r Network Time Protocol (NTP) from the IETF can be used. Regardless of the mobile generation (e.g. 4G, 5G), there are three main deployment scenarios of small cells (as shown in Figure 5.13): Different frequency carriers for macro cellular network and for small cells. This sce- nario consumes more spectrum bands; however, it provides the best QoS due to absence of interference between the carriers. Small cells Macro cells Scenario Different frequency bands for macro and small cells Macro cells carriers Small cells carriers Some frequency bands overlapping Macro cells carriers Small cells carriers Overlapping carriers Macro cells carriers Small cells carriers Frequency Figure 5.13 Small cells scenarios. 5 QoS for Mobile Ultra-Broadband Same frequency band used for overlapping macro and small cells. This is the most typical scenario because the spectrum is scarce and limited, as well as the licensed spectrum having a cost. However, regarding QoS, there is higher interference in this scenario and hence lower bitrates on average. Overlapping carriers. In this scenario the frequency carriers in macro and small cells are partly overlapping, SO this approach provides a hybrid solution by combining the other two scenarios, thus having QoS level in the middle of the other two deployment scenarios. Considering the standardization aspects of small cells, LTE (as 4G technology) has offered deployment on a large scale with LTE-U, LAA, LWA, and MulteFire. However, the expansion of small cells is coming with 5G deployments. Using small cells, 5G can utilize higher frequency spectrum (e.g. 24-86 GHz), which can cover only shorter dis- tances from the base stations. With the capacity of small cells, the 5G mobile networks can compete in capacity with fixed networks. Typical 5G architecture uses macro cells for control, all around coverage and fallback (e.g. when users leave the small cells area), while small cells are used for capacity for ultra-broadband Internet access or for com- munications with IoT devices deployed in the gi