  In underlay heterogeneous networks (HetNets), the distance between a macro
base station (MBS) and a macro user (MU) is crucial for a small-cell based
station (SBS) to control the interference to the MU and achieve the
coexistence. To obtain the distance between the MBS and the MU, the SBS needs a
backhaul link from the macro system, such that the macro system is able to
transmit the information of the distance to the SBS through the backhaul link.
However, there may not exist any backhaul link from the macro system to the SBS
in practical situations. Thus, it is challenging for the SBS to obtain the
distance. To deal with this issue, we propose a median based (MB) estimator for
the SBS to obtain the distance between the MBS and the MU without any backhaul
link. Numerical results show that the estimation error of the MB estimator can
be as small as $4\%$.
