Joint sensing and communication (JSAC) has become increasingly popular in recent years due to spectrum scarcity, hardware limitations, power constraints, and the emergence of applications that require both communication and sensing capabilities. As such, the coexistence of both functionalities remains a challenge for current systems. Therefore, this article proposes a novel orthogonal time-frequency space (OTFS)-chirp waveform. The proposed waveform exploits the sparsity of linear chirps in delay-Doppler domain to multiplex OTFS and chirp in orthogonal manner. This enables simultaneous high-data rate communication and low-complexity accurate sensing simultaneously. Furthermore, we propose a multiuser JSAC scheme where multiple orthogonal chirps (OCs) are assigned to different users within the same OTFS-Chirp waveform. On top of that, a novel chirp-based channel estimation technique is proposed for OTFS systems. The proposed method leverages the sparsity of chirp in both delay-Doppler and Fresnel domains. This approach alleviates the pilot guard overhead and reduces the peak-to-average power ratio (PAPR) of the transmitted signal. The effectiveness of the proposed JSAC waveform is verified by the conducted numerical results that agree with the developed analysis and validate that the proposed waveform design can achieve accurate low-complexity radar parameter estimation while preserving high-data rates.

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.