WLAN Full-Duplex Clock Drift Correction via Pilot Signals
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Solution Overview
Problem
Existing WLAN protocols based on IEEE802.11 half-duplex assumptions limit system efficiency, particularly in scenarios with multiple Access Points (APs) and full-duplex communications.
Innovation Solution
The development of a WLAN protocol that enhances full-duplex communication by implementing three methods: correcting clock drift between primary and secondary APs during joint transmission, facilitating multi-link operations on a single radio band, and enabling simultaneous UpLink reception by multiple APs for diversity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If full-duplex communication is implemented in multi-AP WLAN systems, then system efficiency is improved, but clock drift between APs degrades communication quality
Solution Approach 1:
The patent implements a feedback mechanism where the secondary AP measures the time difference between its local clock and the primary AP's clock using pilot signals, then feeds back this information to correct its clock drift. This continuous feedback loop ensures synchronization is maintained despite inherent clock differences between APs, resolving the contradiction between enabling full-duplex operations and maintaining communication reliability.
Solution Approach 2:
The patent introduces an intermediary synchronization mechanism where pilot signals serve as a mediator to transfer timing information from the primary AP to the secondary AP. This intermediary allows the secondary AP to adjust its clock without direct interference with data transmission, enabling full-duplex operation while maintaining synchronization accuracy.
2Reliability
If multiple APs perform joint transmission, then transmission diversity is improved, but clock synchronization becomes more difficult
Solution Approach 1:
The patent segments the clock synchronization task by designating a primary AP that maintains the reference clock and secondary APs that derive their timing from the primary AP through pilot signals. This segmentation isolates the synchronization complexity to specific synchronization mechanisms rather than requiring all APs to maintain independent synchronization, enabling joint transmission diversity while managing synchronization complexity through structured roles.
Solution Approach 2:
The patent uses pilot signals as an intermediary carrier to transmit timing information between APs during joint transmission. This intermediary allows the system to achieve transmission diversity through multiple APs while keeping clock synchronization manageable by using a dedicated synchronization channel that is separate from the data transmission paths.
3Reliability
If secondary APs correct clock drift during joint transmission, then communication quality is improved, but transmission time is increased
Solution Approach 1:
The patent applies preliminary action by having the secondary AP measure and correct its clock drift during the transmission of pilot signals before the main data transmission begins. By performing the clock synchronization adjustment in advance during the pilot phase, the system minimizes the impact on overall transmission time while still achieving the reliability benefits of synchronized communication.
Solution Approach 2:
The patent implements periodic clock correction where the secondary AP continuously monitors and adjusts its clock based on periodic pilot signal transmissions. This periodic action allows for ongoing synchronization without requiring continuous transmission interruptions, balancing communication quality improvement with minimal time loss by distributing the synchronization overhead across multiple short periods rather than requiring one long synchronization phase.
Data Source
AI summary
Full-duplex (FD) enhancements for three scenarios with multiple APs/BSSs. (1) Multiple-AP joint transmissions on a WLAN. Toward eliminating self-interferences and other issues, certain pilot signals in the PPDU are transmitted only by the primary AP. One or more secondary APs participating in the joint transmission receive the pilots to correct their clock in the following symbols. (2) Communications are performed with extended OFDM symbols sent on a second channel which facilitate NAV decoding for stations transmitting on a first channel. (3) More than one AP can perform a joint Ack/BA to a UL PPDU. The secondary AP may utilize its full duplex capability to determine the difference of receiving status between itself and the primary AP, and forward data to the primary which it had not received.