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A Study on the Power Save Mode of Wi-Fi Direct for Mobile Phone

초록/요약

Recently, there has been an explosion in mobile traffic, which is particularly attributable to requests for high-capacity video data, and this is expected to increase more than tenfold by 2019 [9]. The technique for connecting directly without connecting to a separate Access Point (AP) has become necessary due to the network load incurred by the increased data traffic. Accordingly, Wi-Fi Alliance has announced Wi-Fi Direct, which is an application of traditional Wi-Fi, keeping the strengths such as performance and ubiquity while intensifying its mobility, ease-of-use, and security. Wi-Fi Direct has been widely utilized as an application of sharing, synchronization, and display via a short and convenient connection procedure. Three mechanisms are the main functions for Wi-Fi Direct: P2P Discovery, P2P Group Operation, and P2P Power Management [1]. First, Discovery is the function through which a Wi-Fi Direct device detects other devices in its vicinity, they exchange device information with each other and it also contains the process of device connection. Next, Group Operation covers all processes of communication after the group formation. In the case of power management, it defines two techniques: Opportunistic Power Save (OppPS) and Notice of Absence (NoA), to conserve power through the mobility of Wi-Fi Direct devices [1]. Though it indicates only basic rule and does not specify effective environment and the way of configuration for each parameter. In this paper, we have studied how to optimize the use of the setting parameter that sets the Wi-Fi Direct Power Save Mode(PS Mode). At first, it was focused on one PS Mode of Wi-Fi Direct defined by a standard document, the NoA parameter, which has more variables than the other. The NoA PS Mode has a variety of operations available according to four parameters: Start Time, Duration, Interval, and Count. It is possible to reduce the power consumption by controlling the Transmission Power Level (TPL) according to the channel condition, because the NoA parameter does not contain information about the wireless environment. To maximize this method, it ensures in the packet delivery that the Duration and Interval are dynamically adjusted according to the channel condition during power dissipation as far as possible. That is, it allocates the specified TPL in accordance with the channel condition. The NoA parameter is adjusted for the allocated TPL to control the active time according to the channel condition. As a result, it makes the corresponding channel condition ensure an effective transfer time. To verify the proposed method, a simulation was run on a simplest structure with two mobile devices, each GO and Client was connected to a 1:1 peer-to-peer network using Network Simulator-3, which is based on C++ in Linux OS. A specification of the power is referred to the Broadcom BCM4335 chipset. First, a higher transmission power level tends to increase the power consumption. The Count parameter of the NoA has a large impact on power consumption considering the channel conditions. Finally, compared with the results of the simulation, whether the proposed method is that the active time is dynamically modified or not, it enhances the power consumption by 3.34% when the proposed method is applied. In conclusion, it is necessary to determine an appropriate number of TPL depending on the channel condition and Count depending on the channel condition change frequency to decrease the power consumption by operating Wi-Fi Direct. Therefore, it could improve the efficiency of the PS Mode with NoA Protocol if the transmission power and Count are simultaneously controlled and the active time is dynamically modified

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