A modified power saving mode in IEEE 802.11 distributed coordinator function

Power saving (PS) mode specified in IEEE 802.11 standard is a power efficient method that prolongs the network operation time of battery powered wireless LAN devices. It is a synchronous protocol which requires precise time synchronization among all the participating nodes within the Independent Basic Service Set (IBSS). Therefore, Time Synchronization Function (TSF) is defined for the protocol to operate without the aid of external timing sources. Time synchronization is achieved by periodically transmitting the time synchronization beacon, which will define a series of fixed length beacon intervals. In PS mode for Distributed Coordinated Function (DCF), nodes will wake up at the beginning of each beacon interval for a duration called Announcement Traffic Indication Message (ATIM) window to announce their pending data packets using small ATIM control packets. After the ATIM window, nodes will transmit the announced data packets using contention-based DCF access procedure. This paper proposes a modified mechanism by sending the TSF beacon at the end of each ATIM window and adding certain scheduling information in the beacon to schedule the transmission of announced data packets. The scheduling information will ensure the data packets transmission to be contention-free. Hence, the scheduled data packet transmission will achieve a higher throughput and lower energy consumption. Results based on simulation have shown that as much as 70% of energy saving can be achieved.