This paper considers the problem of downlink localization of user equipment
devices (UEs) that are either in the near-field (NF) or in the far-field (FF)
of the array of the serving base station (BS). We propose a dual signaling
scheme, which can be implemented at the BS, for localizing such UEs. The first
scheme assumes FF, while the other assumes NF conditions. Both schemes comprise
a beam-sweeping technique, employed by the BS, and a localization algorithm,
employed by the UEs. The FF-based scheme enables beam-steering with a low
signaling overhead, which is utilized for the proposed localization algorithm,
while the NF-based scheme operates with a higher complexity. Specifically, our
proposed localization scheme takes advantage of the relaxed structure of the
FF, which yields low computational complexity, but is not suitable for
operating in the NF. Since the compatibility and the performance of the FF-
based scheme depends on the BS-to-UE distance, we study the limitations of
FF-based procedure, explore the trade-off in terms of performance and resource
requirements for the two schemes, and propose a triggering condition for
operating the component schemes of the dual scheme. Also, we study the
performance of an iterative localization algorithm that takes into account the
accuracy-complexity trade-off and adapts to the actual position of the UE. We
find that the conventional Fraunhofer distance is not sufficient for adapting
localization algorithms in the mixed NF and FF environment.Comment: 5 pages, conferenc