## 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
 \tag{8}\]  
where \(q=(n_{e}-1)N_{d}+n_{d},1\leq n_{e}\leq N_{e},1\leq n_{d}\leq N_{d},1\leq n\leq N _{sc},1\leq n_{a}\leq N_{a}\), \(\tilde{y}_{n,n_{e},q}\) is the received signal at \(n\)th subcarrier, when sensing the angle indexed by \((n_{a},n_{e})\). \(\tilde{z}_{n}\) is the noise sample and \(\tilde{s}_{n}\) is the baseband signal for the subcarrier \(n\). While \(T_{s}\) is the symbol duration, \(f_{0}=1/T_{s}\). The number of subcarriers and symbols for coherent processing is determined by \(N_{sc}=c_{0}T_{s}/(2\Delta r)\) and \(N_{d}=c_{0}/(2f_{c}\Delta vT_{s})\), respectively, where \(c_{0}\) is the speed of light in free-space, and \(\Delta r\) and \(\Delta v\) denote the range and velocity resolutions, respectively. It is assumed that the communication beam is constant during \(T_{f}\), the time of one communication packet. At each scanning angle, \(\mathbf{w}_{s}\) and consequently \(\mathbf{w}_{JCAS}\) in (6) are calculated, and \(\tilde{y}_{n,n_{e},q}\) is obtained by (8). * **Range-Doppler Estimates**. To estimate the range-Doppler of targets, first \(\tilde{s}_{n}\) is removed from the received signal and then the inverse fast Fourier transform (IFFT) and fast Fourier transform (FFT) are applied [23] as: \[ \begin{split}&\tilde{c}_{n,n_{e},q}=\tilde{y}_{n,n_{e},q}/\tilde{s}_{ n}=\tilde{h}_{n,n_{e},q}-\tilde{z}_{n}/\tilde{s}_{n},\\ &\mathbf{D}_{n_{e},n_{e}}=\mathbf{FFT}_{n}[\mathbf{FFT}_{k}[ \tilde{c}_{n,n_{e},q}]]\end{split} \] (9)where \(\mathbf{D}_{n_{a},n_{e}}\in\mathbb{C}^{N_{d}\times N_{se}}\) is the range-Doppler profile when scanning the angle indexed by \((n_{a},n_{e})\). * **Angular estimates**. The angle estimation is based on beamforming through weighting vector \(\mathbf{w}_{s}\). As the sensing is in the scanning mode, the Cramer-Rao lower bound (CRLB) for the angle estimation of \(\Delta\) is [10]: \[CRLB_{\Delta}\propto\frac{\theta_{3 dB}^{2}}{SNR},\text{ where }SNR=\frac{\mathbb{E}[|\hat{h}_{n,n_{a},k}|^{2}]}{ \mathbb{E}[|z_{n}/\hat{s}_{n}|^{2}]},\] (10) where \(\theta_{3 dB}\) is the 3 dB-beamwidth of the radiation pattern of the array, which is assumed to be constant for all the angles \(\Delta\)s in FoV, and \(SNR\) is the signal-to-noise ratio defined by (10) according to (9). 3.2 JCAS Scenario 2: Overlapping Communication and Sensing Beams When the UE Blocks the Sensing Target  
**Communication Performance**. When the UE blocks the sensing link, the two beams are aligned and superimposed; the whole energy is captured by the UE, then the spectral efficiency is increased. Since \(\mathbf{w}_{JCAS}=\sqrt{2}\mathbf{w}_{c}\), the superimposed channel is \(R=\text{log}_{2}\text{det}(1+2\mathbf{H}^{*}\mathbf{H}/\sigma_{n}^{2})\). This happens either in the scanning mode of sensing or the tracking mode with the range of the target being larger than the range of UE as in Figure 4b. **Sensing Performance**. When the UE blocks the sensing target, the BS can no longer sense/detect the target and the BS has lost the target; on the other side, the target does not cause communication link degradation. 3.3 JCAS Scenario 3: Overlapping Communication and Sensing Beams When the Sensing Target Blocks the UE  
Let us study the overlapping when the range of the target is smaller than the range of the UE, as in Figure 4c. It is supposed that the human as the target occupies only one angle step, is tracked, and the sensing beam is aligned with the angle of the target. Whether the human is a point or an extended target, depends on the spatial resolutions. The maximum bandwidth of the n261 band of 5G is 400 MHz, which equals 37.5 cm range resolution. Besides, the distance of a human from the BS can be, e.g., 70 m, then in such a distance with a 10\({}^{\circ}\) beamwidth of the aperture, the cross-range resolution equals 6.1 m. The assumption in this paper is that a human can fit in a single spatial bin, and is a point target. The mono-static radar-cross-section (RCS) of the human, which also depends on the incident angle, is \([-3.6,-5.2]\) dBm at 28 GHz [37]. **Communication Performance**.