A Unified Software-Defined Radio Framework for Flexible Waveform Design in Non-Terrestrial Networks

The integration between terrestrial and non-terrestrial networks (T-NTNs) in the framework of “5G and beyond” standardization requires a flexible PHY-layer design. Indeed, it is known that future NTN connections will be characterized by highly heterogeneous data-rate requirements and usage of different frequency bands. Therefore, the waveform design of the non-terrestrial segment should cope with specific end-to-end performance indicators. In our paper, we aim to propose a new waveform design and implementation methodology, based on Software-Defined Radio (SDR), to be deployed in a strongly innovative NTN framework characterized by disruptive concepts like, for instance, megaconstellations of LEO satellites and cell-free massive MIMO. After detailing the communication ecosystem where data are exchanged, the starting point of our analysis relies on the general representation of 6G waveforms in terms of a mathematical time-frequency lattice structure. In our view, such a structure will be propedeutical to define a software-based reconfigurable platform, where the different radio interfaces can be obtained in the baseband domain by adding (or removing) software modules and/or re-parameterizing them. The paper will describe in detail the above-mentioned SDR-based strategy and will provide some useful guidelines for the practical implementation of the reconfigurable NTN transceivers. Preliminary results in terms of waveform implementation and link performance evaluation will motivate the full-software PHY-layer design strategy considered in our work.