e allocation of codes is based on information such as the network configuration and RRM features such as admission control (including also packet scheduling). The allocated codes have to be orthogonal to each other, but in practical conditions (with delays, etc.) the codes are not perfectly orthogonal, SO interference may occur. Code allocation is done by the RNC in two steps: channelisation and spreading. The coding is done in such as way that the scrambling codes are different from each other, having low cross-correlation properties with OVSF channelisation codes being responsible for maintaining the orthogonality between the subscribers. WCDMA RADIO NETWORK OPTIMISATION 7.7 WCDMA RADIO NETWORK OPTIMISATION The fundamental process of WCDMA radio network optimisation is quite similar to that for GSM. The process is, however, much more complicated and critical because of the presence of data, both real-time and non-real-time, with four classes, each class having its own types of application, with each application demanding a different quality aspect. The process of optimisation begins in the early phase of network planning, right after pre-planning. It is slightly different from the network planning process, focusing more on performance optimisation by configuration changes (e.g. improving coverage by antenna height adjustments or by changing antenna tilts) than on launching. The optimisation process starts with existing network data and the master plan made during the initial phase of network planning. Present network data are needed to ascertain whether there have been any deviations from the original plan during the implementation phase. The master plan will show the design targets (both short-term and long-term) for coverage, capacity and quality (Figure 7.8). Definition Network Performance Monitoring RT/NRT Parameter Tuning Network Planning Process Optimised Network Figure 7.8 WCDMA radio network optimisation 7.7.1 Key Performance Indicators Deciding on key performance indicators is the most important part o