Design and analysis of grouping-based DCF (GB-DCF) scheme for the MAC layer enhancement of 802.11 and 802.11e

Abstract

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 (Ng) and group head (Nh) bits (such as 00000100 00000000) information in the TIM field of the beacon frame. Once all stations receive this instruction, the stations which last two LSB bits 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. Analysis shows that the capacity of our GB-DCF will be near to the theoretical capacity limit of 802.11 WLAN even if the distributions of all active stations among all groups are not so uniform. This capacity could be independent of the number of active stations and CWMax (Contention window maximum). This grouping technique can also be applied to all DCF-based protocols such as EDCA (Enhanced Distributed Coordination Access), called GB-EDCA. In this article, we also simulate the behaviors of GB-EDCA and demonstrate that GB-EDCA can solve the delay jittering problem arising too many QoS stations running simultaneously.