Expectation Maximization based Power-Saving Method in Wi-Fi Direct

Wi-Fi Direct has been proposed with the purpose of enabling the connection between any two devices without requiring a wireless access point. Because of the limited battery capacity of mobile devices, it is important issue to provide an efficient energy consumption to the Wi-Fi Direct device. In order to reduce unnecessary energy consumed, Wi-Fi Direct standard defines two power-saving mechanisms: the opportunistic power-saving (OppPS) mode and notice of absence power-saving (NoAPS) mode. In this study, we propose a method to enhance the efficiency of the NoAPS mode for the transmission of multimedia video traffic. The proposed method dynamically determines the length of the awake interval long enough to guarantee the successful reception of the frame in clients with the given outage probability based on the pdf of the video frame size estimated. The shape and scale parameters of the pdf of the video frame size and the weights of all the mixture components are updated by the Expectation Maximization (EM) algorithm whenever a frame is transmitted. Furthermore, we suggest priority-based frame transmission strategy considering the inter-dependency between video frames to reduce the packet loss rate. Results show that the proposed method reduces the energy consumption and the transmission delay of Wi-Fi Direct devices compared to the existing NoAPS method.