## 2 Related Works  
Signal coexistence for achieving higher spectral efficiency has recently garnered significant attention, e.g., in [12; 13; 14; 15; 16]. Reference [12] proposes a system that combines collaborative communication technology with cognitive radio, which improves the overall performance of the system through cooperative spectrum-sharing networks. Reference [13] explored the coexistence of LAA and WIFI over unlicensed bands through a static contention window method. Their work provides practical solutions for achieving technological coexistence in existing network architectures. Reference [14] explores the advantages of integrating sensing and communication technologies (ISAC), including high spectral efficiency, low hardware costs, and improved system performance, as well as the potential for ISAC in future 6G applications. Reference [15] proposed a joint design framework for communication and sensing in small cellular networks, which optimizes the collaborative work of communication and sensing through waveform selection and resource allocation. Reference [16] addresses the practical challenges of residual hardware impairments (RHIs) and imperfect successive interference cancellation, deriving the superior performance of the ISAC framework compared to the sensing-communication coexistence (SCC) framework. It demonstrates that the integration of sensing and communication is a significant trend for future development. In a highly dynamic V2X scenario, JCS systems can make network service adjustments more flexible and robust by simultaneously handling communication and sensing signals and dynamically coordinating [17]. Extensive research has focused on the JCS in vehicular networks, primarily concentrating on signal waveform design [18; 19; 20] and power management [21; 22; 23]. Firstly, extensive research on the design of signal waveforms provide the theoretical model foundation for the feasibility of JCS systems. Secondly, regarding interference and resource management, it can be found that existing research in JCS primarily focuses on large bandwidth millimeter-wave bands or Vehicle-to-Infrastructure (V2I) scenarios, which have certain limitations. The optimization of JCS system resource allocation is a challenge for V2V direct communication with limited resources and no base station assistance. In Release 16, the 3 rd Generation Partnership Project (3 GPP) developed the NR-V2X and defined a new air interface PC5 as the sidelink, which allows for direct vehicle-to-vehicle communication to support various advanced use cases, covering four areas: platooning, extended sensing, remote driving, and autonomous driving [24]. In recent years, research on the sensing capabilities of NR-V2X sidelink signals has been increasingly explored. Studies on the theoretical foundation of CRLB for the sidelink sensing performance highlight the potential value for the resource allocation scheme of the JCS sidelink system. Reference [25] utilizes unused communication subcarriers of the 5G NR waveform as radar sensing subcarriers, aiming to minimize the CRLB of distance estimation by optimizing the amplitude of radar subcarriers, thereby improving sensing performance. Reference [26] derives the CRLB for distance/angle estimation accuracy based on sidelink OFDM signals, demonstrating the feasibility of sidelink JCS signals for near-field localization. References [5; 27] derive the CRLB and mean squared error (MSE) for the sensing location of sidelink signals and analyze in detail the impact of communication physical layer parameters on sensing performance under interference conditions. Reference [28] compares the radar sensing performance of sidelink resource allocation SPS algorithms versus random allocation algorithms under interference, indicating that the JCS resource allocation mechanism is also a key factor affecting sidelink sensing performance. The above existing research contributions can be referenced to conduct a theoretical performance analysis of the sidelink JCS system in this paper.