# Human Activity Signatures Captured Under Different Directions Using SISO and MIMO Radar Systems
## 4 Human Activity Signatures by Using a Distributed MIMO FMCW Radar System
### Results for the Proposed \(2\times 2\) MIMO Configuration  
We have connected the Ancortek MIMO radar system with a signal processor, which processes the MIMO radar's raw IQ data according to the method discussed in Section 2. For this research, we have recorded the radar's raw IQ data for a \(2\times 2\) distributed MIMO radar system, and then we have processed the data offline using MATLAB. Identical but independent radar signal preprocessing chains are implemented for the two subchannels. For each human activity, we have computed the radial velocity distribution \(p_{ii}(v,t)\) using (14) and mean radial velocity \(\bar{v}_{ii}(t)\) using (15) for \(i\in\{1,2\}\). Figures 8 and 9 correspond to Radar\({}_{2}\), which show the TV radial velocity distribution \(p_{22}(v,t)\) for the falling and walking activities, respectively. Note that, for the monostatic SISO configuration and \(2\times 2\) MIMO configuration in Sections 3 and 4, respectively, the positions of the transmitter antenna \(A_{1}^{T_{x}}\) and receiver antenna \(A_{1}^{R_{x}}\) are identical. Therefore, Radar\({}_{1}\) of the \(2\times 2\) MIMO radar system is identical to the monostatic SISO radar system. As a consequence, the TV radial velocity distributions \(p_{11}(v,t)\) corresponding to Radar\({}_{1}\) and the SISO radar system are the same. Recall that the TV radial velocity distributions \(p_{11}(v,t)\) corresponding to Radar\({}_{1}\) are shown in Figures 2 and 3 for the falling and walking activities, respectively. For all observed activities, we have also computed the mean radial velocity \(\bar{v}_{ii}(t)\), which is represented by the black dashed line in Figures 2, 3, 8 and 9. The falling and walking activities were performed in three different scenarios to see the effect of the human activity direction on the measured TV radial velocity distribution \(p_{ii}(v,t)\). Figure 7: Two radar subsystems forming a \(2\times 2\) distributed MIMO radar system in the presence of a moving person in a cluttered indoor environment. In Figure 7, we can see that the direction of movement is parallel to the boresight of Radar\({}_{1}\) and orthogonal to the boresight of Radar\({}_{2}\) for Scenario 1. To perform the walking activity in Scenario 1, the person walks from the position \((x_{3},y_{2})\) towards the position \((x_{1},y_{2})\) in a straight line. Similarly, to perform a falling activity, the person first stands still on the position \((x_{3},y_{2})\) and then falls onto a mattress facing towards the antennas of Radar\({}_{1}\). Figures 2a and 8a show the impact of the falling activity on the measured TV radial velocity distributions \(p_{11}(v,t)\) and \(p_{22}(v,t)\), respectively. For the walking activity, Figures 3a and 9a show the measured TV radial velocity distributions \(p_{11}(v,t)\) and \(p_{22}(v,t)\), respectively. Evidently from Figures 2a, 8a, 3a and 9a, the \(2\times 2\) MIMO radar system is able to acquire good multi-perspective human activity signatures for Scenario 1. As the direction of the activity is towards Radar\({}_{1}\) in Scenario 1, it is obvious that Figures 2a and 3a give better activity signatures than Figures 8a and 9a, respectively. The walking and falling activities are repeated for Scenario 2, where the initial and final positions are at \((x_{2},y_{3})\) and \((x_{2},y_{1})\), respectively, as shown in Figure 7. Thus, the direction of motion in Scenario 2 is orthogonal to the boresight of Radar\({}_{1}\) and parallel to the boresight of Radar\({}_{2}\). In Figures 2b and 8b, the TV radial velocity distribution \(p_{ii}(v,t)\) of the falling activity is shown for Radar\({}_{1}\) and Radar\({}_{2}\), respectively. Analogously, Figures 3b and 9b show the TV radial velocity distribution \(p_{ii}(v,t)\) of the walking activity corresponding to Radar\({}_{1}\) and Radar\({}_{2}\), respectively. From the measurement results, we can see that the distributed MIMO radar system captures good human activity signatures for Scenario 2 as well.