自從WFA 組織提出了Wi-Fi P2P 模式之後, 愈來愈多的P2P 應用也開始產生.
在Wi-Fi P2P 中, P2P 並不需要傳統AP 的存在就能運作, Group Owner 扮演的
就是Legacy Wi-Fi 中AP 的角色, 而Group Owner 也負責管理Group 中與Client
端的連線. 要延長供電時間有限的可移植裝置的壽命在Legacy Wi-Fi 中一直都是
個議題. 而在P2P 中這個問題變得更加的重要, 因為有大量的P2P 應用都是運作
在可移植且電量有限的裝置上. 目前P2P 中效能不彰的控制方式會導致P2P 網路
中Group Onwer 的功率大幅的下降. 本文針對P2P 提供兩個功率控制的機制, 透
過動態蒐集可用的資訊, 例如: 接收的訊號強度與重試的次數, 來完成此項設計. 我
們首先設計一種以Threshold-Based 的機制當作基礎, 透過它來限制連線中重試的
最大次數以減少不必要的功率消耗. 但是, 由於還考量到無線網路環境狀態的變化,
因此再提出另一種自適應功率控制的機制來減少連線中頻繁的重試. 除此之外, 我
們還建立了實驗, 在Nexus7 裝置上實作這兩種機制並量測出這他們的效能. 而實
驗結果顯示出我們的機制很明顯的讓功率消耗變低且讓P2P 連線的功率使用變得
更加有效率.

By enabling device-to-device communications without the presence of a Wi-Fi Access Point (AP) in Wi-Fi, Wi-Fi Peer-to-Peer (P2P) successfully embraces a wider set of applications and use cases. In particular, the P2P group owner (GO) plays the role of the AP and is responsible of managing connections with P2P group client (GC). To extend the lifetime of power-limited portable devices, power control have been carefully examined in legacy Wi-Fi environment. This issue becomes more critical since Wi-Fi P2P GO now is equipped with power-limited battery, and inefficient power control will lead significant power drop on both Wi-Fi P2P GO and GC. By leveraging the information of connections such as received signal strength and retry
count, this paper proposes two novel power control mechanisms for Wi-Fi P2P connections.
We first design a threshold-based mechanism as the baseline, which could
limit the maximum number of connection retries to eliminate unnecessary power consumption. However, considering the dynamic change of wireless condition, an adaptive power control mechanism is consequently proposed to decrease the negative effects of a busy loop for retries. We establish an intensive experiment by practically implementing both mechanisms in the Andriod system over Nexus 7, in order to evaluate the performance of proposed mechanisms. The experiment results show that the adaptive mechanism can significantly decrease the power consumption and thus makes Wi-Fi P2P connection more efficiently.

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