Wireless computing power-saving measures may not be worth the effort

Power Save Mode may leave you powerless

One of the challenges in mobile computing is battery life. It's hard to be productive with a dead battery, so IT personnel and users alike need to think about maximising run time between charges.

Optimising the power conservation settings of a mobile computer or communicator, including dimming the display when on battery, turning off the display and hard drive after a pre-set period of time, suspending (keeping memory alive but the computer otherwise powered down) and hibernating (writing the image of main memory to disk for later resumption) help in getting the most out of any given charge.

And there are also power conservation settings in most Wi-Fi adapters that (at first glance, anyway) are intended to allow a high degree of control over the power consumed by the wireless network interface card (NIC) found in almost all notebooks and many handhelds as well. In gross terms, wireless power conservation involves turning off the radio, synchronously or asynchronously with the fixed infrastructure, for a portion of time — a technique used in various forms on essentially all production wireless systems today, including WANs. But this technique motivates an interesting and fundamental question: do Wi-Fi power-conservation techniques, when enabled, actually save a meaningful amount of energy or have any negative impact on throughput?

We set out to define a simple test to answer these questions as they pertain to 802.11's Power Save Mode (PSM), the most common form of Wi-Fi power saving implemented today. We do note that there are several new power saving mechanisms defined for 802.11n gear, but we have not found those to be widely implemented, so we could not assess those at this juncture.

Vendors have delivered a number of PSM variants, with the primary difference being how quickly and how often the adapter wakes up. Having a NIC wake up faster could negatively affect power consumption, the fundamental tradeoff in this strategy, although this could theoretically improve throughput. The opposite of PSM is Constantly Awake Mode (CAM), in which PSM is disabled. Our test compared various forms and implementations of PSM against CAM and, for good measure, a wired Gigabit Ethernet baseline test.

Using PSM in our tests produced only a marginal benefit in terms of battery life (and was even slightly worse than CAM in one test). In terms of throughput, the results ranged from marginally positive to having a very negative impact on throughput in two cases tested

Bottom line: PSM isn't likely to be of any value in contemporary implementations, and may even hurt performance.

We contacted all vendors whose products were included in this test regarding the results. Only Broadcom's PR department would comment, saying that its internal testing showed that battery life gains from PSM implementations in notebooks varies between brands, sometimes showing that PSM can maximize battery life with no impact on throughput.

Join the Good Gear Guide newsletter!

Error: Please check your email address.

Our Back to Business guide highlights the best products for you to boost your productivity at home, on the road, at the office, or in the classroom.

Keep up with the latest tech news, reviews and previews by subscribing to the Good Gear Guide newsletter.

C.J. Mathias

Network World
Show Comments

Most Popular Reviews

Latest News Articles

Resources

PCW Evaluation Team

Azadeh Williams

HP OfficeJet Pro 8730

A smarter way to print for busy small business owners, combining speedy printing with scanning and copying, making it easier to produce high quality documents and images at a touch of a button.

Andrew Grant

HP OfficeJet Pro 8730

I've had a multifunction printer in the office going on 10 years now. It was a neat bit of kit back in the day -- print, copy, scan, fax -- when printing over WiFi felt a bit like magic. It’s seen better days though and an upgrade’s well overdue. This HP OfficeJet Pro 8730 looks like it ticks all the same boxes: print, copy, scan, and fax. (Really? Does anyone fax anything any more? I guess it's good to know the facility’s there, just in case.) Printing over WiFi is more-or- less standard these days.

Ed Dawson

HP OfficeJet Pro 8730

As a freelance writer who is always on the go, I like my technology to be both efficient and effective so I can do my job well. The HP OfficeJet Pro 8730 Inkjet Printer ticks all the boxes in terms of form factor, performance and user interface.

Michael Hargreaves

Windows 10 for Business / Dell XPS 13

I’d happily recommend this touchscreen laptop and Windows 10 as a great way to get serious work done at a desk or on the road.

Aysha Strobbe

Windows 10 / HP Spectre x360

Ultimately, I think the Windows 10 environment is excellent for me as it caters for so many different uses. The inclusion of the Xbox app is also great for when you need some downtime too!

Mark Escubio

Windows 10 / Lenovo Yoga 910

For me, the Xbox Play Anywhere is a great new feature as it allows you to play your current Xbox games with higher resolutions and better graphics without forking out extra cash for another copy. Although available titles are still scarce, but I’m sure it will grow in time.

Featured Content

Latest Jobs

Don’t have an account? Sign up here

Don't have an account? Sign up now

Forgot password?