by Bill Snyder

Smartphone ‘Subconscious’ Mode: The Key to Longer Battery Life?

Nov 02, 20123 mins
MobileSmall and Medium BusinessSmartphones

Even when your iPhone or Android phone is on standby it is still using power searching for communications channels and listening for messages. Now researchers have found a "subconscious" mode that keeps your phone aware of incoming message without draining the battery.

Wouldn’t it great if your smartphone’s battery could last 12 hours or more without a charge? Right now, the only way to achieve that sort of longevity is to put your phone into “airplane mode,” which means you won’t know if someone is calling or sending a text message.

But researchers at the University of Michigan are developing a novel tweak to how your phone handles Wi-Fi. Rather than just putting your phone to sleep, a state that actually uses a surprising amount of power, Professor Kang Shin says that a mode he calls “subconscious” would greatly reduce power consumption while allowing the phone to be aware of incoming messages. A technique called E-MiLi, or Energy-Minimizing Idle Listening, could extend the battery life of more than 90 percent of the phones on the market by as much as 54 percent, says Shin.   

You may not be aware of this, but when your smartphone is on standby and not actively sending or receiving messages, it’s still searching for a clear communication channel and that takes power. To find out how much time phones spend listening for messages, Shin and his research partner, doctoral student Xinyu Zhang, conducted an extensive trace-based analysis of real WiFi networks.


They discovered that, depending on the amount of traffic in the network, devices in power-saving modes spend 60 percent to 80 percent of their time in idle listening. In previous work, they demonstrated that phones in idle listening mode expend roughly the same amount of power as they do when they’re fully awake. (You can read their research paper here.)

A University of Michigan publication explained how E-MiLi works:

“It slows down the Wi-Fi card’s clock by up to 1/16 its normal frequency, but jolts it back to full speed when the phone notices information coming in. It’s well known that you can slow a device’s clock to save energy.”

The hard part, Shin said, was getting the phone to recognize an incoming message while it was in this slower mode.

“We came up with a clever idea,” Shin said. “Usually, messages come with a header, and we thought the phone could be enabled to detect this, as you can recognize that someone is calling your name even if you’re 90 percent asleep.”

Not surprisingly, there is a catch that will probably slow the adoption of this technology.

“In addition to new processor-slowing software on smartphones, E-MiLi requires new firmware for phones and computers that would be sending messages. They need the ability to encode the message header—the recipient’s address—in a new and detectable way.

“The researchers have created such firmware, but in order for E-MiLi use to become widespread, WiFi chipset manufacturers would have to adopt these firmware modifications and then companies that make smartphones and computers would have to incorporate the new chips into their products.”

Battery life has long been the Achilles heel of consumer technology. As laptops, tablets, and smartphones get bigger screens and greater processing power, they use much more power. But unlike the technology behind semiconductors, there is no Moore’s Law when it comes to batteries.

So when you’re waiting for your flight at the airport, you’re probably competing with other passengers to snag a power outlet that will let you charge up your devices before getting on the plane.

Technologies like E-MiLi may add a bit to the cost of your gadget, but the tradeoff would be more than worth it.

Image source: