Please use the search function, you will find other topics related to UL and OL (i don’t know anything about that, i don’t work with it…)
2/ concentric cells are used in multiband networks, so that outer zone is 900, inner zone is 1800. Goal is to simplify settings (intracell HO), gain 1 TS for TCH, instead of using if for the 1800BCCH), reduce the nulber of neighbours declared in OMCR, etc.
In case of Huawei, you should enable the parameter named Concentric Handover Allowed.
If you have got the LMT installed, please go through the Handover Tab -> Concentric Data, this is where you will find parameters related to Concentric cells. (Rxlevel thresholds etc) Also some switches to enable UL to OL and OL to UL handovers.