Augmenting WiFi Infrastructure with Visible Light Communications

Lead Research Organisation: University of Oxford
Department Name: Engineering Science

Abstract

This proposed project concerns Visible Light Communications (VLC), and in particular the combination of Polymer Optical Fibre (POF) and free space low power VLC to create inexpensive communication links to augment existing WiFi infrastructure.
This project falls within the EPSRC Optical Communications research area.
There is a growing issue of high-density traffic saturation on WiFi. While an Access Point (AP) may have a high capacity of 900 Mbit/s under normal operation, due to concurrency effects 18 connected users will each experience a rate of ~6 Mbit/s. This is an overall throughput far less than the capacity of the Radio Frequency (RF) channels available. This phenomenon is due to users performing access requests, which often clash, so each user must repetitively send an access request again. This effect worsens with more connected devices. As a solution, manufacturers are including more RF channels on their new APs, which will eventually become saturated, only pushing the problem further down the road.
A longer term solution is required, so as an alternative to RF a VLC channel could be used to augment the system and remove RF congestion. The suggested augmentation is using the VLC channThe loel to specifically handle access requests and some data transfer, allowing the use of more of the RF capacity for data transfer.
Oxford has performed a significant amount of research into VLC, and of particular interest is their fluorescent concentrator, developed with St Andrews, which uses a fluorophore that responds to 450nm light. This concentrator offers significant advantages by breaking the limit of etendue while offering a large optical gain and high bandwidth.
Another component critical to achieving this project is POF, which offers mechanical benefits along with being inexpensive. Each POF fibre will carry a VLC channel with a relatively low data capacity, but when aggregated will have the same capacity as one of the AP's channels. This optical fibre could inexpensively be placed in an office's suspended ceiling, and protruded through at a desired transmit location in a minimally invasive fashion.
Localisation of the transmit location offers benefits including potential rate increases through parallel transmissions, increases in security, and decreases in interference risk. The separate optical channels would need to be distributed throughout the space covered by the WiFi, filling the space with (not necessarily separate) regions of VLC coverage.
Although POF usually works in the red, it can work in the blue region and therefore emit light that can be collected by fluorophores. The 405nm wavelength is interesting as it is far less prevalent in the target home and office environments than 450nm. Should other fluorophores exist in the 650nm region of the spectrum (the typical operating region for POF), multiple VLC channels could be transmitted from a single fibre by using different wavelengths.
For the down-link, I aim to exploit the high sensitivity, large area and wide Field of View (FOV) of the fluorescent concentrator with Silicon Photomultipliers, to detect a link from POF at a range of > 3m. The combination of a fluorescent concentrator and Silicon Photomultipliers is something which hasn't been achieved before, and has the potential to perform strongly.
It would be feasible to use another POF as an up-link from a client back to the AP. Coupling the up-link light emitted from a client back into a POF would be a challenge here, as POF typically has a diameter of 1mm. The low power of the emitted light in conjunction with the small area of the POF may require a solution involving a fluorophore coating on the end of a POF, or fluorophore-doped fibres connected to a POF to collect and couple more light. Since access requests are a low rate by nature, it is crucial to explore what allows the up-link to be of a high enough quality to detect network access requests.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/R513295/1 01/10/2018 30/09/2023
2284103 Studentship EP/R513295/1 01/10/2019 31/03/2023 William Alexander Matthews