There are two physically independent cells (two co-site cells with different coverage
radiuses) on different bands are configured with BCCHs and SDCCHs so that the cells form a cell group logically, mapping with the overlaid subcell and the underlaid subcell respectively.For the two cells in the group, the traffic channelresources are shared and the cell load is balanced through the dual-band network algorithm.
Concentric or Co-BCCH
The concentric cell has one underlaid subcell and one overlaid subcell. If they act as a co-BCCH cell,the TRXs in the underlaid subcell are on a different frequency band from the
TRXs in the overlaid subcell. All the TRXs in the same subcell, however, are on
the same band.
In a concentric cll,one BCCH can be saved because the two bands are in the same cell. Thus the capacity is enhanced. Compared with the common dual-band network, the dual-band
network using the co-BCCH cell(concentric cell) function has larger capacity.Also,the no. of neighbours are also lesser in a concentric cell compared to a dual band cell having 2 BCCH.