Optical Wireless Collision Avoidance via Wavelength-Divided Busy Signals
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Solution Overview
Problem
Optical wireless networks face challenges in collision avoidance due to the hidden node issue, where devices cannot sense each other's transmissions, leading to collisions and reduced throughput, especially when using the basic access method of CSMA/CA, which is not effective in directional or wavelength-divided systems.
Innovation Solution
A method involving a busy signal is transmitted on a different wavelength channel when a message is received, allowing other devices to delay their transmissions and avoid channel collisions, enabling the use of the basic access method even when devices cannot directly sense each other's transmissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If devices use directional transmission or wavelength division in optical wireless networks, then data transmission efficiency is improved, but devices cannot sense each other's transmissions causing hidden node collisions
Solution Approach 1:
The patent introduces a mediator device (access point or relay node) that can sense transmissions from all stations in the network. This mediator acts as an intermediary that receives messages from stations, senses the channel state, and transmits busy signals to inform other stations about ongoing transmissions, thereby solving the hidden node problem without requiring direct sensing between all station pairs
Solution Approach 2:
The patent changes the sensing parameter from direct optical signal detection to detection of busy signals transmitted on different wavelengths. Instead of requiring stations to directly sense each other's transmission wavelengths, the system uses a different wavelength channel for busy signal transmission, allowing stations to infer channel occupancy through this intermediary signal
2Reliability
If CSMA/CA channel sensing is required across the whole system, then collision avoidance is improved, but device complexity and energy consumption increase
Solution Approach 1:
The patent segments the sensing function from the transmission function. Instead of requiring every device to perform full channel sensing, the sensing function is concentrated in mediator devices (access points) that have omnidirectional sensing capability, while ordinary stations only need to sense the simpler busy signals transmitted on different wavelengths
3Reliability
If busy signal is transmitted on the same channel as data, then collision avoidance is improved, but full duplex communication is blocked
Solution Approach 1:
The patent moves the busy signal transmission to a different dimension - specifically, a different wavelength channel - from the data transmission channel. This allows the mediator to transmit busy signals while simultaneously receiving data messages on the original channel, enabling full duplex operation without blocking
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces collisions by providing a mechanism for devices to sense channel occupancy through a busy signal, allowing for efficient channel access and potentially increasing throughput by enabling the use of the two-way handshake mechanism in optical wireless networks.
Implementation Method 1
sensing, by a signal sensing component of the first device, at least part of the received message
Implementation Method 2
transmitter of the first device for transmission on a second, different channel having a second, different wavelength of light
Data Source
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AI summary
A collision avoidance method for a wireless network comprising a plurality of devices, the method comprises receiving, by a first device of the plurality of devices, a message from a second device of the plurality of devices, transmitting, by the first device, a busy signal in response to the receiving of at least part of the message from the second device, the transmitting of the busy signal being at least partly simultaneous with the receiving of the message, receiving, by at least one further device of the plurality of devices, the busy signal, and delaying, by the at least one further device and in response to the busy signal, transmission of at least one further message by the at least one further device.