Soft Handoff Method Using Channel Profiles in WLANs
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Solution Overview
Problem
Conventional 802.11 WLAN networks experience significant delays during handoffs, leading to service disruptions in real-time applications due to the break-before-make approach, where mobile devices take time to probe, authenticate, and associate with new access points, especially in large coverage areas.
Innovation Solution
A method where a mobile device connects to a first access point, determines the availability of a second access point before disconnecting from the first, and then connects to the second access point using a channel profile generated from periodic probing, reducing the need for extensive probing during handoffs by using stored channel information for direct authentication and association.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional break-before-make handoff approach is used, then mobile device can switch between access points, but handoff latency increases causing service disruption in real-time applications
Solution Approach 1:
The mobile device performs preliminary actions by probing for available access points and storing their channel profiles in advance before actual handoff is needed. The device maintains a list of probed channels with associated AP information, so when handoff becomes necessary, the device can quickly select from pre-probed channels without performing extensive probing during the handoff process itself.
Solution Approach 2:
The system dynamically adjusts the handoff process by using stored channel profiles when available, allowing the mobile device to skip redundant probing steps. The device adapts its behavior based on whether channel profile information is available, switching between using pre-stored profiles and performing new probes as needed.
2Adaptability or versatility
If mobile device probes all channels for available APs, then complete AP discovery is achieved, but probing time increases significantly
Solution Approach 1:
The mobile device performs channel probing and AP discovery as a preliminary action during normal operation, storing the results in a channel profile database. This advance preparation allows the device to avoid repeating the time-consuming full channel probe when handoff is needed, as the information is already available from previous probing activities.
Solution Approach 2:
The system uses copies of previously gathered channel information and AP profiles stored in the device's memory. Instead of performing complete new probes, the device retrieves and utilizes copies of existing channel profiles that match the current situation, significantly reducing the time required for AP discovery during handoff.
3Reliability
If authentication and association steps are performed during handoff, then proper connection establishment is achieved, but service disruption occurs in real-time applications
Solution Approach 1:
The mobile device performs authentication and association as preliminary actions during normal operation rather than during handoff. By completing these time-consuming steps in advance when the device is stable and connected to a serving AP, the actual handoff process can proceed much faster without causing service disruption in real-time applications.
Solution Approach 2:
The system provides beforehand cushioning by pre-completing the authentication and association process before handoff is needed. This advance completion creates a buffer that allows the actual handoff to occur rapidly without the time-consuming authentication and association steps interrupting real-time application service.
Data Source
AI summary
In the method, communication is established between a mobile device and access points in a wireless local area network by first connecting to a first access point on a first channel. After the first connection is established, the method determines whether a second access point is available before disconnecting from the first connection. If a signal strength of the first connection drops below a signal strength threshold, the method second connects to the second access point on a second channel. The above-described method is an example of a make-before-break or soft handoff methodology.