How Much Localization Performance Gain Could Be Reaped by 5G mmWave MIMO Systems from Harnessing Multipath Propagation?

Millimeter-wave (mmWave) massive multiple input multiple input (MIMO) has shown great potential in user equipment (UE) localization of 5G wireless communication systems. However, mmWave signals usually suffer from non-line-of-sight (NLOS) propagation, which will affect mmWave MIMO-based UE localization performance. Hence, it is non-trivial to reveal how NLOS propagation affect mmWave-based UE localization performance. In this paper, we give a unified analysis framework for UE localization performance gain from harnessing NLOS propagation. Firstly, a closed-form Cramer-Rao lower bound on mmWave MIMO-based UE localization is derived to shed lights on its performance limit. Secondly, NLOS propagation-caused localization error for conventional UE localization methods without harnessing multipath effect is analysed. Finally, the information contribution from NLOS channel is quantified, which sheds light on how to smartly harness NLOS propagation and the associated UE localization performance gain.