Boffins crack smartphone Wi-Fi for greater battery life
Juice magicians
Researchers have worked out another method for dramatically boosting a smartphone's battery life, by devising a new "subconscious" mode of operation.
A couple of boffins from the University of Michigan have created a conceptual system called E-MILi, or Energy-Minimalising Idle Listening, that looks at the energy wasted when sleeping phones are checking for incoming messages. According to the team, E-MILi could extend battery life by up to 54 per cent.
Through an extensive trace-based analysis of real Wi-Fi networks, Professor Kang Shin and doctoral student Xinyu Zhang discovered that depending on the amount of traffic traversing the network, devices in power-saving mode spend roughly 60 to 80 per cent of their time in idle listening - looking to see if data is coming in so it can be received immediately.
Previous work has apparently shown that phones in this state, generally consume the same power as when they're fully awake.
However, E-MILi slows down the Wi-Fi card's clock by up to one-sixteenth its normal frequency and only jolts back to full speed when the phone notices incoming information. With the phone running at such low speeds, the hard part is getting it to recognise when a message is on the way, though.
The team therefore proposes that Wi-Fi chipset manufacturers tweak their firmware to encode the message header - the recipient's address - in a new detectable way. With E-MiLi chips onboard, handsets would then be able to detect the information, without staying in the battery-draining idle listening mode.
To get manufacturers of handsets and those of Wi-Fi chipsets to both adopt the new tech, might be a hard ask, especially when there are many other methods of battery saving technology out there to compete with. But the potential is most certainly there.
The new power management approach will be demonstrated on Wednesday, 21 September at the ACM International Conference on Mobile Computing and Networking. ®
COMMENTS
Look ... it's here ...
http://www.theregister.co.uk/2011/09/16/boffins_boost_battery_life_underclocking_wifi/
other technologies build this in from the start
Digital cellular technologies like GSM and CDMA all knew about this user device battery drain problem when they were designing the network standards. In CDMA it is called "slotted mode", where the network and handset agree how often to send out notifications. By doing that at prearranged times it allows the handset/chipset to drop into deep sleep for a second or so, and only wake up for milliseconds at a time to listen for its name to be called. Tremendous savings in battery power.
It seems that Wi-Fi didn't built it in, so these guys had to find a way to duct-tape one into it?
Anything that helps practically extend battery life works for me.
Well done lads.
??
Their power figures for the stations are way off. RX is definitely much lower than TX. The largest power consumer is the power amp not the ADC.
I think this is a desktop card they have analysed, and these are non optimised for power consumption.
Also this seems to be only for directed packets, and "idle listening" is mostly with non directed packets. Carrier sense is only required before a TX when medium contention occurs. Here also RX can be killed after preamble detection.
So while there is an advantage, the benefit don't seem to be worth the effort, especially as the device is not 802.11 PHY compliant anymore. It can work with older stations, but this is not guaranteed. Those M-preambles before the frame violate the timing.
