RTS CTS Preemption for High-Priority Wi-Fi Traffic
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Solution Overview
Problem
Wi-Fi networks often fail to prioritize higher-priority traffic over lower-priority traffic, leading to interruptions in the delivery of sensitive data transmissions.
Innovation Solution
Implementing an extended RTS/CTS protocol that allows pending transmissions to be postponed or preempted by higher-priority traffic, ensuring that higher-priority data is transmitted without interruption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the distributed coordination function is used for medium contention, then the network operates with simple contention-based access, but higher-priority traffic cannot guarantee uninterrupted delivery when low-priority traffic occupies the medium
Solution Approach 1:
The patent implements dynamic priority-based preemption where the medium access rights are not fixed but can be dynamically transferred from low-priority to high-priority traffic. The AP monitors pending high-priority traffic and can preempt ongoing low-priority transmissions by sending CTS frames, making the medium access control adaptive to changing traffic priorities rather than static
Solution Approach 2:
The access point acts as an intermediary that mediates between high-priority and low-priority traffic. When high-priority traffic is detected, the AP sends a CTS frame to preempt the ongoing low-priority transmission, effectively using the AP as a mediator to transfer medium access rights from the low-priority transmitter to the high-priority traffic without requiring direct contention between end stations
2Speed
If RTS/CTS protocol is extended to allow preemption, then high-priority traffic can interrupt low-priority transmissions, but the protocol complexity increases
Solution Approach 1:
The patent uses preliminary action by having the AP send an RTS frame before actual data transmission to announce potential preemption. The RTS frame includes information about pending high-priority traffic, allowing the AP to prepare for and execute preemption if needed. This preliminary signaling enables fast response to high-priority traffic without requiring complex real-time arbitration during actual data transmission
Solution Approach 2:
The patent changes the parameter of medium access timing by introducing variable interframe spaces. Instead of fixed timing, the system uses different interframe space durations (SIFS for normal RTS/CTS, longer IFS for preempted transmissions) to control when stations can transmit. This parameter change enables priority-based scheduling while maintaining compatibility with existing Wi-Fi timing mechanisms
3Reliability
If low-priority traffic is postponed to make way for high-priority traffic, then quality of service for sensitive traffic is improved, but the overall medium utilization efficiency may decrease
Solution Approach 1:
The patent applies preliminary anti-action by having the AP send a CTS frame to preempt ongoing low-priority transmissions before they complete. This preemptive action stops low-priority traffic in advance to ensure high-priority traffic can proceed without interruption, sacrificing some medium utilization to guarantee quality of service for critical traffic
Solution Approach 2:
The system uses partial preemption where only the necessary portion of low-priority transmission is interrupted to accommodate high-priority traffic. The low-priority transmission can resume after the high-priority traffic completes, rather than being completely abandoned. This partial action approach minimizes the impact on overall medium utilization while still providing the necessary QoS guarantees
Data Source
AI summary
Embodiments herein employ changes to the physical layer of an RTS/CTS protocol to preempt a pending TxOp so that a higher priority TxOp can occupy the wireless network. In the protocol, the AP sends out a physical frame containing an RTS frame indicating that it allows its TxOp to be preempted by a station having a TxOp with higher priority. The physical frame containing the RTS frame can give the indication in various ways. In some embodiments, the RTS can be an MU-RTS, which allows multiple stations to preempt the TxOp. In response to the RTS, one or more stations send a physical frame containing a CTS frame indicating that at least one station will preempt the TxOp. Upon receiving the physical frame containing the CTS frame, the AP yields to the preempting station or stations.