Optimized Design of Multi-Layer LEO Satellite Constellations for Integrated Communication and Signal-of-Opportunity Doppler Positioning

Future low Earth orbit (LEO) communication constellations are evolving into integrated multi-mission infrastructure. Their signals of opportunity (SoP) are therefore becoming attractive for Doppler positioning. However, the conventional coverage- or rate-optimized configurations may not provide favorable Doppler geometry under realistic link-quality constraints. This paper considers this emerging requirement at the constellation-configuration design level and proposes a multi-layer Walker optimization framework for integrated communication and SoP Doppler positioning. A system-level positioning metric is developed to move beyond visibility and dilution-of-precision indicators. A link-quality-constrained multi-epoch Fisher information matrix (FIM) incorporates C/N0-based link measurability and a general carrier-to-noise-density-dependent Doppler-noise formulation. In the reported simulations, C/N0 controls observation admission, while all admitted Doppler observations use a fixed noise standard deviation of 0.5 m/s. An effective position-error bound is then obtained by marginalizing clock-drift and frequency-bias nuisance states. Based on a unified satellite–ground geometry, weighted service coverage, weighted best-link achievable rate, and the proposed positioning metric are jointly optimized using a constrained mixed-integer multi-objective artificial hummingbird algorithm (CMI-MOAHA). The FIM-based metric is consistent with the positioning root mean square error (RMSE) from a separately implemented nonlinear Doppler solver under matched observation and noise assumptions. With the total number of satellites fixed at 2000, the Pareto archive reveals clear trade-offs among coverage, best-link achievable rate, and positioning. When the positioning objective is included, the best obtained positioning metric decreases across all tested constellation sizes, with a maximum reduction of 77.1%. These results show that constellation-level joint optimization is warranted when LEO communication satellites also serve as SoP for Doppler positioning.