福爾摩沙衛星五號有兩個通訊次系統，兩個次系統的使命和運作方式不盡相同：一個屬於衛星本體的 TTC (Telemetry and Telecommand) 次系統，負責衛星和地面的雙向通聯，接收從地面天線發送的控制指 令，也將衛星的本身各項數據資料和「先進電離層探測儀」科學酬載資料下傳至地面。另一個是 XDS (X-band Downlink System) 次系統，負責將「光學遙測酬載」的資料下傳到地面由 X-band 天線系統接收。 以下將簡介這兩個通訊次系統。

This article describes the two communications sub-systems on the Formosat-5 satellite, namely the Telemetry and Telecommand (TTC) sub-system and the X-band Downlink System (XDS) sub-system. They have dissimilar goals and operations scenarios. TTC sub-system, a part of spacecraft bus, is in charge of the bilateral communications between the satellite and the S-band TTC ground stations. TTC receives the commands sent by the antenna on ground, and delivers the state of health data of the satellite together with data of Advanced Ionospheric Probe (AIP) payload to the ground antenna. On the other hand, XDS sub-system downloads the compressed and encoded Remote Sensing Instrument (RSI) payload data (image data) to the X-band receiving antenna system on ground.