Augmenting WiFi Infrastructure with Visible Light Communications

该提议项目涉及可见光通信（VLC），特别是聚合物光纤（POF）和自由空间低功耗VLC的结合，以创建廉价的通信链路，以增强现有的WiFi基础设施。该项目属于EPSRC光通信研究领域。WiFi的高密度流量饱和问题日益严重。在正常情况下，一个接入点（AP）的容量可能高达900mbit /s，但由于并发效应，18个连接的用户每个将体验到6mbit /s的速率。这是一个远低于可用射频（RF）信道容量的总体吞吐量。连接设备越多，这种影响就越严重。作为一种解决方案，制造商正在他们的新ap中加入更多的射频通道，这最终会变得饱和，只会进一步推动问题的发展。需要一个长期的解决方案，因此作为射频的替代方案，VLC通道可用于增强射频系统并消除射频拥塞。建议的增强是使用VLC通道来提供数据链路，从而确保服务质量。硅光电倍增管（SiPM）已被确定为世界上最灵敏的光接收器，并已被证明是VLC系统的理想候选者。这种接收器可以与低功率指示灯led配对，以创建廉价，实用的链接。指示灯led和sipm的组合是以前从未实现过的，并且具有强劲表现的潜力。必须对SiPM接收器进行进一步的表征，以及了解环境光、输出脉冲宽度、均衡方法等对VLC链路的影响。对于实际VLC系统的建议是使用光纤从中心集线器传输整个服务区域的光通道，而不是使用分布式发射机。POF已被确定为一种合适的纤维，它提供机械效益，同时价格低廉。每个POF光纤将携带一个单独的VLC通道划分空间，因此可以同时为多个用户提供服务而不会受到干扰，其他好处包括安全性的提高和平均传输速率的降低。这种光纤可以廉价地放置在办公室的悬挂天花板上，并以微创的方式在所需的传输位置突出。单独的光通道需要分布在WiFi覆盖的整个空间中，用VLC覆盖的区域填充空间（不一定是分开的）。虽然POF通常在红色区域工作，但它可以在蓝色区域工作，因此可以发出可被sipm检测到的光。405nm波长很有趣，因为它在目标家庭和办公室环境中不那么普遍，sipm对它更敏感。探索使用POF传输光无线链路的影响也是必须进行的研究。对于下行链路，我的目标是利用硅光电倍增管的高灵敏度和大面积，在bb0 m范围内检测POF的链路。使用另一个POF作为从客户端返回AP的上行链路是可行的。将从客户端发射的上行链路光耦合回POF将是一个挑战，因为POF的直径通常为1mm。发射光的低功率与POF的小面积相结合，可能需要一种解决方案，包括在POF的末端涂上荧光团涂层，或连接到POF的荧光团掺杂纤维，以收集和耦合更多的光。由于上行链路本质上是一个较低的速率，因此为了保证服务质量，探索什么允许上行链路具有鲁棒性并实现高速率是至关重要的。

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) mayhave a high capacity of 900 Mbit/s under normal operation, due to concurrency effects 18 connectedusers 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 effect worsens with more connecteddevices. 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 RF systemsand remove RF congestion. The suggested augmentation is using a VLC channel to serve a data link, allowing for ensured quality of service.The Silicon Photomultiplier (SiPM) has been identified as the world's most sensitive optical reciever, and has been demonstrated to be an ideal candidate for VLC systems. This reciever can bepaired with low-power indicator LEDs to create inexpensive, practical links. The combination of indicator LEDs and SiPMs is something which hasn't been achieved before, and has the potential toperform strongly. Further characterisation of SiPM recievers must be undertaken, as well as understanding the impacts of ambient light, output pulse width, equalisation methods and more on VLC links.A suggestion for practical VLC systems is to use optical fibre to transport the optical channels throughout the serviced area from a central hub, rather than use distributed transmitters. POF has been identified as a suitible fibre, which offers mechanical benefits along with being inexpensive. Each POF fibre will carry a separate VLC channel dividing space so multiple users can be serived simultaneously without interference, other benefits which arise include increases in security, and decreases in average transmission rate. 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. 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 detected by SiPMs. The 405nm wavelength is interesting as it is far less prevalent in the target home and office environments, and SiPMs are more sensitive to it. Exploration of the impacts of using POF to transport optical wireless links is also research which must be undertaken.For down-links, I aim to exploit the high sensitivity, and large area of Silicon Photomultipliers, to detect a link from POF at a range of > 3m. 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 wouldbe a challenge here, as POF typically has a diameter of 1mm. The low power of the emitted light inconjunction 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 up-links are a lower rate by nature, it is crucial to explore what allows the up-link to be robust and achieve a high rate in order to guarantee quality of service.