## 2 Materials and Methods
### Spatial Simultaneous Functioning-based Joint Design System  
In this subsection, we provide a detailed overview of our innovative JCAS system, which is specifically designed to seamlessly integrate communication and sensing functionalities while effectively addressing interference and achieving performance balance.  
We initiate our discussion by highlighting two fundamental approaches: time division multiple access (TDMA) and spatial simultaneous functioning (SSF). SSF refers to the concurrent execution of communication and sensing tasks within the same frequency band or time frame. This method is advantageous when the communication and sensing tasks do not significantly interfere with each other, enabling continuous operation essential for real-time adaptive applications. Techniques such as multiple input multiple output (MIMO) systems or spatial separation can be used to minimize interference between communication and sensing signals. In contrast, TDMA-based systems alternate between communication and sensing tasks within separate time slots, thereby avoiding interference by ensuring  
Figure 2: JCAS downlink communication scenario.  
that only one type of task occurs at any given time. While this can simplify interference management, it may introduce delays that are less suitable for real-time applications.  
We select SSF due to its several advantages:  
* Real-Time Adaptation: SSF allows for continuous operation of both communication and sensing, which is critical for applications that require immediate responses.
* Efficient Resource Utilization: By enabling concurrent tasks, SSF makes better use of the available frequency spectrum.
* Reduced Latency: Unlike TDMA, which may introduce delays due to alternating tasks, SSF supports instantaneous task execution, reducing overall latency.
* Flexibility and Scalability: SSF can be more easily adapted to varying requirements and can scale with the addition of more MIMO channels or other spatial separation techniques.
* Energy Efficiency: Continuous operation in SSF can lead to more efficient energy use compared to the stop-and-start nature of TDMA.  
The choice between SSF and TDMA-based approaches depends on factors such as interference tolerance, real-time requirements, resource utilization, complexity and flexibility, and energy efficiency.  
We delve deeper into the design of the joint receiver, emphasizing the necessity of simultaneously processing communication and target echo signals. We advocate for SSF over TDMA due to its numerous benefits, providing detailed discussions on signal models and techniques for interference mitigation. Furthermore, we explore the integration of OFDM in both communication and radar sensing domains, covering aspects such as radar parameterization and comprehensive performance evaluations. We also examine the application of MIMO technology in OFDM systems to further enhance overall system effectiveness.  
Finally, we investigate the utilization of deep neural network-based techniques for channel estimation and signal detection, with a particular emphasis on long short-term memory (LSTM) networks and their associated model training methodologies. This multifaceted approach underscores our dedication to leveraging cutting-edge technologies to unlock the full potential of our JCAS system.