Follow Us

We use cookies to provide you with a better experience. If you continue to use this site, we'll assume you're happy with this. Alternatively, click here to find out how to manage these cookies

hide cookie message

A guide to Wi-Fi power-save technologies

Cutting your mobile device's needs.

Article comments

Power management and battery-life conservation have been part of the IEEE 802.11 standard from its first release in 1997. Over time, the techniques and basic technologies involved have become more diverse.

We carried out a test of one such method, Power Save Mode, and found that the benefits were marginal to non-existent.

Power Save Mode is just one of a range of options, however. Here's a list of today's WLAN power-conservation technologies, but keep in mind that not all adapters will implement all of these choices, and specific implementations will vary:

Constantly Awake Mode (CAM). This is how most WLANs are operated today, with power-saving features disabled. This is partly because of fears about reduced performance in terms of throughput when power saving measures are enabled (as we saw in our testing), but such is also the default for most products shipped today, and users typically change few, if any, options of any form upon installation and initial configuration, and very seldom thereafter.

Power Save Mode (PSM). This is the original power-conservation technique defined in 802.11, and was tested in this article. The methodology is for the mobile device to suspend radio activity after a variable but pre-determined (by the vendor) period of inactivity, and then wake up periodically (usually about three beacon frames, which are normally 100 ms each) to see if the infrastructure has queued any traffic for it.

Unscheduled Automatic Power Save Delivery (U-APSD). This is an asynchronous approach to power conservation – defined in 802.11, and serves as the basis of WMM Power Save (below), allowing the client to request queued traffic at any time rather than waiting for the next beacon frame. This technique may thus be more efficient with lighter traffic loads, like voice.

WMM Power Save (WMM-PS). This technique is a product of the Wi-Fi Alliance and was introduced with the development of 802.11e and the corresponding Wireless Multimedia (WMM) specification. It is based on U-APSD, and is often implemented in Wi-Fi handsets. A scheduled (synchronous) version (S-APSD) is also defined.

Power Save Multi-Poll (PSMP). This approach is specified as part of 802.11n, and was developed because of concerns that MIMO-based products, using multiple radios and more circuitry regardless, would become power hogs with a significant adverse impact on battery life. An extension to U-APSD and S-APSD, the scheduled version reserves a time slot for a given client station and thus temporarily silences others associated. This technique may be better with relatively heavy traffic loads.

Dynamic MIMO Power Save. This technique allows MIMO-based (802.11n) radios to downshift to less-aggressive radio configurations (for example, from 2x2 to 1x1) when traffic loads are light.

Wake on Wireless. Atheros implements a technique in some of its WLAN chips that is not unlike the wake-on-LAN frequently seen in Ethernet adapters, allowing the infrastructure to initiate the waking of a dozing radio.

Wi-Fi protocol-related power-saving techniques are, of course, only one piece of the overall mobile power solution. Other elements include the use of low-power semiconductor process technologies and resulting components wherever possible, design engineering (boards and systems) with power consumption in mind, and improvements in batteries – although progress in this area has historically been slow. And, of course, other power-conservation variables like processor speed also must be taken into account.


Share:

More from Techworld

More relevant IT news

Comments



Send to a friend

Email this article to a friend or colleague:

PLEASE NOTE: Your name is used only to let the recipient know who sent the story, and in case of transmission error. Both your name and the recipient's name and address will not be used for any other purpose.

Techworld White Papers

Choose – and Choose Wisely – the Right MSP for Your SMB

End users need a technology partner that provides transparency, enables productivity, delivers...

Download Whitepaper

10 Effective Habits of Indispensable IT Departments

It’s no secret that responsibilities are growing while budgets continue to shrink. Download this...

Download Whitepaper

Gartner Magic Quadrant for Enterprise Information Archiving

Enterprise information archiving is contributing to organisational needs for e-discovery and...

Download Whitepaper

Advancing the state of virtualised backups

Dell Software’s vRanger is a veteran of the virtualisation specific backup market. It was the...

Download Whitepaper

Techworld UK - Technology - Business

Innovation, productivity, agility and profit

Watch this on demand webinar which explores IT innovation, managed print services and business agility.

Techworld Mobile Site

Access Techworld's content on the move

Get the latest news, product reviews and downloads on your mobile device with Techworld's mobile site.

Find out more...

From Wow to How : Making mobile and cloud work for you

On demand Biztech Briefing - Learn how to effectively deliver mobile work styles and cloud services together.

Watch now...

Site Map

* *