ant that the system include flexibility that allows utilization of the band according to the specific require- ments. The LTE control channel has some limitations: LTE downlink Physical Downlink Control Channel (PDCCH) is allocated over the full band, and LTE uplink Physical Uplink Control Channel (PUCCH) is allocated at the band edges. There is no flexibility in LTE control channel allocations if we need, for example, to squeeze down the carrier 3.3 Beamforming LTE downlink LTE uplink PDCCH PUCCH 20 MHz PDCCH PUCCH PDCCH uses full PUCCH is at the Flexible allocation of band allocation band edge PDCCH and PUCCH Figure 3.4 Control channel allocations in frequency domain. narrower from one side. The 5G control channel includes more flexibility, which allows allocation of control channels in suitable locations in the frequency domain. The control channel allocations are illustrated in Figure 3.4. For more details, see Chapter 6. 3.2.5 Dynamic Spectrum Sharing Spectrum refarming from 2G to 3G and to LTE was a slow and relatively complex process. Legacy technology must be eliminated from a part of the spectrum, which must then be allocated for the new technology. It was not possible to share the spectrum between different technologies. Spectrum refarming from LTE to 5G will be simpler with Dynamic Spectrum Sharing (DSS). 5G and LTE can occupy the same spectrum band from the control channel point of view, and the resources are allocated dynamically between the two technologies depending on the instantaneous device distribution and capacity needs. DSS is described in more detail in Chapters 8 and 10. 3.3 Beamforming Beamforming is an attractive solution for boosting mobile network performance. Beamforming can provide higher spectral efficiency, which adds a lot more capacity to the existing base station sites. Beamforming can also improve link performance and provide an extended coverage area. Beamforming has been known in academic studies for many years, but beamforming was not supported by the first LTE specifica- tio