Wednesday, September 21, 2011

#WIRELESS: "Subconscious Smartphone Extends Battery Life"

A new subconscious mode for smartphones, announced at this week’s Mobile Computing and Networking conference, can improve battery life by more than 50 percent using the smarter algorithm. Savvy smartphone users know they can save battery life by switching off WiFi, but few take the trouble since it’s so convenient to just leave it at the ready to speed up Internet access. Now a new subconscious-mode could let smartphone users have their cake and eat it too.
Proposed by University of Michigan professor Kang Shin and prototyped by doctoral candidate Xinyu Zhang, smartphones and other devices with WiFi can license the new subconscious mode to extend smartphone battery life by as much as 50 percent.
WiFi speeds Internet connections by running orders of magnitude faster than typical 3G connections, convincing most smartphone users that it is worth leaving on so that acceleration is automatic whenever a familiar WiFi signal is detected. As a result, smartphones spend most of their time in what is called the "idle listening" mode, waiting for data-packets to arrive that could be transmitted by the nearest, strongest WiFi connection, as well as listening for incoming WiFi communication intended for it.
The team estimates that more than 90 percent of mobile devices with WiFi spend up to 80 percent of their time in idle mode today. The new subconscious mode, on the other hand, cuts power to the WiFi circuits until they are needed, then springs back to life before any data packets can be lost, greatly extending battery life without having to manually turn WiFi on and off.
The official name of the subconscious mode, coined by Shin and Zhang, is Energy-Minimizing Idle Listening (E-MiLi) and is being proposed by its inventors to original-equipment manufacturers (OEMs) of all types of WiFi equipped battery powered devices.
The techniques used by the researchers to achieve the savings was to down-clock the WiFi circuits by 16 times while they are in E-MiLi mode, then quickly ramp the clock speed back up whenever a packet arrives to be transmitted or when the smartphone's address is present in an incoming WiFi header. The outgoing activation was easy to achieve, according to Shin and Zhang, but detecting incoming packets while clocked down required custom algorithms that listen specifically for packet headers addressed to it.
To implement new E-MiLi mode, smartphone makers will have to add the algorithms for varying the WiFi circuits clock rate, plus WiFi chip-makers will have to adopt the new easy-to-recognize header structure that is recognizable even to down-clocked WiFi chips. Shin predicts that other wireless protocols, such as the industrial ZigBee wireless networks, will also adopt the technique to enable similar power savings on their mobile devices.

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