AP MLD MAC Retransmissions with Dynamic Cross-Link Selection
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Solution Overview
Problem
Existing retransmission methods in Wi-Fi 7 are inefficient and inflexible, particularly at the Medium Access Control (MAC) layer, due to limitations such as restricted link usage, buffer size constraints, and unpredictable wireless channel conditions, which hinder the reliability of data frame transmission and retransmission.
Innovation Solution
Implementing a Retransmission Function (RTF) entity and a Traffic Identifier (TID) link mapping (TTLM) procedure for both intra-AP and inter-AP Multi-Link Devices (MLDs) to dynamically select the most suitable links for retransmissions based on real-time evaluation of signal strength and channel conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If data frames are tied to a single serving AP MLD and preassigned links through TID to Link Mapping (TTLM), then the transmission process is simplified and managed, but the flexibility and efficiency of retransmissions are limited
Solution Approach 1:
The patent segments the retransmission process by introducing a dedicated Retransmission Function (RTF) entity that operates independently from the original TID-to-link mapping. This allows retransmissions to be handled separately from initial transmissions, enabling flexible link selection without disrupting the simplified management structure. The RTF entity can select from all available links at the AP MLD, not just the preassigned ones.
Solution Approach 2:
The RTF entity acts as an intermediary between the MAC layer and the physical transmission links. It receives data frames needing retransmission and independently selects the most suitable link from all available links, rather than being constrained by the original TTLM. This intermediary function resolves the contradiction by maintaining simple management while enabling adaptive retransmission.
2Ease of manufacture
If retransmissions are restricted to preassigned links for each TID, then the link mapping procedure is straightforward, but the efficiency of retransmission delivery is reduced due to unpredictable wireless channel conditions
Solution Approach 1:
The patent introduces dynamic link selection for retransmissions through the RTF entity, which evaluates current channel conditions and selects the most appropriate link from all available links at the AP MLD. This dynamic approach contrasts with the static preassigned link mapping, allowing the system to adapt to changing wireless conditions and improve retransmission efficiency while keeping the original mapping procedure simple.
Solution Approach 2:
The system changes the parameter of link selection from fixed (preassigned) to variable (dynamic selection based on channel conditions). The RTF entity monitors channel quality metrics and adjusts link selection accordingly, transforming the rigid link mapping into a flexible mechanism that optimizes retransmission delivery without complicating the initial mapping procedure.
3Device complexity
If all active links are tied to a single serving AP MLD, then the device architecture is simplified, but the reliability of data frame retransmissions is hindered
Solution Approach 1:
The RTF entity provides universal access to all links at the AP MLD for retransmission purposes, regardless of their original assignment to specific TIDs. This multi-functional capability allows any link in the AP MLD to serve retransmission needs, enhancing reliability without requiring complex architectural changes to the overall device structure. The simplification is maintained at the architectural level while flexibility is introduced at the functional level.
4Quantity of substance
If retry count restrictions and buffer size limits are enforced, then resource management is controlled, but the reliability of delivery for individually addressed frames without Block Acknowledgment (BA) agreement is compromised
Solution Approach 1:
The RTF entity implements a feedback mechanism that continuously monitors retransmission success and channel conditions. When channel conditions improve or better links become available, the RTF can retry transmissions even after previous failures, effectively managing retry counts dynamically rather than using fixed limits. This feedback-driven approach maintains resource control while improving delivery reliability for frames without BA agreement.
Data Source
AI summary
Embodiments herein relate to a method and access point multi-link device (AP MLD) for robust retransmissions at a medium access control (MAC) layer for ultra-high reliability (UHR). The method includes transmitting a multi-link capability information element to a non-AP MLD indicating support for cross-link retransmission. Further, the method includes setting a traffic identifier (TID) to-link mapping (TTLM) to all supported links for retransmissions of the AP MLD. The TTLM is applicable for both an intra-AP MLD operation and an inter-AP MLD operation. Further, the method includes transmitting the control information to the non-AP MLD to facilitate the cross-link retransmission. The control information includes all the supported links for retransmissions of the AP MLD.