可見光通訊系統及其應用研究

Abstract

無線通訊是我們日常生活中不可或缺的重要通信方式，由於可用的無線電頻譜資源有限，日益壅塞的頻段促使可見光通訊成為未來5G (fifth-generation) 無線通訊發展關注的焦點之一，因此良好的可見光通訊品質以及應用是迫切需要的。本文提出兩種應用於可見光通訊的接受器：CMOS感測器以及太陽能板。透過互補式金屬氧化物半導體 (Complementary metal-oxide-semiconductor, CMOS) 感測器所獨特具有的滾動式快門效應 (Rolling shutter effect)，我們可以從感測器所錄製的黑白條紋影片中解調出邏輯訊號。而隨著物連網的時代逐漸來臨 (Internet of things, IoT)，不需要額外偏壓就能將光訊號轉變成電訊號的太陽能板將會在物連網中扮演重要的角色。

本篇論文中，首先我們會說明如何運用二階多項式近似和閥值判斷來解調CMOS相機所接收的黑白條紋訊號，並以此為基礎結合太陽能板提出電子標籤與感測系統的應用架構；接著我們將會透過預失真 (predistortion) 的調變方法來增強太陽能板的傳輸速度，並且憑藉著較寬廣的接收範圍，將太陽能板應用在可見光定位系統中。

Wireless communication plays an important role in our daily lives. Since the conventional radio-frequency (RF) spectrum has been congested, visible light communication (VLC) becomes one of the promising candidates for the future fifth-generation wireless networks. Hence, the performance and application of VLC is urgently needed. The thesis presents two kinds of VLC receivers, which are the complementary metal-oxide-semiconductor (CMOS) image sensor and the solar cell. Based on the rolling shutter effect of the CMOS image sensor, bright and dark fringes can be observed in recorded videos. By demodulating the rolling shutter patterns, the VLC data logic can be retrieved. Also, the Internet of things (IoT) is becoming popular nowadays, low power consumed receiver or passive receiver, such as solar cell can play an important role in IoT. The solar cell VLC receiver does not need external power supply to operate, and it can perform energy harvesting to charge up the IoT devices.

In this thesis, we first propose and demonstrate how to demodulate the obtained rolling shutter patterns using a second-order polynomial (SOP) extinction ratio (ER) enhancement scheme, together with three different thresholding schemes. Then, an electronic label and sensor system combined with the solar panel and camera are presented. In addition, a predistortion scheme is applied on solar cell receiver to significantly enhance its response. With much higher field of view (FOV), the solar cell is also good candidate for the visible light positioning system.