Power Management And Partial Implementation In IEEE802.11 MAC Layer

Wireless LAN(WLAN), providing high speed wireless internet access at a low cost, has experienced a spectacular rise in popularity in rencent years. IEEE802.11 is very popular in WLAN standard field, but the key technique is controled by foreign countries, so deep research and development is necessary. Most of the mobile devices are limited with respect to the battery capacity due to size restrictions, thus how to reduce the power consumption in wireless LAN becomes even more important in the implementation of IEEE802.11 standard. This paper provides an overview of IEEE802.11 standard, analyses the power consumption in 802.11 network and the performance of the Wireless network when using 802.11 power save mode(PSM), investigates some improved and extended power management mechanisms based on PSM, analyses its performance contrast with PSM, and proposes a method of primary implementaion for IEEE802.11 MAC in STA(Station) based on the platform of ARM9 and uCOS-Ⅱat last.The additional power consumption caused by overhearing and erroneous carrier sensing(ECS) due to the property of wireless medium and CSMA/CA mechanism. The 802.11 standard provides a power save mode(PSM) in order to save energy, but this paper's analyse shows that PSM will degrade the performance of wireless network, especially in TCP conection (while browsing the web) and VoIP.After investigate some improved and extended power management mechanisms, we find that BSD mechanism is a solution to the problem of minimizing energy comsumption while guaranteeing that a connection's RTT does not increase by more than a factor, but it's not appropriate for real-time communication. UPSD mechanism is designed only for VoIP, it's not fit for Web access. APSM mechanism can upper bound the MAC downlink delay to the frame arrival interval, it's suited for the case of a mix of traffic including Web access, VoIP, e-mail etc, but it modifies the original MAC frame in 802.11 standard, and the algorithm is complicated. E-idling and O-idling mechanisms are proposed only for reducing the power comsumption, When STA starts overhearing or receiving ECS signal, they force the wireless interface to switch to the low-energy idling state. In this way, they offer significant extension in network lifetime, but this gain is traded for an increased packet drop rate.The data flow operations in STA including making a frame, fragmentation, queue and FCS calculation in transmission and the reverse operations in reception have been finished and tested based on the proposed method.