Nowadays, wirelessly connected mobile devices are present almost everywhere at any time. Apart from other available wireless technologies, IEEE 802.11 seems to be the de-facto standard for wireless communications, being supported in millions of devices.
Although several mobile devices have Internet access through mobile operator networks, performance limitations on the support of highly demanding multimedia applications enabled novel and hybrid communication paradigms (e.g. offloading) where IEEE 802.11 plays an important role.
In this context, energy consumption issues of battery-supported devices need to be addressed. In particular, since the Android platform is responsible for a large part of the mobile device market growth, IEEE 802.11 energy management mechanisms in this platform should be carefully investigated.
This work studies and compares, using a real testbed, the most popular IEEE 802.11 power saving techniques implemented on the Android platform. Additionally, in this paper, an Android framework for Extending Power Saving control to End- users (EXPoSE) is proposed, aiming at improving the devices’ energy efficiency by considering end-users demands.
The most popular power saving mechanism for IEEE 802.11 network interfaces is the Power Save Mode (PSM), usually referred to as Legacy-PSM. When operating in Legacy-PSM, this mechanism is usually associated with higher delays, the last generation of mobile devices addressed the problem by implementing an adaptive mechanism to switch faster between awake and sleep modes, commonly named Adaptive-PSM.
In Android, the Adaptive-PSM implementation switches between awake and sleep modes depending on the network traffic, allowing the IEEE 802.11 interface to stay awake only when there is traffic. The Adaptive-PSM implementation in Android devices does not consider traffic type and importance when switching between awake and sleep modes, leading to several unnecessary switches to awake mode.
The EXPoSE framework we propose was implemented as an Android service (EXPoSE Service), plus a lower level control module included in the Android kernel. This module allows the IEEE 802.11 power saving functions to be exposed to higher level layers, enabling better control of power states.
To enable generic communication with the IEEE 802.11 driver, the developed Android kernel module is composed of two distinct components: the “Kernel End-Point” and the “Kernel End-Point Listener”. The communication between the kernel end-point and the driver is performed through the proposed kernel end-point listener. Such abstraction plays an important role concerning energy efficiency, since, although the listener is always active, it is waiting in a semaphore and does not perform any additional processing (with extra energy costs).
The achieved results showed that EXPoSE approaches, namely the pattern-based and the maximum allowed delay, are more energy efficient than both Legacy-PSM and Adaptive-PSM schemes.
Depending on the scenarios and applications requirements, the EXPoSE energy savings, compared to Adaptive- PSM, can go up to 23.53% without violating the application delay constraints. Moreover, if some additional delay is acceptable (e.g., only 75% of the pack- ets arriving on time), the energy savings can be more than 50%, compared to Adaptive-PSM.
Furthermore, the obtained results depicted the EXPoSE capabilities to improve continuous media applications energy efficiency, which is not well supported by Legacy-PSM and Adaptive-PSM strategies.
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