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Analysis of Beam Misalignment Effect in Inter-Satellite FSO Links

Minje Kim, Hongjae Nam, Beomsoo Ko, Hyeongjun Park, Hwanjin Kim, Dong-Hyun Jung, Junil Choi

TL;DR

This work addresses inter-satellite FSO link reliability under beam misalignment caused by both jitter and deterministic orbital dynamics. It develops a unified pointing-error model with an exact closed-form CDF for the channel, and a tractable truncated-CDF approach using a fast bisection-based truncation index. By quantifying misalignment displacement in a receiver-centric frame and solving for signal arrival time via a bisection method, it integrates orbital dynamics into outage analysis. Through constellation-level simulations (Iridium and Starlink) and Monte Carlo validation, the study demonstrates substantial misalignment impact, especially in inter-OP links, and provides practical design insights for beam shaping and constellation topology to achieve target reliability with manageable hardware requirements.

Abstract

Free-space optical (FSO) communication has emerged as a promising technology for inter-satellite links (ISLs) due to its high data rate, low power consumption, and reduced interference. However, the performance of inter-satellite FSO systems is highly sensitive to beam misalignment. While pointing-ahead angle (PAA) compensation is commonly employed, the effectiveness of PAA compensation depends on precise orbital knowledge and advanced alignment hardware, which are not always feasible in practice. To address this challenge, this paper investigates the impact of beam misalignment on inter-satellite FSO communication. We derive a closed-form expression for the cumulative distribution function (CDF) of the FSO channel under the joint jitter and misalignment-induced pointing error, and introduce a truncated CDF formulation with a bisection algorithm to efficiently compute outage probabilities with guaranteed convergence and minimal computational overhead. To make the analysis more practical, we quantify displacement based on orbital dynamics. Numerical results demonstrate that the proposed model closely matches Monte Carlo simulations, making the proposed model highly useful to design inter-satellite FSO systems in practice.

Analysis of Beam Misalignment Effect in Inter-Satellite FSO Links

TL;DR

This work addresses inter-satellite FSO link reliability under beam misalignment caused by both jitter and deterministic orbital dynamics. It develops a unified pointing-error model with an exact closed-form CDF for the channel, and a tractable truncated-CDF approach using a fast bisection-based truncation index. By quantifying misalignment displacement in a receiver-centric frame and solving for signal arrival time via a bisection method, it integrates orbital dynamics into outage analysis. Through constellation-level simulations (Iridium and Starlink) and Monte Carlo validation, the study demonstrates substantial misalignment impact, especially in inter-OP links, and provides practical design insights for beam shaping and constellation topology to achieve target reliability with manageable hardware requirements.

Abstract

Free-space optical (FSO) communication has emerged as a promising technology for inter-satellite links (ISLs) due to its high data rate, low power consumption, and reduced interference. However, the performance of inter-satellite FSO systems is highly sensitive to beam misalignment. While pointing-ahead angle (PAA) compensation is commonly employed, the effectiveness of PAA compensation depends on precise orbital knowledge and advanced alignment hardware, which are not always feasible in practice. To address this challenge, this paper investigates the impact of beam misalignment on inter-satellite FSO communication. We derive a closed-form expression for the cumulative distribution function (CDF) of the FSO channel under the joint jitter and misalignment-induced pointing error, and introduce a truncated CDF formulation with a bisection algorithm to efficiently compute outage probabilities with guaranteed convergence and minimal computational overhead. To make the analysis more practical, we quantify displacement based on orbital dynamics. Numerical results demonstrate that the proposed model closely matches Monte Carlo simulations, making the proposed model highly useful to design inter-satellite FSO systems in practice.

Paper Structure

This paper contains 8 sections, 3 theorems, 49 equations, 11 figures, 1 table, 2 algorithms.

Table of Contents

  1. Introduction
  2. Related Work
  3. Challenges and Contributions
  4. System Model
  5. Pointing Error Channel Model
  6. Displacement Computation
  7. Simulation Results
  8. Conclusion

Key Result

Lemma 1

For a given displacement value $s$, the PDF of the corresponding FSO channel gain $h$ can be obtained by combining the beam power collection model in ep:h_approx with the Rician-distributed pointing error in eq:r. This yields the following PDF expression where the valid domain is $h \in [0, A_0]$.

Figures (11)

  • Figure 1: Inter-satellite FSO communication system with transmit satellite and receiver satellite. Both intra-orbital plane (intra-OP) and inter-orbital plane (inter-OP) links are shown in the figure.
  • Figure 2: Beam waist at the transmitter and divergence of the beam along the propagation axis with Gaussian beam model.
  • Figure 3: Jitter-induced pointing error (left) and joint jitter and misalignment-induced pointing error (right).
  • Figure 4: Misalignment due to movement of satellites.
  • Figure 5: Outage probability according to $P_t$ in an intra-OP link.
  • ...and 6 more figures

Theorems & Definitions (6)

  • Lemma 1
  • proof
  • Lemma 2
  • proof
  • Theorem 1
  • proof