With the demand for high speed, high capacity and high security inter-satellite communication, the importance of inter-satellite laser communication technology continues to increase. Low earth orbit satellites, middle earth orbit satellites, Geo synchronous orbit satellites and inclined Geo synchronous orbit satellites are the core components of space-based information networks. Based on this scenario, the Doppler shift and free-space loss of the laser communication channel are analyzed in details, and their effects on communication performance are discussed. Typical satellites are selected to simulate the Doppler shift and free-space loss. The analysis of these characteristics of the channel can provide theoretical support for inter-satellite laser communication.

Coherent free-space optical communication offers significant advantages in terms of communication capacity, making it particularly suitable for high-speed inter-satellite transmission within satellite communication networks. Nonetheless, the presence of Doppler frequency offset (FO) and phase noise (PN) associated with lasers adversely affects the bit error rate (BER) performance of these communication systems. Conventional methods for FO and phase estimation are usually hindered by high computational demands and phase cycle slips, especially in environments characterized by elevated channel noise. To address these challenges, a noise-tolerant method is proposed to facilitate accurate carrier phase recovery (CPR) with reduced complexity. This method merges a second-order feedback loop and a feedforward stage to achieve accurate estimation. The simulation results indicate that the proposed method surpasses traditional methods in terms of noise tolerance and resource efficiency. Particularly, the BER of the proposed method can be decreased to $6.7\times {10}^{-3}$ at a signal-to-noise ratio (SNR) of 4.5 dB, in contrast to a BER of 0.25 for the traditional method. Additionally, the resource consumption of the proposed method can be decreased by 64% under equivalent conditions. Furthermore, the experimental results reveal that the phase estimation error and BER for the proposed method are $2.1\times {10}^{-4}$ and $7.5\times {10}^{-4}$, respectively, when the received power is −41 dBm. These values are significantly lower than those achieved with traditional methods, which obtain errors of $1.85\times {10}^{-3}$ and a BER of 0.48, respectively.

High-throughput satellite communication based on large-scale multi-beam antennas is a promising technology for sixth-generation (6G) mobile networks. Conventional online calibration methods for large-scale antennas after satellite launch are restricted by communication signals. This paper proposes an online calibration method of amplitude and phase errors without disturbing the normal communication traffic. Two important aspects of calibration are discussed, i.e., closed-form expressions of calibration accuracy and hardware complexity. Simulation results show that theoretical approximation results are close to simulation results when the number of antennas is less than half of the code length. The relative amplitude and phase performance deteriorate by 6.12 dB and 40.96 deg, respectively, when the power is lower than the reference 20 dB. Finally, a calibration experimental system with eight beams is built for verification.

Deep-space optical communication and ranging technologies have attracted much attention for satellite-to-earth and moon-to-earth exploration. In integrated communication and ranging scenarios, non-integer oversampling factors are employed to improve the ranging performance, which can cause accumulated timing errors. We propose a novel pulse position modulation (PPM) symbol decision method based on waveform matching to reduce the impact of accumulated timing errors near the Nyquist sampling limit. Simulation results demonstrate that the ranging accuracy can reach 2.6 and 0.52 mm at sampling rates of 625 Msps and 2.5 Gsps, respectively. The proposed symbol decision method has a gain of over 1.1 dB compared with the traditional method at the bit error rate (BER) of less than 10⁻⁶. The experimental results verify that this method can achieve high-precision measurements of distance and reliable transmission of information.