在可見光通訊(Visible Light Communication)下，為了符合物理元件的需 求，訊號必須使用正實數的數據，因而延伸出多種機制將數據轉換為正實數。 在本篇論文中，我們以已經實現的直流偏置光正交分頻多工(DCO-OFDM)系統為 參考，重新設計多層式不對稱剪裁光正交分頻多工(LACO-OFDM)收發機以及其優 化。 DCO-OFDM 系統存在著功率過高以及錯誤率高的問題，因此我們利用 LACO- OFDM 系統優化。在此系統中，我們使用 16 正交振幅調變技術(16-QAM)與 1024個 子載波。為了克服多路徑效應造成的影響，我們的系統採用 1/16 符元長度的循 環字首(Cyclic Prefix)，並在子載波內擺置領航信號(Pilot Signal)，以及在 傳送端加入前置符元(Preamble)。在接收器，利用領航信號估測頻域訊號的相 位旋轉，以及取樣時脈偏移(Sampling Clock Offset)。基於 Park 演算法利用前 置符元做到時間同步。除此之外，不同於以往的接收機，LACO-OFDM系統需要多 次的迭代來解調訊號，同時需要大量的記憶體來運算。因此額外設計了一個分 解式接收機，在提高錯誤率的代價下，我們大量節省了運算量以及記憶體。 本論文最後採用了 L=4 的 LACO-OFDM 模型，在 1.28 百萬比特串流測試 下，LACO-OFDM系統的峰值僅為DCO-OFDM 的一半。在迭代式接收機的模擬下，以 錯誤率為零為參考點，該系統比 DCO-OFDM系統低了 14dB。在分解式接收機的模 擬下，錯誤率僅降低了 7dB，但相較於迭代式接收機，減少了 3 次快速反傅立葉 轉換(IFFT)以及 3 次快速傅立葉轉換(FFT)，節省了多次迭代過程所耗費的記憶 體。不僅如此，我們也模擬了64 正交振幅調變技術(64-QAM)的情形，結果表 示，當我們採用 64-QAM 的系統，錯誤率最糟的情形僅與 DCO-OFDM 在16-QAM 下相同。

In visible light communication (VLC), in order to meet the requirements of physical components, signals must be positive real data, thus extending a variety of mechanisms to convert data into positive real numbers. In this paper, we redesigned the layered asymmetrically clipped optical orthogonal frequency division multiplexing (LACO-OFDM) transceiver and its optimization with reference to the DC offset optical orthogonal frequency division multiplexing (DCO-OFDM) system which was already implemented .

DCO-OFDM systems have problems of high power comsumption and high error rate, so we use LACO-OFDM system to optimize. In this system, we use 16 quadrature amplitude modulation (16-QAM) techniques with 1024 subcarriers. In order to overcome the effects of multipath effects, our system uses a cyclic prefix (CP) of 1/16 symbol length, and sets the pilot signal in the subcarrier, and adds the preamble to the transmitter. At the receiver, the pilot signal is used to estimate the phase rotation of the frequency domain signal and the sampling clock offset (SCO). Based on the Park algorithm, the preamble is used to achieve time synchronization. In addition, the LACO-OFDM system requires multiple iterations to demodulate the signal and requires a large amount of memory to operate. Therefore, an additional decomposed receiver is designed, which saves a lot of computation and memory at the cost of increasing the error rate.

At the end of the paper, the LACO-OFDM model with L=4 is adopted. Under the 1.28 million bitstream simulation, the peak of the LACO-OFDM system is only half of the DCO-OFDM system. Under the simulation of the iterative receiver, the SNR requirement which is error free of the system is 14 dB lower than that of the DCO-OFDM system. In the simulation of the decomposed receiver, the SNR requirement is only reduced by 7dB, but comparing to the iterative receiver, decreasing the computation and memory usage about 3 fast inverse Fourier transform (IFFT) and 3 fast Fourier transform (FFT). We also simulated the case of 64-quadrature amplitude modulation (64-QAM). The result express that the worst case of LACO-OFDM system is only the same as the DCO-OFDM system with 16-QAM.

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