Multi-Link Quick Ack for Long PPDU Retransmission Latency
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Solution Overview
Problem
The current 802.11 protocol faces challenges in handling latency-sensitive traffic due to the use of long PPDUs, where retransmissions after reception failure can violate latency bounds, and existing methods sacrifice efficiency for quick acknowledgments.
Innovation Solution
The protocol utilizes Multiple-Link Devices (MLDs) with Simultaneous Transmit and Receive (STR) capability, allowing for quick acknowledgments and retransmissions on a secondary link before the completion of the first link transmission, particularly for latency-sensitive MPDUs, using techniques like EDCA-Explicit and EDCA-Implicit confirmations and shared Ack Resource Units.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a long PPDU is used to aggregate multiple users and priorities for efficiency, then network efficiency is improved, but latency increases and retransmission capability is compromised
Solution Approach 1:
The patent segments the acknowledgment process into two parts: a quick acknowledgment sent immediately on the secondary link for latency-sensitive MPDUs, and a final acknowledgment sent after the long PPDU completes on the primary link. This segmentation allows the system to maintain high efficiency through the long aggregated PPDU while providing low-latency feedback for time-sensitive data through the separate quick acknowledgment path.
Solution Approach 2:
The patent introduces a secondary link as an intermediary channel for transmitting quick acknowledgments. This intermediary path bypasses the bottleneck created by the long PPDU duration on the primary link, enabling fast feedback for latency-sensitive traffic without compromising the efficiency benefits of the aggregated transmission on the primary link.
2Productivity
If a long PPDU is transmitted to improve efficiency, then throughput is improved, but retransmission capability deteriorates due to exceeded latency bounds
Solution Approach 1:
The patent performs preliminary acknowledgment actions by sending quick acknowledgments on the secondary link before the long PPDU transmission on the primary link completes. This preliminary action allows the receiver to inform the transmitter early about successfully received MPDUs, enabling the transmitter to prepare for potential retransmissions of only the failed MPDUs rather than retransmitting the entire long PPDU.
Solution Approach 2:
The patent creates a dynamic retransmission mechanism where the transmitter can adaptively respond to quick acknowledgments received on the secondary link. Based on the quick acknowledgment feedback, the transmitter can dynamically adjust its retransmission strategy during the ongoing long PPDU transmission, retransmitting only the necessary failed MPDUs with updated information about channel conditions and receiver buffer status.
3Loss of time
If quick acknowledgments are implemented for latency-sensitive traffic, then latency is reduced, but protocol complexity increases
Solution Approach 1:
The patent makes the secondary link serve multiple functions: it acts as a communication channel for quick acknowledgments, provides an additional path for data transmission, and enables collision detection capabilities. This multi-functionality justifies the added protocol complexity by providing comprehensive benefits that address multiple network requirements simultaneously.
Solution Approach 2:
The patent changes the parameter of acknowledgment timing by decoupling it from the primary link transmission schedule. Instead of waiting for the long PPDU to complete before sending acknowledgments, the system changes the timing parameter to send quick acknowledgments immediately upon receiving latency-sensitive MPDUs, with the specific timing and content of these acknowledgments being configurable based on traffic requirements.
Data Source
AI summary
A wireless communication protocol which operates with multi-link devices (MLDs) having simultaneous transmit and receive (STR) link pairs to allow transmitting a long MU PPDU by an originator on a first link, which is acknowledged (Ack) by a recipient on a second link. The Ack on the second link may be on a single resource unit (RU) which may be shared by multiple stations. The Ack may be received during the MP PPDU on the first link, making it a quick Ack. In many cases this allows the originator to perform a retransmission within the same PPDU, thus especially benefitting real-time traffic which is latency sensitive.