Design and Analysis of Enhanced Grouping DCF Scheme for the MAC Layer Enhancement of 802.11n with Ultra-high Data Rate

The 802.11 has emerged as the prominent wireless LAN technology as the mobile computing devices such as notebooks and PDA have replaced the desktop computers to be the main trend products. However, if the number of active stations is large, that is high-loading condition for the legacy DCF of 802.11, the capacity will be very low due to high collision costs. In this paper, we introduce the TDMA concept to partition all numerous active stations into several groups to avoid all stations transmitting the frames simultaneously. When Point Coordinator (PC, generally referring to AP) finds that the number of active stations (M) is large i.e. bigger than 8, it broadcasts number of groups (N), group head (Nh) bits and start grouping bit sequence (k) (such as 00000100 00000000 00000000) information in the TIM field of the beacon frame. Once all stations receive this instruction, the stations which last two LSB bits (because k=0, N=4) of the MAC address (IEEE EUI-48 or EUI-64) are 00 belonging to group 0 will transfer their frame first. On the contrary, all stations belonging to other groups will set their waiting time, that is, Network Allocation Vector (NAV) much more precisely. In this article, we also proposed a fast selection scheme to get the optimal start grouping bit sequence which aims to partition all the active stations into a few groups more uniformly to reduce the number of members in each group so that we can reduce the Contention window Minimum (CWMiri), that is, backoff´s idle overhead.