Understanding WLAN Power Save Mode

WLAN Power Save

Wi-Fi has been adopted for a variety of devices addressing various use cases. Many of these applications require the devices to conserve power as much as possible. For example, mobile phones should reduce the total power used so that they can last from charge to charge. Maintaining a connection to the Access Point at all times and servicing consumer & enterprise applications over that link can run the battery down significantly. In order to reduce the issue of battery drain, IEEE introduced WLAN Power Save Mode as part of the 802.11 spec.

Power Save Mode is an important feature for end users to save their battery power and use the device for extended hours. It allows the devices to switch between active and sleep states to conserve energy.

Power Save Standards

Power save is classified into two:

• Legacy Power Save Mode?

The client sends UL data and waits for some time. It indicates to the Access Point that it is going to be in a sleep state if no transmission/reception has happened during this interval. The Access Point buffers frames while asleep, then lets the client know that frames are buffered via a beacon.

• Unscheduled Automatic Power Save Delivery (U-APSD)?

A QoS facility that extends the battery life of mobile devices. This feature reduces the latency of traffic flow delivered over the wireless media. Legacy Power Save Mode doesn’t give any gain if the data is of periodic and bi-directional nature (VoIP/ Video Calls). U-APSD is beneficial in these scenarios.?

Power Save Mechanism

• The client will achieve power savings when it goes into sleep mode after it indicates to the access point that it is entering power save mode and shuts down its receive path.
• The Access Point stores frames intended for the Wi-Fi client device in power save mode and sends them to the device whenever requested to do so.
• During association, the client uses the Listen Interval parameter to indicate to the Access Point how many beacon intervals it will sleep before it retrieves the queued frames from the Access Point.
• The Access Point shall not drop any queued frames until the device’s Listen Interval elapses.

Simulating WLAN Power Save Clients

?To assure customers of continuous & extended hours of use, mobile devices have to overcome battery issues during usage. Hence, most of the battery-powered devices come with a power save mode feature (legacy power save across all devices & WMM power save in many of the more expensive ones, especially MACs and iPhones). To test Access Points for power save support, the biggest challenge is to simulate clients with the power save feature in the lab. Now that challenge is solved too…

YES!! WiCheck- Univeral Wi-Fi Testing Solution can give you 100s of Wi-Fi clients that support legacy and WMM power save

WiCheck is a modular and programmable multi-client simulator that can scale from 10s of clients to 1000s, and behave like real users. All this in a quiet dual-band capable box small enough to sit on every developer’s desk. It’s easy to generate clients with legacy and WMM power save options using WiCheck. ?

In the next blog, we will go deeper into how you can do these tests to validate power-saving features at scale in access points.

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