Over wireless multihop networks, one of the most important problems is to increase the network throughput with low power consumption. This paper deals with the cross-layer approach between the physical layer and the transport layer to solve this problem. We propose a new window control algorithm in the transport layer to improve the throughput and a new power control algorithm in the physical layer to reduce power consumption. Through an equilibrium point analysis, it is explicitly shown that the proposed algorithm enhances power efficiency, compared with the constant-power scheme. Through simulation results, it is observed that the proposed algorithm outperforms the existing algorithms in terms of throughput and power consumption.