Super receivers for visible light communications

I.鉴于有限的无线电频谱，目前使用未授权光谱的可见光通信（VLC）为创建用于数据传输和日常室内照明的新无线基础设施提供了机会，在即将到来的物联网（IoT）中发挥着至关重要的作用。与传统射频相比，基于LED的VLC具有更好的保密性和低功耗。它总是不受电磁干扰的影响，特别是在充满电子设备的地方。对这一领域的研究将很快有助于照明和电信基础设施的兼容标准化，并为即将到来的物联网II建立开放式架构指南。一旦新的无线网络直接从现有的原型构建，终端上的光接收器的灵敏度和带宽限制是关键的瓶颈。考虑到眼睛安全和室内照明标准，接收的光量是有限的。因此，VLC系统的最大数据速率最终由接收器的灵敏度决定。对于接收器，重要的约束之一是光学扩展量守恒。增加光电探测器的有效面积可以增强接收的光功率，但由于较大的电容而导致较低的带宽。一旦接收器包括典型的集中器，由于集光率守恒，在光学增益和视场（FoV）之间总是存在折衷。因此，提出了首先吸收然后作为介质再发射的荧光集中器，以同时为接收器提供高的光学增益和宽的FoV。然而，由于低信噪比和低带宽，目前的大多数工作具有10-40 Mbps的有限数据速率。它们很难在水下条件或移动的通信等复杂环境中工作。因此，有必要设计一种超级接收机解决方案来接入物联网中的大量终端，从而保证光无线通信的稳定性和高效性。研究方法鉴于我过去的研究和知识，我将考虑光电器件设计和算法优化，以满足上述挑战。a）荧光聚光器和硅光电倍增管由于长寿命是限制接收器调制带宽的主要因素，因此有必要找到具有高量子效率的短寿命荧光材料。同时，通过薄膜或塑料光纤扩展PD的有源区，可以同时接收来自不同方向的光，并降低对准标准。此外，可以在接收器中引入能够检测单个光子的光检测器以提高灵敏度。以这种方式，实现大规模和高效的探测器阵列将是可能的，其中空间分集可以大大提高数据速率。B）算法优化和扩展得益于色彩转换器的集中性能，我们可以同时支持多个用户，而无需复杂的镜头，并为单个用户提供适度的移动性。利用多址和MIMO方法，系统可以倍地扩展，而不需要通过波长和偏振状态进行额外的分离。为了获得更好的性能，均衡算法包括预均衡，限幅，和复杂的后均衡不可避免地被用来提高数据速率。符合EPSRC的战略和研究领域本项目福尔斯属于EPSRC光通信研究领域。

I. IntroductionConsidering the limited radio spectrum, visible light communication (VLC) using an unlicensed light spectrum nowadays offers an opportunity to create a new wireless infrastructure for data transmission and daily indoor illumination, playing a vital role in the coming Internet of Things (IoT). Compared with conventional radio frequency (RF), VLC based on LEDs has better confidentiality and low-power consumption. It is always immune to electromagnetic interference, especially in places full of electronic equipment. Researching this field will soon contribute to compatible standardization of lighting and telecom infrastructures, and establish an open architecture guide for the upcoming IoT.II. Research QuestionsOnce the new wireless network is constructed directly from existing prototypes, the sensitivity and bandwidth limitations of the optical receivers on terminals is the key bottleneck. Considering the eye safety and standards for interior illumination, the amount of received light is limited. Therefore, the maximum data rate of a VLC system is ultimately determined by the sensitivity of receivers. For receivers, one of the important constraints is the etendue conservation. Increasing the active area of the photodetector can enhance the received optical power but lead to lower bandwidth due to larger capacitance. Once typical concentrators are included for a receiver, there is always a trade-off between optical gain and field-of-view (FoV) because of the etendue conservation. Accordingly, fluorescent concentrators, which first absorb then re-emit as a medium, are proposed to simultaneously provide a high optical gain and a wide FoV for receivers. Nevertheless, most of the current works have limited data rates of 10-40 Mbps due to low SNR and bandwidth. They can hardly work in a complex environment such as underwater conditions or mobile communication. Therefore, it is necessary to design a super receiver solution to access a large number of terminals in the IoT, which ensures the stability and efficiency of optical wireless communications.III. Research MethodologyGiven my past research and knowledge, I will consider optoelectronic devices designs and algorithm optimization to meet the above challenges. a) Fluorescent Concentrators and Silicon PhotomultiplierSince the large lifetime is the main factor limiting the modulation bandwidth of receivers, it is necessary to find a short-lifetime fluorescent material with high quantum efficiency. Meanwhile, extending the active region of PD by films or plastic optical fibers, the light from different directions could be received simultaneously with mitigated alignment criteria. Moreover, a light detector capable of detecting individual photons can be introduced in the receiver to improve the sensitivity. In this way, realizing a large-scale and efficient detector array will be possible, where spatial diversity can greatly enhance the data rate. b) Algorithm Optimization and ExtensionBenefiting from the color converter's concentration performance, we can support multiple users simultaneously without complex lenses and provide a single user with moderate mobility. With the multiple access and MIMO methods, the system could be extended by times, requiring no extra separation by wavelength and polarization states. To obtain better performance, equalization algorithms including pre-leveling, clipping, and complex post-equalization are inevitably utilized to improve the data rate.IV. Alignment to EPSRC's strategies and research areasThis project falls within the EPSRC Optical communications research area.