可見光通訊之研究

A Study of Visible Light Communications

蘇進傳(Chin-Chuan Su)

指導教授 ： 鄒志偉

國立交通大學/電機學院/電機學院電子與光電學程/碩士(2018年)

摘要

近年來發光二極體(LED)漸漸取代傳統光源而且它具有快速開關的特性，可藉由發光二極體的亮(1)與暗(0)來傳遞資訊，因此在可見光通訊(VLC)領域發光二極體是很好的發射器(Tx)，使用光學相機、行車記錄器或智慧手機來當接收端(Rx)構成通訊系統，光學相機通訊系統允許較長自由空間通訊距離像車對車間的通訊，但使用相機對光學相機通訊系統而言是項挑戰。它不像射頻通訊(RF)的接收端(Rx)有相位鎖定機制如相位鎖定迴路(PLL)，RF的Rx可同步到RF的Tx。一般光學相機按快門截取影像是隨機，所以LED送出訊號很難同步到光學相機，在可見光通訊接收端必需有特殊原理UPSOOK(Undersampled Phase Shift On-Off Keying)去找開始框架，以LED顯示半亮做為開始框架，然後UPSOOK利用相位偏移調變技術來編碼傳輸資料。
在這篇研究中，由於傳送端與光學相機不同步，第一個研究我們首先提出使用IR Module從接收端與傳送端同步方向做短距離傳輸研究，經由於光學相機外接ＨＤＭＩ(High Definition Multimedia Interface)轉VGA訊號取出60Ｈｚ垂直同步訊號去推動紅外線輸出模組，３８Ｋｈｚ載波調變後經由自由空間至紅外線接收模組，解調後觸發VLC傳送端（Tx）達到同步效果，進一步實現１５公尺零錯誤率。

關鍵字

同步可見光通訊 ； 紅外線同步可見光通訊 ； 非同步可見光通訊

並列摘要

Light-emitting diode (LED) is gradually replacing the traditional light sources; and besides lighting, LED can be switched on and off very quickly to carry information. Hence LED is a good transmitter (Tx) for visible light communication (VLC). VLC using optical camera or optical camera communication (OCC) is very attractive, since it uses the easily available image-sensor of smart phone or camera as receiver (Rx) and the LEDs as Tx. OCC can also allow much longer free-space transmission distance, such as car-to-car communication. However, using camera for the OCC is challenging. Unlike radio-frequency (RF) communication, the RF Rx has phase-locking mechanism, such as phase-lock-loop (PLL) to synchronize the RF Rx to the RF Tx. However, in typical camera, there is no such phase-looking mechanism. Besides, the sampling of a camera is operated randomly; hence it is not easy to synchronize a camera with the input VLC data signal.In this thesis,we us a special scheme, called Undersampled Phase Shift On-Off Keying (UPSOOK) to find the start frame in the received VLC data signal. In this scheme, the half intensity of LED is to indicate the start frame. Then, the UPSOOK modulation scheme is based on phase shift keying technique to encode the data logic. Due to the camera sampling is done randomly, the interval of the frame sampling varies with different image-sensors
In this sutdy, firstly we propose and demonstrate for the first time a feedback synchronization technique for the OCC. In our proposed scheme, we use the vertical synchronization signal of the High Definition Multimedia Interface (HDMI) out of a camera to drive an infrared (IR) Tx, which will then trigger the VLC Tx. The IR feedback synchronization mechanism will be discussed. Error-free transmission can be achieved with a free-space transmission distance of 15 m. secondly we used the RGB-based LED with white light as the transmitter through free-space, optical camera as receiver captured the light-out of LEDs, decoded it by MATLAB program and calculated the BER(Bit Error Rate) Free,90m transmission distance can be approached.

並列關鍵字

IR Synchronization ； UPSOOK ； LED and OCC for VLC

參考文獻

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