MTIM for IEEE 802.11 DCF power saving mode

In IEEE 802.11 wireless LAN, after the transmission of each beacon frame, there will be a large number of stations in power saving mode (PS mode, PSM) trying to send power saving poll (PS-Poll) frames to contend the right to receive the buffered downlink packets. However, excessive contention results in higher collision probability, higher power consumption and lower throughput than usual. To solve this problem, we propose a downlink access scheme which modifies the traffic indication map (TIM) fields in beacon frames to enhance the control ability of access point (AP). This scheme which can be used in both the basic access scheme and the access scheme with RTS/CTS enables AP to constrain the number of stations in contention to be an optimal number. Furthermore, the proposed MTIM scheme provides a convenient way for quality of service (QoS) differentiation by limiting the PS-Poll transmitting of stations with lower priority. Simulation results provided in this paper prove the performance improvement.