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We propose a quality-of-service (QoS) driven power and rate adaptation scheme over wireless links in mobile wireless networks. Specifically, our proposed scheme aims at maximizing the system throughput subject to a given delay QoS constraint. First, we derive an optimal adaptation policy by integrating information theory with the concept of effective capacity for a block fading channel model. Our analyses reveal an important fact that there exists a fundamental tradeoff between throughput and QoS provisioning. In particular, when the QoS constraint becomes loose, the optimal power-control policy converges to the well-known water-filling scheme, where Shannon (ergodic) capacity can be achieved. On the other hand, when the QoS constraint gets stringent, the optimal policy converges to the total channel inversion scheme under which the system operates at a constant rate. Inspired by the above observations, we then consider a more practical scenario where variable-power adaptive modulation is employed over both block fading and Markov correlated fading channels. In both cases, we derive the associated power and rate adaptation policies. The obtained results suggest that the channel correlation has a significant impact on QoS-driven power and rate adaptations. The higher the correlation is, the faster the power-control policy converges to the total channel inversion when the QoS constraint becomes more stringent. Finally, we conduct simulations to verify that the adaptation policy proposed for Markov channel models can also be applied to the more general channel models.