outer-loop power control algorithm using the leaky bucket (LB) scheme. The characteristics of the algorithm are based on the frame error count, which is increased or decreased by using the leaky bucket principle. The leaky bucket scheme is based on two parameters: T (bucket limit) and D (drip rate). We adaptively adjust step 5izes, T and D. The algorithm will be simulated to prove its advantages for outer-loop power control.