LED-to-LED 무선 가시광 통신 시스템 = LED-to-LED Visible Light Communication System

다국어 초록 (Multilingual Abstract)

As the demand for a higher speed of wireless communication increases, fifth-generation (5G) wireless communication technology has emerged and got standardized. 5G technology exploits the millimeter-wave (mm-wave) band for its information carrier to avoid the use of crowded radio frequency (RF) band and increase the data rate. Similar to this movement, future communication technologies are expected to use a higher frequency of electromagnetic waves.
Optical wireless communication (OWC), an extension of this trend, is the technology that realizes the communication links with the nanometer-wave (nm-wave) band. Depending on the types of the transmitter and receiver or the environmental condition of the system, OWC technology can be classified into four sub-categories: visible light communication (VLC), light fidelity (Li-Fi), free-space optical communication (FSOC) and optical camera communication (OCC).
Among the OWC technologies, VLC has been put into spotlight due to its advantages over conventional RF communication, such as the wide and unregulated spectra, easy implementation nature, high connectivity and high security. As a result, VLC technology has been standardized in IEEE 802.15.7 and widely studied. However, VLC technology has not been commercialized yet. We believe it is due to a lack of commercialization strategies. Therefore, we suggest the LED-to-LED VLC system as a step for the VLC commercialization strategy.
Prior to the discussion of the LED-to-LED VLC system, we covered the special techniques of the VLC system. Due to the difference between the VLC system and RF radio communication technology, techniques used in the conventional wireless communication system are hard to be implemented on the VLC system. In addition, the wireless communication techniques that can be applied for both of the VLC system and RF communication system are studied.
A light-emitting diode (LED)-to-LED VLC system’s performance dependency on the wavelength of the transmitter and the receiver LEDs were investigated by measuring the rise time and signal-to-noise ratio (SNR). With these rise time and SNR results, the channel capacities of each LED color set were calculated using Shannon’s channel capacity law. Then, the LED color set showing the best channel capacity was chosen as the optimal LED color set for the LED-to-LED VLC system.
The LED-to-LED VLC system using direct current biased optical orthogonal frequency division multiplexing (DCO-OFDM) with the optimal LED color set is experimentally demonstrated. The bit error rate (BER) results of full-duplex and half-duplex LED-to-LED VLC systems with the optimal LED sets are shown to compare the performance. Furthermore, we discuss the major distortions in the LED-to-LED VLC system.

목차 (Table of Contents)

• Ⅰ. 서론 1
• 1.1. 무선광통신 1
• 1.2. 가시광통신 4
• 1.3. LED-to-LED 가시광통신 5
• 1.4. 논문의 구성 7
• Ⅱ. 이론적 배경 - 가시광통신 시스템 8
• 2.1. 가시광통신 시스템의 채널 모델 8
• 2.1.1. 가시 경로 채널 모델 10
• 2.1.2. 비가시 경로 채널 모델 12
• 2.2. 가시광통신 시스템의 변조 기법 14
• 2.2.1. 단일 반송파 변조 16
• 2.2.2. 다중 반송파 변조 20
• Ⅲ. 이론적 배경 - 무선통신 시스템 28
• 3.1. 최대 가능도 추정 28
• 3.2. 가산 백색 가우시안 잡음 32
• 3.2.1. 광의의 정상 프로세스 32
• 3.2.2. 광의의 정상 프로세스 신호의 선형 시불변 시스템 통과 특성 34
• 3.2.3. 가산 백색 가우시안 잡음 37
• 3.3. 백색 가우시안 잡음 신호의 RC 필터 통과 특성 38
• Ⅳ. LED-to-LED 가시광통신 시스템 41
• 4.1. PN 접합 41
• 4.2. 광수신 소자로써의 LED 특성 42
• 4.3. LED-to-LED 가시광통신 48
• Ⅴ. 결론 57
• 참고문헌 59
• ABSTRACT 63