Distributed coordination function (DCF) is the main technique of IEEE 802.11, which relies on carrier sense multiple access/collision avoidance (CSMAICA) to reduce collision among stations. In this paper, a scheme is proposed to improve the throughput performance of the DCF in a hybrid environment, where a ready to send (RTS) frame is used when the length of a packet exceeds a threshold. Suppose, e.g., that a RTS frame and a packet are transmifted simultaneously, the result under the legacy DCF is that a collision occurs and both of them fail; the transmission bandwidth is thus wasted. To prevent this, an extra portion is added in front of the packet in the proposed scheme, and its length equals the size of a RTS frame. Clearly, it can prevent the packet from the collision process whenever it experiences a collision with one or multiple RTS frames.