Toward a Common Transceiver Framework for 6G: Orthogonal Coexistence and Structural Unification of DFT Waveforms

In this paper, we propose a unified transceiver framework based on single-carrier interleaved frequency division multiplexing (SC-IFDM) to address key challenges in fifth-generation (5G) and sixth-generation (6G) networks, including spectral efficiency, backward compatibility, structural flexibility, and support for joint sensing and communication (JSAC). Rather than introducing a new parametrizable waveform, we demonstrate that SC-IFDM can serve as a reconfigurable processing backbone capable of generating a wide class of discrete Fourier transform (DFT)-based waveforms through simple phase adjustments and index-specific data placement. This includes orthogonal frequency division multiplexing (OFDM), orthogonal chirp division multiplexing (OCDM), orthogonal time-frequency space (OTFS), affine frequency division multiplexing (AFDM), and frequency modulated continuous wave (FMCW). The framework ensures seamless waveform adaptation and orthogonal coexistence by exploiting sparsity in the DFT domain and maintaining compatibility with legacy systems. We present rigorous architectural analysis, resource allocation strategies, and coexistence mechanisms within shared time-frequency resources. Simulation results validate the proposed scheme, demonstrating its ability to support diverse waveform requirements with improved performance, scalability, and flexibility compared to conventional multi-waveform approaches.