Avalanche Photodiode-Based Deep Space Optical Uplink Communication in the Presence of Channel Impairments  
[PERSON]  
1 School of Engineering Center for Space Utilization, Chinese Academy of Sciences,  
Beijing 100094, China; [EMAIL_ADDRESS] (W.G. ); [EMAIL_ADDRESS] (X.W)1 School of Engineering Center for Space Utilization,  
Beijing 100094, China; [EMAIL_ADDRESS] (W.G. ); [EMAIL_ADDRESS] [5]. Data from European Space Agency (ESA) experiments reveal that transmit-end atmospheric turbulence introduces much higher wavefront aberration variance compared to downlink [6]. Second, deep space optical uplink systems face critical limitations in both hardware miniaturization and signal processing capabilities [7]. Achieving both high photon collection and compact device design requires careful trade-offs due to size, weight, power, and cost (SWaP-C) constraints. For example, NASA's launch standards limit optical receivers to apertures below 0.5 m and total masses below 50 kg [8]. Third, uplink communication proves indispensable in deep space missions by ensuring mission-critical command transmission (e.g., orbital maneuvers) where even 0.1% data loss risks total mission failure. Therefore, this paper focuses on addressing these critical challenges for deep space optical uplink communication. For deep space optical channel modeling, [PERSON] et al. in [3] investigated the Poisson channel in a controlled laboratory environment. Works in [9; 10; 11] took into account the coronal turbulence-induced beam scintillation effect. However, the uplink of deep space optical communication suffers from more impairments. As shown in Figure 1, a schematic of a deep space optical communication system is demonstrated. First, atmosphere and solar wind will result in beam scintillation [10; 12]. For modeling turbulence-induced beam scintillation, various distributions were proposed, such as Log-normal [13], Gamma-Gamma [14], K-distribution [15], Exponentiated Weibull [16], Fisher-Snedecor [17], and Malaga distribution [18]. Gamma-Gamma has higher accuracy than both Log-normal and K-distribution [14]. In addition, the two-parameter structure of the Gamma-Gamma model enables higher computational efficiency than multi-parameter alternatives like Exponentiated Weibull, Fisher-Snedecor, and Malaga distribution [17; 18]. This efficiency benefits real-time optical systems requiring rapid turbulence compensation with minimal latency. Second, beam misalignment is one of the inescapable impairments [19]. Due to the movement of the satellite, it is difficult for an optical beam to aim perfectly at the receiving aperture [20]. Beam misalignments include two aspects, pointing errors and angle of arrival (AOA) fluctuations. In [21], pointing errors were assumed to be identical in both vertical and horizontal axes, and are modeled by Rayleigh distribution. For AOA fluctuations, it was modeled by two-valued (1 and 0) distribution in [22; 23]. Factor 1 shows that no signal power is lost and 0 indicates that complete optical signal dropout occurs. Third, link attenuation is also a serious impairment in the optical uplink [24]. The aerosol particles and molecules in the atmosphere cause the scattering and absorption of the optical beam [25; 26]. Geometric diffusion-induced attenuation is related to link length, beam divergence angle, and optical receiving aperture size [24]. Last, background noise is a non-negligible damaging factor of deep space optical communication, which depends on parameters of noise sources, FOV, optical filter bandwidth, and receiving aperture area [27]. In conclusion, in the uplink of deep space optical communication, atmospheric and coronal turbulence, pointing errors, AOA fluctuations, link attenuation, and background noise are important impairments and need to be considered in the channel model. To address SWaP-C constraints while maintaining high communication performance in miniaturized hardware platforms, pulse position modulation (PPM) and on-off keying (OOK) are widely used [2; 3; 5; 9; 28].