【摘要】 为突破单一系统瓶颈，提出一种将微波光子（MWP）技术与自产生光载卫星导航信号波形相结合的光电融合时频传输方案。可编程门阵列（FPGA）实时生成GPS L1与北斗B1I基带信号，并将本地时间信息准确嵌入到信号波形内，通过码片边界和帧结构实现精确时间对齐，导航信号波形经光电调制后在10 km单模光纤传输，实现低噪声、强抗干扰的时频光域传送；接收端利用FPGA实时导航接收机完成解扩、测量和时间恢复。基于恢复的发射时间与接收时间构建钟差反馈，对远端时间进行粗同步，并结合伪距和载波相位测量值进行进一步修正，实现基于自产生光载卫星导航波形环路的双向时频同步。实验结果表明GPS L1、B1I-D1和B1I-D2时间同步结果变化峰峰值分别为7.62 ps、6.04 ps和5.12 ps，验证了MWP结合时间嵌入自产生光载卫星导航波形的混合时频传输方案具有优异的时间稳定性和工程可行性。更多还原

【Abstract】 Objective Accurate and stable time synchronization is a fundamental requirement for a wide range of advanced applications, including precision instrumentation, large-scale industrial automation, fault localization in power systems, and intelligent manufacturing. These applications impose stringent requirements on time transfer performance, particularly in terms of low latency, high stability, and robustness against environmental disturbances. Conventional global navigation satellite system（GNSS）-based timing methods benefit from global coverage and mature infrastructure, but their achievable synchronization accuracy is inherently limited by ionospheric delays, satellite clock errors, and multipath effects. In contrast, fiber-based time dissemination provides excellent short-term stability and low phase noise, however, it is still affected by chromatic dispersion, bidirectional link asymmetry, and environmental perturbations such as temperature-induced fiber length fluctuations. To address the limitations of individual timing approaches and to exploit their complementary advantages, this work aims to develop a hybrid time-frequency transfer scheme that integrates the structural robustness of satellite navigation signals with the high stability of optical fiber links. The objective of this paper is to propose, implement, and experimentally demonstrate a microwave-photonics-assisted time synchronization system based on self-generating satellite navigation signal waveforms transmitted over optical fiber, achieving high-precision two-way time and frequency synchronization with excellent engineering feasibility.Methods In the proposed scheme, an FPGA-based signal generation module is designed to generate global positioning system（GPS） L1 and BeiDou B1I baseband signals in real time. Unlike conventional timing methods that rely on externally received satellite signals, the proposed system adopts a self-generating navigation signal architecture. In this architecture, the local reference time is directly embedded into the navigation waveform by precisely aligning the spreading code chip boundaries, using navigation data structure, and using frame timing. This approach ensures that the transmitted signal intrinsically carries accurate timing information, eliminating dependence on external satellite clocks and mitigating associated propagation uncertainties. The generated baseband signals are upconverted to intermediate-frequency and radio-frequency signals, and then electro-optically modulated onto an optical carrier using a microwave photonic link. Then the modulated optical signal is transmitted bidirectionally over a 10 km single-mode fiber, enabling two-way time and frequency transfer. Bidirectional transmission effectively compensates for asymmetry in the optical path and mitigates environmental perturbations such as mechanical stress along the fiber. At the receiving end, an FPGA-based realtime navigation receiver performs signal acquisition, carrier and code tracking, de-spreading, and measurement. Both pseudorange and carrier phase observables are extracted in real time. A hierarchical synchronization strategy is employed: coarse synchronization is established using the recovered transmission and reception timestamps to form a clock offset feedback loop, while fine synchronization is realized using high-resolution pseudorange and carrier phase measurements. The closed-loop interaction between local and remote nodes enables two-way time and frequency synchronization with high precision, effectively suppressing the adverse effects of fiber link asymmetry, chromatic dispersion, and environmental perturbations.Results and Discussions Experimental evaluations were conducted after completing system-level simulations and constructing the test link. Carrier phase measurements were used as the primary observable to assess timing precision and stability. The GPS L1 carrier phase difference results show a standard deviation of 0.00199 cycle, corresponding to a time transfer uncertainty of 1.27 ps at 1575.42 MHz, with a peak-to-peak time synchronization variation below 7.62 ps. For BeiDou signals, the B1I-D1 and B1I-D2 carrier phase difference standard deviations are 0.0016 cycle and 0.0015 cycle, corresponding to time transfer uncertainties of 1.03 ps and 0.96 ps at 1561.098 MHz, respectively. The peak-to-peak synchronization variations are below 6.04 ps and 5.12 ps, respectively. These results indicate that both GPS and BeiDou self-generating navigation signals can provide extremely precise time synchronization when transmitted over a microwave-photonics-assisted optical fiber link. A comparison with representative existing schemes demonstrates that the proposed approach significantly improves time synchronization performance. The optical-carrier navigation waveform scheme outperforms previously reported methods in terms of peak-to-peak timing fluctuations, demonstrating the advantage of embedding time information directly into the transmitted signal while leveraging bidirectional optical fiber transmission. Frequency transfer performance was also evaluated. The system-added frequency instability reaches 3.35×10^-12 s^-1 and 2.69×10^-15/1000 s for GPS L1. For BeiDou B1I-D1, the corresponding values are 3.15×10^-12 s^-1 and 2.51×10^-15/1000 s, while BeiDou B1I-D2 exhibits 2.79×10^-12 s^-1 and 1.71×10^-15/1000 s, respectively, demonstrating excellent long-term frequency stability for all signals.Conclusions The combined time and frequency evaluation shows that the system is capable of maintaining high-precision synchronization over both short-term and long-term intervals, confirming the robustness and reliability of the proposed scheme in practical scenarios. These results demonstrate that the proposed microwave-photonics-assisted hybrid time-frequency transfer scheme based on self-generating satellite navigation signal waveforms over optical fiber achieves high-precision synchronization and strong robustness. By embedding local time information into GPS L1 and BeiDou B1I signals and utilizing bidirectional fiber transmission, the system provides accurate two-way time and frequency transfer with excellent short-and long-term stability, highlighting its engineering feasibility for high-precision time-frequency applications. In the future, this approach can provide a stable time-frequency reference for synchronization between 5G/6G base stations, enhancing network coordination and base station synchronization accuracy. Meanwhile, along high-speed railway lines, it is expected to support distributed base stations and trackside equipment with high-stability time synchronization, thereby improving train positioning accuracy and operational scheduling efficiency.更多还原