Choosing Beacon Period for Improved Response Time for Wireless HTTP Clients

A significant contributor to the total energy consumed on many battery-powered mobile devices is the wireless network interface card (NIC). Therefore, minimizing the energy consumption of the NIC can result in significant battery life improvement for a mobile device. One way of achieving this is to transition the NIC to a lower-power sleep mode when possible For example, the IEEE 802.11 wireless LAN standard power-saving mode (PSM) makes access points buffer data destined for a client and uses a periodic beacon to inform the mobile client about any buffered data. This allows the NIC to enter sleep mode between beacons. In this paper, we show that 802.11 PSM performs poorly due to the fact that an access point is unable to adapt to the requirements of each client. Therefore, we propose a novel power saving algorithm, PSM-Dynamic, where the access point uses different beacon periods for different clients. During HTTP downloads, each client carefully chooses a good beacon period for itself, based on the RTT of its current connections, and informs the access point of this beacon period. This technique enables download times for Web pages that are comparable to those without any power-saving and provides energy savings comparable to the standard 802.11 PSM. We show, using real-world easements and results from emulation-based experiments, that it is feasible for both clients and access points to efficiently support such per-client beacon periods, instead of having a common, static beacon for all clients. The solution is simple enough that it can be implemented with just small enhancements to the existing 802.11 specification.