Wi-Fi Power saving and Exit strategy

[Woo-chan Kim]

Hello!!

When I'm reading carefully about the nRF7002 Power save operations, It's hard to understand about Power save Exit Strategy.

https://docs.nordicsemi.com/bundle/ncs-3.0.0/page/nrf/protocols/wifi/station_mode/powersave.html

In the SDK, The code is written like this. (v2.6.4)

/**
 * Wi-Fi power save exit strategy
 */
enum wifi_ps_exit_strategy {
	/** QoS NULL frame based */
	WIFI_PS_EXIT_EVERY_TIM = 0,
	/** Uses a proprietary combination of PS-Poll and QoS-Null/Null */
	WIFI_PS_EXIT_CUSTOM_ALGO,

	/** Last value */
	WIFI_PS_EXIT_LAST,
	/** Maximum value */
	WIFI_PS_EXIT_MAX = WIFI_PS_EXIT_LAST - 1,
};

First Question,

my understanding is  EVERY_TIM means that wifi is waken by every TIM.
but, there is some confusing thing that Listen Interval Parameter.

In the document, the interval means how many TIM needs for wake up to get QoS Data.

can you explain more about this?

Second thing is the relationship between exit strategy and power save mode.

In the documents, Legacy Save Mode uses PS-Poll, but WMM uses Qos-NULL.
however exit strategy has same keyword about this.

In the document, it has no detail description about exit strategy.

Can you give more detail information?

[Susheel Nuguru]

Woo-chan, I am not an expert in this but I have some interpretation of some standard power saving and exit modes described in the spec.

Listen Interval is simply “how many beacons I’ll sleep through before I wake up and check for traffic.” If you set it to 1, the chip wakes on every beacon (about every 100 ms). If you set it to 5, it sleeps through four beacons and only wakes on the fifth.

EVERY_TIM says “whenever I do wake up for a beacon, I’ll immediately send a single ‘I’m here , do you have data?’ frame and pull in everything the AP has buffered.”

In WMM-PS mode that frame is a QoS Null.
In Legacy PS mode it becomes a PS-Poll under the hood.

“Listen Interval” controls when you wake.
“EVERY_TIM” controls how you exit sleep on each wake and grab your data.

The exit strategy you pick just chooses which frame style you use on every wake. EVERY_TIM - one QoS-Null (WMM) or PS-Poll (Legacy) per wake, then go back to sleep or stay up as needed. CUSTOM_ALGO - Nordic’s tuned mix of PS-Poll calls and QoS-Nulls, optimized to reduce overhead during heavy traffic.