Fuzzy Logic WLAN Handover for Reduced Delay and Packet Loss
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Solution Overview
Problem
The existing wireless local area network (WLAN) handover mechanism is inefficient due to single handover mechanisms that cannot adapt to different handover circumstances, leading to prolonged handover delays and packet loss in critical systems like CBTC train-ground communication.
Innovation Solution
A WLAN handover method based on fuzzy rules, where the mobile station receives and processes signal strength and change rate data from current and adjacent access points using fuzzy control and reasoning to determine the optimal handover mode, allowing for adaptive handover decisions and reducing scanning delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional scanning phase is used for handover, then the mobile station can detect available access points, but the handover delay is prolonged due to scanning time requirements
Solution Approach 1:
The mobile station performs preliminary scanning operations before the actual handover is triggered. The scanning phase is executed in advance to detect available access points and prepare handover information, so that when handover becomes necessary, the mobile station can quickly switch without performing a full scanning procedure, thus reducing handover delay while maintaining detection reliability
Solution Approach 2:
The patent applies different scanning strategies to different spatial locations and signal conditions. When the mobile station is in a stable coverage area with strong signal, it reduces scanning frequency to save time. When approaching coverage boundaries or detecting signal degradation, it intensifies scanning locally to detect alternative access points, optimizing the balance between detection reliability and time consumption
2Loss of time
If active scanning mode is used instead of passive scanning, then the scanning delay is reduced, but the power consumption increases
Solution Approach 1:
The patent dynamically switches between passive and active scanning modes based on real-time conditions. The mobile station monitors signal strength and handover likelihood, and only activates active scanning when necessary (e.g., when signal degradation is detected or handover probability is high). This dynamic adaptation reduces overall power consumption compared to continuous active scanning, while still achieving fast scanning when needed
Solution Approach 2:
The mobile station skips the scanning phase under certain conditions by using pre-collected handover information from preliminary scanning. When the handover target access point has been previously detected and evaluated, the system can bypass the time-consuming scanning procedure and proceed directly to authentication and association, thereby reducing both scanning delay and associated power consumption
3Device complexity
If single handover mechanism is used, then the system complexity is low, but the adaptability to different handover circumstances is poor
Solution Approach 1:
The patent segments the handover mechanism into multiple distinct modes: normal handover mode for standard conditions, abnormal handover mode for degraded signal conditions, and forced handover mode for urgent scenarios. Each mode has its own specific procedures and parameter settings. This segmentation allows the system to adapt to different circumstances by selecting the appropriate mode, improving versatility while keeping each individual mode relatively simple and manageable
Solution Approach 2:
The patent creates a universal handover framework that can handle multiple types of handover scenarios through a unified decision-making structure. The fuzzy logic-based handover decision module serves as a universal controller that evaluates various conditions (signal strength, signal change rate, handover probability) and selects the most appropriate handover mode. This multi-functional approach allows a single system architecture to adapt to diverse handover circumstances without requiring separate specialized mechanisms for each scenario
Data Source
AI summary
A Wireless Local Area Network (WLAN) handover method is provided. The method comprises a mobile station receiving probe frames sent in a predefined time interval from a current associated access point and an adjacent access point during a preset time period. The station obtains and stores a signal strength for each access point based on the beacon frames. The station performs fuzzy processing of the signal strengths and change rates of the signal strengths to obtain fuzzy data characterizing levels of the signal strengths and the change rates. The station performs fuzzy reasoning based on the fuzzy data to obtain reasoning outputs. A target access point is determined by the station based on the reasoning outputs. The station authenticates with the target access point, and sends a re-association request frame to the target access point. Re-association is established after a re-association response frame is received by the station.