# Initial Experimentation of a Real-Time 5G mmWave Downlink Positioning Testbed +
## 4 HOP-5G mmWave Positioning Testbed  
The HOP-5G mmWave positioning testbed is based on a fixed mmWave gNB and moving mmWave UE, as it is shown in Figure 3. This testbed follows a modular architecture to enable the operation of each node as transmitter or receiver with specific hardware and software configurations. The key hardware components of the testbed are as follows:  
* mmWave front end: The Sivers EVK02001 is an evaluation kit with an analog beamformer mmWave front end (FE) able to up-convert 5G NR signals from baseband to mmWave or to down-convert from mmWave to baseband, by integrating the Sivers TRXBF02 COTS transceiver. The 16-element antenna array, i.e., non-commercial uni  
Figure 2: Example of beam-based AoA estimation demonstrated on test data obtained with horn antenna as transmitter and beam-sweeping Anokiwave antenna array with fixed gain as receiver: (**a**) maximum power is defined, parabola fit is successful, and AoA is estimated as interpolation between beam directions; (**b**) parabola fit is successful, and AoA is estimated as extrapolation beyond the range of azimuth angle \(\phi\); (**c**) maximum is on the boundary, parabola fit is unsuccessful, and AoA is estimated as a direction of a beam with maximum power value. Note that beam powers are normalized to maximum value. This test setup does not use any SDR. form rectangular array (URA) with 2 \(\times\) 8 elements, enables steerable beams within the beambook upon operator commands. * Software-defined radio: The USRP X310 is a flexible SDR, which here includes a BasicTX or BasicRX daughterboard for transmission or for reception, respectively, and a GPS disciplined oscillator (GPSDO) to increase the stability of the SDR clock. This SDR is used with a sampling rate of 92.16 Msps to stream the baseband samples of the 5G NR signals between the mmWave front end and the host computer. * Host computer: The host computer includes the necessary software modules to establish 5G transmission, 5G reception, GNSS data collection and AoA estimation. At the transmission, the OAI gNB is used to stream the 5G PRS to the mmWave front end through the SDR in real time. At the reception, the OAI UE is used to process the 5G PRS and to obtain ToA and RSRP measurements in real time, and the AoA estimator controls the beams of the mmWave front end and computes the AoA measurements also in real time. In both nodes, the GNSS receiver manager operates and collects the GNSS position solution from the receiver in real time. * GNSS receiver: The u-blox F9P is a multi-band high precision GNSS receiver, whose position solution is used for the ground truth of the field campaign. * GNSS antenna: A survey multi-band GNSS antenna is used at both nodes together with a splitter to feed GNSS signals to the USRP GPSDO and to the GNSS receiver. The AoA estimation software module at the UE host computer controls the mmWave front end to enable real-time AoA measurements. This module connects to the Sivers EVK and initiates its operation. Then, the software proceeds to establish the reception beam on the antenna array. As it is described in Section 3, beam-based AoA estimation is performed with the RSRP measurements of the PRS received from the gNB for each beam. Thus, the AoA algorithm collects RSRP measurements for each beam angle and proceeds to sweep each beam within \(-45\) degrees to 45 degrees with a 4.5-degree resolution per beam. The reception duration for each beam angle is 20 ms, which is sufficient for the OAI UE to perform and disseminate the PRS RSRP and ToA measurements. The measurement dissemination is performed over the MQTT protocol. OAI publishes the measurements messages in a specific MQTT topic, and the AoA algorithm subscribes to this topic to collect the measured RSRP values for each reception beam angle. Since the RSRP collection lasts 20 ms for each beam, the overall measurement collection has a duration of 420 ms for all beams. After the RSRP collection, the AoA algorithm estimates the reception angle in real time.