Lin Chi-Hsiang, Lin Chun-Ting, Wei Chia-Chien, Chi Sien
Opt Express. 2017 Oct 30;25(22):27750-27757. doi: 10.1364/OE.25.027750.
This paper presents a DFT/IDFT-free receiving scheme for spread-OFDM signals. Leveraging sub-Nyquist sampling and proper sampling delay, the proposed scheme enables each user to receive the requested data without the need for DFT and IDFT; thus, the complexity at receiver can be greatly reduced. Nonetheless, DC component is altered in an AC coupling system, such that severe waveform distortion is caused when the process of DFT/IDFT is omitted. Thus, a DC-zeroing algorithm is proposed to guarantee constant DC after sub-Nyquist sampling, thereby eliminating such distortion. To experimentally verify the concept of proposed scheme, a 27.15-Gbit/s optical spread-OFDM signal was transmitted over fiber and received by the DFT/IDFT-free scheme with sub-Nyquist sampling. More users will reduce the required sampling rate at receiver; for the case of 16 users, the required sampling rate for the 27.15-Gbit/s signal is as low as 1 GSample/s. The experimental results show that error-free transmission was achievable, and the penalty due to lowering sampling rate (i.e., increasing the number of users) is insignificant.
本文提出了一种用于扩频正交频分复用（spread-OFDM）信号的无需离散傅里叶变换（DFT）/逆离散傅里叶变换（IDFT）的接收方案。利用亚奈奎斯特采样和适当的采样延迟，该方案使每个用户无需DFT和IDFT就能接收所需数据；因此，接收机的复杂度可大幅降低。尽管如此，在交流耦合系统中直流分量会发生变化，以至于在省略DFT/IDFT过程时会导致严重的波形失真。因此，提出了一种直流归零算法，以确保亚奈奎斯特采样后的直流分量恒定，从而消除这种失真。为了通过实验验证所提方案的概念，一个27.15 Gbit/s的光扩频OFDM信号通过光纤传输，并由采用亚奈奎斯特采样的无需DFT/IDFT方案接收。更多用户会降低接收机所需的采样率；对于16个用户的情况，27.15 Gbit/s信号所需的采样率低至1 GSample/s。实验结果表明可实现无误码传输，并且由于降低采样率（即增加用户数量）导致的代价微不足道。
