bined over one or more HARQ transmission attempts. A retransmission gain of 2 dB is assumed with soft combining of all transmis- sions and using four OFDM symbols per slot. For both the downlink and uplink, one front-loaded DMRS is used as overhead, and a full band (10 MHz) allocation is used for the PDSCH and PUSCH. An aggregation level of 16 is selected for the PDCCH, and the payload is 39 bits. The results show that S BLER of less than 101 can be obtained at the 5th percentile (95% of time) in all four cases at 4 GHz and 700 MHz both in the downlink and uplink. Other cases are in the non-LOS channel except for the 4 GHz uplink in the line of sight. The system-level reliability results are summarized in Table 10.24. 10.13 Mobility and High-Speed Trains PDSCH link performance 1.0E-01 - 7 symbol/slot - 4 symbol/slot 1.0E-02 1.0E-03 1.0E-04 1.0E-05 1.0E-06 SINR [dB] Figure 10.70 Physical Uplink/Downlink Shared Channel (PUSCH/PDSCH) performance with 30 kHz subcarrier spacing, 10 MHz bandwidth, and 3 km/h. Table 10.24 Probability for BLER > 10-5. Number of transmissions 4 GHz 700 MHz Downlink (%) Uplink (%) Downlink (%) Uplink (%) < 0.1 < 0.1 < 0.1 10.13 Mobility and High-Speed Trains The IMT-2020 requirement for mobility is 500 km/h, which is also a relevant case for high-speed trains like Shinkansen in Japan, Train à Grande Vitesse (TGV) in France, Inter-City Express (ICE) in Germany, Eurostar in France, or the Korean Train Express (KTX). Fast-moving UEs are challenging because the Doppler effect degrades the fre- quency tracking accuracy and channel estimation accuracy. This leads to low throughput caused by loss of orthogonality between subcarriers. The Doppler shift also affects detec- tion of PRACH preambles. 3GPP has considered high-speed mobility in 5G physical layer design by including the following items: DMRS, whose frequency can be flexibly defined per UE depending on the mobility requirements. For low-speed scenarios, DMRS uses a low density in the time domain. For high-speed scenarios, the time density