 Handover E-RAB setup success execution drop rate success rate Figure 12.51 Performance improvement after parameter optimization It should also be noted that use of repeaters especially inside the high-speed train tunnels should be carefully designed SO that the transmissions from each repeater are perfectly time aligned and Doppler impact minimized by proper repeater antenna arrangement. 12.9 Network Density Benchmarking The denser the network is the more cells there are; but just plain number of cells is not that good as a benchmark indicator due to the different stages of the network rollout (initial rollout for, e.g. hotspots only, country wide rollout and capacity increase) between the networks in different areas. The number of cells per number of subscribers indicates the absolute density of the network. In Figure 12.52, one example of network density benchmarking is shown as the estimated number of sectors per 1000 subscribers. As it can be seen, the densest networks are in Japan, South Korea, China and Scandinavia where in general the networks are two to three times denser compared to Europe, North America and APAC and up to 10 times denser compared to Latin America, Middle East and Africa. The subscriber numbers include all the technologies (2G, 3G and 4G) in Figure 12.52. The average UE-reported CQI for each network seen in Figure 12.53 shows no big difference between networks with high or low amount of sectors per 1000 subscribers. This means that the high-density networks have good physical layer performance and therefore very high downlink and uplink throughputs can be achieved. However, the more dense the network is the more challenging it is to control the inter-cell interference and physical layer optimization is challenging but excellent results can be achieved as shown in Section 12.3. The KPI optimization actions described in this chapter become more and more important as the number LTE Key Performance Indicator Optimization Network density benchmarking Japan, South Korea, China, Scandinavia 5.