ess impact from the 5G control channels on LTE since 5G does not use any CRS. If all LTE UEs support Transmission Mode 9 (TM9), then the shared carrier has a lower overhead because less CRS transmission is required. Low band 5G can be combined with higher band 5G with carrier aggregation in the same way as carrier aggregation in LTE. Low band 5G can be used for the uplink in the weak signal, while high and low band 5G together can be used for the downlink. The physical channel locations are shown in Figure 10.29 for the case where the downlink uses both low band and high band and the uplink uses just low band. 10.6.3.3 Supplemental Uplink Supplemental uplink solution uses low band 5G but only for the uplink direction. Part of the LTE uplink spectrum is allocated for 5G, while the LTE downlink spectrum is kept Starting point Low band 5G 10 MHz 10 MHz Dedicated band for 5G LTE 5G Frequency domain refarming LTE + 5G Dynamic Spectrum Sharing (DSS) LTE+5G Figure 10.27 Low band 5G deployment options. 10.6 Coverage for Sub-6-GHz Band = LTE PDCCH = LTE CRS = 5G PDCCH 180 kHz = 5G DMRS = LTE/5G PDSCH Figure 10.28 LTE and 5G sharing in time domain. Low band (700 MHz) + high band (3.5 GHz) 5G 5G PDSCH 3.5 GHz 5G PDSCH 700 MHz 5G PUSCH 700 MHz 5G PUCCH 700 MHz Figure 10.29 Physical channel locations with 5G carrier aggregation. Figure 10.30 Supplemental uplink concept. 5G3500 downlink 5G3500 uplink LTE1800 downlink 5G1800 uplink LTE1800 uplink fully allocated for LTE. This approach is quite handy because traffic is highly asymmetric today: downlink traffic is typically 10 times more than uplink traffic. Therefore, the FDD uplink spectrum utilization is lower than the downlink utilization, and it is feasible to allocate part of the uplink spectrum for 5G. The supplemental uplink concept is shown in Figure 10.30. Uplink sharing between LTE and 5G can be done partly in the frequency domain and partly in the time domain. The center frequency of the LTE carrier cannot be changed because the downlink LTE transmission uses full ban