# A Comparative Study of 3D UE Positioning in 5G New Radio with a Single Station
###### Abstract  
The 5G network is considered as the essential underpinning infrastructure of manned and unmanned autonomous machines, such as drones and vehicles. Besides aiming to achieve reliable and low-latency wireless connectivity, positioning is another function provided by the 5G network to support the autonomous machines as the coexistence with the Global Navigation Satellite System (GNSS) is typically supported on smart 5G devices. This paper is a pilot study of using 5G uplink physical layer channel sounding reference signals (SRSs) for 3D user equipment (UE) positioning. The 3D positioning capability is backed by the uniform rectangular array (URA) on the base station and by the multiple subcarrier nature of the SRS. In this work, the subspace-based joint angle-time estimation and statistics-based expectation-maximization (EM) algorithms are investigated with the 3D signal manifold to prove the feasibility of using SSRSs for 3D positioning. The positioning performance of both algorithms is evaluated by estimation of the root mean squared error (RMSE) versus the varying signal-to-noise-ratio (SNR), the bandwidth, the antenna array configuration, and multipath scenarios. The simulation results show that the uplink SRS works well for 3D UE positioning with a single base station, by providing a flexible resolution and accuracy for diverse application scenarios with the support of the phased array and signal estimation algorithms at the base station. os 2021 21178 11.11.11.11.11.11.1.11.1.11.1.11.1.1.11.1.1.1.1.1.1.1.1.1.1.1  
bands, which are heavily polluted. Using cellular for positioning can be traced back to the GSM era. The typical methods used in the GSM system include the cell identification (CID)-based [6] and receiving signal strength-based (RSS) [7] approximating ones that inspired coarse location-based (\(\sim\)550 m accuracy [8]) social media services. Later in the 3G network, the accuracy of the CID-based approach was improved because of the use of smaller cells. More importantly, the timing-based approaches (TDoA, OTDoA, round-trip time (RTT), etc.) pushed the positioning accuracy to the range between 50\(\sim\)200 m [8]. Recent cellular systems such as 4G and 5G have, by design, signaling or reference signals dedicated to synchronization, channel estimation, and localization and therefore can offer competitive performance with respect to the GNSS also in dense urban scenarios. The typical signals for these purposes include the positioning reference signals (PRSs) in LTE Release-8 [9] and the CSI reference signal (CSI-RS) and sounding reference signal (SRS) [10] in 5G NR. Amongst the existing cellular-based localization solutions, 5G new radio (NR) was born to meet the keen needs of high-precision positioning, which is an inevitable technique for many future vertical applications. To be specific, 5G NR allows multi-/single-cell positioning: (i) the sounding reference signal (SRS) is employed for the base station (BS) to perform uplink time difference of arrival (TDoA); (ii) the enhanced capability of beamforming, especially in the mmWave domain, enables the BS to measure the angle of arrival (AoA); (iii) both the BS and user equipment (UE) could apply round trip time (RTT) measurements, which have a low demand for time synchronization and provide extra flexibility for radio planning. In brief, 5G NR promises rich resources for a vast range of vertical applications in the near future. 5G positioning has been studied in many works. For example, a weighted centroid geometric (WCG) solution and an extended Kalman filter (EKF)-based positioning based on AoA and ToA measurements were described in [11]. Distinct from this work, the AoA and ToA initial measurements in [11] were based on Cramer-Rao lower bounds (CRLBs) rather than on estimated values, and the study in [11] focused on the multi-station case, and not on the single-station case as here. 5G positioning with mmWave signals was also studied in [12], with the focus on downlink configurations, not on uplink positioning.