Subsystem Description

Functional Architecture

The communications subsystem is responsible for telecommand reception and telemetry transmission. Being so that the functionality of the satellite's control from the Earth ground station completely relies on the COMMS subsystem. Therefore, it is imperative for the COMMS subsystem to fulfill specific requirements to facilitate accurate communication and seamless operation of the satellite.

It is opted for the utilization of LPWANs (Low Power Wide Area Networks), specifically employing the LoRa (Long Range) physical layer technology. COMMS hardware is located both in the OBC-COMMS board as well as in a lateral board (where the antenna is soldered or screwed). The subsystem can be divided into different blocks to identify their functionality.

The first one is the power circuit, tasked with ensuring the proper power supply and composed by passive components. The transciever is the key component of the SS, responsible of both the recepction as well as the transmission of information from and to the ground station. It communicates with the MCU through SPI, as a slave, and performs signal modulation and demodulation.

The transciever requires an stable reference signal in order to perform its tasks, this is provided by a crystal oscillator.

The RX Line transmits the received signal from the antenna to the transciever. The line is balanced by a balun and impendance matched. The TX Line transmits the transmitted signal from the transciever to the antenna and presents different filters and matchings. The line to be used at each instant is selected by the switch, controlled by the transciever, which is at the same time controlled by the MCU.

Finally, the antenna, connected to the switch through a line that boths filters and matches impedance, is responsible for physically receiving and transmitting electromagnetic waves.

Requirements