vices. TBF blocking is another limiting factor in a GPRS network. As the value of TBF blocking goes higher, the network performance goes down. Delay is another important factor in data networks. Some PS applications are sensitive to delays, but as the loading of the network increases, the response time of the network increases, thereby increasing delays. These GPRS: NETWORK PLANNING AND OPTIMISATION delays may take place from the SGSN to the mobile station or vice versa. For a real-time data service, minimum delay must be the first criterion in terms of quality. Hence, this is one very important KPI to be monitored in the optimisation process. Network Performance Monitoring The data can be collected from drive test results and the network management system (NMS). The process is quite similar to that explained in Chapter 2. Traffic monitoring will be key to optimisation of the network. Both the CS and PS traffic should be monitored, as the alignment of the GSM and GPRS traffic plays an important role in overall network quality (see Figure 5.9). The call voice KPI (mentioned in Chapter 2) and the data performance indicators could be used to monitor the traffic for a substantial time. Total Traffic Load GPRS Traffic Load Circuit Switched 00:00 06:00 12:00 18:00 23:59 Time of Day Figure 5.9 Example of traffic monitoring Network Performance Assessment As for a GSM radio network, assessment of a GPRS network is in terms of coverage, capacity, quality and related parameters. Coverage Drive tests results are used for assessment of coverage in a GPRS network. For the PS traffic, different coding schemes from CS-1 to CS-4 are used. As the coverage in a GPRS network is limited by interference, measurements are made under different propagation conditions and regional types (urban, rural, etc.) SO as to get more accurate C/I criteria for planning coverage. Initial values are based on the link budget calculation in the downlink direction (as it is assumed that the uplink power budget is equal to the downlink power budget). Als