Table 12.3. Table 12.3 Supported cell ranges depending on restricted set of cyclic shift length Delay spread = 5.2 us Ncs CS config Ncs, cs' cyclic Length of single index shift length cyclic shift (us) Kilometres 10.95 13.52 116.9 17.53 145.5 21.82 187.4 28.11 220.8 33.12 LTE Key Performance Indicator Optimization Figure 12.50 Improvement in random access setup success rate after high-speed feature activation. Statistics taken from the eNodeB next to the train tracks The impact of using high-speed support of eNodeB in terms of random access setup success rate improvement is shown in Figure 12.50. The handover execution success rate also improved due to the activation of high-speed support and use of restricted set of cyclic shift lengths to generate preambles. The improvement in handover execution success rate was around 1.2 percentage points due to which the dropped call rate also improved by 1 percentage points. Further optimization requires redesign of below parameter sets: Signalling robustness for call setup and handovers following the methods detailed in Sec- tions 12.4, 12.5 and 12.6. Downlink power allocations in terms of reference signal (RS) boosting can cause unnec- essary large coverage areas and handover execution problems, SO typically RS boosting avoided for the high-speed scenarios. Uplink power settings with full path-loss compensation while maximizing the signalling robustness and minimizing the extra inter-cell interference. Also any scheduling algo- rithms that can minimize the inter-cell interference should be used to improve signalling robustness. Speed up the cell reselection in order to have the UEs always under the best cell but ping pong cell reselections need to be avoided by, for example, speed-dependent cell reselection feature and reduced hysteresis needed to be achieved before reselection can occur. By optimizing the above-mentioned parameters the high-speed train performance can be further improved as shown in Figure 12.51. LTE Small Cell Optimization 12.20% 0.42% 0.30% Rando acces