## 5 Conclusions  
This paper introduces a novel scheme for UV weak light communication, which relies on discrete Poisson channel distribution and optical pulse signal processing algorithms. The scheme undergoes analysis through theoretical derivation and computer simulation, with a focus on the performance evaluation of key decoding algorithms and hardware system implementation. Subsequently, experimental validations are conducted for both NLOS and LOS communication scenarios using the developed hardware system. The experimental findings demonstrate that the system achieves a transmission rate of 5 kbps under 4 FSK modulation. In LOS communication, the BER remains below \(10^{-4}\) for a transmission distance of 400 m and stabilizes at \(10^{-4}\) for transmission distances ranging from 400 to 700 m. Moreover, as the transmission distance increases, the BER gradually rises. In NLOS experiments, conducted with a communication straight-line distance of 65 m and both transmitter and receiver angles set to 20 degrees, the BER is measured at 7.52 \(\times\) 10\({}^{-4}\). Notably, with a receiver elevation angle between \(10^{\circ}\) and \(25^{\circ}\), the BER stabilizes at \(10^{-4}\). However, increasing the receiver angle results in deterioration in the BER. These results were achieved with an SNR higher than 13. It is noteworthy that the UV communication system based on this research scheme surpasses the furthest transmission distance reported in the literature for UV frequency-modulated optical communication systems, exceeding the reported 1.2 kbps rate and 300 m communication range [29].  
In this study, a UV pulse weak signal communication system based on 4 FSK modulation was established, with the following improvements summarized:  
1. Modulation technique optimization: FSK modulation was adopted in place of OOK modulation to enhance the system's resistance to interference and distance tolerance under similar environmental conditions.
2. UV communication frequency modulation scheme optimization: the proposal of the pulse photon detection and decoding algorithm has enhanced the system's ability to detect and decode weak signals under frequency-modulated light communication, increasing the detection recovery capability to 30 photons per symbol, thereby effectively expanding its communication range.
3. Validation of theoretical derivations and simulations: the feasibility of the system design was confirmed through theoretical derivations and simulations of the scattering model to Poisson distribution and signal processing algorithms, guiding the design of system parameters.
4. System integration: Integration of the light source, PMT, optical structure, and circuit boards was performed, reducing the system's volume and weight, and enhancing its stability and reliability. This integrated design can reduce the failure rate by minimizing connections and interfaces between different components.  
These enhancements collectively contribute to the advancement in the UV communication system. Future endeavors will center on theoretical inquiries and system blueprints for UV scattering network communication models, aiming to introduce coding schemes proximal to the information transmission capacity limit, optimize optical path designs, and further refine system performance.  
Conceptualization, Y.Z.; methodology, Y.Z.; software, Y.Z.; validation, Y.Z.; formal analysis, Y.Z.; data curation, Y.Z., A.D. and Y.J.; writing--original draft preparation, Y.Z. and L.K.; writing--review and editing, Y.Z., J.C. and N.S.; supervision, project administration, J.L. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the National Natural Science Foundation of China (NSFC), grant number 62035009.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Data are contained within the article.  
**Conflicts of Interest:** The authors declare no conflicts of interest.