Toward Practical HARQ-Based RC-LDPC Design for Optical Satellite-Assisted Vehicular Networks

Free-space optics (FSO)-based low-Earth orbit (LEO) satellite systems have recently aroused considerable attention as an enabling technology for the Internet of Vehicles (IoVs) applications. However, such systems face critical challenges, including cloud coverage, atmospheric turbulence, and pointing errors. This article addresses a link-layer error-control design solution, which is a combination of the low-density parity check (LDPC) code and the incremental redundancy (IR)-hybrid automatic repeat request (HARQ) protocol. We consider a subclass of rate-compatible (RC)-LDPC code extension, i.e., protograph-based raptorlike (PBRL)-LDPC codes, for the proposed IR-HARQ design. In addition, we provide a comprehensive analytical framework to obtain performance metrics, including goodput, energy efficiency, and average frame delay. Numerical results highlight the outperformance of the design proposal compared to conventional link-layer solutions in FSO-based LEO satellite systems. Also, we provide a design guideline regarding the proper selection of transmitted power and decoding complexity concerns. Furthermore, we investigate the feasibility of our design proposal for a study case involving the existing Japan LEO satellite networks and the moving vehicles. Finally, we conduct the Monte-Carlo simulations to validate the correctness of theoretical results.