# Persistent Homology Approach for Human Presence Detection from 60 GHz OTFS Transmissions
## 4 Experiments  
### Measurement Test-Bed  
Throughout the research described in this paper, we used our 60 GHz test-bed in the joint communication and sensing scenario depicted in Figure 5. The radio frequency transmitter sends the data to the receiver to whom it communicates (communication receiver), while part of the information is eventually reflected from the persons or objects located inside the monitored environment. The reflected signal is processed in the sensing receiver collocated with the transmitter. As our measurement test-bed is equipped with a single receiver only, during the experiments, we have been focusing only on the processing of the reflected signals, i.e., on the sensing task. In the following, we will thus describe the detailed structure of the transmitter and the sensing receiver only. The baseband parts of the transmitter and the sensing receiver are based on two Xilinx Zynq UltraScale+ RFSoC ZCU111 development boards. At the transmitter, fast 4.096 GSps D/A converters (DAC's) of the first ZCU111 board are used to generate an intermediate frequency signal with a bandwidth of up to 512 MHz. The second ZCU111 serves to sample the baseband signals at the sensing receiver with its fast A/D converters (ADCs), also clocked at 4.096 GSps. Both ZCU111 boards are controlled by the host PC via an Ethernet connection, and the received data are stored in the receiving ZCU111 M2 SATA hard drive. The results of the measurements can be transferred to the host PC via an Ethernet connection. Figure 4: Persistent Homology example for one OTFS slot. Delay-Doppler 2D plot (**left**), identified local maxima (**middle**), and the persistence diagram (**right**). The numbers in the middle and right image denote the index of the identified peak, with index 1 corresponding to the most significant one. Figure 5: Test-bed in joint communication and sensing scenario. At the transmitter, the signal in the form of its I and Q components is filtered by a pair of low-pass filters VLFX-2500+, and upconverted to the desired millimeter wave frequency by the Sivers IMA FC1005V/00 up/down converter operational within the frequency range of 57-66 GHz and providing up to 5 GHz bandwidth. The Agilent 83752A generator is used to provide a low phase noise local oscillator signal with stable frequency for the upconversion. The RF signal power is boosted by the QuinStar QPW-50662330-C1 power amplifier (50-60 GHz frequency band, 30 dB gain, P1 dB of 23 dBm) and transmitted using a waveguide horn antenna. At the sensing receiver, the signal reflected from the persons within the monitored area is received by a processing chain analogous to the transmitting side of the measurement test-bed. The signal is received by the same type of waveguide horn antenna and amplified by the Quinstar QLW-50754530-I2 low noise amplifier (frequency range 50-75 GHz, 30 dB gain, and the typical noise figure of 5 dB). If needed, the input level to the downconverter can be adjusted by a variable attenuator. The downconversion is performed by the Sivers IMA FC1003V/01 up/down converter with a local oscillator signal generated by the Agilent E8257D generator. After the low-pass filtering by the second pair of VLFX-2500+ filters, the baseband signal is processed in ZCU111 board. During all experiments, the ZCU111 boards and the two signal generators were synchronized by the 10 MHz reference generated by a Rubidium (Rb) oscillator. The photo of the assembled test-bed is shown in Figure 6.  
The hardware impairments of the RF front-end can seriously degrade the performance of wideband transceivers, including the OTFS millimeter wave systems [14]. Full compensation of the RF impairments is challenging, especially for wideband systems such as our 60 GHz test-bed.