基于ADC欠采样的低复杂度保护频带DDO-OFDM系统的理论与关键DSP算法

Direct-detection optical orthogonal frequency-division multiplexing (DDO-OFDM) has the advantages of great robustness to fiber dispersions and high spectral efficiency etc., has been regarded as one of the key technologies for realizing cost-sensitive applications such as high-speed optical fiber access networks in the future. Compared to the conventional binary modulation scheme, OFDM-based technique has higher hardware implementation complexity. So research on theory and key DSP algorithms of the hardware-oriented low-complexity DDO-OFDM system is a key link of this technology from theory to application. For guard-band DDO-OFDM systems can enable long-haul transmission and high-sensitivity reception, ADC undersampling technology is proposed and combined with low-complexity multi-channel parallel DSP algorithm to reduce hardware implementation complexity of the system in this project. Study on the operation principle of guard-band DDO-OFDM system based on ADC undersampling, and identify the constraints and related impairment mechanisms of the proposed technology; Based on the consideration of the related factors in the process of hardware implementation, study on the timing synchronization algorithm enabled by using cross-correlation between the sign bits of the training sequence (TS) and received signal and combined with threshold decision, simplified single TS-based channel estimation and equalization algorithm, and decision-aided sampling clock frequency offset compensation algorithm. The expected results of the research will provide theoretical and technical support for the practical application of DDO-OFDM technology.

直接检测光正交频分复用（DDO-OFDM）具有出色的光纤色散抵抗能力与高频谱效率等优势，已被视为未来实现高速光纤接入网等对成本敏感应用的关键技术之一。相比传统二进制调制方式，基于OFDM技术的实现复杂度较高，因此研究面向硬件的低复杂度DDO-OFDM系统的理论及其关键DSP算法是该技术从理论走向应用的一个关键环节。本项目拟针对可实现长距离传输与高灵敏接收的保护频带DDO-OFDM系统，提出采用ADC欠采样技术与设计低复杂度的并行DSP算法以降低系统的硬件实现复杂度。研究基于ADC欠采样技术系统的工作原理，明确该技术的约束条件与相关损伤的机理；结合考虑硬件实现相关因素，研究基于训练序列与接收信号的符号位的互相关性，结合门限判决实现的定时同步算法、基于同个训练序列简化的信道估计与均衡算法与基于判决辅助的采样时钟偏差补偿算法。预期的研究成果将对DDO-OFDM技术的实用化提供理论与技术支撑。

随着各种高速互联网与5G技术的日益成熟以及业务的逐步普及，各种短距离应用场景亟需解决高速与高效的传输问题。由于直接检测光正交频分复用技术（DDO-OFDM）具有系统结构简单、频谱利用率高与色散或者多径抵抗能力强等优势，已被视为未来高效实现宽带接入网与高速数据中心光互联的关键技术之一。因此，本项目针对具有高接收机灵敏度的保护频带DDO-OFDM信号产生、传输与接收的相关理论、算法以及硬件实现进行了较为系统性地研究。具体包括：揭示了ADC欠采样技术在保护频带DDO-OFDM系统中的工作原理；系统性地研究了不同系统受限条件下使用最佳预编码技术补偿系统损伤；提出了一种基于训练序列符号位互相关性的定时同步算法，以及符号间与符号内频域平均混合信道估计算法；提出了三种高效的采样频率偏差估计或者补偿算法；基于FPGA设计、实现并验证了一种基于非Hermitian对称的低复杂度光纤实时DDO-OFDM传输系统。此外，针对基带DDO-OFDM系统中FFT运算的共轭特性，提出了一种高效硬件实现并行FFT算法的方法；提出了一种基于时域平均的高速DAC时钟泄漏与ADC直流偏置不匹配的估计与补偿方法；提出了一种高频谱效率的基于预编码技术的滤波器组多载波光纤通信系统；探索了DDO-OFDM技术在实时水下可见通信系统中的应用。本项目所获得的相关研究成果将为高效设计与实现高速、短距离光通信系统提供有价值的理论与技术参考。