AP Preemption for Low-Latency Traffic via xIFS and Control Frames
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Solution Overview
Problem
Wireless local area networks (WLANs) face challenges in providing low-latency communications due to contention for the wireless medium, hidden node problems, channel errors, packet loss, and overloaded networks, which disrupt time-sensitive traffic like voice and video.
Innovation Solution
An access point station (AP) configured for ultra-high reliability (UHR) communication in WLANs enables preemption for low-latency traffic during a transmission opportunity (TXOP) by encoding initial frames to indicate preemption status and using extended short interframe spacing (xIFS) between downlink physical-layer protocol data units (PPDUs), suspending subsequent transmissions to decode preemption request frames, and triggering stations to transmit low-latency traffic.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If WLAN uses shared medium for all clients, then network resource utilization is improved, but latency and jitter increase for time-sensitive traffic
Solution Approach 1:
The patent segments the transmission medium access by introducing TXOP (Transmission Opportunity) allocation that divides the shared medium into dedicated time slots for different traffic types. Low-latency traffic is granted priority TXOPs that are protected from contention by non-time-sensitive traffic, thereby reducing latency and jitter while maintaining overall network utilization through efficient medium sharing.
Solution Approach 2:
The patent implements dynamic TXOP allocation mechanisms where the access point can adjust transmission opportunities in real-time based on traffic conditions. The system dynamically grants priority access to low-latency traffic when needed while maintaining fair sharing for other traffic, allowing the network to adapt to changing conditions and maintain both low latency and high utilization.
2Loss of time
If preemption is enabled during TXOP, then latency for low-latency traffic is reduced, but complexity of transmission control increases
Solution Approach 1:
The patent applies preliminary action by establishing pre-configured preemption rules and parameters before TXOP transmission begins. The access point pre-allocates protection periods and defines preemption conditions in advance, so that when preemption is needed, the system can execute the switch using pre-computed parameters rather than making complex decisions in real-time, thereby reducing latency while keeping control complexity manageable.
Solution Approach 2:
The patent introduces an intermediary preemption indicator field in the physical layer preamble that mediates between the ongoing TXOP and potential preemption requests. This intermediary mechanism allows the system to signal preemption intent without requiring complex real-time negotiations, simplifying the control logic while enabling rapid preemption response for low-latency traffic.
3Speed
If extended short interframe spacing is used between PPDUs, then preemption responsiveness is improved, but risk of collision with preemption requests increases
Solution Approach 1:
The patent uses partial action by implementing extended short interframe spacing (xSIFS) that is longer than the minimum required SIFS but shorter than regular SIFS. This intermediate timing provides just enough separation to allow preemption requests to be detected and processed while maintaining tight coupling for rapid preemption response. The xSIFS is calibrated to balance responsiveness with collision avoidance, providing partial protection without excessive delay.
Data Source
AI summary
An access point station (AP) configured for ultra-high reliability (UHR) communication in a wireless local area network (WLAN) may receive low-latency (i.e., time-sensitive) traffic during a transmission opportunity (TXOP) by transmission of an initial frame encoded to indicate whether or not preemption for low-latency (LL) traffic is enabled during the TXOP. When preemption for LL traffic is enabled during the TXOP, the AP may encode downlink (DL) physical-layer protocol data units (PPDUs) for transmission within the TXOP. The DL PPDUs may be transmitted with an extended short interframe spacing (xIFS) therebetween. Each of the DL PPDUs may indicate whether the xIFS that follows a DL PPDU is enabled for preemption. When a signal comprising at least a legacy short-training field (L-STF) is detected within one of the xIFSs that is enabled for preemption, the AP may suspend a subsequent transmission of at least the next DL PPDU and may attempt to decode a frame that comprises the L-STF to determine if the frame is a preemption request frame. The AP may trigger a station (STA) to transmit LL traffic to the AP when the frame is determined to be a preemption request frame.