Beacon Timing Control for Fast Initial Link Setup
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Solution Overview
Problem
Current passive scanning techniques in IEEE 802.11 standards are too slow to meet the target delay for Fast Initial Link Setup (FILS) in wireless local area networks, as they typically require more than 100 milliseconds for AP/network discovery, which is not feasible with normal beacon intervals.
Innovation Solution
Adjusting the beacon transmission timing of access points to group their beacons together within a single inter FILS beacon duration, allowing stations to scan all nearby access points during this duration, thereby reducing the scanning time and meeting the target delay without introducing additional messaging traffic.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If normal beacon intervals are used for passive scanning, then stations can discover APs using standard IEEE 802.11 procedures, but the scanning time exceeds the target delay of less than 100 msec
Solution Approach 1:
The beacon interval is made dynamic by introducing a scaling factor that adjusts the interval based on the FILS beacon counter. The beacon interval transitions from a normal value to a shortened value as the counter increases, enabling the system to adaptively reduce scanning time while maintaining standard operation during normal conditions
Solution Approach 2:
Multiple beacons are pre-grouped within a single inter-FILS beacon duration before the scanning process begins. This preliminary grouping of beacons from multiple APs allows stations to discover all nearby APs in one scanning cycle, achieving the target delay of less than 100 msec
2Loss of time
If beacon transmission timing is adjusted to group beacons within a single inter FILS beacon duration, then scanning time is reduced to meet target delay, but beacon transmission timing synchronization becomes more complex
Solution Approach 1:
The system implements feedback through the FILS beacon counter, which tracks the number of beacons transmitted and provides information to subsequent APs about the current timing state. This feedback mechanism enables coordinated beacon grouping without requiring complex centralized control, as each AP can independently adjust its timing based on the counter value
Solution Approach 2:
Each access point independently adjusts its own beacon transmission timing based on the FILS beacon counter and the configured scaling factor. This self-service approach allows distributed timing synchronization without requiring complex inter-AP communication or centralized coordination, reducing overall system complexity
3Speed
If beacon intervals are shortened to meet target delay, then scanning speed increases, but normal beacon operations and network stability may be compromised
Solution Approach 1:
The beacon interval is made dynamic by introducing a scaling factor that adjusts the interval based on the FILS beacon counter. The beacon interval transitions from a normal value to a shortened value as the counter increases, enabling the system to adaptively reduce scanning time while maintaining standard operation during normal conditions
Solution Approach 2:
The shortened beacon interval is applied periodically only during the FILS initial link setup phase, as indicated by the FILS beacon counter. After the filtering period expires, the system returns to normal beacon intervals, ensuring that speed improvements are achieved only when needed without compromising long-term network stability
Data Source
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AI summary
A method of broadcasting a first beacon by an access point of a communications system includes obtaining transmission times for second beacons broadcast by nearby access points (block 505), and adjusting a transmission time for the first beacon in accordance with the transmission times for the second beacons to group the first beacon and the second beacons together within a single channel (block 520). The method also includes broadcasting an indicator of the transmission time for the first beacon to stations operating in the communications system (block 525), and broadcasting the first beacon at the transmission time for the first beacon (block 540).