“…With advancements in wireless communication technology, sixth generation (6G) is bringing advanced technologies, such as mm-Wave [ 1 , 2 , 3 ], unmanned aerial vehicles (UAVs) [ 4 , 5 , 6 ], tera-hertz (THz) communications [ 7 , 8 , 9 ], intelligent reflecting surfaces (IRS) [ 10 , 11 , 12 ], non-orthogonal multiple access (NOMA) [ 13 , 14 , 15 ], etc., to overcome the limitations of prior wireless generations. Indoor positioning systems (IPSs) and location-based services have become a fundamental requirement for many Industrial Internet of Things (IIoT) applications [ 16 , 17 , 18 ]. For global positioning in the outdoor environment aspect, global navigation satellite systems (GNSSs), such as GPS, GLONASS, and the BeiDou navigation satellite system, are widely used and can achieve positioning accuracy within a m radius in clear, open spaces [ 19 , 20 ].…”