## 1 Introduction
### Research Gap and Our Contribution  
This paper advocates for the adoption of spatial simultaneous functioning (SSF) over time division multiple access (TDMA) in JCAS scenarios. SSF facilitates the concurrent operation of communication and sensing systems, thereby enhancing flexibility and efficiency, \begin{table}
\begin{tabular}{c c c} \hline \hline
**Properties** & **Radar** & **Communications** \\ \hline \multirow{4}{*}{Signal Waveforms} & Orthogonal signals in multiple input & Mix of modulated and \\  & multiple output (MIMO) radar, & ummodulated symbols, high \\  & unmodulated with wide bandwidth and low & Peak-to-Average Power Ratio (PAPR), & Peak-to-Average Power Ratio (PAPR), complex waveforms. \\  & Pulsed radar includes silent periods between & Packet-based signals without \\ Signal Structure & pulse transmissions, while continuous-wave & replication, varying lengths and \\  & radar allows continuous transmission. & intervals, flexible resource usage. \\  & Full duplex in continuous-wave radar using & Time division duplex or frequency \\  & beat signals, half duplex in pulsed radar & division duplex, full \\  & with quiet periods after transmissions. & duplex undeveloped. \\  & Locked transmitter and receiver clocks in & Transmitter and receiver share \\  & most radar setups. & timing clock; separate nodes may \\  & Traditional continuous-wave radar samples & \\ Receiver Sampling & signals below scanning bandwidth, limiting & bandwidth, providing full \\  & information conveyance. & bandwidth information. \\  & Detection probability, Cramér-Rao Lower & Capacity, Rate, Spectral efficiency, \\  & Bound (CRLB), Mutual Information (MI), & Signal-to-Interference-and-Noise \\  & Ambiguity function. & Ratio (SINR), and Bit Error \\  & Rate (BER). \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison between communication and radar signals and systems [4]. particularly in dynamic environments. While recent research efforts [7; 8; 9; 10; 11; 12; 13; 14; 15] have made significant strides in exploring joint communication and sensing scenarios, it is important to note that these studies primarily focus on the individual facets of the JCAS framework, such as waveform design, receiver architecture, and signal processing techniques. However, none of these studies consider SSF or compare it with TDMA. Recognizing these differences, we bring SSF into the spotlight in our study to showcase its potential advantages over TDMA in joint communication and sensing scenarios. In the context of JCAS, recent research efforts [7; 8; 9; 10; 11; 12; 13; 14; 15] have made notable progress. However, a discernible gap persists in addressing the key aspects comprehensively. The existing studies primarily concentrate on isolated components of the JCAS framework. Yet, there remains a need for a unified approach that integrates these elements into a cohesive framework for both single input single output (SISO) and MIMO JCAS receivers. SSF enables the concurrent operation of communication and radar sensing functions, addressing the growing need for spectrum efficiency and seamless operation in time-critical applications. By opting for SSF, our JCAS system stands to benefit from its simultaneous operation, which offers significant advantages, such as improved spectral efficiency and reduced latency. Furthermore, MIMO techniques can complement SSF by enhancing the performance of our system. MIMO involves using multiple antennas at both the transmitter and receiver ends to improve the communication reliability, increase the data rates, and mitigate interference. In the context of our JCAS system, employing MIMO allows us to spatially separate communication and sensing signals, thereby minimizing interference and maximizing the utilization of the available spectrum. This synergy between SSF and MIMO ensures the efficient and reliable operation of our system in dynamic and challenging environments. Building upon the insights gleaned from prior works, we propose a novel methodology to bridge this research gap.