Collision avoidance and spatial reuse are two important approaches to improving the throughput of ad hoc networks, and many MAC protocols are proposed to achieve these goals. In most MAC protocols, collisions are reduced by solving the hidden terminal problems, but the spatial reuse remains un-optimized in these protocols, which affects network throughput dramatically. Moreover, reception of exposed terminals is not allowed in current MAC protocols even if they can receive packets successfully, which leads to lower spatial reuse. In this paper, a high throughput MAC protocol named e-MAC is proposed. To improve the network throughput, two approaches are used in e-MAC. First, a power controlled busy tone is used to eliminate hidden terminals. The receiver adjusts the transmission power of busy tone, according to a received signal strength from the transmitter, so that the spatial reused is optimized while all hidden terminals are covered by a busy tone. Second, exposed terminals are allowed to receive when the ratio between signal strength of RTS (ready-to-send) and interference satisfies the SINR (signal to interference and noise ratio) requirements, which further improves the spatial reuse. Simulation results show that the average throughput of e-MAC outperforms that of DUCHA (dual channel access) by 87%.