摘 要
可見光通訊是一種使用可見光做為媒介可同時傳送資料和照明用。目前有許多數位調變的方式可以用在可見光通訊系統如開關鍵調變，可變寬度位置調變，脈衝寬度調變和正交分頻多工調變等。為了達到最佳使用頻寬、高傳送速度和對抗多路徑的干擾，正交分頻多工調變是最為廣泛使用在可見光通訊系統上。然而傳統正交分頻多工調變的傳送訊號是雙極性複數訊號，因此無法使用直接用在可見光通訊系統中。目前有三種正交分頻多工調變方式可用在可見光通訊，分別為非對稱剪裁正交分頻多工調變、直流偏壓正交分頻多工調變和翻轉正交分頻多工調變三種。然而這三種調變方式皆會遇到高峰值平均功率比的問題。本論文提出一種運用在直流偏壓正交分頻多工調變為基礎之可見光通訊系統中降低PAPR方法，因為直流偏壓正交分頻多工調變具有較佳的頻譜效率。本論文提出的方法可保持埃爾米特對稱的特性，且提出一個在接收機的半盲式輔助訊息偵測方式。
關鍵詞：可見光通訊、埃爾米特對稱、直流偏壓正交分頻多工調變、半盲式輔助訊息偵測
Abstract
Visible light communication (VLC) is an evolving technology that uses light in the visible region as a medium for data transmission and illumination simultaneously. There are many digital modulation schemes for VLC baseband such as on off keying (OOK), variable pulse-position modulation (VPPM), pulse-width modulation (PWM), and orthogonal frequency-division multiplexing (OFDM). To best utilize the available bandwidth, achieve high rata rate requirements, and resist the multipath fading, OFDM has been publicly considered for VLC baseband transmission. In conventional OFDM, the transmitted signals are bipolar and complex, but these signals cannot be transmitted in an intensity modulated/direct detection VLC system. Currently, there are three different forms of OFDM for VLC systems: asymmetrically clipped optical OFDM (ACO-OFDM), direct current-biased optical OFDM (DCO-OFDM), and Flip-OFDM. In OFDM based VLC systems, light emitting diodes (LEDs) are used as transmitters, and LED can be easily affected by high peak-to-average power ratio (PAPR) of OFDM signals. This research mainly focuses on DCO-OFDM based VLC systems because of its easily configurable DC component and its better spectral efficiency when compared with the other two methods. The proposed scheme can maintain the properties of signaling after applying the Hermitian symmetry by designing the related coefficients. In addition, we devised semi-blind side information detection at the receiver.
Keywords: Visible Light Communication, Hermitian Symmetry, Direct Current-biased Optical OFDM, Blind Side Information Detection