Recently, millimeter-wave (mmWave) 5G localization has been shown to be to
provide centimeter-level accuracy, lending itself to many location-aware
applications, e.g., connected autonomous vehicles (CAVs). One assumption
usually made in the investigation of localization methods is that the user
equipment (UE), i.e., a CAV, and the base station (BS) are {time} synchronized.
In this paper, we remove this assumption and investigate two two-way
localization protocols: (i) a round-trip localization protocol (RLP), whereby
the BS and UE exchange signals in two rounds of transmission and then
localization is achieved using the signal received in the second round; (ii) a
collaborative localization protocol (CLP), whereby localization is achieved
using the signals received in the two rounds. We derive the position and
orientation error bounds applying beamforming at both ends and compare them to
the traditional one-way localization. Our results show that mmWave localization
is mainly limited by the angular rather than the temporal estimation and that
CLP significantly outperforms RLP. Our simulations also show that it is more
beneficial to have more antennas at the BS than at the UE.Comment: This version is accepted for publication as a paper in the IEEE
Transactions on Vehicular Technolog
