e co-channel and adjacent channel interference the system can bear adjacent channel interference better. Interference is normally analysed channel by channel, showing the interference layer on the planning tool. The frequency channels are reallocated to make the interference layer, both co-channel and adjacent channel, as clean as possible. The cell dominance areas are cleared. Some planning tools also provide numerical statistics of the interference, which makes the work of finding the interfered channels and comparing them after changing the plan easier. Co-channel interference clearance of the BCCH layer is preferred over that of the TCH layer. In case bad interference spots are found in this phase a short re-check of the dominance areas can be made. Unnecessarily large coverage makes frequency planning complicated. Earlier mentioned techniques can be used to clear the dominance areas and in this way create a better basis for successful frequency planning: For co-channel interference C/Ic: = 9 dB For adjacent (200 kHz) interference : C/l1 =-9 dB For adjacent (400 kHz) interference : C/la2 -41 dB For adjacent (600 kHz) interference : C/13 -49 dB 2.8 Parameter Planning 2.8.1 Parameter Planning in the GSM Network The Cell Identity (CI) Code, the unique naming of the GSM network cells, is guaranteed with CI coding. This identification is used in the idle mode. Each code is unique inside one location area. The length of the CI code is 16 bits. The Location Area Code (LAC) defines the identification of a location area. The code consists of 2 bits. The location area combines nearby cells to one logical area. In practice, the location areas are physically large. Two types of location updates exist: the MS crosses the border of two location areas or a timer doing the update expires. The location update involves both the Home Location Register (HLR) and Visitor Location Register (VLR). The critical issue in planning the location areas is to define the borders SO that unnecessary location updates can be avoided and no ex