可見光通訊之正交分頻多工收發機

An OFDM-based Transceiver for Visible Light Communications

林威廷(Wei-Ting. Lin)

指導教授 ： 馬席彬

國立清華大學/電機資訊學院/電機工程學系所/碩士(2018年)

摘要

本篇論文中，我們已設計一個可見光通訊的收發機，並藉此達到高傳輸速率的目標。為達到高傳輸速率的目標與適應不同燈具通道衰減不同的影響，因此我們採用正交分頻多工(OFDM)系統來改善，然而因強度調變與直接偵測技術(IM/DD)的緣故，正交分頻多工被更換為直流偏置光正交分頻多工(DCO-OFDM)系統。
在設計系統前，我們設定一些參數來當系統規格。首先，在我們的系統當中，我們使用16-正交振幅調變(QAM)調變技術與1024點快速傅立葉轉換(FFT)。在快速傅立葉轉換的模組中，我們使用單一路徑延遲迴授(SDF)系統來達到高吞吐量的應用；亦用以2/4/8為基底(Radix-2/4/8)的演算法來減少乘法器的使用量。此外， 循環字首(CP)的部分我們採用1/8的比例，它主要是被用來對抗多路徑通道所造成的符元間干擾(ISI)的影響。藉由測量引航符元的角度變化，我們可以容忍±100 百萬分率的取樣時脈偏移(SCO)效應。最後，我們也有使用前置符元作為參考訊號，並使用於訊框偵測。除此之外，我們系統中的位元錯誤率在訊號雜訊比(SNR) 21 分貝下已可以低於〖10〗^(-3)。
因為在這篇論文中，我們合作對象為工研院，所以我們必須與工研院整合許多模組，包括乙太網路、數位類比轉換器(DAC)、類比數位轉換器(ADC)和前端電路。每整合一個模組後，我們都有提供測量結果，藉此證明傳輸無誤。因為前端電路所提供的通道訊號雜訊比未達到16-正交振幅調變的要求，所以目前還未與前端電路進行整合。此外，由於數位類比轉換器與類比數位轉換器的取樣頻率限制，我們以較低的傳輸速率播放影片並測試重新連線的功能，但我們收發機的傳輸速率經高性能機體測試後，證明可以達到100 百萬位元/秒的傳輸速率。

關鍵字

可見光通訊 ； 正交分頻多工 ； 直流偏置光正交分頻多工 ； 收發機 ； 強度調變/直接偵測

並列摘要

In this thesis, we have designed a transceiver for VLC to attain the high-speed transmission. To achieve the goal of high-speed transmission and accommodate different channel decay from different LED, we adopt orthogonal frequency division multiplexing (OFDM) system. However, due to intensity modulation/direct detection (IM/DD) technology, OFDM system is substituted for DC-biased optical OFDM (DCO-OFDM) system.

Before designing the system, we set up some parameters to be the specification. First, we use 16-QAM modulation and 1024 points Fast Fourier Transform (FFT) in our system. In the FFT module, we use single-path delay feedback (SDF) architecture to achieve high throughput application and exploit radix-2/4/8 algorithm to save some multipliers. Next, the ratio of cyclic prefix (CP) which is exploit to combat the effect of inter-symbol interference (ISI) caused by multi-path channel is 1/8. After that, by estimating the phase variety of pilot signal, the effect of SCO we can tolerate was +- 100 ppm. In the end, we also used the preamble signal to be the reference signal for frame detection. In addition, the bit error rate (BER) of our system has been lower than 10^(-3) with 21 dB in simulation.

Because we collaborate with Industrial Technology Research Institute (ITRI) on this thesis, we have to integrate some modules with ITRI, including Ethernet, DAC (Digital to Analog Converter), ADC (Analog to Digital Converter) and front-end circuit. After integrating each module, we have offered the measurement results to show that the transmission is error-free. However, the channel SNR offered from front-end circuit does not meet the demand of 16-QAM, we do not integrate with it yet. In addition, due to the limit of the sampling rate of ADC and DAC, we have displayed video through sub miniature a (SMA) with lower data rate and test the function of reconnection, but the data rate of our transceiver tested by high performance chassis have attained over 100 Mbps.

並列關鍵字

visible light communication ； OFDM ； DCO-OFDM ； transceiver ； intensity modulation/direct detection

參考文獻

Z.-G. Sun, H. Yu, and Y.-J. Zhu, “Robust linear precoding for MU-MISO VLC systems with outdated channel state information,” in 2018, IEEE 15th International Conference, Networking, Sensing and Control (ICNSC), 2018, pp.1-5.

Z. Yu, R. J. Baxley, and G. T. Zhou, “Multi-user MISO broadcasting for indoor visible light communication,” in 2013 IEEE International Conference, Acoustics, Speech and Signal Processing (ICASSP), 2013, pp. 4849-4853.

R. Maré, C. Cugnasca, C. Marte, and G. Gentile, “Intelligent transport systems and visible light communication applications: An overview,” in 2016 IEEE 19th International Conference on, Intelligent Transportation Systems (ITSC), 2016, pp. 2101-2106.

M. V. Bhalerao and S. Sonavane, “Visible light communication: A smart way towards wireless communication,” in 2014 IEEE International Conference on, Advances in Computing, Communications and Informatics (ICACCI), 2014, pp. 1370-1375.

“Purelifi,” December 2018. [Online]. Available: http://purelifi.com/lifi-products/