Investigation of Characteristics of Ultraviolet Light Pulse Weak Signal Communication System Based on Fourth-Order Frequency-Shift Keying Modulation  
[PERSON]  
1 State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China; [EMAIL_ADDRESS] (Y.Z. ); [EMAIL_ADDRESS] (A.D.); [EMAIL_ADDRESS] (A.D.); [EMAIL_ADDRESS] (A.D.); [EMAIL_ADDRESS] (A.D.); [EMAIL_ADDRESS] (N.S.) School of Electronic, Electrical and Communication Engineering, University of Chinese Academy of Sciences, Beijing 100049, China  
1 State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China; [EMAIL_ADDRESS] (Y.Z. ); [EMAIL_ADDRESS] (A.D.); [EMAIL_ADDRESS] (A.D.); [EMAIL_ADDRESS] (A.D.); [EMAIL_ADDRESS] (A.D.); [EMAIL_ADDRESS] (A.D.); [EMAIL_ADDRESS] (N.S.) School of Electronic, Electrical and Communication Engineering, University of Chinese Academy of Sciences, Beijing 1 the signal processing module. Finally, the information is recovered through processing. Figure 1 shows a flow chart of the UV communication system. In the study of ultraviolet communication, the analysis of scattering models is crucial. UV NLOS scatter UV primarily relies on single scattering, with the single scattering channel model being utilized to approximate the path loss of NLOS channels [7]. Several studies have investigated link gain simulations of UV scattering channel models using random geometric frameworks and Monte Carlo methods [7; 8; 9]. In recent years, researchers have conducted experimental studies on short-range NLOS scattering channel models [10]. Additionally, experimental work on the characteristics of UV NLOS scattering channels includes turbulence channel analysis [11; 12], UV photon counting detection [13], and research on long-distance channel characteristics [14]. In recent years, with the development of LEDs, there has been widespread attention towards the use of UV LEDs for ultraviolet NLOS scatter communication [11; 15; 16]. Extensive research has been conducted on both the analysis and experimentation of UV NLOS optical channels [15; 16; 17; 18; 19; 20]. Experimental communication systems have been published, demonstrating data transmission rates of 2 kbps over a distance of 100 m [21]. Real-time systems based on Reed-Solomon (RS)/Low-Density Parity-Check (LDPC) codes have achieved data rates exceeding 2.4 kbps over LOS transmission links of over 90 m and experimental tests of over 500 kbps over NLOS transmission links of over 50 m [22; 23; 24]. In the field of UV communication, challenges still exist regarding OOK modulation. OOK modulation, as a commonly used modulation technique, requires high optical energy to ensure reliable detection, making its performance susceptible to limitations in low signal-to-noise ratio environments. This leads to a system's dependency on high detection power and transmission efficiency issues. In addition to OOK being the primary modulation scheme, other modulation techniques such as PPM, BPSK, and DPIM are also employed in UV communication. The error rates of uncoded OOK and MPPM have been calculated. These models include Gaussian noise models, suitable for scenarios dominated by thermal noise, and Poisson noise models, applicable for detection based on photon counting [25]. Furthermore, more robust variable symbol length modulation schemes, including DPIM, DH-PIM, and DPPM, have been investigated, and their BER performance has been analyzed and calculated [26; 27]. The binary phase shift keying (BPSK) subcarrier intensity modulation technique has been proposed and compared with OOK and PPM modulation formats. Simulation results demonstrate that this method outperforms OOK and PPM significantly in terms of BER performance, data rate, and transmission power [28]. In summary, PPM exhibits a higher energy efficiency than OOK, DPIM modulation performs better than OOK in terms of BER but not as well as PPM, and BPSK outperforms OOK and PPM in terms of BER performance and data rate.