hich the transmission power reaches the maximum value as shown in Figure 12.48. According to Figure 12.48 after activating the four-way IRC reception the number of UEs transmitting with maximum power decreases by 20 percentage points which means longer battery life time as well as less inter-cell interference. LTE Small Cell Optimization After, After, After, After, After, After, After, After, After, day 1 day 2 day 3 day 4 day 5 day 6 day 7 day 8 day 9 Figure 12.47 Average PUSCH SINR improvement by four-way IRC reception over two-way IRC reception After, After, After, After, After, After, After, After, After, day 1 day 2 day 3 day 4 day 5 day 6 day 7 day 8 day 9 Figure 12.48 UE transmission power reduction by four-way IRC reception as a percentage point reduction in the number of UEs transmitting with maximum power LTE Key Performance Indicator Optimization 12.8 High-Speed Train Optimization 3GPP has defined in [11] high-speed and performance limits in case of up to 350 km/h UE speed for band 1. These performance requirements for eNodeB demodulation are discussed in details in [8]; here, only a short summary is presented. When the eNodeB is activated with high-speed support then those performance requirements from [11] are met and performance of PRACH, PUCCH and PUSCH is guaranteed for up to 350 km/h depending on the high-speed scenario. There are two different scenarios defined [11], one for open space (scenario 1) and another for multi-antenna tunnel case (scenario 3). For both scenarios, the Doppler shift is defined according to [11] as shown in Eq. 12.5. In Eq. 12.5 f(()) is the Doppler shift, fd is the maximum Doppler frequency given in Eq. 12.6 and cosine of the signal arrival angle O(t) is defined in [11] and shown in Figure 12.49: fs(t) = fd cos O(t) (12.5) (12.6) In Eq. 12.6, V is the UE travelling speed, fc is the carrier frequency and C is the speed of light. The eNodeB experiences double Doppler shift in the worst case as the UE synchronizes to the downlink frequency which already includes Doppler shi