f the process because it is here that the methodology of optimisation is decided. Owing to the complexity of a WCDMA network, there is an immense number of parameters. However, only a few of these parameters are chosen for optimisation, those that have the most significant impact on the radio network. The initial values of parameters are usually derived from standard formulas. These key chosen parameters are the ones that are responsible directly for the coverage, capacity and 3G RADIO NETWORK PLANNING AND OPTIMISATION quality of the network. The main KPIs may include call success/failure rate, dropped call rate, (soft) handover success rate, average throughput on uplink/downlink, and average throughput on various channels such as RACH, FACH and PCH, etc. When defining the KPIs, it is important to know whether or not tools are available to measure the performance of the chosen parameters. 7.7.2 Network Performance Monitoring The network's performance can be monitored through drive tests and the network manage- ment system (NMS). In a WCDMA radio network, real-time data transfer delay is perhaps the most critical aspect to be monitored (see Table 7.6). Even within real-time data, each application has to be monitored/measured against the backdrop of its own QoS require- ments. With regard to the NMS measurements, as in GSM radio networks, most of the mea- surements are performed on the RNC, based on the key performance indicators on whose bases these measurements are run. The statistics collected from drive testing and the NMS are then used in conjunction with some post-processing tools that provide various types of output and reports. The quality of the network is usually viewed from the perspective of mobile subscribers. This is why drive tests are important. The quality can be assessed right from the time when the first site goes live. The network management system usually comes into place when the network is near launch or has been launched, so can provide statistics when there are certain numbers of subscriber