is the significant difference compared to LTE-unlicensed and LAA schemes. In the case of LWA solution, the aggregation takes place at the radio link level. The Wi-Fi access points can use the LTE core network functions (e.g., authentication, security, etc.). It will be dis- cussed in Section 8.2 that the LWA architecture consists of LWA eNB, LWA-aware Wi-Fi access points, and LWA UEs. The LWA eNB and Wi-Fi AP can be co-located or non-co- located. If non-co-located, data is delivered through IP tunnel between two systems. The LWA eNB performs scheduling of PDCP packets and transmits some of the IP packets over the LTE air-interface and others over the Wi-Fi after encapsulating them in Wi-Fi MAC frames. All packets, received over either LTE or Wi-Fi, are then aggregated at the PDCP sublayer of the LWA UE. The Wi-Fi APs are connected to LWA eNBs and report informa- tion on channel conditions to the LWA eNB. The LWA eNB then determines whether to use the Wi-Fi link or not. The LWA eNB can improve LTE performance by managing radio resources in real-time according to the RF and load conditions of both LTE and Wi-Fi. A Wi-Fi AP can work as a native Wi-Fi AP while not serving the LWA purpose. This Operation in Unlicensed and Shared Spectrum 879 ((Q)) IEEE 802.11 MAC IEEE 802.11 PHY IP packets Wi-Fi carrier User IP packets ethernet Wi-Fi 12345 Access point 54321 Licensed PCell Figure 8.19 Illustration of LWA principle of operation [18]. eliminates potential coexistence issues in the unlicensed bands. However, as LTE data must be split at eNB and then aggregated at UE, the involved nodes such as eNB, Wi-Fi AP, and UE must be LWA-enabled. The LWA architecture, protocol, and operations will have to be defined as well. Fig. 8.19 shows the high-level architecture and operation of LWA scheme [18]. 8.1.4.3 LTE Unlicensed and MulteFire In 2014, a group of companies formed the LTE-U Forum to develop technical specifications based on LTE Rel-12 in the 5 GHz band. LTE-U Forum initially focused on non-LBT mar- kets without modifying 