As we experience the ramp-up of Wi-Fi-enabled handsets, it would seem that 802.11 power-save features would be growing increasingly important.

International researcher Infonetics describes dual-mode Wi-Fi/cellular VoIP devices as the fastest growing segment in the mobile phone market and forecasts a five-year compound annual growth rate of 198% from 2006 to 2010. And the Wi-Fi Alliance says it has certified nearly 100 Wi-Fi-enabled phones (single-mode and dual-mode combined) for basic Wi-Fi interoperability.

Battery-conservation potentially has a large role to play in these small, power-challenged devices. Yet where are the Wi-Fi-certified, power-save-enabled phones?

The Wi-Fi Alliance began certification testing for standard power-saving capabilities in late 2005. However, according to the industry consortium’s Web site, the NEC FOMA N902IL used in Japan is the only Wi-Fi-enabled phone that the alliance has certified for what it terms Wireless Multimedia (WMM) Power Save—the power conservation extension to the 802.11e QoS standard.

The Wi-Fi Alliance’s FAQ page estimates that WMM Power Save can provide from 15% to 40% improvement in battery life, which certainly sounds compelling. It’s not clear if these numbers apply to Wi-Fi phones, though, given that only one phone of record has been certified.

For the power-conservation capabilities to work, both access points (AP) and client devices must be “power save-aware.” The capability allows client devices to “doze” in receive-only mode between transmissions and thus conserve battery life. In addition, applications need to support WMM Power Save to inform the client of the requirements of the traffic they generate.

According to the Wi-Fi Alliance’s Web site, the only enterprise-class wireless LAN systems vendor to support Wi-Fi-certified power save in its APs today is Cisco. It would seem that Cisco’s motivation might stem from the fact that it is also a maker of Wi-Fi phones—except that Cisco 7920 Wi-Fi handsets have not yet been power-save certified.

Granted, the WMM Power Save feature is an option to the standard. However, if you are eyeing voice-over-Wi-Fi communications, investigate and otherwise test the battery issues with any devices you might choose. Discuss the merits and tradeoffs of WMM Power Save with your vendor, as well as your vendor’s plans to support it in small devices.

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