A novel delayed wakeup scheme for efficient power management in infrastructure-based IEEE 802.11 WLANs

In an 802.11 WLAN, it can be observed that the shared wireless channel has a rush hour right after the periodic beacon frames. This is because mobile stations in power save mode (i.e. PSM-STAs) will wake up to retrieve data frames arrived at the access point (AP) while they are sleeping. PSM-STAs will stay awake until all buffered frames are retrieved. Notably, if the channel is congested, having all PSM-STAs staying awake will not improve the system delay performance but consume more power. Aiming at saving battery power while not affecting delay-throughput performance, a novel delayed wakeup (DW) scheme is proposed in this paper. Specifically, we divide a beacon interval (BI) into n sub-BIs. Then based on the amount of backlogged traffic, AP identifies and instructs “excess” stations to sleep immediately and wake up at a non-congested sub-BI later on. “Instructions” are judiciously encoded inside the modified traffic indication map (TIM) in the beacon frame. We show that our modifications are fully transparent to legacy stations. Last but not least, a seamless association procedure is designed to allow coexistence of legacy and DW-capable stations.