Multi-AP TxOP Scheduling for Hidden Terminal Mitigation
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Solution Overview
Problem
Existing wireless local area networks (WLANs) face challenges in coordinating multi-access point (AP) scheduling, leading to increased interference and reduced efficiency in concurrent communications between multiple APs and associated stations (STAs).
Innovation Solution
Implementing a multi-phase/stage approach for coordinated multi-user (MU) transmissions, including a resource offer and request phase and a triggered transmission phase, with mechanisms for a master AP to dynamically allocate resources to slave APs, enabling synchronized and efficient communication between multiple APs and their associated stations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple access points transmit data simultaneously using traditional CSMA/CA protocol, then network coverage and data transmission capacity are improved, but performance degradation occurs due to hidden terminal problems and excessive transmission attempts
Solution Approach 1:
The system performs preliminary actions by having access points exchange capability information and scheduling policies in advance through IEA frames before actual data transmission. This allows the scheduling entity to pre-coordinate transmission schedules, avoiding the hidden terminal problem where stations cannot detect each other's transmissions. The preliminary exchange of capability sets and scheduling parameters enables proactive conflict avoidance rather than reactive backoff retries.
Solution Approach 2:
A scheduling entity acts as an intermediary between multiple access points and stations. This intermediary receives capability information from access points, determines optimal scheduling policies, and coordinates transmission opportunities. The intermediary resolves the contradiction by centralizing the scheduling decision-making process, ensuring that simultaneous transmissions are coordinated to avoid collisions while maximizing network utilization.
2Reliability
If traditional backoff mechanisms are used to resolve transmission conflicts, then collision avoidance is achieved, but transmission latency increases due to multiple retry attempts
Solution Approach 1:
The system implements feedback mechanisms where access points report their capability information and transmission status to the scheduling entity. The scheduling entity uses this feedback to dynamically adjust scheduling decisions and inform access points of approved transmission opportunities. This closed-loop feedback system eliminates the need for blind backoff retries by providing real-time coordination information, thus reducing transmission latency while maintaining collision avoidance.
Solution Approach 2:
Transmission schedules are determined in advance through preliminary capability exchange and scheduling policy determination. Access points receive advance notice of their transmission opportunities, eliminating the need for multiple retry attempts. The preliminary scheduling action provides deterministic transmission timing, reducing latency compared to probabilistic backoff mechanisms.
3Device complexity
If access points operate independently without coordination, then device simplicity is maintained, but network performance degrades due to hidden terminal interference
Solution Approach 1:
The system merges the scheduling function into a dedicated scheduling entity that consolidates the intelligence required for coordination. Access points themselves remain relatively simple, reporting their capabilities and receiving scheduling decisions. This merging of the scheduling brain into a separate entity allows complex coordinated behavior without requiring each access point to be individually complex, thus resolving the contradiction between device simplicity and network productivity.
Solution Approach 2:
The scheduling entity serves as an intermediary that handles the complexity of coordination between access points. This intermediary absorbs the computational and decision-making burden, allowing access points to operate with simpler local logic while achieving coordinated network-wide optimization. The intermediary translates complex scheduling requirements into simple actionable instructions for access points.
Data Source
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AI summary
Methods, systems, and devices for wireless communications are described for coordination between multiple access points (APs) for communications within a transmission opportunity (TxOP). A first AP may gain channel access for a TxOP, and may coordinate with at least a second AP to allow both the first AP and the second AP to transmit and receive wireless communications during the TxOP. The first AP, upon gaining channel access following a successful contention-based channel access procedure, may initiate a scheduling phase with the second AP to schedule of resources within the TxOP for the first and second APs. The first AP may initiate a multi-AP coordinated transmission phase following the scheduling phase, during which both the first AP and second AP may communicate with one or more associated STAs.