Ambiguity-Resolved Waveform Design for Cell-Free OFDM-Based ISAC Systems

Cell-free integrated communication and sensing (ISAC) network architectures offer distinct advantages in collaborative transmission and sensing. However, enabling effective collaborative sensing within cell-free communication systems requires the careful design of orthogonal sensing waveform. Existing frequency-division design approaches for communication typically assume synchronization between the user equipment (UE) and the base station (BS) within the cyclic prefix (CP) duration. However, this frequency-division-based design introduces ambiguity issues in sensing applications. This paper begins by analyzing the distance perception ambiguity caused by frequency-division-based designs from a theoretical perspective. To address this, a pre-detection stage is introduced to eliminate distance sensing ambiguity within orthogonal frequency division multiplexing (OFDM) symbols. Based on this, a sensing frame structure is designed to enable high-precision distance and velocity sensing without ambiguity. Experimental validation confirms the effectiveness of this approach, demonstrating strong performance in sensing applications.