Cellular CDMA networks impaired by Rayleigh fading: system performance with power control

The effect of power control on the performance of cellular code division multiple access (CDMA) networks is investigated. The bit error rate (BER) of a mobile unit at any given distance from the base station is obtained for both the forward link and the reverse link, taking into account Rayleigh fading and UHF propagation attenuation, To this end, a simple multiple-cell-system model is developed. Our work shows the dependence of performance gain on the different user spatial distributions under power control. Also, it is shown that power control in the forward link of CDMA networks may lead to a dismal performance degradation for close-in users. To alleviate this problem, the adjusted power control scheme is revisited. Two different performance criteria are proposed for this purpose, and the optimal threshold values corresponding to these criteria are computed. Results indicate that, although both threshold criteria are acceptable, the second criterion is more recommendable from a BER performance point of view, because it circumvents the so-called service "hole" problem which may occur when one uses the first criterion. The analysis for both the forward and reverse links leads to closed-form signal-to-interference ratio (SIR) results, which not only facilitate physical insight into the impact of key system parameters on the system performance of CDMA networks with power control, but may also eliminate the need for cumbersome Monte-Carlo-type simulations. It is shown that fourth-order power control (n=4) leads to at least a threefold enhancement in capacity for BER=10/sup -3/.<
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