The growing number of space missions adopting small satellites platforms, together with the request of larger data rates, points out the need for efficient software-defined radios providing high reconfigurability. For this reason the Italian aerospace company Argotec has undertaken the development of a software-defined radio transponder for deep space applications, named ERMES. This thesis is focused on the development of the telemetry subsystem for the ERMES transponder. In particular the physical and coding layer will be implemented, focusing on system reconfigurability and compatibility with CCSDS standards. The different components of the transmission chain will be investigated, paying attention to possible hardware-oriented implementations.