DFS Neighbor Lists for Roaming Delay Reduction
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Solution Overview
Problem
In wireless networks, the need for continuous channel availability checks to avoid interference with radar transmissions in the 5.25-5.75 GHz band leads to delays in client roaming, particularly for mobile clients, which can impact real-time traffic such as voice or video calls.
Innovation Solution
The implementation of a wireless network infrastructure that generates and maintains neighbor lists with Dynamic Frequency Selection (DFS) enabling bits, allowing clients to perform active scanning without prior channel availability checks on channels confirmed to be radar-free, and dynamically updates these lists to ensure regulatory compliance and minimize channel move times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wireless clients perform passive scanning to receive beacon transmissions for channel availability checks, then regulatory compliance is ensured, but roaming delays increase due to waiting for beacon periods (up to 100 ms or longer)
Solution Approach 1:
The access point performs the channel availability check and radar monitoring in advance before the client needs to roam. The AP determines channel suitability and prepares enabling signals beforehand, so when the client initiates roaming, the channel status is already known and the client can switch immediately without performing its own time-consuming passive scan.
Solution Approach 2:
The access point acts as an intermediary that performs the channel availability check on behalf of the client. Instead of the client directly scanning and waiting for beacons, the AP monitors the channel, determines radar presence, and communicates the enabling status to the client, thereby eliminating the client's scanning delay.
2Speed
If wireless clients perform active scanning to quickly find neighboring access points, then roaming speed improves, but channel availability checks must still be performed which negates the speed benefit
Solution Approach 1:
The access point performs the channel availability check in advance and includes the result in the enabling signal. When the client performs active scanning and receives this enabling signal, it already knows whether the channel is available, eliminating the need for the client to perform its own channel availability check after scanning.
Solution Approach 2:
The access point serves as an intermediary that transfers channel availability information to the client through the enabling signal. This allows the client to rely on the AP's monitoring results rather than performing redundant channel checks, preserving the speed advantage of active scanning.
3Reliability
If wireless access points continuously monitor the spectrum for radar transmissions, then regulatory compliance is maintained, but system complexity and energy consumption increase
Solution Approach 1:
The access point performs self-service by autonomously monitoring the spectrum for radar transmissions and automatically determining channel availability. The system uses standardized protocols and algorithms to perform DFS (Dynamic Frequency Selection) without requiring external intervention, reducing operational complexity while maintaining compliance.
4Reliability
If wireless clients wait for beacon transmissions during passive scanning, then channel availability is confirmed, but real-time traffic such as voice or video calls experiences interruption
Solution Approach 1:
The access point determines channel availability in advance and communicates this information to the client through the enabling signal before the client needs to switch channels. This preliminary confirmation eliminates the waiting period during real-time traffic, preventing interruptions in voice or video calls.
Solution Approach 2:
The access point acts as an intermediary that provides channel availability information to the client without requiring the client to interrupt its real-time traffic for scanning. The enabling signal conveys the necessary information asynchronously, allowing continuous real-time communication while maintaining channel compliance.
Data Source
AI summary
A wireless access point selection system. In particular implementations, a method includes receiving a notification that identifies a wireless access point that detects radar on an operating channel and identifies the operating channel; updating neighbor lists of one or more neighboring wireless access points to remove the wireless access point from the neighbor list, where the neighbor list comprises neighbor wireless access points, corresponding operating channels, and corresponding enable indications, where each enable indication indicates if a channel availability check is required before performing active scanning; and transmitting the updated neighbor list to the neighboring wireless access points. In one implementation, a system provides a DFS enable indication to wireless clients so they can know whether a channel availability check is required prior to transmitting.