Finite-State Markov Chains Channel Model for CubeSats Communication Uplink

Abstract

This paper proposes a channel model to be applied to the communications systems of CubeSats. The model considers the low earth orbit geometry when a satellite is passing over a ground station, and the propagation surrounding multiple paths of the ground station location in urban areas. The geometry was used to define the deterministic factors, which contribute to the fading of the communication signal, such as Doppler effect and loss in free space. These are parameters that change as a function of time and elevation angle. Thus, a complete digital communication system, at the link layer level, is presented, using Markov Chains to model the previously cited effects in the form of a finite-state Markov channel. The proposed model was used as an uplink channel between a ground station and a CubeSat, both implementing a protocol stack, following the consultative committee for space data systems (CCSDS) recommendations. The ground station and the proposed communication channel were implemented through a functional simulation model and a telecommand and telemetry unit, implemented in hardware, was used as a case study for the CubeSat. Through the analysis of the simulated system, with telecommands sent by the station and responses sent by the hardware unit (in a hardware-in-the-loop setup), it was possible to demonstrate the operation of the proposed channel together with the retransmission mechanism suggested in the CCSDS recommendations, in order to mitigate communication issues.