Performance Evaluation and Optimization of Wi-Fi Display on Android

Abstract

In the mobile networking environment, there is an increasing need for different devices such as computers, smartphones, and smartTVs to interact with each other. One popular type of interaction is screencast (or remote display), where the content on one device’s display appears (synchronously) on another device. To facilitate this type of application, several standards have been proposed, from earlier DLNA (Digital Living Network Alliance), to Airplay by Apple, and Wi-Fi Display by Wi-Fi Alliance more recently. One distinct yet challenging requirement for screencast is synchronicity. However, despite the increasing popularity of screencast and the related standards, their performance metric has received little study. In this paper, we take Wi-Fi Display and its implementation on Android as our target, and perform an in-depth study on its performance. This evaluation identifies an important bottleneck arising from the interactions among a couple of asynchronous threads. From these findings, we propose an event-driven mechanism that shortens the latency among the relevant threads. The experimental evaluation indicates a 20 % reduction on total processing time on screencast at the Source device side, which proves the effectiveness of this new mechanism. In addition, our evaluation also identifies encoding of frame content as another major source of latency. This finding means that we either need more powerful video/image encoding hardware, or an encoding standard that takes computation requirement as a more important metric than compression ratio.