Traffic Indication Map Broadcast for Wireless Power Saving
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Solution Overview
Problem
In wireless communications, stations in standby mode must frequently wake up to receive lengthy beacon frames to determine if an access point has buffered data, leading to increased power consumption and reduced battery life, especially in handheld devices.
Innovation Solution
The method involves transmitting a TIM frame independently of the beacon frame at a predetermined time, using multiple partial virtual bitmaps or multiple TIM frames at different data rates, and incorporating a check beacon indication to signify significant changes, allowing stations to wake up only briefly and efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If stations wake up frequently to receive beacon frames to check for buffered data, then data retrieval reliability is improved, but power consumption increases and battery life decreases
Solution Approach 1:
The beacon frame is segmented into two parts: a truncated version containing only essential information (TIM element) and a full version containing all information. Stations first receive the truncated beacon to check for buffered data, and only wake up for the full beacon if data is available. This segmentation allows stations to make quick decisions with minimal power consumption while maintaining reliable data retrieval when needed.
Solution Approach 2:
Stations perform a partial reception of the beacon frame by receiving only the truncated portion containing the TIM element. This partial action is sufficient to determine whether buffered data exists, allowing stations to avoid the excessive action of receiving the complete beacon frame when no data is present, thus reducing power consumption while maintaining data retrieval reliability.
2Loss of information
If stations receive complete beacon frames to ensure all information is obtained, then information completeness is improved, but the time stations must stay awake increases
Solution Approach 1:
The beacon frame information is segmented into a truncated version (essential information only) and a full version (complete information). Stations first process the truncated beacon to determine if buffered data exists. This segmentation enables stations to minimize wake time by making decisions based on essential information alone, while information completeness is preserved in the full beacon for when it is actually needed.
Solution Approach 2:
The truncated beacon containing the TIM element is transmitted preliminarily before the full beacon frame. Stations perform the critical check for buffered data during this preliminary transmission, allowing them to determine whether they need to remain awake for the complete beacon. This preliminary action significantly reduces the time stations must stay awake while ensuring information completeness when required.
3Adaptability or versatility
If beacon frames are transmitted at low data rates to ensure compatibility, then device compatibility is improved, but transmission time increases
Solution Approach 1:
The beacon transmission is segmented into a truncated version transmitted at low data rates for compatibility, and a full version that can be transmitted at higher data rates. The truncated beacon containing the TIM element is sent first at low rates to ensure all stations can receive it. This segmentation allows compatibility to be maintained for the essential portion while enabling faster transmission of additional information when needed.
Solution Approach 2:
The truncated beacon is transmitted preliminarily at low data rates to ensure universal compatibility and allow stations to determine the presence of buffered data. This preliminary low-rate transmission ensures all devices can participate in the network, while the structure allows for subsequent higher-rate transmissions of the full beacon when stations need complete information, thereby reducing overall transmission time.
Data Source
AI summary
Stations in standby mode periodically wake up to check for buffered data at the access points. Traditionally, the information is available by checking the periodic beacon frame for a traffic indication map (TIM). Unfortunately, the length of beacons has steadily increased with the progression of the various wireless standards requiring stations to wake up for longer periods to merely check for buffered data. Several approaches are disclosed which address this shortcoming, including the broadcast of TIM frames, the partial reception of beacon frames and the use of an embedded TIM frame within a beacon frame.