is that a cell can be more loaded when surrounding cells are unloaded. The less interference there is coming from all the neighbouring cells, the more users can be admitted before the load (interference or transmitted power) of a cell reaches the load target. If the average loading is low, there is extra capacity available in the neighbouring cells. As this capacity can be borrowed from the neighbouring cells, the interference sharing gives soft capacity. The soft capacity has more inpact on high bit rate real time users because of a larger relative change for higher bit rates. The soft capacity can be approximated based on the total interference at the BTS. The total interference includes that of both the own cells and other cells. Therefore, the total channel pool can be obtained by taking the number of channels per cell in the equally loaded case and multiplying that by 1 + i, which then gives the single isolated cell capacity. The basic Erlang B formula is then applied to this larger channel pool. This obtained Erlang capacity is then equally shared between neighbouring (interfering) cells by dividing the maximum offered traffic by 1 + i (in UL the power rise is also taken into account). From the planned load, the number of channels available in the resource pool (an average condition) can be calculated: (2.57) The soft blocking capacity (in Erlang) for RT services can be calculated using the Erlang B table and the equation Erlang B [N(1 blocking %] [Erl] (2.58) The DL soft capacity is calculated using a similar method. Frequency Planning Figure 2.27 Frequency re-use patterns of 7 and 12 cells 2.7 Frequency Planning The dilemma behind frequency planning is to provide needed capacity and coverage within a given frequency band. The frequency channels therefore need to be re-used, but it is wise not to increase the interference level. Interference is caused when two network cells use the same channel too close to each other; more precisely this is a co-channel interference situation. When the interfering channel