A new “subconscious mode” for smartphones and other
WiFi-enabled mobile devices could extend battery life by as much as 54% for
users on the busiest networks.
University
of Michigan computer
science and engineering professor Kang Shin and doctoral student Xinyu Zhang
will present their new power management approach at the ACM International
Conference on Mobile Computing and Networking. The approach is still in the
proof-of-concept stage and is not yet commercially available.
Even when smartphones are in power-saving modes and not
actively sending or receiving messages, they are still on alert for incoming
information and they’re searching for a clear communication channel. The
researchers have found that this kind of energy-taxing “idle
listening” is occurring during a large portion of the time phones spend in
power-saving mode—as much as 80% on busy networks. Their new approach could
make smartphones perform this idle listening more efficiently. It’s called
E-MiLi, which stands for Energy-Minimizing Idle Listening.
To find out how much time phones spend keeping one ear open,
Shin and 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 to 80% 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.
“My phone isn’t sending or receiving anything right
now,” Shin says, lifting his power-skinned iPhone, “but it’s
listening to see if data is coming in so I can receive it right away. This idle
listening often consumes as much power as actively sending and receiving messages
all day.”
Here’s how E-MiLi works: It slows down the WiFi 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 says, was getting the phone
to recognize an incoming message while it was in this slower mode.
“We came up with a clever idea,” Shin says.
“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% asleep.”
When used with power-saving mode, the researchers found that
E-MiLi is capable of reducing energy consumption by around 44% for 92% of
mobile devices in real-world wireless networks.
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.
Shin points out that E-MiLi is compatible with today’s
models, so messages sent with future devices that use E-MiLi’s encoding would
still be received as usual on smartphones without E-MiLi. E-MiLi can also be
used with other wireless communication protocols that require idle listening,
such as ZigBee.
The university is pursuing patent protection for the
intellectual property, and is seeking commercialization partners to help bring
the technology to market.
