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The use of power control to achieve the desired signalto-interferences ratio (SIR) is a crucial issue to ensure the quality of service of a code division multiple access (CDMA) cellular system. Power control based on SIR alone, however, often leads to the problem of vicious circle such that all mobile stations reach their power limits and yet, fail to achieve the desired SIR. In this paper, we present a novel power control scheme, which can significantly reduce the possibility of vicious circle. The new scheme is based on two observations. First, control of the target function SIR must take the signal power into account so as to avoid the problem of trivial optimization. Second, for a given channel operational environment, it is unnecessary and also impossible to pursue an unreasonably high SIR using brute force. The basic philosophy behind the new technique is therefore to define an acceptable SIR region over the entire SIR axis instead and use adaptive technique for two purposes. Namely, adaptively adjust both the target SIR and the step size to approach it according to the changing channel characteristics. The new scheme is essentially a Markov system with adaptive control.

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