WLAN Power Management via TIM Expansion and APSD Service Periods
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Solution Overview
Problem
Conventional WLAN power save mechanisms face inefficiencies, including simultaneous wake-ups of multiple stations leading to traffic delays and increased power consumption, inadequate handling of delay/jitter quality-of-service requirements, and inefficient retrieval of non-periodic bursty traffic.
Innovation Solution
The proposed solution expands the definition of the Traffic Indication Map (TIM) to include both legacy power save and unscheduled APSD methods, allowing stations to determine buffered frames without waking up for beacons and using QoS Data/Null frames for unscheduled APSD, and schedules service periods for scheduled APSD to minimize overlap and reduce awake time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If stations wake up to receive beacons and check TIM for buffered frames, then downlink frames can be delivered to power-saving stations, but multiple stations waking up simultaneously causes traffic delays and increased power consumption
Solution Approach 1:
The patent segments the downlink frame delivery process into two distinct mechanisms: legacy power save mode (using TIM/PS Poll) for traditional traffic, and unscheduled APSD mode (using QoS Data/Null frames) for bursty traffic. This segmentation allows stations to choose appropriate delivery methods based on traffic characteristics, reducing simultaneous wake-ups and associated delays.
Solution Approach 2:
The patent introduces dynamic service periods in unscheduled APSD mode where the AP can immediately transmit buffered frames when a station wakes up with uplink traffic, rather than waiting for the next beacon interval. This dynamic adjustment of delivery timing reduces traffic delays while managing power consumption efficiently.
2Productivity
If stations wake up at every beacon interval to check TIM, then buffered frames can be retrieved, but power consumption increases due to frequent wake-ups
Solution Approach 1:
The patent implements partial action by allowing stations to wake up only when necessary - either to receive TIM in legacy mode or to initiate unscheduled APSD service periods. Stations using unscheduled APSD can remain asleep longer and wake up only when they have uplink traffic to send, reducing unnecessary wake-ups and power consumption while still enabling frame retrieval.
Solution Approach 2:
In unscheduled APSD mode, stations self-initiate the frame retrieval process by sending QoS Data/Null frames when they wake up with uplink traffic. The AP then automatically delivers buffered downlink frames during the service period without requiring additional station actions, enabling energy-efficient self-service frame retrieval.
3Ease of operation
If legacy power save method is used with TIM and PS Poll, then power-saving operation is maintained, but handling of delay/jitter quality-of-service requirements is inadequate
Solution Approach 1:
The patent applies local quality by providing different power save mechanisms tailored to different traffic types: legacy power save mode (TIM/PS Poll) for traditional traffic patterns, and unscheduled APSD mode for traffic requiring better delay/jitter QoS. This localized optimization allows each traffic type to use the most appropriate mechanism, maintaining power savings while improving QoS where needed.
Solution Approach 2:
The patent changes key parameters of the power save mechanism by introducing unscheduled APSD service periods with immediate frame delivery capability. This parameter change (from fixed beacon-interval-based delivery to flexible on-demand delivery) improves delay/jitter QoS while maintaining power-saving operations through selective wake-up based on uplink traffic.
4Use of energy by moving object
If stations use scheduled APSD with service periods, then power consumption is reduced by minimizing awake time, but overlap between service periods of multiple stations increases
Solution Approach 1:
The patent segments the channel access mechanism into scheduled APSD service periods for power-efficient operation and unscheduled APSD service periods for immediate response. This segmentation allows the system to manage service period overlaps by directing traffic to appropriate segments, reducing coordination complexity while maintaining power savings.
Solution Approach 2:
The patent introduces the unscheduled APSD mechanism as an intermediary that handles cases where scheduled service periods overlap or conflict. When stations have urgent uplink traffic, they can initiate unscheduled service periods that immediately resolve potential overlaps, simplifying the coordination of scheduled service periods while maintaining power efficiency.
Data Source
AI summary
A method of providing power management in a Wireless Local Area Network (WLAN) is presented. The method includes receiving a Traffic Indication Map (TIM) at a station, indicating the presence of buffered frames, associated with any AC, for the station at an Access Point (AP). The method further includes sending, by the station, one of an uplink data frame if one is buffered, and a null frame to retrieve the buffered frames from said AP. The station remains awake to receive frames from the AP until a downlink frame is received containing an indication that it is the last frame to be transmitted in the service period. The method may further include determining at the end of service period whether there are more frames remaining buffered for the station at the AP.