Controlling Wi-Fi Radio 'Nap-Time' Saves Power

alphadogg writes "A Duke University grad student has come up with a way to double (or more) battery life in Wi-Fi devices, without any changes needed on the device itself. Essentially, the technique regulates how long and when client radios sleep (PDF), so that data transfers can be scheduled more efficiently. In a test using eight laptops and nine Nexus One Android-based smartphones on an 802.11n network, the researchers found that the scheduling technique, dubbed SleepWell, resulted in energy reductions of 38% to 51% across a variety of online applications, including YouTube, Pandora and Last.fm Internet radio, and TCP bulk data transfers. What's more, they found that as the quality of radio links degrades, the relative energy gains are even higher."

Re:double?

[mwvdlee]

If it's a 51% reduction in power usage, then it would be about a 204% increase in battery life.
I know it's not exactly double, but really, I think you're being a bit harsh here.

Re:enlighten me

[TheRaven64]

I didn't RTFA, but it seemed to be talking about transmit not receive. Generally, transmitting takes a lot more power than receiving. At the TCP level, you need to send an acknowledgement for every group of packets that's been received. If you increase the window size, you send these less frequently. Rather than sending the acknowledgement every n packets, you'd send two acknowledgements every 2n packets. More importantly, if you are downloading over two TCP connections at once, then you can send the replies to both in the same transmit window, so the transmitter is active for a slightly longer time once, rather than a slightly shorter time twice.