WLAN Power Save

WiFi 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 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 the 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:

 

  1. Legacy Power Save Mode – Client sends UL data and waits for some time. It indicates 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

 

  1. 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 to the WiFi 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 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 power save feature in the lab. Now that challenge is solved too…

 

YES!! SWAT WiCheck can give you 100s of WiFi clients that support legacy and WMM power save

 

SWAT WiCheck is a modular and programmable multi-client simulator that can scale from 10s of clients to 1000s, 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.  

 

For more information on WiCheck, please visit https://alethea.in/wifi-test-equipment/

 

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