Symmetric TXOP Truncation for Hidden Node NAV Reset
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Solution Overview
Problem
Current wireless local area network (WLAN) systems, particularly those adhering to the IEEE 802.11 standard, face challenges with the 'hidden node problem' that leads to inequitable access and collision avoidance issues due to asymmetrical reset of the Network Allocation Vector (NAV) when the distance between client stations and access points is large.
Innovation Solution
The implementation of symmetric transmit opportunity (TXOP) truncation systems and methods, where both access points and client stations can truncate their TXOPs by transmitting CF-end frames, ensuring symmetrical NAV reset and resolving the hidden node problem through mechanisms like AP-initiated and station-initiated TXOP truncation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If access points use unicast transmissions to client stations, then power consumption at client stations can be reduced, but inequitable access and collision avoidance issues arise due to asymmetrical NAV reset when distances are large
Solution Approach 1:
The patent applies asymmetry by allowing different NAV reset mechanisms for APs and client stations. APs send CF-END frames to reset NAVs of distant clients that cannot hear their transmissions, while clients use traditional CF-END responses. This asymmetric approach resolves the hidden node problem while maintaining power efficiency for clients.
Solution Approach 2:
The AP acts as an intermediary by sending CF-END frames on behalf of distant client stations that cannot detect each other's transmissions. This mediator approach ensures equitable NAV reset for hidden nodes while allowing unicast power-saving operations to continue.
2Area of stationary object
If client stations are located at large distances from access points, then network coverage area is increased, but the hidden node problem causes inequitable access due to inability to detect each other's transmissions
Solution Approach 1:
The AP serves as an intermediary that detects and resolves hidden node collisions by sending CF-END frames to reset NAVs of distant clients. This allows the network to cover larger areas while maintaining equitable access through AP-mediated NAV management.
Solution Approach 2:
The patent applies local quality by implementing different NAV reset behaviors based on spatial relationships. Clients within range use standard CF-END responses, while distant hidden nodes receive AP-initiated CF-END frames, creating location-dependent access mechanisms that ensure equity across varying distances.
3Reliability
If symmetric TXOP truncation is implemented, then equitable access is achieved through simultaneous NAV reset, but additional message exchanges are required between APs and client stations
Solution Approach 1:
The patent implements partial symmetry by applying CF-END exchange only when hidden node conditions are detected. Normal operations use standard asymmetric CF-END responses, while symmetric exchange is activated selectively to ensure equity only when needed, reducing overall protocol complexity.
Solution Approach 2:
The system performs preliminary detection of hidden node conditions before initiating symmetric CF-END exchange. This preliminary action allows the protocol to maintain simplicity for normal operations while preparing the mechanism for equitable access when distance-related hidden nodes are identified.
Data Source
AI summary
Various embodiments of symmetric transmit opportunity (TXOP) truncation (STT) systems and methods are disclosed. One method embodiment, among others, comprises receiving a frame that truncates a TXOP around a first station, and responsive to receiving the frame, sending a second frame that truncates the TXOP around a second station. Others system and method embodiments are disclosed.