  The fifth-generation (5G) of mobile communication supported by
millimetre-wave (mmWave) technology and higher base station (BS) densification
facilitate to enhance user equipment (UE) positioning. Therefore, 5G cellular
system is designed with many positioning measurements and special positioning
reference signals with a multitude of configurations for a variety of use
cases, expecting stringent positioning accuracies. One of the major factors
that the accuracy of a particular position estimate depends on is the geometry
of the nodes in the system, which could be measured with the geometric dilution
of precision (GDOP). Hence in this paper, we investigate the time difference of
arrival (TDOA) measurements based UE positioning accuracy improvement,
exploiting the geometric distribution of BSs in mixed LOS and NLOS environment.
We propose a BS selection algorithm for UE positioning based on the GDOP of the
BSs participating in the positioning process. Simulations are conducted for
indoor and outdoor scenarios that use antenna arrays with beam-based mmWave NR
communication. Results demonstrate that the proposed BS selection can achieve
higher positioning accuracy with fewer radio resources compared to the other BS
selection methods.
