MS receives both signals by maximal ratio com- bining Rake processing. While in the DL softer and soft HO behave basically in the same way2 and the MS does not see any difference between them; in the UL soft HO behaves differently. For exam- ple, the MS receives the code channel from both BSs. This information then gets routed to the RNC for macro-diversity combining thereby to obtain the same frame reliability indicator provided for outer loop PC, i.e. to select the best frame after each interleaving period within 10-80 ms. Thus, soft and softer HO can also take place in combination with each other. The UMTS Network and Radio Access Technology The MS gets the same signal from both BSs, but with different PC cmds. Figure 8.3 Soft handover event. In general, soft HO will not exceed 40% of the links. However, it will not go below 20% either. Thus, we cannot neglect soft HO overhead when dimensioning. For exam- ple, we must allocate: extra transmission power in the BS, extra BS rake receiver chan- nels and extra rake fingers in the MS, and extra transmission links between the BSs and the RNCs. An appropriate provision and/or an efficient FPC management in WCDMA will maintain most of its total capacity 3 during HO. In FPC we need to deal effectively with the BS power drifting and the accurate detection of UL power control commands from the MS. Inaccurate reception of power control commands in the BS due to propagation impacts, such as delay or shadowing will trigger undesired power events from the BSs, e.g. in- creasing power when expecting power decrease. This power drifting will degrade soft HO. On the other hand, the RNC can control such drifting by limiting the power control dynamics or by obtaining DL reference transmission power levels from the BSs. Then send this reference value for the DL transmission powers to the BSs. In the UL all BSs send independent power control commands to the MS to control its transmission power. The MS can then decrease its power if one BS demands so, and apply maximal ratio combinin