een two handovers of the same type (e.g. the HO period for the PBGT). Averaging The notion of an averaging process in handover control is the same as for other mechanisms such as power control. The idea is to use smoother values for the comparison with the thresholds. Therefore a 'window size' of samples is averaged, while applying a 'weighting' to the last sample. Decision Regardless of the type of handover concerned, decision criteria remain almost the same. If Px values out of Nx from the already averaged samples fulfil the condition, handover can take place. The condition consists of being either greater or smaller than a defined quality, level or interference threshold. To illustrate the notion of decision making either in handover or power control algorithms, a level handover example is considered (Figure 2.72). In this example, the values set for various parameter are as follows: Radio Network Planning and Optimisation Averaging window size: 4 Averaging weighting: 2 HO level threshold: -86 dBm HO level/Px 4 HO level/Nx: 6 In phase 1, only three averaged samples are below the threshold. No level handover is then performed. However, in phase 2, the signal decreases continuously and four samples out of six fulfil the criterion of being smaller than the threshold. At this point, the handover is performed. Adjacency Control As seen before, adjacency management has a special characteristic of handling pairs of cells and not only individual cells. This specification multiplies the complexity of the system because of the increased number of possible combinations. In fact, if an average of 12 neighbours per cell are considered, the number of items to consider in defining adjacent parameters is multiplied by 12. An adjacent relation is defined in both ways from cell A to cell B and from cell B to cell A. Parameters used in both directions can be different. This is what brings flexibility to the system. Setting adequate values for adjacency parameters means defining the way one cell will hand over communications to t