Optical Wireless TDMA Synchronization for Overlap Interference
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Solution Overview
Problem
In optical wireless networks, adjacent coordinators often lack direct communication, leading to unsynchronized MAC cycles that cause interference with network devices in overlapping coverage areas, despite having aligned time slot durations.
Innovation Solution
A network device in the overlapping area derives timing information from downlink communication and sends it via an out-of-band channel to align MAC cycles of adjacent coordinators, using periodic beacons or synchronization messages to adjust their start times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If coordinators use time-division multiple access to share the optical wireless medium, then spectral efficiency is improved, but interference occurs in overlapping coverage areas due to unsynchronized MAC cycles
Solution Approach 1:
A network device located in the overlapping coverage area acts as an intermediary to collect timing information from multiple adjacent coordinators and relay it back to them. This mediator enables the coordinators to synchronize their MAC cycles without requiring direct communication links between them, thus resolving the interference problem while maintaining TDMA spectral efficiency
Solution Approach 2:
The network device receives timing information from coordinators, processes it to determine MAC cycle offsets, and feeds back synchronization recommendations to the coordinators. This feedback mechanism enables continuous synchronization maintenance, preventing interference in overlapping areas while preserving the time-division multiple access structure
2Measurement precision
If coordinators are synchronized using IEEE Std 1588-2008 protocol, then synchronization accuracy is improved, but device complexity increases due to requiring dedicated support from routers/switches
Solution Approach 1:
Network devices in the OWC network perform self-service by autonomously collecting timing information from downlink communications of multiple coordinators and determining MAC cycle offsets themselves. This eliminates the need for dedicated support from external routers or switches, reducing device complexity while maintaining synchronization accuracy
Solution Approach 2:
Instead of requiring complex router/switch support for IEEE Std 1588-2008, a simple network device acts as an intermediary that performs the synchronization coordination function. This intermediary approach achieves high synchronization accuracy without increasing the complexity of core network infrastructure devices
3Loss of information
If coordinators transmit periodic beacons for synchronization, then timing information exchange is improved, but overhead on the OWC network increases
Solution Approach 1:
The network device utilizes existing downlink communication transmissions from coordinators for dual purposes: both for delivering data to network devices and for collecting timing information for synchronization. This multi-functionality eliminates the need for separate dedicated synchronization beacon transmissions, achieving effective timing information exchange without increasing OWC network overhead
Data Source
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AI summary
In an optical wireless communication, OWC, network (100), time division multiple access, TDMA, is commonly used for interference suppression among multiple network devices (D1-Dn) associated to a single coordinator, or among adjacent coordinators (C1-Cn). However, an offset of MAC cycles among two adjacent coordinators (C1-C2) may still result in interference to a network device (D1) located in the overlapping area of the coverage areas of these two adjacent coordinators (C1-Cn). This invention is directed to various methods, apparatus, systems, computer program and computer-readable media for providing a mechanism to make use of an out-of-band channel to send a signal from a network device (D1) to the two adjacent coordinators (C1-C2), for assisting the alignment of MAC cycles among the two adjacent coordinators (C1-C2), and the out-of-band channel has a line-of-sight character, and is out-of-band as compared to the OWC network (100).