Air Interface Design for a TDD-Based 5G NTN System

Traditional satellite communication systems have employed the FDD mode, where the service link benefits from utilizing different frequency bands for uplink and downlink, resulting in better interference isolation and a relatively simple system design. However, with the increasing trend of direct satellite connection for mobile phones, the issue of how the service link can access low-frequency bands to support broadband communication services has become more prominent. In this paper, we propose an innovative design based on the TDD mode for the future evolution of the 5G NTN regenerative processing satellite communication system. The aim is to enhance the availability of spectrum resources for the service link in the low-frequency bands. By analyzing the changes in system design resulting from the use of the TDD mode compared to the FDD mode, we delve into the specific design of the TDD mode. Performance analysis demonstrates that with a compatible 20ms frame structure period the system efficiency of the TDD-based 5G NTN regenerative processing system achieves at least 60% that of FDD mode.