SleepWell for WiFi Puts Mobile Devices to Sleep to Conserve Power at WLAN Book.com

July 2nd, 2011

SleepWell for WiFi Puts Mobile Devices to Sleep to Conserve Power

by Zaib Kaleem

SleepWell for WiFi Puts Mobile Devices to Sleep to Conserve Power

“WiFi continues to be a prime source of energy consumption in mobile devices. This paper observes that, despite a rich body of research in WiFi energy management, there is room for improvement. Our key finding is that WiFi energy optimiza- tions have conventionally been designed with a single AP in mind. However, network contention among different APs can dramatically increase a client’s energy consumption. Each client may have to keep awake for long durations before its own AP gets a chance to send packets to it. As the AP density increases in the vicinity, the waiting time inflates, resulting in a proportional decrease in battery life.

We design SleepWell, a system that achieves energy efficiency by evading network contention. The APs regulate the sleep- ing window of their clients in a way that different APs are active/inactive during non-overlapping time windows. The solution is analogous to the common wisdom of going late to office and coming back late, thereby avoiding the rush hours. We implement SleepWell on a testbed of 8 Laptops and 9 An- droid phones, and evaluate it over a wide variety of scenarios and traffic patterns (YouTube, Pandora, FTP, Internet radio, and mixed). Results show a median gain of up to 2x when WiFi links are strong; when links are weak and the network density is high, the gains can be even more. We believe Sleep- Well is a desirable upgrade to WiFi systems, especially in light of increasing WiFi density.”

“We summarize SleepWell with an analogy. Big cities in the US and other countries face heavy rush hours due to masses of people commuting to office. If work times were flexible, dif- ferent companies could potentially stagger their office hours to reduce this rush. Reduced rush would open up more free time for all, and yet, the total working hours can remain un- affected. This intuition underlies the design of SleepWell.”