Network Controlled Handover in Radio LAN Systems
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Solution Overview
Problem
Current radio LAN communication systems experience significant delays and decreased data throughput during handover due to the need for channel scanning, which also fails to ensure the target Access Point can accommodate the STA and lacks coordinated handover timing, leading to potential data loss.
Innovation Solution
Implementing a Network Controlled HandOver (NCHO) method that uses a controlled scan scheme, where a STA sends a NCHO Setup Request message to a serving AP, receives scan parameters, and broadcasts probe requests over specified channels, allowing an Access Point Controller to determine the target AP and coordinate handover timing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an STA performs active scan to determine target AP for handover, then the STA can identify available APs, but the handover delay increases due to channel scanning and waiting for probe response messages
Solution Approach 1:
The system performs preliminary actions by having the AP proactively discover neighboring APs and pre-evaluate their suitability for handover (including CAC for VoIP capacity) before the STA needs to handover. This eliminates the need for the STA to perform time-consuming active scans at the moment of handover decision.
Solution Approach 2:
The patent inverts the traditional handover approach by having the AP (serving network) take the initiative in discovering and evaluating target APs, rather than the STA performing scans. The AP sends probe requests on behalf of the STA and receives probe responses, reversing who performs the scanning action.
2Reliability
If an STA scans all channels to determine target AP, then the STA can find available APs, but data throughput decreases because the STA cannot exchange data with serving AP during scanning
Solution Approach 1:
The AP performs channel scanning and target AP discovery in advance, before the STA needs to handover. This allows the STA to maintain normal data communication with the serving AP while the AP concurrently performs the scanning operations that would otherwise interrupt data flow.
3Ease of operation
If an STA determines target AP before handover, then the STA can initiate handover, but data may be lost that was transmitted to the original AP until STA accesses target AP
Solution Approach 1:
The serving AP proactively identifies suitable target APs and prepares handover parameters in advance. This allows the network to coordinate the handover timing and implement data forwarding mechanisms before the STA actually switches, preventing data loss during the transition.
Solution Approach 2:
The serving AP acts as an intermediary that manages the handover process, coordinating between the STA and target AP. It can buffer and forward data packets to the target AP before the STA completes handover, ensuring no data is lost during the transition period.
4Device complexity
If an STA performs handover without CAC check, then the handover process is simpler, but the STA cannot determine whether target AP can accommodate it (especially for VoIP calls)
Solution Approach 1:
The serving AP performs Call Admission Control (CAC) checks for VoIP capacity and evaluates target AP suitability in advance, before the STA initiates handover. This ensures that the selected target AP can actually accommodate the STA's requirements without requiring the STA to perform complex checks itself.
Data Source
Figure 1
Figure 2a
Figure 2b~3
AI summary
Provided is a method for performing handover by a STAtion (STA) in a radio Local Access Network (LAN) communication system. The method includes sending a Network Controlled HandOver Setup Request Information Element (Ncho Setup Req IE) message indicating that the STA is to perform a scan operation using a controlled scan scheme, to a serving Access Point (AP); receiving a Network Controlled HandOver Setup Response Information Element (Ncho Setup Rsp IE) message including a scan parameter related to a controlled scan operation of the STA, from the serving AP; and broadcasting a probe request message to the serving AP and neighbor APs over channels according to the scan parameter included in the Ncho Setup Rsp IE message.