l BSCs and some hundreds of sites). Therefore any MSC origin fault will have a sever impact on network quality. As mentioned in the transmission auditing section, radio optimisers are the ones concerned with end user QoS. Radio Network Planning and Optimisation Pre-Study & Analysis Site Survey Site reengineering proposal Site reengineering works Results qualification Figure 2.49 Site re-engineering process Most operators proceed with multivendor networks. In such an environment, it is very important for operators to make sure that the system interoperability functions well. In fact, sets of timers and parameters from both sides (BSC and MSC) should be compatible and settled to the appropriate values at the beginning of the roll-out project. Core optimisation processes are handled in detail Chapter 4. Radio engineers should work in close cooperation with NSS engineers to analyse problems together, especially when it is a matter of A interface tracing. Cooperation between radio and core is also mandatory during a site information update (after BTS re-hosting, LAC/CI modification, etc.) in order to ensure smooth impact on the quality of the network. Site Re-engineering At the beginning of a network deployment, the operator searches for rapid returns on investment. This is the reason why first sites are very high and do not have standard azimuths (0°, 120; 240°). Sectors are directed towards hotspot areas. With network expansion and subscriber growth, it becomes necessary to review the engineering in order to use the frequency spectrum efficiently. Due also to lack of coverage, site physical re-engineering can be proposed. This is one way of optimising antenna coverage in order to improve site performance. This operation can follow the underdescribed process (Figure 2.49). Prestudy and Analysis The first step of the process consists of analysing the situation. Physical re-engineering is proposed for sites having quality problems. That is the reason why statistics and drive tests need first to be analysed. Definition 