The wide-spread deployment of Wireless LANs are underpinned by two most popular variants of IEEE 802.11 standards, 802.11b and 802.11g. The 802.11g extends 802.11b to support higher data rate via new OFDM-based physical layer, but both or them operate at 2.4GHz band and perform medium access with the same MAC protocol. When the 802.11b and 802.11g devices co-exist in the overlapping coverage area, the interoperability between them needs to be dealt with. The 802.11 g defines a protection mechanism to avoid frame collisions between 802.11b and 802.11g devices. Since the legacy 802.11b devices cannot notice a busy channel by sensing the OFDM-modulated 802.11g frames, extra frames (e.g., CTS-to-self frames) are introduced for channel reservation in the protection mechanism. Those frames are understood by both 802.11b and 802.11g devices and transmitted first before sending 802.11g data frames. Nevertheless, they are viewed as overhead because they reduce the available medium resource for data delivery. In this paper, we propose an enhanced protection mechanism to reduce the number of extra frames used for channel reservation. The effectiveness of our proposed solution to improve system performance in the mixed 802.11b and 802.11g WLAN is verified by simulation.
