h carrier aggregation: five carriers, each 20 MHz. The carrier aggregation solution needs common channels on every carrier, load balancing is needed between carriers, and unnecessary guard bands are needed. It is more efficient to use a single 100 MHz carrier than five 20 MHz carriers. The maximum bandwidth of 20 MHz in LTE was a good choice because the spectrum allocation per operator was typically 20 MHz or less in those frequencies where LTE is deployed. There is, however, more spectrum available in the new frequencies where 5G is deployed, like the 3.5 GHz band and millimeter waves, which justifies the larger bandwidth in 5G. 3.2.3 Spectrum Occupancy LTE has been designed to include a 10% guard band to avoid interference between adjacent carriers. 20 MHz LTE has 18 MHz transmission bandwidth, while 2 MHz is reserved for guard bands. The practical deployments show that a 10% guard band is excessive. Also, the RF requirements can be made tighter in 5G compared to LTE. Therefore, the spectrum utilization can be increased from 90% in LTE to up to 98% 5G. Figure 3.3 shows the 5G spectrum utilization compared to the channel spacing for different carrier bandwidths and subcarrier spacings. The deployment case with Table 3.2 Maximum carrier bandwidth with LTE and 5G. 20 MHz 5G sub-6 GHz 100 MHz 5G millimeter waves 400 MHz 3 Technology Components Figure 3.2 5G wideband carrier is LTE 5x20 MHz efficient for wide spectrum allocations. 100 MHz 18 MHz 18 MHz 18 MHz 18 MHz 18 MHz 5G 100 MHz 100 MHz Up to 98 MHz Spectrum utilization Subcarrier spacing 15 kHz 30 kHz 60 kHz Carrier bandwidth [MHz] Figure 3.3 5G spectrum utilization. 100 MHz and 30 kHz has a spectrum utilization of 98%. The case with 10 MHz and 15 kHz has a spectrum utilization of 94%. 3.2.4 Control Channel Flexibility 5G is designed to support flexible bandwidth allocation. There may be cases where a part of the band cannot be utilized, or a part of the band is interfered, or the amount of spec- trum does not match the predefined 3GPP bandwidths. It is import