Joint beamforming and beam scheduling in SWIPT for fractionated spacecraft systems

Fractionated spacecraft is a novel technology to improve flexibility, robustness, and survivability in future satellite systems by decomposing a traditional spacecraft into multiple functional modules. This paper investigates simultaneous wireless information and power transfer (SWIPT) for a fractionated spacecraft system, where a primary satellite (PS) equipped with a large scale antenna array transmits energy signals to charge multiple energy-constrained miniaturized satellites (MSs) in the near field of the PS, and simultaneously sends information signals to serve ground information receivers (IRs) in the far field of the PS. A joint optimization problem of digital beamforming, analog beamforming, and beam scheduling at the PS is developed to maximize the achievable sum rate of the IRs subject to a requirement on MSs’ harvested energy. Due to the highly coupled optimization variables and the binary beam-scheduling variables, the formulated problem is a mixed-integer non-linear programming (MINLP) problem and hence, is difficult to solve. We first develop an alternating optimization algorithm to solve the formulated problem based on the weighted minimum meansquare error method, the manifold optimization method, and the matching theory. To get a low-complexity solution of the formulated problem, we derive the coherence between near- and far-field steering vectors. Then by exploiting the channel coherence, we propose a low-complexity algorithm that transforms the original MINLP problem to a linear programming problem. Numerical results are provided to validate the performance improvement of our proposed algorithms compared to various benchmark schemes, and reveal the practical significance of our developed beamforming and beam scheduling strategies for spectral- and energy-efficient fractionated spacecraft SWIPT.