Transmission power control in wireless ad hoc networks has been widely studied in the academia. In this paper, we propose a new multiple access scheme for power-controlled transmission rate-adaptive ad hoc networks. The proposed scheme exploits the features of physical layer specified by IEEE 802.11a standard in the ad hoc network environment. The proposed cross-layer design explicitly provides different transmission rates for data transmission by tuning transmission power with favorable SINK. The simulation results have proved it to be an effective and efficient MAC protocol in the wireless ad hoc networks