## 2 Proposed STPA Configuration for JCAS, Its Design Pipeline, and Performance
### JCAS Scenarios and Performance Metrics
#### 2.3.1 JCAS Scenario 1: Non-Overlapping Communication and Sensing Beam Directions
When an environment object moves into the Fresnel zone of the communication link, the target first serves as the multipath reflector/scatterer and results in multipath interferenced to the LoS signal of the communication link; then the target, depending on its RCS, could totally block the communication link and cause deep fading and thus severe communication link quality degradation. When the target moves towards the communication link, the beams are overlapping, the LoS link vanishes and blockage occurs. In order to model the blockage, the following channel model from BS to the single antenna UE is considered with and without blockage [38; 39]:  
\[\mathbf{H}= \begin{cases}\mathbf{H}_{LoS}+\mathbf{H}_{NLoS}+\mathbf{H}_{target, 1}&\text{if no overlapping beams,}\\ \mathbf{H}_{NLoS}+\mathbf{H}_{target,2}&\text{if beams overlapping,}\end{cases}  \tag{11}\]  
where:  
\[ \begin{split}&\mathbf{H}_{LoS}=\mathbf{a}_{T}(\theta_{UE}, \phi_{UE})\mathcal{S}_{T}(\theta_{UE},\phi_{UE})g_{R}(\theta_{BS},\phi_{BS}) \frac{\lambda}{4\pi r_{UE}}e^{-j\frac{2\pi}{\lambda}r_{UE}},\\ &\mathbf{H}_{target,s}=\mathbf{a}_{T}(\theta_{t},\phi_{t}) \mathcal{S}_{T}(\theta_{t},\phi_{t})g_{R}(\theta_{r},\phi_{r})\frac{\lambda}{4 \pi d_{t}}\Gamma_{s,s}e^{-j\frac{2\pi}{\lambda}d_{t}},s\in\{1,2\},d_{t}=r_{t}+ r_{r},\end{split}  \tag{12}\]where \(\mathbf{H}_{NLoS}\) is the same channel (5) as described in Section 2.3.1, \(\mathbf{H}_{target,1}\) and \(\mathbf{H}_{target,2}\) denote the channel of BS-target-UE before or after the blockage and during the blockage, respectively. \(g_{T}\) and \(g_{R}\) denote the gains of antennas at BS and UE, respectively. \((\theta_{UE},\phi_{UE})\) and \((\theta_{BS},\phi_{BS})\) are the angles of the UE viewing from BS and BS viewing from UE respectively. \((\theta_{t},\phi_{t})\) and \((\theta_{r},\phi_{r})\) denote the angles of the target viewing from BS and target viewing from UE, respectively. \(r_{t}\) and \(r_{r}\) are the distance between the target and the BS, and the target and the UE, respectively. \(\Gamma_{t,1}\) which models the reflection and scattering from the human is calculated by [38]:  
\[\Gamma_{t,1}(\delta)=\frac{e_{b}\sin\delta-\sqrt{e_{b}-\cos^{2}\delta}}{e_{b} \sin\delta+\sqrt{e_{b}-\cos^{2}\delta}}+\mathcal{CN}(0,\sigma_{b}^{2}) \tag{13}\]  
where \(\delta\) is the incident angle on the body, \(e_{b}\) is the complex permittivity of the body and a zero-mean Gaussian random variable with a standard deviation of \(\sigma_{b}\) models the non-flat body and swinging limbs. Besides, when the human blocks the LoS link, the result is 20 dB attenuation of power at the receiver UE [40], therefore \(\Gamma_{t,2}\), which denotes the diffraction coefficient, equals 0.1 at the operation frequency of 28 GHz. We assume that the target moves in a line perpendicular to the LoS path where \(\phi_{t}=\phi_{UE}\) and only the angle \(\theta_{t}\) varies, and its Doppler effects on \(\mathbf{H}_{target,s}\) are negligible. The channel modeled in (11) is used for calculating the spectral efficiency. **Sensing Performance**. As the sensing is in the tracking mode, we adopt the Bayesian CRLB (BCRLB) for the point target tracking. The Fisher Information Matrix (FIM) at the \(\eta^{\text{th}}\) epoch can be written as [41]:  
\[\mathbf{J}_{\eta}=\mathbf{J}_{\eta}^{D}+\mathbf{J}_{\eta}^{\text{p}}(\mathbf{J }_{\eta-1}) \tag{14}\]  
where \(\mathbf{J}_{\eta}^{D}\) is the data information matrix and \(\mathbf{J}_{\eta}^{D}\) is the prior information matrix that depends on the \(\mathbf{J}_{\eta-1}^{D}\). The elements of the data FIM, \(\mathbf{J}_{\eta}^{D}\) for the delay, Doppler, and angle are related directly to the \(SNR\) at each epoch, however, data FIM for the angle is also inversely related to the 3 dB-beamwidth of the JCAS aperture [41].