AP Multi-Link Roaming with Sequence Number Window Coordination
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Solution Overview
Problem
In multi-AP wireless local area networks (WLANs), the uncoordinated advancement of transmission windows during roaming leads to premature discarding of older data packets, causing significant data loss and reduced reliability, which contradicts the goals of ultra-high reliability (UHR) systems.
Innovation Solution
A method and apparatus for coordinating sequence number (SN) limitation between access point multi-link devices (AP MLDs) to ensure that downlink transmissions from one AP MLD do not exceed the reordering buffer window of the non-AP MLD, synchronizing Block Acknowledgement (BA) and reordering buffer windows to prevent premature advancement and data loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the target AP MLD transmits newer MPDUs with higher sequence numbers during parallel downlink transmission, then the transmission speed and data flow continuity are improved, but the reordering buffer window at the non-AP MLD advances prematurely, causing older MPDUs to fall outside the valid range and be discarded, resulting in data loss and reduced reliability
Solution Approach 1:
The current AP MLD performs preliminary actions by determining the BA window start sequence number and calculating the SN limitation value before the roaming process completes. This advance preparation allows the target AP MLD to control its downlink transmission appropriately, preventing premature window advancement and ensuring older MPDUs are not discarded. The limitation information is transmitted to the target AP MLD in advance through the non-AP MLD, enabling proactive coordination.
Solution Approach 2:
The system implements feedback mechanisms where the current AP MLD provides limitation information (including BA window start sequence number and SN limitation value) to the target AP MLD. The target AP MLD uses this feedback to adjust its transmission behavior, and the non-AP MLD provides feedback through acknowledgment frames (Block Ack, Power Save Poll) to confirm receipt and understanding of the limitation information, creating a closed-loop control system.
2Stability of the object's composition
If the reordering buffer window advances synchronously with the BA window to maintain coordination, then the window synchronization is maintained, but older MPDUs still queued at the current AP MLD fall outside the valid range and are discarded even when successfully transmitted, causing data loss
Solution Approach 1:
The patent applies local quality by differentiating the treatment of different AP MLDs during roaming. The current AP MLD is granted a extended transmission opportunity beyond the standard BA window boundary, while the target AP MLD operates under SN limitation constraints. This localized differentiation allows the current AP MLD to transmit older MPDUs with sequence numbers that would normally be outside the BA window, preventing their discard while maintaining overall system coordination.
Solution Approach 2:
The system changes key parameters during the roaming process. The SN limitation value and BA window start sequence number are dynamically adjusted based on the roaming state. When roaming is detected, the current AP MLD transmits limitation information that effectively extends its valid transmission range by allowing MPDUs with sequence numbers up to the SN limitation value, even when these exceed the standard BA window boundary. This parameter change prevents data loss while maintaining window coordination.
Data Source
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AI summary
A method and apparatus for coordinating downlink transmission during a wireless roaming process are disclosed. A first access point multi-link device, AP MLD, (10) performs frame exchanges with a non-AP MLD (30). During a roaming process where the non-AP MLD (30) transitions to a second AP MLD (20), the first AP MLD (10) transmits first information indicative of sequence number, SN, limitation to the second AP MLD (20). In response, the second AP MLD (20) controls its downlink transmission based on the first information. The control is performed to ensure that MAC Protocol Data Units, MPDUs, transmitted from the second AP MLD (20) to the non-AP MLD (30) are within a reordering buffer window of the non-AP MLD (30), thereby preventing data loss and increasing communication reliability.