具有修復連續錯誤功能之可見光通訊系統

Abstract

可見光通訊亦即使用可見光做為訊號源的通訊系統，近年來 LED 已深入我們的日常生活中，許許多多的光源都漸漸地被 LED 所替換，如大型廣告、路燈和檯燈等照明到手機面板、各式螢幕等都使用 LED 作為其光源，因此以照明用 LED 作為訊號源的可見光通訊也逐漸發展起來。此種可見光通訊使用白光 LED 以人眼察覺不到的高速調變使其帶有傳輸資訊的功能，接收端則以光偵測器接收後經放大轉成電訊號至各種裝置如電腦手機等。 而此類使用既有照明用 LED 做的傳輸系統通常是單向廣播型的通訊系統，易於被外來物如人和手等遮斷，在沒有回傳的情況下訊號會因遮斷而遺失，因此設計出不需額外回授且能修復遺失資訊的方法是相當重要的。本論文所做的是一盞單向傳輸的檯燈型可見光通訊系統，電路方面使用市面上易取得的元件組裝而成，包含 LED 驅動電路、光偵測器與比較器接收電路和序列埠轉 USB (通用序列匯流排) 的模組。用 C# 語言撰寫程式並以電腦控制序列埠進行傳輸與接收，系統的設計目標為利用錯誤更正碼使 1 秒內被連續遮斷的遺失資訊皆能被修復，以達到對訊號遮斷免疫的效果。 本論文的重點在結合錯誤更正碼當中的漢明碼、交錯編碼與計算遺失資訊的時間戳記等技術，以實現一個可以修復不超過 1 秒長時間連續錯誤的編碼法，如此一來，當可見光通訊系統在傳輸的過程中，意外被人、手或其他飛行物遮住 1 秒時，可藉由程式運算來修復遺失的資訊，此法將使可見光通訊有更高的應用價值。

Visible Light Communication (VLC) is a technology that uses visible light as the carrier for signal transmission. Light Emitting Diodes (LEDs) have been widely used in our life, such as billboards, traffic lights. So the VLC that uses LEDs at visible wavelength, which are modulated at a very high speed, to carry the information. The modulated light is received by photodiodes and translate into electric signals. VLC has a potential to combine existing LED systems. For the VLC system based on LED lighting apparatus, the signals are usually broadcasted. In such a system when the light is accidently block by hands or any flying objects, the receiver may lost data. As a result, a system without additional feedback but can fix burst error is important to improve the performance of this kind of VLC. In this thesis, a lamp type visible light communication loopback testing system was built with commercially available component. Include LED driving circuit, photodiode, comparator circuit and FT232 serial to USB module. The software in the host computer for encoding and decoding the data is written in C# and control the data transmission and receiving through the serial port. The key point of this thesis is combining interleaved Hamming code and timestamps that count exact number of lost data to fix the burst error up to 1 second. When the data is interrupted accidently by hands or other flying objects, it can fix it by the software. In this way, the potential of VLC can be improved greatly.