The microwave spectrum line shape and the signal-to-noise ratio of a compact optically detected magnetic-state-selection cesium beam clock are analyzed in this paper. As the noise analysis shows, the performance is related to the atomic utilization ratio and locking parameters when the laser frequency noise is the dominant noise source. Methods are adopted for realizing better short-term frequency stability of the clock, including using a highly efficient state-selection cesium beam tube, optimizing the locking parameters, and stabilizing the microwave power to maximize the error signal. After optimization, the signal-to-noise ratio of the clock reaches 7.0 × 10³ in a bandwidth of 1 Hz and the clock demonstrates a short-term stability of 4.1 × 10⁻¹² τ^−1/2. The five-day Allan standard deviation reaches 7.7 × 10⁻¹⁵.

The time maintenance accuracy of the navigation constellation determines the user positioning and timing performance. Especially in autonomous operation scenarios, the performance of navigation constellation maintenance time directly affects the duration of constellation autonomous navigation. Among them, the frequency stability of the atomic clock onboard the navigation satellite is a key factor. In order to further improve the stability of the navigation constellation time-frequency system, combined with the development of high-precision inter-satellite link measurement technology, the idea of constructing constellation-level synthetic atomic time has gradually become the development trend of major GNSS systems. This paper gives a navigation constellation time scale generation framework, and designs an improved Kalman plus weights (KPW) time scale algorithm and time-frequency steer algorithm that integrates genetic algorithms. Finally, a 30-day autonomous timekeeping simulation was carried out using the GPS precision clock data provided by CODE, when the sampling interval is 300 s, the Allan deviation of the output time scale is 5.73 × 10⁻¹⁴, a 71% improvement compared with the traditional KPW time scale algorithm; when the sampling interval is 1 day, the Allan deviation is 9.17 × 10⁻¹⁵; when the sampling interval is 1 × 10⁶ s, the Allan deviation is 8.87 × 10⁻¹⁶, a 94% improvement compared with the traditional KPW time scale algorithm. The constellation-level high-precision time scale generation technology proposed in this paper can significantly improve the stability performance of navigation constellation autonomous timekeeping.

Coherent state quantum communication is attracting extensive attention for its great value in terrestrial and satellite information networks. This paper proposes a new non-orthogonal quantum multi-user (MU) iterative detection scheme. At the receiving end, we develop a composite quantum receiver with multi-stage measurement instrument and soft iterative MU detector. Furthermore, based on a three-dimensional factor graph, a nonlinear Poisson-Gaussian noise limited coherent state iterative MU parallel interference cancellation (PIC) algorithm is derived. Our results demonstrate that this system can well support MU communication and achieve good performance. Quantitatively, for the 8 users scenario, the BER of $10^{-6}$ can be obtained when the photon number is 19. Further numerical results show that the system we designed exhibits superior robustness against imperfections (e.g., quantum mode mismatch and quantum thermal noise).

The application of the new type Atomic Frequency Standard (AFS) and the onboard clock ensemble technology is the evolution trend to realize the high precision and stability space-based time reference establishment and maintenance for next-generation Global Navigation Satellite System (GNSS). The architecture upgrade with ensemble clock group management mode provides the on-orbit continuous direct measurement and autonomous fault detection and recovery of the AFS group. This research proposes a framework of the GNSS robust heterogeneous ensemble clock system which includes the two-stage Kalman filter logic structure. For the application scenario of single satellite resilient Ensemble Time Scale (ETS) generation, a resilient Kalman Plus Weights (KPW) time-scale algorithm considering dynamic weight factors is designed, and its robustness against clock outages and anomalies is analyzed when using multiple heterogeneous AFS configuration presets. Then an intuitive and practical strategy of control parameter determination is introduced to support the Linear Quadratic Gaussian (LQG) control model to generate appropriate control inputs for optimal frequency steering. The simulation results show that the spaceborne composite clock signal combines the advantages of short and long-term frequency stability, and improves the overall stability performance compared with a single AFS. The long-term stability of the designed primary timekeeping satellite node can reach 4.68E-16/1day and 5.71E-16/1day respectively when adopting two heterogeneous AFS configurations. The research results are expected to be applied to the next-generation GNSS spaceborne time-frequency system development, and improve the operational robustness and autonomous timekeeping capacity of the ensemble clock group.

Underwater wireless optical communication (UWOC) faces substantial challenges in optical signal detection and processing, particularly when traversing the boundary between air and water. To address this issue, this study introduces and validates a method known as time-correlation photon accumulation (TCPA). In addition, the study also analyzed the relative performance of different error-correcting codes. An experimental system for 256-PPM photon-counting communication (PCC) has been developed, demonstrating that the system can achieve a communication sensitivity of 6.7 photons/bit with an accumulation number of 2 when utilizing SCPPM (5006, 5040) and TCPA technology.