WLAN Handoff Method Reducing Latency via AP Intermediary Probing
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Solution Overview
Problem
Current IEEE802.11 standard for WLANs experiences excessive handoff latencies due to prolonged probing times, leading to package loss and reduced voice quality in VoWLAN, as mobile stations must terminate connections to search for new access points, causing conversation pauses and dissatisfaction.
Innovation Solution
A handoff method that switches between data transmission and probing modes at predefined intervals, allowing mobile stations to select channels discontinuously, insert authentication information into probe requests, and implement early connecting and stop-then-resume mechanisms to reduce handoff delays and package loss, using a WLAN communication system with a transceiving and probing module.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a MS sequentially probes all channels to find an appropriate AP before handoff, then the MS can ensure finding the best available AP, but the handoff latency increases significantly and package loss occurs during the probing period
Solution Approach 1:
The system performs preliminary actions by having the current AP proactively send probe requests to neighboring APs and collect their responses before the MS actually needs to handoff. This pre-collected information is stored and used during handoff, eliminating the need for the MS to perform sequential channel probing and reducing handoff latency while maintaining reliable AP selection.
Solution Approach 2:
The current AP acts as an intermediary that performs the probing function on behalf of the MS. Instead of the MS directly probing all channels, the AP intermediates by collecting probe responses from neighboring APs and providing this information to the MS, thereby reducing the time the MS needs to spend on channel scanning while ensuring comprehensive AP evaluation.
2Adaptability or versatility
If a MS terminates connection to current AP to probe channels, then the MS can search for better APs, but continuous package loss occurs causing conversation pause or termination
Solution Approach 1:
The current AP serves as an intermediary that handles the probing function while the MS maintains its data transmission connection. The AP collects probe responses from neighboring APs in the background and provides this information to the MS without requiring the MS to terminate its connection, thus enabling AP selection capability while preventing package loss during the probing period.
Solution Approach 2:
The handoff process is segmented into separate functions: the current AP handles the probing and information collection function, while the MS continues its data transmission function. This segmentation allows the probing operation to occur without interrupting the MS's connection, eliminating package loss while maintaining the ability to select better APs.
3Loss of information
If the MS waits for max channel time to obtain all possible probe responses, then the MS can ensure complete information collection, but the probing time increases significantly
Solution Approach 1:
The system performs preliminary probing actions by having the current AP collect probe responses from neighboring APs before the MS needs to handoff. This pre-collected information is stored and readily available during handoff, ensuring complete information is obtained without the MS needing to wait for max channel time during the actual handoff process.
Solution Approach 2:
The current AP acts as an intermediary that performs the time-consuming probing function in advance, collecting all necessary probe responses and storing them. During handoff, the MS can immediately access this pre-collected information without waiting for probe responses, thus ensuring information completeness while dramatically reducing probing time.
4Loss of time
If authentication information is inserted into probe requests, then authentication delay is reduced, but the probe request structure becomes more complex
Solution Approach 1:
The authentication information is merged into the existing probe request message structure. Instead of creating a separate authentication exchange, the authentication credentials are combined with the probe request, allowing authentication to occur during the probing phase itself. This reduces authentication delay while the increased structure complexity is managed through standardized message formatting.
Data Source
AI summary
A handoff method in a wireless local area network (WLAN) and an apparatus using the same are provided. A mobile station (MS) switches between a data transceiving mode and a probing mode at a predefined interval when the MS is transmitting/receiving packages. In the probing mode, the MS probes one or more channels each time and selects an access point (AP) for handoff from the probing result according to a predetermined rule, so as to re-establish a network connection.