t primarily motivated by the near-far control mechanism in at least one of the cells commands problem as the downlink is orthogonal. However, it is still the UE to do so. Only if all the cells request the terminal useful to combat the fast fading by varying the trans- to increase its transmission power is the power increased. mission power; when the channel conditions are favor- This mechanism, known as or-of-the-downs, ensures the able, less transmission power is used and vice versa. This average transmission power to be kept as low as possible. typically results in a lower average transmitted power Due to the non-orthogonal property of the uplink, any than for the corresponding non-power-controlled case, reduction in average interference directly translates into thereby reducing the average (inter-cell) interference an increased capacity. and improving the system capacity. Soft handover, or macro diversity as it is also called, is a key feature of WCDMA. It implies that a terminal is 4.6.1.3 Resource handling and communicating with multiple cells, in the general case packet-data session with multiple NodeBs, simultaneously, and is mainly used for terminals close to the cell border to improve With the above discussion in mind, a typical packet-data performance. The set of cells the UE is communicating session in the first release of WCDMA can be briefly with is known as the active set. The cells that are part of outlined. At call setup, when a connection is established the active set is determined by the RNC based on mea- between a UE and the radio-access network, the RNC surements from the UE. checks the amount of resources the UE needs during the In the downlink, soft handover implies that data to session. a UE are transmitted simultaneously from multiple cells. In the downlink, the resources in principle consist of This provides diversity against fast fading - the likelihood channelization codes and transmission power. Since the that the instantaneous channel conditions from all cells RNC is responsible for a