o, in the initial network design the C/I and S/N values are considered to be similar. However, in a practical network they are usually different, so the actual coverage region may be quite different from the theoretical one. Thus, measurements and modifications leading to more realistic values of C/I and S/N are necessary. Degradation of C/I values (and therefore coverage) may be due to multiple factors such as weak signal power (possibly due to propagation conditions), huge interference problems due to repeaters or an external source, or even poor frequency planning. Whatever the reason, insufficient cell coverage may lead to 'blind zones' or 'overlapping' in the radio network. The condition can be improved by increasing/decreasing the power of the BTS antennas (i.e. by adjusting the power budget) or by adjusting the cell selection parameters. NETWORK OPTIMISATION Capacity A 'capacity bottleneck' in a GPRS network will most often be at the air- and Gb interface. These two interfaces will always have a direct impact on the system capacity and hence its quality. At the air-interface, the number of PDCHs will have an impact on capacity, so if capacity limitation is causing quality degradation then the number of PDCHs should be increased in the appropriate locations (e.g. hot spots, or areas where traffic increases during the busy hour). The PCU also directly affects the allocation of radio resources. Whenever the PCU is short of capacity, TBF blocking will take place. Reduced throughput per time slot can be due to an increase in interference levels, or to the sharing of a time slot between several users. Thus, TSL capacity analysis becomes a part of the optimisation process. The number of TSLs defined for voice and packet traffic will need to be reviewed. It is possible that, during the launch of the network, the first TSL is a dedicated one while the remainder are for voice traffic. When the PS data traffic increases, the number of TSLs required for data also increases. Moreover, the RLC protocol performance and t