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.

中文翻译：

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立方体卫星通信上行链路的有限状态马尔可夫链信道模型

本文提出了一种应用于立方体卫星通信系统的信道模型。该模型考虑了卫星经过地面站时的低地球轨道几何形状，以及城市地区地面站位置的多条路径周围的传播。几何结构用于定义导致通信信号衰落的确定性因素，例如多普勒效应和自由空间中的损耗。这些是作为时间和仰角的函数而变化的参数。因此，在链路层级提出了一个完整的数字通信系统，使用马尔可夫链以有限状态马尔可夫信道的形式对先前引用的影响进行建模。提出的模型被用作地面站和立方体卫星之间的上行链路信道，两者都实现了一个协议栈，遵循空间数据系统咨询委员会 (CCSDS) 的建议。地面站和提议的通信信道是通过功能仿真模型实现的，在硬件中实现的遥控和遥测单元被用作 CubeSat 的案例研究。通过对模拟系统的分析，站发送的遥控命令和硬件单元发送的响应（在硬件在环设置中），可以演示所建议信道的操作以及重传机制CCSDS 建议中的建议，以减轻沟通问题。地面站和提议的通信信道是通过功能仿真模型实现的，在硬件中实现的遥控和遥测单元被用作 CubeSat 的案例研究。通过对模拟系统的分析，站发送的遥控命令和硬件单元发送的响应（在硬件在环设置中），可以演示所建议信道的操作以及重传机制CCSDS 建议中的建议，以减轻沟通问题。地面站和提议的通信信道是通过功能仿真模型实现的，在硬件中实现的遥控和遥测单元被用作 CubeSat 的案例研究。通过对模拟系统的分析，站发送的遥控命令和硬件单元发送的响应（在硬件在环设置中），可以演示所建议信道的操作以及重传机制CCSDS 建议中的建议，以减轻沟通问题。