igu- ration and interference minimizing features. Thus, the four actions or steps outlined above do have an iterative process. 7.2.1 Coverage and Capacity Trade-off in the FDD Mode From the practical side as mentioned in earlier chapters and Section 7.4 of this chapter, in the FDD mode, which uses WCDMA techniques, the interference increases with the number of active users, thereby limiting capacity. Within this soft limitation, the system quality decreases continuously until service performance degrades to an intolerable state. This state leads to the breathing cells phenomenon, i.e. when user numbers gets too high, the quality of users at the cell-edge degrades rapidly to the point to drop the link or the call. Such event implies that cell radio coverage shrinks. On the other hand, when call drops occur, interference decreases for the remaining users and cell area cov- Deploying 3G Networks erage grows again. This is what we call the trade off between capacity and coverage in the FDD mode. Cell coverage and capacity thus depend on the received bit energy to total noise plus interference ratio Eb/(N0 + I) on each cell part for the DL and in the BS for the UL. This means that any parameter, which affects the signal level and/or the interference¹, or reduces the Eb/(N0++ requirements², has impact on cell coverage and capacity, as well as on the overall system. 7.2.1.1 Soft Handover and Orthogonality We described soft handover in Chapter 4 from the design side; here we look at it from the performance and dimensioning side. In this context, a MS performs handover when the signal strength of a neighbouring cell exceeds the signal strength of the current cell with a given threshold. In soft handover position, a MS connects to more than one BS simultaneously. Thus, the FDD mode uses soft handover to minimize interference into neighbouring cells and thereby improve performance through macro diversity, i.e. we combine all the paths together to get a better signal quality. We also reduce power originating from two or more