According to the carrier sensing mechanism adopted by Distributed Coordination Function (DCF) in IEEE 802.11 standard, a node defers its communication if it senses the medium busy. However, this deferment might block more concurrent communications than necessary. In addition, in DCF, the time duration of deferment is not delivered to all potential interferers, particularly those in the distance. This paper proposes Collision-Aware DCF (CAD) that efficiently utilizes the available channel resource along both the spatial and time dimensions. Basically, CAD embeds the spatial and time reservation requirements in the PHY header, which is transmitted at the lower data rate, so that a larger group of potential interferers become aware of the ongoing communication and thus avoid collisions. Extensive simulation based on the ns-2 has shown that CAD offers as much as 21% higher packet delivery rate and 91% lower packet delay than DCF with the CBR (constant bit rate) traffic.