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Green computing: do Wi-Fi power saving adaptors work?

We put their power-saving consumption rates to the test

Many Wi-Fi adaptors claim to have power-conservation capability. We set out to test just how useful they are.

Our test procedure involved first establishing a baseline for performance in terms of throughput. We then repeated the test with each Wi-Fi client adaptor/access point pair, in each case the only variable being the changing of the level of client Wi-Fi power conservation. Both laptops kept the hard drive on all the time, and the Acer was set to 50 percent display brightness while the HP's display was kept all the way up. We used a spectrum analyser to monitor for any high-amplitude interference that might affect results throughout all test runs, and none was observed.

Less than satisfying results

What jumps out almost immediately from this data is that PSM in any form delivered very little in terms of additional run time, and occasionally had a major detrimental impact on throughput.

The best improvement in runtime that we saw was a little over 8 percent in the case of the Linksys AP/Linksys adaptor running on our HP laptop with PSM enabled. That said this combination also simply decimated throughput to less than half that of the CAM case. Interesting, this same combination of gear with 'Fast' PSM enabled still resulted in 4 percent better run time and yielded a 0.5 percent gain in throughput.

Overall, though, it was clear that PSM was not contributing to significantly longer runtimes, and thus appears to have a negligible impact on laptop battery life. Moreover, in most cases, throughput was adversely affected and, where it was not, no real benefit was noted.

And the reason for this is the relatively large amount of power consumed in modern laptops in comparison with the energy used by today's Wi-Fi adaptors.

The 802.11 standard was initially developed during a time when processor clocks were in the 100MHz to 200MHz range, and initial WLAN designs involved a significant number of power-hungry components. Today, however, Wi-Fi adaptors are highly integrated - meaning fewer chips are required to implement a Wi-Fi solution - and designs are more power-efficient. While the laptops' other components, most notably the processor (because of higher clock rates) and display and backlighting (due to much higher resolutions) - often consume more energy than in the past.

Laptop designers have compensated with larger batteries and a continual emphasis on power-conservative designs and provisions for a high degree of end-user control over power conservation settings in many cases, but the proportion of energy consumed between the computer and the WLAN adaptor has clearly flipped.

NEXT PAGE: Our verdict on power saving Wi-Fi adaptors

  1. We put power-saving consumption rates to the test
  2. Test configuration and procedures
  3. How power-saving adaptors fared in our test
  4. Our verdict on power saving Wi-Fi adaptors

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