10.4 Delay of the Active DAS
Connecting external equipment between node B and the antenna will cause an offset of the timing in the cell. In reality this delay will result in an increase in cell size (timing window). An active DAS connected directly to the node B will typical add 2–3 km to the cell size. This delay or offset depends on the delay in the active DAS amplifiers, but also on the length of fibers and CAT5 cables. The longer the fiber and cable runs, the longer the delay will be, in some cases exceeding 15–20 km offset of the cell size. Some operators will set a given cell size according to the environment the cell is serving.
Typically, a node B serving an indoor solution would be set to a cell size of 2 km, so that node B does not pick up any traffic distant to the cell. Therefore if one does not consider the delay on an active indoor DAS, and sets the cell size to 2 km, the cell might not be able to set up calls on the indoor system, due to the delay of the DAS.
Set the cell size to cope with the offset caused by the delay in the active DAS.