on Interference When a cell experiences quality degradation at a good signal level, an interference handover is performed. Power budget (PBGT) handover is also called the comfort handover. It means that it is a handover triggered in nonurgent conditions. This is why it has the lowest priority. It consists of moving from the current cell to a cell with less path loss. In general, and since almost all cells transmit at the same power, the PBGT threshold assessment finally becomes a received signal level comparison. Power budget handover is allowed between cells belonging to the same layer. Umbrella Umbrella handover indicates a passage from one layer to a lower one. Generally, very high macro sites have a specific parameter set that redirects traffic to "normal" macro sites as soon as level conditions permit. The aim is to decrease the traffic load on umbrella sites. Target Cell Evaluation Target cell evaluation is based on the following criteria: Radio link properties Threshold comparison Priority levels of neighbouring cells Load of neighbouring cells Rx level comparison When more than one cell fulfills the criteria, the one that has the strongest level and priority is chosen. In order to prevent the ping-pong phenomenon in handovers, the network does measurement averaging through the use of four notions: window size, weight, Nx and Px (explained earlier in the power control subsection). In umbrella handover, for example, adjacent cells are qualified according to radio link properties in addition to the power class of the mobile station, which determines the size of the cell. In fact two methods can be used to estimate the size of an adjacent cell, either the use of the adjacent cell layer parameter, which indicates lower, same and upper layers, or the maximum RF power an MS is allowed to use, which rules the power budget calculations. A list of candidate target cells is then set and ranked according to priority. Adjacent cell layer management is also related to the MS speed detection. Firstly, whether an MS is m